Active Food Packaging

ACTIVE FOOD PACKAGINGEdited by M.L. ROONEY Principal Research Scientist CSIRO Division of Food Science & Technology North Ryde New South Wales Australia BLACKIE ACADEMIC & PROFESSIONAL An Imprint of Chapman & Hall London • Glasgow • Weinheim • New York • Tokyo • Melbourne • Madras Published by Blackie Academic & Professional, an imprint of Chapman & Hall, Wester Cleddens Road, Bishopbriggs, Glasgow G64 2NZ Chapman & Hall, 2-6 Boundary Row, London SEl 8HN, UK Blackie Academic & Professional, Wester Cleddens Road, Bishopbriggs, Glasgow G64 2NZ, UK Chapman & Hall GmbH, Pappelallee 3, 69469 Weinheim, Germany Chapman & Hall USA, 115 Fifth Avenue, Fourth Floor, New York NY 10003, USA Chapman & Hall Japan, ITP-Japan, Kyowa Building, 3F, 2-2-1 Hirakawacho, Chiyoda-ku, Tokyo 102, Japan DA Book (Aust.) Pty Ltd, 648 Whitehorse Road, Mitcham 3132, Victoria, Australia Chapman & Hall India, R. Seshadri, 32 Second Main Road, CIT East, Madras 600 035, India First edition 1995 © 1995 Chapman & Hall Typeset in 10/12 pt Times by Photoprint, Torquay, Devon Printed in Great Britain by St Edmundsbury Press Ltd, Bury St Edmunds, Suffolk ISBN 0 7514 0191 9 Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the UK Copyright Designs and Patents Act, 1988, this publication may not be reproduced, stored, or transmitted, in any form or by any means, without the prior permission in writing of the publishers, or in the case of reprographic reproduction only in accordance with the terms of the licences issued by the Copyright Licensing Agency in the UK, or in accordance with the terms of licences issued by the appropriate Reproduction Rights Organization outside the UK. Enquiries concerning reproduction outside the terms stated here should be sent to the publishers at the Glasgow address printed on this page. The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made. A catalogue record for this book is available from the British Library Library of Congress Catalog Card Number: 94-74368 ^ t Printed on acid-free text paper, manufactured in accordance with ANSI/ NISO Z39.48-1992 (Permanence of Paper) Preface Food packaging materials have traditionally been chosen to avoid unwanted interactions with the food. During the past two decades a wide variety of packaging materials have been devised or developed to interact with the food. These packaging materials, designed to perform some desired role other than to provide an inert barrier to outside influences, are termed active packaging. The benefits of active packaging are based on both chemical and physical effects. Active packaging concepts have often been presented to the food industry with few supporting results of background research. This manner of introduction has led to substantial uncertainty by potential users because claims have sometimes been based on extrapolation from what little proven information is available. The forms of active packaging have been chosen to respond to various food properties which are often unrelated to one another. For instance, many packaging requirements for postharvest horticultural produce are quite different from those for most processed foods. The objective of this book is to introduce and consolidate information upon which active packaging concepts are based. Scientists, technologists, students and regulators will find here the basis of those active packaging materials which are either commercial or proposed. Some types of active packaging are inevitably omitted but the book should assist the inquirer to understand how other concepts might be applied or where they should be rejected. Chapter 1 is the editor's overview of the field. Here I have sought to define active packaging and to establish its limits and the background to its development. The history of oxygen scavenging is used as a case study. Chapter 2 is contributed by Dr Devon Zagory of Devon Zagory & Associates Inc., California. Dr Zagory has been a major contributor to present knowledge of modified atmosphere packaging of horticultural produce. In this chapter he discusses the background to the use of active packaging to remove ethylene from the headspace of respiring produce. He discusses the options currently available and their limitations. Chapter 3, by Dr Kit Yam of Rutgers University, New Jersey and Dr Dong Sun Lee of Kyungnam University in South Korea, address the interface between active packaging and equilibrium modified atmosphere packaging now in use. They introduce a simple method of modelling gas atmospheres to show where additional active packaging concepts are required. Chapter 4 is the editor's discussion of the field of active packaging based on polymers. This includes use of thermoplastics for films and more rigid containers but also provides background useful when consideration is given to other polymer-based coatings. The aim has been to unify the many alternative unrelated concepts being offered to packers of both fresh and processed foods. Chapter 5 is contributed by Dr Bernard Cuq and Dr St6phane Guilbert of CIRAD-SAR, and Dr Nathalie Gontard of ENSIA-SIARC, all of Montpellier, France. Their research into the edible coating of foods needs no introduction. They describe in this chapter how edible coatings are often already active packaging and introduce the current and potential use as delivery systems for food additives. Chapter 6 is contributed by Dr J.P. Smith of McGiIl University, Montreal, Canada, Yoshiaki Abe, President of Mitsubishi Gas Chemical Europe GmbH and Dr Jun Hoshino, Chief Microbiologist of Mitsubishi Gas Chemical Company, Inc., Tokyo. Jim Smith has published the results of many of the key investigations of the impact of modified atmosphere and active packaging on food microbiology. Mr Abe and Dr Hoshino have been responsible for the introduction of 'Ageless' oxygen scavenging sachets, particularly outside Japan. In this chapter they consolidate knowledge of sachet-based technologies. Chapter 7 is co-authored by Dr John Budny, President of PharmaCal Ltd., California and Dr Aaron Brody, who is Managing Director of Rubbright Brody Inc. Dr Brody was formerly with Schotland Business Research of Princeton and is a widely respected packaging consultant and author. These authors provide the background to and opportunities for the use of enzymes in active packaging. This is still a frontier field and requires the carefully explained background presented in this chapter. Chapter 8 is contributed by Dr Fred Teumac of ZapatA Technologies Inc. of Hazleton, Pennsylvania, USA, who was jointly responsible (with Advanced Oxygen Technologies Inc.) for developing the first commercially successful oxygen scavenging closures for bottled beer. In this chapter he presents this and other systems as case studies in active package development. Chapter 9, by Stanley Sacharow, President of The Packaging Group Inc., New Jersey, is an examination of the role played by active packaging in current commercial use. Stan Sacharow is a leading international consultant in packaging and has written several books and many articles on packaging technology. This chapter provides the necessary understanding of the status of active packaging in the USA today. Active packaging for microwaveable foods is a key topic. Chapter 10 is by Dr Jeremy Selman, Head of the Food Technology Division of the Campden Food and Drink Research Association in the UK. Dr Selman is widely respected for his work on food quality monitoring via time-temperature indicators (TTIs). In this chapter he provides the background to TTIs and summarizes their role with much tabulated information. He provides substantial unity to the TTI field by discussing their recent introduction to thermal process validation. Chapter 11 completes this work by drawing together the implications of active packaging for food safety. Prof. Joseph Hotchkiss of Cornell University, New York, has contributed widely to research and discussion of the role of packaging in food safety. In this chapter he draws together the safety issues which arise from the use of active packaging and illustrates how active packaging can itself contribute to food safety in the use of antimicrobial films. Acknowledgements I extend my thanks to all the contributors, many of whom I have known and all of whom I have respected for several years. I appreciate their commitment in working within the tight schedule required. I also thank Lyn Keen for her tolerant preparation and reorganization of much of the manuscript, and Andrew Sennett for preparing so many versions of some of the graphics. My thanks also go to Drs Bob Holland, Brian Patterson, Bob Johnson, Mark Horsham, Alister Sharp, Candiera Albert and Michael McNaIIy for refereeing my contributions within CSIRO. I appreciate the advice and forbearance of the staff at Blackie A&P. Finally, I thank my wife Sally, and my children Helen, James and Kathy for their quiet patience and active support during the preparation of this book. M.L.R. Germany Rubbright-Brody Inc. Selman JLP. USA D. Inc. Cornell University. USA PharmaCal Ltd. Canada Vice-President Research and Development. 1-1. CFDRA. Korea Principal Research Scientist. 119 Stocking Hall. Westlake Village. Nijuku 6-Chome. BP 5035. Breton. Guilbert J. Teumac . Tokyo 125. Suite 107. Masan City 630-701. PO Box 52. USA CIRD-SAR. Macdonald Campus 21. PO Box 345. 40210 Dusseldorf. CSIRO Food Research Laboratory. 34032 Montpellier. UK McGiIl University.H. Department of Food Science and Agricultural Chemistry. 111 Lakeshore. 34032 Montpellier. Katsushika-ku. USA Director of Food Technology Division. Chipping Campden. 733 Clovelly Lane. 34033 Montpellier.. Immermannstrasse 45.L. Quebec. Ithaca. France ENSIA-SIARC. BP 5098. France CIRD-SAR. Rooney Department of Food Engineering. PA 19333-1808. Smith F. 1101 Avenue Agropolis.D. 73 rue J. NJ 08850. Cuq N. Gloucestershire. Budny B. Milltown. Australia The Packaging Group Inc. CA 91362. Japan AX. BP 5035. Hoshino J. 449 Wolyoung-dong. Gontard S.Contributors Y. Hotchkiss Institute of Food Science.F. Brody JA. 31308 Via Colinas.S. ZapatA S.. GL55 6LD.N. Sacharow J. NY 14853-7201. Breton. Ste-Anne-de-Bellevue. France Mitsubishi Gas Chemical Company. Deutsch-Japannische Center. Lee M.F. New South Wales 2113. H9X 3V9. Abe Mitsubishi Gas Chemical Europe GmbH. Kyungnam University. Devon. 73 rue J. North Ryde. New Brunswick. PA 18201. PO Box 231. Humboldt Industrial Park.L. USA Devon Zagory & Associates. Davis. CA 95616. 759 North Campus Way.Technologies Inc. USA K. Postharvest Technology Consultants. Forest Road. Hazleton. Zagory . Rutgers University. PO Box 2278. NJ 08903-0231. USA D.. Department of Food Science. Yam Assistant Professor. ..................2...................4 1.......7 1........................................... iii v vi 1 1 3 3 4 10 12 17 20 27 29 31 32 33 33 Literature Review ................... Intelligent and Modified Atmosphere Packaging .............. Implications for Other Packaging .............. 1..................... 1...............1 1...............................1 1............................. Contributors ...................3 1.............. Historical Development ........................ References ...Contents Preface ....1 Whole Packages Designed to Be Active ...1 Do-it-yourself Active Packaging ...................9 Why Active Packaging ........2 Active................................... Physical and Chemical Principles Applied ............. 1.2 1......5 1...............................2........... Origins of Active Packaging . Limitations of Current Approaches .................................. Overview of Active Food Packaging ..... Regulatory Considerations ................ Scope for Application of Active Packaging ..................................... Acknowledgements .................... Future Potential .............4................................6.....................8 1..... 1..............6 1.................................................................................................. This page has been reformatted by Knovel to provide easier navigation................ 1.... viii ..................... .........4 2.......................... Plant Sources . .......................................2 2........... Microorganisms ............... Ethylene Sources in the Environment .............3 2........3....5...................... ix 38 38 38 39 40 41 42 42 42 43 43 43 43 44 44 44 45 45 45 45 46 46 46 46 46 47 48 Deleterious Effects of Ethylene ........ Ozone ..........3.................... This page has been reformatted by Knovel to provide easier navigation........5 2...1.............................4 2.3 2................2 2.. Adsorption and Absorption .... Chlorophyll Breakdown ..........2....4....1 2........4................................1 The Chemistry of Ethylene .. Oxygen .......2................ Combustion ....2 2..........................3 2.. Commercial Applications in Packaging .... Flower and Leaf Abscission ............. Degradation ..... Interactions of Ethylene and Other Gases .................5.......2.......2.. 2. Petal Inrolling in Carnations ........ Ethylene-removing Packaging ..................7 2..3 2.......... Fluorescent Ballasts and Rubber Materials .4......2 2...2 2.............. Postharvest Disorders ........... Fruit Ripening and Softening .............5.................2..............................................1 2.........Contents 2..........................1 2................ Potassium Permanganate-based Scavengers .........1 2.....................5 2...2..........4 2..4. 2............3 Synthesis .3 2.......................1... Activated Carbon-based Scavengers ................ Susceptibility to Plant Pathogens .....3.................................... Activated Earth-type Scavengers ..................5 2.........4................1...............2................ Carbon Dioxide ......... Respiration ........................... Ripening Rooms .............................................1 2...........6 2.2 2................................................................ .......x Contents 2................1 3..............4.................. Design of Modified Atmosphere Packaging for Fresh Produce ...... Active Packaging in Polymer Films ............7............ References .............................................................................................3 3....3................................1 3..... Nomenclature ....... References ....................6 3..................................7......................................6.......................... Ceramic-filled Films ............................................. 50 51 51 Acknowledgements ... Temperature Compensating Films .......... Perforation and Microporous Films ............... Respiration Rates .......1 3............ Polymeric Films for MAP Applications .7 3...................... Measurement of Respiration Rates . 4....2 3....... Flow-through System .............5......... Closed System Method ....2 3....................1 3.................................. 3.....................................................................6.................... Unsteady-state Equations ............ 4...............................................1 3................7..3 3........4 New and Novel Approaches to Ethyleneremoving Packaging ....................4 3.....5 Introduction ............................... Temperature Effect ....5.... Concluding Remarks ............................ Feasibility Study ........1 Introduction ................ 55 55 57 59 60 61 61 62 62 63 64 65 66 67 68 70 70 70 71 72 Model Equations and Package Requirements ..1 3........ ....................................................2 3.......5....................... Literature Review .................... 3..... 74 74 This page has been reformatted by Knovel to provide easier navigation............................................ 3...2 3............ Steady-state Equations ...............................................................8 Optimum Conditions ... ..............1 4............................................. 126 Conclusion ..... 105 Current Use Commercially .................... Chemistry of Oxygen Scavenging .............. 135 References ...............................2 5......5 Introduction ....5 4...............4 4....... Edible Films and Coatings as Active Layers .............6 4...........Contents 4.......7 4.............................. 4...........................................................2 4..................................2................................................................. xi 74 76 77 80 83 92 94 95 96 99 Moisture Control Films .............................. 111 Use of Edible Active Layers to Control Water Vapor Transfer ............................................ 106 Regulatory and Environmental Impacts .......................................4 5.........................1 Ingredient Release .. 111 5..............2 Oxygen Scavenging .....................3 4............................................................2.. 106 References ........... 107 5........... 4.................2.................................. Chemical Barrier to Oxygen Permeation .. Plastics Packaging as Media for Oxygen Scavenging ...............3......2.............. 102 Antioxidant Release from Plastics . ...................................5 4............ Brief History of Oxygen-scavenging Films ..... 135 This page has been reformatted by Knovel to provide easier navigation........................................ Removal of Taints and Food Constituents ..4 4........... 103 Permeability Modification ..................... 121 Modification of Surface Conditions with Edible Active Layers ......................8 Forms of Oxygen-scavenging Packaging ............................... Humidity Buffering .....3..3 4...3 5.................................................................1 5...... 114 Use of Edible Active Layers to Control Gas Exchange ....2...... Liquid Water Control ......................2 4......1 4.... 134 Acknowledgements ..................5........ ....................................4 Conclusion ................... 143 Oxygen Absorbents ..... 161 Effect of Oxygen Absorbents on Aflatoxigenic Mold Species .......................4 6.........2 6......3.... .....2.................. 171 Advantages and Disadvantages of Ethanol Vapor Generators ................1 6............... 172 7.......2..................1 6............................ 164 6.......1 6...........................................................3 6.. 172 References ........... 176 History ................................ 166 Uses of Ethicap for Shelf-life Extension of Food ..2.................................. 168 Effect of Ethanol Vapor on Food Spoilage/food Poisoning Bacteria ..... 153 Advantages and Disadvantages of Oxygen Absorbents ...........2 6..........................3.....................................2 Introduction ....5 6.3 6............2...2.4 Enzymes ..................................3......xii 6.......3 7.........................1 7....................6 6............................ 145 Main Types of Oxygen Absorbents .. Contents Interactive Packaging Involving Sachet Technology ......................... 152 Application of Oxygen Absorbents for Shelf-life Extension of Food .............. 144 6....2....... 143 6............................... 149 Factors Influencing the Choice of Oxygen Absorbents ....... 178 Oxygen Removal .....................................3 Classification of Oxygen Absorbents .................. Enzymes as Active Packaging Agents ..............................................................................4 6.2 7.3........ 174 Potential Roles of Enzymes in Active Packaging .................................. 164 Ethanol Vapor Generators ... 179 This page has been reformatted by Knovel to provide easier navigation........................... 171 Ethanol Vapor . 174 7................................. .....3...................... 193 8...2 8.......................1 9................................ 193 8....... 203 9.6 The Effect of Scavenging Closures on Beer Flavor ................2...................................................... 191 8.............2 8............... 195 Combining the Effect of Initial and Ingress Oxygen ......... Commercial Applications in North America ........ 186 Time-temperature Integrator-indicators ................................................. 197 Commercial Activity ...........................4 8.. 201 9................ 200 The Future of Oxygen Scavenging Closures ............3 8......................1 8.....4 8........... 197 Health and Environmental Concerns ........................2.....................2...... 203 Marketplace Susceptors ..........3 8.................................3 Techniques for Measuring the Oxygen Content of Bottles ............2 Packaging Overview ... 188 Lactose Removal .... 204 Field Intensification Devices ..... ..5 8.. 199 Oxygen Scavenger Liners ................Contents 7....................5 7............................. 193 Oxygen Measurements ............................3...................6 7.................................................................. 189 Cholesterol Removal .............................................. 206 This page has been reformatted by Knovel to provide easier navigation..................................... 190 References .........................2 Susceptor Types .. 203 9..1 9.............. 193 Results of Measurements ...........2 Background ............... 200 References ............1 8.......................8 xiii Antimicrobial Effects ..............1 8................................ 194 Oxygen Ingress . 197 8..2.................................................................2............................ 199 The Advantages of Oxygen Control Bottles ................ The History of Oxygen Scavenger Bottle Closures ....3...2..............7 7......... 196 Theoretical .. ..... 234 11....................... 215 10... 240 11...........4................. Safety Considerations in Active Packaging ................................................................................1 Oya Produce Bags ............................... 227 10........ 210 Modified Atmosphere Produce .........................4............... 230 10........ 234 References ...........4 Chemical Indicators for Thermal Process Validation .................3 9.................. 209 9.1 11...................1 Introduction ...................................................3.......... 209 Active Packaging – Produce ...4 Active Safety Interactions ..... 211 Other Applications ................... 209 Oya Test Results ......................................................... 215 10............. 238 11......... 240 Prevention of Migration ......... 213 Oxygen Absorber Food Applications .............................................................................. 213 References ............... .....4 Susceptor Applications ....................... 238 11......2 Packaging and Food Safety .....3..............xiv Contents 9.................................................... 217 10..3 9...................2 9. Time-temperature Indicators .......2..... 238 11.......... 214 10....................5 9.. 241 Emitters and Sorbers ..............1 Barriers to Contamination ..........................................................2 Indicator Systems ........................... 242 This page has been reformatted by Knovel to provide easier navigation.5......4....5 Conclusions .....3 Indicator Application Issues and Consumer Interests ..........6 9.........................4.... 211 Bottle Closures – Oxygen Scavengers .................................1 9...3 Passive Safety Interactions ....... 243 11....... 208 Application of Temperature Indicator to Microwaveable Packaging ............................................................................................................................................3 9...........1 Introduction ..2 11................ .......4....8 11......5 11.................... 256 This page has been reformatted by Knovel to provide easier navigation...6 11....5 Conclusions ..........7 11... 252 References ...........4. 244 Indicators of Safety/spoilage .......... 250 11................4.........9 xv Active Packaging and Migration ..2 11.............................. 248 Rational Functional Barriers ....4.4..................................3 11..............................................Contents 11................................ 246 Modified Atmosphere Packaging ...........4................ 245 Direct Inhibition of Microbial Growth ....... 243 Barrier to Contamination . 244 Indirect Effects on Safety ......... 252 11...... .............................................4 11..................... 253 Index .............. 246 Antimicrobial Films ................................4..10 Combined Systems ......4...........................4....... and this is important in that it differentiates clearly between unwanted interactions and desired effects. Regional differences in terminology are also seen. In this sense. for caps for similar use. free-oxygen absorbers (FOAs) and deoxidisers. ROONEY 1. 1989.1 Overview of active food packaging M. Accordingly a range of types of active packaging has been developed. most packaging media are active to some degree. The term equilibrium modified atmosphere (EMA) . 1992). Active packaging has developed as a series of responses to unrelated problems in maintenance of the quality and safety of foods. There has been a range of trade names for those packages where a generic form has not been coined.L. These latter two aspects also reflect that active packaging is something that is designed to correct deficiencies which exist in passive packaging. This definition reflects the element of choice in how active packaging performs and the fact that it may play some single intended role and otherwise be similar to other packaging in the remainder of its properties. Hotchkiss (1994) includes the term 'desired' when describing the role.Advanced Oxygen Technologies) for closures for beer bottles and Oxyguard for Toyo Seikan Kaisha Ltd. Each of these has a range of descriptive terms. However. A simple example of this situation is when a plastics package has adequate moisture barrier but an inadequate oxygen barrier. and microwaves can be controlled in packages by susceptors or shields (Sacharow and Schiffman. Louis and de Leiris. intelligent and modified atmosphere packaging Packaging may be termed active when it performs some role other than providing an inert barrier to external conditions.1 Active. actually respond to changes'. Horticultural produce has for some years now been packaged in 'smart films'. The terms 'freshness preservative' and 'functional' and 'avant garde' are also used to describe active packaging materials (Katsura. 1991). Active packaging solutions could be the inclusion of an oxygen scavenger. with the result that we have SmartCap (ZapatA . and in some cases. or an antimicrobial agent if microbial growth is the quality-limiting variable. They interact with the product. Smart packages have been defined by Wagner (1989) as 'doing more than just offer protection. there are forms of packaging which are clearly distinct subclasses. and oxygen has been removed from package headspaces by oxygen scavengers. Carbon dioxide can be released by emitters or can be absorbed by getters. theft protection. like the pellets. a grouping of technologies defined in the CEST publication by Summers (1992) as 'an integral component or inherent property of a pack. This grouping covers the area of product identity. biochemical) effects. Probably the closest area is Intelligent Packaging. There is some benefit in such a description as it links desired and undesired interactions of foods and their packaging.packaging is used to distinguish the situation where the choice of the permeability ratio of oxygen/carbon dioxide determines whether respiring horticultural produce generates a viable gas atmosphere or not (Gill. If the physical interactions of a package with the food are removed we are left only with the chemical (and increasingly. tamper evidence. such as flavour scalping (Hirose et . To date they have been used in the form of tablets to indicate when oxygenscavenging sachets have achieved their purpose (Anon. Some aspects of EMA packaging are discussed in this book because the limitations of conventional packaging films are being increasingly addressed using active materials.1%. undated). There have been steady efforts made for several years to produce oxygen-indicating printing inks but thus far. traceability. they play a role in defining the steps that need to be taken to ensure the quality and safety of the packaged food. product or pack/product configuration which confers intelligence appropriate to the function and use of the product itself. Thus where modified atmosphere packaging (MAP) is used with processed foods and involves merely flushing with an initial gas mixture the packaging is not active. The description of this field as interactive packaging is also seen. 'doneness indicators'. these indicators largely change colour at oxygen levels below 0. These are described together with temperature sensitive labels that help determine when food is cooked. The active packaging so described includes susceptors and reflectors in microwaveable packs as well as horticultural smart films that absorb ethylene. Time-temperature indicators also fit the definition of active packaging given above. i. Such a restriction is probably unduly strict and in time we should expect to see further subdivision of active packaging to take account of whether 'activity' is a property of the packaging material itself or of inserts within the package. EMA packaging is one of the borders between active and passive packaging. 1994).e. A somewhat related field of packaging which so far has fallen between the two definitions is that of gas composition indicators. and quality as indicated by timetemperature indicators. 1990). There are other areas of packaging developing concurrently and there are areas of overlap with active packaging as noted with MAP above. The latter was originally included by Labuza (1987) in his seminal review of active packaging. We are beginning to see reference to the benefits of active packaging in the popular press with reference to 'packaging that is niftier and cooks your food' and 'Hi-Tech' packaging (Sprout. authenticity. oxygen-scavenging sachets are bonded to the lid to consume oxygen passing through the trays. It is rather the application of specific packaging properties to specific situations. the suppression of enhanced oxygen permeation of retortable trays (caused by retorting) by application of a desiccant layer is important while the water is being absorbed rapidly during retorting. 1989). in order to impart multi-year shelf-life at ambient temperatures.al. The result of this matching is therefore optimisation of shelf-life and permitting processes. It is in this area that antimicrobial packaging may make a substantial contribution as it develops from its current early stage. hence the naming of this book. Thus. such as making up for an inadequacy of a packaging material . It should be emphasised that active packaging is not a generally applied concept like. containment. For example. we see a large number of niche markets. for instance. this lack of distinction is probably a disadvantage overall. This is particularly important in the area of fresh and extended shelf-life foods as originally described by Labuza and Breene (1989) but not only in that area. Ethanol-releasing sachets are used with bakery products of high aw to suppress mould growth because low oxygen barrier packaging is used. water vapour barrier packaging plastics. 1993). 1. This has been demonstrated by Alarcon and Hotchkiss (1993).1 Why active packaging Inherent in the definition is the point that active packaging now plays a role in the protection of the food which is additional to the classic purposes of any packaging. convenience and communication (Robertson. some niches being very . These examples show that there are opportunities to reduce the cost of packaging materials or packaging processes by use of active packaging with cheaper passive packaging.which is already a compromise. This role can be addressing a single aspect of the packaging requirements of a food. The key focus of active packaging therefore is the match of the package properties to those of the food. a target that normally has been considered to require compromise. The key to using chemical forms of active packaging for economic benefit is that the benefit must be achievable before the chemical is exhausted. formulations and presentation which were previously impossible. In this way. who showed that crusty bread rolls packaged in a medium barrier plastics laminate had a shelf-life similar to that provided by a more expensive foil laminate (see Chapter 6). However. for semiaseptic or retort trays of steamed rice.2 Origins of active packaging 1. It is possible to add hurdles to enhance the safety of food packaging processes. viz. especially when retorted.2. protection. The latter. It also contributes to development of the flavour associated with die 'traditional' canned orange juice. zinc or manganese powders to remove oxygen from the headspace of cans. is now commonplace .1 Iron-based oxygen scavengers. Just how good a barrier the skin is to oxygen permeation is not known. A subsequent development was the introduction of sulfur-staining resistant lacquers (or enamels). This invention paved the way for the subsequent development of the iron-based oxygen scavengers of commerce today.large indeed as with oxygen scavenging crown closures for bottled beer. in a patent. with its two readily accessible oxidation states. while concurrently saving the food from contamination with large amounts of iron. so staining the metal surface. Since tinplate cans were the basic packaging of processed foods for most of the past century. This has been demonstrated by Naito et al (1991) who showed that use of an oxygen absorber alone suppressed growth of bacteria and of yeast (Hansenula anomala) in packages of sponge cake but that the inclusion of an ethanol or carbon dioxide emitter was even more effective. Probably the earliest form of active packaging was the wine skin which. The tin also acts as a reducing agent for food constituents such as pigments. it is not surprising that the next development was also targeted at canned food. described the use of iron.see Chapter 6. The sulfur staining is due to the decomposition of sulfur-containing amino acids in foods to produce compounds which react with the tinplate. The most obvious commencement of active packaging was the use of tinplate for construction of cans. 1. so this is a far from perfect example. albeit somewhat artificially. The tin is sacrificially corroded. .2 Historical development Because it applies to a collection of niche markets. into processed food packaging and fresh food packaging. The introduction of zinc oxide results in a reaction which forms products not observable in the otherwise white lacquer. for instance. In some instances we see the need for application of two forms of active packaging to achieve a goal.2. protecting the iron base can. This became economically significant with the introduction of aluminium cans when it was observed that the 'traditional' flavour was not generated in the absence of tin. This aspect can best be examined by seeking to subdivide it. while causing a variety of unwanted interactions.2. Tallgren (1938). The use of combined-effect sachets.2. was intended to collapse as the wine was consumed without necessarily increasing the quantity of oxygen within. can function as an autoxidation catalyst when residual oxygen is present. active packaging has a very uncoordinated history. 1. copper or nickel since non-food applications also constitute a very large potential market.1 show the distribution of such early applications for composition claims over the 20-year period from 1975 to the first half of 1994. both based on the use of sachets. The steps involved in the scavenging of oxygen by such agents are shown in the following equations (Nakamura and Hoshino. found via the Derwent Index. Concurrent with the development of iron-based scavengers was the development of other inorganic and organic systems. 1977 Mitsubishi. Any applications for coverage of the same matter in other countries are indexed therewith.1 which shows movement from Europe to Japan as development of commercially useable systems occurred. water Alkali metal halides Ammonium chloride Sodium chloride Un-named Form powder powder powder powder powder powder powder film Reference Tallgren. Na2S2O4 + Ca(OH) 2 + O Na 2 S 2 O 4 + O 2 Ca(OH)2 + SO2 2 -* -> -> Na 2 SO 4 + CaSO 3 + H2O Na 2 SO 4 + SO 2 CaSO 3 + H2O (1. The results in Figure 1. 1982 Fujishima. The reaction of sodium dithionite with oxygen can be triggered by the presence of water from a food headspace. The incremental unit is 2 years and the applications were distinguished by their involvement with or frequent inclusion of zinc. 1992 Country Finland UK Germany Japan Japan Japan Japan Japan The development of iron-based oxygen scavengers is summarised in Table 1. 1943 Buchner. The interest in systems not involving elemental metals was initially the strongest although claims for metallic systems peaked around 1980 after .1) (1. for systems which do not involve iron can be seen in Figure 1. 1977 Kureha. The Derwent Index catalogues patent applications by the earliest national application. commencing with catechols and related substances and resulting in the widespread claims of use of ascorbic acid in patents in recent years. 1938 Isherwood.3) The reactions involved in the scavenging of oxygen by iron-based compositions are discussed in Chapter 6. These results were generated by taking the numbers of earliest applications without consideration of the number of additional countries covered. Not all applications are necessarily granted but patenting activity is an indication of interest in developing new ideas.2) (1. 1983). 1968 Nawata el al.Table 1.1.1 History of iron-based oxygen scavengers Additional reagents Water absorbents Iron compounds Sodium carbonate Carbon. The recent growth in the number of patent applications.. Additional processes involving organic chemicals have also been developed. 1985 Koyama/Oda. innovation was directed towards establishing claims for novel compositions and that the level of activity between 1977 and 1982 was almost the same as that between 1989 and 1994. squalene and rubbers. increasingly strong activity in both areas of chemistry reflects the need for processes which overcome deficiencies in existing products. greatest interest was shown in the reactions undergone by various sulfites in the presence of alkali powders which absorb the sulfur dioxide formed. Subsequent developments were based on oxidation of iron powder or ferrous compounds and this has continued with the growth in the number of compositions based on organic reactions. Some active packaging technologies have been based on the introduction of a sachet into the package of food and thus have the characteristics of the protective and functional packaging of any other sensitive product. Mitsubishi Gas and Chemical Co. Prominent among these is oxidation of ascorbic acid or of ethylenically unsaturated compounds such as fatty acids.1 Substrates described in patent applications for oxygen scavengers. including its packaging. The subsequent. . The results in Figure 1. Initially.2 show that. released Ageless sachets in 1978. initially.Metal Other Applications rears Figure 1. What has changed are the chemical reactions involved in these compositions. The fall in the number of patent applications in the mid-1980s is reflected in both the number of metallic compositions and that of other compositions. If the preparation of an active packaging material or process is viewed as a product development topic in its own right then there are two facets which should be evident. The first is the composition and the second is the design of the remainder of the product. Besides the main lines of research and development of oxygen scavengers referred to above there have been other. Chapter 4 deals with development of scavenging plastics for packages in general. and Toppan Printing Co. with the numbers of design applications over the last 10 years exceeding those for new compositions. Another of the aspects of oxygen-scavenger development is the respective positions of sachet and film-based technologies. Europe and Australasia.Applications Composition Design Years Figure 1. especially as liners for crown seals for beer bottles. less popular. Design patents were scarcely considered for the first 8 years of this period until the products of companies such as Mitsubishi Gas and Chemical Co. Evidence of the maturity of this field of active packaging is shown by the trend in patent applications for novel designs aimed at overcoming deficiencies in either handling or effectiveness found in the early versions. made an impact on food packaging in Japan. and the specific commercial application to bottle closures. These aspects are considered in detail in Chapter 4. several hundred million in the USA and some tens of millions in Europe. The current production of oxygen-scavenging sachets alone is understood to exceed 7 billion per annum in Japan.2 Patent applications for oxygen scavengers based on composition or design. The ease of triggering an active state in oxygen-scavenging compositions is more important than with most other forms of active packaging. This maturity of the market is seen in the progressive expansion of use of such products in the USA. is discussed in Chapter 8. rather than being used in a sachet which hitherto had been the main commercial application. A recent trend is the incorporation of scavengers into the packaging material itself. lines of research and . Since that time the number of applications for new designs has increased sharply. This applies also to packaging for microwaveable foods where there is the potential for one form of active packaging to interact with another.2. and is potentially useful where packages already have some carbon dioxide in the atmosphere.2 Composite systems. 1. The potential for generation of conditions suitable for growth of anaerobic pathogenic microorganisms exists if oxygen scavengers are used inappropriately. in a sachet bonded to the inside of the lid of the tray with a hot melt adhesive. The oxidation of glucose. initially in tinplate cans then in laminate pouches.commercial development. The latter may be tolerable in rigid packaging where the seal integrity is good. The catalytic conversion of hydrogen to water. . Such systems are based on either ferrous carbonate or a mixture of ascorbic acid with sodium bicarbonate. There has also been continuous research into ways of stabilising enzymic catalysts for oxygen removal. ascorbic acid. The simultaneous release of carbon dioxide by sachets which consume oxygen was devised by several companies (see Chapter 6). The concentration of this gas needs to reach 20%.. This performance of commercial dual-function scavenging sachets is discussed in Chapter 6. This concurrent release of carbon dioxide can be additionally useful in the suppression of microbial growth (Naito et al9 1991). but in flexible packs pressure decreases of as little as a few kPa result in package collapse where the headspace is small. has been studied intermittently following the work with OxyBan by Scott and Hammer (1961). Thus there is the need to ensure that oxygen-scavenging sachets do not interfere with microwave heating of packages of ready-to-eat foods such as retorted steamed rice. was first described by King (1955) who saw the need for removal of oxygen from spray-dried canned milk powder. the release of ethanol or carbon dioxide concurrent with oxygen removal has been cited for this purpose by both Toppan Printing KK (1985) and Leon et ah (1987). catalysed by glucose oxidase. Accordingly. The historical development of other forms of emitters of ingredients such as flavours. More effective use of dual-function active packaging inserts has been foreseen by several companies in this field. An additional approach to overcome the same problem.2. An early observation was that in-pack removal of oxygen from package headspaces creates a corresponding decrease in pressure which results in either package collapse or development of a partial vacuum. also by Mitsubishi Gas and Chemical Co. This product is marketed with an organic reagent. is the patenting of scavengers based on boron and its compounds. antioxidants and antimicrobial agents is dealt with in other chapters. This subject is discussed in detail in Chapter 7. preferably more. 1. and controls levels of water vapour. During the 1980s. when marketing of films containing inorganic powders was commenced. and with subsequent patches. however. As long ago as the 1970s choices were made between packaging films in an effort to achieve a modified atmosphere which suppressed respiration and lengthened shelf-life (Prince. or by inclusion of crushed rocks. (1970). highly permeable porous patches were introduced. 1989). Thus films have been made porous by inclusion of porous powders such as zeolites or volcanic rock. oxygen and carbon dioxide in the pack. It has long been known that respiring produce will generate its own modified atmosphere. This field has developed either by use of patents or merely by use of advertising claims with little or no scientifically developed results supporting such claims. This is unsuitable for developing equilibrium modified atmospheres close to the optimum for all produce but is useful both in preventing injury due to excessively high concentrations of CO2 and in stopping anaerobic respiration from being initiated. Recently. is a freshness preservative.2.2. has been the subject of considerable research since the work of Scott et al. some considerable scientific modelling effort has been focused on the use of a single pore in a package to achieve the necessary rate of gas exchange (Mannapperuma and Singh. Since there was difficulty in achieving satisfactory performance with many produce-film combinations. This enabled packers to use film of any commodity while ensuring that there was adequate exchange of oxygen and carbon dioxide. Concurrently. 1994). Claimed benefits include preservation of the produce and absorption or scavenging of ethylene. Evidence for removal of ethylene from package headspaces other than by enhanced permeation through porous solids or porous film does not appear to be substantial. Chemical scavenging of ethylene. Their work with potassium permanganate in porous slabs of vermiculite in bags of bananas . More recently. Active packaging for horticultural produce has evolved via the concept of 'smart films'. other workers have approached the same problem by seeking to make the entire packaging film more permeable or by seeking to develop some enhancement of selectivity. This approach has been developed progressively in the USA with the patches of microporous film developed by Hercules Freshold Corp. Katsura (1989) reports that FH film containing Oya stone dispersed on the film surface absorbs ethylene. again. the gas permeability of which changes with the degree of hydration.3 Horticultural active packaging. Some films containing inorganic powders are claimed to offer multiple benefits for packaging of horticultural produce. widely ranging claims were made for effects such as the emission of infra-red radiation from ceramics. porosity has been increased by burning or etching controlled diameter holes to prevent both condensation and oxygen depletion. but in so doing it may reach a stage of ripeness which is not desired. The literature in this field consists very largely of patent applications. . The recent introduction of minimally processed fruits and vegetables in packaged form has heightened awareness in this area. 1989). The latter have often been presented at conferences where specialised audiences have been able to take up the ideas presented. The essential features of these 'freshness enhancers' have been summarised in a short review by Sacharow (1988). Rooney (1989a. Wagner (1989) summarised the range of smart packages and emphasised the role of microwaveable-food packaging. The role of oxygen scavengers in maintaining the benefits of MAP for processed foods was reviewed by Smith et al. The use of edible or otherwise non-toxic coatings on fruit skins as vehicles for active chemicals has been known for several years. The potential for antimicrobial edible films is reviewed in Chapter 5. The detail of the historical development of research and commercial development of such processes is described in Chapter 2. (1990) following their own research into suppression of microbial growth (see Chapter 6).demonstrates the early success of this approach. and modified-atmosphere packaging (Labuza and Breene. Katsura (1989) reviewed the range of functional packaging materials which had been commercialised with particular reference to Japan. 1990) concentrated on chemical effects. He demonstrated the attention that had been paid to freshness preservative packaging. Sneller (1986) reported on the impact of smart films on controlled atmosphere packaging although the first broadly based reviews were presented in Iceland and Australia in 1987 (Labuza.b. 1.3 Literature review Active packaging has developed as a series of topics which are related only because they involve the package influencing the environment of the food. some of which now represent the borderlines between active. who defined active packaging as a range of technologies. 1987. technical leaflets and reviews. Reports of academic scientific investigation have been limited largely to occasional assessments of the appropriateness of some of these technologies. Rooney. The modification of the atmosphere close to the skins of fruit has been achieved by shrink wrapping. The importance of hygiene in the preparation of sliced and diced produce has been discussed by Varoquaux and Wiley (1994). 1987). The first use of the term active packaging was proposed at that time by Labuza. particularly oxygen scavenging. The literature in this field is therefore discussed in terms of the reviews. Both these techniques assist in eliminating the build-up of surface water as a cause of microbial growth on fruit surfaces. 'intelligent'. It was noted that initial developments were directed at the needs for lowtemperature maintenance and moisture control. The use of the term active packaging rather than smart films was noted by that reviewer and by Sacharow (1991) who also noted the use of sachets of potassium permanganate in silica gel for ethylene removal in produce packs. Abe gave the first comprehensive quantitative assessment of the impact of active packaging. Louis described several innovative active packages which generated modified atmospheres. The boom in 1987 was the consequence of the attention being paid to gas composition control and ethylene removal. Ishitani (1993a. The emphasis was placed on crown seals for bottled beer. Ishitani (1993a) observed two factors that led to much rethinking.The International Conference on Modified Atmosphere Packaging at Stratford-upon-Avon (UK) in 1990 organised by the Campden Food and Drink Research Association included several reviews relating to active packaging. The review by Robertson (1991) emphasised the application of active packaging to processed foods. Over the first two years the annual rate was around 35 applications.7 billion oxygen-scavenging sachets and 70 million ethanol-generating sachets were manufactured in Japan in both 1989 and 1990. 1993). The estimated market for films containing mineral powders was only 1000 tonnes in 1989 with 40% of consumption as home use.b) surveyed the number of patent applications for this purpose from 1984 to 1989. 1993. He estimated the market size for each of the broad classes of such packaging systems. Ishitani (1994) concentrated on . His review reveals that around 6. More recent developments have been focused on ethylene removal at high humidities and on matching gas composition and temperature to the requirements of enzymic systems of plants. By this time the claimed benefits of freshness preservation technologies for horticultural products were being examined critically. Miltz et al (1994) reviewed the field in general. oxygen-scavenging plastics films and microwave susceptors. Several recent books on MAP have included discussion of the gas-packaging requirements for horticultural produce as well those for some processed foods (Ooraikul.Food Packaging Material held in Sweden in June 1994. especially in Japan. Parry. These were the lack of data on the requirements of produce and doubts about the capacity of powder-filled plastics to remove enough ethylene. The current state of development and commercial application of active packaging has been reviewed in three papers at the symposium Interaction: Foods . By 1989 gas composition was the main object of developments but moisture control and coating methods were also important. This increased to a peak rate of 220 per annum in the second half of 1987 before dropping to around 60 per annum in 1989. Rooney (1991) addressed some issues drawing attention to the need to consider the nature of the packaging which can be replaced by these new technologies. The environmental aspects of active packaging have not been considered to any great extent in reviews to date. Grace Company and presents a somewhat pessimistic picture. Several posters described original research and that of Paik described photoprocessing of a film surface to generate antimicrobial properties. 1. Early among these was the use of the reaction of lime with water to generate heat for selfheating cans of sake (Katsura.4 Scope for application of active packaging Active packaging is still developing as a collection of niche markets so it is not surprising that a diverse range of packages active in the physical and chemical sense are either proposed or commercially available. . especially antimicrobial films. Perdue (1993) has briefly reviewed antimicrobial packaging from the viewpoint of the Cryovac Division of W. The Verifrais process for meat Respiring Produce Delayed ripening Temperature abuse Fungal growth Aseptic Liquids Oxidation active packaging Prepared Meals Microwave cooking Oxidation Hydration Dry Foods Colour Retention Chilled Meats Mould Growth Bakery Products REQUIREMENT FOODCLASS Figure 1. 1989).R.3 Properties of foods amenable to active packaging. Day (1994) concentrated on fresh produce and Guilbert and Gontard (1994) focused on edible and biodegradable packaging.Japanese developments. A second aspect of active packaging is that it can be involved in the preparation of the food for consumption. water. or facilitate serving of the food for consumption. cooling and foaming. Passive packaging has been used in an effort to minimise the deleterious effects of a limited number of external variables such as oxygen. There have been several reports published on approaches to modelling such systems. These properties therefore include heating. including those thermally processed. However. Some properties of foods which can be addressed by active packaging are summarised in Figure 1. The ways in which such packaging performs these roles are elaborated in the remainder of this section. crustaceans and other seafood can be stored and/or shipped over long distances provided the respiration requirements are satisfied under controlled temperature conditions. suppress insect or microbial life in any foods. 1989). This aspect of active packaging is a unifying theme and crosses the border between foods such as plant produce. These properties are grouped depending upon whether they are designed to sustain living foods. Non-processed. particularly as allowance must be made for temperature abuse. dust microorganisms.3. respiring food such as agricultural and horticultural produce. This includes aspects of temperature modification either for organoleptic or food safety purposes. and they have been compared by Solomos (1994). The carbon dioxide released helps to suppress microbial growth. prevent oxidative attack on food constituents. achievement of the optimum balance of oxygen and carbon dioxide concentrations by use of plastics films alone is frequently impossible. heat. who has tabulated the characteristics provided for in each of the models. retain flavour. Hence. an enhanced period of prime-quality life can often be achieved. Thus if the packaging can regulate the supply of oxygen to the animal or produce such that a minimum respiration rate can be sustained. fish. The generation of elevated levels of carbon dioxide to suppress ethylene synthesis and to suppress microbial action can be achieved by selection of plastics films of appropriate permeabilities. In plant products the optimum oxygen concentration of the environment varies with the species. and levels down to 1% may be possible without inducing anaerobic respiration (Labuza and Breene. It is possible to predict the potential packaging requirements for horticultural produce by modelling the properties of the food and the packaging film. active packaging has the potential to continue some aspects of the processing operation or to maintain chosen variables at particular levels. . and processed foods. light.packaging uses the reaction of organic acid with bicarbonate to produce carbon dioxide in response to meat drip in foam trays. rodents and to some extent. Active packaging can been seen in one sense as a means of maintaining the optimum conditions to which a food was exposed at the immediately preceding step in its handling or processing. An alternative involves pores in portions of a package which open when the temperature exceeds a precisely set value. This wax. Predictive research and some experimental verification of the effects of single pores in produce packages have been reported (Mannapperuma and Singh. The visually unpleasant appearance in retail packs is frequently overcome by antifogs in the plastic . have been presented (Gill. The effects of changes in temperature on gas composition need to be evaluated. Some results for P-Plus. a temperature drop from 12°C to 110C at the pack surface can cause condensation. coral and synthetic zeolites have been incorporated into extruded film but there has been very little disinterested scientific evaluation done. is drawn away by a wick such as a microporous film to leave the pore open to gas exchange. One which is still in its infancy is the use of liquidcrystal polymers which undergo a phase change at a characteristic temperature. but research has opened up this possibility. The water relations between the horticultural foodstuff and its atmosphere need to be balanced both to prevent dehydration and to avoid condensation induced by temperature abuse. Bristol (UK). Several approaches to overcoming the limitations of these films have been reported. as mentioned previously. when liquid. The present state of the art is not sufficiently advanced to cover EMA films which match produce over a wide temperature range. Such films extend the range of gas permeability values of the commodity films in current use. EMA packaging involving selection of polymer films is. Since the RH of such packages exceeds 95%. This type of high-temperature emergency valve is applicable to packages over a wide range of sizes. Chapter 3 shows how modelling can indicate quickly whether available packaging plastics are going to be suitable for maintaining EMA over the temperature range chosen. 1990).Some of these are quite complicated and they are set out in Chapter 3 to provide an easy-to-use model. This has been achieved by filling pores in a patch on a package with a wax which melts appropriately (Cameron and Patterson. This form of packaging is commonly termed modified atmosphere packaging (MAP) or more appropriately equilibrium modified atmosphere (EMA) packaging. Several forms of crushed rock. a porous film currently manufactured by Sidlaw Packaging. Extension of the post-harvest life of fruits and vegetables requires more than EMA packaging. The permeability of the polymer to oxygen sharply increases as this temperature is exceeded. 1994). the borderline between active and passive packaging. The use of pores in packaging materials to actually balance the atmosphere in packages of respiring fruit has been the subject of some research and a large amount of marketing. thus providing the oxygen necessary to prevent packaged horticultural produce from switching from aerobic to anaerobic respiration. 1992). Microporous patches are already used commercially on retail trays of some fruit. which is described in Chapter 2. Chapter 2 includes the approaches taken both commercially and in research reports. Since ethylene is both produced by ripening fruits and triggers their ripening it is essential to prevent those fruits which are further along the ripening process from triggering ripening of others in the same enclosed space. Thus there have been patents of combination CO2 emitter/water vapour absorbers and otherwise similar compositions but including an oxygen scavenger as well. The rapid oxygen scavenger films of Rooney (1982) and Maloba (1994) could be suitable for this purpose if they met with regulatory requirements. Produce packages normally have large headspaces so both sachet and packaging film scavengers should prove acceptable. Lactic acid bacteria lower the pH and suppress the growth of Bronchothrix thermosphacta and Pseudomonas spp. it is no longer capable of doing so for the remainder of the desired storage period. 1992). for instance. Since the quantities of ethylene are tiny. usually 4-8 weeks. Microporous pads containing inorganic salts have been shown to buffer the water vapour pressure (Shirazi and Cameron. particularly with climacteric fruit. There is scope for oxygen scavenging films in bag . This would bring the advantages of reducing the time the packaged horticultural product is subjected to high oxygen levels and inhibiting the onset of ripening. and other species. Some of these are used commercially in the USA and Japan but others are close to commercial development. This matter is dealt with in more detail in Chapter 2. there is the very important field of chilled meats which retain muscular respiration for some hours or days postslaughter. is capable of oxygen scavenging by muscle respiration for a few days at meatworks chiller temperatures of-1°C to 1°C. There have been some patents directed towards use of combination effects in active packaging for horticultural produce. Besides horticultural produce and living seafood which are meant to be kept alive during transportation. Several other 'freshness enhancing' properties have been claimed for some commercial films but the processes occurring therein have not been clarified. While beef. Injured fruits are a particular problem in this regard and this emphasises the need for strict quality control in EMA packaging.and innovative forms of active packaging are described in Chapter 4. The isolation of packages containing fruit rapidly generating ethylene may be the appropriate target of technologies for ethylene removal. The challenge appears to be to provide independently verifiable chemical processes which function satisfactorily to remove ethylene at physiologically significant concentrations in packages under conditions of high humidity and possibly in the presence of condensation. the cost should not be the major obstacle to commercial development. Yet another is Neupalon. Other approaches to enhancing the storage life of horticultural produce have been directed towards removing ethylene produced by ripening fruits and vegetables. so oxygen scavengers would need to operate wet in this environment. An additional definition of active packaging specific to horticultural produce distinguishes between passive and active modified atmosphere packaging (Zagory and Kader. Zagory and Kerbel. One benefit to researchers of oxygenabsorbers is allowing ultimate effects of near-zero oxygen content atmospheres to be evaluated so that prediction of shelf-lives under other less perfect conditions can be more firmly based. cheese and fresh pasta areas. is dependent on MAP (Castelvetri. which has been a recent success internationally. nutrient degradation such as vitamin C loss which can result in browning products (Waletzko and Labuza. although the option of adding other active agents has also been considered (Kader. 1976). and current commercial practice. Modified atmosphere packaging of non-living foods is now a mature area of research and has resulted in filling significant niche markets. The growth of moulds. much recent research and development has been directed towards scavenging polymers which can address problems with oxidisable liquids such as beer. Although initial development. chemical effects such as oxidative attack on colours in preserved meats (Andersen and Rasmussen. and rancidity generation in fats and oils (Nakamura and Hoshino. sophisticated packaging processes in this case. Oxygen concentrations below 0. because of their ease of melt formation. There is a need to remove most residual oxygen which may reach more than 1% when flushing is used without prior evacuation. Besides mould growth. as in the Captech process (Gill. 1990). The carbon dioxide levels are normally very high (> 99%). particularly in the bakery. particularly as carbon dioxide is lost by permeation of packaging films. as in pizza-type cheeses and some MAP meats. Fresh pasta. wines. Polymers. 1989). is based on sachets of scavengers inserted into packs.construction to prevent oxygen permeation and for lactic-acid-releasing films to enhance this effect in some cases. while suppressed by elevated carbon dioxide concentrations. 1992). fruit juices and other beverages. 1989). can take the scavenging capacity to localised .1% are desirable especially when cut surfaces are exposed. The substantial development work aimed at overcoming these problems is demonstrated by the results shown in the Historical Development section of this chapter. is not uniformly affected across the range of species. The passive form which we are considering as EMA involves choice of the packaging material for its ratio of permeabilities to O2 and CO2 as well as for their absolute values. Active MAP has been defined as gas atmosphere replacement by flushing or evacuation-back flushing. 1983) can be prevented or minimised by use of oxygen scavengers. 1988). Low levels of oxygen can in some cases support some species of mould. The removal of residual oxygen from MAP meat packs by oxygen scavengers would increase security and decrease the need for slow. areas such as closures and to areas of close contact of product and package as found with meats. 1989). Besides antimicrobials and antioxidants there is a wide variety of other agents that can be added to foods or which can act on them. In Australia at least. Water-triggered sachets of silica containing ethanol are very much a first generation approach to this form of packaging. At this point the packaging ceases to be active in the sense of the present definition and can be described as intelligent in the definition of the CEST report (Summers. the use of such packaging has been restricted to controlled release of antioxidant into cereal products (Miltz et aL. 1988) or antioxidant (Han et aL. can be seen as a natural extension of the systems used . There is also the potential for foods to be self-promoting via the aroma of their packaging. enzymes can remove oxygen or other undesirable food components. cheeses and wet foods generally. The role of edible food coatings in release of food additives is discussed in Chapter 5.4. In an extreme case. For active packaging to fulfil a useful role in this field it will be necessary for it to provide controllable. This effect has been noted by Smith et aL (1990) who investigated the effectiveness of ethanol-emitting sachets on the growth of Sacchawmyces cerevisiae on apple turnovers. Thus flavours can be added to offset degradation on storage. 1. This includes antimicrobial action (Halek and Garg. as with oxygen-scavenging sachets in Japan. This applies especially to high-water-content foods in which diffusion from the surface into the bulk can deplete surface concentrations (Torres et aL. supermarkets might become a confusing garden of unbalanced aromas competing for the organoleptic senses of the customer in much the same way as package print attracts the customer visually. slow release matched to the needs of the food. particularly following opening of the original package. The ability of polymers to act where there is close contact opens the way to provide a variety of food additives via a diffusive mechanism. the USA and Australia where the "Do not eat label" is required. Introduction of many of these forms of active or related packaging technologies will necessitate serious consideration of explanatory labelling. The benefit of slow release of antimicrobial agents and antioxidants is the potential for maintenance of the requisite high concentration at wet food surfaces. and insecticides can repel insects or kill them with permitted fumigants.1 Do-it-yourself active packaging Shelf-life extension of foods in the home. Thus a desirable flavour might be generated by an outer layer of a package to attract customers rather than being released from an inner layer to offset scalping or processing losses. To date. 1985). 1987) effects. In some cases this may require regulation. minimum sizes are specified to reduce risk of ingestion. There is a potential ethical dilemma which may arise from the application of such approaches to food packaging. 1992). zeolite Anico .in previous centuries. Following the successful introduction of cling-wraps as short-term moisture barriers in the home. An exception to this would be a desiccant pack for cookies or biscuits replacing the early canisters with regenerable silica gel desiccant in the twist cap insert in the lid. Such desiccant could be regenerated in the oven with gentle heating. or on a perforated roll (as with polyethylene bags for plant produce in supermarkets) is particularly effective. Perforations in the Ziploc recloseable bags of Dowbrands (USA). were the predecessors of self-cooling cans frequently invented but less frequently manufactured (Katsura. ANICO bags have a different type of inclusion in the polymer. although the mechanism has not been demonstrated in detail. 19 cm x 27 cm. undated). there has been a steady progression of developments in active packaging for in-home use. It is surprising that such a packaging adjunct is not widely available since biscuit packs made from oriented polypropylene readily tear and generally are not resealable. Most of these forms of packaging are directed towards refrigerated items.2 'Do-it-yourself active packaging Process RH Modification Freshness Freshness Natural radiation Oxygen scavenger Example Pichit . The sale of such film in domestic packs of 10 sheets. The potential for the reduction of the surface aw of food pieces by Pichit multilayer film is described in more detail in Chapter 4. Different approaches to modification of water vapour transfer from foods such as produce are found in the various perforated bags available in many countries. 1989). Examples of do-it-yourself active packaging already available are listed in Table 1.humectants Asahi . Japan).iron powder . consisting of iron and ascorbic acid (Anico.iron sulfate + ascorbate Ceramic particles Mitsubishi . Australia) is an extension of the Spanish wine-skin concept. are a clear example. which are discussed in as much detail as is possible in Chapters 2 and 3. Evidence is presented for reduced microbial growth on four foods Table 1. For instance the modern bag-in-box systems such as Intasept (Southcorp Flexible Packaging. Such bags as are made by Mitsubishi and Asahi are claimed to have 'natural radiation' or 'infra-red radiation' effects. The latter contains zeolite particles with large pores and is available for meat packaging or produce packaging in retail sizes. Typical applications are the short-term packaging of unused food portions such as chicken or fish pieces or freshness retention in vegetables. Less quantifiable are the effects of mineral-loaded bags such as are supplied as Natural Radiation Bag (Mitsubishi. Freshness may be enhanced by release of superoxide. Various evaporative coolers for bottled wine or butter etc.2. This is particularly effective in removing the oxygen from the headspace within 10 h as shown in Figure 1. Results presented demonstrate the removal of ammonia. Some such complexes reversibly bind oxygen until its partial pressure becomes so low that the rate of dissociation equals that of association.4 Oxygen scavenging from loosely packed biscuits packs (•) compared to tightly packed packets (A) (simulating domestic use).4. By Oxygen (%) Time (hours) Figure 1. This type of domestic active packaging is very suitable for foods unlikely to be affected by anaerobic pathogens. An entirely different approach has been developed by Mitsubishi in the form of bags with a 'roll-over and clamp' style of removable pressure seal in kit form for use with cookies. hydrogen sulfide and methyl mereaptan by the reactive ingredients in solution.when wrapped in paper impregnated with ANICO. The cookies are placed in the oxygenbarrier laminate bag and an oxygen-scavenger sachet is removed from a protective metallised film sachet and inserted before the pressure seal is applied. The regulatory dilemma arises in assessing the likelihood of domestic purchasers using such a scavenger system with raw fish or vegetables prone to pathogen infestation. A partially regenerable system involving use of haemoglobin analogues to buffer the oxygen concentration at low levels might be useful in some instances. The result is buffer action. This might take advantage of the high equilibrium constant for reversible binding of oxygen to a cobalt complex. . The quantity of powdered inclusions is insufficient to cause substantial change in the water vapour transmission rate. 1994) to the incorporation of coral sand (Abe. Table 1. Cameron and Patterson (1992) devised a system that allows sufficient oxygen to prevent anaerobic respiration to enter a package if the temperature is raised too high . This process could. susceptor films consisting of paper/adhesive/metallised polyester have been marketed in Australia since the mid 1980s. 1990). be repeated until the accumulation of products of side reactions resulting in cobalt (3) formation reduced oxygen uptake unacceptably.5 Physical and chemical principles applied The fact that active packaging has developed as a series of responses to the needs of niche markets should not hide the small number of underlying principles being applied (successfully) thus far. Researchers in modified atmosphere packaging of respiring horticultural produce have long sought to generate equilibrium modified atmospheres (EMAs) by use of the permselectivity towards carbon dioxide over oxygen of plastics films. 1990). in principle.Next Page careful choice of the equilibrium constant for binding.4). Other military applications were provision of oxygen for welding on warships and for provision of life-support oxygen in high-altitude aircraft. A metal complex would require a high binding constant for oxygen at 4°C and a much lower one at 1000C.3 summarises the use to which these principles have been applied either commercially or in patent applications or other publications. Accordingly. 1. The temperature-controlled opening of pores in polymer films is a substantially more difficult concept to apply in practice. Although the ratio of permeability to carbon dioxide to that of oxygen commonly varies from 3.1. However. Hence research became directed more at methods of controlling the size and distribution of pores in packaging materials. This research has ranged from the modelling of the size of single pores in a package (Mannapperuma and Singh.1 Porosity control. (USA) investigated the use of such complexes for extraction of oxygen from seawater for submarine use.3 (see Table 4.5. 1. It should be noted that oxygen levels needed for anaerobe suppression are higher than has often been claimed (Smith et al. this range is insufficient when considered in conjunction with the absolute values of these properties. an oxygen concentration which is a compromise between protection against oxidation and suppression of anaerobic organisms could be achieved.. the oxygen can be desorbed by immersion of the device in boiling water before reuse. Retail sales of microwave susceptor films have been limited.3 to 8. presumably as a result of the US FDA concerns about the effect of high temperatures on the adhesives which bind the polyester layer to any backing. Aquanautics Inc. . This process could.1. A metal complex would require a high binding constant for oxygen at 4°C and a much lower one at 1000C.Previous Page careful choice of the equilibrium constant for binding.4). in principle.3 (see Table 4. the oxygen can be desorbed by immersion of the device in boiling water before reuse. Accordingly. However. Hence research became directed more at methods of controlling the size and distribution of pores in packaging materials. presumably as a result of the US FDA concerns about the effect of high temperatures on the adhesives which bind the polyester layer to any backing. This research has ranged from the modelling of the size of single pores in a package (Mannapperuma and Singh. 1994) to the incorporation of coral sand (Abe.1 Porosity control.3 summarises the use to which these principles have been applied either commercially or in patent applications or other publications. (USA) investigated the use of such complexes for extraction of oxygen from seawater for submarine use. 1. 1. Retail sales of microwave susceptor films have been limited. 1990).5. Other military applications were provision of oxygen for welding on warships and for provision of life-support oxygen in high-altitude aircraft. Aquanautics Inc. susceptor films consisting of paper/adhesive/metallised polyester have been marketed in Australia since the mid 1980s. 1990). Researchers in modified atmosphere packaging of respiring horticultural produce have long sought to generate equilibrium modified atmospheres (EMAs) by use of the permselectivity towards carbon dioxide over oxygen of plastics films. this range is insufficient when considered in conjunction with the absolute values of these properties. an oxygen concentration which is a compromise between protection against oxidation and suppression of anaerobic organisms could be achieved.3 to 8. The temperature-controlled opening of pores in polymer films is a substantially more difficult concept to apply in practice. be repeated until the accumulation of products of side reactions resulting in cobalt (3) formation reduced oxygen uptake unacceptably.5 Physical and chemical principles applied The fact that active packaging has developed as a series of responses to the needs of niche markets should not hide the small number of underlying principles being applied (successfully) thus far. Cameron and Patterson (1992) devised a system that allows sufficient oxygen to prevent anaerobic respiration to enter a package if the temperature is raised too high . Table 1. It should be noted that oxygen levels needed for anaerobe suppression are higher than has often been claimed (Smith et al. Although the ratio of permeability to carbon dioxide to that of oxygen commonly varies from 3. Their approach was to block a pore in a package with a wax which melted at the chosen upper temperature limit. The use of sophisticated pore control is not limited to respiring produce packaging.3 Physical and chemical principles applied in active packaging Principle Porosity Control Polymer Permeability Melting of Waxes Thermal Expansion Energy Shielding Application Gas pressure release Gas composition balance Gas composition balance Temperature compensation Time-Temperature indicators Temperature compensation Doneness indicators Microwave shielding Thermal insulation Shock absorption Microwave crisping UV absorption Oxygen scavenging Oxygen permeation barrier Oxygen indicator Carbon dioxide generation Ethylene scavenging Taint removal Oxygen scavenging Time-Temperature indication Lactose removal Cholesterol removal CO2 absorption CO2 generation Odour absorption Taint removal Oxygen scavenging Ethylene scavenging Water removal Humidity buffering Condensation control Drip collection Sulfur dioxide release Benomyl release Ethanol release Hinokitiol release Water release Ethylene removal Oxveen barrier Energy Transfer Inorganic-Organic Oxidation Enzyme Catalysis Acid-Base Reaction Adsorption Absorption Hydrolysis Desorption Organic Reactions during distribution. When molten. DRG Flexible Packaging pic introduced the Ventflex® tray in which long capillaries formed horizontally in the lid to regulate gas . the wax was drawn away by an absorbent wicking material.Table 1. Polymer blending has been used to develop sufficiently high permeability to water vapour and smoke flavours at 400C while retaining a substantial oxygen barrier at 23°C.1. However.exchange. Modelling produce requirements with film properties is becoming increasingly popular (Chapter 3). This valve has gone through at least two designs with the early protrusion from the package surface being replaced by a design with the valve flush with the outer surface.1. This property was used for indicating temperature abuse.5. with temperature abuse in produce distribution.5. 1. 1. Yet another approach is to weld a plastic pressure-release valve into the wall of packs for freshly roasted coffee beans to release the carbon dioxide held in the beans under pressure for some days. The accrued knowledge of polymer permeability properties is already very great and other applications in active packaging may be expected. Hence a film which allows generation of a satisfactory EMA at one temperature may cause anaerobic respiration at another. 1. Other forms of time-temperature indication may replace these devices but a considerable amount of modelling of thermal processing may need to be done first. A review of this area is also found in Solomos (1994). especially in chilled and frozen foods (see Chapter 10). insulation has been brought into retail units in .1. Equilibrium modified atmosphere generation is still the major goal of polymer permeability modification. As the package is being used more extensively as the vessel in which foods are reheated or cooked. Use of liquid crystal polymers is an approach to solving this problem but those currently available do not offer large enough changes in permeability to be very significant at present.1. The insulation of foods by corrugated fibreboard cartons or polystyrene foam cartons scarcely satisfies the definition of active packaging. It is perhaps surprising that thermal expansion has not yet been used in temperature compensating devices for balancing gas compositions in EMA packs of horticultural produce. However.2 Polymer permeability. 1. Use of wax melting for porosity controlled temperature compensation has been mentioned above.5 Energy shielding.3 Melting of waxes. the opportunities for indicating completion of the heating of the food are expanding.4 Thermal expansion.5. the temperature dependence of film permeability to oxygen and carbon dioxide is quite different from that of the respiration rate. These plastic inserts in the food expand when the temperature at a predetermined depth reaches a chosen value. To date the so-called 'doneness' indicators for turkeys are an initial example. 5. This makes possible the engineering of food products with mixtures of components with very different heating requirements (see Chapter 9). 1989).1. 1994). The ease with which energy is converted from one form to another has led to the development of microwave susceptors (Robertson.5. The introduction of adsorbents into food packages. Energy transfer has long been used in protection of plastics for use in exposed conditions (Brydson. 1982). either by the process of internal conversion or by energising chemical reactions. This approach is not substantially different from the application of shrinkable foamed sleeves to glass soft-drink bottles. 1. wood fibres and other forms of cellulose as well as various clays and crushed rocks (Labuza and Breene. A higher level of sophistication is found in the inclusion of selective shielding of portions of microwaveable meals by appropriate placement of metallised strips in the top dome of packs. Such processes have been proposed increasingly for food packaging. The concept of shielding the food from energy applied externally can also be applied to shock absorption by layers of foam. and binding odorous products of some oxygen- . 1.1. adsorbing water vapour (Wagner. for intercepting taints permeating plastics packages (Kiru Kogyo KK. 1990). Labuza and Breene (1989) reviewed novel two-layer packages both with and without an intermediate layer such as a chillable gel which imparts an increased thermal load. 1993).6 Energy conversion. One such laminate is described by Yoshizaki (1976).5. Absorption of this energy has normally been followed by energy conversion to heat. in the patent literature. 1991).such novel ways that they deserve attention. 1992). or proposed for use. The major advantage such materials have over chemical reagents is their absence of migration into the food. releasing water as a reagent in oxygen scavenging (see Chapter 6). their potential in the crisping of pastries and other foods has been widely accepted (Sacharow and Schiffman. This follows the demonstration of the effects of light. Although the regulation of susceptors is complicated by concerns about migration. both in the near UV and visible regions. The use of labels which expand to give an insulating foam when plastics lunchcups are retorted is a novel example. adsorbing ethylene to some extent (Louis and de Leiris. has been one of the main approaches to active packaging. on foods (Andersen and Rasmussen.7 Adsorption. both in sachets and dispersed in plastics. They have been used. zeolites. 1992). silica gel. Adsorbents used or described in the literature include activated carbon. A disadvantage of adsorbents is the often-reversible nature of the bonding and the limited capacity. or their inertness. Toppan Printing Co.1. 1989). Water vapour from the grapes is absorbed and releases the gas which is required to act as a fungicide to prevent attack at .scavenging reactions (Inoue and Komatsu. 1. 1988) and in oxygen or ethylene scavenging in the TM Corrugated case (Louis and de Leiris. but meeting a complex need. This absorption process has been coupled with carbon dioxide release in the case of the Verifrais process (Sacharow. 1988. Jobling and Moradi (1993). a. very little use has been made of hydrolytic reactions.10 Hydrolysis. The desorption of ethanol from dry silica gel is the basis of Ethicap sachets (Freund Co. (3 and 7. Carbohydrates such as dextrins have been the subject of substantial research as vehicles for carrying ingredients in the pharmaceutical and flavour industries because of the range of binding forces which can be found. The use of paniculate solids as vehicles for delivery of active ingredients has been a commonly used process commercially.5. Use has been made of the release of sulfur dioxide from sodium metabisulfite in quilted pads of microporous material which are placed in cartons on top of table grapes. respectively. 7 and 8 anhydroglucose units joined. 1991). 1989). which consist of ring-shaped molecules with 6.) which consist of 55% silica gel and 35% ethanol. More complicated. Absorption processes in active packaging have largely involved control of the availability of water in packages. are the humidity-buffering and condensationcontrol systems for cartoned horticultural produce described by Patterson. 1. The humidity-buffering action can also be seen in the carbohydrate and glycol mixture used in Pichit sheet for food-surface de watering in the home (Labuza and Breene.5. Cyclodextrins in particular are attractive because of their cyclic structure and owing to their favourable regulatory status in some countries.).. 1992). When these are exposed to water vapour in the headspace of a food pack. The desorption of ethanol mentioned above may involve some hydrolysis. 1. To date.1.5.8 Absorption.1. The simplest form of absorption has been removal of weep from meats orfishby microporous pads containing superabsorbent polymers.9 Desorption. The use of a variety of porous solids such as vermiculite to hold water for oxygen scavenging has already been mentioned and is described in Chapter 6. they desorb ethanol and a masking flavour. These processes rely on the stronger binding of water to silica gel displacing the more weakly held ethanol. To date they have been used to release hinokithiol antimicrobial agent from non-woven fabrics and plastics films under the Hosenshi trade name of Seiwa Chemical (Katsura. An extension of this is the concurrent ethanol release and oxygen scavenging by Negamold (Freund Co. Cyclodextrins exist in three forms. 1. 1993). The abundance of food constituents and permitted additives which are mildly acidic or basic has facilitated the introduction of acid/base reactions for altering packaged food environments. Thus far. with the result that excessive rates of release can cause partial bleaching of the grapes.5. 1. . The use of food acids dispersed in polymer films for removal of malodorous amines from fish has been patented by Hoshino and Osanai (1986). fatty acids and ascorbic acid has been developed for oxygen permeation barriers in plastics films (Chapter 4). the removal of unwanted carbon dioxide from packs by reaction with lime in coffee packs has also been introduced commercially (Russo. 1994).5. Conversely. there has been no satisfactory method of controlling the rate of hydrolysis. Carbon dioxide generation is possible as ferrous carbonate is oxidised by molecular oxygen. The oxidation of metals had been limited to headspace oxygen scavenging but recent developments in bringing water. The fungal inhibition results obtained when the film was placed in contact with inoculated agar indicated detachment of the fungicide from the polymer and diffusion into the agar. 1986). The Verifrais system and related systems which have followed involve a superabsorbent polymer to absorb water. This has been patented for applications where package collapse on oxygen scavenging cannot be accepted.12 Inorganic/organic oxidation.1. Since oxygen scavenging was one of the earliest forms of active packaging to be introduced the use of oxidation reactions for several other purposes readily followed. 1. Dyes which can be reversibly oxidised have been developed as indicators of oxygen concentration by formulation with reducing agents (Nippon Soda KK. The interest in deodorising food packaging in Japan should result in more research and development in this area. The reaction of ascorbic acid with sodium bicarbonate is commonplace in oxygen scavengers which replace oxygen consumption with carbon dioxide generation.. Oxidation of organic substrates such as polyamides. rubbers. An unintended hydrolytic reaction appears to have been found by Halek and Garg (1988) who set out to bind Benomyl fungicide to a carboxylicacid-containing film. the latter dissolving an acid and bicarbonate to release carbon dioxide in a controlled manner.the stem junction of the fruit. Combinations of many of these principles are found in commercial packages and in proposed systems. Surlyn (Dupont).11 Acid/base reactions. Katsura (1989) noted that Nippon Unicar has introduced a flavonoid-based compound in low-density polyethylene for this purpose also. oxygen and iron together in plastics films has made an oxygen permeation barrier possible by this method (anon. 7. glucose oxidase. 1993). The enzymatic hydrolysis of a lipid has been introduced as a timetemperature indicator by I-Point Biotechnology in the USA. A range of other applications of enzymes in active packaging are discussed in Chapter 7.5. Whereas such non-specific oxidising systems have the possibility of generating taints. Their regulatory status should be examined before they are used. Kuhn and Kuhn (1991) have claimed spreading either the enzyme or glucose on the packaging material and adding the other component immediately before sealing. Ernst and Vonraffay (1991) and Ernst and Ernst (1992) described compositions of silica gel. The compositions can be pellets. glucose and water. 1989) so there is considerable interest in making such systems function efficiently. One of the earliest attempts at producing a sachet-based oxygen-scavenging system was based on the reaction of glucose with oxygen. undated). 7. Ethylene removal by reaction with tetrazines has been demonstrated to occur efficiently at physiologically important concentrations (Holland. L14 Enzymic catalysis. Otherwise unclassified organic reactions have also been proposed in several patent applications. a variety of these rather non-specific oxidant sachets have become available. The water can be supplied absorbed in microcrystalline cellulose. The resulting change in pH was detected by means of a dye following mixing of the substrate and enzyme. 1.75 Organic reactions. Several systems involving both sachet and in-film chemistry have been developed but have not yet been proven in commercial practice.5. Glucose oxidase has been given GRAS status in the USA (Labuza and Breene. 1992). This listing of principles and applications is not intended to be exhaustive but rather is aimed at indicating the basis and diversity of active packaging approaches.Following the early work of Scott et al (1970) on oxidation of ethylene by potassium permanganate. . 1961). catalysed by glucose oxidase in the presence of catalase (Scott and Hammer. The Maillard reaction seems to be the basis of a patent in which reducing sugars and amino acids are brought together under moist conditions in a plastic film (Goyo Shiko KK. the reaction of ferrous iron with organic acids has been developed in plastics films for oxidative removal of taints (Anico. in sachets or between two layers of an oxygen-barrier laminate. The products are claimed to reduce oxygen permeation but may also migrate into packaged liquid food to act as antioxidants. Carbon dioxide can be formed as oxygen is removed if an alkaline earth carbonate is included in the composition. 1990). 1994).6 Implications for other packaging The decision to address at least one attribute of a food by means of active packaging can have a significant impact on the choice of the total package. 1991). used at 1% concentration in the heat-seal polyethylene layer of a laminate. 1990) and oolong tea (Ishitani. When multilayer structures are used this implies that the heat-seal layer contains the active components. It is manufactured by Shinanen New Ceramic Company in association with Mitsubishi (Abe. Zeomic is a zeolite in which silver ion is bonded in the surface layer of the pores. The aim of this work was to determine whether a surfacebound antifungal agent would be effective.1. Alternately it might be necessary to use more expensive materials in order to gain the benefits of the active agents. It was therefore essential that the heat-seal layer should be the Surlyn. While there is still discussion as to whether the microorganisms need to come in contact with the silver surface. The impact can vary from the choice of resin into which to blend zeolites or ceramics for permeability modification to the temperature stability of outer packaging of microwave-reheatable packs for pastries. or onto. In fact. Halek and Garg (1988) demonstrated the antifungal effect of Benomyl bound to the ionomer film Surlyn (Dupont) by coupling with dicyclohexyl carbodiimide. Several forms of active packaging require direct contact between the food and the active components of the package. 1989) or microencapsulation agents either within the heatseal or other layers. The only requirement therefore is that the layer(s) . it was demonstrated that some of the Benomyl probably broke free of the ionomer and diffused into the agar test medium. thus reducing the chance of the residues remaining in the food. In this laminate the cast polypropylene layer containing Zeomic zeolite is closest to the food. Other silver zeolites are available. (Louis and de Leiris. The cells are spread on the surface in aqueous suspension. the food there may be less restriction on the location of the film layer. can reduce the surface bacterial count on the plastic from 105-106 cells/ml to 10 cells/ml in 24 hours. as with the use of oxygen scavengers in packaging relatively short shelf-life foods. Impacts may be such as to allow the use of cheaper packaging. such as Bactekiller manufactured by Kanebo Zeolite Co. The zeolite particles have a larger diameter than the thickness of this foodcontact layer and are thus exposed to any liquid at the food-package interface. Thus there are opportunities to use slow-release binding agents such as cyclodextrins (Katsura. Hirata (1992) has found that silver zeolite. it seems far more probable that the silver ion is dissolved in the liquid by leaching (Ishitani. This form of packaging has been used for fresh oysters (Abe. Where it is intended that the active agent is to be released into. as with Zeopac antimicrobial trays offered commercially by Mitsubishi in Japan. 1994). When the container fabricated from these plastics is retorted at 12O0C for 30 min. Another form of active packaging which can also reduce complexity of oxygen-barrier packaging is ethanol release. Similar considerations to the above apply when active packaging is chosen to remove a food/headspace component such as oxygen. Most frequently.between the active one and the food is sufficiently permeable. 1981. (both of Tokyo) and Multiform Desiccants Inc. This is the basis of the ethanol-releasing sachets Ethicap and Negamold (both from Freund Ltd. The need to separate the scavengers from the food by a layer impermeable to the scavenger has thus far been relatively simple. Toyobo. of Buffalo. 1990).. Hirata (1992) has . 1981). microporosity of a hydrophobic film material has been made use of to achieve this. water vapour permeating the container wall is absorbed and takes part in the rusting of the iron. NY. The careful choice of food contact layer plastics for retortable packages by Toyo Seikan (Koyama and Oda. Toppan Printing Co. This is the opposite situation to that with conventional passive retort package material based on EVOH where retention of water in the EVOH lowers the oxygen barrier and increases oxygen availability to the packaged food for many weeks after retorting (Tsai and Wachtel. 1983). The choice of film materials permeable to oxygen. 1992) and in proposed systems (Teijin. The premature oxidation of the reduced iron scavenger in the Toyo Seikan Oxyguard process at extrusion temperatures of around 220 0 C is minimised by keeping the plastics dry. carbon dioxide or odours. problems are encountered with the polyolefins which are highly permeable to non-polar gases and vapours but are not sufficiently permeable to water vapour. This problem is overcome in sachet manufacture by use of microporous films which are hydrophobic and resist liquid water penetration (Mitsubishi. Retention of water by the composition allows the Oxyguard to continue to act as a chemical oxygen barrier when the package returns to room temperature. Substantial numbers of patents describe methods of achieving the requisite permeabilities to water and oxygen using this approach. carbon dioxide or organic off-flavours has been relatively simple as polyolefins serve this purpose well. The Oxyguard and other oxygen-scavenging plastics compositions can reduce the cost of the barrier layer by reducing the need for inclusion of mica platelets in the EVOH or for desiccants in the polypropylene layer of retortable trays. as inorganic substances such as iron powder have been used both commercially (Koyama and Oda. Where concurrent permeation of the barrier layer to water is also required. The permeability of the sachet material to water vapour or ethanol is of critical importance in the application of these sachets.. 1992) and American Can Company has resulted in the development of heat-triggered oxygen scavengers which function when the water vapour transmission rate of the laminate reaches the necessary value. Tokyo) and of the CO2-releasing sachets manufactured by Mitsubishi Gas and Chemical Co. 1989). Control of carbon dioxide concentration in packs for meat or fish under modified atmospheres is the aim of a French . It is necessary to shake the can to ensure the mixing of the salts with water. Packages for chilled foods have also been redesigned to allow for the presence of an active component. The exposed corrugating medium provides a heating surface claimed to be ideal for such crisping. 1992. Redesign of packages is necessary for some effects to be achieved. Thus in those applications where suppression of mould by ethanol is possible. Wagner (1989) reported that in 1988 Japan exported over 30 million selfheating cans for sake alone. A corrugated fibreboard base for a susceptor film is also used to drain fat coining from foods like fish on heating. Self-cooling cans have also been marketed in Japan for raw sake. Aluminium cans for sake are heated when lime and water in the base are mixed. Amcor Fibre Packaging in Australia has developed a susceptor-coated corrugated inner layer of packs for pastries. Other examples are the various forms of porous or mineral-filled plastics which can be used with respiring horticultural produce. Steel cans for coffee are also heated using the same chemistry. In some instances the consumer may not be aware that the package is different from its passive counterpart as with the oxygen-scavenging closures for bottled beverages. because the location of the shields is critical (Sacharow and Schiffman. Examples of these include the insertion of the various sachets which modify the gas atmosphere. This process also has been used to heat lunch boxes (Katsura.1 Whole packages designed to be active Some forms of active packaging do not require changes in design of the package in order to achieve their effects. simple packaging materials can be considered since oxygen control may not be necessary. with the result that present opportunities are limited. The use of susceptors to achieve surface crisping of foods means that the distance between the food surface and the susceptor must be carefully controlled. particularly when some of the physical principles listed in Table 1.3 are involved. Smith et ah (1987) have suggested that the use of ethanol could reach approval status in North America for 'brown and serve' products such as pastries. as described in Chapter 6.6. This is particularly important where shielding of components in microwaveable meal packs is desired. 1. The endothermic dissolution of ammonium nitrate and chloride in water is used to cool the product. Robertson.shown that common commodity polymers such as oriented polypropylene form a sufficient barrier to ethanol permeation to retain this sterilant in the package for extended periods of time. described in Chapter 8. 1993). Currently ethanol use in this way is not widely permitted. not all horticultural active packaging is so simple. The delay in access of the liquid to the sachet is controlled by an absorbent paper pad located between the sachet and the porous tray. Oxygen can enter through the same channels or more slowly through the polyester barrier film forming the lid. These chemicals help to reduce package collapse owing to outward permeation of carbon dioxide by generation on a continuous basis. has no microporous food contact polymer but does contain a ceramic claimed to absorb ethylene. The shelf-life of fish can be extended similarly to 10 days versus 4-5 days under MAP. The Ventflex laminate pack introduced by DRG Packaging in the UK relies on channels between the layers lidding the film to allow some regulation of evolution of carbon dioxide by the packaged produce. and sodium carbonate (25%). Redesign of packages has also been used to address the problems of . 1990). which. The packaging material needs to have a strong heat-seal if leakage is to be avoided within the first day of packing. while superficially similar to the above. 1987). 1991).package designed to be active (Louis and de Leiris. The carton is lined with three additional layers which provide in-pack buffering of the water vapour in the carton headspace. Although the mineral-filled and other porous horticultural-produce carton liners differ very little from conventional liners. The preferred chemicals are sodium chloride (50%). A more recent variant on this design has the carbon-dioxide-generating components concealed in a foam tray with channels for juice drainage (Leon et ai. A porous sachet containing sodium bicarbonate and ascorbic acid is in the base. An alternative to these active packaging processes is the Valle Spluga process which involves insertion of a pellet of solid carbon dioxide into the pack before sealing to provide sufficient additional gas to retain package shape (Louis. Release of carbon dioxide from the sachet serves to offset this loss. The aim is to prevent growth of anaerobic pathogens on meats and seafood packed in low-oxygen-content modified atmospheres. The commencement of dissolution of the acid and bicarbonate can be delayed for up to 24 hours. citric acid (25%). The carbon dioxide is pelletised in-line to a predetermined dosage. Meats can have a shelf-life of up to 21 days at 2-4°C in this pack compared with the 10-15 days under normal MAP (Louis. The condensation control carton design of Patterson et al (1993) reduces substantially the chance of produce damage by water condensation caused by temperature abuse. 1990). This carton lining is designed to act as a humidity buffer. Louis and de Leiris (1991) describe the TM corrugated case of the Mantsune Co. by which time the carbon dioxide concentration can be decreasing due to dissolution in the meat and permeation of the tray and lid. The Verifrais package manufactured by Codimer consists of a heat sealable lid with a tray with a false bottom which is perforated to allow juice from the product to drain into the base of the tray. The chemicals can be in aggregate form rather than held in sachets as with Verifrais. The forms of active packaging which involve minimal changes to the preexisting package design have been most readily adopted commercially so far. 1988). Current commercial active packages do not meet these criteria although there are some which are second-generation concepts. USA) offer some answers to the temperature problem (Stewart et al. The expansion of this market appears to have been limited by the preference of food manufacturers not to include sachets in the packages with the foods. 1994). Taylors of Harrogate. 1986). (UK) pack the beans in foil laminate pouches which resist the pressure of carbon dioxide evolved by the beans. Horticultural active packaging is not yet based on films with a sufficiently wide range of CO2-O2 permeability ratios. There is a lack of convincing evidence that several of the films designed to scavenge ethylene do in fact work satisfactorily under actual conditions of use. Recent introduction of sachets bonded to the package walls should facilitate greater market penetration (see Chapter 6). The Taylors' bag contains a one-way plastic release valve welded into the face of the bag and this prevents seal rupture. 1990). The latter include meat packs with inserts which release carbon dioxide in response to absorption of weep or juice (Sacharow. The General Foods pack did not require redesign to accommodate the sachet. CA. The number of oxygen-scavenging sachets manufactured in Japan in 1989 was estimated at 6. A Mitsubishi Ageless sachet which absorbs carbon dioxide and oxygen was included with the coffee in their packs (Russo. Tea and Coffee Ltd. This ratio would need to be temperature responsive in the same manner as the enclosed fruit or vegetable. The control of humidity in liner bags of fruit and vegetables is still in its early stages of . The Intellimer side-chain-crystallisable polymers from Landec Corporation (Menlo Park. An alternative approach was adopted by General Foods in the USA. The original valve design had a protruding component and so was welded into the side gusset. 1.packaging of freshly roasted coffee. Both active packaging approaches were designed to retain the easily oxidised fresh coffee flavours normally lost when coffee is allowed to stand for 24 hours to desorb carbon dioxide. This gas evolution usually occurs for at least the first day after roasting. The widespread use of sachets for headspace atmosphere modification demonstrates this point. Industry confidence would be well served by self-indicating films which change colour on reacting with ethylene at physiologically important concentrations.7 Limitations of current approaches The ideal active package would sense the requirements of the food and adjust its properties in order to meet them.7 billion (Abe. At the same time this would be cost-effective and have minimal environmental impacts. Horticultural produce. electronic components. metals and many more areas. Current commercial oxygen scavenging sachets are supplied in a wide variety of forms to suit particular temperature and relative humidity conditions. These designs place limitations on the shelf-life of the sachets once the master-packs are opened and before insertion into the food package. Some early steps towards overcoming the shelf-life limitation have been reported in the patent literature. active packaging has a bright future. It is clear from patent searches that inventors of active packaging frequently see potential applications for their concepts in several industries. Commercial development therefore will be driven by needs as perceived in the food industry or in other industries with related problems. Inserts or films capable of regulating humidity levels are required. fine chemicals such as amines. The use of oxygen-scavenging plastics as chemical barriers to permeation should allow retortable plastics to provide product shelf-lives closer to those found using metal cans. Acceptance of active packaging solutions to food industry problems will continue to depend upon evidence of effectiveness demonstrated by independent investigators. Some iron-based oxygen scavengers have been suggested for use in hand-warmers for skiers. This is evident in claims for use of oxygen scavengers in the packaging of clothes.development. especially where temperature abuse is likely. If the potential of active packaging technologies is to be realised there will need to be a recognition that changes in packaging can open up new methods of presenting foods. The use of a peelable barrier on a sachet with a self-adhesive backing has been proposed. such as flowers.8 Future potential The future of any innovation in packaging depends upon the extent to which it can satisfy the requirements of the product packaged. should be transportable internationally with reduced losses. The use of sealed plastic bags for equilibrium modified atmosphere generation makes this requirement more critical. 1. . printing inks. pharmaceuticals. Compositions which are able to withstand extrusion and yet be activatable are required. An ideal sachet would be useable under a wide variety of conditions and activated for a particular application by the food packer. If the majority of patent claims already made prove useful and economically viable. The lack of hard evidence supporting many claimed benefits of some early horticultural produce packages has inhibited commercial usage. Attempts to include oxygen scavengers in plastics packaging materials have not yet been successful commercially except in closure liners for beverage bottles. may facilitate the approval procedures for active packaging. The manner in which oxygen scavengers are used may be subject to regulation. Proceedings International Conference on Modified Atmosphere Packaging. First. . thermal history.9 Regulatory considerations At least three types of regulation have an impact on the use of active packaging in foods. A substance may migrate into the food or may be removed from it. Developments in active packaging discussed in this book are not necessarily commercial and care should be taken in using any of them. 15-17 October. NY. Food-contact approval will often be required because active packaging may affect foods in two ways. environmental regulations of packaging material usage can be expected to increase in the coming years. Alarcon. Dept. pp. Some form of external labelling may be required when various forms of indicator come into use. Stratford-uponAvon. Technical Report. any need for food-contact approval should be established before any form of active packaging is used. Part 1. References Abe. B. The effect of active packaging materials on recycling may need to be determined on a case-by-case basis. etc. Some active packages may be expected to look different from their passive counterparts. It may be advisable to use labelling to explain this even in the absence of regulation. (1990) Active Packaging . 1-7. Environmental regulations for packaging materials often refer to recyclability or identification to assist in recycling. ethanol emitters. or 'done-ness' in the case of microwaved foods. Cornell Univ. Labelling is currently required to reduce the risk of ingestion of sachets of oxygen scavengers. and the chance of the European Union adopting similar concepts later. of Food Science. (1993) The effect of FreshPax oxygen-absorbing packets on the shelf-life of foods. Food additive regulations require identification and quantitation of any such migration. The likely introduction of the 'Threshold of Regulation' concept by the US FDA early in 1995.1. and Hotchkiss. Y.H. Third. Unintended additives include active substances which achieve their purpose inside the packaging material and do not need to enter the food. Such indicators would show gas composition. Removal of oxygen from packages may lead to the growth of anaerobic pathogens in some cases. The intended migrants include food additives which would require regulatory approval in terms of their identity and concentration. Migrants may be intended or unintended. Second. there may be a need for labelling in cases where active packaging can give rise to consumer confusion. UK.. Active packaging is often used currently to allow foods to be packaged with simpler materials than would otherwise be possible. The environmental impact of the food-package combination should be considered. J.a Japanese Perspective. F. 11-15.. (1992) Modified atmosphere packaging. M. A. Halek. Feb. Japanese Patent 86209612. J. (1990) High Permeability Films for MAP of Fresh Produce. Anico Co.contains porous pptd. Technol. 365. Stratford-uponAvon. Cameron. 27. Food Safety. (1994) Edible and Biodegradable Food Packaging. G. Butterworths-Heinemann. British Food J. Proceedings 'Interaction: Foods . J.A new age in food preservation. N. (1943) Removing oxygen from a container containing vacuum or gas packed food in which a metal (ex Fe) absorbs oxygen to form an oxide. 15-17 October. S. K. Proceedings International Conference on Modified Atmosphere Packaging. Han. Japan. and Vonraffay. Japanese Patent 6020986. (1988) Oxygen absorbent compositions . JJ. and Gontard.) ACS Symposium Series No. R. (1992) Oxygen absorbent for keeping food fresh . Lund. National Food Research Institute. Anon. in press. R. Mitsubishi Gas Chemical Co. Miltz.A. Lund. and Gray. R. Fujishima. and Ernst.H. Harte. J.R. Australian Institute of Food Science and Technology. Washington DC. Yokohama-shi. UK. F. Hirata. T. T. US Patent Application 155283. HJ. Ltd. (1986) Packaging Films for Deodorization. Food Sci. Part 1. B. (1991) Oxygen absorbent for keeping food fresh . Eng. Polym. Sales Pamphlet. (1968) Oxygen-absorbing Inclusions in Food Packaging. Proceedings 'Interactions: Foods Food Packaging Material'. J. glucose and glucose oxidase. pp. 934-8. (undated) Ageless .. Japanese Patent 5186635. J. Australian Patent Application 9219767. Tsukuba. Gill. J.. Hotchkiss. 124-35.. silica. European Patent Application 359925.A. and Rasmussen. Hoshino. (1987) Loss of 2-tertiary-butyl4-methoxy phenol (BHA) from high density polyethylene film.R.. Proceedings 1st Japan Australia Workshop on Food Processing. B. Holland. 4th edition.. Canberra. (1994) Recent Research in MAP and Active Packaging Systems. 8-10 June.F. In: Food and Packaging Interactions. Gothenberg. and transition metal or absorbent. US Patent 5028578. Isherwood. (1992) Recent Developments in Food Packaging in Japan. 1-8. Giacin.comprises high molecular substance amino acids and hydroxyl group containing reducing resin.A. . Goyo Shiko KK (1993) Packaging material with good gas-barrier property and oxygen absorbing property . and Garg. 19. Stratford-upon-Avon.K. (1989) Packaging of meat for prolonged chilled storage. 8-10 June.Andersen. American Chemical Society. (1992) Interactive packaging as protection against photoreduction of the colour of pasteurised. UK. Miltz. Day. M. (1990) Modified Atmosphere Packaging of Italian Style Fresh Pasta Products.. Technical Pamphlet. (1994) Use of a new container requiring no deoxidizer. silica. glucose and glucose oxidase. Gothenberg. Y. Part 1. (1992) Absorbent material and uses thereof Australian Patent Application PJ6333. base. C. S. in the form of solid or aqueous solutions. in press. and Fujishima.R. anon..Food Packaging Material'. SIK. A. Sci.D. 9. Castelvetri. UK. Brydson. Buchner. Proceedings International Conference on Modified Atmosphere Packaging. Anico (undated) Chemically active substance containing divalent ions. Ernst. 28-41.W. Oxford.P. A. British Patent 553991. and Osanai. (1989) Sorption of a-Limonene by Sealant Films and Effect on Mechanical Properties. 215-22.comprises unsaturated fatty acid or derivative. Abstracts. 27. SIK. Japan. J. CO. Harte. (1982) Plastics Materials. pp.. V. West German Patent 1267525. and Patterson. (1985) Oxygen-removing agents. T. J. J. water. and Komatsu. Guilbert. sliced ham. (1988) Funga inhibition by a fungicide coupled to an ionomeric film. B. 77-95.V. Hirose. T. July. N. Hotchkiss (ed. Gill. B. (1994) Active Packaging for Fresh Produce. J. Packaging Japan. Inoue.contains porous pptd.R. Ernst. 15-17 October.. Giacin. and Stine. water. 91. B. 27th Annual Convention. Intl. (1987) Sealed food pack with concealed chemicals to sustain aerobic or inert to suppress distortion or development of toxins by anaerobic degradation. J. Proceedings 'Interaction: Foods . Maloba Wakwabubi.G. (1983) Techniques for the Preservation of Food by Employment . Iceland.D. alkali metal halide.using oxygen-scavenging system comprising glucose and glucose oxidase introduced separately. Passy.Hawkesbury. Katsura. used for vegetable and fish preservation. Packag. 4.. W. Australia.. December.. F. University of Western Sydney .. Atlanta. D. (1989) Applications of 'Active Packaging' for improvement of shelf-life and nutritional quality of fresh and extended shelf-life foods.Oxyguard. Lund. 53. N. Zagory. Stratford-upon-Avon.. and Kerbel. (1991) Active Packaging. (1994) Trends and Applications of Active Packaging Systems.R.R.. (1991) Packaging of solid foodstuffs . Ishitani. Proceedings International Conference on Modified Atmosphere Packaging. (1992) Oxygen scavenging technology for packaging . Food ScL Nutr.K. C H . Package Japan. Loevenburg. Part 1. Leon.M. and Oda. Sept. April.G. and Hoshino. and Yamaguchi. (1989) Modified atmosphere packaging of fruits and vegetables. T. 441. pp. Han. Mitsubishi Gas Chemical Company (1983) Food storage bag containing oxygen absorbentbars sheet with fine apertures which are gas permeable but waterproof at atmospheric pressure.H. J. Preservat. (1991) Studies on the behaviour of microorganisms in sponge cake during anaerobic storage. Farming Japan.having a plastic functional layer containing adsorbent e.P. Sept. 10-17. and Troadec. (1987) Applications of 'Active Packaging' for Improvement of Shelf-Life and Nutritonal Quality of Fresh and Extended Shelf-Life Foods. Special Issue. Nakamura. 1-69. (1990) Advanced MAP and Related Modified Atmosphere Systems From Around the World. J. Kiru Kogyo KK and Marutani Kakoki KK (1994) Functional container for medical supplies or foods .. 8-10 June.. (1989) Loss of antioxidants from high-density polyethylene: its effect on oatmeal cereal oxidation. Miltz. In: Food and Packaging Interactions. B. in press. 30-7. Louis. US Patent 4421235. J-P. GA. US Patent 4664922. Japanese Patent 52104490. King. (1994) Resonance Energy Transfer. Japan. Japanese Patent 6080163.Food Packaging Material'. F. Reykjavik. European Patent Application 417793. 4333-44. Japanese Patent 8224634.K. (1994) Design of Perforated Polymeric Packages for the Modified Atmosphere Storage of Fresh Fruits and Vegetables. and Mannheim.and opt. 1-30. Proceedings of Pack Alimentaire '92. P J . A. IFT Annual Meeting. and de Leiris. Koyama. J. Harte. J. (1993a) The present state and problems of freshness preservation from the viewpoint of packaging technology. filler . Mitsubishi Gas Chemical Company (1977) Oxygen absorbent comprising e. Etude technologique. Hoojjat. iron.P. June 25-29. PJ.) ACS Symposium Series No. Kureha Chemical Industry Company (1982) Deoxygenator composition. Louis. Hotchkiss (ed. 8-10 June. and Breene. and Gray. I J .L. Rev. silica gel. (1955) Catalytic removal of oxygen from food containers. H. Y. (1994) Active packaging for Foods in Japan. Lund. 21-6. S. Book of Abstracts. Miltz. T. J. Multiclient International Packaging Club. Washington DC. Kuhn. PhD Thesis. SIK. 13.Ishitani. Ishitani. Singlet Oxygen Sensitization and Application. zeolite on inner surface of outer layer of sealed container. Y. Kader. sodium sulfate. (1993b) Freshness-keeping technology for fruits and vegetables: its present and future. Icelandic Conference on Nutritional Impact of Food Processing. 30.. Mannapperuma. Proceedings 'Interaction: Foods Food Packaging Material'. 28. E. Gothenberg. Packaging Technology and Science. R. J. J. Session A-I... Okada. SIK. Giacin. (1989) Present state and future trend of functional packaging materials attracting considerable attention. in press. 83-93. Paris. 365. N. J. 15-17 October. T. Gothenberg. J. Naito. T. M. UK. Food Manuf. JR. H.g. and Singh. H.g. Labuza. J. T. Crit. Food Proc. and Kuhn. Labuza.P. American Chemical Society. T. UK. F. May 1990. Japanese Patent 93033347. (1989a) New Technologies in Flexible Packaging Materials. and Roberts. Expt. J. December. J. R. Koersen. and Moradi. and process for storing coffee by using same. M. but not everything's practical. Food Technol. CT. 99-102. Rooney. (ed. Robertson. F. and Lawrence. Patterson. R. 121-2.J. A.B.R. (1989b) In-Pack Systems for Oxygen Removal. 32-3. Perdue. basic substance aluminium hydroxide and water-repelling binder. 419-30. B.L. Sacharow..L. 565-9. and Schiffman. Abstracts Annual Convention of the Institute of Food Scientists and Technologists. Rooney. Sydney. S. (1988) Freshness enhancers: the control in controlled atmosphere packaging. Atlanta. Section B-2.836.. 67-100.. (1989) Modified atmosphere packaging of horticultural commodities. (1991) Packaging meets 1990s need through active technology. M. 99-104. Prepared Foods. 34. Pira International.A. Aust.F. University of Queensland. S.y 47.L. Scott.J. (1982) Oxygen scavenging from package headspaces by singlet oxygen reactions in polymer media. 24-8. Scott. Feb. B.L. Ellis Horwood. 4. In: Controlled/Modified Atmosphere/Vacuum Packaging of Foods.5. VoI 2. Hortscience. Film and Foil Converter. / Food Sci.C.A. AgHc. S. Russo.L.D.. reducing sugar. July.101. Food Microbiol. May...R. M. A. European Patent Application 81. Brody (ed. T. (1987) Shelf life extension of a bakery product using ethanol vapor.. T. Marcel Dekker. M. 10.L. VoI III. Rooney. Anim. Proceedings of Pack Alimentaire '90.R. McGlasson.. Parry. Shirazi. Trumbull. van de Voort. G. Ooraikul. Auckland.A. E.L. Sacharow. Australia. W.L. Nippon Soda KK (1993) Oxygen sensor for use in highly humid conditions is made from moulded mixture of methylene blue. (1993) Water Relations After Harvest . S. New York. 26-32. USA. 119-34. R. Innovative Expositions. (1987) Modern Approaches to Packaging for Improvement of Quality and Storage Life. Sacharow. Aug. Blackie Academic & Professional. (ed. Rooney. (1992) Controlling relative humidity in modified atmosphere packaging of tomato fruit. Princeton. 8th National Convention. K. 6-7 November. New Jersey. Paper. Food and Nutrition Press Inc. Cereal Chemistry Division. Prince. Proceedings 8th International Seminar on Packaging.D. Sydney. 13. San Francisco. Leatherhead. Packaging (Chicago). 1st November.). and Ohtsuka. (1994) Oxygen-Scavenging Plastics Activated for Fresh and Processed Foods. 83-90. (1992) Microwave Packaging. 75. Proceedings of the Australasian Postharvest Conference. Proceedings Royal Australian Chemical Institute. Proceedings 18th Asian Packaging Federation Congress. (1986) Innovative packages at General Foods. and Hammer. (1993) Food Packaging principles and practice. Glasgow. 298. E. Hush. B.) (1993) Modified Atmosphere Packaging of Food. M.. (1991) Smart Packaging Films: New Opportunities for Food Processors. Queensland. (1970) Potassium permanganate as an ethylene absorbent in polyethylene bags to delay ripening of bananas during storage. R. and Cameron. 237-40. Food Proc. Robertson.. A. Ooraikul. Proceedings Auspack *89 Seminar. J. 31(8). . M. Rooney.) (1993) Principles and Applications of Modified Atmosphere Packaging of Foods.L. NY. (1993) Antimicrobial packaging: anything's possible. (1990) New Methods of Maintaining Product Quality through Package Interaction. Smith. Sydney. New York. T. Komatsu. (1961) Oxygen-scavenging packet for in-package deoxygenation. Jobling.L. (1991) Are Active Packaging Systems Environmentally Sound? Proceedings 2nd Australia Intl Packaging Conference.P. D. Jackson. Rooney. M. M. G. Rooney.Nawata. Gatton. 291-4. NY.New Technology Helps Translate Theory Into Practice. J. 329-37.T. (1981) Oxygen and carbon dioxide absorbent. W. K. used to preserve food packed in low gas permeable envelope. R. J.. Torres. and Wachtel. Charpentier (eds) ACS Symposium Series No.P. British Patent 496935. (1990) Developments in food packaging technology. and their Kin for Food Preservation.. Getters.. 183-225. Hosahalli. and Emitters. Budd.. Wiley (ed. 9. Chapman & Hall.C. A. UK. Toppan Printing Company (1992) Oxygen absorbent composition which functions in dry atmospheres . Stewart. J. Summers.A. H. 11. R. T. (1990) Barrier properties of ethylene-vinyl alcohol copolymer in retorted plastic food containers. 226-58. Pratt and B. J. Sprout.. 520. and Wiley. Mod. and Simpson. (1976) Packaging bags for food .New Packaging that's thriftier. 16(9).F.. pp. R. B.M.R. Centre for Exploitation of Science and Technology. 192-202.F. and Karel. B. W J . T. Trends in Food ScL Technol. J. Toppan Printing KK (1985) Food preservative of ascorbic acid derivative and ferrous salt with ethanol retained in starch or dextrin etc. and Anul. Solomos.A Comprehensive View of Absorbers. Japanese Patent 56060642. Storage aspects. Food Technol.A. M. Japanese Patent 56159166. niftier and cooks your food! Fortune. (1994) Some biological and physical principles underlying modified atmosphere packaging. S. Toyobo KK (1981) Plastics laminate with improved gas barrier properties manufactured by applying an aqueous solution and/or dispersion containing oxygen barrier polymer and oxygen absorber to thermoplastic resin film.contains unsaturated fatty acid. Intl.Properties and Applications. Wagner. Control of surface preservative concentration. December. J. (1992) Intelligent Packaging. Yoshizaki. oxidation catalyst. (1994) Temperaturecompensating films for modified atmosphere packaging of fresh produce. Mohr.K. Preservat. (1976) Accelerated shelf-life testing of an intermediate moisture food in air and in an oxygen-free atmosphere. 8. L. 58-9. A. X.with shock absorbent thermoplastic resin film and aluminium foil between resin films. M. 70-7.. (1994) Biological and biochemical changes in minimally processed refrigerated fruits & vegetables.A. Zagory. In: Minimally Processed Refrigerated Fruits and Vegetables. (1989) The advent of smart packaging.). Part II. D. Intl. Wiley (ed. 1. Motoki. 1.C. New York. Varoquaux. (1938) Keeping food in closed containers with water carrier and oxidizable agents such as Zn dust.C. 5 September. pp. Japanese Patent 51089579. New York.). D. (1985) Microbial stabilization of intermediate moisture food surfaces.. . American Chemical Society. E. J. Sneller. In: Minimally Processed Refrigerated Fruits and Vegetables. New Jersey.P. 1338-44. Japanese Patent 60070053. 75-92. active clay and deodorant. A.M. and Labuza. (1986) Smart films give a big lift to controlled atmosphere packaging. Chapman & Hall.C.Smith. Innovative Expositions. J. Plast. London. El-Nokaly. B. Tallgren. M. J. (1990) Getting to Know the Packaging Activists . R. Washington DC. Lok.A.A.L. Teijin KK (1981) Oxygen absorbing agent obtained by dispensing oxygen absorbing material in a polymer. P. In: Barrier Polymers and Structures. Section B-2. Waletzko. Japanese Patent Application 4298231. Tsai. Food ScL 41. P. and evaporating water to obtain sheet. Washington DC. Mn dust etc. Wagner. American Chemical Society. J. Food Process. pp. and Kader. Fe powder. In: Polymeric Delivery Systems . Food Eng.). 111-18. 42. (1994) Technology to watch . Proceedings Pack Alimentaire '90. Koros (ed. Princeton. (1988) Modified atmosphere packaging of fresh produce.P. ubiquitous chemical that has diverse and profound effects on the physiology of plants.1 Synthesis Ethylene can be synthesized both biologically and non-biologically. is effective in such low concentrations. 2. For this reason. physiology and agricultural effects of ethylene preparatory to describing the research and commercial effort undertaken to incorporate ethylene control agents in packages for horticultural products. being simply two carbons linked by a double bond with two hydrogen atoms on each carbon. Ethylene has so many different effects on plants. often ethylene has been seen to be detrimental to the quality and longevity of many horticultural products. 2. Some of the diverse ways in which to absorb. it is timely to review the basis and activities relating to these products to better elucidate the possible forms that they can and will take and to point out some of the advantages and disadvantages of the various approaches likely to emerge. Such a simple molecule can be synthesized through several different pathways and is subject to many kinds of chemical reaction.1 The chemistry of ethylene The ethylene molecule is of the alkene type. with the rapid growth of packaging of fresh fruits and vegetables. particularly fresh cut salads and fruits.2 Ethylene-removing packaging D. there has long been interest in removing ethylene from the horticultural environment and in suppressing its effects. It is a common component of smoke and can be found as a product of aerobic . such as induction of flowering in pineapples. and its effects are so dose-dependent. Therefore. adsorb. but much has not. ZAGORY Ethylene is a chemically simple. Some of this effort has met with commercial success. Though many of the effects of ethylene on plants are economically positive.1. that it has been identified as a plant hormone. However. de-greening of citrus and ripening of tomatoes. counteract or chemically alter ethylene have led to products designed to reduce its deleterious effects. This chapter will briefly review the chemistry. opportunities for such products are bound to increase. Atomic oxygen will also react with ethylene and can form an array of compounds . 2. The pathways for synthesis in bacteria appear to be diverse since any of several carbon sources other than methionine will serve as precursors (Sato et al. 1964). is thought to be an efficient oxidizer of ethylene (Abeles et al. The pathway of synthesis from methionine has been described in detail for higher plants (Yang and Hoffman. some algae. 1992). 1992). 1966). ethylene absorbs ultraviolet (UV) radiation at 161. it is not necessary to go into the details of production by different organisms. carbon dioxide (CO2). 1984. UV light will effectively eliminate ethylene even in low O2 atmospheres (Shorter and Scott. 1973) and yields primarily hydrogen. 1968). 1989a). Because of its double bond. However. 166 and 175 nm (Roberts and Caserio.combustion of almost any hydrocarbon. The biosynthetic pathways for ethylene are diverse among these different organisms. carbon monoxide (CO). The pathways of plant and fungal ethylene synthesis appear to be distinct. The pathway of ethylene synthesis in nonvascular plants may be different from that in vascular plants (Osborne. Ultraviolet photodecomposition of atmospheric ethylene is an important environmental ethylene sink (Scott and Wills. Thus. both visible and invisible. n-butane and ethane (Noyes et al. Because this chapter is primarily concerned with methods of eliminating ethylene. as the inhibitor rhizobitoxin blocks synthesis in plants but not in the fungus Penicillium digitatum (Owens et al. the reaction is inefficient at very low ethylene concentrations such as those found in fresh produce environments so the commercial potential of ozone as an ethylene scrubber is limited. The important point is that environmental ethylene can be biologically produced by a wide range of organisms. not producing it. and formaldehyde (Scott et al. acetylene. It is thus a common air pollutant. 1957). Ultraviolet light will interact with oxygen (O2) in air to form ozone which breaks down ethylene. This has been reviewed in detail elsewhere (Abeles et al.1. Nitrogenfixing bacteria can reduce acetylene to ethylene (Dillworth. Hag and Curtis. and such sources ought to be considered when devising strategies to reduce ambient ethylene. its chief source being automobile engines. Approximately 25-30% of fungal species tested produce ethylene on appropriate media (Fukuda et al. Mycobacterium paraffinicum. but UV light will directly degrade ethylene as well. Ethylene reacts with ozone to yield water. 1971). Soil microorganisms can degrade ethylene and at least one species. 1967).2 Degradation Ethylene undergoes several types of degradation reactions. 1984). Biological sources of ethylene include higher plant tissues. 1986). several species of bacteria and fungi. 1987). and some liverworts and mosses. Kieselguhr. bromine also reacts with water to form HBr and Br2 gas is released from the carbon filter. Ethylene will react with halogens (chiefly chlorine and bromine) through halogenation and hydrohalogenation reactions to form dihaloalkanes. 1983). brominated activated charcoal is hygroscopic and will become wet in humid conditions. ethane. silica gel (Kays and Beaudry. However. many different methods have been used. A number of clay materials have been reported to have ethylene adsorbing capacity. The double bond will undergo hydrogenation. Up to 90% of the bromine will react with ethylene. Ethylene reacts with concentrated sulfuric acid to form ethyl hydrogen sulfate or with water in the presence of acids to yield ethanol (Morrison and Boyd. many of the common reactions undergone by ethylene require high concentrations of ethylene and/or high temperatures and pressures. molecular sieves of crystalline aluminosilicates.including ethylene oxide. SO2. many of the processes most commonly used to modify ethylene in the petrochemical industry are not appropriate for the conditions generally found in a food package environment. in the presence of any of several metal catalysts. 2. butanol. brick dust. ethylene will react with hydrogen halides to form ethyl halides (Morrison and Boyd. 1966). The double bond of ethylene makes it very reactive through a number of reaction pathways. These compounds are injurious to plant tissues and corrosive to stainless steel. CO. This creates a diversity of opportunities for commercial methodologies for the removal of ethylene and. NO and NH3. In addition. to yield ethane (Morrison and Boyd. Brominated charcoal filters are relatively efficient removers of ethylene. Thus. ethylene can be eliminated from air by passing it over brominated activated charcoal to form dibromoethane (Talib. Therefore. propanol. 1966). silica gel or alumina pellets. > 5% AlO 2 . propylene. Certain oxidizing agents react with ethylene to form glycols. in fact. . acetaldehyde. ethylene can be absorbed or adsorbed by a number of substances including activated charcoal. 1961). Potassium permanganate is often adsorbed onto Celite. 1987).13 Adsorption and absorption In addition to chemical cleavage and modification. 1966). bentonite. 1987) and aluminium oxide (Goodburn and Halligan. > 1% Fe2O3) (Kader et ai. Alternatively. vermiculite. The most common of these oxidizing agents is potassium permanganate (KMnO4) which oxidizes ethylene to ethylene glycol and thence to CO2 and water (Morrison and Boyd. H2S. Examples include cristobalite (> 87% SO2. However. Fuller's earth. 1966). hydrogen and dioxyketone (Leighton. It is clear that ethylene is a very reactive compound that can be altered or degraded in many ways. Permanganate scrubbers are also effective in adsorbing air pollutants such as O3. polyethylene and polystyrene (Rizzolo et a/. The salutary properties of the cave are thought to reside in the largely zeolitic stone interior. will effectively oxidize ethylene. Apiezon M. squalene. 1987b). cupric oxide-ferric oxide pellets and powdered cupric oxide. Clearly such systems would be inappropriate for food packaging applications. Examples include potassium dichromate. in very low amounts. Ohya-ishi (Oya stone) and zeolite (Urushizaki. Some adsorbents have been combined with catalysts or chemical agents that modify or destroy the ethylene after adsorption. iodine pentoxide. will react rapidly and irreversibly with ethylene at room temperature and remove ethylene from the atmosphere.. Metal catalysts immobilized on absorbents. A number of catalytic oxidizers have been combined with adsorbents to remove ethylene from air. KMnO4. Oya stone is mined from the Oya cave in Tochigi Prefecture in Japan. The cave has been used to store fresh produce and is reputed to confer added storage life. hexylene glycol (Rizzolo et al. The mixture is then kneaded and heated to 200-9000C. triazines and tetrazines.1989).2 Deleterious effects of ethylene Ethylene has long been recognized as a problem in postharvest handling of horticultural products. and silver nitrate. pyridines. such as platinized asbestos. Examples of such adsorbents include propylene glycol. activated charcoal has been used to adsorb ethylene. In some cases. For example. then oxidized with ozone or electromagnetic radiation (Urushizaki. but in many cases the reactions require high temperatures ( > 1800C). 1992). sulphones and esters (especially dicarboxyoctyl. Such compounds can be embedded in permeable plastic bags or printing inks to remove ethylene from packages of plant produce (Holland. 1987a). such as benzenes. can be responsible for a wide . 1983). 1986b). Some regenerable adsorbents have been shown to have ethylene adsorbing capacity and have the benefit of being reusable after purging. Since the discovery in 1924 that ethylene can accelerate ripening in fruits (Denny. dicarboxydecyl and dicarboxymethyl ester groups).5M H2SO4 to eliminate the activity of the ethylene (Osajima et a/. Electron-deficient dienes or trienes. 1978). To improve its ethylene adsorptive capacity. diazines. 1986a).. having electron-withdrawing substituents such as fluorinated alkyl groups. the activated charcoal has been impregnated with bromine or with 15% KBrO3 and 0. each respectively on silica gel (Eastwell et al. It is now recognized that ethylene. 1924) it has become clear that ethylene can be the cause of undesirable ripening of fruits and vegetables. 2. the Oya stone is first finely ground with a small amount of metal oxide. phenylmethylsilicone. 2. and softening of fruit tissues (Abeles et aiy 1992). ethylene induces a reversible increase in respiration. This is achieved through the direct or indirect stimulation of synthesis and activity of many ripening enzymes by ethylene. vegetables and ornamental plants. are often deliberately exposed to high concentrations of ethylene (~ 100 ppm) to induce rapid ripening.2.2 Fruit ripening and softening Ethylene has been referred to as a 'ripening' hormone because it can accelerate softening and ripening of many kinds of fruit.. In most cases. The diverse physiological effects of ethylene have been extensively reviewed elsewhere (Abeles et ai. In the case of climacteric fruit. petioles. dates. 2. In most cases. so diverse. Exposure of mature fruit to ethylene leads to increased respiration.1 Respiration Perishability of produce generally is well correlated with respiration rate. In non-climacteric plant organs. ethylene can induce a rapid and irreversible elevation in respiration leading directly to maturity and senescence. dried fruits. Reducing the temperature rapidly reduces the respiration rate of the product.3 Flower and leaf abscission Cell wall hydrolysis of specific cells at the base of leaves. such as bananas and tomatoes. 1992) so only those effects that are deleterious to packaged plant produce will be discussed here. pedicels and fruit leads to abscission of the distal organ (Abeles et al. exposure to a few parts per million (ppm) of ethylene leads to increased respiration and increased perishability. Ethylene accelerates the respiration of fruits. potatoes and onions that have very low respiration rates have postharvest lives measured in months (Kader. 1992).array of undesirable effects in plants and plant parts. for packaged fruits it would be desirable to prevent exposure to ethylene and thereby prevent rapid ripening. Those commodities such as nuts. Reduction of respiration rate increases postharvest life and elevation of respiration rate generally decreases it. having postharvest lives measured in days. 1985). 2. The physiological effects of ethylene are so important. increased production of endogenous ethylene. . and are induced by such small amounts of ethylene that it is considered a plant hormone. petals. This is one of the reasons why low temperature is so important in postharvest management. broccoli and mushrooms that have very high respiration rates are very perishable.2. Some fruits.2. Commodities such as asparagus. immature fruits such as cucumbers and squash. 1985b). Kusunose and Sawamura. Some carnations are so sensitive to ethylene that they have been used as ethylene bioassays. 1985b). This can be of particular concern in the case of leafy green vegetables such as spinach. 1985a).5 Petal inrolling in carnations Low concentrations of ethylene (< 1 ppm) cause inrolling (or sleepiness) of the flower petals of sensitive carnation varieties accompanied by a loss of turgor in the petal tissues (Halevy. BarkaiGolan and Lavy-Meir.7 Susceptibility to plant pathogens Many postharvest plant pathogens are opportunistic microorganisms that thrive on injured or senescent tissues. 1993). In addition. plants and plant parts (Jankiewicz. it also enhances the opportunities for pathogenesis. 2. Examples include russet spot (small oval brown spots. The presence of low levels of ethylene can cause yellowing and reduced quality. Such sensitive varieties are often subjected to a pulse treatment with silver thiosulphate to render them insensitive to the effects of ethylene (Cameron and Reid. 1990) and this ethylene may compromise the natural defences of the plant tissues.6 Postharvest disorders Ethylene can be responsible for a number of specific postharvest disorders of fruits and vegetables. . and toughening of asparagus (Reid.2. 2. Knee. 1985. several postharvest plant pathogens produce ethylene (Barkai-Golan. The growth of a number of postharvest pathogens is directly stimulated by ethylene (Barkai-Golan. 1989). 1986). To the degree that ethylene accelerates senescence and causes specific physiological disorders. 1990. 1980. 2. and flowers such as broccoli (Reid. Reid. 1983). 1989. though not all. 1983).4 Chlorophyll breakdown Ethylene increases the rate of chlorophyll degradation in leaf.2. 1990. fruit and flower tissues (Aharoni.Ethylene has been shown to accelerate abscission for many. Ethylene causes flower and leaf abscission of many potted ornamental plants (Cameron and Reid.2. primarily on the midrib) of crisphead lettuce. Osborne 1989b. sprouting of potatoes. Kepczynska. 1989. formation of bitter-tasting isocoumarins in carrots.2. Makhlouf et al. 2. 3 Interactions of ethylene and other gases The activity and reactivity of ethylene depends.1 and 32% by volume. Upon exposure to higher O2 concentrations. 1992) and the concentration of CO2.4% O2 (Banks et al. whether biological or chemical. In some cases.2. the accumulated ACC will be rapidly converted into ethylene so low O2 must be maintained continuously to maintain low ethylene concentrations. 1986) but K1n values for other plants organs are generally 3-10% (Burg and Thimann.3. 1966). 232 Carbon dioxide Carbon dioxide may stimulate. Ethylene at concentrations between 3. Bufler and Streif. chlorophyll loss (Aharoni and Lieberman. More importantly. are oxidative conversions or cleavages. Imaseki et al. 1973). However. 2. resulting in accumulation of ACC (Burg and Thimann. The K1n for conversion of 1-aminocyclopropane-l-carboxylic acid (ACC) to ethylene in apple is about 1. . reduced O2 in a package may more effectively reduce ambient ethylene through reduced ethylene synthesis than ethylene-adsorbing capacity built into the package. Lieberman et al. 1959. Neither of these conditions occurs in packages. 1959. Most pathways of ethylene synthesis. Jackson et al. Although rice and some other aquatic plants have been reported to synthesize ethylene in the absence of O2 (Ku et al. depending on the plant tissue (Abeles et al. thereby preventing abscission (Wittenbach and Bukovac. biosynthesis and explosiveness are all related to ambient oxygen concentration. 1975. 1967). However. in part. ozone and ethylene and their interactions with each other and with plant tissues. the oxygen affinity of ethyleneforming enzyme (EFE) is much less than that for respiratory enzymes. inhibit or have no effect on ethylene synthesis. Hansen. is explosive in air (Reid. 1968). The user of packaging materials for the removal or inactivation of ethylene should consider the presence and concentrations of oxygen. 1942. 1985b). 1984. 1979) and growth (Chadwick and Burg. reduced O2 apparently slows the conversion of ACC to ethylene. The combustion of organic materials requires O2 and results in ethylene as one of the combustion products.. CO2 renders normally sensitive plant tissues insensitive to the effects of ethylene.1 Oxygen Ethylene production. on the presence of other atmospheric gases. 1970). 1978). carbon dioxide. most plants require O2 for ethylene synthesis. floral senescence (Nichols. shipping containers.001-0.1 ppm for 8 h (Anon. However. however.4.. 2. Sensitive products should not be held or stored in proximity to ethylene-generating products or product-ripening rooms. As most methods of adsorbing or decomposing ethylene have finite capacities for activity. it seems prudent to reduce environmental ethylene to avoid saturating the environment of the package with ethylene. Such high levels are sufficient to have physiological effects on some fresh produce. California. plantgenerated ethylene can be significant (Abeles et al. 1992). It is a common pollutant that can be detected with sensitive instruments. Removing agricultural sources of ethylene and insulating storage rooms from ethylene air pollution can significantly reduce ambient ethylene.5 ppm have been measured (Scott et al. In closed areas. 1957). urban air levels as high as 0. diesel. ozone would not normally be found or introduced into a food package. the heat generated by combustion (from forklifts. and industrial stack emissions are all common sources of ethylene. cigarette smoke.2 Plant sources Growing plants do not normally produce enough ethylene to alter ambient atmospheric levels of the chemical. greenhouses and warehouses..4 Ethylene sources in the environment Ethylene is ubiquitous at low levels in the environment.2. packing houses. In addition. Such levels are below damage thresholds for all but the most sensitive horticultural commodities. 2. USA standards recommend human exposures to no more than 0. Burning agricultural wastes. ozone oxidizes ethylene to simple breakdown products and has been used experimentally to remove ethylene from produce storage areas.005 ppm (Abeles et al. truck and auto exhaust. 1992)..3 Ozone As was mentioned above. such as storage rooms.3. 2.1 Combustion Ethylene is a common breakdown product of virtually all aerobic combustion processes. Ethylene can come from many sources both within and outside the package. Although there are no national standards for environmental ethylene. wildfires. Ambient atmospheric levels of ethylene are normally in the range of 0.4. . for example) can raise the temperature of the product sufficiently to stimulate production of productgenerated ethylene.5 ppm for 1 h or 0.or propanepowered forklifts. 1962). As is common in the commercial sector.4. In addition. some of the claims for ethylene ad-/absorbing capacity for these packaging materials have been poorly documented and thus the efficacy of the materials is difficult to substantiate. If that produce were packed in ethylene-adsorbing packaging.3 Ripening rooms Bananas and tomatoes are routinely ripened by exposure to 50-100 ppm ethylene in large sealed rooms.1 Potassium permanganate-based scavengers Many vendors offer ethylene adsorbers based on KMnO4 immobilized on any of several minerals. others degrade it.5 Microorganisms Although several soilborne microorganisms produce ethylene. The net effect appears to be that the soil serves primarily as a sink for ethylene.5. the dispersal of ethylene can be significant. Most substances designed to remove ethylene from packages are delivered either as sachets that go inside the package or are integrated into the packaging material. These products are available in sachets for packages and on blankets that can be placed in produce-holding rooms. AU infested foodstuffs should be immediately discarded. 2. When such rooms are vented.4. the ethylene at such levels might saturate the packaging and render it ineffective. Postharvest plant pathogens growing on stored products in enclosed holding areas can be important sources of ethylene.2. the ethylene can come in contact with other products being held in the warehouse. rubber materials exposed to heat or UV light can release ethylene (Reid. Potassium permanganate is not integrated into food-contact packaging because of its . 1985b). 2. 2.4 Fluorescent ballasts and rubber materials The ballasts that hold fluorescent lights are sources of ethylene. 2.5 Commercial applications in packaging Several of the technologies described above have been incorporated into packaging materials that are either commercially available or are likely to become available in the near future. When ripening rooms are built into produce storage or distribution warehouses. usually a plastic polymer film or the ink used to print on the package.4. IL 61350 Complete Control PO Box 1006 Stafford. CA 94545-0044 Loomix.toxicity. Inc. 1992).1. Hatton and Reeder. 1972. such products contain ~ 4-6% KMnO4 on an inert substrate such as perlite. TX 77477 Cams Chemical Company. Inc. alumina. Georgia 30366 Purity Corporation 9539 Town Park Houston. known as swingtherm ethylene converters. Inc. PO Box 398 Pleasonton. avocados (Ben-Arie and Sonego. is reported to use potassium permanganate by Abe (1990) in his listing of ethylene absorbers. are based on such a system. PO Box 571 Selma. PO Box 80434 Chamblee. Liu. The Japanese company Sekisui Jushi has developed a product. CA 93662 ExtendaLife Systems PO Box 55044 Hayward. vermiculite. Scott et al9 1970). Maotani et al. TX 77036 Note: Nippon Greener Co. The performance and useful lives of these scavengers depends on the substrate surface area and the content of reagent (KMnO4).2 Activated carbon-based scavengers Various metal catalysts on activated carbon will effectively remove ethylene from air passing over the bed of carbon. Some suppliers of KMnO4-based ethylene scavengers are listed in Table 2. 405 E. CA 93420 Purafil. Inc. Formulations differ in density and surface area of substrate and the loading of reagent. persimmons. However.1 Suppliers (USA) of potassium permanganate ethylene scavengers Air Repair Products. activated carbon or celite (Abeles et al. 1001 Boyce Memorial Drive Ottawa. Activated charcoal impregnated with a palladium catalyst placed in paper sachets effectively removed ethylene in an experiment on maintaining quality of lightly processed kiwifruit. 1985. broccoli and spinach (Abe and Watada. Krishnamurthy and Kushalappa. This table is not a complete listing of all companies supplying such products but only those known to the author at the time of writing. CA 94566 Ethylene Control. silica gel. 1971. Typically. . Inc. Neupalon. sachets could be used inside produce packages and have been shown to effectively scavenge ethylene from packages of bananas. 1991). PO Box 1006 Stafford. banana. kiwifruit. 2. Inc. 1970. 1985. TX 77477 DeltaTrak. that is a sachet containing activated carbon and a water absorbent capable of Table 2. Branch Street PO Box 490 Arroyo Grande. However. Fuchs and Temkin-Gorodeiski. Commercial units.5.9 1982. they require heat and movement of gases and so are not applicable to packaged produce. 1989). The zeolite is reported to adsorb 8% ethylene by weight . which is used to hold fresh produce. of the bags are marketed by Japanese or Korean companies. of Korea markets a film bag called the Orega bag. zeolite. 1991). Adsorption of this small amount of ethylene may not be helpful for some situations. A product called Ethad® has been developed by the Rubber Research Institute of Malaysia. though some are also sold in the United States and Australia. 1991). The Cho Yang Heung San Co. of Japan (Someya. Many. though not all. The product comes in woven sachets that can be placed in packages of produce.005 ppm ethylene per hour per m2 (Choi. nor plasticizers. Ltd.absorbing up to 500-1000 times its weight of water. 2. 1992). Fine porous material derived from pumice. It is unlikely such bags could be used in most developed countries due to the reaction of bromine compounds with water. The product is based on powdered zeolite in viscous oil or grease. The company provides data showing that Neupalon adsorbs 40 ml ethylene per m2. Ltd. also in Japan. are apparently suitable for these applications (Choi. This film incorporates finely ground coral (primarily calcium carbonate). Another such film is described in a US Patent assigned to Nissho and Co. the coral is claimed to absorb ethylene. The inorganic materials have pores ranging from 2000 to 2800A and the resulting film is reported to have the capacity to adsorb at least 0. it releases ethylene in order to stimulate the production of latex by rubber trees. Honshu Paper. based on the US patent of Dr Mitsuo Matsui (Matsui. has a product called the Hatofresh System that is based on activated carbon impregnated with bromine-type inorganic chemicals.3 Activated earth-type scavengers In the past several years a number of packaging products have appeared based on the putative ability of certain finely dispersed minerals to adsorb ethylene. The carbon-bromine substance is embedded within a paper bag or corrugated box. no data have been presented to support this claim. They claim that the bag will adsorb 20 ml ethylene per g of adsorbent.000-500. After incorporation in a polyethylene film. Mitsubishi Chemical Company of Japan produces a product called SendoMate which is based on palladium catalyst on activated carbon which adsorbs ethylene and then catalytically breaks it down. cristobalite or clinoptilolite is sintered together with a small amount of metal oxide before being dispersed in a plastic film. having pore sizes in the range of 100. active carbon. Typically these minerals are local kinds of clay that are embedded in polyethylene bags which are then used to package fresh produce. However. which can release toxic bromine gas.5. They do not specify which bromine compounds are used.000A. Neither plastics containing chlorine such as polyvinyl chloride or polyvinylidene chloride. Furthermore. In addition. offers shelf-life data for several fresh commodities to demonstrate the benefits of their bags. of Japan. In a study performed in Australia with BO film. Such evidence generally shows an extension of shelf-life and/or a reduction of headspace ethylene. 1988). These effects can improve shelf-life and reduce headspace ethylene concentrations independently of any ethylene adsorption. 1988). The bags are. the data supporting the commercial products incorporating these minerals fail to demonstrate such capacity. presumably. polyethylene with Japanese Oya stone dispersed within the film matrix. in studies with pure mineral granules of Cera-sutora A. Because ethylene will diffuse much more rapidly through open pore spaces within the plastic than through the plastic itself. Such data are unconvincing. The evidence offered in support of this claim is generally based on shelf-life experiments comparing common polyethylene bags with mineralized bags. they will also open pores within the plastic bag and alter the gas-exchange properties of the bag. A product called BO Film is marketed by the Odja Shoji Co. Apparently Ethad® has not been used to adsorb ethylene in packages. There are many other similar bags being sold throughout the world offering improved postharvest life of fresh commodities due to the adsorption of ethylene by the minerals dispersed within the film. Although the minerals in question may have ethylene-adsorbing capacity. Hercules Chemical Company relied on this effect while using calcium carbonate to improve the gas-transmission properties of their Fresh Hold breathable bags without making any claims regarding ethylene adsorption (Anderson. Evert-Fresh Corp. In fact. Ltd. Once the ethylene has diffused part-way through the plastic film.(Abeles et ah. Oya stone has putative ethylene-adsorbing capacity. CO2 will leave these bags more readily and O2 enter more readily than is the case for a comparable polyethylene bag. almost any powdered mineral can confer such effects without relying on expensive Oya stone or other speciality minerals. Even if they do have ethylene-adsorbing capacity. the mineral in the bag took up little ethylene (Joyce. thus greatly slowing any processes of adsorption. 1989). Although the finely divided minerals may adsorb ethylene. The ethylene would have to diffuse through the plastic matrix before contact with the dispersed mineral. one would expect ethylene to diffuse out of these bags faster than through pure polyethylene bags. It is a low-density polyethylene film extruded with finely divided crysburite ceramic which is claimed to confer ethylene-adsorbing capacity (Joyce. venting to the outside may be nearly as fast and effective as adsorption on embedded minerals. Evert-Fresh Corporation markets Evert-Fresh bags in the USA. the author found that the ethylene . 1992). it is possible that they will lack significant capacity while embedded in plastic films. 2. Perhaps the most promising new development in ethylene-removing packaging is the use of electron-deficient dienes or trienes incorporated in ethylene-permeable packaging. polystyrenes. Our conclusion was that none of the four films adsorbed measurable amounts of ethylene (Zagory et al.170 nmol/g after 15 h at 200C (Joyce. polyethylenes and polypropylenes. the author tested four proprietary bags from Japan. The nature of the chemisorbent and data supporting the . Direct measurement of ethylene depletion in closed systems containing samples of the bags without any produce to confound the results would be much more instructive. The product consists of a chemisorbent of small particle size dispersed among the fibers in the early phase of paper production.5 A New and novel approaches to ethylene-removing packaging There are some new and unusual approaches to developing ethyleneremoving packaging that deserve mention.0 M dicarboxyoctyl ester of tetrazine incorporated in such a film was able to effect a ten-fold reduction in ethylene in sealed jars within 24 h and a 100-fold reduction within 48 h (Holland. since tetrazine is unstable in the presence of water. such studies should be done at low temperature and high relative humidity to mimic the conditions under which they will be expected to perform. it would be useful if companies claiming ethylene-adsorbing capacity for their products presented direct evidence for these claims. We injected a known quantity of ethylene into each jar. 1988). A new product called Frisspack has been developed in Hungary for use in storage of fresh fruits and vegetables. ethylene-permeable plastic film that does not contain hydroxyl groups (Holland. A second set of jars were left empty. We could detect no differences in ethylene concentrations between the jars with film and those without film. This amount of ethylene sorption is insignificant. Shelflife studies and headspace analysis of ethylene concentrations do not support claims of ethylene-adsorbing capacity.9 1988). The preferred diene or triene is a tetrazine. Each day for seven days we sampled the ethylene concentrations in each jar. Approximately 0. Furthermore. In studies in the USA. Appropriate films would include silicone polycarbonates. The tetrazine film has a characteristic pink color when it is new and turns brown when it becomes saturated with ethylene so it is possible to know when it needs replacing.01-1. The result is a paper sheet with putative ethyleneadsorbing capacity. However. In the future. 1992). 1992). it must be embedded in a hydrophobic.sorption capacity of the material was only . all containing dispersed minerals and all claiming ethylene-adsorbing capacity. Weighed samples of each bag were placed in sealed jars with sampling ports attached. G. Boca Raton. Aharoni. G. Morgan. References Abe. Berkeley. (1986) Ethylene biosynthesis of Golden Delicious apples stored in different mixtures of carbon dioxide and oxygen. J. In many cases. and Watada. M. 335-44. Elyatem. N.. 45. (1990) Active packaging . 56(6). Y. and Strief. and Hammat.claim of ethylene adsorption are not available.E. Anon. 30. R.W.H. Bufler. Plant Physiol. ScL. 1589-92.P. L. Technical Report. the elevated carbon dioxide levels common in modified atmosphere packages may obviate the need for ethylene removal. Calderon and R. 2. N. Barkai-Golan. Michael Rooney. T. 4842875. Natl Acad. (1979) Ethylene as a regulator of senescence in tobacco leaf discs. Academic Press. (1989) Interrelationship between ethylene and growth regulators in the senescence of lettuce leaf discs. CRC Press. Supplement No. and Sonego. A. 263-72.. (1964) California Standards for Ambient Air Quality and Motor Vehicle Exhaust. Anderson. S. Acta Hon. N. 391-6. Michael Reid. F. 64. Cheryl Reeves.a Japanese perspective. R. BioL. Aharoni. 414 pp. No response was received from the vendor following the author's request for information. (1990) Postharvest disease suppression by atmospheric modifications. 801-4. US Patent No. S. (1992) Ethylene in Plant Biology. State of California. Proc.B. 8. Appl. and Lavy-Meir. (1989) Effects of ethylene on the susceptibility to Botrytis cinerea infection of different tomato genotypes. Additional Ambient Air Quality Standards. October 15-17. R. In addition. and Saltveit. . Food ScL. Burg. Mikal Saltveit and Kit Yam. Proceedings of the International Conference on Modified Atmosphere Packaging. K. Abe. In: M. Although there are many packaging products claiming ethylene-removing capabilities. (1959) The physiology of ethylene formation in apples. In other cases. Scientia Hortic. Campden Food and Drink Research Assoc. 114. (1991) Ethylene absorbent to maintain quality of lightly processed fruits and vegetables. a thorough understanding of the physiological effects of ethylene and its importance in sealed permeable packages should precede any use of these products. Plant Growth ReguL. 257-60. (1989) Controlled atmosphere package. M.. J. Ann. (1984) The oxygen affinity of ethyiene production by slices of apples fruit tissue. Barkai-Golan (eds) Food Preservation by Modified Atmospheres. 25 pp. Dept. 2151 Berkeley Way. and Lieberman. Barkai-Golan. Acknowledgements Thanks for literature and helpful discussion are owed to: Linda Dodge.E.V. Inc. and Thimann. H. few of the claims are backed up with reliable data. Abeles. P. CA. Banks. Standardized procedures for demonstrating efficacy would aid the development of this growing industry.. 1990. ethylene-adsorbing capability may be crucial in the maintenance of shelf-life and commercial quality. 177-85. Public Health. 309-17.S. K. (1985) Modified-atmosphere storage of kiwifruit (Actinidia chinensis Planch) with ethylene removal. 157. 27. Ben-Arie. J. with very sensitive commodities such as kiwifruit and carnations. Scientia Hortic. Cameron, A.C. and Reid, M.S. (1983) Use of silver thiosulphate to prevent flower abscission from potted plants. Scientia Hortic, 19, 373-8. Chadwick, A. V. and Burg, S.P. (1967) An explanation of the inhibition of root growth caused by indole-3-acetic acid. Plant PhysioL, 42, 415-20. Choi, S.O. (1991) Orega ultra-high gas permeabilityfilledfilmfor fresh produce packaging. CAP'91, Sixth Int. Conf. CA/MA/Vacuum Packaging. Schotland Business Res., Inc. pp. 197-208. Denny, F.E. (1924) Hastening the coloration of lemons. / Agr. Res., 27, 757-69. Dillworth, MJ. (1966) Acetylene reduction by nitrogen-fixing preparations from Clostridium pasteurianum. Biochem. Biophys. Acta, 127, 285-94. Eastwell, K.C., Bassi, P.K. and Spencer, M.E. (1978) Comparison and evaluation of methods for the removal of ethylene and other hydrocarbons from air for biological studies. Plant PhysioL, 62, 723-6. Fuchs, Y. and Temkin-Gorodeiski, N. (1971) The course of ripening of banana fruits stored in sealed polyethylene bags. J. Amen Soc. Hort. ScL, 96, 401-3. Fukuda, H., Fujii, T. and Ogawa, T. (1984) Microbial production of C2-hydrocarbons, ethane, ethylene and acetylene. Agric. Biol. Chem., 48, 1363-5. Goodburn, K.E. and Halligan, A.C. (1987) Modified atmosphere packaging - a technology guide. Publication of the British Food Manufacturing Association, Leatherhead, UK. pp. 1-44. Halevy, A.H. (1986) Pollination-induced corolla senescence. Acta Hort., 181, 25-32. Hansen, E. (1942) Quantitative study of ethylene production in relation to respiration of pears. Bot. Gaz., 103, 543-58. Hatton, T.T. and Reeder, W.F. (1972) Quality of LuIa avocados stored in controlled atmospheres with or without ethylene. / Amer. Soc. Hort. ScL, 97, 339-41. Holland, R. V. (1992) Absorbent material and uses thereof. Australian Patent Application No. PJ6333. Hag, L.L. and Curtis, R.W. (1968) Production of ethylene by fungi. Science, 159, 1357-8. Imaseki, H., Kondo, K. and Watanabe, A. (1975) Mechanism of cytokinin action on auxininduced ethylene production. Plant Cell PhysioL, 11, 827-9. Jackson, M.B., Gales, K. and Campbell, DJ. (1978) Effect of waterlogged soil conditions on the production of ethylene and on water relationships in tomato plants. J. Exp. Bot., 29, 183-93. Jankiewicz, L.S. (1985) Mechanism of abscission of leaves and reproductive parts of plants. A model. Acta Soc. Bot. PoL, 54, 285-322. Joyce, D.C. (1988) Evaluation of a ceramic-impregnated plastic film as a postharvest wrap. HortScience, 23, 1088. Kader, A.A. (1985) Postharvest biology and technology: An overview. In: A.A. Kader, R.F. Kasmire, F.G. Mitchell, M.S. Reid, N.F. Sommer and J.F. Thompson (eds), Postharvest Technology of Horticultural Crops. University of California, Cooperative Extension Special Publication 3311, 192 pp. Kader, A.A., Zagory, D. and Kerbel, E.L. (1989) Modified atmosphere packaging of fruits and vegetables. Crit. Rev. Food ScL Nut., 28(1), 1-30. Kays, SJ. and Beaudry, R.M. (1987) Techniques for inducing ethylene effects. Acta Hort., 201, 77-116. Kepczynska, E. (1993) Involvement of ethylene in the regulation of growth and development of the fungus Botrytis cinerea. Plant Growth Regul., 13, 65-9. Knee, M. (1990) Ethylene effects in controlled atmosphere storage of horticultural crops. In: M. Calderon and R. Barkai-Golan (eds.), Food Preservation by Modified Atmospheres. CRC Press, Boca Raton, pp. 225-35. Krishnamurthy, S. and Kushalappa, CG. (1985) Studies on the shelf-life and quality of robusta bananas as affected by post-harvest treatments. /. Hortic. ScL, 60, 549-56. Ku, H.S., Suge, H., Rappaport, L. and Pratt, H.K. (1970) Stimulation of rice coleoptile growth by ethylene. Planta, 90, 333-9. Kusunose, H. and Sawamura, M. (1980) Ethylene production and respiration of postharvest acid citrus fruits and Wase Satsuma Mandarin fruit. Agr. Biol. Chem., 44, 1917-22. Leighton, P.A. (1961) Photochemistry of air pollution, Academic Press, NY. Lieberman, M., Kunishi, A., Mapson, L.W. and Wardale, D.A. (1966) Stimulation of ethylene production in apple tissue slices by methionine. Plant Physiol, 41, 376-82. Liu, F.W. (1970) Storage of bananas in polyethylene bags with an ethylene absorbent. HortScience, 5, 25-7. Makhlouf, J., Willemot, C , Ami, J., Castaigne, F. and Emond, J.-P. (1989) Regulation of ethylene biosynthesis in broccoli flower buds in controlled atmospheres. J. Amer. Soc. Hort. ScL, 114, 955-8. Maotani, T., Yamada, M. and Kurihara, A. (1982) Storage of Japanese persimmon of pollination constant non-astringent type in polyethylene bags with ethylene absorbent. J. Jap. Soc. Hort. ScL, 5, 195-202. Matsui, M. (1989) Film for keeping freshness of vegetables and fruit. US Patent No. 4847145. Morrison, R.T. and Boyd, R.N. (1966) Organic Chemistry, 2nd edition. Allyn & Bacon, Inc., Boston, USA 1204 pp. Nichols, R. (1968) The response of carnations (Dianthus caryophyllus) to ethylene. J. Hort. ScL, 43, 335-49. Noyes, W.A., Jr., Hammond, G.S. and Pitts, J.N., Jr. (1964) Vacuum ultraviolet photochemistry. Adv. Photochem., 3, 226-9. Osajima, Y., Sonoda, T., Yamamoto, F., Nakashima, M., Shimoda, M. and Matsumoto, K. (1983) Development of ethylene absorbent and its utilization. Nippon Nogeikagaku Kaishi, 57, 1127-33. Osborne, DJ. (1989a) The control role of ethylene in plant growth and development. In: Clijsters, H. et al. (eds.). Biochemical and Physiological Aspects of Ethylene Production in Lower and Higher Plants. Kluwer Academic Publishers, pp. 1-11. Osborne, DJ. (1989b) Abscission. CHt. Rev. Plant ScL, 8, 103-29. Owens, L.D., Lieberman, M. and Kunishi, M. (1971) Inhibition of ethylene production by rhizobitoxin. Plant Physiol, 48, 1-4. Reid, M.S. (1985a) Ethylene and abscission. HortScience, 20, 45-50. Reid, M.S. (1985b) Ethylene in postharvest technology. In: A.A. Kader, R.F. Kasmire, F.G. Mitchell, M.S. Reid, N.F. Sommer and J.F. Thompson (eds) Postharvest Technology of Horticultural Crops. University of California, Cooperative Extension Special Publication 3311, 192 pp. Reid, M.S., Paul, J.L., Farhoomand, M.B., Kofranek, A.K. and Staby, G.L. (1980) Pulse treatment with the silver thiosulphate complex extends the vase-life of cut carnations. /. Amer. Soc. Hort. ScL, 105, 25-7. Rizzolo, A., Polesello, A. and Gorini, F. (1987a) Laboratory screening tests of some suitable regenerable adsorbents to remove ethylene from cold room atmospheres. 1. Glycols and polyglycols. In: Third Subproject: Conservation and Processing of Foods - A Research Report (1982-1986), National Research Council of Italy, Milano. pp. 99-100. Rizzolo, A., Polesello, A. and Gorini, F. (1987b) Laboratory screening tests of some suitable regenerable adsorbents to remove ethylene from cold room atmospheres. 1. Apolar phases. In: Third Subproject: Conservation and Processing of Foods - A Research Report (1982-1986), National Research Council of Italy, Milano. pp. 101-2. Roberts, J.D. and Caserio, M.C. (1967) Modern Organic Chemistry, Benjamin, NY. Sato, M., Urushizaki, S., Nishiyama, K., Sakai, F. and Ota, Y. (1987) Efficient production of ethylene by Pseudomonas syringae pv. glycinea which causes halo blight of soybeans. Agric. Biol Chem., 51, 1177-8. Scott, W.E., Stephens, E.R., Hanst, P.C. and Doerr, R.C. (1957) Further developments in the chemistry of the atmosphere. Proc. Amer. Petrol. Inst., 37, 171-83. Scott, KJ., McGlasson, W.B. and Roberts, E.A. (1970) Potassium permanganate as an ethylene absorbent in polyethylene bags to delay ripening of bananas during storage. Aust. J. Expt. Agric. Anim. Hush, 10, 237-40. Scott, KJ. and Wills, R.B.H. (1973) Atmospheric pollutants destroyed in an ultraviolet scrubber. Lab. Pract., 22, 103-6. Shorter, AJ. and Scott, KJ. (1986) Removal of ethylene from air and low oxygen atmospheres with ultraviolet radiation. Lebensm. Wiss. U. Technol., 19, 176-9. Someya, N. (1992) Packaging sheet for perishable goods. US Patent No. 5084337. Talib, Z. (1983) Ethylene in the storage of fresh produce. In: Developments in Food Preservation, Vol. 2, S. Thorne, (ed), Applied Science Publishers, London and New York. pp. 149-77. Urushizaki, S. (1987a) On the Effects of Functional Films. Autumn Meeting of Japan Society Horticultural Science. Symposium: Postharvest Ethylene and Quality of Horticultural Crops. University of Kyushu, October 8, 1987. Urushizaki, S. (1987b) Development of Ethylene Absorbable Film and its Application to Vegetable and Fruit Packaging. Autumn Meeting of Japan Society Horticultural Science. Symposium: Postharvest Ethylene and Quality of Horticultural Crops. University of Kyushu, October 8, 1987. Wittenbach, V.A. and Bukovac, MJ. (1973) Cherry fruit abscission: Effect of growth substances, metabolic inhibitors and environmental factors. /. Amer. Soc. Hort. ScL, 98, 348-51. Yang, S.F. and Hoffman, N.E. (1984) Ethylene biosynthesis and its regulation in higher plants. Ann. Rev. Plant Physiol, 35, 155-89. Zagory, D., Brecht, B. and Kader, A.A. (1988) Unpublished data. 3 Design of modified atmosphere packaging for fresh produce K. L. YAM and D. S. LEE 3.1 Introduction Controlled atmosphere (CA) storage and modified atmosphere packaging (MAP) are two useful technologies to extend the shelf-life of fresh agricultural and horticultural produce. Simply stated, these technologies involve storing a fruit or vegetable in a modified atmosphere usually consisting of reduced O2 and elevated CO2 concentrations compared to air. The modified atmosphere reduces the rates of respiration and ethylene production, which are often associated with the benefits of retardation of physiological, pathological, and physical deteriorative processes occurring in the product. Aerobic respiration is a complicated process that involves a series of enzymatic reactions taking place through the metabolic pathways of glycolysis, the tricarboxylic acid (TCA) cycle, and the associated electron transport system (Kader, 1987). However, the overall reaction describing the respiration process may be simply expressed as C6H12O6+ 6 O2 -> 6 CO2 + 6 H2O + heat (3.1) that involves the oxidation of organic substrates (such as starch, sugars, and organic acids) to CO2 and H2O along with heat generation. Kinetic theory and Equation (3.1) suggest that the respiration rate may be reduced by decreasing the O2 and/or by increasing the CO2 concentration. There are differences between the ways CA storage and MAP create and maintain a modified atmosphere. In CA storage, a gas generator is usually used to create and control the modified atmosphere in a cold warehouse where the product is kept. In MAP, the product is kept in a carefully designed permeable package, and the modified atmosphere is created and maintained through an intricate interplay between the respiration of the product and the gas permeation of the package. MAP is a more economical technology because an expensive gas generator is not needed; however, it is also a more difficult technology to implement because of the rather complicated interactions between the product and the package. This chapter is focused on the design of MAP for fresh produce. The modified atmosphere in MAP can be created by either active or passive modification. In active modification, the modified atmosphere is created rapidly by flushing the headspace of the package with a desired gas mixture. In passive modification, the modified atmosphere is created by allowing the produce to respire inside the package so that an equilibrium is slowly attained. In both cases, once the modified atmosphere is established, it is maintained through a dynamic equilibrium of respiration and permeation. Designing MAP for fresh produce is a complicated task, requiring good understanding of the dynamic interactions among the product, the environment, and the package. The food technologist who is asked to design MAP for fresh produce faces many difficult but practical questions, such as whether the MAP technology is applicable to the product, what is the optimum gas composition, what kind of packaging material is needed, and Conduct literature review Conduct feasibility study Could CA storage provide" benefits? Neither CA storage nor MAP is suitable for the product Determine optimum conditions and tolerant limits Determine respiration rates Use mathematical model to determine package requirments I Verify model predictions with experiments Is suitable permeable film available? Only CA storage is suitable for the product Design of MAP possible Need to develop new permeable films for MAP Figure 3.1 Flow chart for designing MAP for fresh produce. how to protect the product from the potential hazards of a modified atmosphere. 1994). To fill this gap.1 Recommended optimal modified atmosphere conditions for produce Commodity Vegetables Asparagus Broccoli Brussels sprouts Cabbage Cauliflower Corn. sweet Grapefruit Peach Pear Persimmon Strawberry 0-5 0-5 5-13 12-15 0-5 0-5 10-15 0-5 0-5 0-5 0-5 90 90 85-90 85-95 90-95 90-95 85-90 90 90-95 90-95 90-95 2-3 2-3 2-5 2-5 0-10 3-10 3-10 1-2 2-3 2 10 1-2 2-3 3-10 2-5 11-20 10-12 5-10 5 0-1 8 15-20 0-5 0-5 0-5 0-5 0-5 0-5 8-12 0-5 0-5 8-12 0-5 8-12 95 95 95 90-95 95 95 90-95 95 90 90-95 95 85-90 air 1-2 1-2 3-5 2-5 2-4 3-5 2-5 air 3-5 air 3-5 5-10 5-10 5-7 5-7 2-5 10-20 0 0 10-15 2-8 10-20 0 Temperature range (0C) Relative humidity (%) Modified atmosphere O2 CO2 From Labuza and Breene (1989). Prince (1989) has reported that the majority of modified atmosphere packages are designed by trial-and-error methods. The process is necessarily somewhat simplified because many biological aspects underlying the effects of modified atmosphere on the shelf-life of plant tissues are still not understood (Solomos. and Katzyoshi (1992) . sweet Cucumber Lettuce Mushroom Pepper Spinach Tomato. The steps involved in the design process are outlined in the flow diagram of Figure 3. a simple process for designing MAP of fresh produce is presented in this chapter. the first step is to determine whether CA storage can indeed provide benefits for the product. Powrie and Skura (1991). Although numerous articles have already been written on the various aspects of MAP. almost none of them provides an overview of the design process. 3. partly ripe Fruits Apple Apricot Avocado Banana Blueberry Cherry.2 Literature review Before designing MAP for a product. Reviewing the Table 3. which often lead to poor designs that are either ineffective or injurious to the product.1. literature data should be used only as a reference because discrepancies sometimes exist among data from different sources (due to possible reasons Blackberry. and relative humidity). the more rigid is the design requirement. whether the product is climacteric or nonclimacteric. Ne< arine.1. Singh and Oliveira. The data may also be represented in the form of CO2 versus O2 plots (such as in Figures 3. The recommended O2 and CO2 concentrations for some fruits and vegetables are listed in Table 3. Pineapple Avocado Persimmon Banana Kiwi. However.literature data is a good start to gather preliminary information about the product or similar products. Helpful information that may be available in the literature is assessment of the potential benefit of CA storage and MAP. The size of a window has a practical implication in that the smaller it is.8 Orange Grape Cranberry Plum LDPEp = Cy O2 Concentration (%) Figure 3. Peach Apricot Grapefruit Air P = 0. 1994. 1989.2 Recommended gas concentrations for CA storage of fruits. Blueberry. Strawberry CO2 Concentration (%) Cherry Mango. Raspberry. (Redrawn from Singh and Oliveira. More data are available elsewhere (Prince. temperature below which chilling injury of the product occurs. temperature. respiration rate. and so on.3). Labuza and Breene. optimum storage conditions (such as gas concentration.2 and 3. O2 and CO2 tolerance limits. Fig. in which the windows represent the boundary of recommended gas concentrations.) . Papaya. 1994). 1989. with permission. 3 Feasibility study A simple feasibility study consists in conducting experiments to monitor the quality of the product as a function of time under various modified atmospheres.8 Lettuce O2 Concentration (%) Figure 3. 1994. odor.3 Recommended gas concentrations for CA storage of vegetables. nutritional quality. particularly if no literature data are found for the product of interest. a set of instrumental and sensory quality attributes must be selected. Although the selection procedure is different for each product. To define quality.8 CO2 Concentration (%) Mushrooms Asparagus Leeks Broccoli Brussels ! >pr< >uts' Beans Cabbage Parsley Spinach Okra Cauliflower Tomato Pepper Artichokes Radish LDPE B = 0.) . and microbial growth. Therefore conducting a feasibility study is often required.such as maturity and cultivar of the product) and the criteria used in making recommendations are seldom reported. flavor. with permission. The effects of CA storage on the sensory and nutritional quality of fruits and vegetables have been reviewed by Weichmann (1986). it generally includes assessment of texture. Air P = 0. color. 3. (Redrawn from Singh and Oliveira. The response or dependable variables are two or three relevant quality attributes for the product.4a) that involves storing the product in a glass jar that has an inlet port and an outlet port through which a pre-mixed gas (consisting of lowered O2 and elevated CO2) passes. There are three major design constraints: O2 tolerance limit. while keeping temperature and relative humidity constant. CO2 tolerance . The modified atmosphere can be created using the flow-through system (Figure 3. 33. The suggested temperature and relative humidity are 5°C and 90%. If the results are not favorable. The purpose of the feasibility study is to determine if CA storage can provide better storage quality than air storage. The question then is whether the same benefit can be achieved by MAP without the use of an expensive gas generator. respectively. and the food technologist should avoid spending more time on designing MAP for this particular product. the authors suggest the use of a 3-level factorial experimental design with O2 and CO2 concentrations as independent variables. Since the feasibility study provides only preliminary data. The O2 and CO2 ranges are to be selected between 2 and 10% and O and 20%. more experiments are needed to more closely define the optimum conditions. Air (21% O2 and 0% CO2) should always be used as a control. This should be done by extending the experimental design to include additional O2 and CO2 concentrations that are expected to give good results.4 Flow-through system (a) and closed system (b).1 Optimum conditions Further work is justified if the feasibility study confirms the benefit of CA storage for the product. it is likely that MAP is not a suitable technology.(a) Gas In Gas Out Gas Sampling Port Product Samples Figure 3. The effects of additional temperatures (O and 10°C) and relative humidities (85 and 95%) on storage quality should also be examined. respectively. For this feasibility study. 34. In practice. The O2 tolerance limit may be determined by monitoring the increase in ethanol content of the tissue.The respiratory quotient (RQ) is a convenient term. The external factors include temperature. 1987. and whether the product is climacteric or nonclimacteric.3) . resistance of plant tissue to gas diffusion. RQs are reported to range from 0. and the equations for rate of O2 consumption and rate of CO2 evolution are /?O2 = R°2exp(-£O2/R7^ #co2 = Rco2 exp(-£CO2/R 7^ (3. the CO2 tolerance limit varies between 10 and 20%. The Arrhenius model is often used to describe the temperature dependence of respiration. otherwise.1) shows. Kader et aly 1989).1 Temperature effect Temperature is the most important factor because it affects both the respiration rate and the permeability of the package. the longer the storage life (Powrie and Skura. maturity.limit. most products experience some temperature fluctuations during storage and distribution. As Equation (3. depending on the product . Keeping CO2 concentration below the CO2 tolerance limit is necessary for protection of the product from unfavorable physiological disorder such as breakdown of internal tissues. and the chilling temperature varies between O and 15°C. Internal factors include the type of product and cultivar. The respiration rates are known to be affected by several internal and external factors (Robertson. depending upon the metabolic substrate (Kader. 1991.2) (3. 1992). Keeping the product above a certain temperature is necessary for avoiding cell damage leading to loss of flavor and invasion of spoilage organism. respiration involves the rate of O2 consumption (R0) and the rate of CO2 evolution (RCo2). Respiration is often a good index for the storage life of fresh produce: the lower the respiration rate. anaerobic respiration will lead to the formation of off-flavor and off-odor inducing compounds such as alcohols and aldehydes.7 to 1.4 Respiration rates Respiration rate values are required for mathematical modeling and for defining the package requirements. which is defined as the ratio of CO2 evolution to O2 consumption. Usually the O2 tolerance limit varies between 1 and 3%. 3.3. C2H4 concentration. Keeping O2 concentration above the O2 tolerance limit is necessary for maintaining aerobic respiration. Lebermann et aL> 1968). O2 and CO2 concentrations and stress due to physical damage or excessive water loss. and temperature below which chilling injury occurs.the actual values can be determined experimentally using the flow-through system illustrated in Figure 3.4a. 8) where the subscripts in and out denote the inlet and the outlet concentrations.6) 3. they must be determined by experiment.5. the closed system.4(a).4. (3. The flow-through system has an advantage of being able to . The steady-state inlet and outlet concentrations are measured with an instrument such as a gas chromatograph. Arrhenius-type equations can also be used to describe the temperature dependence of gas permeabilities.5 at 10-200C.5 Measurement of respiration rates Because respiration rates under modified atmospheres for most fruits and vegetables are not available in the literature. Mathematically. 1992).5-4. The flow-through system and the closed system are illustrated in Figure 3. a condition satisfied by most practical circumstances. and the permeable system (Lee.7 Flow-through system The experimental setup of the flow-through system is shown in Figure 3. The equations for calculating the respiration rates are (3. 5. and 1. defined as 10 Respiration rate at (T + 10)°C " ~ Respiration rate at rC which is applicable to either O2 consumption rate or CO2 evolution rate. There are three methods for measuring respiration rates: the flow-through system. It is important to position the inlet and the outlet tubes sufficiently far apart to ensure thorough mixing of the gas in the jar. Typical Q10 values for vegetables are 2.Another common way to express the temperature dependence is Q10.0 at 20-300C. 2. respectively. Similarly.0 at 30-400C (Robertson.0 at 0-1O0C.5-2. 1.7) (3. 1987). the activation energy is approximately linearly proportional to Q10 if the temperature range of interest is small (less than 400C difference).0-2.5-2.5) (3. 11) (3. 1992). 3. The respiration rates at these O 2 and CO 2 concentrations may be calculated using the equations (3. reduce the gas flow rate.. Another drawback of the flow-through system is that each experiment measures only the respiration rate at a single gas concentration.8): work only with produce of high respiration. The initial gas concentrations inside the jar are usually those of air. because the differences between the inlet and outlet concentrations are usually rather small.2 Closed system method The closed system method (Figure 4b) is more efficient for measuring respiration rates as a function of gas concentrations.10) The negative sign in Equation (3. but other gas concentrations may also be used. increase the sample weight.9) (3.5. the usefulness of the flow-through system is limited by the precision of the gas chromatography measurements. the gas concentrations in the jar change with time . and thus much time and labor are required if respiration rates at many gas concentrations are to be measured.9) signifies that the O 2 concentration in the jar decreases with time. However.12) and their first derivatives are . the data of gas concentration versus time should first be curved fitted. The recommended functions for fitting the data are (3. as suggested by Equations (3.7) and (3.provide more accurate data than the closed system. This method involves monitoring the O 2 and CO 2 concentrations inside a closed jar containing the product as a function of time (Haggar et al. There are three ways to increase the concentration differences.from high O2/low CO 2 concentrations at the beginning to low O2/high CO 2 concentrations toward the end. As the product respires. In order to evaluate the first derivatives. (3.13) (3.14) The validity of Equations (3.11) and (3.12) should be confirmed by comparing the fitted values with the experiment data. If the comparison is poor, other forms of functions should be attempted. For convenience, the conversion factor a is omitted in Equations (3.13) and (3.14). The respiration rates calculated from Equations (3.9) and (3.10) are at O2 and CO2 concentrations unique to a particular closed system experiment. It is usually difficult to design a priori a closed system experiment to generate certain desired gas concentrations. The question is how the respiration rates obtained from closed system experiments can be useful to estimate the respiration rates at other gas concentrations. An answer is to first fit the respiration rate data with a model and then use the model to estimate the respiration rates at the desired gas concentrations. The best model presently available for this purpose is the enzyme-kinetic type respiration model proposed by Lee et al. (1991). (3.15) The model requires two different sets of adjustable coefficients (Vm, Km, and Kj): one for ROi and the other for Rcc>2. The model has been verified quite extensively using experimental data for a wide variety of products. Since the model is based on the principle of enzyme kinetics, it requires less adjustable coefficients and is likely to be more predictive than those purely empirical models (Cameron et a/., 1989; Yang and Chinnan, 1988) used in the literature. However, the applicability of the model to any new set of data should always be confirmed by comparing the predicted values with the experimental data. Overextending the model to predict respiration rates at concentrations very different from those generated from the closed system experiments should be avoided. Table 3.2 lists the model parameter values and respiration activation energies for some fruits and vegetables. The activation energies are not strong functions of O2 and CO2 concentrations (Haggar et aL, 1992). 3.6 Model equations and package requirements Mathematical models are useful for defining the package requirements for MAP. Several models (Jurin and Karel, 1963; Veeraju and Karel, 1966; Table 3.2 Respiration model parameter values and respiration activation engergies for some products Respiration model parameters Commodity Blueberry "Coville"3 Broccolib Cauliflower0 Green pepperd a Temp. (0C) 15 7 13 10 Respiration expression O2 consumption CO2 evolution O2 consumption CO2 evolution O2 consumption CO2 evolution O2 consumption CO2 evolution vm (mg/kgh) 68.0 51.0 210.3 235.2 133.7 134.4 54.3 31.8 (% O2) 0.4 0.2 0.6 1.7 1.7 1.4 6.0 2.4 (% CO2) 2.9 4.9 2.3 1.93 3.0 3.1 1.3 4.3 Activation energy (kJ/mol) 147.3 163.3 62.7 66.1 21.2-48.2 21.2-48.2 48.7-57.3 48.7-57.3 Song et al (1992); bHaggar et al. (1992); cYam et al. (1993) and Exama et al. (1993); dExama et al. (1993). Hayakawa et al., 1975; Deily and Rizvi, 1981) are available in the literature, and some of them have been reviewed by Zagory and Kader (1988). Basically those models use the principles of O 2 and CO 2 mass balances to describe the interactions among the respiration of product, the permeability of the package, and the environment. 3.6.1 Unsteady-state equations A simple model based on the principle of mass balance requires that Rate of O2 or CO2 accumulated in package _ Rate of O2 or CO2 permeated into package Rate of O2 or CO2 generated by respiration and the mass balance equations for O 2 and CO 2 are (3.16) (3.17) where the subscripts i and o denote the inside and outside of the package, respectively. Equations (3.16) and (3.17) are first-order linear differential equations that can be solved quite easily using a computer. They are useful for describing the unsteady-state behaviour of the MAP system, such as during the process of passive modification and during temperature fluctuations. The equations can be tailored to fit a particular physical situation through the application of initial boundary conditions. For example, the initial conditions for passive modification are [O2]; = 21 and [CO2]; = O at t = O. Note that the respiration rates R02 and RCOi are functions of O2 and CO2 concentrations, which can be expressed using the enzyme-kinetic model of Equation (3.15). 3.6.2 State-state equations When the accumulated terms are zero, Equations (3.16) and (3.17) are reduced to the steady-state equations (3.18) (3.19) where the subscript s denotes steady-state condition. Equations (3.18) and (3.19) describe the dynamic equilibrium behaviour of the MAP system, when the CO2 evolution rate equals the efflux rate of CO2 through the package and the O2 consumption rate equals the influx rate of O2 through the package. In most situations, steady-state or dynamic equilibrium is approached within two days. For long storage of the product, the dynamic equilibrium behavior is more important than the unsteady-state behavior. To use Equations (3.18) and (3.19) as design equations, it is necessary to keep track of how many independent or design variables are available. There are a total of 11 variables: R02, RCOi, and W are associated with the product; P02, PCQ2, S, and L are associated with the package; [O2]o, [O2J1 s, [CO2]O, and [CO2I1 s are associated with the environment. (Although temperature is not explicitly shown, it is an implicit variable that affects both the respiration rates and the permeabilities to O2 and CO2.) Once the product and the temperature are selected, six out of the 11 variables are already decided: R02 and RCOi are determined by the flow-through system or the closed system experiments; [O2J1 s and [CO2], s are assumed to be the optimum O2 and CO2 concentrations; [O2]o and [CO2J0 are 21 and 0%, respectively. With six variables fixed and two equations to satisfy, there are only (11-6-2) = 3 design variables. That is, only three out of the remaining five variables (W, 5, L, P 02 and PCO2) can be specified arbitrarily. For example, if the food technologist chooses to specify the dimensions of W, S, and L (within practical limits), the permeabilities P 02 and PCO2 must then be determined by Equations (3.18) and (3.19). The equations also provide a convenient means to reject films not suitable for a particular application. Dividing Equation (3.19) by Equation (3.18) yields (3.20) where [O2]0 and [CO2I0 are assumed to be 21 and 0%, respectively. Further, if RQ is assumed to be 1 and PCQJPOi is defined as (3, Equation (3.20) may be rewritten as (3.19) Equation (3.19) may be represented as a straight line with slope P on a plot of [CO2I1 s versus (21 - [O2]; s). Two such lines (P = 0.8 and (3 = 5) are shown in Figures 3.3 and 3.4. As an example of application, cauliflower requires a P = 5 (Figure 3.3), and thus a film with (3 varying considerably from 5 (such as 2) should be rejected for packaging cauliflower. However, there is no guarantee that a film with (3 = 5 will work well for cauliflower because, in addition to (3, the individual F 02 and PCOi must be also determined by solving Equations (3.17) and (3.18) simultaneously. Satisfying Equation (3.19) is a necessary but non-sufficient requirement for selecting a suitable polymeric film. There are on-going research efforts being made to develop more sophisticated models for more accurate prediction, since none of the existing models considers every factor of the MAP system. A more complete model should include the generation of H2O and heat and the effects of N2 and C2H4 in addition to balancing the O2 consumption rate and CO2 evolution rate. In the meantime, the simple model described above can be used to provide helpful information for preliminary design of MAP. 3.7 Polymeric films for MAP applications Since there are many varieties of produce, a wide range of permeabilities is required. High permeabilities are needed for rapidly respiring produce, low permeabilities for slowly respiring produce. Table 3.3 lists the permeabilities, (3 values, and permeability activation energies of some common food packaging polymeric films. Among them, low-density polyethylene and polyvinyl chloride are most widely used for packaging fruits and vegetables (Zagory and Kader, 1988). A fortunate situation occurs when the desired P 02 and PCOl requirements are met by one or more existing commercial films. If this is the case, a good chance exists for a successful design. Unfortunately, this is not often the case because the choices of suitable commercial polymeric films are rather limited. The problem can be appreciated by examining Table 3.3, which reveals that the (3 values for most films fall within a rather narrow range al (1993). Table 3.3 Permeabilities at 100C and permeability activation energies for polymeric film Permeabilities (ml mil/m2h atm) Polymeric films Polybutadiene Low-density polyethylene Ceramic-filled LDPE Linear low-density polyethylene High-density polyethylene Cast polypropylene Oriented polypropylene Polyethylene terephthalate Nylon laminated multilayer film Ethylene vinyl acetate Ceramic-filled polystyrene Silicone rubber Perforation (air) Microporous film PQ2 1118 110 199 257 2.1 53 34 1.8 1.7 166 116 11170 2.44 X 109 3.81 X 107 PQ2 9892 366 882 1002 9.8 151 105 6.1 6.0 985 630 71300 1.89 X 109 3.81 X 107 PCO2 PQ2 8.8 3.3 4.4 3.9 4.6 2.9 3.1 3.3 3.5 5.9 5.4 6.4 0.8 1.0 Activation energies (kJ/mol) Ep.o2 29.7 30.2 36.8 35.1 26.8 52.6 48.4 34.5 8.4 3.6 13.0 E P,co; 21.8 31.1 28.4 30.1 25.9 50.0 37.0 26.2 0.0 3.6 3.7 From Exama et al (1993); Lee et al. (1992); Lee et al. (1994); Ohta et al (1991); Mannapperuma and Singh (1990); Anderson (1989); and Shelekshin et al (1992). between 3 and 6; however, Figures 3.3 and 3.4 show that many fruits and vegetables require P values outside this narrow range. This problem has also been recently investigated by Exama et al. (1933), who conclude most films do not satisfy both the gas flow and selectivity requirements for many fruits and vegetables packaged in typical MAP configurations. There are at least two possible solutions for this problem. The first solution is to compensate the inadequacy of the films with techniques such as placing oxygen absorbers in the package or using two different films to selectively control the permeability. The second solution is to look for new and better films - some recent advances in the development of polymeric films suitable for fresh produce are discussed below. 3.7.1 Perforation and microporous films A major challenge is to develop films that have greater permeability and have a wider range of p values than existing types. Films of enhanced permeability are necessary for packaging high respiration rate products and for preventing the development of anaerobiosis. A wider range of (3 values, especially those below 3, is necessary to better match the respiration behavior of many products. The use of either perforation systems or microporous films is a possible solution to meet these two requirements. These systems and films have Emond et al (1991) have studied gas exchange through perforation systems. particle size of filler. They developed empirical equations to predict the effective permeabilities to O 2 and CO 2 for various diameters. The average pore size ranged between 0. Good results were reported for strawberries. After sealing. The uses of perforation systems or microporous films in MAP are currently being studied in several laboratories.00159 m thick) could provide an effective solution. Mizutani et al (1993) reported that microporous polypropylene sheets could be prepared by biaxially stretching filler-containing polypropylene sheets. experiments are required to confirm these computer predictions. The bag was flushed with N 2 or CO 2 as a preservative gas before sealing.8 and 1 (Anderson.500 and 465.permeabilities many orders of magnitude higher than those of non-perforated polymeric films. The microporous membrane was a biaxially oriented film composed of a blend of propylene homopolymer and a propylene-ethylene copoylmer having an ethylene-moiety concentration of 2-5% by weight.000. could provide favorable conditions for broccoli. thicknesses. and temperatures. the film was perforated to assure gas outflow from the bag. Meyers (1985) described the use of perforations in MAP of fruits. the permeance (defined as permeability per unit thickness) of the film ranged between 77. and degree of stretching. consisting of silicone membrane with area of 0. as well as (3 values between 0. . a perforation system (with perforations 0.008 m in diameter and 0. The film was filled with 40-60% CaCO 3 based on the total weight of the film. to prevent distortion and to provide a gas pressure within the bag sufficient to inhibit air inflow into the container. mushrooms. However.0061 m2 and perforations of 0.0127 m thickness. a combined system.14 and 1. The gas permeabilities of those sheets were controllable by adjusting filler content. Anderson (1989) has described the use of microporous films for MAP of fruits and vegetables.4 juum. and broccoli florets with the proper selection of permeance. The packaging of strawberries and nectarines using this technique was described.006 m diameter and 0. Their computer simulations showed that neither a silicone membrane alone nor a perforation system alone could provide a satisfactory gas concentration for broccoli. The package was constructed of a gas-impermeable material having a microporous membrane panel to provide controlled flows of O 2 and CO 2 through its walls.000 ml/m2 day atm. Their other computer simulations also showed that while no polymeric film or silicone membrane could provide satisfactory conditions for strawberries. However. Depending on the loading of CaCO 3 . Examples of fillers were CaCO 3 and SiO2. The technique involved placing the product in a bag (or on a tray) constructed of a high-barrier film such as polyvinylidene chloride. 1989). Joyce.8 Concluding remarks This chapter provides some practical suggestions for designing MAP of fresh produce.7. . diffusivity of skin and flesh to O2 and CO2. research is being done on developing a new class of polymeric films with permeation activation energies more closely matching the respiration active energies of fresh produce. As mentioned before. it is expected that higher loadings of ceramic filler should yield higher permeabilities. but the permeabilities of existing packaging films are only slightly affected by temperature. CO2. Although some workers (Isaka. Lee et al (1992) have reported that the O2. and C2H4 permeabilities of ceramic-filled LDPE films are higher than those of plain LDPE film. the benefit of using such films has not been reported in other laboratories. 3. The model equations are a time-saving tool to reduce the number of experiments and to answer many 'what-if questions. The films usually contain about 5% of very fine ceramic powder. The problem of developing such films is the mismatch of the activation energies for respiration and permeation: respiration rates of produce are strongly affected by temperature. effect of C2H4. Since ceramic is a filler. commercial ceramic-filled polymer films have been introduced in Japan and Korea for packaging fruits. The higher permeabilities make these films more suitable for packaging high respiration rate products.2 Temperature compensating films Another challenge is to develop films that can tolerate temperature fluctuation during storage and distribution.3. This class of polymeric films exhibits dramatic changes in permeability by transforming the polymer matrix reversibly from a crystalline state to an amorphous state as temperature is increased above a switch temperature. This switch temperature can be controlled within ± 2°C by changing the polymer side-chains. Presently. etc.7. In some cases. Thus the model predictions should be used with an understanding of their limitations. and must always be verified with experimental data. and the manufacturers claim that these films emit far-infrared radiation or absorb C2H4 that can help to extend the shelf-life of the fruits.3 Ceramic-filled films In recent years. 1988. 1988) have reported that these films seem to improve the storage quality (especially color) of fresh produce. 3. the model equations are oversimplified because they do not include many factors such as transpiration of the product. a situation that may damage the product. even a small temperature increase will cause rapid accumulation of CO2 and depletion of O2 in the package. and that the temperature dependence of the permeabilities follows the Arrhenius relationship. M e n t e n constant (% O 2 ) Inhibition constant (%• C O 2 ) Thickness of film ( m m ) Molecular weight of C O 2 (0.314 J/mol K) Pre-exponential factors for respiration (mg/kg h) Rate of CO 2 evolution (mg/kg h) Rate of O 2 consumption (mg/kg h) Package surface areas (m 2 ) Time (h) Absolute temperature ( 0 K) Free volume in package or in jar (ml) Maximum respiration rate (mg/kg h) Product weight (kg) . 0% for air O 2 concentration (%) O 2 concentration inside the package at any time (%) Inlet O 2 concentration in flow-through system (%) Outlet O 2 concentration in flow-through system (%) Steady-state O 2 concentration inside the package (%) O 2 concentration outside the package (%). C1. b 2 . E02 EpCO2. EpOi F K1n K1 L MCO2 M02 Patm ^co2> ^ 2 PCO2 P02 P R ^Co2' R o 2 RCo2 RQ2 S t T V Vm W % CO 2 concentration % CO 2 concentration inside the package at any time % CO 2 concentration inside the package at steady state Inlet CO 2 concentration in flow-through system (%) Outlet % CO 2 concentration in flow-through system CO 2 concentration outside the package (%). c 2 JE1CO2.Nomenclature [CO 2 ] [CO2J1 [CO2J1 s [CO 2 ] in [CO 2 ] out [CO 2 ] O [O 2 ] [O2J1 [O 2 ] in [C^lout [Cy^s [O 2 ] o a (S a t . PCQJPO2 (dimensionless) Coefficients (Ir 1 ) Coefficients (dimensionless) Activation energies for respiration (J/mole) Activation energies for permeability (J/mole) G a s flow rate (ml/h) M i c h a e l i s .044 kg/mole) Molecular weight of O 2 (0. a2 bj. 2 1 % for air Conversion factor (1 hr"1) Permeability ratio.032 kg/mole) Pressure of 1 atmosphere (atm) Pre-exponential factors for permeability ( m g mil/m 2 h atm) Permeability to CO 2 (mg mil/m 2 h atm) Permeability to O 2 (mg mil/m 2 h atm) Pressure in the package or the jar (Pa) Gas constant (8. (1988) Evaluation of a ceramic-impregnated Plastic Film as a Postharvest Wrap. 1365-70. and Gilbert. USA.H. (1989) Controlled atmosphere package. J. Cameron. Y.A.References Anderson. (1992) Application of ceramic-filled polymeric films for packaging fresh produce.. A. Report of Ginki Chogoku National Agricultural Experimentation Station. and Breene.. J. Food Technol.). 1. (1994) Design of Perforated Polymeric Packages for the Modified Atmosphere Storage of Fresh Fruits and Vegetables. and Singh. Yamaguchi (eds). Food ScL. K. CJ..M. 1991 IFT Annual Meeting. and Desilets. Lebermann. In: Food Product-Package Compatibility.S. D. Mannapperuma. 1-69. 27.R. P. Yasmoto. Lee. T. Meyers. Calif. Proceedings. Food ScL. Boylan-Pett. K. T. 1421. Nagota. and Karel. Yoza. (1987) Respiration of gas exchange in vegetables. K. Y. Joyce. (1985) Modified Atmosphere Package and Process. 34(1). D. B. Weichmann (ed. Jurin.Z. Xl. Jpn. 28(1).. (1987) The design of controlled or modified packaging systems for fresh produce.L. M. 5(1). T. J. Miltz (eds). HortScience. A. L. D. (1988) Recent trends in use of far IR radiations: use on packaging films. Mannapperuma. K. Haggar. / Food Proc. Food Technol. A. 221-7.P. Food Process Engineering. Marcel Dekker. (1981) Optimization of parameters for packaging of fresh peaches in polymeric films. C. P. Nakatani.C. 186-91. Ami. 56(6).G. F. 365-74.. Lee. (1963) Studies on control of respiration of Mclntosh apples by packaging method. Packaging Technology and Science.C. In: Proceedings of the Fifth International Conference on Controlled/Modified Atmosphere/Vacuum Packaging-CAP90. R. In: Handbook of Food Preservation. January 17-19.. (Shokuhin Kogyo. K. J. K. Chem.P. Lee. J. (1993) Microporous polypropylene sheets. 22(4)..P. Deily. Respiration of shoots and color of flower head..L. V.D. and Rizvi.. and Kerbel. PA. Lee. . J. In: Post Harvest Physiology of Vegetables. (1993) Suitability of plastic films for modified atmosphere packaging of fruits and vegetables. (1992) Application of an enzyme kinetics based respiration model to closed system experiments for fresh produce.P.. W. A.S. (1989) Design of modified atmosphere packaging systems: modeling oxygen concentrations within sealed packages of tomato fruits. Ind. Paper 21-8.E. (1968) Post-harvest changes of broccoli stored in modified atmosphere: I. (1991) Gas Permeability of Commercial Plastic Films. and Singh. and Yam... Saio. Gray. 5. Ohta.S. and Yam. 1088. Lancaster. Food lnd.W. 23. 43-6.E. and Steinberg. Mizutani..L. 239-45.R..E. T. 23-41. Kader. A. 32. (1989) Application of 'active packaging' for improvement of shelf-life and nutritional quality of fresh and extended shelf-life foods. /. Hayakawa. E. 40.. K. P. and Pres. Utagawa. Transactions of the ASAE. Haggar. K.I. Res. Zagory.A. W.). Lee. Lee. J. Katzyoshi. A. J. (1990) Micromodel optimization of modified atmosphere vegetable/fruit packaging. and Lee. Toupin. and Toupin.I. Emond. 82. and Yam. D. R. Castaigne. Lencki.W. T. 13.. Kader. R.. T. 31(24). 104-8. Isaka.. Creative. K. Henig. H. Eng. (1992) Freshness keeping packaging. CRC CHt. 1413-16. Labuza. Y. US Patent 4842875. J. H. 1580.. J. (1991) Model for fresh produce respiration in modified atmosphere based on principles of enzyme kinetics. J. A. et al. US Patent 4515266. K. S. (1989) Modified atmosphere packaging of fruits and vegetables. M. S. D. 143-57. 143-6. Food ScL Nut. Umeda.. Food ScL.D. (1975) Formulae for predicting gas exchange of fresh produce in polymeric film package. Exama. J. J. Food ScL. J. Rev. 27-30. (1991) Mathematical Modeling of Gas Exchange in Modified Atmosphere Packaging. D.S. New York. 15. Nelson. 58(6). Technomic Publishing. 54. Tokyo.S. and Ishitani. Chapter 3. Yokoyama and T..S. Food Processing. Harte and J. R. Haggar.L..P. San Jose. Amer. BJ.H. 101-27. Kim. (1988) Modified atmosphere packaging of fresh produce. J. 233-44. T. Soc. Veeraju. (1994) Minimal Processing of Foods and Process Optimization. Ellis Horwood.G. Dixon. Zagory.S. Food Technology. Boca Raton. Wiley (ed. Yang.C. and Kader. Florida. Hort. and Oliveira. Brody (ed. 31. (1992) Respiration of blueberry in modified atmosphere at various temperatures. Sci. Prince. New York.L. Ooraikul and M. Haggar. Food & Nutrition Press. ASAE. (1966) Controlling atmosphere in fresh-fruit package. Singh. 117(6). 170. In: Modified Atmosphere Packaging of Food. J. 40. (1994) Some biological and physical principles underlying modified atmosphere packaging. Rev.. 172. T. Modern Packaging.). H.Powrie. 183-225. / Membrane ScL. M. (1993) Modeling respiration of low CO2 tolerance produce using a closed system experiment. Chapman & Hall. Foods Biotechnol. D. (1986) The effect of controlled-atmosphere storage on the sensory and nutritional quality of fruits and vegetables. New York. R. and Ma.A. 254. D. Robertson. 22-5. (1988) Modeling the effect of O2 and CO2 on respiration and quality of stored tomatoes.S. CRC Press. and Skura. B.. 8. Permeation of gases in microporous glass membranes. G. CC. In: Food Packaging: Principles and Practice.B. A. 174. 70-7. (1992) Packaging of horticultural products. (1991) Modified atmosphere packaging of fruits and vegetables. Shelekhin. Trumbull. Marcel Dekker. 438-9.. permeation. Connecticut... Song. F. In: Minimally Processed Refrigerated Fruits and Vegetables.P. 75. Yam. and Karel. R. Y.L. M. 920-5. Stiles (eds). New York. Solomos. 2(1). 168. A.K. (1989) Modified atmosphere packaging of horticultural commodities.D. K. and Yam.S. Hort. K. II.L. 42(9).E.E. . (1992) Adsorption.L. and Lee. Trans. Y.). In: Controlled/Modified Atmosphere/Vacuum Packaging of Foods.. W. 67-100. 470-506.A. A. and diffusion of gases in microporous membranes. M. and Chinnan. 925-9. P. Weichmann. A. 1 Introduction Polymers constitute either all or part of most primary packages for foods and beverages and a great deal of research has been devoted to the introduction of active packaging processes into plastics.2 Oxygen scavenging The removal of oxygen from package headspaces and from solution in foods and beverages has long been a target of the food technologist. These polymer films might be used as closure wads. lacquers or enamels in cans and as the waterproof layer in liquid cartonboard. either commercialisation or extension of the current range of application. The development of plastics active packaging systems has been more closely tied to the requirements of particular food types or food processes than has sachet development. their chemical or physical basis and their application to foods and beverages. Oxygen scavenging sachets were introduced to the Japanese market in 1978 (Abe and Kondoh. 1989) whereas the first oxygen-scavenging beer bottle closures were used in 1989 (see Chapter 8). ROONEY 4. Most forms of active packaging involve an intimate interaction between the food and its package so it is the layer closest to the food that is often chosen to be active. The commercial development of active packaging plastics has not occurred evenly across the range of possible applications. and obstacles to. Research continues to be popular in both these areas. This chapter surveys the range of polymer-based active packaging processes that have been reported. Introduction of vacuum packaging and inert-gas flushing has provided solutions for some . Some processes which have become economically important are treated individually in other chapters.L. 4. Plastics are thermoplastic polymers containing additional components such as antioxidants and processing aids. Thus polymer films potentially constitute the position of choice for incorporation of ingredients that are active chemically or physically.4 Active packaging in polymer films M. Physical processes such as microwave heating by use of susceptor films and the generation of an equilibrium modified atmosphere (EMA) by modification of plastics films have been available for several years. Chemical processes such as oxygen scavenging have been adopted more rapidly in sachet form rather than in plastics. Attention is given to opportunities for. or as packages in their own right. . coating. Bacterial growth and the growth of yeasts can be a problem in high wateractivity foods including meats and prepared dishes. bag-in-box film. resin Flexibles film.1% or lower are required to prevent the growth of many moulds.1 Food characteristics influenced by oxygen scavengers Characteristic Microbiological status Infestation Chemical degradation Physiological changes Targets Moulds. resin Flexibles film. The properties of foods that can be influenced by the presence of oxygen scavengers are shown in Table 4. tea Cereals Dried Fruit Dried Foods/Nuts Fried snacks Fruit/Vegetables Milk powder Meat . etc. film. adhesive. aerobic bacteria Insects. . This allows the opportunity for tailoring the packaging to the requirements of the product. Flexibles film. Oxygen levels of 0. the opportunity to improve on the benefits gained by application of those technologies.1. eggs Rancidity.Table 4. Closures. Oxygen scavengers can prevent oxidative damage to flavour and colour in a wide range of foods. etc. bag-in-box film. etc. they can maintain atmospheres with oxygen concentrations too low for insect survival in agricultural and horticultural products. etc. as well as in juices. However. Flexibles film. Flexibles film. Table 4. etc. has led to the current interest in oxygen-scavenging plastics. etc.. closures film. etc. etc. etc. larvae. etc. their type of packaging and the forms in which the scavenger might be applied. lidding resin resin. Flexibles film. etc. ink Flexibles film. The list in Table 4. etc. Crown seal liners Resin. trays.2 Potential applications of oxygen scavenging plastics Product Aseptic liquids Bakery products Beverages Beer Cheese Coffee. flexibles film.fresh . Likewise.processed Pasteurised liquids Retorted foods Packaging Component Cartonboard. The growth of moulds is particularly important in dairy products such as cheese and in bakery products. The package converter can decide the nature and quantity of active components used in plastics packaging. etc. Flexibles. browning Respiration of the problems of distribution of oxygen-sensitive foods as described by Brody (1989). pigment/nutrient loss. Flexibles. Flexibles film. organosol Flexibles film. as well as the chance to treat the problems of distribution of foods individually.2 is indicative of the range of foods which could benefit from oxygen scavenging. Closures. bottles Can lacquers. Some are suitably packaged using existing processes.3 Comparison of headspace oxygen removal systems System a b c d e Vacuum N2 Flush a+b Scavenger b+d Residual O2 kPa < 1. Abe and Kondoh (1989) have shown the need for oxygen removal by in-pack systems when the economic limit of around 0. the scavenger can be hot-melt bonded to the inner wall of the package. who compared sachet technologies with vacuum and gas-flush packaging systems. This figure can vary in practice as residue levels of around 2% are often encountered when form-fill-seal (ffs) gas flushing is used commercially. 4.1 <0. Koros (1990) has set out the maximum quantity of oxygen which a generalised range of foods can take up and still have a shelf-life of one year. The expected benefits of use of oxygen-scavenging plastics are to minimise the materials cost by matching the quantity of scavenger to the need. This is done using the Mitsubishi Ageless scavenger sachet attached to the lid of the steamed rice packages Table 4. The factors which may need to be considered.3 which is based on a similar table devised by Hirata (1992).5 1-2 < 1. are summarised in Table 4. Alternatively. and particularly beverages. and to keep the filling speed high. However.1 Forms of oxygen-scavenging packaging In-pack oxygen scavenging involves use of a variety of forms of scavenger. and estimates of efficiency when sachets are used.Wagner (1990) lists a wide range of oxygen-sensitive prepared foods which are of increasing importance in consumer societies.1% oxygen can be found in vacuum packs of beef primals where muscule respiration and bacterial action scavenge oxygen. its prior processing and the packaging machinery and the way it is distributed.5% is reached in the general case. This is particularly important when reduced levels of additives have been chosen for regulatory or marketing reasons.2. The most appropriate method of removal of oxygen from a food package depends on the nature of the food. This would allow use of different packaging materials and distribution systems. less than 0. Alternatively. These quantities are generally in the 1-200 mg/kg range. Sachets merely inserted into the food package constitute most of the present systems in commerce. Some foods.1 Capital investment High Medium High Low Medium Film cost High High High Medium Medium Filling speed Low Medium Low High Medium . cannot be stabilised adequately with existing packaging technologies in order to allow use of the full range of desired distribution systems. quality can often be retained longer if residual oxygen is removed.0 <0. Such requirements therefore rule out the common heat-seal polymers and thin layers of the more mediocre barriers like polyester (PET) and nylon 6. This allows all exposed surfaces of the food to be deoxygenated or protected from oxygen ingress by permeation.2. but are more .2-butadiene) and appears to be directed at that market. This liner was developed by Advanced Oxygen Technologies Inc. Beyond the concept of adhesion of sachets to the package lies a wide range of possibilities and it is to this area that much of the recent research and development has been directed. Both companies manufacture in the USA. The industrial development and history of oxygen-scavenging closures is discussed in detail in Chapter 8. such as found in cans. as in the case of the PET or PVC bottle. 4. The self-adhesive label concept of US company Multiform Desiccants is used in the Marks & Spencer retail chain's preserved meat packs in the UK. and Zapata Industries Inc. Abe and Kondoh (1989) recommend that Ageless sachets should be used in packages with an oxygen transmission rate less than 20 ml/m2/atm/ day.2 Plastics packaging as media for oxygen scavenging Oxygen-scavenging packaging has to date been applied only in packs which have inherently a substantial barrier to oxygen ingress by permeation or leakage. Sachets can be a highly efficient form of oxygen scavenger but their nature does not favour contact with liquid foods or where cling of the package to the film may isolate the sachet from areas of oxygen entrapment or ingress. However. Alternatives include package inserts in the form of cards or sheets. In such situations it would be preferable to have the scavenger in the packaging material. Alternatively an iron-based system has been developed under the name Oxyguard by Toyo Seikan Kaisha Ltd in Japan. printing ink. there can be situations such as in transportation of beef primal cuts in which a shorter period of absolute barrier to oxygen is desirable and these plastics might be used as the barrier. Low molecular weight ingredients may be dissolved or dispersed in a packaging plastic or the plastic may be made from a polymeric scavenger. An example is the beverage crown seal liner currently used in the beer industry. lacquer or enamel. or jar or cup. The patent of Speer and Roberts (1993) describes a system involving oxidation of poly(l. The commonly found oxygen barriers may be in the form of a single-layer package. Grace and Company and under the name Daraform. The scavenger may be incorporated into a solid which is dispersed in the plastic or may be introduced into various layers of the package such as in the form of adhesive. under the name SmartCap and independently by W. or layers coated onto the inner wall of the package.R. Oxygen-scavenging films or other plastics packaging materials are alternatives to sachets.manufactured in Japan by Ajinimoto under the Take Out brand name. The fact that a molecule can migrate fast enough to fail food-contact regulatory tests does not indicate that it can be used in an oxygen-scavenging system.Table 4.922) Polystyrene Polyvinylchloride (Reproduced from Paine. Table 4.40 O2 O053 0.4 Permeability coefficients P X 1010 (cm3 mm cm"2 sec"1 c m 1 Hg) @ 30 0 C Film material Polyvinylidene chloride Polyester (Mylar A) Polyamide (Nylon 6) Polyethylene (d = 0. The high gas and vapour permeability of the common heat-seal polymers allows them to be used as reaction media for oxygen scavenging in laminates.) N2 0. The use of plastics as media in which to disperse or dissolve oxygen scavengers places a severe limitation on the number of reactions which can be involved in the scavenging process. unlike there case where solid particles are used.05 0.0 1. Such a characteristic of the polymer helps offset the disadvantage of plastics-film-based compositions in comparison with sachets where the scavenging powder has a large reactive surface area exposed. However. if the scavenger is incorporated . A further challenge is to establish whether the breakdown of iron particles on oxidation occurs as freely in a polymer matrix as it does in powder form in sachets.53 1. A more extensive tabulation of film permeability values can be found in the review by Bixler (1971).6 35 352 88 10 likely be part of a multilayer package. Oxygen-scavenging compounds can be dispersed or blended in highpermeability films such as plasticised PVC and polyethylene.0094 0.6 55 11.4 shows the oxygen permeability of a range of polymers.2 CO 2 029 1.9 0.22 0. 1962. The particular advantage of such polymers is that they allow rapid diffusion of oxygen and water (at elevated temperatures) from the headspace or food in to the reactive ingredients.10 2. Polyethylene and polyvinyl chloride (plasticised) are nominated as the reaction medium in crown closure liners for beverage bottles such as for beer.960) Polyethylene (d = 0.38 10. Thus the use of iron oxidation in polymers has been a challenge for some years requiring all reagents to be intimately mixed. The presence of the oxygen scavenger in the heat-seal layer allows maximum advantage to be taken of the full thickness of the physical barrier to oxygen permeation of the barrier layer. larger molecules behave as if they were immobilised. with permission. Labuza and Breene (1989) note that virtually all of the iron in commercial sachets is available for oxygen removal. as described in detail in Chapter 8. Where the oxygen scavenger is molecularly dispersed in the polymer it is available to oxygen in its entirety. Indeed this has been proposed in a large number of patents such as those of Hofeldt and White (1989) and Farrell and Tsai (1985). Whereas molecules of the size of oxygen or water can diffuse at an adequate rate.7 19 2. The permeability of the heat-seal layer to both oxygen and water vapour can be limiting as in the mixed sulfite/acetate layer in retort pouches patented by Farrell and Tsai (1985). This is claimed to be useful for packaging liquid foods (Ohtsuka et al. Various sulfites can be held in a fibrous layer sandwiched between. A second patent describes a package consisting of three layers. Traditionally. In this case the water is needed in substantially larger quantity than the oxygen in order to dissolve the deliquescent potassium acetate in which solution the potassium sulfite dissolves and reacts with oxygen. Depending upon the chemistry involved. water is absorbed by the EVOH in such large quantities that the barrier layer becomes quite . most oxygen barriers are now water sensitive. The outer layer is a plastics film. 1990) that portion closer to the outside becomes exposed to relatively large amounts of oxygen. poly(vinylidene chloride) copolymers have provided a water-insensitive oxygen barrier when used as a layer in laminates. together with traditional nylons. especially if the hydrophilic layer is protected by a water-barrier layer such as polypropylene as in the case of retortable lunch-cups. Several recent patent applications describe claims of enhanced availability to the package atmosphere of granular reagents. as with crystalline sulfites at room temperature or the reaction can require the presence of an additional species as with the rusting of iron. 1984). the oxidation reaction can be inherently slow. as in that of Mitsubishi Gas Chemical Industry Co. and a second of a plastic or paper with an oxygen permeability greater than 7000 ml/m2/day atm. Such a change may render a material which is suitable for packaging an oxygen-sensitive food at low relative humidity into one which is most unsuitable at high relative humidity. coated films or coextrusions. The plasticising effect of water on the barrier properties of EVOH (or other hydrophilic barriers) is time dependent. An approach to overcoming any limitation on scavenging rate by the heatseal layer's permeability has been to use microporous polymers such as nonwoven polyolefins. The permeability to oxygen of EVOH copolymers increases approximately 10-fold when exposed to a relative humidity change from about 40-100%. When such retortable packs containing a wet food such as an entree are subjected to steam retorting. The permeability of the polymer medium in which the scavenging reaction occurs need not be the limiting variable determining scavenging rate.into the barrier layer as in the Ox-bar bottle of CMB Technologies pic (Folland. the middle is a perforated or nonwoven layer containing an oxygen scavenger and the inner layer of the package is a microporous film which resists the flow of liquids through its pores. Such films cannot be used where transparency is required but may have application in many forms of packaging. one layer of foil. for example. The introduction of ethylene-vinyl alcohol copolymers (EVOH) and poly(vinyl alcohol) means that. Although addition of desiccants to the polypropylene (Tsai and Wachtel.R. 1990) is used to reduce this impact there is an opportunity here to include an oxygen-scavenger layer in the coextrusion to absorb the oxygen. In fact there has been a recent news report of the introduction of an oxygen scavenger into such packages by Toyo Seikan Kaisha Ltd. W. and oxygen scavengers which remove oxygen when it does pass through the hydrated barrier layer. The photoinitiated system described by Rooney (1994) has been shown to function at 00C. 2-butadiene). providing: desiccants which absorb water in polypropylene. The reaction of hydrogen with residual oxygen on palladium has been taken further by Hayashi et al (1986) who vacuum-metallised polyester film at 2.4% in 1 day. These systems were based on the earlier work of King (1955) and Abbott et al (1961) who applied palladium metal to the inside surface of can lids. this layer was found to be effective in catalysing the conversion of oxygen to water.3 Brief history of oxygen-scavenging films The initial oxygen-scavenging packaging film was a multilayer described by Kuhn et al (1970) and by Warmbier and Wolf (1976). 4.permeable to oxygen. When a bag made from this laminate was filled with 500 ml of a mixture of hydrogen-nitrogen 8:92% by volume. 1990) and mica platelets to the EVOH (Bissot. particularly during the period of enhanced permeability. Grace (1994) have investigated the effect of low temperatures on their (optionally photosensitised) metal-catalysed oxidation of syndiotactic poly(l. although production of a thinner metal layer may change future economics. Whereas elevated temperatures and high humidity have been used to advantage in the research of Farrell and Tsai (1985).5 x 10"^ moles of Pd/m2 and laminated this to high density polyethylene. reducing the oxygen content from 3-4 to 0. Due to the expense of this process it would be suitable for packaging high-valued items such as probes for an oxygen analyser. and certain other low crystallinity polymers with glass transition temperatures below -15°C. The rate of water release through the outer polypropylene layer becomes very slow on cooling. They have foumd that this polymer. so the oxygen permeability can remain elevated for many weeks (Tsai and Wachtel. 1990).2. The earliest investigation involving reaction of oxygen in homogeneous . The cans were flushed with mixtures of hydrogen (8%) in nitrogen to give a mixture in which the residual oxygen could react with hydrogen to form water on the palladium surface. scavenge at least 10 ml/m2/day O2 at 100C or lower. Thus active packaging has the potential to contribute to solving the permeability problem in two ways. the effect of temperature on the performance of oxygen scavengers in polymer-based films has been reported in only rare cases. However. there was a slow growth in the number of plastics-based systems devised until the numbers were equal for both types of system in 1993-94. The histogram shows that whereas initially only sachet technologies were considered. 1982). The most evident trend in oxygen-scavenging system development during the past 20 years has been the increasing importance of patent applications for compositions and designs based on plastics. numerous patents and some conference proceedings give sufficient detail to allow a comparison of the systems reported. Very few of these have involved actual polymer oxidation but rather have required the reactive ingredients to be dispersed within the polymer matrix or to be sandwiched between film layers. The increasing number of plastics-based systems results from a substantial overall increase in the interest in oxygen-scavenging systems. Very little investigation of the chemistry of oxygen-scavenging films has been published in peer-reviewed journals. Rooney. not from a decrease in the numbers of sachet technology applications. .1 Patent applications for oxygen scavengers involving sachets and plastics. This technique takes advantage of the ease of excitation of oxygen from its ground state to its first singlet excited state and has shown that use of polymers as scavengers or reaction media need not inhibit rapid oxygen removal.1 which shows the numbers of initial applications for new compositions or designs without consideration of whether additional applications for the same idea have been lodged in other countries. An examination of patent applications worldwide gives the results shown in Figure 4. This has resulted from a more lateral approach to potential reactions coupled with approaches Sachet Plastics Applications Years Figure 4. Holland and Shorter (1981) and by Rooney (1981.polymer films was described by Rooney and Holland (1979). Grace and Co. Some patents involve claims of conventional antioxidants as oxygen scavengers. In one example linseed oil. This process relies on the presence of water from the food or beverage as well as the presence of isoascorbic acid or a metallic sulfite such as sodium sulfite. the shelf-life of carbonated beverages like beer is limited by the loss of carbon dioxide by permeation. calcium carbonate and active clay are mixed with activated carbon to give a solid oxygen scavenger (Toppan. In each case the transition-metal catalysed oxidation results in development of odorous compounds such as low molecular weight aldehydes which are adsorbed by zeolites. 1992). so the mode of action of this process is still uncertain. The results suggest that beer held in such a bottle would be saved from oxygen ingress via the bottle wall for at least 12 months thus providing oxygen-barrier performance functionally equivalent to that of glass. iron oleate. appear not to include an adsorbent for odorous products. One combines oxygen scavenging with the antimicrobial action of a silver zeolite (Shimagawa Nenryo KK. Several other applications for oxygen-scavenging plastics containing ascorbic acid have subsequently been lodged. oxygen-scavenging plastics are designed to achieve a specific effect . R. such as that of W. Some compositions. W. The advantage of this system is that water is not needed as a reagent. As with any form of active packaging. 1971). carbon or other adsorbents. 1992).R. An example of the performance of a bottle made from the Ox-Bar (Trademark of CMB Technologies pic) has been given by Folland (1990).to overcoming previous deficiencies. CMB Foodcan pic has developed a novel system for use in blow-moulded bottles made from PET into which up to 7% MXD-6 nylon had been blended (Cochran et ai. These antioxidants are normally associated with reactions of primary products of reaction of molecular oxygen with polymers. Thus the effect of the oxygen-scavenging bottle would be to change the nature of the limiting . 1991). The process is now commercial and follows the patent of Farrell and Tsai (1985) who patented the sandwiching of either a sulfite alone. As it turns out.in this case protection of a packaged food from oxygen. between the layers of a retortable pouch structure. has applied for patents for the use of ascorbic acid dispersed into plastics such as the common heat-seal plastics or closure liners (Hofeldt and White. for oxidation of squalene with a transition metal catalyst (Ebner et al9 1992). The use of bifunctional antioxidants at up to 2% in rigid poly(vinyl chloride) was claimed to reduce the permeability of that polymer 20-fold although the period of effectiveness was not reported (Wijbrief. 1989). Grace and Co. This is particularly evident in patent applications for systems involving oxidation of carbon-carbon double bonds in small molecules like squalene and fatty acids or in polymers like rubbers. or one mixed with potassium acetate. An additional catalyst in the form of a polymer-soluble cobalt salt such as cobalt stearate was necessary to cause the nylon to react with oxygen. Brief exposure to light for activation of o chain reactions. This requirement is elaborated in the discussion on sachet technologies in Chapter 6. containing MXD-6 nylon blended into the PET for instance. Thus the catalyst and the oxidisable substrate can be kept apart until the bottle is blown. laminations or other plastics layers with high oxygen permeability are normally activated by one of the following mechanisms. Such packaging systems would include blow-moulding of beverage bottles which often occurs on the premises of the beverage filler. • • • • Supplying a reagent on package filling. In some instances activation might not be a necessary consideration if the package is prepared from all constituents immediately before filling. Continuous exposure to light as energy source. viz. What is particularly interesting in this case is that the use of a cobalt salt catalyst in PET appears to have satisfied some national regulatory authorities. The systems which have been developed for use (or prospective use) in coatings. the water can come from the food itself as described in the Oxyguard process of Toyo Seikan Kaisha Ltd. This process has not reached the market place since the reaction products need to be defined in greater detail. e.4 Chemistry of oxygen scavenging Unlike most other forms of active packaging. as in the OxBar process developed by CMB Technologies pic. oxygen-scavenging films must be stable in the oxygen-rich environment of air prior to use. or in the variety of patents referred to in Chapter 1. This has presented a problem to chemists formulating such systems and surprisingly few methods of activation appear either in the patent literature or in commercial practice. the oxygen permeability of the bottle is so low that a delay between blowing and closure is quite reasonable. In the case of the PET bottle. A further factor is the nature of the packaging material carrying the oxygen scavenger. .variable if used in those countries where beer has a high level of carbonation.g. autoxidation o rapid photoreduction of scavenger precursor In each of the above processes several variants exist. hydrogen or water Supplying water as a solvent or swelling agent on filling. 42. A general guide to such circumstances is that if the plastic material actually carrying the oxygen scavenger is exposed to the outside air during its life as a package the system can probably be chosen not to have an additional activation step. For instance. The oxidation of hydrogen by molecular oxygen requires metal catalysis at room temperature. (1961) was particularly successful for removing oxygen which desorbs from canned spray-dried milk powder. 4. Tsai and Wachtel (1990) have shown that EVOH trays can take up as much as 2. It is doubtful whether an adequate rate of oxygen scavenging can be achieved when the polyolefin heat-seal plastics are used as the reaction medium at room temperature. water ingress is generally needed. also of Surlyn. On storage the milk desorbed oxygen which diffused. is sandwiched a layer of powdered alumina upon which palladium metal has been deposited. Where patents describe incorporation of treated iron powder into plastics. Indeed such a process has long been used by microbiologists to generate low-oxygen-content environments for cultivation of anaerobic microorganisms. Between this Surlyn and the heat-seal layer. There appears to have been very little use of this system. This is probably for the purpose of introducing sufficient water on to the iron surface to carry out the reactions described in Chapter 6.Water needed as a reaction solvent or to burst micro-capsules can be supplied from the retorting steam in the case of retortable plastics packages which are processed at around 1200C.5% hydrogen is specified in plants for production of chlorine by electrolysis. The quantity of water which was formed was calculated by the authors to be insufficient to affect the food.1 Supplying a reagent. together with the hydrogen.8% extra water on retorting. It should be noted that an explosion limit of 6. The hydrogen content of the flushing gas is limited to 7% or less to avoid the risk of explosion. In this case water vapour permeation can be sufficient from the outside of the pack as well as from the food itself and here heat is also a trigger for commencement of the process. The application of this process to packaging by King (1955) and Abbott et al. The oxidation of iron in the presence of electrolytes has been well established in the sachet technologies reviewed in Chapter 6. through the Surlyn to react on the catalyst surface. marketed as Maraflex 7F by American Can Company. The surface of palladium metal either as mesh or deposited on porous alumina catalyses the reaction to form water. The bag was flushed with the above-mentioned H2ZN2 mixture before heat sealing. . Some specify the need for such materials to be used under retorting conditions. Conventionally a mixture of hydrogen (8%) in nitrogen is either flushed into the cultivation chamber or hydrogen is generated in a sealed anaerobic jar in the presence of an air headspace. with foods although it was used in the US space programme.4. and this diffuses out slowly over a period of some weeks. The laminate bag described by Warmbier and Wolf (1976) consists of a polyester outer layer bonded to aluminium foil then Surlyn.2. the predecessor of Advanced Oxygen Technologies Inc. The presence of such a strong adduct is effectively equivalent to oxygen removal by means of an irreversible reaction. The potassium acetate is deliquescent and absorbs sufficient water to dissolve when the food-filled pouch is retorted. The sodium sulfite dissolves in the potassium acetate solution and reacts with oxygen diffusing into this solution from the food and especially from the retort atmosphere. They incorporated a mixture of potassium acetate and sodium sulfite crystals (or potassium sulfite alone) between the barrier and heat-seal layers of a retort pouch laminate which had five layers overall. This type of oxygen absorber was the subject of extensive research by Aquanautics Inc in the USA. The resultant metal chelate forms an oxygen adduct with a binding constant greater than 105M'1. The sulphite reacts with oxygen as in Equation 4. as in the headspace of some food packs.g. the microcapsules absorb water and swell. The reaction of oxygen with a metal complex can also involve a weak coordinate bond without converting the metal ion to a higher oxidation state. An early example of the dissolution of a salt was patented by Farrell and Tsai (1985). at least to some extent (see Chapter 1). This type of reaction is the basis of blood oxygenation and can frequently be reversed. as steam) can be sufficient to dissolve the reagent thus enabling oxidation to proceed rapidly. When the package is exposed to high humidity and elevated temperatures the rate of transmission of water from either the food or the outside (e.1) Although this process can result in the presence of an aqueous solution in the laminate.2.9 1992).4. This results in bursting of the microcapsules and mixing of the complexing agent and the salt under moist conditions. Ascorbic acid and isoascorbic acid react readily with oxygen. 2Na2SO3 + O2 -> 2Na2SO4 (4.1. The water vapour permeability of the laminate can increase 1000-fold from 210C to 121°C.4. The use of metallic salts of these acids is described in . Some packaging applications potentially permit the use of scavenging components as heterogeneous additives to the packaging material. more rapidly at high pH. the rate of reaction with atmospheric oxygen can be acceptably low for incorporation into packaging. A process such as this which requires both heat and high humidity is really limited to applications which involve retorting or substantial heat-treatment of the packaged food.2 Supplying water as a solvent or swelling agent. Particularly where reagents are in the crystalline form or coated with a low-permeability substance. A recent patent describes the incorporation of a metallic salt and a complexation agent in separate microcapsules within a polymer film (Zenner et al. On exposure of the film to an atmosphere of high relative humidity. it should be possible to consider use of some form of binder for the solution after retorting. 2. There is thus the potential for use of ascorbic acid as an intermediate in the 2NaOH HOHC CH2OH HOHC BROWNPRODUCTS Figure 4.patents from many sources. The initial step is the formation of dehydroascorbic acid and this step is strongly dependent upon pH. depending upon the conditions. consisting of a series of consecutive and concurrent reactions. The chemistry of oxidation of ascorbic acid is complex. It is particularly interesting that the patent of Hofeldt and White (1989) describes the optional use of sodium sulfite in combination with ascorbic acid (and its isomers) in their oxygen-scavenging closure liner for use with beverages such as beer. Ascorbic acid can be regenerated by reaction with mild reducing agents such as metallic sulfites. A simpler summary is shown in Figure 4. The steps involved in the commercially accepted scavenging compositions have not been described in the scientific literature. . It has been observed in the author's laboratory that cellulose acetate films containing dissolved ascorbic acid turn light-brown in colour after standing in darkness under ambient temperature and humidity conditions for one to two years. The steps involved in ascorbic acid oxidation in solution have been reviewed by Tannenbaum (1976) who summarised the reactions involved in the oxidation of ascorbic acid.2 Oxidation of ascorbic acid. 3). The steps in the process are shown below.2 one of the reaction products of oxidation of ascorbic acid to dehydroascorbic acid is hydrogen peroxide or initially the hydroperoxy free radical. 1976).R. (4. The use of sodium sulfite. In this form the dye can pass the excitation to oxygen by the process of triplet- . and Zapata Inc oxygen-scavenging closures in common use in some beer bottles. which involves transfer of visible light energy to oxygen via the intermediacy of a dye. (Equation 4. Given the heterogeneous nature of the reaction mixture it is doubtful whether this desirable regeneration occurs to a very great extent in commercial practice without the formation of an aqueous solution as described by Farrell and Tsai (1985).6) (4. Further hydrogen abstraction by this radical forms hydrogen peroxide.4) (4. Grace and Co. 3D. visible or near infra-red irradiation of appropriate wavelengths. Such a film must contain a photosensitising dye and an electron-rich oxidisable compound termed a singlet oxygen acceptor. and these occur within the matrix of the polymer film.5) (4. would therefore seem to be desirable if the ultimate re-introduction of an oxidising agent is to be avoided.2. As can be seen from the summary in Figure 4. absorbs light (hx>) it is excited to a short-lived higher energy singlet state. The oxygen-scavenging process occurs when the film is illuminated with UV.2) which largely converts to the longer-lived triplet excited state. or another reducing agent. Whether this occurs in the ambient or low-temperature storage of beer has not been described in the literature. The use of ascorbic acid or its isomers or salts is the basis of the W.3 Continuous exposure to light as an energy source. A polymer film can be the medium for these photosensitised oxygenscavenging reactions. 4. The role of ascorbic acid as a promoter of browning when oxidised in foods is already known (Tannenbaum. (Equation 4. D.7) When a suitable photosensitiser. *D.oxidation of sodium sulfite to the sulfate.4.2) (4.3) (4. Some oxidation reactions which do not occur when oxygen is in its unexcited (ground) state can be brought about by the process of photosensitisation. 10~3 M.3 shows the rate of scavenging of oxygen from air. Ethyl cellulose has an oxygen permeability coefficient at 25°C of 7 Barrers (cm3 (STP) cm/cm-2 s"1 cm"1 Hg x 10~10) compared with that of 0. for instance. in a 10 cm x 10 cm pouch coated on the inside with either natural rubber dyed with tetraphenylporphine.6 M with respect to PEF and 10~3 M with respect to tetraphenylporphine. The distance singlet oxygen can diffuse before quenching in a polymer matrix is of the order of IOOA depending on the polymer permeability and other factors (Turro et a/. for such a process to be useful the polymer matrix (such as an inner layer of a laminate) would need to be very permeable to oxygen. This was interpreted as being due to the higher concentration of double bond (13.5) provided they are within the distance the singlet oxygen can diffuse before it is quenched back to the ground state (Equation 4. 1981). The sensitisers include erythrosine or me^o-tetraphenylporphine and the acceptors are bis(furfurylidene)pentaerythritol and ascorbic acid. It was subsequently shown that the rate of oxygen scavenging reaches a maximum at a concentration of tetraphenylporphine above 10~3 M but less than 10~2 M. It was found that the permeability of the polymer film is an important determinant of scavenging rate.7 Barters for cellulose acetate (Bixler.2 equivalents/litre of film) in the .9 1981). This chemistry has been used in the laboratory as an oxygen-scavenging process where the polymer matrix is. When the scavenger film was used as a roll it was found that the rate was dependent upon the length of film in the roll consistent with increased access of oxygen to the film. 20 ml. or ethyl cellulose 0. Once excited to its singlet state the oxygen can react with any electronrich acceptors. The rubber scavenged oxygen substantially faster than the PEF in the ethyl cellulose. Thus. The process occurs only within the lifetimes of the excited sensitiser (Equation 4. The light intensity used was 2 x 10 5 -7 x 105 Lux. The singlet oxygen acceptor does not need to be a small molecule dissolved in the polymer.6). present in the polymer matrix (Equation 4. It has been shown the double bond of natural rubber can be photo-oxidised at a rate sufficient to bring about rapid oxygen scavenging from the headspace of a package.7) and singlet oxygen and so requires continuous illumination. This is of the order of 10-1000 microseconds. It was also found that the rate of scavenging of oxygen from a pouch by the film is limited by light intensity initially but becomes diffusion limited when the oxygen partial pressure reaches low values (Rooney et al. 1982). 1971).triplet energy transfer (Equation 4. 1981.. with the ethyl cellulose being a better matrix for rapid scavenging than cellulose acetate.. cellulose acetate or ethyl cellulose (Rooney et al.4). Rooney.5 equivalentsflitre) in the rubber than the concentration of furan rings (1. The oxygen diffusing into the polymer from the package headspace (for instance) needs to come very close to the excited. A. Figure 4. immobile dye molecules during the triplet lifetime of the latter. it would be expected that the more highly methylated rubber poly(dimethylbutadiene) would react more rapidly with singlet oxygen. 103M.5M in ethyl cellulose a. It is significant that the reaction occurring in natural rubber occurs on the polymer chain and therefore is not dependent on the free rotation of the acceptor. The photo-oxidation of the tacky natural rubber layer resulted in rapid crosslinking as indicated by the loss of tack within minutes. The oxidation of the rubber continued on dark storage resulting in formation of a brittle powdery film.(bifunctional) PEF.3 Oxygen scavenging by natural rubber •.) . pouch area 100cm2. and PEF 0. Based on the reactivity of simple low-molecular weight analogues of these polymers. An unpleasant odour was also generated. Volume of air. The potential for use of synthetic rubbers in place of natural rubber was investigated in order to determine whether the nature of the rubber monomers affects the rate of scavenging. (Reprinted from Rooney.4 show the rate of oxygen scavenging by poly(dimethylbutadiene) (PDMB). presumably due to the low oxygen permeability of PDMB of 2. Thus permeability rather than reactivity can be the important % Oxygen Time (min) Figure 4. However. The results in Figure 4.1 Barrers compared with values of 20 Barrers and 24 Barrers for PB and PI. both dyed with tetraphenylporphine. cispolybutadiene (PB) and ra-polyisoprene (PI). the inverse relationship is observed. although the higher permeability of rubber towards oxygen (24 Barrers) than that of ethyl cellulose (7 Barrers) is also likely to contribute. 1982b. 20ml. with permission. Thus curcumine. since illumination with white light of polymer films containing only one dye is wasteful of potentially usable energy (Rooney et ai. It has been found that even dyes which are not photosensitisers can harvest energy and transfer this energy to a photosensitiser also in the film. 1994).. 1994). . volume of air 20 ml. The effectiveness of such a film in suppressing rancidity in sunflower oil has been investigated and found to be substantial at 230C and 37°C (Maloba et al. cis-polyisoprene O. was shown to enhance the rate of oxygen scavenging photosensitised by eosine in ethyl cellulose.oxygen (%) time (minutes) Figure 4.4 Oxygen scavenging by polydienes. a natural food colour and a poor photosensitiser (Chignell et ai. cispolybutadiene A. variable in an oxygen-scavenging polymer system as was found to be the case with PEF dissolved in cellulose acetate and ethyl cellulose. Coatings on inner surface of pouches of area 100 cm2. poly(dimethylbutadiene) +. The use of multiple dyes in oxygen-scavenging films has been investigated. 1994). 4.2.4.4 Brief exposure to light for activation. 4.2.4.4.1 Chain reactions. Continuous exposure of a package to light places an intolerable restriction on the way in which most foods would need to be stored and distributed. It is not surprising therefore that the use of light to activate reactive polymer-based systems has been investigated. The problem, inherent in all oxygen-scavenging systems, of using compounds reactive towards oxygen but stable towards thermal processing of the packaging material needs to be addressed. The use of autoxidation of fatty acids for oxygen scavenging has already been claimed but this process seems likely to result in formation of the same volatile oxidation products which are undesirable in foods (Frankel, 1982). Some sachet patent applications describe the use of adsorbents in the sachets to bind volatile off-flavours generated in this way. Mitsubishi Gas and Chemical Company has claimed that activated alumina, silica gel or charcoal absorbs any odour formed on the oxidation of fatty acids or oils catalysed by transition metal compounds in the presence of alkaline earth bases (Inoue and Komatsu, 1988). Toppan Printing Company (1992) claimed a similar composition involving addition of activated clay. The benefit of such systems is independence from water for the reaction. The research effort put into development of photodegradable plastics packaging over the past two decades has provided a background to one approach to this problem Rabek and Ranby (1975) show how a transition-metal metal salt and a photosensitiser dispersed in a plastic can cause it to degrade in darkness once exposed to sunlight for some days. This form of photodegradation involves a substantial extent of hydrogen abstraction from the polymer backbone coupled with hydroperoxide formation, particularly on tertiary carbon atoms. Subsequent breakage of the hydroperoxy bond leads to formation of either keto or aldehyde groups which become additional photosensitisers or result in polymer chain scission. It is in the prevention of the latter reaction that the opportunity for development of oxygenscavenging polymers exists. The scavenging of oxygen including oxidation of hydrocarbon polymers impregnated with salts of transition metals has been described by Speer et al (1993). The novelty of their method is that the oxidation process is activated by brief exposure to light of wavelengths less than 750 nm. The optional use of a photosensitiser is reported to increase the rate of activation, particularly in the presence of an antioxidant. As with the photodegradable plastics processes, the chemistry involves initiation of the free radical process on the polymer chains by changes in the oxidation state of the transition metal ion, preferably cobalt. The redox reaction on the polymer chain involves either hydrogen abstraction in polypropylene or polyethylene or oxygen attack on the double bond in the case of poly(l,2-butadiene). The hydroperoxide formed by reaction of either the polymer free radical or by direct attack on the polymer decomposes to form ketones, aldehydes, peroxides or carboxylic acids, in some cases with chain scission. In the case of poly(l,2-butadiene) it is the aim to localise the oxidation to the side chain containing the double bond. Speer et al. (1993) report that this polymer retains its physical properties even when most or all of its oxidisable groups have been reacted. Since this is a typical autoxidation that is also thermally activated, the polymer needs to be stabilised against premature initiation in the extruder or moulding machine in package fabrication. Antioxidants provide this protection. The quantity of antioxidant is chosen both to provide this protection and to retard the autoxidation chain reaction for a selected period of time between activation and package filling. Removal of antioxidant from the polymer appears likely to increase the likelihood of taint formation due to unrestricted polymer oxidation. Attention should probably be given to inclusion of odour absorbents in the composition as proposed by Toppan (1992). The manner in which such a system could be used is particularly broad but one suggested is to laminate or coextrude the reactive layer with an oxygen-barrier layer. Such an application would be appropriate for many packaging processes such as in the storage of cheese, nuts and meats such as beef primal cuts. The use of such compositions at the low temperatures required for storage of meats and cheese requires that the reactive layer be readily permeable to oxygen. Speer and Roberts (1993) have specified that the compositions containing their oxidisable components should be largely amorphous and have a glass transition temperature below -15°C. 4.2.4.4.2 Rapid photoreduction of a scavenger precursor. Research into systems involving this form of triggering indicate that this approach overcomes some of the limitations of other methods already proposed (Rooney, unpublished results). 4.2.5 Chemical barrier to oxygen permeation Implicit in the use of oxygen scavenging inserts (sachets) or closures is the effect these have on the consumption of oxygen as it enters the product during its storage life. The results in Table 4.5 show the calculated impact of Table 4.5 Calculated life of chemical oxygen barriers Film _ _ _ _ PET 25 nm/LDPE 25 \x.m PVDC-coated OPP 25 jjum Metallised PET 12 ^m/LDPE 25 |xm OTR cm3 m~2 day"1 atm~l _ _ 63 9 0.5 Barrier life (days) _ 56 362 7250 the oxygen transmission rate of packaging materials on the period of effective oxygen scavenging by a commercial oxygen-scavenging sachet with an absorption capacity of 50 ml of oxygen. The packages are 10 cm x 20 cm and initially contain 100 ml air. LDPE is low-density polyethylene, OPP is oriented polypropylene, PET is polyester and PVDC is poly(vinylidene chloride). However, in a food-packaging situation where the food is tightly packed, the sachet can be expected to deoxygenate only a small portion of the headspace and combat permeation of oxygen that is accessible to it. Close-fitting packages such as vacuum packs for block cheese and meats or aseptic cartons of beverages are examples where the headspace is very small and oxygen permeation is the prime cause of quality loss. It is in such circumstances that oxygen-scavenging plastics films are particularly needed. The use of the oxygen-scavenging reaction to intercept oxygen diffusing through the package wall is an example of a chemical barrier as distinct from the physical barrier normally provided by aluminium foil and vacuum metallising or crystalline polymers such as poly(vinylidene chloride). The use of a chemical oxygen barrier offers the opportunity to cheapen barrier packaging for relatively short shelf-life products such as wholesale or export units or for some fresh foods. This can be achieved by using a barrier film of intermediate performance coupled with a chemical barrier. This combination was investigated by Rooney and Holland (1979) and the results in Figure 4.5 demonstrate a period of total barrier to oxygen permeation from air at 25°C. A laminate of polyethylene/nylon 6/cellulose acetate containing oxygen-scavenging reagents was used to separate the two compartments of a glass permeability cell. When the ethyl cellulose layer contained 0.5 M fe-furfurylidenepentaerythritol, illumination with fluorescent light resulting in a barrier life of around 30 days was followed by a period of oxygen transmission at a rate less than that found in darkness. In this case the chemistry used was a singlet oxygen reaction which requires constant illumination to photo-excite the oxygen. Other chemistries can be used to achieve similar reactions in darkness and Speer et al (1993) identified this application for their photoinitiated chain reactions in rubbers, and Cochran et al (1990) devised the Ox-Bar process largely for this purpose. The use of oxygen-scavenging sachets to allow the use of a cheaper packaging material has been described by Alarcon and Hotchkiss (1993) and their work is reviewed in Chapter 6. Although use of multilayers of plastics films appears the most appropriate approach to solving permeability problems, there have been early attempts to carry out scavenging reactions in liquid layers. Oxygen scavenging in liquid layers was one of the earliest processes described in the patent literature. Cook (1969) claimed that bilayers of plastics films separated by a layer of a solution of one of several antioxidants in high boiling point solvents Next Page in darkness illuminated % Oxygen Time (days) Figure 4.5 Barrier to oxygen permeation of polyethylene/Nylon 6/cellulose acetate laminate. Cellulose acetate 26 |xm thick containing PEF (0.5 M) and erythrosine, 5 X 10~3 M. Oxygen concentration measured in a cell on the cellulose acetate side of the laminate, air on the other side. demonstrated a reduced oxygen permeability. Whereas the mechanism was unknown, all of the common antioxidant classes were claimed to be effective. Use of an aqueous solution of an oxygen-scavenging reducing sulfite as a layer between two polymeric layers has been claimed by Scholle (1976). As with the organic system of Cook (1969), the purpose was to reduce the oxygen permeability of the laminate. In the case of Cook's system the role appears to have been to improve shrinkable packaging, as for meat, whereas the Scholle system was particularly suitable for bag-in-box liners since the packages consist of, at least, a collapsible duplex which is sealed together only at the edges where the liner forms a bag (and around the tap fitting). Such a system requires an oxygen scavenger for oxygen-sensitive products due to the gas space between the two film layers. 4.3 Moisture control films Moisture affects the gas and vapour permeability of hydrophilic plastics packaging films (Davis, 1966). Fruit cakes packed in films with an appropriate water vapour permeability can have long shelf-lives because the surface dries somewhat. This creates conditions unfavourable to mould growth. Nitrocellulose-coated regenerated cellulose has been used because it Previous Page in darkness illuminated % Oxygen Time (days) Figure 4.5 Barrier to oxygen permeation of polyethylene/Nylon 6/cellulose acetate laminate. Cellulose acetate 26 |xm thick containing PEF (0.5 M) and erythrosine, 5 X 10~3 M. Oxygen concentration measured in a cell on the cellulose acetate side of the laminate, air on the other side. demonstrated a reduced oxygen permeability. Whereas the mechanism was unknown, all of the common antioxidant classes were claimed to be effective. Use of an aqueous solution of an oxygen-scavenging reducing sulfite as a layer between two polymeric layers has been claimed by Scholle (1976). As with the organic system of Cook (1969), the purpose was to reduce the oxygen permeability of the laminate. In the case of Cook's system the role appears to have been to improve shrinkable packaging, as for meat, whereas the Scholle system was particularly suitable for bag-in-box liners since the packages consist of, at least, a collapsible duplex which is sealed together only at the edges where the liner forms a bag (and around the tap fitting). Such a system requires an oxygen scavenger for oxygen-sensitive products due to the gas space between the two film layers. 4.3 Moisture control films Moisture affects the gas and vapour permeability of hydrophilic plastics packaging films (Davis, 1966). Fruit cakes packed in films with an appropriate water vapour permeability can have long shelf-lives because the surface dries somewhat. This creates conditions unfavourable to mould growth. Nitrocellulose-coated regenerated cellulose has been used because it Melting of ice. There are. The problems which arise from these circumstances are the result of build-up of liquid water. These include: • • • • Transpiration of horticultural produce. Alternatively. which may have a variety of other names. The duplex sheet is sealed at the edges and is normally quilted to . Some of the ways of addressing these problems via packaging are considered in detail in terms of either liquid water control or humidity buffering. The results of the presence of water in unwanted quantities include bacterial (yeast) and mould growth as well as fogging of films and mobile blood and tissue fluid.g. Other active packaging systems go further in removing liquid water from food contact. Drip of tissue fluid from cut meats and produce.prevents contamination with moulds and allows substantial water vapour permeation. such as polyethylene or polypropylene. assisting the customer to see the packaged food clearly. Temperature fluctuation in high erh food packs. several sets of circumstances in food packaging where greater selectivity in control of liquid and gaseous water is required. Several companies manufacture drip-absorbent sheets. between which is placed a superabsorbent polymer in the form of free-flowing granules. The fog droplets therefore coalesce and form a transparent film on the plastic. Anti-fog treatments are a cosmetic form of active packaging. Basically they consist of two layers of a microporous or non-woven polymer. however. 4. Moisture migration via the vapour phase can result in transient formation of regions without adequate preservative or where the aw is high even though the food is packed at lower aw. There is no change in the availability of liquid water in the package and this has the potential to cause produce spoilage unless managed by one of the processes described below.3. e. in fish transportation. the natural water level in the tissue can be undesirably high near the surface for microbiological stability under the chosen storage conditions. This film may even flow on sloped surfaces and gather at the bottom of the pack in extreme circumstances. These additives are blended with the resin before extrusion and migrate to the surface after film formation.1 Liquid water control Temperature cycling of high erh foods has led most film manufacturers to use heat-seal plastics with anti-fog additive. The additives are chosen for their amphiphilic nature with the non-polar chain in the plastic and the polar end group at the interface. The result is a lowering of the interfacial tension between water condensate and the plastic film. Such polymers tend to become slimy when swollen with large amounts of water. Given the interest in reducing the volume of solid waste by decreasing foam polystyrene usage. This approach allows the food packer or even the householder to reduce the surface concentration of water in a food by reducing the in-pack relative humidity.allow the water absorbent to be held in place rather than aggregating towards one edge of the sheet when tilted towards one edge. 1990). The film duplex is described as containing an alcohol.3. thereby preventing discoloration of either the meat or the white foam tray.2 Humidity buffering An entirely different approach to the control of excess moisture in food packages is to intercept the moisture in the vapour phase. An example of this type of product is Pichit manufactured by Showa Denko in Japan. an effect that is controlled somewhat by the quilted seal pattern. 4. Such sheets are then used either as pads under whole chickens or chicken pieces to absorb drip. at great cost. This would necessitate use of a sealed outer pack.. The superabsorbent polymer used in the Thermarite® Pty Ltd sheet manufactured in Australia is capable of absorbing at least 100 times and possibly as much as 500 times its own weight of liquid water depending dramatically upon salinity (Malouthi et al. The aluminium construction of aircraft makes them easily susceptible to corrosion damage. The strong association of the polysaccharide chains is disrupted allowing the starch to exercise its affinity for water by hydrogen bonding. This effect can be controlled by choice of the amount and the capacity of the superabsorbent polymer. The significance of such active packaging in seafood shipment by air lies in the removal of the potential for spillage of salt water from cartons in aircraft holds. A recent patent application in Japan describes a water-absorbent sheet which has a high barrier to oxygen for use with fresh meat (Showa Denko KK. the use of drip-absorbers may become even more necessary to prevent water damage to the more hydrophilic alternatives. both of which are humectants. This can be done by placing one or more humectants between two layers of a plastic film which is highly permeable to water vapour. 1994). The swelling of the polymer on hydration results in substantial distortion of the duplex sheet. described by Labuza (1989) as propylene glycol and a carbohydrate. Such copolymers consist of a polysaccharide backbone with synthetic polymer chains radiating from the starch backbone. although graft copolymers of starch can also be used. The preferred polymers used to absorb the water are polyacrylate salts. Another product of this type is Toppan Sheet manufactured in Japan. Large sheets are used for absorption of melted ice in the packaging of seafood for air transportation. . A recent development has been the water-barrier coating of the inside of fibreboard cartons to allow moist produce to be placed directly into the carton.0 Toppan sheet _ 0. shown in Table 4.2 22. Louis (1991) reports the availability of an additional moisture control film which plays the same role as Pichit in the Japanese market.4 3.7 1. Currently the packages are wholesale fibreboard cartons of produce. Besides the introduction of liquid water with the produce. The potential for use of such materials for quality retention in the home appears to be considerable and this type of film should be subjected to detailed objective evaluation for use in the domestic situation where excess portions of flesh foods need refrigerated storage for some days. usually with a polyethylene liner or consisting of the very expensive waxed fibreboard without a liner. Distilled water 5 g was placed in each of two petri dishes (with lids) and these were enclosed with either Pichit or Toppan Sheet (450 cm2) in a highbarrier package.6.6 15. Pichit is marketed for home use in roll or single sheet form for wrapping pieces of flesh food such as fish or chicken to reduce the aw proximate to the food. The packages were opened at intervals and the petri dishes were weighed to give the per cent loss of weight of water. A different approach to humidity buffering has been under investigation for use in the distribution of horticultural produce.4 8.8 The effectiveness of such a combination material in comparison with a superabsorbent polymer absorbent for liquid water is shown in Table 4. whereas the superabsorbent polymer has a far greater capacity for liquid water uptake. Louis and de Leiris (1991) suggest two to three days of fresh storage is possible. packing into closed spaces allows the build-up of water vapour. It has been suggested by Labuza (1989) that the permeability of poly(vinyl alcohol) to propylene glycol may be sufficient to allow some of the latter to diffuse to the food surface. Propylene glycol is a GRAS substance in the USA. If this is the case. followed by re-use. the humectant-based film more rapidly absorbs water vapour.6.2 8. At present there is a lack of experimental verification of the significance of this effect.Table 4. is an attractive incentive for active packaging use in the home provided absence of microbial contamination can be demonstrated. The produce . The potential for washing the surfaces of sheets like Pichit.6 Water vapour uptake by Pichit and Toppan sheet YimQ (h) __ 3 4 24 26 Weight loss from petri dish (%) Pichit -_ 2. some antimicrobial action might be expected. Thus. The performance of this system is demonstrated in Table 4.1 (0. and. the growth of microorganisms on fruits and vegetables.7 taken from Patterson et al. Two widely different approaches have been taken to buffering the humidity in the cartons in order to prevent condensation while not concurrently causing desiccation of the produce.0 (0. When the temperature rises the multilayer releases water vapour back into the carton in response to a lowering of the RH. with this. the multilayer of material on the inside of the carton is able to take up water in the vapour state when the temperature drops and the RH rises. The control of moisture is one of the main impediments to the introduction of EMA packaging. Both these studies involved use of heat-sealed liners which were concurrently being evaluated for their performance to maintain equilibrium modified atmospheres (EMA) generated by the fruit (see Chapter 3). there is every likelihood of condensation. a paper-like material bonded to the barrier and which acts as a wick. (1993) which shows the results of a comparison of the free Table 4. This approach lends itself to combination with EMA generation less readily as the humidity is buffered at the interface with the fibreboard.7)* 0. The designs of Patterson and Joyce (1993) involve: an integral water vapour barrier layer on the inner surface of the fibreboard. Accordingly.0)* Cooled from 22 to 3°C 22. Since temperature cycling is very difficult to avoid during handling.2)* . The critical characteristic of the system is the capacity of the wick layer for water. The most recent alternative involves the use of the carton as the active package rather than an insert. Indeed it is common to package potatoes in perforated sacks to prevent unwanted build-up of condensation.7 Free water in carrot packs on cooling Packaging Polyethylene liner Condensation control carton •Standard error of the mean (n = 5) Cooled from 10 to 3°C 10. This was proposed by Shirazi and Cameron (1992) who showed that an equilibrium relative humidity of around 95% above produce can be reduced to around 80% by use of sachets of desiccant salt such as sodium chloride. and a layer highly permeable to water vapour but unwettable next to the fruit or vegetable.2 (0. One is to include microporous bags or pads of inorganic salts and the other is to line the carton with a protected layer of a solid polymeric humectant. The approach of using microporous sachets of inorganic salts has been used in the US tomato market in recent years.6)* 0. The condensation control system therefore acts as an internal water buffer. The latter layer is spot welded to the layer underneath. The application was extended by Hudson (1991).continues to lose water by evaporation during distribution and the relative humidity in the lined carton can reach close to 100%.9 (0. reaches concentrations exceeding 8-12 mg/kg (Chandler et al. In periods as short as 2 weeks at 24°C. plastics packaging has not been used to remove selectively components of the flavour or aroma of foods which are considered undesirable. when cans lined with acetylated filter paper containing juice with 14. It appears that this process has not been taken up commercially although it offers considerable potential for freshly squeezed Navel juice marketing . Some varieties of orange. were cooled to 3°C from either 100C or 22°C and after 3 days the amount of free water in the boxes and on the carrots was measured. especially through the flavour 'scalping' which is of considerable commercial interest. but a potential opportunity has been available for over a decade. inclusion of the absorbent in the packaging might remove it as it is extracted.water found in cartons of carrots with a conventional liner with the condensation control multilayer. limonin. Shrink wrapping is an alternative approach to the use of active packaging systems for control of condensation on spherical fruits such as citrus. 1979). almost 30% of the limonene was found in the Surlyn-1601 and 20% in the polyethylene layer in brick packs. Similarly. The cartons containing carrots. Hirose et al. such as the Navel. to which he has made such a large contribution. 1968).9 mg/kg limonin were spin cooked and allowed to stand. A simple active packaging process was suggested by the same authors. Commercially. Processes have been developed for debittering such juices by passing them through columns packed with cellulose triacetate or nylon beads (Chandler and Johnson. BenYehoshua (1989) has reviewed this field. contain a tetraterpenoid of the formula C26H30O8 which is initially present in the albedo but which is extracted into the juice on standing or heating. who proposed that since the juice extracts the bitter principle on standing for 24 h. 4. To this end they proposed using their absorbents in film form such as cellulose triacetate or as acetylated paper. 6 kg. the juice was only slightly bitter after 4-13 days. Thus the juice of such oranges becomes bitter on pasteurisation when this compound. The results demonstrate the capacity of such a system for water uptake under circumstances likely to be found in commerce.4 Removal of taints and food constituents The interaction of packaging plastics with food aroma has long been recognised. They showed that a 1-litre plastic bottle coated internally with cellulose acetate-butyrate reduced the limonin content of 500 ml of juice from 42 to 11 mg/kg after 3 days' refrigeration. (1989) demonstrated the impact of the nature of the metal ion in Surlyn film layers in aseptic brick-packs on the scalping of limonene from orange juice. A later approach to removal of amines odours has been provided by the ANICO Company Ltd in Japan under the trade name ANICO BAG. 1989). 1986). R.L. Two types of taints amenable to removal by active packaging have been identified by researchers responsible for current commercial products.. Examples of such products would be fried snackfoods such as potato crisps. Questions such as these are of particular interest to regulatory authorities.(Johnson. and the potential for several active packaging systems to generate mobile reaction products is considered in Chapter 11. biscuits and cereal products. Hence the earliest work involved incorporation of such acids in heat-seal polymers such as polyethylene and extruding them as layers in packaging (Hoshino and Osanai. Thus opportunities for active packaging can be closely related to problems of food-package interactions. private communication). . the sorption of limonene oil from packaged juices by heat-seal layers has been the subject of several studies (Mannheim et al. Questions which would need to be answered are What is the nature of the products of such reaction and What is their fate. The remaining methods described in the literature to date for removal of taints or off-flavours have largely involved incorporation of ingredients with a specific interaction or reaction with a functional group known to be present in the taint or undesirable food component. The amines formed in fish muscle degradation include strongly basic compounds and thus are potentially strong in their interaction with acidic compounds such as citric or other food acids. On the other hand. Hirose et al. A closely related goal had long been achievable commercially in the tinplate canning of foods in which protein degradation resulted in the release of sulfur compounds from the food. Early developments occurred in Japan where there was seen to be a need to remove amine smells from fish which was stored in domestic refrigerators. 1989. Bags made from film containing ferrous salt and an organic acid such as citric or ascorbic acid are claimed to oxidise the amine or other oxidisable compound as it is absorbed by the polymer. If these materials can be shown to be effective there is an opportunity to determine which variables optimise their rate and extent of reaction. These sulfur compounds cause the phenomenon of 'sulfur staining' on the tinplate and so it has been the practice to disperse zinc oxide in tinplate lacquers to intercept such compounds reacting with them before they can diffuse to the tinplate surface. The formation of aldehydes can make a wide variety of oil-containing foods organoleptically unacceptable well before there is significant damage to the nutritional or functional properties of the food. These are amines resulting from protein breakdown in fish muscle and aldehydes formed from the breakdown of peroxides which result from the initial stages of autoxidation of fats and oils. 6-octadiene) has been found to react with traces of styrene or acrylonitrile when the latter are present in acrylonitrile-butadiene-styrene copolymers or blends being extruded (Tokas. for their recently introduced tie layer Bynel IXPlOl which is a high-density polyethylene (HDPE) resin masterbatch. The restriction in this case. Packaging Division.g. It will be necessary for industry and regulators to ensure that such processes are not used to conceal the marketing of sub-standard or even dangerous products if for instance microbial odours were to be scavenged. One such reaction would be the formation of a Schiff base by reaction of the aldehyde with an amino group. It is interesting to note that the use of a form of active packaging can place restrictions on other components of the packaging. There may well be a wide range of food constituents which can be removed by making use of specific interactions with selected packaging components or by chemical reaction with them. 1979). Addition of myrcene is claimed to introduce no new taint while reducing residual levels of the monomers. It is specified that the heat-seal layer should not be a 'good to excellent gas barrier' (Dupont. The adsorbent is chosen for expected taints and is kneaded onto the outer layer. The chemistry of the process is not described but such a process would require the reaction with the aldehyde to be effectively irreversible at least over the temperature range the package is likely to encounter. foods packaged in plastics consisting of more than one layer are claimed to be protected against taints from the outside by inclusion of the appropriate adsorbent in the outer layer (Kiru Kogyo KK. monomers) or outside but permeating the packaging material continues to be a source of problems for the food industry. The tainting of foods by compounds originating either in the packaging material itself (e. These are formation of chemical barriers as distinct from physical barriers like aluminium foil or crystalline polymers. A fertile research field would seem to be open especially with liquid foods since solubility and diffusion of food constituents in the packaging can be utilised so that the removal process is not limited to compounds with a significant vapour pressure at distribution temperatures. Myrcene (7-methyl-3-methylene-l. apparently retaining the taints there. The amino group would need to be rather stable to heat and oxygen in order to remain unaffected after the extrusion at temperatures up to 2200C in an air atmosphere. and many others. The period of this type of equilibrium adsorption . 1994).5-12%) with unmodified HDPE or other linear polyethylenes to form an intermediate layer in coextrusions. 1993). The approaches described above may contribute to their solution but additional approaches have been described in the patent literature. is that the extrusion temperature should not exceed 2200C to avoid fuming.Removal of aldehydes such as hexanal and heptanal from package headspaces is claimed by Dupont Polymers. In another patent. This masterbatch is blended (2. 4*5 Ingredient release Active packaging materials considered so far have exerted their action on the packaged food by removing unwanted components of either the food or of the headspace enclosed with the food. Another mechanism of flavour loss is the scalping of some flavour components by plastics used in packaging (Mannheim et aL. derived from cypress bark.8 Substances emitted by Active Packaging Substance Carbon dioxide Ethanol Silver ion Organic acids Sulfur dioxide Benomyl Flavours Hinokitiol BHT Enzymes Purpose antimicrobial antimicrobial antimicrobial antimicrobial antimicrobial antimicrobial fortification antimicrobial antioxidant various Source film sachet sachet film film sachet film film film film film Reference Rooney. especially where scalping or flavour degradation occurs after packaging. This is more a legal matter of consumer protection than a technical one as the question arises of when Table 4. A compound which while not a taint is often found undesirable in packages of respiring horticultural produce is the gaseous auxin ethylene. Davis et aL9 1978). The potential benefits resulting from such removal are particularly great and are discussed separately in Chapter 2. 1992). 1989). however. also known as p-thujapricin (Hirata. 1990 Han et a/. especially when a package is subjected to temperature changes. 1992 Hotchkiss. This may have application in areas where products are to be stored or shipped together with odorous products which are inadequately packaged.. 1987 Budny. 1990 Abe. is an additional antimicrobial compound specific to the Japan market. Hinokitiol. Some substances released commercially or which have been the subject of investigation are listed in Table 4. 1975. 1988 Venator. There is. although sulfur dioxide also serves as a chemical stabiliser of colour and flavour by preventing progress of the Maillard reaction which causes non-enzymic browning of products such as dried fruit and wines (Davis. 1993 ICI Australia Halek and Garg. 1990 Hirata. Another form of interaction is by release of desirable ingredients into the food from the packaging materials or from inserts packaged with the food. Most are used for their antimicrobial activity. 1990 . There is therefore the opportunity to replace these lost food constituents by diffusion from the packaging. 1986 Abe. the question of whether a food is being sold as fresh when this is not so.8. Processing of foods often results in loss of flavour by degradation or evaporation. 1989 Abe.needs to be established. The first of these is the need of the industry to respond to pressure by some consumer advocates for reduced use of food additives (Smith. 1992). or other approved food antioxidants in polymer stabilisation replacing some of those developed specifically for plastics. The loss by outward migration was 70%. In the case of liquid foods or solids with close-fitting packaging the process could be based on diffusion alone and not require the antioxidant to be able to evaporate.1 Antioxidant release from plastics Two factors acting concurrently are likely to influence the use of packaging materials as sources of antioxidants in some foods. Master batches of plastics with concentrations of up to 40% of the flavour have been marketed with a view to obviate the effects of flavour scalping. The workers compared the impact of two starting levels in the film on oxidation of the cereal oil and found that with an initial 0. although the ease of oxidation of many flavours suggests an opportunity to provide slowrelease flavour precursors in the packaging material. This work has been taken further by Han et al.02%. (1987) who determined the effect of temperature on both the diffusion coefficient of butylated hydroxytoluene (BHT) in HDPE and the rate of its evaporation into the package of oat flakes.flavour addition to a food fabricated from many ingredients becomes contrary to consumer interests. 4.. Release of very few flavours has been investigated to date. After 6 weeks the HDPE film was free of antioxidant and 19% of that originally in the film remained in the cereal. thiodipropionic acid. The outward loss can be controlled by use of a layer of film with low permeability to the antioxidant or by use in a closure. The manufacture of flavour concentrates in the common commodity plastics has been described by Venator (1986). 1993). It was found that at 39°C only 55% of the original BHT remained in the film after 1 week. and 25% of the BHT was found in the cereal. are approved food additives in some countries and are used as stabilisers in food-grade polyethylene (Anon.32% BHT there was less oxidation than with 0. The potential for evaporative migration of antioxidants into foods from their packaging plastics has been studied by CaIvert and Billingham (1979) who developed a theoretical model.5. Commercial use of this approach to antioxidant release has been reported by Labuza and Breene (1989) who noted that waxed paper has sometimes . These results of Han et al (1987) demonstrate the potential for release of antioxidant into foods provided the rate of diffusion can be matched to the food's needs. The second is the renewed interest of plastics resin manufacturers in using natural. Dilaurylthiodipropionate and its base acid. given the hydrophilic nature of the polymers involved. The inventors nominate liquid foods in cans as a target product area and. slippery surface. These compositions would be expected to undergo the Maillard reactions but their rate would depend upon the thermal conditions used in preparing the packaging and any thermal processing of the packaged product. Other antioxidants might also be used in this way. The authors concluded that the order of descending resistance of films to the insects was permethrin-treated film. to four insect populations. There is an opportunity to investigate whether oils can be stabilised by diffusive addition of antioxidant at sustained low levels from the packaging. polypropylene/polypropylene/polyethylene laminate. Packages such as sacks and lined cartons containing these products are often attacked by insects during warehousing and transport. The patent of Goyo Shiko KK (1993) describes application of amino acids and saccharides which produce reducing sugars on decomposition and perform as oxygen scavengers when used in coating or lamination of packaging films. it appears likely that Maillard reaction products could be extracted into the food to act as antioxidants as well as scavengers. The effect was not entirely consistent since the treated pouches failed at 24 months with one insect species and were better than polyester with one of the remaining species and worse than polyester with the other. The observation of Han et al (1987) that BHT was lost outwards from HDPE film packs points to an otherwise unrelated opportunity for active packaging. Their work involved exposing: polyethylene. The inclusion of low-toxicity fumigants such as pyrethrins in an outer layer of packaging material offers the opportunity to achieve sustained insecticidal activity without substantial addition of fumigant to the food. the latter containing permethrin in the outer layer. and polyester/polyethylene pouches of many foods. Highland and Cline (1986) found that polypropylene containing 203 mg m~2 of permethrin provided rather similar resistance to attack by burrowing insects to that provided by polyester which has a harder. The permethrin-treated pouches were resistant to two insect species for 24 months. This work has been extended by Anese et al (1993). private communication). The potential for applying such antioxidants to foods via packaging materials has been suggested (Eriksson. It has recently been shown that polyethylene bottles stabilised with vitamin E cause less noticeable flavour in distilled water than bottles stabilised with either BHT or Irganox (a hindered amine antioxidant for polymers). There has been constant pressure from importers of grains and other agricultural products for reduced levels of pesticide residues in these products at the time of delivery. polyethyl- .been used as a reservoir for antioxidant release by the US cereal industry. polyester film. Lignert and Eriksson (1980) found that Maillard reaction products have a strong antioxidant function. 1988). 90% RH. The permethrin or alternative treatments would need to be submitted for regulatory approval. probably to achieve effects such as antimicrobial action. including the cost of repeated fumigations with methyl bromide approximately bi-monthly. This work might be developed to provide a low-cost answer to some of the major problems of fumigation. The subject of enzymes in active packaging is discussed in Chapter 7. The importance of predicting the requirements of plastic film's permeability to carbon dioxide and oxygen in packaging of fresh horticultural produce has been discussed in Chapter 3. The result might be prevention of cloud drop in fresh orange juice (R. This high WVTR should favour rapid transmission of polar flavours. 4. Kureha Chemical Co. as well as reducing the exposure of staff to fumigant application conditions. Enzyme inhibitors might also be bound to a film surface. It is possible to modify the permeability of a window in a package and to control gas exchange through this limited area. 60% RH and a water vapour transmission rate of (WVTR) 60 g/m2/day at 400C. Subsequently the effect of sorbed water on cellulosic patches has been claimed to give selectivity in gas permeability matched to the respiration rates of some produce. An example would be the binding of the inhibitor of methyl esterase to the package surface to bind methyl esterase. polypropylene film. The use of enzymes in edible coatings is discussed in Chapter 5.L. It has been suggested recently that enzymes might be released into foods from packaging materials. There are other substances which need to be selected for entry into plastics packaging.ene film and worst. These are films of polyamide alloy which are highly permeable to water and oxygen under conditions of high temperature and high humidity and highly impermeable to oxygen at room temperature under dry conditions (Nishini and Yoshii. Of particular interest is the ability to selectively transmit smoke flavours through films which are useful as skins for ham and other preserved meats. A variety of semipermeable patches were initially developed by the Hercules company in the USA. Hirata (1992) described one such type of film as having an oxygen transmission rate of 8 ml/m2/day at 200C.6 Permeability modification There are a number of circumstances in which it is desirable for the packaging material to be more permeable to one substance than to another. . Labuza and Breene (1989) have reviewed the potential for release of bound enzymes into foods. Johnson. private communication). (1986) described a polyamide film for this purpose with an OTR in the range 50-300 ml/m2/day for film thicknesses of 5-50 |xm. The low oxygen permeability is necessary for colour retention of preserved meats. especially in the European Union. and so additional ingredients will need to be evaluated for their impact. Barrier packages used . with the exception of moisture control packaging. The effect of environmental considerations on plastics-based active packaging will vary with the nature of the product/package combination. owes much to substantial prior scientific research. regulatory authorities must become involved in many developments. This research into equilibrium modified atmosphere packaging has been based on the work of Kader (1980) and earlier workers including Jurin and Karel (1963).8 Regulatory and environmental impacts Since plastics-based active packaging involves not only changing current materials somewhat but also inclusion of reactive components in some cases. It is in the processed food field that commercial development of plastics-based systems can be expected to be substantial over the next few years. condensation control and equilibrium modified atmosphere packaging will continue to be emphasised. Active packaging for processed foods is still based largely on sachet technologies.7 Current use commercially The commercial development of plastics-based active packaging has not occurred evenly either geographically or in terms of their field of application.4. Indeed regulatory considerations appear to have caused the delay in the introduction of a chemical barrier to oxygen into PET beverage bottles. This success. Since some of the active packaging technologies currently commercial are scarcely improvements on existing technologies there will probably be significant realignment in the marketplace. 1994). Ltd is the first example. The major field to date has been horticulture in which several forms of enhanced permeability films have been commercialised for both trade and home use. Ethylene scavenging. causing. as is planned. Commodity films used for produce packaging may become the object of recycling schemes. 4. This tray has been described as 'epoch making'. Perhaps Toyo Seikan Kaisha's planned manufacture of an oxygen-scavenging laminate for the semi-aseptically packaged boiled-rice market by Sato Food Industry Co. in spite of a lack of soundly based evidence of effectiveness in many cases. The substantial impact on the marketplace of oxygen-scavenging crown seals for beverages. The need for active packaging solutions to problems in the storage and distribution of horticultural produce may well ensure that the development of the most soundly based technologies is commercialised. metallised polyester microwave susceptors and timetemperature indicator strips is discussed in other chapters. a 100 000 meals/day operation to be more cost effective (Anon.. /. M. and Hotchkiss. J. 85-130. Princeton. 83-6.. Food ScL. McBean. Chandler.F. and Nicoli. 19. (1989) Oxygen absorbers. 59. B. J. Brody (ed. Anon. Reszka. Sweeting (eds). safety and shelf-life extension will need to be considered in a holistic approach to environmental impact assessment. Morgan. 59.. J.L. active packaging plastics should be judged on the basis of their contribution to the quality and safety of food. USA.. Motten.P.. Trumbull.for processed foods at present are generally not amenable to economic recycling.. Cholesterol and Oxygen from Foods.. Y. In: Science and Technology of Polymer Films. A. p. Food and Nutrition Press. 101-18. (1994) Spectral and photochemical properties of curcumin. 13. Cook. (1989) Modified atmosphere packaging of seafoods. Kefford. Wiley-Interscience. (1993) The effect of Fresh-Pax oxygen-absorbing packets on the shelf-life of foods.C. (1968) Removal of limonin from bitter orange juice. 235-41.H. Food Agric. ScL FoodAgric.. 92-4. S. R. CT. 57-62. D. (1971) Barrier properties of polymer films. P. (1979) New Sorbent gel forms of cellulose esters for debittering citrus juices. (1978) The performance of liners for retail wine corks. e. 295-302. and Ziemelis.. and Dahl.McG. 285-92. W. M. (1969) Flexible film wrapper.E.. Ital. Pittia. Accordingly. NJ. Cornell Univ. Australian Standard 2070. (1994) Use of a New Container requiring no deoxidizer. (1992) Composition for scavenging oxygen especially to protect oxygen-sensitive products. Speer. and Rooney. A. A study by Kooijman (1994) of food packaging in the Netherlands demonstrated that 'the packaging sub-system cannot be studied or optimised in isolation'. Packaging Japan. Trumbull. References Abbott. 75-9.V.. Food Sci. J. Chandler. Abe. G.). D. Brody.. Food TechnoL. Q.. and Speer.. (1990) Performance of high-barrier resins with platelet-type fillers. Waite. M. Inc. A. pp. 28. p. Y..g. In: Barrier Polymers and Structures. Food and Nutrition Press. 825-32. pp. T.comprises . Anese.H. pp. 1-7. and Kondoh.). November. Bixler. Sci. CF. and Hearne. /. American Chemical Society. Budny. Innovative Expositions Inc. Brody (ed. Brody (ed. Food and Nutrition Press. J. J. J. Alarcon. Photobiol. Davis.L. Food TechnoL.C. July. Anon.. Session B-2. Dupont Polymers (1993) Bynel IPXlOl.). HJ. Dairy Res. food . (1993) Oxygen consuming properties of heated glucose/ glycine aqueous solutions.M. 19. Ben-Yenhoshua. HJ. Vol. CR.L. New York. Temporary Product Data Sheet. Koros (ed. and Johnson.. V. E. Dept. (1990) The Use of Enzymes in Packaging for Selective Removal of Lactose. A. E. (1975) Packaging of foods that contain sulfur dioxide.. WJ. 2. E. NY. (1989) Individual seal-packaging of fruit and vegetables in plastic film. B.V. The benefits of active packaging in terms of food quality. pp. 35. Bilski. 225-38. 20. USA. (1992) Plastics for food contact. Roberts. Trumbull CT.F. Davis. Photochem. (1966) Texture changes in salted peanuts in flexible film and tinplate containers. Bixler and OJ. In: Controlled/Modified Atmosphere/Vacuum Packaging of Foods A. Ebner. In: Controlled/Modified Atmosphere/Vacuum Packaging of Foods. KJ.A. Sik. Interactive packaging resin. Technical Report.G. 1..L. J.G.G.). T. R. P. In: Controlled/Modified Atmosphere/ Vacuum Packaging of Foods. Chignell. US Patent 3429717. CSIRO Food Res. (1961) Gas packing milk powder with a mixture of nitrogen and hydrogen in the presence of palladium catalyst. J. 151.L.. 30. CL.G. Washington DC. R. Davis. Bissot.V. Proceedings Pack Alimentaire '90.. B. US Patent 4536409. (1994) Resonance Energy Transfer. Singlet Oxygen Sensitization and . e. silica gel.N.M. Technol ScL9 7. F. (1986) Packaging Materials. Lignert. M. Japanese Patent 5186635. Paris. Farrell. J. European Patent Application 89301149. J.g. (1994) Environmental assessment of food packaging: impact and improvement.W. M. September 15th. Improved oxidative stability of Sunflower oil in the presence of an oxygen scavenging film. Prog. 17(6).g. Inst. Food Proc. Labuza. 79. (1989) Applications of 'Active Packaging' for improvement of shelf-life and nutritional quality of fresh and extended shelf-life foods..M. and Garg. 215-22. Rooney. Y.P. L. Amer. G.A. CJ. (1970) Oxygen Scavenging System for Flexible Packaging of Whole Dry Milk. Kuhn. P. and Karel. 77-95. 161. and Zimmerman. Packag. T.L.F. S. 1-69.. Hoshino. National Food Res. A. water absorption and oxygen permeability. and Komatsu. A. Hofeldt. K. (1989) Container closures and materials for use in these. Japanese Patent 61293846.comprises unsaturated fatty acid or derivative. Goyo Shiko KK (1993) Packaging Material with good gas-barrier property and oxygen absorbing property — comprises high molecular substance amino acids and hydroxyl group containing reducing resin. J. Highland. (1986) Packaging films for deodorization. (1988) Oxygen absorbent compositions . and de Leiris. Louis. (1943) Removing oxygen from a container containing vacuum or gas packed food in which a metal (ex. Preserv. P. H. and Cline. Kooijman. Japanese Patent 6080163.P. Session B-2. Sydney.. Thesis. J. Food Technol.H. Preserv. Fe) absorbs oxygen to form an oxide. K. Jurin. Wormell. (1990) Ox-bar. PJ. K. T. Japan.. T.having a plastic functional layer containing adsorbent e. Products from sugars and free amino acids. M. 4. 527-9. Isherwood. Entomol. (1985) Oxygen Scavenger. Innovative Expositions. (1980) Prevention of ripening in fruits by use of controlled atmospheres. Inoue. zeolite on inner surface of outer layer of sealed container. (1986) Resistance to insect penetration of food pouches made of untreated polyester or permethrin-treated polypropylene film. Maloba Wakwabubi. Hirata. (1991) Modified Atmosphere Storage of Tomatoes. Oil Chem. Proceedings Pack Alimentaire '90. (1986) Packaging film for smoking food has at least one layer and includes nylon layer of predetermined thickness. R. F. Folland.. British Patent 553991. and transition metal or absorbent.. US Patent Application 155283. Food Proc. 34(3). Japanese Patent 60180832.ethylenically unsaturated hydrocarbon. Hayashi. and Osanai. Weinke. / Food Safety. pp. Proceedings 1st JapanAustralia Workshop on Food Processing. A Total Oxygen Barrier System for PET Packaging. Kureha Chemical Co. Halek..4. Kader. (1992) Recent Developments in Food Packaging in Japan. 9. A. (In French) Maloba Wakwabubi. (1955) Catalytic removal of oxygen from food containers. B. 30. A.L. 1-33. 441. Japanese Patent 86209612.A. Inc. T. A. J.E. Lipid Res. V. Pennsylvania State Univ. International Packaging Club. Kawakami. Tsukuba. Soc. (1988) Fungal inhibition by a fungicide coupled to an ionomeric film.. C E . Econ.. J. Kiru Kogyo KK and Marutani Kakoki KK (1994) Functional container for medical supplies or foods . Princeton. King. Food Manuf. squalene and transition metal catalyst. and Kosuge. R. and Eriksson. E. Australia. W. 111-21. Proceedings of 9th Milk Concentrates Conference. 104-8. Frankel. 22. and Tsai. J. and Breene. 1. P. British Patent 9201126. 51-4. (1982) Volatile lipid oxidation products. University of NSW. and White. K. NJ.D. (1963) Studies on control of respiration of Mclntosh apples by packaging methods.A... F. (1980) Antioxidative Maillard reaction products. H. and Nguyen. Hudson. 13. Food Technol.C. submitted. (1991) Active Packaging. base. (1976) Multiple wall packaging material containing sulfite compound. S. US Patent 4180486. (1993) Methods and compositions for oxygen scavenging. Japanese Patent 2192941. Australia. Queensland. (1976) Vitamins and minerals. Ind. B..D. Holland. J. N.L. 68-82. (1982) Oxygen scavenging from air headspaces by singlet oxygen reactions in polymer media. Wormell. (1984) Oxygen absorbent package has absorbent in three layer wall including microporous plastics film or nonwoven fabric. D. and Morgan. Koros (ed..L. British Patent 496935. active clay and deodorant.V. and Takahashi. and Cameron. (1938) Keeping food in closed containers with water carrier and oxidizable agents such as Zn dust. US Patent 4485133. (1979) Singlet oxygen: an intermediate in the inhibition of oxygen permeation through polymer films. Rooney.168.C. NSW. Hotchkiss (ed.).. A. Fennema.Food ScL. (1979) Dry blend of styrene polymer and myrcene scavenger .contains unsaturated fatty acid. Glasgow. Mn dust etc. J. and Wachtel. American Chemical Society. (1993) A package allowing cooling and preservation of horticultural produce without condensation or desiccants. Washington D C . Tallgren. US Patent 5211875.. PhD Thesis.P. (1990) Barrier properties of ethylene-vinyl alcohol copolymer in retorted plastic food containers. 9-13 May. ScL Food Agric.with low residual monomer content. 13. Abstracts Annual Convention of the Institute of Food Scientists and Technologists. Rooney.L. R. Australia. pp. Chem. Tokas. P. A J . Patterson. University of Queensland. H. J. Australia. M. R. University of Western Sydney . and Joyce.V. J.V. 347-86. (1981) Removal of headspace oxygen by a singlet oxygen reaction in a polymer film. D. oxidation catalyst. J. B. Fe powder. 900-1.. Miltz. 32. VoI 1. (1992) Controlling relative humidity in modified atmosphere packages of tomato fruit. Rabek. Gatton. Tannenbaum. Inc. W J . US 93/09125.has a free-oxygen absorber on outside and an oxygen penetrating resin material containing silver ion substituted alumino-silicate formed on inside.. 62.L. Atlanta. W. Australian Institute of Food Science & Technology.L. Shirazi.H. Marcel Dekker. 298. London.L. (1975) Photodegradation.C. Kondoh. In: Barrier Polymers and Structures.). and Moradi.. C. and Nguyen. (1994) Switched-on Active Packaging for Foods. Scholle. Mannheim. J. E. Paine. J. . US Patent 4041209. M. Photo-oxidation and Photostabilization of Polymers. Speer. ACS. H.F. T. Tsai. 99-102. HortScience. Jobling. S. Japanese Patent Application 4298231. 565-9. 197-8. and Shorter. In: Food Chemistry. 265-72. Showa Denko KK (1990) Heat shrinkage laminate wrapping material -for meat has water absorbing agent and water permeable film with oxygen barrier layer. In: Food and Packaging Interactions.072. (1993) Water relations after harvest . Roberts. 291-4. (1993) Improved oxygen scavenging. B.D.A. B. S.C.new technology helps translate theory into practice.A.R. Blackie and Son.P.Applications.. M.. Y. Komatsu. (1982b) Oxygen Scavenging: a novel use of rubber photooxidation. John Wiley & Sons. W. and Ranby. Toppan Printing Company (1992) Oxygen absorbent composition which functions in dry atmospheres .R. and Holland. Canberra. and Roberts. Rooney.. Proceedings of the Australasian Postharvest Conference. Speer. pp. (ed. Shimagawa Nenryo KK (1992) Freshness maintaining packaging body . useful as packaging. C R . A. Abstracts 27th Annual Convention. and Passy.). New York. Patterson. Japanese Patent 4. F. M. International Patent Application PCT/AU93/00398. Chem. O. Rooney. (1989) Interaction between aseptically filled citrus products and laminated structures.. Ohtsuka. M. M. W. PCT Application.V. Rooney. M.Hawkesbury. Rooney. (1994) Oxygen-Scavenging Plastics Activated for Fresh and Processed Foods.F. Maloba Wakwabubi. F. D. (1962) Fundamentals of Packaging. 47. 192-202. Ind. Packaging. and Wolf. 30.F.. 85.. Getters. J. diffusivity and quenching of singlet oxygen in polymer matrices investigated by chemiluminescence methods. (1986) Fragrance and flavour interactions with plastics Packaging Materials. 3014. 38. M. (1990) Getting to Know the Packaging Activists . Decastro. Warmbier. Phys. Chem. Proceedings Pack Alimentaire '90.containing chelated transition metal immobilised on solid phase. N. Wagner.A Comprehensive View of Absorbers. October.F. US Patent 5096724. (1981) Generation.E. (1976) Modern Packaging. and Blaustein. T. B. B.C. New Jersey. Innovative Expositions.. M. /. Princeton. MJ. and their Kin for Food Preservation. Zenner. Venator.Turro. and Emitters. H. . Section B-2. especially for scavenging oxygen in containers. Chow.A. and Ciccone. E. (1992) Ligand extracting composition . 1973. The basic materials can be classified in three categories: polysaccharides.. ovalbumin. 1984a. 1969. casein. Many protein materials have been tested: collagen. chocolate coatings for confectionery. contrary to polysaccharides which are monotonous polymers. Edible films and coatings formed with several compounds (composite films) have been developed to take advantage of the complementary functional properties of these different constitutive materials and to overcome their respective drawbacks. 1986. The most common examples are wax coatings for fruit (used in China since the 12th century). They . Coatings are formed directly on the food product using either liquid filmforming solutions (or dispersions) or molten compounds (e.) have good film-forming properties. celluloses and derivatives. 1972). surface-active agents. Many lipidic compounds. wheat gluten.5 Edible films and coatings as active layers B. Most composite films studied to date combine a lipidic compound and a hydrocolloid-based structural matrix (Cole. protein-based films have highly interesting properties. GUILBERT 5. Films formed from these hydrophilic compounds provide efficient barriers against oils and lipids (Murray et al. CUQ. starches. Kamper and Fennema. but there can be problems concerning stability (particularly oxidation).1 Introduction Edible films and coatings are traditionally used to improve food appearance and conservation. Daniels. b). proteins and lipidic compounds. acetoglycerides. Formulations for edible films or coatings must include at least one component able to form a suitably cohesive and continuous matrix. Guilbert. and soy milk-based lipoprotein films to improve the appearance and preservation of certain foods in Asia.). etc. GONTARD and S. proteins have a specific structure which confers larger potential functional properties (Guilbert and Graille. waxy taste). soybean. They are generally used for their excellent moisture barrier properties. Kester and Fennema. (Guilbert and Biquet. texture and organoleptic quality (opacity.g.9 1994a. lipid films to protect meat products. N. this is due to the fact that. 1989. such as animal and vegetable fats (natural waxes and derivatives. etc. 1986). Although not as extensively studied. lipids). Polysaccharides (vegetable and microbial gums. The mechanical and barrier properties of these films are generally better than those of polysaccharidebased films. Gontard et al. 1989). etc. zein. have been used to make edible films and coatings (Guilbert and Biquet. but their moisture barrier properties are poor. 1994). ).e. Kroger and Igoe. drying conditions) and conditions in which the film is used (temperature. For example. Edible films can also be used to package components or additives that are to be dissolved in hot water or food mixes (Daniels. It is sometimes difficult to obtain adequate adhesion of the film to the food product. general appearance. solutes. 1973. Many functions of edible films are the same as those of synthetic packaging (water. etc. 1991. 1971). Guilbert et aL. etc. by drying a film-forming solution on a drum-drier. 1995). Allen et al. .). surface-active agents can be coated on the food or added to the film-forming solution.9 1992): formulation (characteristics and concentration of the basic and secondary components.). or a material capable of adhering to both components can be applied as an intermediate precoating (e. type of food product and main deterioration mechanisms). etc. by cooling a molten compound. ethanol. crosslinking agents. Application of an edible barrier layer is an easy means to structurally strengthen certain foods. fluidizing. pH. for instance. An edible film is an integral part of the food product it encloses and therefore must have neutral sensorial properties (or compatible with product nature) so as not to be detected during consumption. etc.or acetic acid-based) which can contain several additives (plasticizers. surface texture and color of beef steaks and pork chops. Films are preformed separately from the food product. Edible films or coatings act as an additional parameter for improving overall food quality and stability. In such cases. 1989. The film-forming solution is spread in a thin layer.g.g. denaturing conditions. to reduce particle clustering and to improve the visual and tactile features on the surface of the product. they must be chosen according to their specific application (i. dipping-dripping. thermoforming or extrusion techniques for thermoplastic materials (Guilbert and Biquet. precoating with cocoa before sugar-coating peanuts).can be applied by different methods: with a paint brush or by spraying. opacity. gas and solute barriers. Kester and Fennema. or through standard techniques used to form synthetic packagings. The production process from a film-forming solution generally includes a first step with macromolecule solubilization in a solvent medium (often water-. usually followed by a drying treatment. However. relative humidity). Gontard et al. e. film-forming conditions (type of surface upon which the film-forming solution is spread. The functional properties of the film are dependent on a number of parameters (Gontard. 1994. (1963b) used alginate and cornstarch coatings to improve texture juiciness. 1966). mechanical properties. for instance when a hydrophobic film-forming material is used to protect a hydrophilic food product. The degree of cohesiveness of the matrix is a critical parameter affecting the functional properties of edible films (Banker. They represent one way to apply hurdle technology to solid foods without affecting their structural integrity (Guilbert. They can be produced. 1986). 1 Schematic representation of food preservation with (top) or without (bottom) edible films and coatings as active layers.Films with substantial gas and moisture barrier properties are required for many applications: to control gas exchange for fresh foods and oxygen exchange for oxidizable foods and to reduce moisture exchange with the external atmosphere (Guilbert and Biquet. Guilbert. from dehydration or moisture uptake. from dehydration or moisture uptake (b). Torres and Karel. i.1 gives a schematic representation of food preservation with edible films and coatings as active layers when the first mode of deterioration results from respiration. or from microbial development or oxidation (c). Torres et aL. 1985a. 1973. 1989). . Guilbert and Biquet. The protective features of edible films and coatings are dependent on gas and water vapor barrier Food additives (e. (De Savoye et ai9 1994. Retention of specific additives in edible films can lead to a functional response generally confined to the surface of the product (modification and control of surface conditions). Oil and solute penetration into foods during processing can also be limited by edible coatings (Daniels. 1985).g. when the first mode of deterioration results from respiration (a). b.e when the edible film contributes by itself to the preservation. 1989). antioxygen and antifungic agents) Diffusion of food additives Gas Transfers Storage Water Transfer Food additives in AOffiWOLM SURFACE RETENTION of food additives CONTROL of Gas Transfers Storage CONTROL of Water Transfer Figure 5. In this chapter. or from surface microbial development or oxidation. we will expand on the use of edible films and coatings as active layers. 1988. Figure 5. Watters and Brekke. 5.1). inversely. 1961). 1963. 1984. water. P. 1985. this is not always possible and may result in drastic modifications of the sensory and physiochemical characteristics of the product (Guilbert.2 Use of edible active layers to control water vapor transfer Moisture transfers due to water vapor pressure or concentration gradients have major effects on the organoleptic and microbiological qualities of food products. on modification of surface conditions and on their own antimicrobial properties. using aw lowering agents (salts. is equal to the product of the diffusion coefficient D. 1981. biscuits. 1970. etc.. 1985). Heiss.properties. 1967). 1986. Kochnar and Rossell. 1983. candies and chocolate-coated products (Andres. 1985) may become unsatisfactory as a result of moisture gain or loss. Cosier. moisture uptake in dry or semi-moist foods.g. pizza crust. The diffusion coefficient can be obtained by taking . polyols. Lowe et a/. 1984. 1968. Surface drying on some fresh and frozen foods or. Jokay et al. Moisture exchanges are difficult to control in multicomponent foods such as mixtures of dehydrated foods. However. Marston. Katz and Labuza. can also be hindered by using films with a low water permeability (as schematized in Figure 5. 1977. 1982. For example. 1976). and pizzas. through a membrane is determined by steady-state measurements: P = AWx AtAAp where AW is the permeant weight that passes through a film of thickness x and area A. where At is the time and Ap is the differential partial pressure across the film. dry crackers. Karel.. Labuza. Feuge. faults or membrane punctures. pies. permeability P.). 1985). jelly-filled cookies. representing the mobility of permeant molecules in the polymer. Permeability is defined as a state which permits the transmission of permeants through materials (Mannheim and Passy. e. and the solubility coefficient S. and filled bakery crust (Dhale. 1983. representing the permeant concentration in the film in equilibrium with the external pressure: P = DxS In practice. gas or solute permeability. Another solution consists in using edible films or coatings with good moisture barrier properties to separate compartments and thus control further moisture transfer (Guilbert. sugars. 1976. When there are no pores. Kamper and Fennema. products such as raisins (Bolin. 1957. Moisture transfer can be limited by reducing the vapor pressure gradient between components. Barron. The solubility coefficient can either be calculated from P and D. the presence of plasticizers or additives. Water vapor permeabilities of some edible and synthetic films are given in Table 5. for most edible films. such as paraffin wax and beeswax. Schwartzberg. 1985). 1993. 1985). The permeability of an edible film is thus defined as a property of the film-permeant complex. Kumins. For instance. such as fatty acids. coating fresh fruit and vegetables with wax reduces desiccation-induced weight loss during storage by 40-75% (Kaplan. 1986). when Fick's and Henry's laws apply.e. The diffusion and solubility of permeants are affected by temperature and by the size. 1993.1). are less resistant to water vapor transmission since their polar groups attract migrating water molecules and thereby facilitate water transport. in relation to the water vapor permeability of hydrophilic polymer films. 1985. are the most effective barriers. Permeability is clearly high in edible films formed from hydrophilic materials. 1984b). Permeability is only a general feature of films or coatings when the diffusion and solubility coefficients are not influenced by permeant content. Gontard et ah. The moisture barrier capacities of different films can be classified in increasing order of efficiency. Water is not very soluble or mobile in lipid-based films because of the low polarity and dense. More hydrophilic lipids. these two parameters depend on film characteristics. the water solubility and diffusion coefficients increase when the water vapor differential partial pressure increases because of the moisture affinity of the film (nonlinear sorption isotherm) and because of increased plasticization of the film due to water absorption (Gontard et ai. under specified temperature and water activity conditions. the crystallinity. as follows: liquid oils < solid fats < waxes (Gontard et ah. The film thickness can also influence permeability when using film-forming materials that do not behave ideally. 1965. or measured in a separate experiment (sorption isotherms). etc.1. the permeant interacts with the film and the D and S coefficients are dependent on the difference in partial pressure. For instance. Schwartzberg. well-structured molecular matrixes that can be formed by these compounds. i. Moreover. Lipidic compounds are often used to make moisture barrier films and coatings (Table 5. (De Leiris.measurements before the steady state is reached. In practice. Pascat. 1958. the degree of cross-linking between molecules. including the type of forces influencing molecules of the film matrix. Moisture resistance of lipid films is inversely related to polarity of the lipids. 1994a. Hydrophobic alkanes and waxes. This efficiency order has been . Kamper and Fennema. shape and polarity of the diffused molecule. Swenson et aLy 1953). These films can only be used as protective barrier layers to limit moisture exchange for short-term applications or in lowmoisture foods such as dried fruits (Forkner. 1985. Landman et al. MC = methylcellulose.000289 T (0C) 38 26 30 21 25 26 21 21 25 21 27 21 30 30 30 30 23 30 23 23 38 25 20 25 38 25 25 30 25 38 25 38 Thickness (X 103m) 1.0360 0.84 2. Kester and Fennema. 1994. Kester and Fennema. 1993a(5).7 34.050 0.707 0. 1991(9).050 0. RH = relative humidity. 1993b(6). Aydt et al.750 0. 1989a(15).0122 0. 1960(16). b.23 5.025 0. fusion and solidification ranges. PEG = polyethylene glycol. 1993(2). oxygen and other components of the food product influence the physico-chemical.025 RH % conditions 100-30 100-50 60-22 85-00 100-00 100-50 85-00 85-00 52-00 85-00 85-00 100-75 11-00 100-00 100-00 100-00 11-00 11-00 11-00 11-00 95-00 97-67 81-00 100-00 95-00 97-00 100-00 100-00 100-00 97-00 97-00 95-00 Film Starch.075 0. Hagenmaier and Shaw.127 0. 1984a(l4).11 2. Park et al.0482 0. confirmed by Kester and Fennema (1989a) in a study on the resistance of various lipids.100 0.120 0. functional and organoleptic properties of lipid-based films (Fennema et al.45 5. 1991(19).22 0.075 0. Greener and Fennema.125 0. 1949(20).130 0.090 0.2 24. HDPE = high-density polyethylene.025 0.100 0. 199(F.28 1. in addition to the interaction with water. Gennadios et al.91 3.050 0.78 6. Donhowe and Fennema.190 0. LDPE = low-density polyethylene. Kamper and Fennema.7 22. 1993a(8).89 2.400 0. Gennadios et al. Park and Chinnan. Gontard.040 0. HPMC = hydroxypropyl methylcellulose.0230 0.96 5. .08 4.051 0. lipid crystalline structure.250 0. 1961(17).199 0. 1991(3). heated and adsorbed into filter papers.1 Water vapor permeability of various films Water vapor permeability (X 10'2 mol m m~2 s"1 Pa"1) 142 69. 1990(l8).200 0.0320 0. to water vapor transmission. Kamper and Fennema.15 3.48 1.7 13.3 34.0185 0. Composition. Donhowe and Fennema. 1989a(ll). 1994a(10).85 5. Avena-Bustillos and Krochta. 1989a).Table 5. 1963a(1). 1988(4). 1989(l2).025 0.8 13. Schultz et al. 1984a. T = temperature). Guilbert and Biquet. Myers et al.100 0.019 1. 1990(13).0122 0. Gontard et al. Biquet and Labuza. cellulose acetate(1) Wheat gluten(3) Casein-gelatin(20) Wheat gluten(l5) Sodium caseinate(2) Cornzein(33> HPC and PEG(I8) MC and PEG(I8) MC and PEG(5) Corn zein(18) HPMC(13) Glycerol monostearate(16) MC (I6) Wheat gluten and glycerol(9) Wheat gluten and oleic acid(10) Wheat gluten and carnauba wax(l0) Wheat gluten(8) HPC (I9) Wheat gluten and soy protein(7) Wheat gluten and mineral oil(8) Corn zein and oleic acid(12) HPMC and palmitic acid(l4) Dark chocolate(4) MC and beeswax bilayer<n) LDPE(17) HPMC/MC and beeswax bilayer(15) Beeswax(6) Wheat gluten-beeswax bilayer<9) Carnauba wax(6) HDPE(!2) Beeswax(16) Aluminium foil(17) (According to Allen et al.610 0.6 7.) (HPC = hydroxypropylcellulose.040 0.075 0. Kamper and Fennema. The coating operation used. However. 1984b and 1985). fatty acids. Fettiplace and Haydon. who investigated the moisture permeability of multicomponent films composed of methylcellulose. This is a consequence of enhanced mobility of hydrocarbon chains and less efficient lateral packing of acyl chains caused by a reduction of interchain van der Walls' interaction (Jain.2).050 0. and HPMC and stearic-palmitic acids (at 9 mg/cm2) Water vapor permeance (X 108 mol m~2 s'1 Pa'1) _ 7. MC = methylcellulose. 1980.090 0. 1975).040 0. composed of soluble cellulose esters and a mixture of palmitic and stearic acids. etc. i.. 1978.125 84-22 84-22 100-00 100-00 100-00 85-00 85-00 85-00 Film _ _ MC and paraffin wax (emulsion)(1) MC and paraffin wax (bilayer)(1) Glutten(2) Gluten and beeswax (emulsion)(2) Gluten and beeswax (bilayer)(2) HPMC(3) HPMC and fatty acids (emulsion)(3) HPMC and fatty acids (bilayer)(3) (According to Debeaufort et al. Taylor et al.00643 1£7 T (0C) _ 25 25 30 30 30 25 25 25 Thickness RH % (X 103 m) conditions _ _ 84_22 0.In general.4 mg/cm2). gluten and beeswax (at 2.130 0.090 0.e. Martin-Polo et al (1992). 1984b(3).2 Effect of coating operation on water vapor permeance of edible multicomponent films composed of MC and paraffin wax (weight ratio 1:1). Kamper and Fennema (1984a..39 0. pectinate or gluten and various lipids (waxes. affects the water vapor barrier properties of these films (Table 5.1). Kamper and Fennema. emulsion (suspension or dispersion of nonmiscible compounds). RH = relative humidity. The water vapor barrier properties of a lipid-hydrocolloid composite film is generally determined by the potentials of its component parts (Table 5. Gontard et aLy 1994a(2).) .251 10.120 0.040 0. and Table 5.727 0.).0257 8. T = temperature.) (HPMC = hydroxypropylmethylcellulose.02 0. successive layers (multilayered films) or solutions with a common solvent. b) carried out detailed studies of films. 1972. Fettiplace. 1955. Debeaufort et al (1993) and Gontard et al (1994a). According to Schultz et al (1949).1 0. it is better to form two successive layers than to apply a dispersion in solvent. specific information on the water vapor barrier properties of films of more hydrophobic lipids is lacking. 1993(l). and almost all the information available has been gathered using a 100-0% RH gradient which is not commonly encountered during storage of foods under commercial conditions. the rate of transmission of water through a lipid film increases as the length of the lipid hydrocarbon chain is decreased and the degree of unsaturation or branching of acyl chains is increased (Archer and Lamer. For instance.10 Effect of reduced surface pH on the microbiological quality of an intermediate moisture cheese analog coated with a carrageenan and agarose film. an increase of glyceride sucro ester (beeswax. De Leiris.or hydroxypropyl methylcellulose-) based composite films. Solidification of lipids (especially saturated) in a densely organized crystalline structure results in a very significant reduction in moisture permeability (Kamper and Fennema. 1961). 1989b. (Avena-Bustillos and Krochta. Gontard et al. m . form and orientation of the crystals) of the lipid layer related to the film-forming process and to coating operation. remains relatively low: film permeability is minimal at this point. Hagenmaier and Shaw. Kamper and Fennema. Pa *) Lipid Materials Content (%w/w) Figure 5. Kester and Fennema. m*. 1993. increasing aw leads to an Water Vapor Permeability (i ltf2 mol. As expected in a hydrophilic film (Barrie. could explain this discrepancy. . 1985). At low aw. Permeability of composite films decreases substantially when the proportion of lipids increases. 1984b. and especially the water solubility coefficient. s l . Pascat.(caseinate. 1988. 1985. water diffusion. Biquet and Labuza. stearic acid or monoglycerides) contents in gluten.88 and 35°C) (after Torres and Karel. Landman et ai. 1994a. Schwartzberg. The number of hydrophobic residues (from lipid derivatives) in the matrix affects the water interaction potential. 1990). 1985). 1984a. Crank. 1975. Watters and Brekke. challenged with Staphylococcus aureus S-6 (aw = 0. 1960. Variations in homogeneity and/or structure (size. and consequently the barrier properties. Water vapor permeability variations relative to aw reveal the non-Fickian behaviour of biological materials.2). 1968. causes a substantial reduction in water vapor permeability (Figure 5.demonstrated that application of emulsions resulted in reducing moisture permeability by 10-fold relative to bilayer systems. 1986. 1993). and particularly of gluten. 1989a.increase in film moisture content (rise in the sorption isotherm) and so induces an increase in water vapor permeability. r 1 ) Water activity Figure 5. extensive swelling of the protein network with water probably enhances water molecule diffusion and such films would clearly not be efficient water vapor barriers (Figure 5. gluten at 300C. temperature and moisture content. 30 and 500C. c).3 for gluten films). 1959. simple edible films (protein or cellulose-based) or composite edible films (cellulose derivatives and lipids). 1984a). iff2. In films formed with hydrophilic materials.76 mg/cm2) at 25°C and 32% RH gradient (according to Kamper and Fennema. MC and C 1 8 -C 1 6 at 25°C (WVT x 0.3). the structure/property relationships of hydrated proteins.. m . and of edible wheat gluten films at 5. Higuchi and Aguiar. This is often characterized by Arrhenius-type representations (Donhowe and Fennema. and 10% RH gradient (according to Gontard et al.3 Effect of average water activity on water vapor transmission rate of edible films composed of methylcellulose and palmitic-stearic acids (at 0. Kester and Fennema. Many authors have studied the effect of temperature on water vapor transfer using synthetic. At high aw.4). However. According to Levine and Slade (1987) and Slade et al (1989). could be better understood through the theories of glass transition used in polymer science. D. in terms of critical variables of time. D. Glass transition Water Vapor Transmission Rate (WVT). it was difficult to interpret the temperature dependence of the effect of hydration on water vapor permeability of gluten film in terms of disruptive water-polymer hydrogen bonding in a polymer hydrogen-bonded network. The critical role of water as plasticizer of gluten film appeared to be highly temperature dependent. D. temperature-dependent variations in barrier properties are affected by the moisture level (see Figure 5. •. A rise in temperature causes an increase in water vapor permeability (Figure 5.1). gluten at 5°C . 1993b. (x 108 mol. gluten at 500C. (1963a) to reduce moisture loss by 40-48%. thus resulting in a drop in the glass transition temperature. 1975).. at RH conditions 97-0% (according to Kester and Fennema. temperature and moisture content.m . 1972). 1986). 1994).4 Effect of temperature on water vapor permeance of edible wheat gluten films.. 1989b).1). Hoseney et al. s l ) Temperature (0C) Figure 5. at RH conditions 90-80% (according to Gontard et al. (1993) found that sodium caseinate and stearic acid emulsion coatings improved the storage stability and reduced water loss of peeled carrots. It is well established that plasticization by water affects the glass transition temperature of amorphous or partially crystalline proteins such as gluten (Gontard et al. a. and particularly of gluten. The use of sucrose esters of fatty acids. MC and beeswax. (x 10* mol. 1975. A. For example. Glass transition is typically described as a transition from a brittle glass to a highly viscous or rubbery solid. 1959). and the sodium salt of carboxymethylcellulose coatings allowed the increase of water vapor resistance (up to 75%) in zucchini fruit (Avena-Bustillos et al.hydrated proteins. gelatin (Marshall and Petrie. Scandola et al. 1980. meat coatings composed of corn starch and alginate were used by Allen et al. Yannas. Gluten (WVP X 0. Wax is commercially applied to Water Vapor Permeance (WVP). at RH conditions 100-0% (according to Higuchi and Aguiar. Avena-Bustillos et al. could be better understood through the theories of glass transition used in polymer science. . 1981). monostearate. 1993. m 2 . of edible glycerol monostearate films.. in terms of critical variables of time. 1993).. and of edible films composed of methylcellulose and beeswax. mono. collagen (Batzer and Kreibich. The anomalous diffusion behavior of glassy polymers may be directly related to the influence of the changing polymer structure on solubility of the penetrant and diffusional mobility of the penetrant (Crank. 1981) and elastin (Kakivaya and Hoeve. •..and diglycerides. The water vapor barrier properties of edible active films and coatings have been used in several food systems. 1985. 5. edible oxygen barrier films can be used to protect foods that are susceptible to oxidation (rancidity. apples.3 Use of edible active layers to control gas exchange The gas barrier properties of edible films and coatings are potentially of great interest. etc. to prune plums (Bain and McBean. a relatively high gas permeability is necessary for fresh fruit and vegetable coatings (especially carbon dioxide permeability). 1970). (1991) used edible chitosan coating to reduce water loss of cucumber and bell pepper fruits. 1988. The knowledge of the influence of parameters such as structure and composition of film-forming materials. Landman et al. 1988. several studies have confirmed the efficiency of chocolate and cocoa butter coatings as moisture barriers (Biquet and Labuza. 1967). ethylene) allows the control of respiration exchange and microbial development and seems very promising for achieving a * modified . Rico-Pena and Torres (1990) tested composite films (methylcellulose and chocolate and methylcellulose. One standard example of moisture transfer control in heterogeneous food is the wafer-ice cream system of ice cream cones. In addition. El Ghaouth et al. the wafer loses its crispness after three months' storage at -23°C. The use of edible films to lessen internal migration of moisture in foods has been studied by several investigators. peas. 1967. Rico-Pena and Torres. Neidiek. and peaches. 1981. 1978. These examples show that water vapor transfer in food products can be controlled using edible films and coatings.g. tomatoes. Soboleva and Chizhikova. Films based on methylcellulose. 1989d. 1990). Kester and Fennema. Kamper and Fennema. 1981). 1993. Ukai et al (1976) used hydrophobic emulsions to coat fruits and vegetables such as orange. pears. carbon dioxide. In contrast. Lidster (1981) suggested the use of xanthan gum applied to cherries as a postharvest dip to prevent water loss. Kempf. allows modulation of the water barrier properties of these edible active layers either on the food surface or in multicomponent foods. Films can limit moisture transfer during ice cream cone storage at -23 0 C or -12°C and preserve wafer crispness. to apples (Hall. Bursewitz and Singh. to oranges (Albrigo and Brown. Lidster. The development of edible films with selective gas permeability (oxygen. 1953). 1970. Trout et al. loss of oxidizable vitamins. green beans. chocolate and palmitic acid are the most efficient. This qualitative degradation is due to moisture transfer between the ice cream and the wafer. 1960. In standard conditions. Eaks and Ludi. 1966. Greener and Fennema. chocolate and palmitic acid) to separate the two components. 1989b. For instance. 1974). Tiemstra and Tiemstra.). 1985. e. 1981). and some of these films appear promising for commercial use (Fennema et al. and to sweet cherries (Drake et aL.many fruits and vegetables to reduce dehydration and improve consumer appeal (Hall. . the oxygen permeability of wheat gluten film was 800 times lower than that of low-density polyethylene and twice as low as that of polyamide 6. The oxygen permeability of hydrocolloid-based films (at 0% relative humidity) is often lower than that of common synthetic films such as polyethylene and non-plasticized PVCs. Gas permeability can be measured using air porosimeters and specific permeability cells. The effect of temperature on gas permeability is similar to that reported for water vapor permeability (Donhowe and Fennema. The following barrier efficiency order was observed by Kester and Fennema (1989c): stearic alcohol > tristearine > beeswax > acetylated monoglycerides > stearic acid > alkanes.3). These differences can be explained by the presence of pores or cracks. These variations can be characterized by Arrhenius-type representations. Films formed with lipid derivatives have suitable oxygen barrier properties. the oxygen permeability value for beeswax film lies between those of low-density and high-density polyethylene (Table 5. 1994b). as far as gas solubility decreases with temperature increase. Increased unsaturation (or branching) and a reduction in the length of the carbon chain result in decreased oxygen permeability. But.9 1993).atmosphere' effect in fresh fruit and for improving the storage potential of these products (Smith et a/.3).. the oxygen permeability is reduced by about 30% for a composite gluten and beeswax film (Table 5. where hydrophilic materials are not effective as gas barriers (see below). For example. 1989b. polysaccharides) generally have good oxygen barrier properties.91. For example. the addition of lipidic compounds results in a decrease in the gas permeability of the film. and by the homogeneity of the composition density of the network (Kester and Fennema. For example. As in the case with moisture barrier properties. Films formed with hydrocolloids (proteins. formulation of composite films allows advantage to be taken of the complementary barrier properties of each component. The oxygen and carbon dioxide permeability values of various edible films and synthetic films are given in Table 5..3. According to Blank (1962 and 1972). c). the increase of gas permeability with temperature is lower than for water vapor permeability (Gontard et a/. 1987. Trout et al. The network density is dependent on the polymorphic shape and orientation of the chains and morphological differences in the lipid layers. At high aw. 1993b. particularly under low-moisture conditions. High aw conditions cause an increase in gas permeability in hydrophilic . at aw = 0. 1953). As previously mentioned for water vapor permeability. lipids with the best oxygen barrier properties are those formed with straight-chain and saturated fatty acids. a well-known high oxygen barrier polymer. as schematized in Figure 5. manufacturing and environmental parameters have an impact on a film's response to gases.1. the formulation. Gennadios et al. 0 0.0 11.27 6.0 0.50 1.2 8.0 0.24 1.6 1.91 .155 19400 1170 961 682 406 227 224 130 50.0 0.50 2.0 0.3 Oxygen and carbon dioxide permeabilities of various films Film _ _ _ HDPE (3) Rigid PVC (II) PET<3) Polyamide 6(3) PVDC (3) Cellophane(3) EVOH (H) Polybutadiene<3) Polypropylene(3) LDPE (l3) Flexible PVC film(3) Uncoated cellulose 0} HDPE (3) HDPE (I) Cellophane (H) Polyvinyl alcohol(1) PET (3) PET™ Nylon 6 (I) Cellophane (l4) EVOH (I3) MCandPEG ( I O ) MCandPEG ( 1 0 ) MC and beeswax<9) Beeswax<5) HPC and PEG(IO) HPC and PEG(IO) MC and palmitic acid (l2) Carnauba wax(5) Corn zein(2) Cornzein (2) Wheat gluten and glycerin(6) Cornzein ( l 0 ) Wheat gluten protein (l0) Wheat gluten protein (l0) Corn zein(10) Wheat gluten protein(2) Soy protein(6) Wheat gluten and mineral oil(7) Wheat gluten(8) Wheat gluten and soy protein(4) Wheat gluten protein(2) Pectin<8) Wheat gluten(8) Wheat gluten(8) O2 Permeability (X 1O18HIoImIn-2S-1Pa-1) __ 285 16.0 0.0 0.00 0.0 1.50 0.0 0.0 0.0 0.9 11.3 12.0 0.6 16.65 703 29900 28900 216 119 95.8 24.0 0.50 i.0 0.50 1.50 0.0 0.0 0.34 0.95 1.96 0.1 34.0 0.20 522 499 480 470 190 81.92 3.70 1.0 0.00 0.00 0.8 19.0 0.Table 5.1 8.00 0.0 0.19 1340 1290 982 CO2 Permeability (X 1018 mol m m 2 s 1 Pa 1 ) _ _ 972 37.0 0.2 10.50 0.0 0.0 0.0 0.30 1.86 1.95 0.20 21300 36700 24500 T (0C) __ 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 30 21 25 25 30 21 24 25 38 23 23 30 30 21 21 38 23 23 25 25 23 25 25 25 aw 0 0 0.00 1.95 0.5 7.50 0.0 0.6 19.0 0.0 0.0 0.0 0. T = temperature. Gennadios et al. 1993 (A. •. Gontard et al. MC and palmitic acids. Carbon dioxide permeability in hydrocolloid-based films is often much Oxygen Permeability (x 10* mol. Rigg. PVC = poly(vinyl chloride). PVDC = poly(vinylidene chloride). Taylor..93 0. Donhowe and Fennema. LDPE = low-density polyethylene. 1965). m 2 . s 1 . Gennadios et al. In these hydrophilic films. Greener and Fennema. Rico-Pena and Torres. Poyet. 1990(l0). Poyet. 1986 (l3) . Nylon 6). 1993a(7). Rico-Pena and Torres. P a ! ) Water activity Figure 5.91 0. 1993(4). increased aw promotes both gas diffusivity (due to the increased mobility of hydrophobic macromolecule chains) and gas solubility (due to the water swelling of the matrix). . 1990 (D.) (aw = water activity. leading to a sharp increase in gas permeability (Kumins. 1993 (n) . 1989a(9). Bakker.5). m. (1994b) respectively. at weight ratio 3:1).3 Continued Film Wheat gluten and beeswax (8) Chitosan(8) MC and palmitic acid(12> O 2 Permeability CO 2 Permeability T ( X 10 l 8 molm HT2S-1 Pa"1) ( X 1018 mol m m"2 s"1 Pa"1) (0C) 687 472 407 6614 8010 25 25 24 aw 0. HDPE = high-density polyethylene. (MC is methylcellulose. Brandeburg et al. 1986(3). EVOH. The effects of aw on gas barrier properties of composite films (methylcellulose and palmitic acid) and of gluten protein-based films was studied by Rico-Pena and Torres (1990) and by Gontard et al. and are compared in Figure 5. Aydt et al.5 with oxygen permeabilities of synthetic hydrophilic films. Park et Chinnan. PEG = polyethylene glycol. 1994b (o. 1994b(8). Salame. 1985 (l) . 1986(l4). gluten). cellophane)). PET = polyester. 1993b(5).Table 5.5 Effect of water activity on oxygen permeability of edible and synthetic films at 25°C (according to Gontard et al. 1979 (•..) films but generally not in synthetic hydrophobic films which are not water sensitive (Figure 5. 1990 (l2) . 1990(6). MC = methylcellulose.79 (According to Ashley. 1991 (2) . EVOH is ethylene-vinyl alcohol). EVOH = ethylene-vinyl alcohol. at aw = 0. MC = methylcellulose.) (aw = water activity. HPC = hydroxypropylcellulose.0 0. Park and Chinnan.5 6.25mmol/l at 25°C and 105 Pa).higher than oxygen permeability (Table 5.0 0.0 25.35 0.0 0. 1972(2).) . the addition of lipidic components to gluten film results in a high decrease of carbon dioxide permeability. but the sharp increase of permeability is more important. The selectivity coefficient between carbon dioxide and oxygen is defined as the ratio of the respective permeabilities of both gases.7 31. whereas the selectivity coefficient for synthetic polymers remains relatively constant.e.0 0.62 0. oxygen solubility = 1. 1994b). In fact. 1994b(1).0 4. At high aw. i.91.0 17.0 0. This could be explained by the differences in water solubility of these gases (Schwartzberg. 1990(3). 1985).0 4. Lefaux.0 at aw = 0. (Gontard et aL.3).93 0.6 4. the effect of an aw increase on permeability is greater for carbon dioxide than for oxygen. PP = polypropylene.91 0.0 0.30.2 5.56 0. In hydrophilic materials. The effect of film aw on carbon dioxide permeability is similar to that on oxygen permeability.95). PVC = poly(vinyl chloride).6 16.5 23.96 0. at 4 to 5 (Table 5. the carbon dioxide permeability is reduced by about 75% for a composite gluten and beeswax film (Table 5.5mmol/l at 25°C and 105 Pa.3). the selective coefficient of edible gluten films varies from 4.0 0. This could be related to the hydrophobic characteristics of these components which for the same aw reduce the amount of water available for solubilisation of carbon dioxide. Edible films with selective gas permeability can be applied to reduce degradation of some fresh fruits and vegetables.6 40.0 0. The selectivity of these materials is thus sensitive to moisture variations (for example. carbon dioxide is very soluble (carbon dioxide solubility in water = 34. PEG = polyethylene glycol.4).4 Gas selectivity coefficient of various films (CO2/O2) Film PP(2) PA(2) PVC(2) Wheat gluten(3) Corn zein(3) HPC and fatty acid(3) MC and PEG(3) HPC and PEG(3) Gluten(I) Gluten(1) MC and beeswax(l) Gluten and beeswax 0} Pectin(l) Chitosan(1) Gluten(l) Gluten*'> Gas selectivity coefficient (CO2/O2) 4.95 (According to Gontard et aL. For example.7 9.8 7. the diffusion of Table 5.5 9.91 0.0 2$A T (0C) 23 23 23 25 25 25 25 25 25 25 25 25 25 25 25 25 aw 0. to 25 at aw = 0. PA = polyamide. waxing increased the carbon dioxide content and decreased the oxygen content of the orange's internal atmosphere (Eaks and Ludi. to coat candies and dried products (Grouber. Olson et al.. 5.. calcium alginate-based films were tested to limit microorganism contamination on the surface of beef pieces (Williams et al. 1991).and diglycerides) would produce a semipermeable modified atmosphere within fresh fruit after application.while carbon dioxide flux is only decreased by about half (Banks. Cameron and Reid. 1974.. 1984). on pears (Elson et al. Surface microbial growth is a main cause of spoilage for many food products (Gill. 1953). 1974). These films were found to have a significant effect . 1978). 1978. 1983) and to microencapsulate flavors (Anandaraman and Reineccius. The development of edible active films with selective gas permeability seems have considerable potential applications for achieving a modified atmosphere effect for fruits and vegetables. Other examples of gas permeability control by edible active layers are gelatin films used to protect frozen meats from rancidity (Klose et ah. 1985. sucrose fatty acid esters and mono. They can be used as surface retention agents to limit food additive diffusion in the food core. The post-storage uses of these coatings were investigated on apples (Chu. Smith and Stow. 1985. The improvement of food microbial stability can also be obtained by using edible active layers which have specific antimicrobial and pH lowering properties. the selective gas permeability properties of these films applied on bananas can reduce oxygenfluxfivefold. Vitkov. 1987. 1983.oxygen and carbon dioxide between fruit or vegetables and the environment is a basic element in the post-harvest physiology of fruit (Burton. Lowings and Cutts. Edible films and coatings can be used in combination with treatments such as refrigeration and controlled atmosphere to improve the microbiological quality of certain foods.4 Modification of surface conditions with edible active layers Edible active films and coatings can be applied on foods to modify and control surface conditions. 1988). on limes (Motlagh and Quantick. Lowings and Cutts (1982) reported that an edible composite coating (carboxymethylcellulose. on bananas (Banks. Maxci. 1973. 1979. Drake et a/. The type of coating material applied alters the relative effects on the skin permeability to oxygen and carbon dioxide (Trout et a/. Chitosan coatings retarded ripening and prolonged storage life of tomatoes. 1980). 1960).. The coating of peach surfaces with beeswaxcoconut oil emulsion decreased oxygen gas transfer (Erbil and Muftugil. For example. Elson et al. 1982). 1986). 1981. 1988) and on mangoes (Dhalla and Hanson. For example. cucumber and bell pepper fruit without affecting their ripening characteristics (El Ghaouth et a/. 1952).y 1985). For example. 1982). 1990. 1984.. 1984). 1981. 1991) used chitosan-based coatings to protect fresh vegetables (cucumbers.e. can be attributed to the specific antifungal properties of chitosan molecules (Allan and Hadwiger. absorption of sorbic acid during the processing of dried prunes. 1989. Lueck. 1986. 1980. Development of processes that specifically enhance surface microbial stability is required. Vojdani and Torres. the shelf-life extension achieved by these surface treatments is limited by problems related to potassium sorbate (or sorbic acid) stability and diffusion. Potassium sorbate (or sorbic acid). 1979. storage of foods in contact with wrapping materials or films containing sorbic acid (absorption by dairy products covered with paper saturated with sorbic acid) and storage of foods coated with an external edible layer highly concentrated in sorbic acid (Guilbert. 1979. Kester and Fennema.1). El Ghaouth et aL (1990. 1978. e.g. to a considerable extent. Zamora and Zaritzky. Robach and Ivey. 1979. which has also been obtained on strawberries. Zein-based films have been found to successfully reduce microorganism penetration into chicken egg shells after surface inoculation (Tryhnew et aL. 1988. 1981. It is important to be able to predict and control surface preservative migration between phases during food treatments (e. which has a wide range of bacteriostatic and mycostatic properties. a reduction of its total amount in the food for the same effect (as schematized in Figure 5. Robach and Sofos. 1984. This effect. Hirano and Nagao. D'Aubert et aL. 1988). 1982. Edible films and coatings can be used as food preservative media (particularly as antioxygen and antifungal agents) and as surface retention agents to limit preservative diffusion in the food core (Guilbert. 1990). 1973).g. Stossel and Leuba. 1987). 1987a. can be used by dipping to reduce the total number of viable bacteria at both refrigeration and elevated temperatures (Cunningham. . Torres. i.g. 1983). peppers). Torres et aL. storage of composite foods (e. The stability of sorbic acid (in its active non-dissociated form) is dependent on application conditions. at the surface of the food to reduce aerobic contamination and/or oxygen influence. b. 1985b. 1986. 1985b. 1984). Robach. a lowered pH improves stability (Eklund. or its loss during cooking of fabricated foods). However. The specific antimicrobial activity of calcium alginate coatings has not yet been explained. food processors have used preservative dips and sprays. b).on microbial growth (natural microflora and coliform inocula). Torres et aL. but could be partially due to the presence of calcium chloride. The diffusion into the core of the food results in a reduction in preservative concentration on the surface which allows microorganisms to overcome the sorbate-induced bacteriostasis (Greer. To and Robach. dairy products or cakes containing pretreated fruits). 1989a. Maintaining a local high and effective concentration of preservative may allow. 1980. These coatings improved fruit appearance and reduced microbial degradation. Swelling and poor retention were observed with the gelatin film (30% retention after 10 days). The low solubility of tocopherol in water.95). and in composite polysaccharide-lipid derivative films (Vojdani and Torres. gelatin layer .aqueous model food. These active layers enriched with tocopherol could be used to reduce the oxidative deterioration in some food products. Guilbert (1988) also investigated the retention of sorbic acid in gelatin and casein films treated respectively with tannic and lactic acid. 1990). gluten-based and pectinbased films (De Savoye et aL. •.aqueous model food. After 35 days at 25°C. a retention of 30% was observed with the treated casein film. •.6). 1994). Gelatin layer . and placed over an aqueous model food system (aw = 0.margarine. 1988). The rapid decrease of tocopherol content in the gelatin layer in contact with margarine is due to the high apparent solubility of tocopherol in fatty material. 1985b) and casein-based films (Guilbert. Cross-linking treatment with tannic acid increases tocopherol retention by the gelatin layers in contact with margarine.margarine. Sorbic acid retention has been studied in zein-based (Torres et aL. 1988). Guilbert (1988) determined the retention rate of a-tocopherol in gelatinbased films formed on intermediate moisture foods and margarine (Figure 5.6 Tocopherol retention at 25°C in gelatin layers and in gelatin layers treated with tannic acid in contact with aqueous model food (aw = 0. D. In an intermediate . The sorbic acid permeability values determined for these films can also be compared with published apparent diffusion values for sorbic acid in food systems. 1986.95) or in contact with margarine (according to Guilbert. explains the retention effect exerted by the gelatin layer in contact with aqueous model food. gelatin layer treated . o.% Retention Time (days) Figure 5. and so its low diffusivity value. gelatin layer treated . 0 x 10"10m2/sec (Table 5.77 Film Chitosan MC HPMC MC and palmitic acid (weight ratio 3:1) HPMC and palmitic acid (weight ratio 3:1) Zein Sorbic acid permeability (x 108 g mm m"2 s'1 (g/1)"1) 0.5).205 Similar values (According to Torres et al. storage conditions (temperature.6). Torres et al. there is a 75% reduction for a hydroxypropyl methylcellulose edible film. Preservative diffusion through edible films is influenced by various parameters: film characteristics (type.0 x 10~10m2/sec.88. (1985) reported a value of 2. duration.) .865 0. b.0 3. These few examples indicate that edible films could be used for additive retention on the surface of food products.. and in cheese analog coated with edible zein films Experiment Agar gel and sucrose(1) Cheese analog(2) Agar model(2) Agar gel and glycerol(1) Cheese analog and zein Cheese analog and two zein film(2) films(2) Diffusion coefficient (m2 s~') 0.to 300-fold lower than those determined for model intermediate moisture foods (Table 5. 1986a(l).5 1. Vojdani and Torres.120 0. The sorbic acid diffusivity values in edible films were found to be 150.830 0.) (HPMC = hydroxypropylmethylcellulose. MC = methylcellulose. food characteristics (pH. a 65% reduction of the sorbic acid permeability of a methylcellulose edible film is observed when palmitic acid is added to the hydrocolloid matrix.) moisture agar model system. (1985b) found with an intermediate moisture cheese analog a value of 1. It appears that film composition (type of film forming agent.3 X 10~13 6.Table 5.) and solute characteristics (hydrophilic properties. Table 5. 1985b(2). molar mass). aw).6 Sorbic acid permeability of various edible films at 24°C and aw = 0. 1989a.8 X 10~13 (According to Giannakopoulos and Guilbert.5).5 Apparent coating diffusion coefficients for sorbic acid in intermediate moisture model food (agar model or cheese analog) at 24°C and aw = 0. in agar gel (with sucrose or glycerol) at 25°C and aw = 0.0 2. For example. manufacturing procedure). 1985b.88.5 X X X X IO"10 IO"10 10"10 10"10 3. Guilbert et al. etc. Torres et al. The effect of the film-forming material on sorbic acid permeability has been studied for various edible films (Table 5. presence of lipids) affects even the sorbic acid permeability.334 0. 1 ) Sorbic Add Diffusivity (xlO lf m ' .According to Vojdani and Torres (1990). . and on sorbic acid diffusivity in agar gels with sucrose (•) or glycerol (o) at 25°C (according to Giannakopoulos and Guilbert. 1989a.nr 2 . (1968) found that increasing the lecithin fatty acid chain length decreased the permeability of glycerol and erythritol through these artificial membranes. it also decreases as the length of the carbon chain in fatty acids increases and with the presence of double bonds. 1991). temperature and relative humidity affect the permeability of edible film to sorbic acid (Figure 5. This is consistent with published data on the solute permeability of synthetic lecithin liposomes. the sorbic acid permeability for an emulsion composite film of methylcellulose and palmitic acid was 3 times lower than for bilayer composite film.7). 1986a) where sorbic acid diffusivity rises at high aw. sorbic acid permeability decreases in composite films (hydroxypropyl methylcellulose or methylcellulose and fatty acids) as the lipid derivative concentration increases. De Gier.7 Effect of water activity on sorbic acid permeability of edible multicomponent films composed of methylcellulose and palmitic acid (weight ratio 3:1). Rico-Pena and Torres. (according to RicoPena and Torres. 1986b). The composite film-forming technique used to form composite films or coatings (emulsions or multilayers) also affects the sorbic acid barrier properties. 1991). For example. According to Vojdani and Torres (1989a) the lowest permeability values are found with bilayer composite films. s 1 ) Water activity Figure 5. (1970) showed that the permeability of liposomes was altered by the geometrical configuration and the number of double bonds in the fatty acid component.**/!). At constant temperature. This is consistent with studies in food model systems (Giannakopoulos and Guilbert. at 24°C (•). McElhaney et al. Sorbic Add Permeability (xlO f g. et al.m. As noted for water vapor and gas permeability.* 1 . the sorbate permeation rate decreased as aw decreased (Vojdani and Torres. Longer surface retentions of sorbic acid are possible at higher pH (and also at lower aw and lower temperature). pectin (SAP X 0. MC. relative to microbial stability of the food product (Torres et al. 1985b.77 (according to Vojdani and Torres. formed on the surface of intermediate moisture cheese analogs.8). MC and palmitic acid. 1985). It should be noted that the higher retention at higher pH would help balance the lowering of sorbic acid effectiveness as pH is increased (Eklund. A. which suggests that the diffusion process in the film occurs mainly through the aqueous phase. Vojdani and Torres (1989b) noted that activation energy is affected by the solvent embedding the film. HPMC and palmitic acid. The microbiological analyses carried out have confirmed the sorbic acid retention efficiency of zein-based edible films.Sorbic Add Permeability (SAP). The sorbic acid permeability of edible films varies according to pH (Figure 5. •. 1983). s ! . Consequently.0 (according to De Savoye et al. These variations can easily be analysed through Arrhenius-type representations.005). possibly due to a change in the sorbic acid formed around the pKa (equal to 4. at aw = 1. chitosan. sorbic acid permeability decreases when pH increases. thus modifying the diffusion properties. a.9). and of edible pectin films. HPMC.8). A. At constant aw and temperature. 1989b and 1990). m . Torres and Karel. An increase in temperature causes a decrease in film sorbic acid barrier properties (Figure 5. of edible chitosan films. An increase in pH lowers permeability. (x 108 g . at aw = 0. the performance of edible coatings controlling surface preservative concentration will depend strongly on the composition of the aqueous phase of the coated food. •.. (g /1)') Temperature (0C) Figure 5. o. nr*.8 Effect of temperature on sorbic acid permeability of edible multicomponent films composed of methylcellulose (MC) or hydroxypropylmethylcellulose (HPMC) and palmitic acid (weight ratio 3:1). These edible . 1994).. For example.0 and aw = 0. (x 10f g. For example. 1991) and of edible pectin (Psa X 0. (g / W ) pH Figure 5.0 and 200C (according to De Savoye et ah. The fact that casein film with sorbic acid was less effective than the carnauba wax with sorbic acid may be explained . 1987. these values increase to 82 and 328 days respectively (Torres. 1989a). The coating efficiencies were in the following order: carnauba wax + sorbic acid > carnauba wax > casein + sorbic acid > casein > no coating. (1985b) have assessed the potential sorbic acid retention efficiencies of edible films according to utilization conditions. Guilbert (1988) conducted microbiological tests on intermediate moisture fruit pieces (Table 5. Torres et al. m2 . then the permeability = 0.1 mm film and 0. these estimations need to be confirmed using a specific food system and challenging microorganism. According to these authors. m.01) films (D) at aw = 1. The effect that edible active film (according to sorbic acid permeability) has on increased surface microbial stability has been estimated by Torres (1987). the surface protection can be predicted to last 30 and 120 days for a 0.9 Effect of pH on sorbic acid permeability of edible multicomponent films (•) composed of methylcellulose and palmitic acid (weight ratio 3:1).77 and 24°C (according to RicoPena and Torres. Vojdani and Torres. Significant improvement of the microbial stability was observed with coatings containing sorbic acid and no spoilage could be detected after 40 days' storage in the case of papaya cubes coated with carnauba wax containing sorbic acid. with the use of a methylcellulose and palmitic acid (weight ratio = 3:1) edible film on food stored at 24°C.042 g mm m"2 24 h"1 (g/1)"1. a composite film (methylcellulose-palmitic acid) applied to a food item (at pH = 5. If the item is stored under refrigeration (at 5°C). 1994). at aw = 0.8) stored at 24°C reduces the amount of sorbic acid diffused in the food mass by more than 50%. s '.7).Sorbic Add Permeability (SAP).2 mm film respectively. barrier layers double the shelf-life of the food product before the appearance of microorganisms. 90 4 1 4 2 10 17 10 14 10 > 40 by the poor retention properties and the high initial pH of the casein film (Guilbert. . challenged with Staphylococcus aureus S-6 (aw = 0.10 Effect of reduced surface pH on the microbiological quality of an intermediate moisture cheese analog coated with a carrageenan and agarose film.) (a) (b) (a) (b) (a) (b) (a) (b) (a) (b) aw 0. The improvement of food microbial stability can also be obtained by reducing surface pH. 1988). Torres and Karel (1985) succeeded in obtaining a temporary pH difference between the surface and the core of intermediate moisture foods by adding lactic acid to zein-based edible films. 1985). This can be achieved by using films or coatings that immobilize either specific acids or charged macromolecules.71 >40 >40 >40 >40 > 40 >40 > 40 >40 > 40 > 40 aw 0.Table 5.84 13 3 12 2 22 >40 > 28 >40 32 > 40 aw 0.75 >40 >40 >40 >40 > 40 >40 > 40 >40 > 40 > 40 aw 0. The development of edible films that immobilize Contamination: togN (cells / cm2) (uncoated control) (reduced pH surface) Time (days) Figure 5.7 Stability of coated intermediate moisture papaya cubes (as a function of a w ) at 30 0 C inoculated with Aspergillus niger(a) or Staphylococcus rouxii{h) Delay for first apparent spoilage (days) Control (non coated) Coated with casein Coated with casein and sorbic acid Coated with carnauba wax Coated with carnauba wax and sorbic acid (According to Guilbert.88 and 35°C) (after Torres and Karel. 1988. The active edible layers concept can thus be extended to new fully adapted superficial or internal applications for food products. or with flavor.). etc. 1985). layers enriched with susceptors for microwave treatments or with catalyst for specific reactions on the one hand. Among these new potential applications. etc. the layer composition must be compatible with the product characteristics and regulation. etc. oxygen. Microbiological analyses have confirmed the antimicrobial efficiency of this type of surface treatment (Torres and Karel. A Donnan equilibrium model for semipermeable membranes containing charged macromolecules can be used to assess the possibility of obtaining a permanent pH difference between two components separated by a membrane. Studies of bacterial growth (Staphylococcus aureus) on intermediate moisture foods revealed improved microbiological stability with the use of carrageenan-based edible films (Figure 5. A decrease in surface pH can also improve the stability and efficiency of antimicrobial agents such as sorbic acid. In addition to carrageenans.) between the food product and the ambient atmosphere. slightly esterified pectins could probably be used for similar applications (Guilbert and Biquet. for slow-release systems on the other hand. and by industrial .charged macromolecules has made it possible to obtain a pH difference between the surface and core of enveloped intermediate moisture food products. ethanol. They could also be used to achieve the slow release of flavor compounds during food storage or consumption.. The development of an active edible layer is mainly limited by formulation constraints.and carrageenan-based edible films (with charged macromolecules) decreases the surface pH by about 0. level of specific functional agents. i.e. microbiological and physicochemical changes in food products. Initial choices of film-forming materials and of fabrication conditions allow modification of solute retention properties of these edible active layers. or between components in a mixed food product. 5.10).5 Conclusion Edible films and coatings can be used to control gas exchange (water vapor.5. can be mentioned. Edible superficial layers provide supplementary and sometimes essential means to control physiological. according to specific needs. and to modify and control food surface conditions (pH. and allow selection of the efficient functional properties in relation to each specific application. It should be stressed that the characteristics of the film or coating and the application technique must be adapted to each specific utilization. 1989). carbon dioxide. preservative. The use of agarose. Edible films and coatings are a useful mean to reduce the rate of some deteriorative reactions such as surface microbial development or oxidation. Banks. M. Aymard Christian (CNRS. J..M. and Hadwiger. Avena-Bustillos. Mycol.F. 55. 197-214. (1991) Mechanical and barrier properties of edible corn and wheat protein films. Salveit. (1966) Film coating. 207-11.N.P.). (1985) Permeability and plastics packaging. Food Technology. Andres. Transactions of the ASAE. M. Avena-Bustillos. them. References Albrigo. France). 22-5. M. pp. (1955) The rate of evaporation of water through fatty acid monolayers.. (1993) Water vapor permeability of caseinate-based edible films as affected by pH. 904-7. Anandaraman. Journal of Food Engineering. Steinberg. Australian Journal Biol.. May. coatings or preformed films applications procedure must be realizable on the industrial scale and be easily integratable in the food processing line. CL.H. 3. J. 36(3).I. 17. J. and LaMer. G. New York. J. R. Montpellier. 48. and Testin. Thibaut Romain (CIRAD-SAR.e.A. J. RJ. 34. 1442-46. (1993) Optimization of edible coatings on minimally processed carrots using response surface methodology. L.. Journal of Pharmaceutical Sciences.. Bakker.. Montpellier. 127-34. (1963b) Edible corn-carbohydrate food coatings. 20. 269-307. CR.M. RJ. calcium crosslinking and lipid content.. 200-7. Nelson.A. Bain. RJ. RJ. Food Technology. In: Polymer Permeability. Allan. and McBean. 2. Journal of Experimental Botany. Development and physical testing of a starch-algin coating. Sci. G. Horticultural Science 5. Steinberg. . (1984) Natural edible coating has excellent moisture and grease barrier properties. L. 17. theory and practice.0125. 801-5. A. Montpellier.CT92 . Krochta. Inc. Transactions of the ASAE. G. 1437-42. T. 895-900. and Reineccius. and Krochta. C. Food Processing. Allen.. (1983) Evaluation of methods for determining internal gases in banana fruit. France). RJ.I.P. A.N. Acknowledgements Dalle Ore Florence (CIRAD-SAR.M. FlPP. Banker.. Cisneros-Zevallos.. and Salveit. Allen..E. J. 285-7. J. M. Ashley. France) and Cuq Jean Louis (Universite de Montpellier II. (1994) Optimization of edible coating formulations on zucchini to reduce water loss.E. and McGiIl. Aydt. France) are gratefully acknowledged for helpful discussions and technical assistance. Exp. (1980) Microencapsulation of flavour. /. Phys. Elsevier. Archer.A..P. (1967) The structure of the cuticular wax of prune plums and its influence as a water barrier.. (1970) Orange peel topography as affected by a preharvest spray. L. 470-2. N. RJ.CIRAD-SAR. L.production constraints. (1963a) Edible corn-carbohydrate food coatings. 45. 1. Avena-Bustillos. and Sauceda-Perez.G. V. 34. J.S. 21(2). Krochta. S.M.K. M. L. Evaluation on fresh meat products.E. 58(4). 81-92.M. Nelson. i. and McGiIl. 59. (1979) The fungicidal effect of chitosan on fungi of varying cell wall composition. London. Rojas-Villegas. Comyn (ed. Journal of Food Science. Weller. John Wiley & Sons. D. Part of the work presented here was supported by the EC project: AIRl . and Brown.. Montpellier. (1986) The Wiley Encyclopedia of Packaging Technology. Donhowe. 41-88. (1988) Effect of permeable coatings on the storage life of fruits. and Voilley. Mandersloot. Blank. Clarendon Press. A.M. Food Nutrition Press.R.G.). G. Park Ridge. 989-98. and Hanson. (1988) Evaluation of the moisture permeability characteristics of chocolate films as an edible moisture barrier. De Savoye.. p. H. and Labuza. 21. J. Lamer (ed. In: Controlled Atmospheres for Storage and Transport of Perishable Agricultural Commodities. Miller (eds). New York.). J.H. H. (1962) In: Retardation of evaporation by monolayers: transport processes. Julie). (1974) Some biophysical principles underlying the controlled atmosphere storage of plant material.H. P.R. Patrick (eds). 7-9 September. 213. and Kreibich. Dalle Ore. R. Debeaufort. M. p. Brusewitz.P. CL. pp. R. Mathlouthi (ed. Journal of Food Science. I. France. (1973) Edible coatings and soluble packaging. Politi. pp. F. Journal of Food Science. Journal of Food Processing and Preservation. S. Biquet. CT.L. (1957) Methods of producing zein-coated confectionery.Banks. US Patent 3479191. W. 23. 181-92 Chu.G.K.W. Industrie Alimentari. Journal of Food Science. and Simonetti.P. (1994) Surface Retention of Preservative Agents Using Edible Films and Coatings: Improvement of Fresh Fruits and Vegetables Shelf-Life and Quality. J. Annals of Applied Biology.L. N.. 1-9. Academic Press.H. Academic Press. H. (1985) Poststorage application of TAL Pro-Long on apples from controlled atmosphere storage. Applied Science Publishers. 259. NJ.M. (1979) Shelf-life quality characteristics of poultry parts dipped in potassium sorbate. Biochemical Biophysical Acta. M. Batzer. Barrie. (1982) Diffusive resistance: importance and measurement in controlled atmosphere storage. Dhale. 759. Cameron. Journal of Food Technology. 149-68. Crank.G.P. Journal of Food Science 58(5). 75-9. (1984) Some effects of TAL Pro-Long coating on ripening.F.. and Singh. Polymer Bulletin. (1975) Non-Fickian diffusion. L. J. R. Cole. T. 78. and Fennema. (1968) Water in polymer. cv. 585. R. HortScience. (1969) Method for coating dehydrated food. 9. Weller. L. F.. De Leiris. Elsevier.G. 12. A. J. Bolin.M. N. Stromberg and R. Gontard. (1993) Polarity homogeneity and structure affect water vapor permeability of model edible films. and Guilbert. 19(10). Dhalla. Martin-Polo.B.R. 1316. Barron. 73. and Van Deenen. Cunningham..F. Marcel Dekker. 53(4). (1985) Natural and applied wax coatings on oranges.T. P. Pro-long treatment of mangoes (Mangifera indica L. In: The Mathematics of Diffusion.A. H. 267. (1977) The expansion of wafer and its relation to the cracking of chocolate and 'Bakers Chocolate' coatings. Burton. (1978) Biochemical and physiological effects of modified atmosphere and their role in quality maintenance. pp. J. Hulhn and M.K. M. (1976) Texture and crystallization control in raisins.C. Journal of Food Science. Cosier. S. (1983) Two-phase food products with reduced inter-phase moisture transfer. 58(2). W.. Brandeburg. S. L. (1985) Water activity and permeability. II. Park (eds). In: Food Packaging and Preservation: Theorie and Practice. International Journal of Food Science and Technology. 150. De Giers. O. (1993) Edible films and coatings from soy protein. and Testin. Good. (1980) Potassio sorbato e conservabilita del pollame. New York. New York. 41. US Patent 4401681. 5. Timber Press. Crank and G. U. S. (1972) In: Techniques of surface and colloidal chemistry and physics. F. (1981) Influence of water on thermal transitions in natural polymers and synthetic polyamides. M. A. O. B.S. Journal of Experimental Botany. CL.E. 107-12. In: Postharvest Biology and Technology Westport. 863-4.). International colloque 'Le froid et Ia qualite" des legumes frais'. 127-37.O. 35(150). Noyes Data Corporation. 1086-9. 426-9. (1993a) The effects of plasticizers on crystallinity. R. 44. RJ. 166. Brest. New York. S. Burton. 97-110. Blank. D'Aubert. pp. In: Diffusion in Polymers. . Daniels. and Reid. Oxford. F.G. (1968) Lipid composition and permeability of liposomes. V. Beaverton (ed. US Patent 2791509. J. and Muftugil. Chicago. (1985) Development of the Differentially Permeable Fruit Coating 'Nutri-Save' for the Modified Atmosphere Storage of Fruit. Journal of Applied Bacteriology. and Testin. CL. Schueman (eds). (1960) Effects of Temperature. 513. and mechanical properties of methylcellulose films.A. 10. 60. N. Forkner. R. and Ludi. 447-85.E. presented at the International Winter Meeting of the American Society of Agricultural Engineers. (1979) A review. (1986b) Sorbic acid diffusivity in relation to the composition of high and intermediate moisture model gels and foods. Weller. Fellman. 54. Proceedings of the Fourth National Controlled Atmosphere Research Conference Department of Horticulture. Journal of Applied Bacteriology. Donhowe. Cereal Chemistry.Y. D. France.K.. El Ghaouth.. (1991) Films et Enrobages Comestibles: Etude et Amelioration des Proprietes Filmogenes du Gluten. Tucson. Cuq. 22. US Patent 2821477. (1993b) Water vapor and oxygen permeability of wax films. A. (1970) Moisture transmission through fats. JJ. CM.. W. (1993a) Modification of physical and barrier properties of edible wheat gluten-based films. O. December. R. Journal of Food Science. Physiological Review. CO. Gill. LG. Paper No. (1980) Water permeability of lipid membranes. 1-10. K. (1958) Jelled material in food preservation. (1986a) Determination of sorbic acid diffusivity in model food gels. 269-79. Washing and Waxing on the Composition of Internal Atmosphere of Orange Fruits.. PhD Thesis. 29.F. 21. S. 87th Annual Meeting of the American Horticultural Society. Erbil. R. and Lidster. Duchez. 367. J.R. 1993.. International Journal of Food Science and Technology. Ponnampalam.. (1987) Postharvest use of sucrose polyesters for extending the shelflife of stored 'golden delicious' apples. Raleigh. J.F. T. 17(4). 90-6504. AVI Publishing Company.O. Journal of Food Processing and Preservation. CL. LG.A. (1993) Edible films: barriers to moisture migration in frozen foods. E. 339-53. H. and Kester. R.. Pratt. and Guilbert. LL. Feuge.. Donhowe. C. Gennadios. Inc. Biochemical Biophysical Acta. Arul.W. and Guilbert. 426-9. USA. R. (1991) Use of chitosan coating to reduce water loss and maintain quality of cucumber and bell pepper fruits. 359-68. (1990) The Use of Chitosan Coating to Extend the Storage-Life of Tomato Fruits. 15. 225-39. Westport.. Donhowe. (1994a) Edible composite films of wheat gluten and lipids: water vapour permeability and other physical properties.. Weller. Fennema. (1994) Lipid type and location of the relative humidity gradient influence on the barrier properties of lipids to water vapor. 220-8. J. O. Gennadios. 39-50. Journal of Food Engineering. North Carolina State Univ. R. A. Fettiplace. N. (1978) The influence of the lipid on the water permeability of artificial membranes. K.D. and Kester. 52(5). P. and Haydon. Drake.L. Giannakopoulos. 521-5. 76. 1086. A. Arizona. S. Journal of Food Technology. R. 383-9. 1283-5. and Guilbert. Eklund. A. E. 47. Hayes. 867-73. and Ponnampalam. N. Weller. and Arul. CL.W. (1993b) Temperature effect on oxygen permeability of edible protein-based films. CD. Eaks. LG.H. 58(1). (1990) Modification of Properties of Edible Wheat Gluten Films. Gontard. Fennema. Elson. CT. and Testin. Gennadios. 510-50. 70(4).. NC.. McCloskey and H. . 247-57. J. 111. A. Journal of Food Science. JJ. J.R. Journal of the American Oil Chemists' Society. de Vadetzky. R. A. 45(11).F. University des Sciences de Montpellier. Gontard. S. 25. 21. Langwili. El Ghaouth. O. and Testin. and Nelson. Journal of Food Technology. Proceedings of American Society of Horticulture. Intrinsic bacteria in meat. Fettiplace. II.permeability. Food Australia. (1986) Lengthening the postharvest life of peaches by coating with hydrophobic emulsions. Journal of Food Processing and Preservation. and Fennema. A. 70(9). S. Journal of Food Processing and Preservation. Giannakopoulos. In: Twenty Years of Confectionery and Chocolate Progress.E. (1983) The antimicrobial effect of dissociated and undissociated sorbic acid at different pH levels. . (1984) Additifs et agents depresseurs de l'activite de l'eau. 1393-9.Problemes et Techniques. 199-227. Tech. B. N. 1017-25. Guilbert.). Hall. and . Higuchi. (1966) A study of the surface wax deposits on apple fruit. 55. Multon (ed. LK. Martinus Nijhoff Publishers. S. R.. (1981) A research note: Mechanism of beef shelf life extension by sorbate. In: Food packaging and preservation. Food Chem. Universite des Sciences de Montpellier. (1986) Wheat gluten: a glassy polymer.L. Guilbert. N. Hagenmaier.C. 82-6. N. Journal of Food Protection.. controles. Hoseney. 7. Elsevier Applied Science Publishers. Agric.E. Giannakopoulos. 343. (1993) Water and glycerol as plasticizers affect mechanical and water vapor barrier properties of an edible wheat gluten film. Journal of Food Science. APRIA. 199-219. Guilbert. (1983) Les gelatines: proprietes. Thibaut. T. 57(1). J. USA. (1989) Les films et enrobages comestibles.. France. N. J.. 190-5. 337. In: Additifs et Auxiliaires de Fabrication dans les Industries Alimentaires. bilayer films. M. Paris. 18-19 Mai. Guilbert. S. Paris. D. CO. Multon (eds). (1985) Effet de Ia Composition et de Ia Structure des Aliments sur l'Activite et Ia Mobilite* de l'Eau ou de Solutes. (1995) Superficial edible films and osmotic dehydration: Application of hurdle technology without affecting the food integrity. Bureau and JJ. S. et Doc. A. et D o c .Gontard.L. I. Berlin. (1990) Moisture permeability of edible films made with fatty acid and (hydroxypropyl)methylcellulose. (1959) A study of permeability to water vapor of fats. K. Mathlouthi (ed. Springer Verlag. 19. S. pp. (1994) Edible coatings and osmotic dehydration. S. Journal of Food Science. and Cheftel. Multon (eds). Seow. New York. 63. and Biquet. (1981) Innovations in citrus waxing . S. D.M. waxes. Journal of Food Science'. In: Uemballage des Denrees Alimentaires de Grande Consommation. (1968) 'Haltbarlceit und sorptionverhalten wasserarmer lebensmitteV. and Guilbert. J. Tech. 38. 258-63. Ltd. (1994b) Oxygen and carbon dioxide permeability of edible and biodegradable packaging: influence of relative humidity and film composition.L. and Shaw. principales applications. Guilbert. S. Greer. 58(1). 45. Guilbert.M. Guilbert. Zeleznak. 285. Teng and CH. O. 909-16. Guilbert. Dordrecht. France. LaboPharma . In: Properties of Water in Foods in Relation to Quality and Stability. Submitted. and Cuq. 54(6). Gontard. CC. and Fennema. bilayer films for use as moisture barriers for food. J. Technomin Publishing.. (1989b) Evaluation of edible. 1400-6. S. Greener. Collection 'Les colloques de TINRA'. (1994) BiomateYiaux et molecules fonctionnelles. and Fennema. O. G. R. (1986) Technology and application of edible protective films. and Raoult-Wack. 320-59. 1799-803.D. Paris. Nantes. and Aguiar. Lavoisier. Grouber. and Cuq. Science. Guilbert. P.an overview. pp. T.C (1985) Diffusivity of sorbic acid in food gels at high and intermediate water activities. Simatos and JJ. Netherlands. Gontard. R. S. 206-11. Heiss. pp. / . and Graille. Guilbert. Hall. and Lai. S. Cuq. Journal of Food Science. Guilbert. A. (1988) Use of superficial edible layer to protect intermediate moisture foods: application to the protection of tropical fruit dehydrated by osmosis. Quah (eds). D. pp. 94. II. Cereal Chemistry. Final Report FLAIR Concerted Action No. G. S.T. Acta of 'Ler Colloque National sur les Valorisations Non Alimentaires des Grandes Productions Agricoles'. (1992) Edible wheat gluten films: influence of the main process variables on film properties using response surface methodology. B. To be published in Food Preservation by Moisture Control. B. Australian Journal of Biol. Welti-Chanes (ed).). In: Food Preservation by Combined Processes. Gontard. Subgroup B. J.. (1989a) Barrier properties and surface characteristics of edible.G. New York. Proceedings Florida State Horticultural Society. Elsevier Applied Science Publishers. p. In: Food Preservation by Moisture Control.. R. PhD Thesis. A. Journal of Food Science. Lavoisier. S. LL. CS. 371-94. Greener. 1154-7. Parker (eds). 66(7). 106. UK. Kamper. P. O.L. Nagy and W. (1984b) Water vapor permeability of edible bilayer films.P. 478. and Fennema. 109. 72(9). Journal of the American Pharmaceutical Association. E. fatty acid. S. Journal of Food Science. lysozyme and chitinase on the growth of several phytopathogens. (1967) Development of edible amylaceous coatings for foods. . In: Food Chemistry. The AVI Publishing Company. (1989) Effect of chitosan. Klose. N. LaboPharma . Journal of Food Science. and Feuge. M. 55-62. Acad. Hamilton. 578-83. 48(10). S.O. 38. E. (1975) The glass point of elastin.other enteric coating materials. S. pectic acid. JJ. Journal of the American Oil Chemists' Society.P. Applied Science Publishers. M. CA. Nelson. Wardoski. waxing. 66(8). 54. (1971) Edible containers. 10.. (1981) Some effects of emulsifiable coatings on weight loss. and Powell. O. R. M. G. Lidster. W. Kamper. 21. A. Mecchi. Food Technology. S. Nat. (1963) Continuous raisin coater. (1986) Edible films and coatings: A review. Lefaux. 47-59. R. 379. Journal of Food Science. 1-4. Proc. 1478-81. Kroger. 308-15. 40(12). Journal of Food Science. R.O. Lowe. 1-9. New York. O. New York. (1989c) Tempering influence on oxygen and water vapor transmission through a stearyl alcohol film. 203. (1982) A vegetable oiling agent for dried fruits. N. A. 50. Kester. (1965) Transport through polymer films.W. 1390-2. and Fennema. JJ. E. Journal of Food Science. and surface damage disorders in 'Van' sweet cherries..R. Kakivaya. Karel. Westport. and Fennema. and Fennema. Kester. Science. JJ. 53 3065-6. bilayer film...E. Food Technology. 4. N. G.G. E. and Fennema. 3505. W. Lovegren. 74-9. (1972) The Biomolecular Lipid Membrane: a System. Kaplan. p.L. 49(6). Jain.L.B. Kester. Kempf. Fennema (ed. 1482-5. Kester. O. 6. JJ. 54(6). JJ. 47(7). p. (1971) Permeability des matieres plastiques aux gaz et aux vapeurs organiques: applications dans les domaines pharmaceutiques. (1960) Permeability of some fat products to moisture. R. J. Food Technology. 1139-46. Jokay. Journal of the American Oil Chemists' Society.L. 49(6). W. 17. T. Part C.Problimes et Techniques. Davies.I. Landman. R. S. stem discoloration. Agricultural and Biological Chemistry. Von Nostrand Reinhold. (1984a) Water vapor permeability of an edible. S.E. S. O.D. 403. Food Technology. (1989a) An edible film of lipid and cellulose ethers: barrier properties to moisture vapor transmission and structural evaluation. 37.G. G.E. and Labuza. and Hoeve.L. CA. CT.. 1383-9.. (1952) Use of antioxidants in the frozen storage of turkeys. and Nagao. H. November. Manuf Confec. and color-adding. London.P. Katz.L. 382-4. (1986) Washing. Kamper. and Fennema. 45. and Fennema. Journal of Polymer Science. O. Journal of American Society of Horticultural Science.) Marcel Dekker.K. and Igoe. O.F. Journal of Food Science. Kochnar.P. Inc. (1989b) Resistance of lipid films to water vapor transmission. 1064. Journal of the American Oil Chemists' Society. Watter. and Hanson. In: Intermediate Moisture Foods. Kumins. (1989d) An edible film of lipids and cellulose ethers: performance in a model frozen-food system.S. and Rossell. Durkee. and Fennema. 11. 913. Food Technology.tests on the moisture barrier properties of coatings. (1967) The conching process . O. p. and Morgan. Labuza. Food Product Development. In: Fresh Citrus Fruits. L. (1985) An integrated approach to food chemistry: Illustrative cases.V. HJ. (1976) Technology and application of new intermediate moisture foods. E. Kester. Birch and KJ. (1985) Use of an edible film to maintain water vapor gradients in foods. Hirano.. Grierson (eds). 661. (1981) Effect of water activity on the sensory crispness and mechanical deformation of snack food products. T. J. V. and Quantick. R. Journal Photogr. 27.. J. Chemistry Technology. Preliminary Notes.S. (1979) Measurement of permeability of chilled meat packaging film under conditions of high humidity.S. Persian). and Ivey. Swaminathan. pp. In: Food Packaging and Preservation. Pratt. Wond. 99-105. De Gier. (1961) Studies in the gas and vapor permeability of plastic films and coated papers. MI. Paper No. CCB Rev.). Presented at the Congres SAGE. M.. (1978) Antimicrobial efficacy of a potassium sorbate dip on freshly processed poultry. 1990. and Van Deenen. Poyet. using a potassium sorbate dip. Weller.Lowings. 6(2).E. 149-55. M. February. Motlagh. Journal of Food Science.. C. Biochemistry and Biophysical Acta.. McElhaney. 58. D. (1992) Hydrophobic films and their efficiency against moisture transfer. I. R. Marshall. (1990) Edible methylcellulose-based films as moistureimpermeable barriers in sundae ice cream cones. 36-40. (1982) Use of sorbates in meat products. Effect of five cycle rapid freeze-thaw treatment in conjunction with various chemicals for the reduction of Salmonella typhemurium. 727. 284-8. M. International Journal of Food Science and Technology. 42. and Boettger. A.. FJ. 407-12. H J . PJ.G. Nottingham.F. Rico-Pena. 90-6510 presented at the American Society of Agricultural Engineers.M. P. Lueck. Multon (eds). Mannheim. M. Fleischwirtsch. WJ. 23. (1981) Marketing and products. In: Properties of Water in Foods. CL. Journal of Agricultural and Food Chemistry. and Passy. C. Science. fresh poultry and poultry products: A review. US Patent Reissue. 14. A. and Szwarc. and Chinnan. A. 128. and Voilley. D. 1361-4.L. 17. 855.S. (1993) Permeability and mechanical properties of cellulose based edible films. T. J. Rico-Pena.F. 1822. Vergano. D. Bakery. Poultry Science. Journal of Food Technology. E. Simatos and J.. S. Influence of film preparation techniques.C and Torres. Journal of Food Protection. pp.C and Sofos. (1980) Thermal transition in gelatin and aqueous gelatin solutions. Journal of Food Science.M. France. New York. B. and Stadelman. Journal of Food Science. and Testin. M. 40. Marston. (1990) Properties of Edible Coatings for Fruits and Vegetables. the Netherlands. Robach. UK.C (1979) Extension shelf life of fresh. 374-83. 1 et 2 Avril. M. 245. and Kumosinski. 44. E. N.A. A.L. (1988) Effect of permeable coatings on the storage life of fruits. 60. 41(4). Proceedings Institute Food Sciences and Technology Annual Symposium.F. 7-24. Olson. 45. 45(4). (1985) Study of some factors affecting permeability. (1982) The preservation of fresh fruits and vegetables.N.E.H. 28. J. Mardtta. Park.. Dordrecht. B. and Torres. R. 'L'Alimentarit6 dans les Matieres Plastiques et les Caoutchoucs'. (1993) New coatings for cut fruits and vegetables. pp..N. D. D. HJ. Journal of Food Protection. Paris. Pavlath.. July. (1970) The effect of alterations in fatty acid composition and cholesterol content on the permeability of Mycoplasma laidlawii B cells and derived liposomes. (1984) Sorbinsaeure und sorbate. P. A. 56(2).B. L. (1985) Choice of packages for foods with specific considerations of water activity. (1983) Moisture content and migration in bread incorporation dried fruit. . CE. Elsevier Applied Science Publishers. (1993) Les Polymeres 'Barrieres'. 35(10). R. and Cutts.A. D. (1991) Sorbic acid and potassium sorbate permeability of an edible methylcellulose-palmitic acid film: water activity and pH effects. Maxcy.C.E.W.. J. (1981) Surface microenvironment and penetration of bacteria into meat. 64. P. (1981) Problems of exchange reactions during conching (II).A. Mauguin. 550. Meyer. 531. Martinus Nijhoff Publishers. V. 375-92. Martin-Polo.E.G. TAPPI. St Joseph. 219. and Petrie. Robach. N. Food Technology (Australia). Pro-Long treatment of limes (Citrus auratifolia cv. Park.. Myers. Pascat. J. 1991. Rogers. 58(6). 52-67.C. 463. M. Murray. whole broilers. Rigg.M. D. Robach. Journal of Food Protection. Journal of Food Protection. (1972) Amylose coating for deep fried potatoes. The permeation of water vapor. WJ. H. Niediek. Chocolate Confect.W. 55(5).F. Stannett. Mathlouthi (ed. On the presence of salmonellae.A. 329.). Appl. Slade. 726. (1989) Protein-water interactions: water as a plasticizer of gluten and other protein polymers.. Macromol.G. H.I. . (1986) Barrier polymers. E. Bio.Peanut Science. Journal of Milk.C. 3. PJ. 38.G. J.V.M.W. J. W. III.A. S. (1985a) Microbial stabilization of intermediate moisture food surfaces. K.L..D. In: The Wiley Encyclopedia of Packaging Technology. L. Miers. Journal of Food Processing and Preservation. II. N. pp.C. Paper No. V. 9. and Maclay. (1953) Pectinate and pectate coatings. New York.B. Veteranarnomeditsinski Nauki. J. Schultz. Z. In: Food Packaging and Preservation.. Hall. New York.H.A. (1987) Production of modified atmosphere in deciduous fruits by the use of films and coatings. T. (1986) Cellophane. J. pp. J. and Spencer. (1973) Hygienic studies on the production of poultry meat. John Wiley & Sons.R. O. Smith. 22(5).A. M. Marcel Decker. (1973) Effect of selected coating materials on the bacterial penetration of the avian egg shell. Phytopath. Owens. New York. and Chizhikova. Food Technology. 159-63. and Owens.. K. (1981) Water clusters in elastin.C.. (1974) Hygienic studies on the production of poultry meat.W. 82-90.T. Torres. In: Protein Quality and the Effects of Processing. J. Miers. and Robach. Food Technology. 115-35. and Marakami. Inc. Control of surface preservative concentration. (1985) Modelling of gas and vapor transport through hydrophilic films. (1984) Effect of chitosan. In: Water Activity: Theory and Applications to Food. L. Tiemstra. (1975) Effects of structural variation in 0monoglycerides and other lipids on ordering in synthetic membranes. Khlebopekarnaya i Konditerskaya Promyshlemost. (1984) The potential of a sucrose ester coating material for improving the storage and shelf-life qualities of 'Cox's Orange Pippin' apples. (1985) Microbial stabilization of intermediate moisture food surfaces. J. Colloid Chem. Tsutsumi. Cecorulli.. E. 147.H. I l l .D. HortScience. J. To. (1987) Microbial stabilization of intermediate moisture food surfaces. (1974) Moisture transmission through peanut oilfilms. and Stow. 11(1). Finlay (eds).. M. W. Poultry Science.. presented at 69th Annual Meeting of American Association of Cereal Chemists. G. M. 17. Vitkov. 9. Stossel. M. Geeson. T. Schwartzberg. Gunaratne. J.R. New York. M. Taylor. II. P. Control of surface pH. In: The Wiley Encyclopedia of Packaging Technology. 772-6. /. Bouzas.. (1949) Permeability of pectinate films to water vapour.. and Karel. and Stow. Bakker (ed. 272-5. chitin and some aminosugars on growth of various soilborne phytopathogenic fungi. Application to nuts and fruit products. (1984) Starch Properties in Processed Foods: Staling of Starch-Based Products. (1978) Protective properties of chocolate coatings (Russian). 59. Lipids. M.C (1980) Potassium sorbate dip as a method of extending shelf life and inhibiting the growth of Salmonella and Staphylococcus aureus on fresh. M. John Wiley & Sons. (1976) US Patent 3997674. J. M.W. S.. H. and Finlay.M. Marcel Dekker. LJ. Motoki. Tryhnew. Australian Journal of Agricultural Research. Smith. and Skyes. Scandola.. and Varanasi. 9. BioL. Roubal. 535-41. R. D. 232-5.S.Salame.R. 10(9). S. H. S. 4. Journal of Food Processing and Preservation. T. On the superficial contamination of poultry meat. Levine. pp. 1320-30. Torres. Taylor. II. 104. Ishibashi. Vitkov. 48-54.S.P. Mathlouthi (ed. I. M. 10. L. 55. Washington. A. H. Torres. New York. Ann. whole broilers. Veteranarnomeditsinski Nauki.G. H.A.). M. Phillips and J. J.. M.B. 4. 383. II. 112. and Tiemstra.. Bakker (ed. and Karel. 47. Inc. 53. 57-81. p. S. 107-19. J. Effects of surface preservative concentration and surface pH control on microbial stability of an intermediate moisture cheese analog.A. Elsevier Applied Science Publishers. 93-106. Internat. Slade. Rockland and L. and Leuba. Phys. 75-92. M. (1953) Effects of skin coatings on the behavior of apples in storage. Beuchat (eds). Swenson. 36(5). 7. Trout. Schultz. and Karel. J. Ukai.O. pp. M.).. Journal of Food Processing and Preservation.. CC. 1(2). Soboleva.M. Torres. M. and Pizzoli.. LC. (1985b) Microbial stabilization of intermediate moisture food surfaces. J. 9. 292-6. Watters. M. G.C. M. Sci.Vojdani. 55(3).E. 257-62.A.G. 12. J. J. 33-48. Macromol. and Torres.E. Vojdani. Food Technology. methylcellulose and hydroxypropyl methylcellulose. (1989a) Potassium sorbate permeability of methylcellulose and hydroxypropyl methylcellulose multi-layer films. J.K. Journal of Food Science. J.. J. (1961) Stabilized raisins for dry cereal products. Yannas. A. (1978) Evaluation of a calcium alginate film for use on beef cuts. Zamora. 43. 7. 13. (1989b) Potassium sorbate permeability of polysaccharide films: chitosan. Journal of Food Process Engineering. and West. 52(2).C. 52(6). Chem. F. F.Revs. Journal of Food Science. (1987b) Potassium sorbate inhibition of microorganisms growing on refrigerated packaged beef. 5. F. Journal of Food Science.L. and Torres. R. . and Zaritzky. and Zaritzky. and Brekke.E. (1987a) Antimicrobial activity of undissociated sorbic acid in vacuum packaged beef. N.A. Oblinger. 236-8.. 49. Zamora. LV. Macromol. N. and Torres. / . 841-6. Williams. S. Journal of Food Science. Vojdani.L. (1972) Collagen and gelatin in the solid state. . Journal of Food Processing and Preservation. 417-30. (1990) Potassium sorbate permeability of methylcellulose and hydroxypropyl methylcellulose coatings: effect of fatty acids. 1449-53. P. ABE 6.g. These include . J. However.. aerobic spoilage can still occur in these packaged products depending on the level of residual oxygen in the package headspace. and inadequate evacuation and/or gas flushing (Smith et ai. 1990). the latter involving various mixtures of CO2. either alone or in conjunction with nitrogen and sometimes oxygen depending on the product gas packaged.. and consumer needs for convenience foods with extended shelf-life yet retaining their fresh characteristics. ability of the food to trap air. 1986). some of which have been discussed in previous chapters of this text. reduce microbiological growth and retard enzymatic spoilage with the intent of extending shelf-life' (Young et aL. HOSHINO and Y. Although this form of interactive packaging can be used to extend the shelf life and keeping quality of food. freezing or thermal processing. novel methods of oxygen control and atmosphere modification have been developed. There are many examples of interactive packaging technologies including antimicrobial and antioxidant films. there has been a tremendous growth in interactive packaging for shelf-life extension of food. and one which fulfils the above definition in all aspects. Packaging can be defined as 'interactive' when it 'performs some role in the preservation of the food other than providing an inert barrier to outside influences' (Rooney. SMITH. e. meat or fruits and vegetables (Smith et al. The growth in MAP technology has resulted from advances in packaging technology. 1992). ethylene absorbing sachets and temperature control indicators. primarily by the Japanese. In recent years.1 Introduction Over the past decade. perhaps one of the best examples of interactive packaging. MAP has been defined as 'the enclosure of food products in a high gas barrier film in which the gaseous environment has been changed or modified to slow respiration rates. The atmosphere in MAP foods has traditionally been modified by vacuum or gas packaging.6 Interactive packaging involving sachet technology J. The level of residual oxygen in vacuum/gas packaged products could be due to a number of factors such as oxygen permeability of the packaging material. the food industry's need for less energy-intensive forms of food preservation than drying. 1988). is modified atmosphere packaging (MAP). leakage of air through poor sealing. 1). the first North American oxygen scavenger (Table 6.. Like its predecessors. Multiform Desiccants in the United States introduced FreshPax. oxygen absorbents were first marketed by the Mitsubishi Gas Chemical Co.. and ethanol vapor generators. FreshPax is extremely effective in lowering package oxygen from 20% to less then 0. the methods by which these sachets actively modify the gas atmosphere in the packaged product. Japan Toppan Printing Co. under the trade name Ageless (Table 6. and their uses. has about 11% of the market with nine other companies sharing the remaining 16% of the market. acceptance of oxygen scavengers in Table 6.1). In 1989. The Mitsubishi Gas Chemical Co. Another important factor for their success is that Japanese consumers are willing to pay higher prices for preservative-free products with an increased shelf-life. US Product name Ageless Freshilizer Freshpax . oxygen absorbents/carbon dioxide generators. Several years after the Mitsubishi Gas Chemical Co. dominates the oxygen absorbent market (73%) while the Toppan Printing Co. almost 7000 million sachets were sold in Japan with sales of absorbents growing at a rate of 20% annually. personal communication). This technology involves the use of sachets which can be placed alongside the food and actively modify the package headspace thereby extending product shelf-life. Japan Multiform Desiccants. Several other Japanese companies also produce oxygen absorbents with the best known being the Toppan Printing Company which produces a range of oxygen absorbents under the label Freshilizer Series (Smith et al..oxygen/carbon dioxide absorbents. unlike the Japanese market. advantages and disadvantages for shelf-life extension of food.. including the hot and humid climate during the summer months which is conducive to mold spoilage of food products.. 1990). Oxygen absorbent technology has been successful in Japan for a variety of reasons. successfully launched oxygen absorbent technology onto the marketplace. Oxygen absorbents can be defined as 'a range of chemical compounds introduced into the MAP package (not the product) to alter the atmosphere within the package' (AgriFood Canada. Developed in Japan in 1976. However.2 Oxygen absorbents One novel and innovative method of oxygen control and of atmosphere modification involves the use of oxygen absorbents. 6.05% in about 36 hours.1 Major companies producing oxygen absorbents Company Mitsubishi Gas Chemical Co. This chapter will review the various types of absorbent/generator sachets available in the marketplace. Water is essential for oxygen absorbents to function.1. not produce toxic substances or offensive odors/gases. they actively modify the package headspace and reduce the oxygen levels to < 0. although several major companies in both continents are now using this technology. These sachets come in a variety of sizes capable of absorbing 20-2000ml of headspace oxygen. When placed inside the packaged food.2). be handled easily.2.2. and be economically priced (Harima. the oxygen .2. In moisture dependent types. any material that reacts easily with oxygen can be used as an oxygen scavenger.North America and Europe has been slow. have an appropriate oxygen absorption speed. 6.2. • • • • • • • It It It It It It It must must must must must must must be safe. 6. 1990). In theory. some are designed to scavenge oxygen at refrigerated or frozen storage temperatures and are used to further extend the shelf-life and keeping quality of muscle foods. Each category will be briefly reviewed. Iron powder and ascorbic acid are commonly used in existing oxygen absorbers with powdered iron being most frequently used either alone or in conjunction with other specific chemical compounds in dual function absorbents (Table 6. This oxygen-free environment protects the food from microbiological and chemical spoilage and is also effective in preventing damage by insects. In the self-reaction types. However. The classification and the main types of oxygen absorbents will now be briefly reviewed. However. Oxygen absorbents comprise of easily oxidizable substances usually contained in sachets made of air-permeable material. which facilitates the marketing of oxygen absorbents. absorb a large amount of oxygen.1.1 Classification according to material. water required for the chemical reaction is added and the absorbents must be handled carefully as the oxygen absorbing reaction commences as soon as the self-reacting absorbent is exposed to air. because the technology involved is used mainly for food preservation.01% within 1-4 days at room temperature. 6. be compact in size.7 Classification of oxygen absorbents Oxygen absorbents can be classified into several different categories as shown in Table 6. the material used inside the sachet must meet the following criteria prior to approval by regulatory agencies.2 Classification according to reaction style. A combination of some or all of these factors helps maintain the quality and freshness of food. 5 days Ageless SS Ageless FX Vitalon LTM Tamotsu A Tamotsu P 3 to 8 days 1 to 4 days Ageless E Ageless G Toppan C Vitalon GMA O2I & CO2I O2I & CO2T Iron + Calcium Ascorbic acid Self-working type Self-working type Ascorbic acid + Iron O2I & Iron + EthanolT Ethanol/Zeolite Moisture dependent type Moisture dependent type Negamold .13 Classification according to reaction speed.5 days 3 days at .65 Dried beef High aw aw > 0. However.2.65 Nuts High aw aw > 0.25°C Raw fish Moisture dependent type Catechol Self-working type High aw aw > 0. 62. these type of absorbents are easier to handle as they do not react immediately upon exposure to air.85 Cakes Absorption speed 4 to 7 days Product Ageless Z-PK Vitalon T Ageless Z Keplon TS Ageless S Sequl CA 1 to 3 days 0.3 < aw < 0. The average time for oxygen absorption is 0. general effect.25°C 0. they absorb oxygen quickly after sealing and oxygen can be absorbed within 0. 1990).absorption reaction only takes place after moisture has been absorbed from the food.3 Tea. 1-4 days for the general type. Examples of self-reacting and moisture dependent types of oxygen absorbents are shown in Table 6.. Oxygen absorbents can be classified as immediate effect.65 Cakes Roasted coffee Medium aw 0.2 Classification of oxygen absorbents Function O2I Iron Reactant Application Self-working type Dry aw < 0.5-1 day in certain products. and slow effect types (Harima. and 4-6 days for the slow Table 6. nuts Medium aw aw < 0.5-1 day for the immediate type.65 Cakes Bakeries Frozen temp + 3 to .85 Cakes High aw aw > 0.85 Pastas Medium aw aw < 0.5 Nuts High aw aw > 0. 2. Most oxygen absorbents are used with foods stored at ambient temperature. O2 concentration (%) Time (day) Figure 6.O2 concentration (%) Time (day) Figure 6. a self working type (fast working type) of oxygen absorber. reacting type (Harima. a self working type (medium working type) of oxygen absorber. The effect of storage temperature on oxygen absorbing speed is shown in Figures 6.2 Effect of storage temperature on oxygen absorbing speed of Ageless Z-100. 1990).1 and 6. . The reaction time depends on storage temperature and water activity (aw) of the food.1 Effect of storage temperature on oxygen absorbing speed of Ageless S-IOO. In general.1. which are not susceptible to microbial spoilage but to chemical spoilage. some absorbents can now scavenge oxygen rapidly from the package headspace of food stored under lowtemperature conditions. and oxygen absor- 02 concentration (%) AGELESS FX-100 Time (day) Figure 6.3 Effect of frozen temperature (-250C) on oxygen absorbing speed of three types of oxygen absorbents. A comparison of the oxygen absorbing speed of one such type of oxygen absorbent (Ageless SS) with absorbents which function mainly at ambient storage temperatures. These include oxygen-carbon dioxide absorbents for use in coffee. dual functional absorbents have been developed for use in specific products.5 Classification according to function. General type absorbents are used with intermediate moisture food products where a moderate speed of oxygen absorption is required. However. Examples of the application of the various categories of oxygen absorbents are shown in Table 6. is shown in Figure 6. 6. foods with a high moisture content are more susceptible to mold spoilage. Therefore.1.2. if used with refrigerated or frozen products these absorbents react very slowly.3.absorption of oxygen. Oxygen absorbents can be used for a variety of foods with different moisture contents ranging from very moist to very dry food products. To overcome this problem.2. For low moisture food products.2.4 Classification according to use. 6. The majority of absorbents have only one function . . a slow effect oxygen absorbent can be used.However. an immediate effect absorbent would be used with these products to rapidly absorb oxygen and extend the mold-free shelf-life of the product. intermediate moisture products. Ageless.2 Main types of oxygen absorbents 6. The latter type of sachets absorb O2 and generate the same amount of CO2 as that of absorbed oxygen. low moisture product foods and foods containing or treated with oil.2. However. the iron is contained in a sachet (like a desiccant). 1990.bents-carbon dioxide generators. 1992): Fe -> Fe2+ + 2e ^O2H.g. FM and SE (Table 6. The main types of absorbents are types Z. e. Three new types of Ageless are commercially available in Japan. These are Ageless types SS. under appropriate humidity conditions. The sachet material is highly permeable to oxygen and.3). made by the Mitsubishi Gas Chemical Co. S. The basic system is made up of finely divided powdered iron which.. These absorbents could be used to control the growth of facultative bacteria and yeasts which grow under reduced oxygen tensions. Examples of single function and dual function oxygen absorbents are shown in Table 6. it completely removes all traces of residual O2 and protects the packaged food from aerobic spoilage and quality changes.e. Another dual functional absorbent scavenges oxygen and releases alcohol vapor.2. They are mainly used in products where package volume and package appearance is critical. E and G.. i. The oxidation mechanism can be expressed as follows (Harima.2.-> Fe(OH)2 Fe(OH)2 + J^O2 +\ H2O -> Fe(OH3) To prevent the iron powder from imparting color to the food.. to water vapor. 1990). While both organic types (based on ascorbic acid) and inorganic types (based on iron powder) are available. 1990.H2O + 2e -> 2OHFe2+ + 2(OH). packaged peanuts.1 Ageless.2. uses up residual oxygen to form nontoxic iron oxide. . Since Ageless relies on a chemical reaction and not on the physical displacement of oxygen as in gas packaging. FX. it rusts. These sachets contain iron carbonate and ascorbic acid as the reactants. 6. in some cases. Smith et ai. this type of dual functional absorber is not widely used by the Japanese food industry (Harima. Smith. Several types and sizes of Ageless sachets are commercially available and are applicable to many types of foods including those with a high moisture content. the inorganic types are most commonly used in the Japanese market. consists of a range of gas scavenger products designed to reduce oxygen levels to less than 100 ppm in the package headspace. A commonly used absorbent is type E which also contains Ca(OH)2 in addition to iron powder.65 > 0. Marketed under the brand name Fresh Lock.3.0 0.0 2-3 (0-4 0 C) 10 ( .85 < 0. However. It is available in sizes that can scavenge 20-2000 ml of oxygen (an air volume of 100-10 000 ml).Table 6. to maintain the package volume and hence appearance of the product.5-1.5-2.85. Thus.3 Types and properties of Ageless oxygen absorbents Type Z S SS FX FM E G SE Function Decreases O2 Decreases O2 Decreases O2 Decreases O2 Decreases O2 Decreases O2 Decreases CO2 Decreases O2 Increases CO2 Decreases O2 Increases ethanol Moisture status Self-reacting Self-reacting Self-reacting Moisture dependent Moisture dependent Self-reacting Self-reacting Moisture dependent Water activity <0.0 3-8 1-4 1-2 Type Z is designed for food products with water activities of less than 0. . Type S.5-2 days).2 5 0 C ) 0. Type FX is moisture dependent and does not absorb oxygen until it is exposed to an aw greater than 0. The various types of Ageless and their characteristics are summarized in Table 6. Absorbent type SS is similar to type S.65 and reduces residual headspace oxygen to 100 ppm in 1-3 days.5-1. Yet another new absorbent is type FM which can be used with microwaveable products (Table 6. on the other hand. They have the same oxygen scavenging capacity as above.65 > 0.85 > 0. such as nuts. Type G is a self-working type and absorbs oxygen and generates an equal volume of CO2. it has the ability to rapidly scavenge oxygen under refrigerated and frozen storage conditions. Two other types of Ageless (FX and S) work best at higher water activities and have a faster reaction rate (0.5 >0. It is used for ground coffee. Another new innovation is Ageless type SE. This type of absorbent requires careful handling since it begins to react immediately on exposure to oxygen. fish and poultry. it is used in Maxwell House ground coffee cans (Table 6. contains moisture in the sachet and is a self-working type.3).3 0.3-0.3). It is used mainly with snack food products. Two other types commonly used in the Japanese market are type G and type SE. This absorbent is moisture dependent and absorbs oxygen and generates ethanol vapor. It is used to extend the mold-free shelf-life of bakery products in Japan.85 Absorption speed (day) 1-3 0. Type E scavenges CO2 as well as O2.85 >0. These absorbents (Ageless type SS) are widely used to extend the refrigerated shelf-life of muscle foods such as fresh meat. where CO2 removal reduces the chance of the package bursting. it can be easily handled if kept dry. Type CV absorbs both oxygen and carbon dioxide and was developed for use with roasted or ground coffee (Table 6.5-1. Series F Freshilizers use mainly ferrous metal and absorb only oxygen. Japan. 6. 1989).9 < 0.4 Types and properties of Freshilizer oxygen absorbents Type Function Moisture status Self-reacting Self-reacting Moisture dependent Self-reacting Self-reacting Self-reacting Water activity <0. The Freshilizer C series of absorbents comprises types C. Three types are commercially available .4. > 0.types FD. The Freshilizer Series of freshness keeping agents made by Toppan Printing Co. Type C is used in foods with an aw of 0.e. CW and CV.2.0 3-5 2-3 3-8 F Series (ferrous metal) Decreases O2 FD Decreases O2 FH Decreases O2 FT C Series (Non-ferrous metal) C Decreases O2 Increases CO2 Decreases O2 CW Increases CO2 Decreases O2 CV Decreases CO2 Courtesy of Toppan Printing Co.6-0.2.8). Type FT works best in foods with water activities greater than 0.8 (nuts. tea.2. 1989).8 0.. Japan.Table 6. Toppan Technical Information.6 to 0.9 and is used mainly with beef jerky and salami to maintain the color of these products.9 > 0.. chocolate) while type FH is suitable for use in products with a range of aw values ranging from 0. consists of the F series and the C series (Table 6. Series F absorbents can absorb 20-300 ml O2 corresponding to a package volume of 100-1500 ml of air (Toppan Technical Information.8 or less (nuts) while type CW is suitable for foods with higher aw values (i. a leading manufacturer of desiccants and other protection products for more than 30 years.4). FreshPax is a patented oxygen absorbing system developed by Multiform Desiccants.2.8 such as pizza crusts. Types C and CW absorb oxygen and generate an equal volume of CO2 thereby preventing package collapse. Type FD is designed for use in food products with aw values less than 0.8 < 0. like other oxygen absorbent technology provides an alternative to gas/vacuum packaging to extend the shelf-life and keeping quality of products while simultaneously reducing costs and increasing . Manufactured in the United States. 6. FreshPax.3 FreshPax.3 Absorption speed (day) 1-3 0. Type CW is commonly used to prevent mold growth in sponge cakes.0 0. FH and FT.2 Freshilizer series.5-1. These sachets consist of non-ferrous metal particles and can therefore be used in products which must pass through a metal detector.8 0.8-0. Tokyo. 2.200C Decreases O2 Decreases O2 Increases CO2 Moisture status Moisture dependent Self-reacting Self-reacting Moisture dependent Water activity > 0. Several interrelated factors influence the choice of the type and size of absorbent selected for shelf-life extension of food products (Harima. 1992).type B. > 100 cm3 mil m~2 day"1 atm"1.0 Courtesy of Multiform Desiccants.5-2. Buffalo. 6. type R and type M (Table 6.95 > 0. 1994).65 Absorption speed (day) 0. These are: • • • • • • The The The The The The nature of the food. shape. amount of dissolved oxygen in the food.5 Types and properties of Freshpax™ oxygen absorbents Type Type B Type D Type R Type M Function Decreases O2 Decreases O2 at 2° to .3-0.7 0.e. NY.5. oxygen permeability of the packaging material. non-toxic ingredients (mainly iron oxide) that rapidly absorb oxygen before the food deterioration process begins. size. It is mainly used to extend the shelf-life and keeping quality of muscle foods.g. desired shelf-life of the product.) 0.. < 10 cm3 mil m 2 day 1 atm 1 such as PVDC coated nylon/LDPE.0 0.. However.5-1.g. The latter parameter is critically important for the overall performance of the absorbent and shelf-life of the product. FreshPax Technical Pamphlet. Produced in sachet form. Smith et ai.0 0. type D.65 < 0.5). i.1% using safe. 1990. the oxygen concentration in the container will reach zero within a week but then returns to ambient air level after 10 days due to the fact that the absorbent is saturated.. weight. e. initial level of oxygen in the package headspace. the headspace O2 will be reduced to 100 ppm within 1-2 days and remain at this level for the duration of the storage . Smith. Type R can be used to scavenge oxygen at refrigerated or frozen storage temperature and is similar to Ageless type SS. e. Type M is used with most or semi-moist gas flushed products to maintain package volume and to remove all traces of residual oxygen (Table 6. FreshPax absorbs headspace oxygen to < 0. if films of low O2 permeability are used.3 Factors influencing the choice of oxygen absorbents Oxygen absorbent sachets come in a range of sizes capable of absorbing 5 ml to 2000 ml of oxygen.Table 6. If films with high O2 permeabilities are used.5-4. Four main types of FreshPax are commonly available . aw of the food. profitability.0 (depending on temp. 1990.5-2. Type B is used with moist or semi-moist foods while type D can be used with dehydrated or dried foods. Examples of appropriate packaging materials for use with oxygen absorbents and their permeability characteristics are shown in Table 6. EVOH = ethylene vinyl alcohol. Similar redox indicators are made by the Toppan Printing Company. PP = polypropylene.Table 6. and rancidity problems in high fat foods. especially molds.5.. 6.6 < 4 < 8 < 40 < 100 <20 < 6 < 5 Short-term preservation Not appropriate OTR = oxygen transmission rate. Examples of products found in Japanese supermarkets with extended chemical and microbiological shelf-life as a result of oxygen absorbent technology are summarized in Tables 6.11.. When placed inside the package alongside an Ageless sachet.1 In Japan. in intermediate moisture and high moisture bakery products. Harima. 1990.4. e.g. 1990). As a result of these studies. oxygen absorbent technology is being used extensively in Japan to prevent chemical problems.4 Application of oxygen absorbents for shelf-life extension of food 6.7).6. Table 6. MVTR = moisture vapor transmission rate. A rapid and efficient method of monitoring package integrity throughout the storage period is through the incorporation of a redox indicator. If the indicator reverts back to its blue color. fried rice cake and chocolate covered almonds (Figures 6.6 < 3 < 15 < 16 < 15 < 200 < 2000 < 3000 MVTR (g/m2/d) < 0. period providing packaging integrity is maintained. 1994) Film laminates including Long-term preservation Aluminium EVOH PVDC Nylon PET Cellophane PP PE OTR (ml/m2/d) < 0. More detailed information on the use of both Ageless and Freshilizer oxygen . Oxygen absorbents are also used effectively to inhibit growth of aerobic spoilage microorganisms. such as peanuts. intermediate and high moisture food products using oxygen absorbent technology (Nakamura and Hoshino.6 Examples of films used with oxygen absorbents (Freshpax Technical Pamphlet. e. discoloration problems in highly pigmented products.005%.8-6. Minakuchi and Nakamura.4 and 6.g. PE = polyethylene. PET = polyester. Ageless Eye. 1989. Several studies have reported significant extension in the chemical and microbiological shelf-life of low. it is indicative of poor packing integrity caused by poor sealing of the film or minute pin holes in die film. PVDC = polyvinylidene chloride. 1983.2. the color of the indicator changes from blue (oxidized state) to pink (reduced state) when the oxygen content of the container reaches < 0. Abe and Kondoh. such as cured meat products and tea.2. . 200 ml.fluorescentlight. Ageless Z-50. Sunlight. 100 g. Conditions: Material.4 Effect of an oxygen absorbent on the vitamin C content of Green tea. S. storage temperature. F. absorber. Bag made from oriented nylon/polyethylene/foil/polyethylene.5 Effect of oxygen absorbents on the peroxide value (POV) of packaged fried rice cakes by comparison under photo-irradiation. air.Total Vitamin C (mg/100g) AGELESS AR I (MONTHS) Figure 6. 25°C. AR I POV (peroxide value : meq/kg) N 2 gas AGELESS Time (day) Figure 6. 01 2. absorbents for shelf life extension of food can be found in the excellent articles referenced at the beginning of this section.1 5 18.5 2.3 1.1% (almond). contains iron powder for absorption of oxygen and calcium hydroxide which scavenges carbon dioxide. staling.12. meal ready-to-eat (MRE) bread prevented mold growth on bread for 13 months at ambient storage temperature. two companies. 1988). good aroma and good flavor. Moisture content: 2. Flavor score: 5 = no rancid smell. Examples of the known US companies currently using oxygen absorbents for shelf-life extension of products are shown in Table 6. which if not removed.e. The earliest use of this technology was with Maxwell House coffee which used a dual function absorbent (Ageless E).01 1.8 1 Air (Almond without chocolate coating) Air O2(%) 14.3 16. 2 = rancid smell and flavor weakened. would cause the packages to burst. 0. 62. 3 = little rancid smell but good flavor. showed that a FreshPax oxygen scavenger enclosed in a high gas barrier pouch made of polyester/aluminium foil/HDPE with baked.5 1. Ener-Getic. Stored: 25°C. marketed under the trade name Fresh Lock. their use in North America is still in its infancy. Japan.0 5 13.31.01 1.42 In the USA. More recently. a mold-free shelf-life of 1 year has been achieved for a specialty therapeutic gluten-free bread.1 2 1.0 4 9. Water activity: 0.5 23.2 3 6. This absorbent.7 28. Studies by Powers and Berkowitz (1990) at the US Army Natick Research. were minimal at the end of storage in the gluten-free bread (Anon.4 1.. 40 days Ageless O2(%) POV almond POV chocolate Flavor score O2(%) POV almond POV chocolate Flavor score 0. 4 = aroma slightly lost but good flavor.8 0.Table 6. The bread is packaged in a copolymer film of Mylar/EVOH/Surlyn film with 100% carbon dioxide and a Freshilizer oxygen absorbent/carbon dioxide generator (type CW) supplied by the Toppan Printing Company.7 Effect of an oxygen absorbent on the shelf life quality of chocolate-coated almonds. Sterling Foods .2 1.8% (chocolate). 1 = obvious rancid smell and flavor loss.9 4 3 months 0.3 POV almond 14. The bread remained mold-free for 1 year at room temperature and physico-chemical changes.2 7.0 Flavor score 2 Material: 20Og in an ON/PVDC/PE bag.1 1 6 months 0. Ageless: Z-50PK. i. The use of this absorbent in coffee delays oxidative flavor changes and absorbs the occluded carbon dioxide produced in the roasting process and. Based on the results of this study. While oxygen absorbents are used extensively in Japan..7 21. AC = acrylonitrile. EVAL = ethylene vinyl alcohol.85 0.92-0.6 0. PVDC = polyvinylidene chloride.9 0.9 Packaging materials KON KON KON KON KON KOP KON/Box PET/PVDC/PE KON KON KON/PS Tray PP/EVAL/KON/PE Type and size of Ageless S200 SIOO S200 SlOO FXlOO SlOO Z200 S50 S200 S10-15 ZPTl 00-200 S200 Prevents Mold growth/oxidation Oxidation/mold growth Mold growth Mold growth Moid growth Mold growth Oxidation Mold growth Mold growth Mold growth Mold growth Mold growth Shelf-life @ RT* 1 month 1 month 1 month 1 month 3-4 weeks 3-4 weeks 6 months 7-10 days 1 month 1 month 2 months 2-3 weeks *RT = Room temperature PET = polyester.Table 6.92 0.94 0.8 Use of Ageless for shelf-life extension of bakery products Type of food Cheesecake Buttercake Plain sponge cake Egg bread Pumpernickel bread Pita bread Tortilla chips Custard cakes Blueberry cheesecake Soy bean pie Bean/jam cake Steamed bean/jam cake Water activity of food 0. . KOP = PVDC-coated polypropylene.9 0.93 0. KON = PVDC-coated nylon. PP = polypropylene.9 0.86-0.88-0.9 0. PE = low-density polyethylene. PS = polystyrene.88 0.88-0.9 <0. 8 0.7-0.7-0.6-0.3°C 3 months 2 weeks at .88 0.3 0.8-0.99 0.8 0.Table 6.85 0.30C 6 months at -200C 1 month at 100C 1 month 3-6 months 6 months at .99 0.8 < 0.7-0.8 < 0.7-0.7 0.50C .6-0.8 < 0.98 Packaging materials PET/AC/PE KON KON KON KON/PET Tray KOP KON Nylon/PVDC/PP KON KON KON KON KON KOP Wood Tray/KON Type and size of Ageless ZlOO Z50 Z100-200 S200 S2000 ZlOO ZlOO SSlOO FXlOO ZlOO FXlOO TypeZ200+100%N 2 SSlOO Z200 SSlOO Prevents Oxidation/Discoloration Oxidation/Discoloration Oxidation Oxidation/Mold growth Oxidation Oxidation Oxidation/Mold growth Oxidation/Discoloration Discoloration Mold growth/Discoloration/Oxidation Oxidation/Mold growth Oxidation/Discoloration Discoloration Oxidation/Mold growth Discoloration/Bacterial growth Shelf-life @ RT* 1 year 3 months 6 months 1-2 months 1 month 6 months 3 months 1 week at .9 Use of Ageless for shelf-life extension of fish products Type of food Dried seaweed Dried salmon jerky Dried sardines Dried shark's fin Dried rose mackerel Dried cod Dried squid Fresh yellow taile Sliced salmon Dried/smoked salmon Dried octopus leg Dried bonito Salmon roe Dried squid/vinegar/ soybean sauce Sea urchin * RT = Room temperature Water activity of food <0.6 0.9 0.8 0. 5-0.99 0.99 0. RT = Room Temperature.6 0.94-0. Water activity of food <0.99 0.6 Packaging materials Tin/Plastic/Aluminium lid KON KON/Paper box KON KON KON Paper/AC/EVA Tin can Tin can KON Type and size of Ageless ZlOO GlOO Z200 Z30-100 FX50+100%N2 S30-50 FX20 ZlOO Z50 Z50 Prevents Oxidation/Rancidity Oxidation/Rancidity Oxidation/Rancidity Oxidation/Rancidity Oxidation/Rancidity Oxidation/Mold growth Discoloration Oxidation/Rancidity Oxidation Oxidation Shelf-life @ RT 1 year 6 months 9 months 9 months 1 month at 0-40C 1 month at 0-40C 3 months 6-12 months 1 year 1 year .99 0.8-0.Table 6.95 0.6 0.3 0.3 <0.3 0.5-0.9-0.8-0.5-0.11 Use of Ageless for shelf-life extension of miscellaneous products Type of food Rice crackers/fried bean Peanuts Peanut butter/chocolate coated Chocolate peanuts Candy-type cheese Smoked cheese Soy bean paste Bakery food (milk powder) Green tea Flavored tea EVA = ethylene vinyl acetate.9 0.85 Packaging materials KON KON KON PS Tray/KON KON KON KON Type and size of Ageless FX200 S200 FX50 SlOO FXlOO Z50 SlOO Prevents Mold growth Mold growth/Discoloration Discoloration/Rancidity Discoloration/Rancidity Discoloration/Rancidity Discoloration Discoloration Shelf-life @ RT 2 months at 50C 2 weeks at 50C 3 weeks at 0-40C 3 weeks at 0-40C 3 weeks at 0-40C 1-2 months 1 month Table 6.85 0.8-0.3 <0.95 0.10 Use of Ageless for shelf-life extension of meat and deli products Type of food Pizza crust Pizza Fresh carved sausage Pre-cooked hamburgers Pre-cooked chicken nuggets Salami slicks Sliced salami Water activity of food ~ 0.85 < 0. there is. 1986). when Ageless (Type S or Type FX) was packaged alongside crusty rolls. Clearly. there is an increasing interest by many companies. can tolerate and grow in < 1% (v/v) headspace oxygen even in the presence of elevated levels of CO2. 1986).Table 6. While the mold-free shelf-life of crusty rolls can be extended by packaging in 60% CO2 and 40% N2. More recently.2. tremendous interest and ongoing research in this innovative method of atmosphere modification. Although the use of oxygen absorbent technology has not been accepted commercially with the same enthusiasm in North America compared to Japan.3 Research activities in oxygen absorbent technology. While a longer extension in the mold-free shelf-life was possible using oxygen absorbents.4. either alone or in conjunction with gas packaging. This was due to absorption of headspace gas and package collapse resulting in some products being tightly wrapped with the packaging film.. read-to-eat uses Ageless oxygen absorbents to prevent rancidity and mold problems in packaged tortes (Table 6. . This clearly demonstrates the need for a free flow of gas around the product if Ageless is to be totally effective as an oxygen scavenger (Smith et al. mold growth still occurred after 19 days due to the oxygen permeability of the packaging film. in the use of oxygen absorbent technology as an alternative or adjunct to gas packaging to prevent the perennial problem of mold growth. This created pockets of localized environments between the product surface and the film where the oxygen concentration may have increased to a level sufficient to permit mold growth. however. 6. particularly baking companies. However. headspace O2 never increased beyond 0. the major spoilage isolates of crusty rolls. Studies have shown that Aspergillus and Penicillium species.. Ageless oxygen absorbents have been used in our laboratory to extend the mold-free shelf-life of fresh bagels and pizza crusts. Studies in our laboratory have shown oxygen absorbents to be three times more effective than gas packaging for increasing the mold-free shelf-life of crusty rolls (Smith et al. 1986). mold problems occasionally arose in the Ageless packaged product.12 Use of oxygen absorbent technology in USA _ _ Company General Foods Ener-G Foods Sterling Foods Franz Bakery The Famous Pacific Dessert Company 1 2 Product Maxwell House coffee Ener-Getic gluten-free bread MRE2 bread MRE bread/buns Fruit tortes (months @ RT1) 12-36 12 36 6 6-9 RT = room temperature MRE = meals.05% and the product remained mold-free for > 60 days at ambient storage temperature (Smith et al.12). Studies by Alarcon and Hotchkiss (1993) have shown that FreshPax oxygen absorbents can prevent mold growth in preservative-free white bread and low moisture. The use of absorbent technology for shelf-life extension of food has also been extensively studied by Cryovac. retail cuts of meat/poultry are packaged in trays with an oxygen permeable overwrap. 1986). This created pockets of localized environments between the product surface and the film where the oxygen concentration may have increased to a level sufficient to permit mold growth. Extensive research on Freshilizer absorbents has been conducted by Multiform Desiccants in conjunction with Dr Joe Hotchkiss at Cornell University. Cryovac in the US has been given the distribution rights to Ageless in North America by the Mitsubishi Gas Chemical Company. Other areas of applied research by Cryovac involving oxygen absorbents include prevention of rancidity problems in snack food. In the MasterPak. low fat mozzarella cheese for 8 weeks at .with the packaging film. the use of specific types of absorbents appeared to have an anti-staling effect on bagels. prevention of flavor changes in wine stored in oxygen permeable PET bottles using a barrier pouch overwrap with an oxygen absorbent. Oxygen absorbent technology has also been investigated to inhibit mold growth and rancidity problems in fresh pasta and pizza crusts. gas flushed and heat sealed and distributed under refrigeration to the retailer where the individual packs are removed from the MasterPak and displayed on retail shelves. Using a combination of oxygen absorbent technology and Cryovac's high barrier shrink film. This latter concept is in response to consumer concerns about absorbents being visible inside the packaged food product. Color or 'bloom' returns to the meat/poultry due to the low barrier characteristics of the overwrap. More recently. discoloration and flavor changes in cooked cured sausage.. The system is then evacuated. and master packaging of fresh meat and poultry. These are placed inside a cardboard carton with a high gas barrier film and absorbents added.3% before products are exposed to retail display lighting. cooked poultry and smoked poultry chops. a world leader in vacuum packaging technology. Ageless oxygen absorbents have been used in our laboratory to extend the mold-free shelf-life of fresh bagels and pizza crusts. Furthermore. Further studies are now underway to compare the anti-staling effects of oxygen absorbents with other methods of atmosphere modification for shelf-life extension of bakery products. Thus. This clearly demonstrates the need for a free flow of gas around the product if Ageless is to be totally effective as an oxygen scavenger (Smith et a/. oxygen absorbent technology can be used to inhibit photodegradation of meat pigments in cured meat products thereby enhancing consumer appeal for such products (Cryovac. Researchers at Cryovac have found that oxygen absorbent technology can be used to prevent mold growth. personal communication). headspace oxygen (which can reach 4-7% due to entrapped oxygen in the foam tray) is reduced to < 0. ambient/refrigerated temperature. Furthermore, oxygen absorbents were also effective in reducing the oxidative formation of rc-hexanal (an indicator of off-flavor development) in both sunflower seeds and cornchips. Sensory panel analysis also showed that absorbents inhibited the formation of undesirable rancid odors during accelerated storage tests (Alarcon and Hotchkiss, 1993). These authors also reported that FreshPax oxygen absorbents were also effective in controlling permeated oxygen, and hence iiiold growth ai/id rancidity problems, in bread and cheese packaged in jnedium barrieij films with an OTR of about 32 ml/m2/day. Therefore, medium barrier] films could be substituted for a high barrier and more expensive film if an oxygen absorber pack was included in the package (Alarcon and Hotchkiss, 1993). 6.2.5 Advantages and disadvantages of oxygen absorbents Oxygen absorbents have several advantages for the food processor, both from a marketing and food quality viewpoint (Harima, 1990; Smith et ai, 1990; Smith, 1992). These are: Inexpensive and simple to use. Approved by the US Food and Drug Administration as non-toxic and safe to use. • Prevent aerobic microbial growth and extend shelf-life of product. • Arrest the development of rancid off-flavor in fats and oils. • Maintain flavor quality by preventing oxidation of the flavor compounds. • Maintain product quality without additives. • Increase product shelf-life and distribution radius. • Allow a long time between deliveries and allow fewer, longer deliveries. • Increase length of time product can stay in the distribution pipeline. • Reduce distribution losses. • Replace chemical pesticides to prevent insect damage of foods. • Reduce evacuation/gas flushing times in gas packaged products thereby increasing product throughput. • Reduce costs required for gas flushing equipment. A few of the disadvantages of oxygen absorbents are (Harima, 1990; Smith et aL, 1990; Smith, 1992): • • There needs to be a free flow of air surrounding the sachet in order to scavenge headspace oxygen if an O2 absorbent is used alone. May cause package collapse; this can be overcome by using an O2 absorbent/CO2 generator. • • • • • • O2 absorbents/CO2 generators may cause flavor changes in high moisture/fat foods due to the dissolution of CO2 in the aqueous/fat phase of product. Cost - approximately 2.5-10 cents per sachet depending on size of sachet and volume ordered. Many processors regard oxygen absorbent sachets too expensive. Consumer concerns about sachets inside the packages and possible consumer misuse of sachets. May promote growth of potentially harmful anaerobic bacteria. The two latter concerns will be briefly discussed. 6.2.5.1 Consumer resistance to sachets. The two main consumer concerns about sachets being placed inside the packaged food product are: fear of ingestion even although the contents are safe and the label clearly says 'Do not eat'; and spillage of sachet contents into food and consequent adulteration of the food product. These concerns have been addressed by the Mitsubishi Gas Chemical Company by producing the deoxidizer in a tablet form or in a board form and affixing it to the lid or to the bottom of packages. This approach has been successfully used for health foods sold in bottles and with individually wrapped teacakes in the Japanese marketplace. An alternative method is to package the primary packages inside a secondary packaging containing the absorbent. This is the principle behind the MasterPak system, i.e., bag-in-box system, designed to hold 12-48 consumer-size primary packages made of material with a higher oxygen transmission rate than for secondary containers, as discussed in the previous section. The main advantage of this approach is that the consumer never sees the absorbents, thus eliminating the possibility of consumers misusing the packets or reacting negatively to the absorbents (Smith, 1992). Another approach to overcome consumer resistance to sachets is to incorporate the oxygen scavenging capacity in the form of a package label. This approach has been developed by both Mitsubishi Gas Chemical Company and Multiform Desiccants. This latter company currently markets both Type B and Type M absorbents in the form of labels marketed under the trade name FreshMax. This label can be backed with various adhesives for different product applications. The technology has a printed surface and is contact acceptable (oil/grease resistant). The label can be applied at conventional line speeds and is compatible with both moist and dry food products. The prototype FreshMax is 2.5" x 2.5" and 15 mil thick. It is capable of absorbing 100 ml of oxygen in 24 h and can be made into various shapes. The labels can reduce headspace oxygen to less than 0.01% (100 ppm) and can be used to retard both chemical and microbiological spoilage in stored products. Marks & Spencer Ltd., London are now using FreshMax labels to extend the shelf-life and keeping quality of deli meats. The new labels cover only one third of the lid surface, providing consumers with a clearer view of the product yet absorb oxygen and protect products from the adverse oxidizing effect of light and oxygen on meat pigments (Multiform Desiccants, personal communication). 6.2.5.2 Public health concerns. Another consumer and regulatory concern about oxygen absorbent technology is that the anaerobic environment created inside the package may be conducive to the growth of facultative anaerobic or strictly anaerobic food pathogens. These concerns are justified in view of the ability of many food pathogens to grow at refrigerator temperatures, e.g. Listeria monocytogenes and Clostridium botulinum type E; the inhibition of aerobic microorganisms as indicators of spoilage; and the potential for temperature abuse. Recent studies have shown that average temperatures of retail cases in supermarkets were about 12°C while temperatures of domestic refrigerators ranged from 2 to 200C (Palumbo, 1986). Nakamura and Hoshino (1983) reported that an oxygen-free environment alone was insufficient to inhibit the growth of Staphylococcus aureus, Vibrio species, Escherichia colif Bacillus cereus and Enterococcus faecalis at ambient storage temperature. For complete inhibition of these microorganisms they recommended combination treatments involving oxygen absorbents with thermally processed food or refrigerated storage or a CO2 enriched atmosphere. Using this latter combination, i.e., low O2-high CO2 gas atmosphere, they found that this modified atmosphere inhibited the growth of S. aureus and E. coli but promoted the growth of E. faecalis. While low levels of CO2 (20%) failed to inhibit the growth of B. cereus, higher concentrations (100%) completely inhibited the growth of this microorganism in an oxygen-free environment. When similar studies were done with Clostridium sporogenes, some interesting results were obtained, as shown in Table 6.13. These studies demonstrated that an O2/CO2 absorbent will inhibit the growth of C. sporogenes while an O2 absorbent-CO2 generator will enhance its growth, indicating the importance of selecting the correct absorbent to control the growth of Clostridium species in MAP food. In challenge studies with C. botulinum type A and B spores, Lambert et al. (1991a) observed that Table 6.13 Effect of various gas atmospheres on the growth of C. sporogenes (adapted from Nakamura and Hoshino, 1983) Packaging conditions _ Ageless oxygen absorbent generating carbon dioxide Ageless oxygen absorbent not absorbing carbon dioxide Ageless oxygen absorbent absorbing carbon dioxide Growth of C. sporogenes _ 4+ 2+ 1+ - = no growth; 1+ = slight growth; 2+ = medium growth; 3+ = heavy growth; 4+ = extensive growth. package headspace was not significant in affecting the time until toxin production (Lambert et al, 1991b,c). In more recent agar plate studies with Listeria monocytogenes, high CO2 levels (> 60%) promoted the growth of this pathogen at 10-150C (Morris et al, 1994). However, when an oxygen-free environment was achieved using Ageless SS, growth of L. monocytogenes was completely inhibited even at mild temperature abuse storage conditions. Further studies are now underway to determine the antimicrobial efficacy of Ageless SS and gas packaging on L. monocytogenes in packaged pork. 6.2.6 Effect of oxygen absorbents on afiatoxigenic mold species While the use of oxygen absorbent technology may fail to completely inhibit the growth of facultative or strictly anaerobic pathogenic bacteria, it is very effective in controlling the growth of Aspergillus flavus and Aspergillus parasiticus. In inoculation studies with these aflatoxigenic molds in peanuts packed in air alone and with an oxygen absorbent, mold growth and aflatoxin were completely inhibited in absorbent packaged peanuts while ~1000 ppb (1000 ng) of aflatoxin B1 were detected in all air-packaged samples after only 6 days at room temperature (Ellis et al, 1993). Similar control of A. parasiticus has also been reported in inoculation studies with peanuts using oxygen absorbent technology (Ellis et al, 1994). However, this control was dependent on both the OTR of the packaging films used and storage temperature. While packaging in high-medium barrier films inhibited aflatoxin B1 production, aflatoxin was detected in all absorbent packaged peanuts using a low barrier film (OTR -4000 ml/m2/day). However, when absorbent packaged peanuts were packaged in medium barrier films (OTR - 5 0 ml/m2/day), aflatoxin production occurred in all peanuts stored at 300C (Ellis et al, 1994). This was attributed to the greater permeance of the film to oxygen at higher storage temperatures, resulting in saturation of the absorbents, a concomitant increase in headspace oxygen, and subsequent mold growth and aflatoxin production. Similar results were obtained with a CO2 generating oxygen absorbent (Ageless G), indicating the importance of packaging film permeability to ensure the efficacy of oxygen absorbents and the public health safety of absorbent packaged peanuts. 6.3 Ethanol vapor The use of ethanol (ethyl alcohol) as an antimicrobial agent is well documented. Alcohol was used by the Arabs over 1000 years ago to preserve fruit from mold spoilage. However, alcohol is most commonly recognized as a surface sterilant or disinfectant. In high concentrations (60-75% v/v), ethanol acts against vegetative cells of microorganisms by denaturing the protein of the protoplast (Seiler and Russell, 1993). Lower concentrations of alcohol (5-20% v/v) have also been shown to have a preserving action against food spoilage and pathogenic microorganisms in agar model systems. In tests with surface inoculated agar medium containing concentrations of ethanol ranging from 4 to 12% (v/v) ethanol was shown to be effective in controlling 10 species of mold including Aspergillus and Penicillium species; 15 species of bacteria including S. aureus and E. coli; and 3 species of spoilage yeasts (Freund Technical Information, 1985). Most molds were inhibited by 4% ethanol while yeasts were more resistant and required 8% ethanol for complete inhibition. However, S. aureus required 12% ethanol for complete inhibition (Freund Technical Information, 1985). Shapero et al. (1978) reported that the effectiveness of ethanol against S. aureus was a function of water activity (aw). They reported that in broth media adjusted to aw 0.99, 0.95 and 0.9 with glycerol, inhibition of S. aureus occurred at 9, 7 and 4% of ethanol respectively. A similar synergism between aw and the antimicrobial efficacy of ethanol against A. niger and R notatum has been observed by Smith et al. (1994). In studies with unadjusted Potato Dextrose Agar (PDA) plates a concentration of 6% ethanol was required for complete inhibition of these common mold contaminants of bakery products. However, complete inhibition of A. niger and P. notatum was observed with 4 and 2% of ethanol respectively in plates adjusted to aw 0.95 and 0.9 with glycerol. These results confirm previous observations that lower concentrations of ethanol can be used to extend the mold-free shelf-life of food products with a low aw. The antimicrobial effect of low concentrations of ethanol for shelf-life extension of bakery products has also been demonstrated. Plemons et al. (1976) showed that the mold-free shelf-life of pizza crusts could be extended for about 20 weeks at ambient temperature by spraying the crusts with 95% ethanol and overwrapping in a large unsealed polyethylene bag (Seiler, 1978; Seiler, 1988). Seiler and Russell (1993) also reported a 50-250% increase in the mold-free shelf-life of cake and bread sprayed with 95% ethanol to give concentrations ranging from 0.5 to 1.5% by weight of product. Both these studies indicate the potential of ethanol as a vapor phase inhibitor. However, a more practical and safer method of generating ethanol vapor is through the use of ethanol vapor generating sachets, which will now be discussed in greater detail. 6.3.1 Ethanol vapor generators A novel and innovative method of generating ethanol vapor, again developed by the Japanese, is the use of ethanol vapor generating sachets or strips. These contain absorbed or encapsulated ethanol in a carrier material and enclosed in packaging films of selective permeabilities which allow the 3 g of ethanol.15 Types of alcohol generators _ Type Ethicap (Antimold 102) Negamold Function Generates EtOH vapor Absorbs O2 Generates EtOH vapor Application Moisture dependent Cakes/ Bread Moisture dependent Cakes/ Bread _ products > 0.85 > 0. like its competitor.33 to 3.14). again developed by the Japanese. which can be evaporated.6 to 6 G or 0. To mask the odor of alcohol. Negamold. Ethicap consists of food grade alcohol and water (55% and 10% by weight respectively) adsorbed on to silicon dioxide powder (35%) and contained in a sachet made of a laminate of paper/ethyl vinyl acetate copolymer. Ageless type SE. Another type of ethanol vapor generator is Negamold (Table 6.I Ethanol vapor generators A novel and innovative method of generating ethanol vapor. and the desired shelf-life of product. These contain absorbed or encapsulated ethanol in a carrier material and enclosed in packaging films of selective permeabilities which allow the slow or rapid release of ethanol vapor. Sachet sizes of Ethicap range from 0. then a 2 G size of Ethicap Table 6. with the most commercially used system being Ethicap or Antimold 102 produced by the Freund Industrial Co.6. can be used to extend the shelf-life and keeping quality of bakery products. For example. Ltd.. which scavenges oxygen as well as generating ethanol vapor. However. is the use of ethanol vapor generating sachets or strips.. This interrelationship is shown in Figure 6. some sachets contain traces of vanilla or other flavors as masking compounds. Negamold is not widely used since it does not generate as much ethanol vapor as Ethicap (Freund Technical Information. The actual size of the sachet used depends on the weight of food. Several Japanese companies produce ethanol vapor generators. aw of food. if the aw of the product is 0.95 and a 1-2 week shelf-life is desired.85 .14 Manufacturers of ethyl alcohol generators Trade name Antimold (Ethicap) Negamold Oitech ET Pack Manufacturer Freund Freund Nippon Kayaku Ueno Seiyaku Sachets/yr 60m 9m 1m Entered 1978 1982 1980 1988 6J. 1985).Table 6. Japan (Table 6. The sachets are labelled 'Do not eat contents' and include a diagram demonstrating this warning.15). .5% v/v at a water activity of 0. 1-2 weeks. 1987)..7. Smith et al. moisture is absorbed from the food.7% v/v at a water activity of 0.85 (Smith et al. and ethanol vapor is released from encapsulation and permeates the package headspace. 8-13 weeks.85 with glycerol and packaged in a film of low ethanol vapor permeability with a 1 G and 4 G (E1 and E4) size of Ethicap respectively. E4 (Smith et al. When food is packed with a sachet of Ethicap.1 g ethanol) should be used per 100 g of product. However.2% v/v at the highest water activity under investigation and remained at these levels for the duration of the storage period (Smith et al. if a longer shelf-life is desired (2-3 months). However. Ltd. as shown in Figure 6. higher trend was noted for headspace ethanol generated from 4 G of Ethicap. Japan. and absorption of ethanol from. (1987) examined this relationship in PDA plates adjusted to aw 0.6 Relationship between aw of food and required size of Ethicap sachet.99 to 0.4% v/v at a water activity of 0.85 compared to 0. These studies indicated the importance of product aw on the vaporization of ethanol into. after 7-10 days' storage. (Reproduced with permission from the Freund Technical Co. long term.(~ 1. a 4 G size of Ethicap should be used for the same product (Freund Technical Information. A similar.95 and 0.) . 1987). the package headspace. the level of headspace ethanol generated from a 1 G sachet of Ethicap (E1). Short term. both the initial and final level of ethanol vapor in the package headspace is a function of sachet size and water activity.. headspace ethanol was approximately 0. 1987). However. After day 1.. ranged from 0. Required sachet size of ETHICAP® per 10Og of food for long term for short term Water activity of food Figure 6. 1985). 95 + E1.O Z < Z Ul Ul O (0 -I* Ul X S DAYS STORAGE 25 *C Figure 6. A 5-20 times extension in mold-free shelf-life has been observed for high ratio cakes depending on the size of Ethicap used (Freund Technical Information. Another important factor in using Ethicap as a food preservative is to package the product in a film with a high or medium barrier to ethanol vapor. 0. A 0. Generally. 0. o. 0. o. •.7 Effect of water activity (aw) on generation and absorption of ethanol vapor. The ethanol vapor permeabilities of appropriate packaging materials are shown in Table 6. 0. 1985). Results also showed that products with sachets did not get as hard as the controls and results were better than those using an oxygen scavenger to .85 + E1. 0. 6.*. a film with an ethanol vapor permeability of < 2 g/m2/day @ 300C is recommended (Freund Technical Information.2 Uses of Ethicap for shelf-life extension of food Ethicap is used extensively in Japan to extend the mold-free shelf-life of high ratio cakes and other high moisture bakery products.99 + E1.95 + E4.16.3.99 + E4. 1985). •.85 + E4. 76 0.17.7 8. However.8 2. 1985).92 0. 1985") Food Bakery products Bread Cupcake Jam doughnut American cake Rice cake Chocolate sponge cake Fish products Smoked squid Boiled squid Boiled & dried squid Boiled & dried small fish 0.1 4.63 IG 0. PP = cast polypropylene. indicating that the ethanol vapor also exerts an antistaling effect (Freund Technical Information.9 1.0 1.0 56. LDPE = low-density polyethylene.0 4.2 1.1 PVDC = polyvinylidene chloride.72 IG 3G 3G 2G 4G 2G OPP OPP/PP OPP OPP/PP OPP/PP OPP/PP 1 week 2 months 20 days 6 months 2 months 6 months aw of food Size of Ethicap Packaging material Shelf-life @ RT . inhibit mold growth.80 0.5 1.16 Ethanol vapor permeability of certain plastic films (adapted from Freund Technical Information. Pafumi and Durham (1987) also found that the mold-free shelf-life of 200 g Madeira cake could be extended for about 6 weeks at room temperature using a 3 G sachet of Ethicap. there was a significant change in Table 6.85 0.85 0.6G IG OPP OPP OPP/PE OPP 3 3 2 3 months months months months 0. 1985) Film _ _ _ _ _ OPP/EVOH/LDPE PVDC/PET/PP PVDC/OPP/PP AL/PET/LDPE PP/PVDC/PP PET/PP OPP/PP HDPE OPP PP LDPE EVA/LDPE Ethanol vapor permeability (g/m2/day) @ 300C ___ 0. OPP = oriented polypropylene.83 0. PET = polyester.0 19.69 0. HDPE = high-density polyethylene.17 Use of Ethicap for shelf-life extension of food (adapted from Freund Technical Information. PA = nylon.6G 0.Table 6. Ethicap is also widely used in Japan to extend the shelf-life of semi-moist and dry fish products. AL = aluminium. EVA = ethylene vinyl acetate.8 0.68 0. Examples of bakery and fish products preserved by Ethicap in the Japanese market are shown in Table 6. 1993). a 6 G Sachet of Ethicap failed to inhibit yeast spoilage in cherry cream cheese cake (Ooraikul. Indeed. it failed to eliminate the stale flavors in the pita bread (Black et al. While the effect of increased firmness due to staling was reversed by microwave heating. Therefore. 1987). these authors reported that ethanol vapor had little anti-staling effect on pita bread. However. The authors also observed a slight increase in headspace oxygen in all gas packaged products stored with Ethicap. . when Ethicap (E4) was incorporated into the packaged product either alone or in conjunction with gas packaging. Indeed. and CO2 production by. However. are required to inhibit yeast growth compared to mold growth. Ethicap has also proved effective in controlling secondary spoilage problems by 5. had a shelf-life of 14 days when packaged in a CO2: N2 (60:40) gas mixture at ambient temperature due to growth of and CO2 production by Saccharomyces cerevisiae. cerevisiae in both strawberry and vanilla layer cakes. cerevisiae in gas packaged strawberry and vanilla layer cakes and cherry cream cheese cake. agar model studies have shown that yeasts can grow in media containing 8% (v/v) ethanol while most molds were inhibited by 4% ethanol (Freund Technical Information.93. 1987). yeast growth was completely suppressed and all packages appeared normal at the end of the 21-day storage period (Smith et al. the sensory quality of the product was not significantly extended (Pafumi and Durham. 1993). such as ethyl paraben.quality after 3 weeks. while Ethicap could be used to extend the mold-free shelf-life of the product. to control secondary yeast fermentation problems in cherry cream cheese cake (Ooraikul. characterized by a loss of moistness and firmness of the texture and development of soapy and rancid flavors. However. Ethicap has also been used as a means of further extending the shelf-life of gas packaged apple turnovers (Smith et al. Ooraikul (1993) reported that the aroma of the cake packaged with Ethicap was more pleasant than that of the fresh cake and that the taste also remained excellent. These studies show that larger sizes of Ethicap. This size of the Ethicap sachet had no adverse effect on the organoleptic quality of cakes. 1987). 1993). They hypothesized that the ethanol vapor may have dissolved in the film and acted as a plasticizer. 1985). They reported a 14 day mold-free shelf-life for pita bread packaged in 40% CO2 (balance N2) or 100% CO2. thereby affecting the permeability of the film to both oxygen and carbon dioxide (Black et al.. the shelf-life was doubled when an Ethicap sachet was incorporated into the gas packaged products (Black et al. However. He recommended a 7-8 G sachet of Ethicap in conjunction with a preservative. Ooraikul (1993) reported that 5 G sachets of Ethicap inhibited growth of. 1993). Apple turnovers. with a water activity of 0. and hence higher levels of ethanol vapor. 5. 1993). Black et al (1993) examined the combined effect of gas packaging and Ethicap (size unknown) to extend the shelf-life of pita bread. These studies clearly illustrate the antibacterial properties of ethanol when incorporated directly into media or a food product. while a longer shelf-life may be possible by packaging product with Ethicap.1% by heating product at 375° F prior to consumption. delayed the onset of 'rope' caused by the growth of Bacillus subtilis. the level of ethanol in apple turnovers can be reduced to < 0. They observed that a 4 G sachet of Ethicap could control the growth of L.5-1% by product wt.45-1.. 1978). Another disadvantage is cost. which limits its use to products with higher profit • . the latter storage conditions representing mild temperature abuse. However. A disadvantage of using ethanol vapor for shelf-life extension is its absorption from the package headspace by product. a psychrotrophic food-borne pathogen of public health significance. More recently..52%) was within the maximum level of 2% by product weight when ethanol is sprayed onto pizza crusts prior to final baking (Smith et al. its use as a food preservative may be limited to 'brown & serve' or microwaveable products. 1985.633 Effect of ethanol vapor on food spoilage/food poisoning bacteria While most studies to date have focused on the use of Ethicap as an antimycotic agent. Morris et al. (1987) the advantages of Ethicap are: Ethanol vapor can be generated from sachets without having to spray ethanol directly onto product surface prior to packaging. the concentration of ethanol found in apple turnovers (1. Seiler and Russell (1993) also reported that ethanol at a level of 1% by product wt. Further studies are now underway to determine the volume of ethanol vapor generated at these storage temperatures and the effect of these concentrations on the microbiological and chemical shelf-life of fresh packaged pork. monocytogenes (Scott A) on agar media at 5. • Sachets can be conveniently removed from packages and discarded at the end of the storage period. Ethanol. Shapero et al. when incorporated into agar media. • It eliminates the need for preservatives such as benzoic acid or sorbic acid to control yeast spoilage. has proved to be effective against several spoilage and pathogenic bacteria (Freund Technical Information.) inhibited bacterial growth in both whipping cream and custard.. two wellknown vectors of food poisoning bacteria in filled bakery products. 10 and 15°C. few studies have evaluated its potential to control food spoilage and food poisoning bacteria. Therefore. • It can control mold spoilage and delay staling in bakery products. They also reported that low concentrations of ethanol (0. 63 A Advantages and disadvantages of ethanol vapor generators According to Smith et al. 1987). However. (1994) examined the effect of Ethicap on the growth of Listeria monocytogenes. Simpson. 72.D. Freund Industrial Co. K. Dept. 54. A.D. B.H. S. Y. 149-58. J. (1991c) Effect of initial O 2 and CO2 and low-dose irradiation on toxin production by Clostridium botulinum in MAP fresh pork. J. Academic Press PubL. and Hotchkiss. Kuzyk. Smith. FreshPax Technical Pamphlet (1994) Protect and preserve your products and profits with FreshPax. B.. 939-44. and Doyon.. irradiated fresh pork.P. M. 8. Khanizadeh. Alarcon. J. Food Research International. K. Academic Press PubL.. (1993) Control of growth and aflatoxin production by Aspergillus flavus under modified atmosphere packaging (MAP) conditions..J. A. Lambert. Simpson.P.L.. Anon. / . and Nakamura. References Abe.K.. Food Australia. Smith. 6. 70. Freund Technical Information (1985) No-mix-type mould inhibitor Ethicap. 54.. L. 588-92.. and Kondoh. G. (1994) Effect of films of different gas transmission rates on aflatoxin production by Aspergillus flavus in peanuts packaged under modified atmosphere packaging (MAP) conditions. Reyes. Food Protection.G. Minakuchi. J.P. Ltd. (1990) Food Packaging. and Dodds. Food Protection. J. H. pp.4 Conclusion In conclusion. M.P. pp. one of the most exciting interactive packaging technologies available to the food industry. 54. / . consumer resistance to the inclusion of sachets in packaged products and lack of regulatory approval for Ethicap. pp. and Ruddick. Smith. 9-21. Technical Report. London. (1991b) Effect of headspace CO2 on toxin production by Clostridium botulinum in MAP. Nevertheless. 10. Buffalo. Food & Nutrition Press PubL. 505-12. 1-7.. Multiform Desiccants. 97-104.O. Smith. Cornell University. Harima. Ethicap is a viable alternative or supplement to gas packaging to extend the shelf-life of baked bakery products in relation to both mold and yeast spoilage and to prevent staling.O. and Dodds. Tokyo.K. Ellis. 387-91.L. Japan. Food Protection. Trumbull. Y. Lambert. (1989) Controlled/Modified Atmosphere/Vacuum Packaging of Foods. Nevertheless. their use to date in the North American market is limited due to the cost of the sachets.. R. NY. While both oxygen absorbent technology and ethanol vapor generators are used extensively in Japan to extend the shelflife and keeping quality of a variety of products. 1-14. 357-78.H. the use of gas absorbents/ ethanol vapor generator sachets or labels offers the food industry a more viable alternative method of interactive packaging than vacuum/gas flushing for shelf-life extension of its products. (1993) Shelf-life extension of pita bread by modified atmosphere packaging.D.P. (1993) The effect of FreshPax oxygen-absorbing packets on the shelf-life of foods.. . and Dodds. Smith. S. (1991a) Combined effect of modified atmosphere packaging and low-dose irradiation on toxin production by Clostridium botulinum in fresh pork. London. A. (1990) Food Packaging. Quail. pp.. J. (1988) Ener-Getic all year long. Food Microbiology. 45. B.margins. NY. K. W. 75. Ellis. the use of gas absorbents and ethanol vapor generators is. UK. Y. Lambert.. and Oldham. Packaging Digest. Black. K. without doubt. of Food Science. CT. 229-52. / . 27. J. UK.L. W. 78-82. (1993) Food Preservatives. 286-7. WJ. 4. 39. and Durham. Japan. B. Shapero. D.. Ooraikul. J. 2.P. Koersen.. pp. and Hoshino. I. Pafumi.. (1976) Process for retarding mold growth in partially baked pizza crusts and articles produced thereby. Rooney. Nakamura. Blackie Academic & Professional. (1988) Fresh red meats: a place to apply Modified Atmospheres..R.R. F. Smith. In: Proceedings of the First Japan-Australia Workshop on Food Processing. and Cole. Japan. Ramaswamy. Food Microbiology. 153-71. London. J.P. E. (Submitted for publication). 43. .M. A. and Jackson.. 767-71. NY. and Lawrence. Nelson.. (1986) Novel approach to oxygen control in modified atmosphere packaging of bakery products. H. B. Ellis Horwood Publ. Smith.. pp. Part 2: Storage aspects. Toppan Technical Information (1989) Freshness keeping agents.. J. UK. D. Lyver. Tsukuba. /. Palumbo. 53. Seiler. pp. Smith.P.) (1993) Modified Atmosphere Packaging of Food.A. (1990) Developments in food packaging technology.L. J.. M.A. L. Toppan Printing Co. UK.A. 48. 65-9. (1986) Is refrigeration enough to restrain food borne pathogens? /. R. (1987) Shelf life extension of a bakery product using ethanol vapor.B. and Cameron. Staff. 339-44. 49. J. Food Technology.L. Reviere. R. (1994) Effect of ethanol vapor on the growth of common mold contaminants of bakery products.. H.D. (1992) Reactive Packaging Materials for Food Preservation. Smith. van de Voort. /. D. Food Science.. R. 42. 329-37. E.F.A. Glasgow. Jackson. 37-41.P. pp. Academic and Professional Publ. Koersen. and Morris. 1003-9. T. Smith. Ooraikul. 112-19. Food Technology in Australia. D..D. Mitsubishi Gas Chemical Co. and Berkowitz.. Food Trade Review. and Simpson. B. J.A. 134-69. Food Microbiology.. S. Ooraikul.D. Seiler. (1990) Efficacy of an oxygen scavenger to modify the atmosphere and prevent mold growth in meal. F. Japan. Trends in Food Science and Technology. (1983) Techniques for the preservation of food by the employment of an oxygen absorber. Young. 49-117. Tokyo. (1994) Combined effect of chitosan and MAP on the growth of Listeria monocy togenes. (1988) Microbiological problems associated with cereal based foods. Tarte.. US Patent 3979525.Morris. J. (ed.P. Food Science and Technology Today. and Labuza. Ltd. (Submitted for publication). (1978) The microbiology of cake and its ingredients. Food Microbiology. 315-20. J. Food Protection. Powers. M.Principles and Applications. New York. J. R. and Farber. Plemons.K. and Russell. WJ.P. 1. 1-8. 3. D.. ready-to-eat pouched bread.A. CH.P. NJ. Seiler. J. B. (1992) MAP Packaging of Food . E. 1467-9. Smith.L. A. 1-45. (1987) Cake shelf life extension. Tokyo. Food Microbiology. Food Protection.L. (1978) Ethanol inhibition of Staphylococcus aureus at limited water activity. pp. J.. as one or more variables are changed. usually in an irreversible manner. enzymes will function to catalyze chemical. in catalytic processes physiochemical or chemical reactions occur in which the catalyst remains effective and intact.A. When the proper enzymes are introduced under the proper conditions. 7.L.1 Enzymes Enzymes are biological catalysts which are found in all living cells. However. they are capable of catalyzing reactions which can either prevent the product from being changed or extend the function of packaging beyond its accepted or previously understood functions by actively serving as a processing unit. whether plant or animal. with the result that the active component is effectively consumed or changed as the internal package environment is changed. accelerate chemical reactions but are not consumed as a result of the reactions. opens.7 Enzymes as active packaging agents A. contracts. or more specifically biochemical. Enzymes accelerate chemical reactions that occur in biological systems by factors that exceed a million over their uncatalyzed rate. closes. Within limits. In chemical or physiochemical reactions. A simple reaction of the formation of carbonic acid from carbon dioxide and water occurs 107 times faster with the enzyme carbonic anhydrase than the nonenzymatic or chemical reaction. These macromolecular proteins exhibit two outstanding characteristics in addition to the fact that they occur naturally and are found in living systems. The first characteristic is their catalytic power. for as long as reactants or substrates are present. Enzymes. In essence. reactions. . etc. a component of the total package reacts with the package structure or component. enzymes allow living systems to carry out reactions that would not ordinarily occur or occur so slowly that the rates would not be of any practical significance. In a physical action. which is usually external. BUDNY This chapter discusses the role of enzymes in active packaging. Almost all mechanisms in which packaging structures function in response to a stimulus involve physical. chemical or physiochemical actions. the active element of the material. expands. which are biological catalysts. BRODY and J. especially as oxygen scavengers. As with all catalysts. The catalytic potential of enzymes and the speed at which they facilitate chemical reactions lies in their ability to reduce the Gibbs Free Energy of Activation (Ea). followed by the release of the product which generates the free enzyme again. the enzyme reacts with another reactant or substrate molecule.. The kinetics of enzyme reactions are obviously of great importance in considering their potential commercial applications. Consequently. and the rate of conversion of reactant to product plateaus at the maximal reaction rate or velocity. . When all of the enzyme exists as ESC. there is a unique enzyme required for the optimal production of reaction products. shape and type of substrates or reactants which can be catalyzed by the enzyme. enzymatic reaction rates are linear with time until all of the free enzyme is used to form the ESC. it follows that there are many different enzymes. or as soon as the product is formed. it is not surprising that the active site represents only a small percentage of the total enzyme. The participation. It is also not surprising that the polymeric catalysts are three dimensional. and for any type of chemical reaction. a specificity for the reactant or substrate. This spatial characteristic of the active site defines the size. An enzyme increases a forward reaction in the same way and to the same extent that it increases the reverse reaction. With so many different biological reactions.e. and hence the reactivity. At the outset. enzymes accelerate the rate at which a chemical equilibrium is reached but an enzyme does not distort the ratio of the equilibrium concentrations of the products to reactants. Enzymes accomplish their catalytic objectives. for each chemical reaction that occurs in a biological system. Because enzymes are high molecular weight polymers which are made up of amino acids. Once the initial velocity has been achieved. enzymes do not alter equilibrium conditions.The second important characteristic of enzymes is their specificity. The active site is an area or region of an enzyme where the bond-breaking and bond-forming of the reactants and products occur. i. and consequently the active site has a size (volume) shape to it. Enzymatic specificity takes on two distinct forms: the type of chemical reaction. This new or different transition state is the enzyme-substrate complex (ESC) where the reactant becomes associated or bound to the free enzyme at the reactive center or site. all of the enzyme exists as the ESC. The now free enzyme is once again available to combine with another molecule of reactant to repeat the process. The net effect of this sequence is that reactant or substrate becomes product and the enzyme is unchanged. not by reducing the Ea of the uncatalyzed reaction but by creating a new and different transition state and hence a different reaction path or mechanism. of an enzyme for a particular substrate-product pair is determined by the amino acid sequence and the geometric or spatial arrangement of the enzyme. to cite a few. proteases in laundry detergents to assist in protein stain removal. these are designations for broad families to break proteins of entities that are specific to a single protein or lipid under a particular set of circumstances. For in-package situations. Enzymes are proteins whose reactivity is quite sensitive to temperature. or placing it in a static position where it may function for an indefinite period. juice extraction from fruits and production of flavor enhancers. Active packaging in general often involves the incorporation of a . Other. An enzyme suitable for a single 16 carbon fatty acid oxidation reaction will not catalyze an 18 carbon fatty acid oxidation even though the actual reactions at the sites may be identical. in reality. the enzyme must be immobilized and the substrate. the catalytic reactivity of the enzymes may be temporarily or permanently disrupted. reactant or a constituent circulated past the site to initiate a reaction. various oxidases to accelerate oxidative reactions. This characteristic may be viewed as beneficial in that only the specific reaction and no other is catalyzed by the enzyme. etc. the enzyme may be added directly to the product to effect a reaction or may be incorporated into the package structure. Among the many enzymes functioning in reactions that have been and are being used commercially are rennin (chymosin) to precipitate the casein of milk in cheese making. enzymes may be viewed as chemicals to be added to the product to catalyze a reaction as one way to affect batch processing. beer and wine fermentation. more generic applications of enzymes include stereospecific amino acid production. milling and baking. This temperature sensitivity is an important consideration in the commercial application of enzymes in processing operations. 7.Although enzymes may be classified according to the substrates they affect. tenderizing meats. On the other hand. amylase to convert starch to sugar for brewing. and catalase to remove hydrogen peroxide that might be formed during prior oxidative reactions. juice and wine clarification. At temperatures as low as 1400F (680C). thus rendering enzymes among the most vulnerable of all biological matter.2 Potential roles of enzymes in active packaging In many commercial situations. this attribute may be regarded as undesirable since a specific enzyme is required for a specific reaction. and no single enzyme can effect a series of related reactions. To function within a package material.. Immobilization of an enzyme. as. high fructose sugar production. lactase to break down lactose in milk. lipases for lipids. may be accomplished by making the enzyme an integral part of the packaging material. proteases for proteins. for example. The addition can occur to the in-plant batch or individual package. • A United Kingdom patent application (Thomas and Harrison. The objective here was to consume the residual fermentable sugars.. 1983) which describes an in-package secondary fermentation system using immobilized yeast within a liquid porous container immersed in an alcoholic beverage. • In-package production of lactic acid for pickles. and the range of environmental conditions for the functioning of the enzyme is a relatively narrow band. • Time-temperature integrator indicators which are triggered enzymatically. that are adequate and even appropriate for non-enzyme packaging components render the use of enzymes inappropriate. In one manifestation. the enzyme is vulnerable to variations in temperature. Consequently. the inventors refer to isolated enzyme complexes as being useful as yeast substitutes. harsh manufacturing processes. • Production of 'natural' antimicrobial agents such as benzoic or propionic acids to help preserve the product contents. Often. • Removal of products of microbiological degradation by glucose oxidase/ catalase. etc. etc.chemical into the package material. new and innovative methods are likely to be required for the incorporation of enzymes into packaging materials. sauerkraut or sour dairy products. converting them into carbon dioxide and water. The key differences are that the enzyme is not changed by the reaction and can continue to function indefinitely. • Incorporation of lactase to remove lactose from milk. Examples of those that have been actively pursued include: • Oxygen removed by means of glucose oxidase plus catalase. Further. Active packaging employing one or more enzymes involves the incorporation into the package material of the specific enzymes in much the same manner as the incorporation of a more conventional chemical to create the active package. geometric configurations. only a relatively small number have actually been attempted on a practical basis. Examples of enzymatic reactions that have not found general use but which might have some future potential and require development include: • Conversion of sugar into alcohol and carbon dioxide in secondary fermentations of wine to produce champagne-like products. These key considerations which affect the ability of the enzyme to function require special processes and techniques for incorporating enzymes into packaging materials. Although a broad range of enzymatic reactions stemming from enzyme incorporation into package materials can be conceived. the container was a flexible pouch. . pH. • Incorporation of cholesterol-changing enzymes to remove cholesterol from liquid egg or milk. etc. • Lactase to remove lactose. physically evaluated three areas in which immobilized enzymes within package structures would catalyze reactions of products contained within packages. among which have been enzymatically actuated versions. ketones. the co-author of this article. Removal of undesirable end products of microbiological or endogenous enzymatic reactions such as polypeptides. non-oxidative Maillard browning reactions. In reality. beginning in the 1970s. The exponential growth of modified atmosphere packaging in the 1980s led to the notions of oxygen and carbon dioxide and moisture control using in-package sachets of chemicals. suggested and. and is removed by catalase which breaks it into water and oxygen. volatile acids. the initial action of glucose oxidase is with residual quantities of glucose. The applications during the 1940s and 1950s appear to have been largely confined to very long term storage of military foods. Almost simultaneously with the idea of protecting against browning of dry foods such as eggs by removing residual oxygen. This company and its principal. 7. whose objective was to develop the application of enzymes in unit size situations. in some instances. Highly reactive hydrogen peroxide is produced by glucose oxidase. Tenderizing of fresh meat such as beef by proteases such as papain. The concern for the adverse effects of temperature abuse on frozen foods led to numerous ventures into development of time-temperature indicators. a reducing sugar active in the non-enzymatic. interest increased with the formation of PharmaCal. the notion of in-package glucose oxidase/catalase reactions was born. carbonyls. Towards the end of the 1980s. an analogue of the commercial incorporation of sachets of desiccants to reduce the in-package relative humidity. Whether or not the communications emanating from PharmaCal were . Some enzymatic agents were included in these chemicals. Removal of undesirable respiratory end products such as ethylene that accelerate the respiratory processes of fresh fruits and vegetables. Ltd.3 History Although many enzymes and their roles have been known for several decades. This concept was put into practice by employing porous packets of the enzyme mix in which the enzymes slowly reacted with minute quantities of residual oxygen. • Cholesterol reductase to remove cholesterol. • Glucose oxidase/catalase to remove oxygen.• • • • Destruction of natural toxins in foods. the notion of incorporating them into package materials to achieve a desirable result dates back only to the 1940s. The patent also mentions the incorporation of lactase to hydrolyze lactose into glucose and galactose which are then oxidized in the presence of oxidases. the patent suggested the use of enzymes to reduce the lactose content of milk. is 2G + 2O2 + 2H2O -> GO + 2H2O2 where G is the substrate. protects them from oxidation.directly responsible. 'In some instances. Among the interesting aspects of this early patent is the notion that as the oxygen in the product is removed. milk. Baker's invention was implemented by introducing one or more pellets of the enzyme into the product such as beer or orange juice. oxygen is a highly reactive gas which can cause deterioration of almost all food products in terms of flavor. Since hydrogen peroxide is a very good oxidizing agent. the presence of oxygen is essential to the growth and potential deteriorative effects of aerobic microorganisms including most bacteria. several other enzymatically based active packaging oxygen control devices have been proposed since that time. thus removing oxygen from the headspace. peas. 7. it is 'just as objectionable. it is better to produce in the product a substrate for the oxidase that is to be introduced rather than to use a substrate already present. or even more so. According to Baker (1949. corn. color. Thus. nutritional value and safety. Baker's patent indicates that if the oxidase produces an objectionable end product such as hydrogen peroxide. The patent does not explicitly describe precisely how the enzymes are incorporated. yeasts and molds. but evidently conceived in 1944) the addition of an oxidase to liquid-containing food products such as beer. catalase is introduced to break down the hydrogen peroxide 2H2O2 + catalase -» 2H2O2 + catalase The sum of these two reactions yields half the oxygen originally present and therefore ultimately the free oxygen approaches zero. now very well known. The reaction. glucose originally present or added can be oxidized to gluconic acid.4 Oxygen removal As is documented elsewhere in this book.' Thus. apple cider or orange juice. free oxygen in the headspace is further dissolved by equilibrium dynamics. The inference is that the enzymes are introduced directly into . than is the original molecular oxygen. minimization or removal of oxygen is an important factor in prolonging the quality retention of many food products.' For example. Further. Perhaps without realizing the significance of this assertion. then an additional enzyme might be introduced to remove the undesirable end product. starch. styrene. published a paper on Enzymatic Oxygen Removal from Packaged Foods in which enzymes were incorporated into packaging materials or introduced into packets.. but the enzymes glucose oxidase and catalase in a solution were impregnated into or on a moistureproof or fabric sheet. . food . butter. the package material is described as having \ . incidentally. frozen foods subject to browning. . Scott (co-inventor on the 1956 Sarett patent) of Fermco Laboratories. (Sarett. The enzyme-coating face must contact the moist product to ensure that the requisite oxygen reduction reactions take place. the same basic enzymatic reactions as in the Baker patent were reiterated as a reference. . etc. was not actually moistureproof) was often used to package butter and cheese. This concept of enzyme incorporation into a package material was first overtly described in a 1956 patent (Sarett. Although during the period of the patent a Kraft packaging paper called moistureproof (which. 1956). The enzyme system was indicated to serve as a barrier to oxygen which would otherwise be transmitted through the sheet. . Products described as being benefited by this system of oxygen reduction include cheese.the product. Thus. In 1958. filtered and further purified. an exposed surface covered with a gas-permeable packaging material and having an inter layer between and in contact with packaging material and . inter layer providing an oxygen barrier. rubber hydrochloride with impregnation employed for the papers and coating for the plastic and cellulose films. Also cited as being suitable substrates were wax paper. Fermco Laboratories was a manufacturer of enzymes. Experiments discussed in the body of the patent indicated results in which oxidation of cheese surfaces was retarded by the presence of the enzymecontaining package material. one category of which was labeled Fermcozyme antioxidants. ' The specific package materials identified were moistureproof cellophane. and of the packets which were named Oxyban. This paper marked the first publication to our knowledge on the use of packets of chemicals in packages.) In this patent. Expressed differently. The enzyme was bound to the sheet with a water-dispersible adhesive such as polyvinyl alcohol. The glucose oxidase/catalase systems were derived from mold mycelia which were disrupted. the patent does not indicate the use of this material. as it happens. was the assignee for the Baker patent. . paper. To be effective in . polyethylene and vinyls. although the 1949 patent described perhaps for the first time the employment of enzymes to eliminate inpackage oxygen. . Rather.. casein or carboxymethyl cellulose. it did not indicate that the enzymes were part of the package material or structure. this patent does not indicate that the enzymes are either part of the package structure or in an independent packet within the primary package. • • • . with oxidative rancidity delayed in the former class of products and color fading (e. the dried enzyme system was coated on the surfaces of package materials for processed cheese. the Oxyban was placed in small packets in which it reacted with oxygen in packages of roasted and ground coffee. in mayonnaise or carbonated beverages. glucose oxidase/catalase systems must be used in gas-tight packages. they proceeded forward to a more commercially viable mechanism. When the dry and therefore inactive enzyme picked up moisture from the product.g. Necessity to neutralize gluconic acid to avoid enzyme deactivation. grape-flavor carbonated beverages) as well as flavor oxidations delayed in the latter. The mayonnaise and carbonated beverage examples involved incorporation of the enzyme system directly into the products. The author noted that this in-package packet was analogous to the desiccant packet. The dog food example was also a direct addition to retard surface discoloration on the top of the dog food in retorted cans. as for chow mein noodles. smoked yeast or egg solids. Fermco's Oxyban product was a dry glucose oxidase/catalase/glucose/ buffers blend to be incorporated into products to reduce headspace and occluded and dissolved oxygen in dry foods such as coffee or soup. Non-aqueous foods • direct incorporation. in packets in situations in which the enzyme and the product should be kept separate. but clearly some moisture from the product was required. Among the problems they enumerated were: • • • Oxygen-scavenger surface area owing to the gas phase reaction. • in packets. As a coating. 1958). Exactly how the enzyme was activated without moisture was not indicated. Deposition of the enzymes was in solution form or via incorporation into a dry starch mixture prior to 'dusting' the package material surface. In another manifestation. elaborated on the oxygen-scavenging packet for in-package deoxygenation. Another series of experiments focused on obviating oxidative gray coloration on the surfaces of luncheon meats. surface treatment in canned dog food. Scott. Three years later. it was activated and was a sufficiently good oxygen interceptor to control the formation of brown ring.reducing oxygen.. Using the same glucose oxidase/catalase packet system described earlier from their laboratory experiments. Among the applications indicated were: Aqueous foods direct incorporation. then with Hammer (Scott and Hammer. The need for moisture (cited above). of Helsinki. the growth of aerobic microorganisms was significantly retarded. The enzyme layer was applied on the film by gravure or screen technique with the layer thickness being about 12 fim. the type of package material used for the packet was not indicated. As little as 15 g of Oxyban enzyme mix in a packet was capable of removing all measurable oxygen from a sealed No. 1991) described a package material containing an enzyme system to remove oxygen from the interior of the package by enzymatic reaction. The enzyme is not directly in contact with the contents. This patent application from Cultor Ltd. potato granules and ice cream mix. . fish and cheese products but without elaboration. i. By removing the oxygen. in turn. The background of this patent cited a 1969 German publication describing the use of glucose oxidase in package materials for the surface protection of meats. for example. The film produced was employed either as the cover film layer or as the thermoformable bottom layer for tray-type packages. and so this technology was favorable to shelf-life from both microbiological and chemical standpoints. The gluconic acid problem was obviated using phosphate buffers. and may also be mixed with a filler. the layer containing the oxygen-consuming enzyme was sandwiched between two plastic film layers. the outer of which might be polyamide or polyvinylidene-coated polyester. glucose oxidase. led to an increase in the amount of hydrogen peroxide which would. was incorporated into a package material with a gas-impermeable layer on the exterior and a gas permeable layer on the interior. 2 size can held at ambient temperature. (1989) described a similar technology of coating plastic film with glucose oxidase catalase. And. of course. An interesting side note was an exploration of the use of glucose oxidase alone which. slow the subsequent rate of oxygen uptake. Once again. details a flexible package structure containing an enzyme system in the liquid phase trapped between films. the classical review paper by Labuza et al.• Package material structure allowing passage of oxygen but not moisture. The enzyme solution contains a buffer and a stabilizer.. An international patent application (Lehtonen et ai. Finland.e. of course. The enzymes of choice were oxidases of the oxidoreductase family using oxygenases and hydroxylases which bind oxygen to oxdizable molecules. The products benefited by the total system were primarily dry milk. The enzyme. The inner film would be polyethylene which is generally not a good gas barrier. with the enzyme system activated by moisture from the food as Scott had previously cited. 1991). Ltd. there have not been any fundamental changes or additions to the necessary requirements for containers or packages. permits the enzymes to be retained for a reaction described in a 1989 patent application (Budny. has been able to expand the concept of packaging to include processing steps. Ltd. added a third dimension to packaging by allowing an individual package to become a processing unit or to perform a process step or function that previously was limited to in-plant operations. value-addition to packaged products and increased processing efficiencies. have been actively researching enzymes for active packaging since the 1980s. Throughout history. With a combination of patent applications and proprietary technology. Calcium carbonate. A container with an internal reactor. and protection of the contents. but their role in enzyme-based active packaging has been regarded as a more advanced application. 1989). The use of the enzymes to remove oxygen has been acknowledged as not new. magnesium carbonate or disodium hydrogen . Ltd. a lid or a multi-layer stock.9% of air to about 1% at ambient temperature within 24 hours.1 illustrates the mechanism in which packaged liquid reacts enzymatically with glucose in the package wall to form gluconate. they should protect the contents and not leak. while there have been advancements in materials and approaches. to enzymes in active packaging was to expand the concept of packaging beyond the two long-regarded functions of packaging: containment of the product. The contribution of PharmaCal. the gas permeability of package materials increases and so also does the ability of the enzyme system to reduce the oxygen content from the 20. Ltd. The resulting hydrogen peroxide is enzymatically reacted with catalase to produce oxygen and water that re-enter the contained product liquid. this Finnish work is so precise as to imply a major advance in the ability to implement the principles of enzymes as active package components. Co-author Budny and his company PharmaCal. PharmaCal. These requirements originally were embodied in wine skins that ancient goat.and sheepherders used for their sustenance beverages. Figure 7. described a glucose/glucose oxidase enzyme mixture in a porous precipitated silica acid carrier. PharmaCal.The inventors noted that with increasing temperature. PharmaCal. A 1991 patent (Ernst. Whether they are animal skins. in reality an integral section of the package wall through which the liquid contents may flow. has developed a two-enzyme system involving glucose oxidase and catalase to intercept oxygen and has applied the technology for enzymes in active packaging to improve the proven concept of oxygen removal with the dual enzyme system of glucose oxidase and catalase. calcium hydrogen phosphate. Ltd. From technological and potential commercial perspectives. 1992). Both red and white wines were treated with materials supplied by Oxyrase. A five-fold increase in the time to the onset of browning of cut surfaces of bananas and apples was observed at ambient temperature. fruits. carbonate may also be employed as carriers or reaction accelerators. The oxygen scavenger may be in the interior of in-package sachets. Examples of products from which oxygen might be removed by the system include beer. . The beads are then blended into a thermoplastic coating in the multilayer film. the active component of membrane fragments in this technology must constitute the enzyme system. The inventors note that the major mechanism to effect the reaction is incorporation of the membrane fragments into the product.Head space Gluconate Glucose oxidase enzyme Glucose Packaged liquid Catalase Outside of container enzyme Inside of container Container wall Figure 7.1 Oxygen removal from liquid products. Dissolved oxygen was removed within 16 minutes at 37°C. wine. Developers from chewing gum producer. 1991) describes the incorporation of oxygen scavenging cell membrane fragments which contain an electron transfer system in solutions containing alcohol or acids to reduce oxygen to water. The porous particles are made from styrene divinyl benzene. William Wrigley. Less than 12 minutes was required to remove 100% of the oxygen from beer or tomato juice. Inc. with the enzyme incorporated mechanically. Although neither purified nor crude enzymes. which is also the patent assignee. have described the use of porous polymeric beads containing glucose oxidase in multilayer flexible package materials (Courtright et al.. and that these active components may also be made part of the package structure. Jr. A 1991 patent (Copeland et al.. Sources of the membrane fragments were cell membrane of bacteria such as Escherichia coli and/or mitochondrial membranes. juices and a variety of non-food products. Since many foods may have minimal contact with the package surface.1 X 1 [0. Based on this. . there would be the need to scavenge 1 ml/day. To counteract the quantity of oxygen passing through an aluminum foil lamination an enzyme surface will have to react with oxygen in the following manner: Rate = permeability X area X oxygen pressure difference between the outside and inside Rate = 0. Thus at room temperature.21-0. precluding this application. a i m square surface with 1 mg of enzyme spread out on it should be able to handle all the oxygen passing through any package film. and the rate at which oxygen permeates into the package. The lactone then spontaneously reacts with water to form gluconic acid. with only 0. A film could be made equivalent to a barrier by binding the oxygen scavenging enzyme to the inside surface of the film to react with the excess oxygen. For the worst case and with a pinhole or cracked score.Labuza and Breen (1989) have analyzed the issues involved in the incorporation of glucose oxidase into package materials. Glucose oxidase bound to a plastic surface has been shown to undergo a 50% drop in activity in 2-3 weeks followed by little loss over the next four weeks. a normal contaminant of commercial glucose oxidase. One advantage is that both polypropylene and polyethylene are good substrates for immobilizing enzymes. An unknown factor is how stable the enzyme will be on the film over time. pure glucose oxidase has a rate of oxygen consumption of about 150 000 (il/h/mg. this may not be the best approach for oxygen scavenging. this would be equivalent to reacting with all the oxygen passing through a film with an oxygen permeability of about 18 000 ml/day m2 atm. and spreading 1 mg per m2 on a film. to reach zero oxygen. the glucose oxidase will be inactivated. At 30-400C. Pure glucose oxidase without catalase is reportedly expensive. If no surface exists for the peroxide for diffusion. except on the sides and bottom. One factor to take into account is the stability of the enzyme when bound to the film.01] = 0.2 ml per day per m2 = 20 jxl/day The calculation above assumes air outside and < 1% oxygen inside. One mole of glucose will consume one mole of oxygen and so a package with 500 ml headspace is required.0043 mole of glucose needed as a substrate. In the presence of catalase. the amount of glucose available. decreasing the overall effectiveness of the system. The major factors are the speed at which the enzyme works. the hydrogen peroxide is broken down. Glucose oxidase transfers two hydrogens from the -CHOH group of glucose to oxygen with the formation of glucono-delta-lactone and hydrogen peroxide. and so with catalase one mole of glucose will react with only a half mole of oxygen. However. The university researchers' experiments (which had begun . At the University of Rhode Island. supplied by Fermco) were applied to fresh flounder fillets or whole fish by dips. especially with regard to fish (Field et aL. in his continuing research on the technology of glucose oxidase. other enzymes have potential. The enzymes (not coincidentally. 7. the use of immobilized enzymes in commerce has increased significantly. The reaction is extremely rapid. Scott (1975). Besides glucose oxidase mentioned previously. Rand and his co-workers conducted research and development on catalase-free glucose oxidase as a food preservative. Hopkins et a/. which is an insoluble polymeric carbohydrate from shellfish shells. selective control of aerobic bacteria can occur. allow the overgrowth of pathogenic anaerobic bacteria which.The Japanese have worked on binding of enzymes to chitosan. noted that catalase-free glucose oxidase might exert antimicrobial effects due to the production of hydrogen peroxide. Since the enzyme is a protein and can serve as a nutrient for microbes along with the glucose substrate. immersion in ice or by enzyme/ algin blankets. but a 70% loss in activity for bound glucose oxidase has been reported. Meanwhile. An alcohol substrate either from the product or introduced into the package from the exterior is required to remove the oxygen from the package headspace. this method of bacterial control can. One such enzyme is ethanol oxidase which oxidizes ethanol to acetaldehyde. independent of whether the organisms are aerobic or anaerobic. the enzyme system included catalase and/or glucose. During the 1970s. In some experiments. By controlling the amount of available oxygen.5 Antimicrobial effects The use of enzymes in active packaging to control microbial growth and subsequent packaged-product degradation can be achieved by two independent approaches. 1986). Glucose oxidase immobilized on polyethylenimine-coated glass beads retained 78-87% of its activity and was more stable to heat inactivation. under certain circumstances. Neither the literature nor the memories of the authors indicates the commercial implementation of the Fermco products. may be worse than aerobic bacterial overgrowth. A second approach that has been implemented by several investigators is non-specific relative to oxygen requirements and is a direct attack on the organisms present. This second approach can be either by a direct attack on bacteria (both aerobic and anaerobic) or by the production of broad-spectrum antimicrobial agents. from a human view. a microbial inhibitor may be needed in the film. (1991) describe a package in which alcohol or oxidase or cellular extracts of Pichia pastoris cells containing alcohol oxidase are the enzymes used for oxygen scavenging in dry foods. A German patent assigned to Continental Group (Anon. The authors cited a Japanese patent in which catalase-free glucose oxidase was demonstrated to be effective in preserving other proteinaceous foods such as ground chicken and tofu (Fukazawa. The notion of hydrogen peroxide as an intentional active antimicrobial agent is somewhat of a contradiction since this chemical is quite reactive with many food constituents. COOH. The enzyme was subsequently applied as a coating from an aqueous dispersion. 1980). however. OH phenol. They also suggested that the generation of hydrogen peroxide might inhibit the growth of psychrotropic microorganisms which are reported to be sensitive to the chemicals used.during the early 1980s) demonstrated that the enzyme treatments retarded the onset and magnitude of adverse microbiologically triggered spoilage odors. perhaps the proposed system may warrant further consideration. especially lipids. imidazole and sulfhydryl were cited as examples. The researchers explained the result as due to reductions in surface pH under the refrigerated conditions of the test. is synergistic with the oxygen removal aspects of the enzyme system. of course. The polymer was described as a terpolymer of monomer alkyl acrylate and vinyl aromatic applied to the interior of a glass container from a solvent and dried by heat. . and residual free hydrogen peroxide is not readily accepted by regulatory officials. 'Non-essential' functional groups such as NH2. reported to be a binding agent for water and metal ions. This last. thus increasing shelf-life without heat. These changes influenced the metabolism of putrefactive microorganisms. and gluconolactone. If the hydrogen peroxide is fully reacted with microorganisms as in aseptic packaging. The enzymes were intended to destroy microorganisms by breaking cell walls and also to consume oxygen. Enzymes such as muramidase for cell wall destruction and glucose oxidase for oxygen interception were attached to the internal polymer by covalent bonds. work did not specifically state the incorporation of enzymes into package materials. Another factor reported by the group was an altered gaseous microenvironment in which oxygen in the muscle interstices was depleted by the enzymatic action thus retarding the growth of aerobic psychrophiles. Other possible microbistatic agents include gluconic acid. 1977) describes incorporation of biologically active enzymes into polymers on the interiors of package structures to destroy microorganisms of contained products. Unfortunately. work at the University of Rhode Island on this topic has been discontinued. Either of these could have been relatively easily substituted with a skin package material which had been surface tested with the enzyme system. the implications were sufficiently clear in the examples of the enzyme-containing ice and the enzyme-containing algin blanket. Although the Rand et al. The applicable products were beer and fruit juices. reportedly a metal complexing agent. On the other hand. and another basic question. called I-point® TTM.' The reaction was based on enzymatic degradation to colored end points. size. The device was a two-part system. and so evidently indicative of actual biochemical changes arising due to the temperature-time experience. . no reference was made to the type of enzyme used. reliable and economic indicator of total temperature-time exposure of food products. one containing an enzyme and pH indicator since the system was based on pH change caused by enzymatic activity plus a substrate. Although the original objectives were aimed at frozen food defrosting devices. Although the indicators reportedly functioned very effectively. cost. Sweden. both length and degree of all temperature exposures. integrating or measuring time-temperature. accuracy. understandable message and ability to integrate ' . Among the routes has been the application of the principles of temperature sensitivities of enzymes. This product was another manifestation of the application of enzymes in package systems to an inactive mode. stated that their device met all the requirements of reliability. how well the measurement represents the effect of the temperature-time integral on the food itself. . the temperature response was exponential with increasing temperature. accuracy over the entire range. Kramer and Farquhar (1976) listed a number of the problems in their evaluation of five commercial. The authors. of Kockums Chemicals of Malmo. Among the issues are activation only when actually at the beginning of shelf-life. 1989) claimed a temperaturechange indicator composed of an enzyme and substrate. 7. One might speculate on the simple glucose oxidase-catalase system producing gluconic acid as the reaction proceeded. time-temperature indicating and defrosting devices. more recent interest has been focused on chilled foods. No descriptions were given the mechanisms for sensing. accurate. how reflective the integrator-indicator is of the actual temperature-time experience. This appears to be the first reference to actually incorporating an enzyme into an interior package wall to achieve an enzymatic antimicrobial effect. a colorimetric . efforts have been underway to develop a practical. A 1989 US patent (Klibanov and Dordich. Because of the enzymatic core of the pH change. Blixt and Tiru (1976) described a commercial enzymatic time-temperature monitor.6 Time-temperature integrator-indicators For many years.Tests indicated highly significant reductions in oxygen concentrations within the glass jars due to the conversion of glucose to gluconate in an oxidative enzymatic reaction. into its component parts glucose and galactose. Ltd. . Ltd. Rather. flatulence and diarrhea. its presence can cause discomfort in the form of cramps. Persons with lactose intolerance either avoid milk or introduce lactase enzyme into their milk prior to consumption. A British patent assigned to Tetra Pak International AB (Anon.7 Lactose removal Lactose intolerance is a dietary problem affecting a minor but nevertheless substantial fraction of the population. No further reference to the use of this enzymatic temperature indicator has been found in the literature. Lactase is necessary to break the disaccharide lactose. Applications were as monitors on the exterior of distribution packages of pharmaceutical and food products. or milk sugar. 1975) describes incorporation of lactase into pasteurized or sterilized milk prior to packaging to split the lactose after packaging. bloating. The organic solvents claimed were basically paraffins. at PharmaCal. extended and improved the Tetra Pak approach and made the process a true enzymatic active packaging process. Another enzyme cited as being effective was polyphenol oxidase. Ltd. 7. a solution of enzyme is added directly to the individual package just prior to sealing. The patent notes that the milk must remain for about a day at a temperature of at least 80C for the lactase to function. PharmaCal. PharmaCal. Individuals affected by this problem suffer from a lack of the enzyme lactase in their intestinal wall.2). (1990) incorporated the lactase. The lactose must be sterile and is added aseptically. Since lactose cannot be absorbed from the gastrointestinal tract.indicator and a trigger mechanism of a solid organic solvent system that melted when a specific temperature range was reached to permit the enzyme system to respond to temperature stimulus over time. the Tetra Pak approach is batch processing done on a miniature scale.. has proprietary designs and approaches for commercializing this active package (Figure 7. with the result that 30-70% of the lactose was removed in 24-36 hours at 3-4°C. The Tetra Pak approach differs from the previously discussed examples of active packaging because the enzyme has no relationship to the packaging material. Ltd. this approach does point out that an active enzymatic process can be carried out in a sealed container. within the individual container. However. Budny. In reality. using proprietary technology of PharmaCal. The enzyme and substrate cited in the reduction process was peroxidase and peroxide with a /7-anisdine colorimetric indicator. Milk Lactase enzyme Glucose Galactose Lactose Outside of container Container wall Inside of container Figure 7. Rather. Ltd. all food packages in the United States must be labeled for cholesterol content. To demonstrate the awareness in the USA of the cholesterol content of foods. active packaging and the technology of PharmaCal. as he employed for enzymatic oxygen removal or lactose splitting.2 Lactose removal from liquid products.3. Ltd. in the package structure. . This system.8 Cholesterol removal The widespread information on the effects of excess cholesterol in the diet does not require discussion here.7. the fluid milk contents are exposed to the enzyme to convert its cholesterol to coprosterol which is not absorbed by the intestine. Using much the same proprietary technology of PharmaCal. reduces the extensive in-plant processing required by supercritical fluid extraction systems to produce cholesterol-reduced fluid milk products. allows untreated fluid milk to be packaged. cholesterol reductase. Co-author Budny (1990) suggests the removal of cholesterol which is present in whole milk by incorporating the enzyme. illustrated in Figure 7. (1990) Fermentation opportunities ripen. (1990) Packaged milk containing lactose enzyme-giving milk with reduced lactose content. UK Patent Application. and Tiru. 237. German Patent DE2817854A. 159. Best. References Anon. and in the time taken to transport the package to the consumer. (1989) A transporting storage or dispensing container with enzymatic reactor. J.L. US Patent 2482724.Milk Cholesterol reductase enzyme Coprosterol Cholesterol Outside of Container container wail Inside of container Figure 7. M. 20 September. California. Budny. K. San Francisco. Anon. (1990) Presentation at Pack Alimentaire. it conceivably could become free of cholesterol. Prepared Foods. May. 5. International Symposium on Freeze-Drying Biological Products. While the commercial implementation has not yet been completed. International Patent Application WO89/06273. J. (1977) Packagedfoods and drinks in containers coated internally with polymer carrying enzyme with sterilising action. . (1949) Deoxygenation Process. Blixt. 36. (1977) An Enzymatic Time/Temperature Device for Monitoring the Handling of Perishable Commodities. Baker. D. the component elements of the application have been successfully demonstrated.3 Cholesterol removal from liquid products. Budny. D. Field.B... Sarett. Handbook of Enzyme Biotechnology. Scott. 30 June. US Patent 5028578. UK. Karilainen. (1992) Food packaging improvements. F. J. (1961) Oxygen scavenging packet for in-packet deoxygenation. (1991) Process utilizing alcohol oxidase. (1994) Enzymes. Ernst. and Rand. (1975) Enzyme utilization in industrial processes. (1965) Oxidoreductase. (1991) Oxygen absorbent and use thereof 2 July. Academic Press. Today's Chemist at Work.M. Barnett. Copeland. Thomas. Enzymes in Food Processing. and Kymolainen.Copeland. K. 2 May. D.L. the catalysts of life. (1991) A packaging material which removes oxygen from a package and a method of producing the material. Smith. and Banasiak. L. US Patent 2765233. (1976) Testing of time-temperature indicating and defrost devices. J. Lehtonen. and Richey. Pivarnik.. T. Fukazawa. D. International Patent Application WO 91/13556. A. Scott. A. 10 December. Ellis Horwood. A. A.G.N. and Farquhar.F. Food Processing and Preservation. D. Adler. and Breen. (1985) Method and apparatus for secondary fermentation of beverages. (1991) Method and composition for removing oxygen from solutions containing alcohols and/or acids. Scott. McGrew. S. Labuza. (1989) Enzymatic temperature change indicator. NY. S. Food Science. Food Technology.M. (1956) Enzyme treated sheet product and article wrapped therewith. B. L. US Patent 4826762. and Dordich. March.A. Food Technology. J . P. G.I.D. VJ.. Jaakkola R. (1986) Utilization of glucose oxidase for extending the shelf-life of fish. Japanese Patent 23071180. S. RJ.W. 15(12). 51. J. 12(7).S. (1958) Enzymatic oxygen removal from packaged foods. and Crow. Courtland. 13. 1. H. R. D. (1989) Active Packaging. . Don and Hammer. W. T. Kramer. 30.S. and Harrison. UK Patent Application 2143544A. Wiseman. C .R. Klibanov. J. U. R. US Patent 5071660. C . W. 99. and Scott.. Food Technology. 7. 56. Hopkins. R. (1980) Methods of preventing spoilage of foods. XJS Patent 4996073. US Patent 5126174. 2 Oxygen measurements 8. Stone. but increases the level of calcium to a level that forms hazes. and Kincaid (1963) reported that the inclusion of oxygen scavengers in the lining of cans improves the storage stability of canned beer. He found that the use of reductones made from sugar reduces oxygen. assumptions and corrections must be made to determine oxygen. 8. and phosphites were too slow. He recommended adding ascorbic acid just prior to bottle filling. TEUMAC 8. The reactions with sulfur dioxide. Oxygen and nitrogen can be measured in a gas sample directly by gas chromatography or by removing carbon dioxide. Hoag.8 The history of oxygen scavenger bottle closures F. separating the other gases and measuring with a mass spectroscopy detector. Thomson (1952) reported extensions of the earlier work in the Brewers' Guild Journal. The sample is withdrawn with a Zahm-Nagel device. For a gas sample. The foam should be allowed to settle. and Atkin (1948) measured oxygen content of bottled beer and correlated oxygen presence with off-flavor development. The prime candidates were sulfites and ascorbic acid.2. the bottle should be equilibrated by shaking. Gray.1 Background The early history of the use of scavenger chemicals with beer has played an important part in the development of oxygen scavenger closures.1 Techniques for measuring the oxygen content of bottles Before withdrawing gas samples from a bottle for measurement.N. The report made to the American Society of Brewing Chemists concluded that the addition of anti-oxidants to beer should be studied. Using chromatography. Klimovitz and Kindraka (1989) published in the Master Brewers Association of the Americas Technical Quarterly that a combination of sodium isoascorbate and potassium metasulfite when added to the silica hydrogel mixing tanks significantly improved product flavor stability. Reinke. The advantage of the mass spectroscopy detector is that . sodium formate. Glucose oxidase-catalase was preferred to sulfur dioxide and isoascorbic acid. this might require several hours. These brewers provide an initial oxygen content of about 900 ppb. so comparisons must be made on different crowns under the exact same bottling conditions on the same batch of beer.2 Results of measurements Depending upon the equipment capability of the brewer. and the oxygen and nitrogen concentration in the head-space. Brewers that use the best equipment available. The initial oxygen in the package is about 1700 ppb. The oxygen depletion in the bottle proceeds at the same percentage rate as in the first category. the bottle should first be equilibrated. An initial value of 400 ppb is common. Again. 54% the second day. Each beer is different. • • The effect on flavor deterioration of bottling under different conditions is difficult to gauge. Liquid samples can be withdrawn and measured with polarographic techniques. 42% the first day. other data can be gained by comparing the ratios of the three gases. Since the Zahm-Nagel device pierces the closure. This decreases by 30% during pasteurization. 8. The initial values vary because maintaining the lower value requires the filler to be in top condition. The oxygen depletion in the bottle proceeds at the same percentage rate as for the other two classes. the temperature.argon is detected directly. and 95% in a week. Because nitrogen and argon do not react with the bottle contents. Brewers using 10 ppm or more of sulfur dioxide obtain values of 200 ppb oxygen. The total oxygen and nitrogen can be calculated from the measured headspace. the oxygen content of bottled beer can be seen to correspond to three categories of brewer: • Brewers incapable of performing a final blow down with purified carbon dioxide and without new high technology fillers. The total oxygen of the bottle can be calculated. The few valid comparisons made prior to the introduction of scavenging crowns indicated that beer bottled with less oxygen had better shelf-life. it must be assumed that all the bottles were the same at bottling. each bottle can only be sampled once. brewers with 8 or less ppm sulfur dioxide experience values of 350-800 ppb of oxygen depending on the maintenance of the equipment. but do not have new high technology fillers. . These brewers usually compensate by adding 10 ppm or more of sulfur dioxide to the beer. In order to follow the changes in the bottles. Brewers capable of good oxygen control up to the last step.2. This requires the most reproducible conditions possible. The reaction of oxygen with the bottle contents is rapid. It is the difference in the partial pressure between the respective sides of the liner. this is determined empirically for a specific polymer or polymer compound and is specific to the gas and the conditions of the test.2. it is the flow of a specific gas through the portion of the container in question. The instrument is used primarily to measure transmission through a permeable membrane. (A X p) PERMEABILITY = P — L Permeability as used here means the flow of any gas per unit of time. Wisk and Siebert (1987) at Stroh and Heyningen et al. that would be the case. EVA. p is the driving force of each gas. As metal has no permeability.8. For a container. A plastic closure is totally made up of permeable material. Teumac. so the area is quite large. or polypropylene. P is the permeability coefficient. For a polymeric material like PVC. For years a crown or closure was defined as a hermetic seal. it is the partial pressure of the particular gas. A simpler method uses an instrument sold by Modern Controls. Because of uncertainties of the dimensions of L and A in a . ZapatA Industries studied oxygen ingress in crowns. Ross and Rassouli (1990) confirmed the earlier conclusions. The bottle must contain nothing that can react with oxygen. A is the area of the compound surface involved in the transfer. gas will flow from the higher partial pressure to the lower. There are several models of an instrument commonly called the Mocon. The concept of oxygen ingress into the bottle gained slow acceptance because it is difficult to envision how oxygen will penetrate a bottle with 3 atmospheres of pressure within from an ambient pressure of 1 atmosphere. The phenomenon has. however. An aluminum closure provides a very small area. Oxygen ingress can be measured by placing a closure on a bottle containing a known amount of oxygen and periodically measuring the oxygen in the bottle. A for a crown is the area of the liner compound between the metal and the glass. If there were a physical leak. Inc. (1987) at Heineken separately challenged this assumption and came to the same conclusion: crowns allow oxygen ingress. It is based on a well established equation that describes permeability through a permeable polymer (the liner or gasket). A pressure of three atmospheres in a bottle does not mean that all gases will move outward from a bottle. This work was extended to include both plastic and aluminum closures (1991). L is the length of the route followed by the gas. been proven using several techniques by several workers in the references cited above. and recommended some improvements to eliminate oxygen ingress.3 Oxygen ingress Closure of the bottle does not mean that the battle with oxygen is over. It should be emphasized that it is not the total pressure. epoxy Solder Figure 8. plate Hot melt lueor min. 8. For example.2A Combining the effect of initial and ingress oxygen The bottler must consider both the oxygen trapped in the bottle at filling and oxygen ingress. .1 is a schematic of the apparatus. a steady state is reached where the oxygen in the stream is a measure of diffusion of oxygen through or around the closure. By keeping the nitrogen flow rate constant. A crowned 12 ounce bottle will allow another 750 ppb to ingress in 3 months or 2000 ppb in 8 months.1 Schematic of Mocon apparatus.crowned bottle. the measurements on a closure are best made by modifying the Mocon to measure the transmission directly for a closed bottle. The initial oxygen level would be 490 ppb. Figure 8. The amount of oxygen available to react with the product can be calculated from measurements and extrapolated. The bottle is closed with the test closure and then cut and sealed to a metal block containing a sealed inlet and outlet. a brewer with good oxygen control techniques will fill bottles with beer containing 50 ppb oxygen and entrap another 440 ppb. Oxygen-free nitrogen is flushed into the bottle carrying any oxygen in the bottle out to the detector. The amount of oxygen that has reacted with the product can then be calculated by subtracting the measured oxygen from the total oxygen § Brass mtg. 3 Oxygen scavenger liners 8. (ii) The scavenger is included in the liner compound. but prevents the scavenger from leaching back into the bottle.OXYGEN (Reacted) 8.exposure (initial + ingress). The scavenger must be effective at levels that do not interfere with compound processing. the compound must be permeable to water vapor and oxygen. About two-thirds of the oxygen in a bottle is in the headspace. the design and placement of the compartment must allow normal closure handling and bottling procedures. (i) A compartment is placed in the closure that separates the scavenger via a membrane that allows oxygen and water vapor to permeate the liner. All of the oxygen that gets into the bottle is either measurable or has reacted. This approach lessens the concern of product contamination by the scavenger. The instruments cited are capable of making meaningful measurements that reveal the oxygen chemistry taking place in the bottle. the permeability of the compound. This approach has not been commercially tested. The rate of oxygen removal will be determined by the concentration and reactivity of the scavenger. For example. In order to be practical. Plasticized PVC can tolerate fillers without significant loss of . Scavengers can be incorporated into the closure by two different means. 8. To be effective. enzymes such as glucose oxidase-catalase are very reactive. or the closure performance on the bottle. The fabrication of such a closure would add significant cost and require process changes by the brewer. and the surface area of liner exposed. but are destroyed by plastics processing conditions and are much too reactive for normal filling procedures. it increases the choices of potential scavengers.3. Because of close contact with the product the scavenger should not be noxious from a health or organoleptic standpoint. The scavenger should not become degraded during processing thereby losing activity and should be immune to activity loss during normal handling. It is not surprising then that the most successful scavengers are the materials tested earlier as direct beer additives.3. There are many patents describing this approach. In other words: OXYGEN (Initial+ Ingress) = OXYGEN (Measured) .2 Commercial activity PVC compounds lend themselves particularly well to use as scavenger additives. closure lining. thus.1 Theoretical Removal of oxygen from a bottle by a closure requires that the reaction occurs with gaseous oxygen in the headspace of the bottle. The preferred catalysts are copper and iron salts. Essentially. Inc. It appears that a PVC compound is being used on a low alcohol beer. gives a surprising benefit. (ii) Aquanautics Corporation. besides keeping it out of the beer.. (i) W. A joint effort was launched in early 1989. alkali metal erythorbates. By reading the patents and analyzing liner materials. so the sulfite is required for the rate of activity. Grace. The ascorbates by themselves are very weak scavengers. The exact extent of Grace's commercial success is not known outside of Grace. it is evident that the Grace scavengers contain up to 7% sodium sulfite and up to 4% sodium ascorbate. had developed some expertise in removing oxygen from sea water and recognized an opportunity in removing oxygen from bottles of beer. Foster's Special Bitter. Earlier workers had observed a . Polyolefins have sufficient oxygen permeability. Several patents have been granted and applications are in the process of being approved.R. but all transition metal salts increase the reaction rate. Placing the same materials in a plastic liner earlier placed in beer greatly minimizes the fear of product contamination. Courage Beer uses Daraform 6490 for the AnheuserBusch beer produced under license in the UK. Different reactions occur. alkali metal ascorbates. The new technology employs ascorbic acid as the reducing agent. introduced a scavenger product in a polyolefin liner to Heineken in the Spring of 1989. The addition of very small amounts of metal catalysts to ascorbate or erythorbate-containing liners greatly enhanced the rate of reaction with oxygen. Separating the scavenger system from the beer. but are less permeable to water vapor. A PVC compound from Grace is being intensively tested at one major Canadian brewer and several smaller US brewers. Trials are being performed with Daraform 6490 at several European brewers. For some beers the low activity is not a disadvantage and may even be an advantage. An elaborate business plan was developed and eventually sold to ZapatA Industries. the type and amount of catalyst determines the reaction rate. A system was developed that was based on the beer chemistry described earlier. Heineken dropped scavengers when they became more interested in other aspects of crown performance. The small amount of catalyst enclosed in the plastic liner yields undetectable amounts of leach in beer. now Advanced Oxygen Technologies. they describe using ascorbates and similar chemicals with or without sodium sulfite in a thermoplastic matrix. Daraform 6490 is a polyolefin liner compound containing an oxygen scavenger. Grace has published and been granted several patents on their scavenger system.properties and is sufficiently permeable to oxygen and water vapor to allow good reaction rates. Alternatively. The amount of ascorbate or erythorbate determines the oxygen reduction capacity. Inc. or erythorbic acid can be used. through Tapon France (a crown manufacturer). In 1993. over 1 billion PureSeal crowns were sold. each supplier will document the acceptability to potential customers. The reason for this is that all beers contain trace amounts of organic compounds.reversal of the benefits of adding ascorbates directly to beer. this is not observed when the ascorbate is placed in the liner.3. rapid oxygen reduction is not always beneficial.4 The effect of scavenging closures on beer flavor There are several large brewers. Working with these brewers has resulted in a better understanding of the role of oxygen in beer flavor chemistry. The original goal of the project was to remove as much oxygen as quickly as possible. There was concern that the new conditions created in the bottle would cause off-flavors to be created. Oxygen participates in the reactions that reduce these flavors. actually hundreds of them. The commercially employed oxygen scavenging chemicals have not been listed as environmentally harmful. ZapatA provides trial recommendations and an oxygen testing service for PureSeal trials. 8. Other crown manufacturers have been provided with lining compound for crown trials. Smartcap and the improved PureSeal® crowns are marketed by ZapatA Industries and affiliated companies in other countries. 8. 'Sulfury' beers bottled with low initial oxygen require a lower . Extensive research and large trials are resolving their concerns and demonstrating the value of oxygen scavenging crowns. and those that have started subsequently. The reaction with oxygen is enhanced by the paucity of moisture found in the liner. Another surprising benefit is that the reaction rate is significantly increased by placing the scavenger in the liner. As the initial oxygen approaches 250-350 ppb. was introduced in a controlled manner in 1991. The brewers that started using the liners commercially in 1991. rapid removal is beneficial.3 Health and environmental concerns This history implies ready acceptance by health authorities. they have been evaluating PureSeal oxygen control crowns for about 2 years. The Aquanautics-ZapatA liner. have not had a documented incident of off-flavor development attributable to the liner. Smartcap®. Some of the sulfide-containing organic compounds included in this number have a low flavor threshold. With one exception. and they can afford and use excellent oxygen control. For bottles containing more than 600 ppb oxygen. The difference is first noticeable between 1 and 3 months of storage and is maintained to between 9 and 12 months. Trials at 60 brewers have proven that the liners always reduce the oxygen level in the bottle and usually reduce oxygen damage to the beer during storage. packaging materials. processing. Brewers lack the control they would like on the distribution of their beer. Beer carefully brewed to have certain flavor characteristics can now be delivered to customers all over the world in shipments in the same condition. A summary of the results was reported at Pack Alimentaire (1993). Properly designed oxygen control bottles will provide a fresher tasting beer compared to a bottle with a standard crown after approximately 30 days. can be protected by less severe heat or additive treatment. and the amount of headspace place limitations on package design. Oxygen control bottles would allow raising of the limit. package. PureSeal liner compounds are readily adjusted to achieve both goals. and distribution. by extending the expected shelflife. total removal of some organisms has been achieved by rapid depletion of oxygen in the bottle.rate of oxygen depletion to allow some of the oxygen to react with the sulfury components.5 The advantages of oxygen control bottles The advantages are most obvious to exporters.6 The future of oxygen scavenging closures The use of oxygen scavenging crowns for beer is increasing rapidly. 8. Most beer is sold through distributors. the limiting factor on how fast a filling machine can operate is often the initial oxygen level. At the same time. they can now lessen the concern on how long beer is on the shelves or give the distributors more leeway. 8. the cost premium over standard crowns will diminish with increased volume. Most large brewers have rigid standards on initial oxygen levels and dump beer that exceeds the limit. like beer. Oxygen control liners should be used in the standard crown . Production departments can use oxygen control bottles as a tool to solve manufacturing problems. with oxygen control bottles. Limitations of filling lines. There is little similarity between beer purchased in the area of origin and that purchased elsewhere. the amount of oxygen. new packages can be designed for the same filling line. The effect on the bottle of day-to-day variations in oxygen level at the filling line or between filling lines can be minimized. Acidic beverages. There is some evidence that reduction of oxygen in a package can reduce spoilage caused by organisms. for example. Brewers will become more comfortable with this trend. In fact. This provides more freedom of design in the product. 122-6. the potential for organoleptic problems increases. M. change in texture. The food scientist should become familiar with the latest developments and only then very carefully plan and execute experiments. (30). Teumac. (1948) Systematic study of the influence of oxidation on beer flavor. L. pp. and Atkin. F. Damage might be in the form of discoloration. 679-86. 175-80. EBC Congress. MBAA Technical Quarterly. H. I. As beverage makers begin to use more natural materials such as fruit juice.. (27). Oxygen scavenging closures can be part of the oxygen control procedure of a winery. (1990) Air ingress through bottle crowns. 'quick and dirty' methods are commonly found. (1987) Permeation of gases through crown cork inlays. 101-12. 201-10.. and Kincaid. et al. M. R. and Rassouli. (1989) The impact of various antioxidants on flavor stability. differing in many respects from the beer industry. Ross. This lack of precision will lead to faulty conclusions or indicate no significant difference. Ross. (1991) Oxygen Ingress Into Soft Drink Bottles. Oxygen control liners have been introduced for aluminum roll-on closures to complete the closure requirements for beer. Klimovitz. B. loss of flavor. J. B. Control of the initial oxygen content and a valid means of measuring a change in properties are essential features. Nonetheless. . Reinke. Wine chemistry has dealt with oxygen for centuries. MBAA Technical Quarterly. The use of oxygen control for other beverage products is a new frontier.employed by the beer industry. P. Sacrificial reduction of metal and use of preservatives are becoming less acceptable.. C. 70-4. Many food products are damaged by oxygen. The effect is obvious and well understood by food processors. L. ASBC Proc. or the generation of off-flavors. it is a matter of how much oxygen at what stage. and Kindraka. Hoag. Package oxygen control affords a different means of protecting food from oxygen damage. refined constituents such as sugar. and Rassouli. but additives must be listed on the label.. and citric acid have been used. Society Of Soft Drink Technologists. Until recently. Measuring techniques and equipment are now available for evaluation of the control of oxygen in any package. corn syrup. artificial flavors. These problems can be off-set with additives. D. Heyningen. Wines and coolers also contain hundreds of organic compounds that can react with oxygen. Teumac. Wine makers understand the role of oxygen in maturation and/or spoilage in wine. (1963) Effect of antioxidants and oxygen scavengers on the shelf-life of canned beer. Stone. There were relatively few substances that had the potential of becoming oxidized to off-flavors. ASBC Proc. It is a relatively new industry involved in this field. Proceedings of the 38th Annual Meeting. References Gray. F. . Proceedings of Pack Alimentaire '93. K. Brewers' Guild Journal. Amer. F. Thomson. 45. (1952) Practical control of air in beer. 167-84. T. (1987) Air ingress in packages sealed with crowns lined with poly vinyl chloride. Brew.Teumac. and Siebert. Soc.. R. 38(451). /. 14-18. Wisk. Chem. (1993) Case Studies of Oxygen Control in Beer. crisping and ultimately browning result. these properties have been expanded to include both the environmental disposability of the package material as well as the ability of the package to perform far beyond the inherent property of the package media.1 Packaging overview Packaging exists because it performs four basic functions which may vary in importance depending on the nature of the products and their modes of distribution.2 Marketplace susceptors In its classical definition. SACHAROW 9. the ability to 'cook' the product or other changes in the product caused by the packaging material. The classic functions are: 1. Temperatures high enough to produce drying. Examples of active packaging existing in the North American marketplace will be discussed in this chapter. thereby yielding the desirable effects associated with conventional infrared oven cooking. 2.. in response to excitation. 9. Susceptors (also sometimes called receptors) are materials which convert sufficient microwave energy into heat to result in temperature increases that exceed those produced by either the direct heating of foods or the boiling of water into moisture vapour. 4. sugar and fats. Protection Containment Information Utility of use In recent years. 3. an active package (within the microwave field) is one that changes the electric (or magnetic) field configuration and ultimately the heating pattern of the product packaged (Packaging Gp. especially water. Active packaging is the term used for a package that changes the characteristics of the product packaged. . This may include characteristics such as enhanced shelf-life.9 Commercial applications in North America S. 1987). Microwave cooking alone produces temperatures limited by the temperatures developed by the food components. 9. an infrared heating source such as a heating coil. Foods containing fat. Microwaves are not yet suited for crisping and browning. This complicates the heating of meals made up of foods differing in response to microwaves. such as vegetables with gravy-covered meat. pizza crusts. limited of course by the exposure time.2. and sugary foods. breads. such as bacon. a susceptor. ions or molecules onto a substrate . there can exist orders of magnitude differences in heating rate. Foods containing mixtures of water and sugars or fats achieve temperatures determined by the concentrations and distributions of ingredients. 'thick' and 'thin' are differentiated by the form which the deposited material takes during the deposition process. Foods that require surface drying include pastries. If heating continues in the absence of sufficient relief of internally-generated pressures. and other dough-based compositions. watery and high moisture foods. Two outcomes are desired of a susceptor: • • rapid rise to the required temperature constant temperature thereafter Only the first of these has been achieved in practice. Crisping and sometimes browning is needed in some of these same foods and additionally in certain meat products as well as roasts. They must rather be implemented with some method of raising local temperatures to 1500C or higher (3000F or higher) to make them function as do browning dishes and conventional ovens or frying pans. in the oven to provide air at temperatures up to 2500C (4800F). but self-limiting susceptors that satisfy the second are receiving considerable research attention and should be on the market within a few years. such as vegetables. Methods include (1) use of a browning element.• • • Foods containing mostly water. exacerbated by initial temperature and specific composition. Susceptors help to overcome these differences.7 Susceptor types In the parlance of deposited films. reach temperatures of frying. foods containing fats and oils. Among dry foods. which may exceed 2000C (392°F). thus reach boiling temperature. which reacts to microwaves by becoming hot enough to create the desired temperature. • thin films are direct condensations of individual atoms. mashed potatoes and a dessert of cherry cobbler. The characteristic temperature-time curves for foods in a microwave oven vary over a considerable range. bursting can result. Thus potatoes baked in the microwave are first deeply pierced so moisture has exits. and (2) a surface. from a paste Thin films may be only a few angstroms up to a thousand or more angstroms (1 angstrom = 10~8 cm = c. or lack of crisping in some areas of the food when other areas were done.• thick films are deposits onto a substrate from dispersions of the material as. perhaps the root mean square thickness might be more apropos. (ii) In addition. 50%) and in fact overlap the lower end of the range of thicknesses used in window films.7 cf) sharply increased demand for convenience foods most likely to require crisping and browning. the adhesive. the film base or metal or combinations. though some remain. emanated from the paperboard substrate. detracted from the favourable impression this new technology offered. which since that time have been largely corrected or eliminated entirely. especially in the frozen category where uniform temperature attainment is difficult at best. Two examples are: (i) A strong unpleasant odour. typically less than 500 W and 201 capacity (0. but they also produced problems in some cases. through ohmic heating. The most interesting and potentially most useful effects pertaining to aluminium in microwave packaging are those which occur at thicknesses corresponding to Macbeth optical densities (OD) between 18 and 28. At thickness yielding OD = 35. Most of the recent offerings of susceptor-crisped foods seem to overcome the early problems. the rapid growth in use of compact ovens. Thickness is a misleading term to apply to these extremely thin coatings because their surfaces are quite irregular. 4 x 10~9 inch) in thickness. In this range. Moreover. particles form a discontinuous film of non-uniform thickness .which responds to microwaves by becoming increasingly hot. These coatings are largely transparent to visible light (% transmission c.1987) yielded promising heating results which produced the desired cripsing and browning. . Standing time of 5 min narrowed the difference between highest and lowest temperatures from 44 to 33°C (80 to 60 0 F). emitting from the oven or on opening the door after heating. centre line temperatures from middle to ends after the recommended heating time varied from 71-27°C (160-80 0 F) and were not improved with additional heating up to the maximum recommended using the sleeve susceptors provided. In tests of oval cross-section frozen dough-encased pasties (meat pies). for example. as deposition continues. Early susceptors (c. The accompanying rush to formulate suitable foods and packages led to some sub-optimal results. 1986 .an array of electrical resistances . Uneven crisping. the susceptor efficiency was noticeably better at the base of the pies than at the upper surfaces. thickness increases. arcing occurs. Resistive coatings. Two classes of materials are available for producing susceptors. 9. In an experiment with a sleeve susceptor around a frozen waffle. The dome positions the aluminium array with respect to the food and. calls their MicroMatch™ system for field intensification a field management system which focuses and directs the incoming energy. and charring. Other materials may find use for specific reasons. precludes direct contact of the tray with oven walls. the time of microwaving was extended by one-fourth with the result that the sleeve and the waffle began to char. polyarylenes. and others listed among high temperature tray materials for dual oven ware. Alcan found that efficient designs consisted of patches of aluminium arranged on a polymeric.and the distance of the target plane(s) from the antenna. (i) . microwave-transparent.Further advances in susceptors technology are anticipated. thereby reducing the chance for arcing to occur. are potential candidates. Alcan. Such a self-limiting device may be found in current early stage research and development activities.2 Field intensification devices Field intensification devices focus microwave energy to increase local intensity above that which would otherwise exist. In development of the MicroMatch container. FIDs therefore function in a manner similar to optical focusing lenses. These latter offer the possibility of setting specific upper temperature limits on susceptors. not least of which could be greater resistance to heat as higher temperature performance is achieved. snap-fit dome used as a cover for the food tray.a metal antenna . A key need is a susceptor the temperature of which rises quickly to the desired value and holds it nearly constant for the time required. nylons. The extent of intensification depends on the geometrical design of the focusing system . by virtue of an overlap of the tray. (ii) Ferromagnetic/electric materials. The practical application of microwave-susceptible materials to heating of foods is to produce crisping and browning (see Table 9. Engineering thermoplastics including the liquid crystal polymers. Ltd.. i. such as local hot spots. thus overcoming some of the disadvantages of resistive coatings. polysulfones. but the second class may become important when the expected technology is developed during the next five years. Other metals may be used in the future. Susceptors are made of either aluminium or stainless steel deposited on substrates. Susceptor substrates thus far have been limited to polyester films and paperboard.2. Resistive coatings are currently used exclusively in susceptors. materials whose electrical resistance in the form in which they are deposited is high enough to produce ohmic heating.1).e. Inc. MA) Printpak. Excellent 2. Other two are not yet commercial. (San Diego. one product on market has been withdrawn. (Taunton.1 Comparative performance of various susceptor technologies Technology name 'Micro-Match' Firm Alcan. (licensees) Good Good 1. No market success. Accu-Wave' 3. 'BarrierWave' 'Susceptor Film' 'InconaT (Alloy metal) Dupont. Advanced Dielectric.Table 9. Cello-based demetallized 2. PET stainless steel metallized film 'Micromet' (pattern susceptor) Printpak. Inc. Not yet commercial. Inc. CA) Printpak. Presently there are two paid licensees in North America. 'Meals on Wheels'. Inc. Inc. Only one commercial product in North America. Comments Cumbersome Expensive Over-engineered No tray use 1. Now being licensed under technical agreeemnt. About to be taken off R & D program . Good Gaining one customer per month Good Excellent rapid heating Good Rapid heating for French fries and pizza Still somewhat on drawing board Good Excellent Good Lawson Mardon Midsomer North (UK) Good Good Excellent Only limited commercial trials. Only use is in pizza boxes (Healthy Choice brand). Deposition Technologies. however. Ltd (Montreal PQ) Browning Good Crisping Depends on product packaged Even heating Excellent Commercial status Limited success. 1. 'Accu-Crisp is the mainstay' as a 'patterned susceptor'. Excellent 3. 'Acan-Crisp' 2. Inc. a FID dome on an aluminium tray directs and focuses energy to provide both control for uniformity and a means of regaining the speed lost by virtue of the tray's inability to transmit MW energy. A FID dome on an aluminium composite tray in which the tray base is plastic or paperboard would overcome the speed loss and would supposedly heat food faster than the same tray without the field intensification. thereby facilitating heating of each food in a multi-component meal to its proper temperature faster heating relatively direct application in manufacturing and ease of changing the required patterns to fit individual food suppliers' needs functioning from above and without direct contact with the food makes possible the browning and crisping of foods having soft and sticky surfaces. . but licensing is reportedly underway in the USA and Germany. Cost of the FID dome will no doubt be a major factor in determining its market niche. Coating increases the electrical potential required for arcing from 30 000 V to c. Alcan has concluded that acceptance would be enhanced if packaging companies better known in the food industry were to handle commercialization. which is not feasible with contact susceptors Use of the MicroMatch container does not always obviate the need to rotate the food to achieve even heating .2.many cheaper MW ovens have no mode stirrer. In addition. the UK for pappadums. The extra space required to accommodate the dome shape and its manufacturing cost will likely limit its use to the more expensive meal offerings. and in Sweden for frozen meat entrees.No commercial application for MicroMatch is yet in place. The aluminium tray is coated to lend greater assurance against arcing. New Zealand for French Bread. Susceptors have been used in Israel for bourekas. Aspects of the system which appear to make it attractive include: • • • • the ability to design the antennae to provide optimal focusing on different areas of food. meat pies and various 'crust' items lend themselves quite well to susceptor utilization. but arcing can occur in either case. 50 000 V.3 Susceptor applications There are numerous packages in the supermarket that utilize susceptors from microwaveable popcorn (reducing the amount of unpopped kernels) to microwaveable pizza (offering a crisp crust). Thus. fruit pies. Another reason for coating that is not usually mentioned is that coating improves appearance and corresponding consumer appeal. 9. Consumers will require convincing evidence of resulting better quality. entrees. By absorbing the gas.4. The success of this cave as an ideal storage space can be attributed to constant levels of high humidity.0 cm (21 in) deep.. and 7. The bags also have minute pores that allow the gas to escape and prevent the accumulation of moisture that could result in the development of bacteria. the bags slow down the ripening process and keep foods fresh longer. a company in Houston. But.0 cm (5 g in) wide. the MW bottles incorporate front and back paper spot labels. which is given off by many fruits and vegetables and hastens ripening. But.produce 9. when the bottle is put in an oven and heated to bubbling according to directions on the black label. NY. hollow handle that is pinched closed where it joins the container's body and shoulder. The study of the caves gave scientists the . the squat PP bottle incorporates a fat.8 cm (6 § in) high 13. 'Evert-Fresh Bags' are reported to be impregnated with processed Oya Stone which has its origins in a cave in Japan. The greenish polyethylene bags are impregnated with a finely ground stone of the zeolite family that has high absorption properties. darkness and. the face of the front labels features an illustration of a microwave oven. Texas makes a new kind of bag for storing produce (Evert-Fresh. on the MW bottles. Minneapolis. Like their counterparts.9. the door of the oven appears black. Syosset. The bags are re-usable if rinsed and turned inside out to dry.) In the bags. (Similar minerals are used to make products like Odor Eaters for shoes. The cave has been used for three centuries to store fresh produce. the microwave-ready bottles are currently in supermarkets across the USA. static temperature.1 Oya produce bags Evert-Fresh.. Squat PP jugs of Hungry Jack pancake syrup to be heated in household microwave ovens feature thermographic 'temperature indicator' labels that tell consumers when the syrup is hot. Extrusion blowmoulded by Continental Can Co. On the shelf. The handle design is meant to warn consumers and prevent them from burning themselves when handling the heated bottle.3 Application of temperature indicator to microwaveable packaging An interesting American microwave innovation not utilizing a susceptor. most importantly. but still an * active package' form is a microwaveable polypropylene bottle for pancake syrup. Developed by Pillsbury Co. The 24 oz bottles stand 16.4 Active packaging . 9. 1994). the mineral absorbs ethylene gas. the ability to absorb the gases discharged by the stored produce. the black oven door on the front label fades to yellow and the word 'HOT appears in the centre. MN. lettuce. Also proven is the use of modified atmosphere storage to control the carbon dioxide and oxygen levels which affect vitamin C retention. cabbage and green beans indicated that vitamin C loss was reduced in excess of 50% using the Evert-Fresh bag for long term storage. AU of these are major factors in successful long-term storage of produce. vitamin C and (3-carotene losses in leafy vegetables are well over 50%. Storage evaluations of leaf spinach. The Vitamin C contents were determined using the Indophenol Method. light. 9. Under these conditions. can depend upon the nature of the vegetable.2 Oya test results A substantial portion of the vitamins and minerals in the American diet come from fruits and vegetables. Tests regarding vitamin C retention using the Ever-Fresh bag and ordinary polythylene bags were conducted in Japan by the Consumer's Products Company. has demonstrated that the susceptibility to heat destruction of 3-carotene. maintains temperature control. Crown Daisy Evert-Fresh Polyethylene After 12 days 60% 40% Final results indicated that Evert-Fresh reduced vitamin C loss by 50% over a 12 day storage period during the Crown Daisy test. testing with vegetables. For example. maintains humidity. oxygen and pH. •CROWN DAISY is an edible flower popular in Japan . rapid transpiration occurs and vegetables wilt. when refrigerated. which is a pre-cursor for vitamin A. Combine these two elements with modern refrigeration (temperature) and three of the four factors that affect vitamin retention are excluded. the bag is green in colour to reduce light transmission and made breathable to enhance the transpiration of gases (O2 and CO2). Control of temperature and humidity are necessary since if low humidity conditions prevail. Broccoli After 3 days After 6 days After 12 days Evert-Fresh 95% 90% 77% Polyethylene 90% 80% 50% Final results indicated that Evert-Fresh reduced vitamin C loss by 54% over a 12 day storage period during the broccoli test. broccoli. Stability of vitamins in produce is affected by a number of factors.key to developing the Evert-Fresh film that absorbs ethylene. It is reported that this bag does effectively reduce vitamin loss. such as whole cabbage and green beans. including heat. Specifically. and. is permeable to other gases.4. Approximately 50% of the vitamin A and over 90% of vitamin C come from this food group. 9. the remaining 30% is shared by approximately 15 other Japanese producers.9. the trend toward fresh produce has resulted in products such as fresh cut packaged vegetables. Products are designed to be moisture-activated preventing primary oxidation until time of use.1). Inc. and now reportedly command over 70% of the 10 billion unit per year Japanese market. for use in a wide variety of food packs. while others are for dry applications. .4. The rate of package material gas permeation is controlled to allow for natural respiration to occur with the product distributed under refrigerated conditions. the concept does utilize controlled permeation. or for Figure 9.5 Oxygen absorber food applications In 1977. In 1988 Multiform Desiccants introduced Fresh Pax™ oxygen absorbers (Figure 9. 1994). as the first US producer of oxygen absorbing packets. These are prepared using ultra-clean processing and packaging.3 Modified atmosphere produce With the exception of the Oya type consumer produce bags. Mitsubishi Gas Chemical introduced 'Ageless' oxygen absorbers in Japan.1 Fresh Pax oxygen absorbers introduced by Multiform Desiccants. Between 1988 and 1994 Multiform developed a family of products to meet the specific needs of the North American marketplace (Multiform. While not strictly an 'active' package form. and dehydrated foods.Pioneer beef jerky Figure 9.2 Multiform Desiccants. adhesives and custom print are available. 8 oz refrigerated sliced peperoni Marks & Spencer . oxygen absorbers can be found in medical devices. refrigerated pasta.FreshPax 3 oz bottled bacon bits. the most common uses for oxygen absorbers are in protecting processed and cured meats. vitamins and in protecting valuable collectibles. peanuts. Fresh Max can be automatically applied within packages using conventional labelling equipment.DiGiorno refrigerated pasta Goodmark . snack foods. smoked and cured meats.situations where carbon dioxide is present. high value baked goods. In 1992 Multiform introduced FreshMax® oxygen absorbing labels (Figure 9.beef jerky Melody Foods . are as follows: • • • • • Hormel Foods corp. or to control oxygen removal rate at a wide range of temperature conditions. Outside the Orient.2) designed to meet a market desire to make the absorber an integral part of the package system. .. Some common items containing the absorbers manufactured by Multiform Desiccants Inc. treats. . pet foods. Formulations are being adapted from FreshPax development. and other nut varieties. introduces FreshMax oxygen absorbers for processed. and a wide variety of substrates. In addition to human foods.St Michael's sliced meat products (UK) Kraft . artemia. Inc. NY.oxygen scavengers This subject has been extensively discussed in Chapter 8. makes up 30-35% of the paper's weight. and used in various beer bottle crown liners. New applications are evolving almost weekly.fresh pasta (DiGiorgio brand) Penge Foods . Mitsubishi Gas Chemical Americas' 'Ageless' absorbers (Mitsubishi.poultry Dokosil Foods .sliced peperoni.6 Other applications International Paper. and Full Sail Brewing Co.shelf stable bread... and whole fat powdered milk. and filters. chow mein noodles. replacing clay and other fillers typically used in paper. Des Plaines.shelf stable bread In addition to this list. marketed by ZapatA Industries. IL supplier of Abscents deodorizing powder. The powder. feminine hygiene products. however. bacon bits Kraft General Foods .beef jerky Goodmark Foods . Purchase.sliced ham and poultry 9. . nuts. ZapatA is actively pursuing this market (ZapatA. Sanfillipo .shelf stable tortillas Dietary specialties .coffee beans Advanced Development Corp . potato sticks John B.powdered drink Tyson Foods . Aquanautics Corp is the developer of 'Smartcap'®. No large volume beer application yet exists. has developed an odour-trapping paper in conjunction with UOP. At present. International Paper is still investigating uses to see if paper with Absents is a viable. Paper made with Absents powder has been tested in surgical face masks. potato chips. cost-effective product. Abita Brewing Co. 1994).5. 9. hamburger buns. 1994) are used as follows: • • • • • • • • Hormel Foods Co. Microbreweries using ZapatA's PureSeal® include Sierra Nevada Brewing Co.• • • • US Military . cake.beef jerky Victor coffee .1 Bottle closures . which absorbs odours instead of masking them. an estimated 20 microbreweries use the Pureseal® liner in various applications. Cellis Brewing Co. . the institutional and food service markets have used oxygen absorbers to protect such products as processed meats..bulk peanuts and almonds NASA . commun. September. TX). NY) September. 1994. NJ). Multiform (1994) pers. (1987) Microwave Packaging. Inc. with Mitsubishi Chemical (New York City. 1994.International Paper foresees applications in the medical industry. commun. commun. (Milltown. 1994. References Evert-Fresh (1994) pers. with Multiform Dessicants (Buffalo. food packaging and household deodorization. NY). commun. A multi-client study published by the Packaging Group. Mitsubishi (1994) pers. ZapatA (1994) pers. Packaging Gp. The company is also testing uses for automotive products. . October.. with ZapatA Industries. 1994. with Evert-Fresh (Houston. August. acetaldehyde. but they are likely to be based on the detection of volatile microbial metabolites such as CO2. and there has been considerable interest in small temperature indicators (TIs) and time-temperature indicators (TTIs) for monitoring the useful life of packaged perishable products. For example. retailers and consumers alike with assurances of integrity. and some of the latest research directions are highlighted. This chapter reviews some of the physico-chemical principles utilised by different types of indicator. Other intelligent product quality indicators might include microwave doneness indicators. and physical shock indicators. SELMAN Time-temperature indicators are part of the developing interest in intelligent packaging. UK) which provides a tamper evident recloseable pouch that . There are over 100 patents extant for such indicators based on a variety of physico-chemical principles. however.D.1 Introduction Time-temperature indicators are one example of intelligent packaging. quality and authenticity. (Sale. Partial history indicators will not respond unless some temperature threshold has been exceeded. and discusses the various issues concerning their application. including consumer interests.10 Time-temperature indicators J. widespread commercial use has been very limited for a number of reasons. The most familiar types include the physical barriers such as plastic heat shrink sleeves and neck bands. More sophisticated systems include Vapor-Loc introduced by Protective Packaging Ltd. and interest in this is growing because of the need to provide food manufacturers. ammonia and fatty acids. TTIs must be easily activated and then exhibit a reproducible time-temperature dependent change which is easily measured. tape and label seals. This change must be irreversible and ideally mimic or be easily correlated to the food's extent of deterioration and residual shelf-life. Similar principles are being used in indicator systems for validating heat processes. while full history indicators respond independent of a temperature threshold. No microbial growth indicators are commercially available yet. 10. and paper/plastic/foil inner seals across the mouth of a container. microbial growth indicators. alcohols. depending on their response mechanism. Tamper evidence and pack integrity indicators are perhaps the most well developed category. TTIs may be classified as either partial history or full history indicators. have been discussed by others (Woolfe. A number of other developments are on the horizon. . However. Full history (continuous response). Bhattacharjee (1988). magnetically coded closures and electrochemical devices. electromagnetic ink scattering. and so on. Farquhar (1977). • • • • • Chill temperatures (go/no go basis). Olley (1976. indicators must be able to function in order to monitor one or more of the following. Frozen temperatures (go/no go basis). In the area of product authenticity and counterfeiting. Secondary tamper evident features rely on subtle devices based on chemical reactions.combines the security of a barrier pouch with the ease of a recloseable zipper seal. Some that are now commercially available utilise pattern adhesive labels and tapes. thermochromic and photochromic inks. optically variable films. there is a large range of intelligent package devices which are being developed for use in various industrial sectors. Many different types of indicator have been devised over the years and general reviews have been presented by several authors. and Selman (1990). Cook and Goodenough (1975). In general terms. solvent soluble dyes and encapsulated dyes. optically variable films and holographic tear tapes. and temperature monitoring and measurement. gas sensing dyes are the most advanced. Selman and Ballantyne (1988). including Schoen and Byrne (1972) covering patent literature from 1933 to 1971. TTIs usually utilise a physico-chemical mechanism that responds to the integration of the temperature history to which the device has been exposed. a CO2 sensing dye could be incorporated into the laminated top web film of a modified atmosphere pack. Kramer and Farquhar (1976). Schoen (1983). There is continuing interest in the monitoring of temperature in the food distribution chain from factory to the consumer. including the application of smart cards within caps. 1978). particularly of chilled foods. Some of these will be applicable to the food industry and include the use of holograms. 1992). biological markers. Ulrich (1984). Temperature abuses. As part of the approach to assuring product quality through temperature monitoring and control. For example. and concealing techniques. biotags. Temperature indicators may either display the current temperature or respond to some predefined threshold temperature such as a freezing point or a chill temperature such as 80C. computer scrambled imaging. and this could be designed to change colour when the CO2 level falls below a set concentration. attention has focused on the potential use of indicators. especially for modified atmosphere packs. IR and UV bar codes. Partial history (response over threshold). .2 Indicator systems There are a variety of physico-chemical principles that may be used for indicators. time and irreversibility. i. The sensory quality of food deteriorates more rapidly at higher temperatures due to increasing biochemical reaction rates. UK).In order to achieve the monitoring objectives. UK).e. enzyme reaction.. . the reaction rate approximately doubles for each 100C temperature rise. including melting point temperature. many indicators give one of three responses: colour change. • Response accuracy. as a sticky-backed paper label (Avery Label Systems Ltd. For many chemical reactions Q10 has a value around 2. the deterioration rates of stored foods follow similar patterns. movement. chemical reactions can be used in indicator systems so that by design the reaction rate can be made similar to that of the rate of deterioration of the food. This is important for two reasons: firstly. 1989a. it may therefore be important that the indicator reaction has an activation energy that is similar to that of the food deterioration (Taoukis and Labuza. Such increasing reaction rates are often measured in terms of Q10 (the ratio of the rate at one temperature to that at a temperature 100C lower). including: Ease of activation and use.1. say from 3 to 20. by Schubert (1977) and Olley (1978) for frozen products. there are several important requirements for indicators. Tables of product activation energies or Q10 values have been given by Hu (1972) for ambient shelf-stable foods. polymerisation. a number of types of labels are discussed below.Indicator may need to be stored and stabilised below threshold temperature for several hours before use • Response to temperature or to cumulative effect of time and temperature.g. and liquid crystals. although Q10 values may be higher. Ruislip. and by Labuza (1982). • Correlation with food deterioration. corrosion. Cambridge. 10. those manufactured by Liquid Crystal Devices Ltd. and secondly. and Hayakawa and Wong (1974) for the scientific evaluation of shelf-life. e. Liquid crystal graduated thermometers may be familiar to some (e. Using these systems. UK) or designed to show selected temperatures as with the Hemotemp II (Camlab..g. or both colour change and movement. • Correlation with distribution chain temperature/time. and they can be engineered in different ways. 1989b). A variety of patents have been recorded and some of these are summarised in Table 10. Maidenhead. As different foods lose quality at different rates. The • . D.87 French Patent 2625-599A 28. Minnesota Mining MFG Mitsubishi Heavy Ind.88 French Patent 2626-072A 20.03. B.88 .M.88 W.09. The process is irreversible and operates quickly Use of vegetable leaves to indicate thawing . French Patent 2626-668A 29. Levin. German Patent 3716-972A 20. W. irreversible on thawing This device is a sealed unit containing ice which changes shape on thawing Sphere of ice suspended in the centre of a capsule This device has a geometrically shaped column of ice coloured with phosphorescent material at the centre.green colour turns to black.12.87 European Patent 310-428A 02.88 This device reveals an indicator when the frozen liquid thaws This is a defrost indicator which consists of blotting paper that becomes coloured by afrozenaqueous dye when it thaws A defrost indicator for frozen foods. KK Perez Martinez. J. Gradient.01.10. W. KAO Corp.07. F.82 British Patent 2209-396A 04.05. German Patent 3731-268A 17. B.Based on Ice Melting Bigand. Wanfield-Druck KaId French Patent 2441-076A 23.01. Fauvart. Holzer. Y.Cold chain monitoring systems Thaw Indicators . F. German Patent 2824-903C 13.89 French Patent 2641-61IA 09.01.01. Toporenko. When these thaw they lose their shape This device consists of an evaluation indicator which is stable when frozen but separates on thawing This indicator uses an irreversible change of state system: once a temperature change occurs it is recorded This consists of a microporous sheet which becomes wetted when the liquid thaws.1 Some recent patents . Perinetti. Holzer.87 W.09.89 W.88 European Patent 2002-585A 10.07. F. Loss of geometry indicates thawing Solvent/membrane indicator.88 French Patent 2616-596A 06.S.87 Japanese Patent 0031-809 21. it uses a windowed packaging system to observe change of shape due to thawing This device makes use of an ice tablet and an empty chamber which willfillup with water if the temperature rises This device consists in developingfrozenhemispheres of ice on the surface.10.Table 10.01.87 Japanese Patent 2021-229A 08. when solvent melts colour is developed Bi-metal stripflexesto display colour to indicate critical temperature reached Uberai. Dye diffusion in agar.87 W. hydroquinones. US Patent 4892-677 19. amino compounds.88 Also US Patent 4929-020A US Patent 4804275 14. I. The sheet indicates the time elapsed at 50C temperature intervals Bramhall. quinones and nitro compounds This sytem comprises liposomes containing a quenched fluorescent dye. Lifelines Tech.87 Japanese Patent 1250-090A 03. e. It is enclosed in a transparent case. Rame.S. the rate is determined by time and temperature Twin lapse display.10. e.12.1 Continued Electrochemical Time-Temperature Devices Grahm.89 Temperature history indicating label. albumin World Patent 9004-765A 24.03. J.12.09.03.11.89 US Patent 4825-447A 21. It does not react to short temperature changes This device consists of a microcapsule layer containing an achromatic lactone compound pigment precursor and solvent. With retarder. Johnson Matthey Dry Diffusion in Gels Toppan Printing KK Japanese Patent 1141-973A 28. German Patent 3907-683A 09. It measures positive and negative temperature deviations Diacetyiene monomer which polymerises to a dark compound.g. The device consists of a dye diffusing into a gel.88 Three S Tech BV Japanese Patent 1012-237A 22. Inc.87 This is a time indicator to show the expiry of foods started at ambient temperature. P.06.Table 10. the electrodes of a galvanic circuit form a temperature-responsive device Tungsten trioxide electrode/weak acid Toppan Printing KK Chemical Reactions Badische Tabakmanuf Time-temperature indicator based on colour development with time when two chemicals are brought into contact. Thefluorescenceis released by lysis when the product temperature fluctuates. the intensity of which depends on time-temperature exposure A thermal inertia temperature indicator which reacts at a certain preset threshold temperature.g.87 .02.84 French Patent 2613-069A 25. dyed compound contained in a porous reservoir (Thermographic Measurements Ltd. allowing wicking to occur when the melt temperature is reached. UK). Flemington. small and inexpensive. causing it to break. When the dome is pressed. and this is complete when all five windows are blue. compared to the reversible technology exhibited by liquid crystals. a domed indicator paper is separated from a reservoir by a small distance. To activate this partial history indicator. 3M Monitormark indicators consist of a paper blotter pack and track separated by a polyester film layer (3M Packaging Systems. An indicator tag labelled 51. Burton. the two materials come into contact. South Weymouth. e. Andover. would indicate a response temperature . Although these two did semi-quantify the changes. Ambitemp (Andover Monitoring Systems Corp.Freezewatch indicator (PyMaH Corp. Bracknell. a self-adhesive label (18 mm in diameter) which utilises temperature sensitive paints chosen to respond at a variety of threshold freezing and chilling temperatures. If the temperature falls below the response level of the tag. The response temperature of the indicator is therefore the melt point of the chemical used.. the faster the diffusion occurs along the track. then the reaction stops. the polyester film layer is removed. their size and cost did not meet the further important requirements for the indicators to be simple. others quantify the change. Thermographics (see above) have now launched the Thawalert. staining the backing paper. Before use the indicator has to be preconditioned by storing at a temperature several degrees below the response temperature of the indicator. the liquid thaws and flows out. Each indicator has five distinct windows which allow an estimate of exposure time above present values to be made. The higher the temperature above the response level. + 9 or + 200C. USA) was a more recent version of Ambitemp which gave a read-out in degree minutes that could be interpreted from a chart. the liquid inside the ampoule freezes. Tempchron (Andover Laboratories Inc. USA) was a time-temperature integrator which functioned with a fluid that has a specific melting point related to the product to be monitored. The indicator is designed as an abuse indicator which yields no response unless a predetermined temperature is exceeded. UK). by contrast. The above types are based on simple colour development. Chillchecker operates by means of a meltable. NJ. When frozen. Under abuse conditions the melted liquid moves along the capillary tube.. Response of the indicator is measured by the progression of the blue dye along the track. USA) is. The Chillchecker can be designed for different threshold temperatures. If the temperature rises to -4°C. so that at the start of the reaction the chemical/dye mix is solid. allowing the melted chemical and dye to diffuse irreversibly along the track. for example. Incorporated into the paper blotter pad are chemicals of very specific melting points and a blue dye.g. In the inactivated form... a simple irreversible indicator based on some threshold temperature. An alternative I Point indicator (type B) is also available. So. Similarly. which was a common complaint with type A models. colour 3: 130% TTT). Malmo. The development of a yellow colour then indicates product approaching the end of its shelf-life. response times of 7 days and 14 days are available on tags. green to red). The biochemical solutions must be accurate. Taoukis and Labuza. 1984. The device works as a thaw indicator by triggering off an enzymic colour reaction when the solid paraffin melts. The device consists of a two-part material.(melt temperature) of 5°C with a response time of 2 days. the other a lipid substrate and pH indicator. Each indicator model is provided with the same time-temperature characteristics as type A. In model B only two visible colours are seen: green and yellow. 1988. . 1983. 1988).3 kcal/g mole (Wells and Singh. the indicators actually remain green for most of the storage life. whilst responding to the temperature history. This single colour change was designed to reduce variability in colour determination by different personnel. 1987.0 to 14. Blixt and Tiru. 1989b. the lipid substrate is hydrolysed and a pH change results in colour change through four colour increments (0-3. Blixt. Each label has a colour scale to be used as a matching reference. Morris. This is based on enzymic reactions taking place many orders of magnitude faster in liquid paraffins than in solid ones. As the reaction proceeds. one part containing an enzyme solution. Singh and Wells. A range of indicators (A and B with varying TTT) are available. with response temperatures varying from -170C to + 48°C (Byrne. This response refers to the time taken to complete blue colour for all five windows at a constant 2°C above the response temperature of the tag. 1985. 1989a. To activate. These labels have been the subject of several studies (Byrne. Grisius et ai. 2180 and 2220 range from 14. Ballantyne. 1976. Only in the final 5% of preset TTT (95-100%. 1987. Another enzyme based time-temperature indicator has been experimentally developed by Boeriu et ah (1986). results may tend to become less reproducible at longer intervals. I Point labels are 'full history' indicators showing a response independently of temperature threshold (I Point A/B. I Point have made a freezer indicator. 1989). Ballantyne. colour 2: 100% TTT. Using the same technology. Activation energies of the models 2140. the seal between the two parts of the indicator is broken and the contents become mixed. 1976. but the difference occurs in the colour change interval. time to colour in type A) does the indicator change from green to yellow. Sweden). 1988c). This reaction is irreversible and will proceed faster as temperature is increased and slower as temperature is reduced. lasting from 2 years at -18°C to 2 days at + 300C. 1988. Taoukis and Labuza. Manske. which can also be expressed as a percentage of set time-temperature tolerance (TTT) elapsed (colour 1: 80% TTT. 1977. Once manufactured. the more rapidly the polymer changes. The Lifelines system consists of three distinct parts: a printed indicator label incorporating polymer compounds that change colour as a result of accumulated temperature exposure.200C and below. The polymer.Lifelines' Fresh-Scan labels provide a full-history TTI. subsequently falling during storage as the reaction proceeds and the colour darkens. Lifelines' labels immediately start reacting to environmental temperature. 1988). The colour change is based on polymerisation of diacetylenic monomers. A mathematical model can then be prepared to compensate for the differences in reaction rates of indicators and product degradation and allow prediction of product quality from one indicator reading. 1988b). The portable hand-held computer reads both the bar codes and the indicator codes. and the second is the indicator code containing polymer compound that irreversibly changes colour with accumulated temperature exposure. Therefore. During the last two years several American companies have been using these labels on a trial basis. Data from the hand-held computer are transferred to a host computer. 1989).1986. A small circle of polymer is surrounded by a printed reference ring. gradually deepens in colour to reflect cumulative temperature exposure. Consumers may then be advised on the pack not to consume the product if the polymer centre is darker than the reference ring. reflectance of the indicator code is high (approximately 100%). leading to more rapid darkening of the indicator bar (Fields and Prusik.. 1990). 1988a. and software for data analysis (Lifelines Technology Inc. which starts out lightly coloured. Krai et ai. product freshness measurements are entered into the system. USA). 1988). Byrne. Trials at Campden and Chorleywood Food Research Association found these labels to be more reliable than I Point indicator labels (Ballantyne. 1983. The Lifelines Fresh-Check indicator has been developed for the consumer in a simple visual form (Anon. Initially. a microcomputer with an optical wand for reading the indicator. providing information on product and indicator type. which proceeds faster at higher temperatures.8 to 21.3 kcal/g mole (Wells and Singh. to maintain high initial reflectance values. Morris Plains. again showing a response independently of a temperature threshold. 1989). The software package has been designed to correlate reflectance measurements to predetermined time-temperature characteristics. and a comparison is made between the product freshness curve and the response kinetics of the Lifelines labels (ZaIl et al. The first is the standard bar code. Once again the required polymer response can be engineered. 1986. regardless of the use-by date (Fields.. Again. and the system has been found . The indicator label consists of two distinct types of bar code. the higher the temperature. indicators must be stored at temperatures of .. with activation energies for the indicators ranging from 17. Studies have found that the colour changes correlate well with quality loss in tomatoes and UHT milk. 3M Monitormark. The dissolution of the metal anode in acid is temperature sensitive and results in a colour boundary which moves down the strip at a rate governed by the temperature. (Madison. The packaging itself may provide the food with some insulation from the environment and the food temperature will therefore lag behind any changes in outside temperature. However. These have been the subject of a number of independent validation tests. the I Point type. If thawing has occurred. the indicator system is placed inside the pack but with its response change visible externally. USA) have developed a quality freshness indicator. In the case of this label.useful for determining shelf-life expiry when products are held under proper refrigerated conditions. When one of the substrates becomes depleted. where they have been applied to over a dozen types of chilled retail products (Monoprix. with a hazard warning area visible externally.. . Oscar Mayer Foods Corp. also claim good correlation with the quality life of cooked ready meals. with a metal overprint at one end. 1989). and the potential exists for miniaturisation of such indicators.e. It consists of a film of electrochromic material (in this case tungsten trioxide). The indicator can be engineered to respond to short total times and shows some promise in this respect. and the polymerisation reaction is influenced to some extent by light. use is still limited by the lack of response to short periods of temperature abuse. and that is that all other indicators are placed on the outside of a pack and therefore respond to the environmental temperature. There is at present considerable interest in these indicators. and the test systems and references are given in Table 10. The most prominent of the indicators to date have been the three referred to above. the red dye moves along the label and exposes a warning printed in hydrophobic white ink. Lifelines Inc. and their Fresh-Check label has been trialled in some of the department stores of the French company Monoprix. a rapid pH change occurs. for example for fresh eggs where short time-temperature rises may not directly affect quality. During 1991. Marupfroid (Paris. This is based on pH-sensitive dyes in contact with a dual reaction system which simultaneously produces acid and alkali to maintain a constant pH. i. fresh chicken and yoghurt. The part of the tag containing the redcoloured ice is located inside the pack next to the frozen food. 1990). One very important point must be highlighted here. and the Lifelines Fresh-Scan and Fresh-Check.2. Johnson Matthey has patented a system based on the corrosion of an indicator strip (US Patent. A rise in temperature causes a shift in the equilibrium and the colour changes. resulting in a sharp visual colour change (green to pink). printed onto a card. Lifelines continued to evaluate their polymer-based indicators used in both the food and pharmaceutical industries. The latest types are light-protected by a red filter. France) has developed a partial history freezer label based on the melting point of ice. (1987) Wells and Singh (1988b) Wells and Singh (1988b) Wells and Singh (1988b) Wells and Singh (1988b) Malcata (1990) Chen and ZaIl (1987a) Chen and ZaIl (1987b) ZaHetal. (1988) Krall et al (1988) Singh and Wells (1986) Taoukis and Labuza (1989a) Taoukis and Labuza (1989b) WeUs and Singh (1988c) Fields (1985) Fields (1985) Ballantyne (1988) Wells Wells Wells WeUs and and and and Singh Singh Singh Singh (1988b) (1988b) (1988b) (1988b) I Point .2°C) Response to isothermal conditions (4-300C) Response to non-isothermal conditions (4-300C) Response to temperature (0-370C) Response to temperatures (5°C and 100C) Green tomato maturity (10-200C) UHT sterilised milk (5-37°C) Fruit cake Lettuce 0 Reference Wells and Singh (1988a) Grisius et al. (1986) Krall et al.2 Validation tests on time-temperature indicators Model Lifelines Fresh-Scan Fresh-Check System test Tomato firmness (10-20 C) Microbial growth in pasteurised milk (0-50C) Green tomato maturity (10-200C) UHT sterilised milk (5-37°C) Fruit cake Lettuce Pasteurised milk (pallet) Milk. cream and cottage cheese Orange juice UHT milk freshness Orange juice concentrate (frozen) Fresh produce (chilled) Hamburger patties UHT milk freshness (21-45°C) Orange juice (7.Table 10. 4 to .4-100C) Response to isothermal conditions (4-300C) Response to non-isothermal conditions (4-300C) Response to isothermal conditions (4 . beef patties.15°C) Milk (4.1O0C) Unspecified (two models) Response to isothermal conditions .20 to + 300C) Milk (4. macaroni cheese (pallets) (.12°C.17°C) 0 0 Reference Grisius et al.2 Continued Model System test Pasteurised whole milk (0 C. . -100C) 3M Monitormark Hamburger rancidity (>. (1987) Singh and Wells (1985a) Singh and Wells (1987) Singh and Wells (1985b) Olsson (1984) Olsson (1984) Kramer and Farquhar (1977) Mistry and Kosikowski (1983) Taoukis and Labuza (1989a) Taoukis and Labuza (1989b) Wells and Singh (1988c) Wells and Singh (1985) Ballantyne (1988) Wells et al. beef patties and macaroni cheese (pallet loads) (.20 to .4-100C) Response to isothermal conditions (4-300C) Response to non-isothermal conditions (4-300C) Response to isothermal conditions Response to isothermal conditions (.Table 10.18 to + 5°C) Response to isothermal conditions (+ 2C. (1987) Singh and Wells (1986) Wells and Singh (1985) Kramer and Farquhar (1977) Mistry and Kosikowski (1983) Taoukis and Labuza (1989a) Taoukis and Labuza (1989b) Ballantyne (1988) Arnold and Cook (1977) Steak. (1987) Wells et al.12 to + 350C) Seafood salad (pallets) (.100C) Codfish(frozen) (pallets) Steak. + 100C. 5°C and 10 C) Hamburger rancidity (frozen) Hamburger rancidity Strawberries (.23.20 to + 300C) Pizza (. UK) uses a thermochromic ink which undergoes an irreversible colour change (Summers. and the principal element in its makeup is a shape memory alloy. France) have launched their re-usable thermomarker. UK) have recently launched their Reactt TTI self-adhesive label for monitoring freezing and chilling distribution temperatures (Pidgeon. Food Guardian (Blandford.Imago Industries (La Ciotat. In the device itself. The label indicates the time on the scale for which the temperature has been above the designated temperature. Senders (London) have developed a threshold label for application to large boxes and pallets. if the liquid thaws. In the case of microwaveable products. all points within the food should be reheated to an equivalent of 700C for 2 min. The Reactt doneness indicator from Bowater Labels is a modification . However. That from 3M (Bracknell. At the point of freezing. A patent from Microtechnic (Germany) apparently uses the alignment of two magnets as an indication of the thawing of a frozen food. This is solid and relatively large (88 x 53 mm). Courtaulds Research (Coventry. which is self-activating before use and shows an irreversible colour change to reveal an underlying symbol warning. the Smartpak 1812 label self-activates when it is frozen below -18°C. The labels remain inert until activated. a spring made of shape memory alloy changes size according to predetermined temperatures within a programmed range. then change from blue to red to reveal underlying graphics when preset time/temperature limits are exceeded. 1994). UK) make cold chain indicators which can produce either an abrupt change of colour (yellow to blue) at its end point. and a second indicator showing the need for rejection. then the attraction by the opposite poles of the magnets will promote movement and the two magnets come together. UK) has also just launched its Smartpak label. indicating that thawing has occurred. Albert Browne (Leicester. Trigon Industries Ltd. UK) have begun to promote their label which has a thermometer profile. UK) have considered developing a temperature-sensitive colour in acetate film. This could be used to detect when a product is fully defrosted and ready for cooking. research has shown that for microbiological and other quality criteria. This in turn activates a system which ejects different coloured balls that signal the reaching of the various temperature thresholds. two magnets are held unaligned in a small liquid container. and this consists of both a warning indicator that the temperature is getting too high. and subsequently indicates the temperature rising above -12°C. 1992). or a more gradual change depending on its application. assuming no storage abuse. They have specialised in thermal indicators for many years and are now promoting their time-temperature cold chain indicators in both the food and pharmaceutical industries. To date only two doneness indicators are available. For example. Bowater Labels (Altrincham. The alloy effectively 'memorises' two distinct shapes associated with predefined temperatures. (Telford. For example.of the TTI self-adhesive label and works on the same colour-change principle described earlier.3 Indicator application issues and consumer interests It is generally agreed that there are a number of potential applications for which the above-mentioned indicators could be used regarding the monitoring of various aspects and parts of the chilled and frozen distribution chains (Singh and Wells.50 for bar code labels and 3. In 1991. 1990). TIs and TTIs represent new applications of technology. and cost benefits. with little or no history of successful and reliable application. Ideally. The latter lower cost related to production runs in excess of 10 million units. For example. most indicators will not react rapidly enough to respond to such regimes. including on pallets or consumer packs. in particular relating to reliability and reproducibility. chilled and frozen foods should be stored at the appropriate temperature. and two hours at 200C did not show a response that was significantly different to the control at 5°C (Ballantyne.250 for Fresh-Checks.50. retail shelf-life. the potential exists for indicators to be used in several ways. response to environment temperature but not necessarily food temperature. although the challenge of measuring and correlating cold point temperatures with overall pack temperatures remains considerable. Lifelines have done work over the last two years and now claim that a dual chemistry system can be engineered to specifications required.5 to 1. Risman (1993) refers to the gel indicator technique developed at the Swedish Food Research Institute for assessing the reheating performance of domestic microwave ovens for ready meals. in 1988 Lifelines bar code labels cost 30-70p each (scanning system US$20 000). the proliferation of TIs and TTIs now being offered. a Lifelines indicator subject to 24 hours at 5°C. Lifelines' prices in the USA ranged from 7. Therefore. parts or all of the distribution chain. Such periods may be short. Other devices are being developed at this time. for stock rotation. 10. sensitivity to short-timetemperature abuse. 1988). Also. there may be several points in the distribution chain where the environmental temperature is raised. Provided these concerns are addressed by a given indicator for a specified product (or range). To date. from a few minutes to several hours. is of concern as this is likely to confuse the consumer. the industry has been expressing concern regarding several issues about all types of indicator. and as a simple consumer guide. However.5 to 3. I Point labels 15-2Op each. However. six hours at 100C. which should remain constant. involving many different forms of indication. . for small trial quantities. there may be some important limitations of some indicators that must be recognised. and the 3M Monitormark about £1. and until recently there has been no standard against which their performance could be assessed. An incorrectly applied date mark is self-evident. and no reasonable possibility of preactivation. Almost all respond to temperatures on the outside of the pack. A TI or TTI which reflects product temperature would be of far greater value and relevance than one which responds to the temperature on the outer surface of the pack. The legal requirement for a best before and use by date on the pack will continue for the foreseeable future.To be effective and of value to manufacturer and consumer. every indicator should be supplied with a clear indication to the manufacturer. Related to this. Hence. Measurement at this point may be of value. when it is activated. In particular. unsubstantiated claims should not be made regarding any role in relation to safety. at least to the manufacturer at the point of application. the point at which product life starts can be clearly defined for the purposes of declaring a 'best before' or 'use by' date. over the full range of temperatures likely to be experienced and when the temperature fluctuates. or whatever other timetemperature related factor is liable to affect the quality of the foodstuff. The quality management of the manufacture. or especially post-activation. This should be no less clear and unambiguous to the great majority of the population than the current minimum durability instruction. None is known to measure food centre temperature. but the limitations in terms of usefulness and relevance of such measurement need to be made clear to the user and the consumer. which is claimed to measure food surface temperature. TTIs in general do not measure product temperature. Only one commercially available type is known. A TI or TTI also needs to be able to cope with fluctuating temperatures (including elevated temperatures for a short time) and to respond accurately and reproducibly at the extremes of temperature likely to be experienced by the product. they will require a range of TIs or TTIs designed with related performance characteristics. distribution and storage of the TTI and the reproducibility of its performance must be of at least as high an order as the food product it seeks to monitor. In addition. some consumers may have difficulty in detecting the difference between two colours. consumer instructions on the pack will need to clearly indicate the action to be taken when there is conflict between end of product life indication as given by the best before and use by date and the TTI. i. There is also concern that where TIs and TTIs may have a role to play with regard to product quality over life. or shades of one colour. . there is concern that the wrong TI or TTI may be applied to a given product. TIs and TTIs must provide an indication of the end-life of the product. can also be known for certain. 1990).e. where this forms the end point. It is essential that the start point of the life of the TTI. with selfindication that this has occurred. A TTI may need to mimic the growth of food spoilage microorganisms. Therefore. partial activation. where there may be some thermal insulation between product and indicator (Malcata. As manufacturers may be producing simultaneously a range of products with different predicted lives. nearly half those questioned would trust the TTI response if it had not changed but the product was beyond its durability date. A joint Ministry of Agriculture. and the clarity and accuracy of end point determination.g. In order to address these issues of concern. the industry concluded recently that a specification was required which could be common to all types of TIs and TTIs. The indicator or the package should self-indicate if removed from the product. TIs and TTIs in themselves must not represent a hazard to the consumer. In the retail situation. This specification defines the testing scope for indicator type and application. 1991). the need for evidence of tamper abuse.distributor. and has completed a food industry specification (George and Shaw. but only grasped their concept after some explanation. indicated that almost all respondents (95%) thought that TTIs were a good idea. the indicator compatibility with food. the majority of respondents (57%) would use their own judgement in . at the same time. indicating that substantial publicity or an education campaign would be required. A survey of 511 UK consumers. It covers evaluation of the accuracy of indicator activation point. and the enforcement authorities of the precise temperature threshold or time-temperature integration to which the indicator will respond. In particular. and the evaluation of the kinetic constants of the indicator. It refers to the quality management of the indicator manufacture. Such a specification would address the basic technical requirements for the performance of such indicators. The relationship and possible conflict between the indication of the TTI and the durability date on the food was considered a problem. e. It is hoped that this will provide a basis for indicator manufacturers to design the performance of their indicators to meet the needs of the food industry. It then outlines test protocols for indicator response to temperature. and indicator labelling. Finally. including temperature cycling and abuse. care needs to be taken to make the indicator 'child-proof. and finally simulated field testing. if swallowed. with clear instructions about what to do when the indicator changed colour. and which could be used by manufacturers of such indicators in order to meet the requirements of the industry and of the consumer. Fisheries and Food (MAFF)/industry working party met during 1991 at the Campden and Chorleywood Food Research Association. although it is accepted that commercial reasons may influence the decision to use indicators for a particular application. carried out by the National Consumer Council (MAFF. Use of TTIs would have to be in conjunction with the durability date. retailer. The TI or TTI needs to be no less resistant to malpractice and tampering than is the printed date on the pack. and at the same time provide a basis for the users of such indicators to check the indicator performance against their requirements. if removed it should damage the packaging in such a way that a fresh indicator cannot be applied without detection. 1992). If the TTI changed before the end of the durability date when stored at home. their spores (viability) or enzymes (activity) upon heating is the basic working principle. Current research is directed towards evaluating new systems which may give precise quantitative indication. the value of TTIs was recognised for raising confidence in retail handling. and could identify whether the ovalbumin had been heated to lower than 65°C or higher than 85°C. Marin et al (1992) studied the effects of graded heat treatments of 30 min from 40 to 1000C on meat protein denaturation. application in the food material. They measured the remaining antigenic activity of the meat proteins and found this was significantly correlated with the heating temperature. 1972). For biological TTIs. Hendrickx et al (1993) have conducted an extensive review and have classified time-temperature indicators. origin. It is clear that there is a future for TTIs in monitoring the chill chain.deciding whether a food was safe to eat. and location in the food. potential has been shown for correlating the loss of food pigments such as chlorophyll. However. the change in biological activity such as of microorganisms. as shown in Figure 10. and changes in anthocyanins. type of response. with heat treatment (El Gindy et al. using differential scanning calorimetry to measure changes in protein conformation (De Cordt et al.1.3. in terms of working principle. Varshney and Paraf (1990) used specific polyclonal antibodies to detect heat treatment of ovalbumin in mushrooms. Other food compounds may . 1990). and improving hygiene practices when food is taken home and stored in refrigerators. and some examples of commercially available indicator systems are summarised in Table 10. 1992). Brown (1991) studied the denaturation of several enzymes and suggested that an approach which measures the status of a number of enzymes in terms of pattern recognition would be better than using a single enzyme to indicate retrospectively the heat process that had been applied. Most of these tend to give qualitative indications. However. 10. with at least 25% putting some of the blame on the food suppliers. and the advantages and benefits of increased food safety for the higher-risk foods that would result. the consumer can appreciate the concept. 1994). Development of different indicators is still in progress and technical difficulties have to be overcome by carrying out the appropriate tests (George and Shaw. The use of inoculated alginate particles is an example of the use of spores (Gaze et al.4 Chemical indicators for thermal process validation Similar approaches to temperature indication have been taken for assessing pasteurisation and sterilisation processes. Recent studies on enzyme activity have shown potential for the use of a-amylase. Brown (1991) also determined the feasibility and potential for ELISA techniques for retrospective assessment of the heat treatment given to beef and chicken. In terms of chemical systems. ..3 min Steam autoclaves . (Flemington.4-1040C Black to red White to black or red Purple to green SteriGage Thermalog S A blue colour front diffuses along a transparent window of an accept/reject band . Twickenham. NJ. (Flemington.colour change over 100-1800C for a range of exposure times Dry heat = 1600C for 120 min to 1800C for 12 min Ashby Technical Products Ltd. ketone based Immediately temperature is reached Irreversible indicator. stearothermophilus) over a range of timetemperature combinations Reatec AG (Switzerland) (Barbie Engineering. semiintegrators using chromium chloride complex for different temperatures (110-126.70C) and times (0-150 min) calibrated against spore destruction The presence of saturated steam lowers the melting point of a chemical tablet Diffusion of the blue colour front has been calibrated against spore destruction (B. Wigan. UK) Trade name Autoclave Tape Thermometer Strips TST Steriliser Control Tube Colour White to black (stripes) Silver to black Yellow to mauve Red to green Change characteristics 121°C for 10-15 min and 134°C for 3-4 min for fully developed colour change Immediately temperature reached Set to 121°C for 15 min or 134°C for 5. USA) (Temperature Indicators Ltd. UK Agent) PyMaH Corp. eight ranges selectable. UK) PyMaH Corp. USA) Colour Therm (Surrey. CA. UK) 3M Industrial Tapes and Adhesives (Manchester. Wigan. UK) Cardinal Group (Tiburon. UK) Albert Browne Ltd.Table 10. USA) (Temperature Indicators Ltd.3 Commercially available time-temperature thermal process indicator/integrators Manufacturer 3M Industrial Tapes and Adhesives (Manchester. (Ashby de Ia Zouch. NJ. (Leicester. (Leicester. UK Agent) ATP Irreversible Temperature Indicators Easterday Colour-Therm Cook-Chex Silver to black Self-adhesive segmented labels giving colour change when temperature exceeds set point by 1°C Set at 2400C for 20 min. UK Agent) Reatec White to black Immediately temperature is reached: 54. UK) Albert Browne Ltd. 77. Change set for 30 min at 116°C or 15 min at 127°C Organic thermo-chromic ink. UK) Thermographic Measurements Ltd. UK) Pasteurisation Check White to black or white to red Thermax Autoclave Indicator TLC 8 Silver grey to black Red to green Red to black . colour changes immediately temperature is reached Thermographic Measurements Ltd. (Deeside. irreversible colour change paints. S. UK. USA) (Temperature Indicators Ltd.Table 103 Continued Manufacturer Redpoint (Swindon. UK) Trade name Spectratherm Colour From light blue to a colour in the spectrum donating maximum temperature Change characteristics Liquid crystal colour change immediately temperature is reached Irreversible colour labels. 40-2600C. UK) Mauve to green Integraph Brown to black Cross-checks White to black Thermindex For crayons and paints. (Burton. Wigan.D. Wigan. reversible strips.. 37-2600C Autoclave ink. UK Agent) Celsistrip Celsidot Celsipoint Celsiclock White to black Immediately temperature is reached: 40-2600C S. a range of colours dependent on temperature reached Three-stage semi-integrator using chromium chloride Selected precise time and temperature.. European Agent) Thermographic Measurements Ltd. UK) TLC Ltd.. S. Other temperature ratings on request Adhesive strips. UK Agent) SteriTec (Colorado. 82°C and 88°C ratings ± 1°C. USA) (Temperature Indicators Ltd. 40-700C Spirig Earnest (Germany) (Cobonic Ltd. lacquers. Wirral. Burton. UK Agent) Thermindex Chemicals & Coatings Ltd. 40-lOloC. (Deeside. Wirral.. Clwyd.. Special Coatings (Barking. UK) Temperature Tabs SteriTec (Colorado. Wigan. S. Surrey. UK (Temperature Indicators Ltd. 121 to 134°C Adhesive strips 40-2600C Reversible and irreversible inorganic pigment colour change either immediately temperature is reached or after a few min exposure. Wirral. (Burton. 50-10100C Immediately temperature reached: 71. while intrinsic TTIs are intrinsically present in the food. In terms of the Working principle Biological Chemical Physical Response Single Multi Origin Intrinsic Extrinsic Application Dispersed Permeable Isolated Location Volume average Single point Figure 10. there is some basis for assessing heat treatment received as the kinetic characteristics make them suitable as markers for bacterial destruction. such as a spore or a nutrient. . where a food contains either of these sugars. Regarding the origin of the TTI.1 General classification of time-temperature indicators (after Hendrickx et al. an extrinsic TTI is a system added to the food. Kim and Taub (1993) have been studying the thermally produced marker compounds 2. and glucose yields only the latter compound.3-dihydro-3. Potential exists for multicomponent TTIs in the evaluation of thermal processes (Maesmans et al. 1994). Both these compounds are produced when D-fructose is heated. For example.exhibit heat-induced changes. 1993). when subjected to the same thermal process.5-dihydroxy-6-methyl-(4H)-pyran-4-one and 5-hydroxymethylfurfural. Hence. As before. the kinetic response requirement which a TTI should fulfil can be derived theoretically and should match the response of the target index. Such developments will assist in the assurance in and broader introduction of new heat processes such as microwave sterilisation.application of the TTI in the food product. Blixt. is leading to the development of new indicators that are much more precisely designed to meet the needs of the food industry. Brown. (1977) An enzymatic time/temperature device for monitoring the handling of perishable commodities.the state of the art. Dordick. When using intrinsic components as the TTI. Blixt. CH. 36. Elsevier Applied Science Publishers.1) can be used as the basis for single point evaluations. Campden Food and Drink Research Association. Eriksson (eds). M. In: Thermal Processing and Quality of Foods. In the broader context of time-temperature integration. DJ. 997-9. recognise a variety of benefits that can stem from the application of indicators in aiding the monitoring and assurance of distribution chains. This. 525-29. 333-7. Overall. as well as the consumer. 473. Campden Food and Drink Research Association.. (1991) The Use of Chemical and Biochemical Markers in the Retrospective Examination of Thermally Processed Formulated Meals. and indeed other sectors such as the medical and pharmaceutical industries. Food Technology. (1984) The I-Point TTM . . and Cook. (1986) Enzymatic reactions in liquid and solid paraffins: application for enzyme-based temperature abuse sensors. Bio/Technology. Glos.M. it is likely that there will continue to be exciting developments during the next five years. Journal of Food Technology.C. Chipping Campden..M. Technical Memorandum No. (1988) Photoactivatable time-temperature indicators for low-temperature applications. Bhattacharjee. Boeriu. the TTI will be more or less evenly distributed throughout the food. 4. Arnold. It is clear that the food industry. in turn. Byrne. Glos. J. whilst all three approaches (see Figure 10. 30(6). Zeuthen. K.S. A. 66-8. References Anon. Chipping Campden. (1989) Is it time for time-temperature indicators? Prepared Foods. G. (1977) An evaluation of the performance claimed for a chemical time/temperature integrating device. Ballantyne. (1976) Temperature indicators . K. 625. dispersed systems allow the evaluation of the volume average impact.a versatile biochemical time-temperature integrator.5 Conclusions The interest in this subject has generated numerous research studies and practical evaluations of indicator systems. London. applications for thermal process assessment are receiving further attention and novel approaches are actively being researched. UK. Cheftel and C. P. 36(3). H. Developments in Biological Standards. H. 12. and Klibanov. C. 158(12). A. 237.. 10. and Tim.R. Technical Memorandum No. (1988) An Evaluation of Time-Temperature Indicators. J. and this also eliminates heat transfer limitations. Journal of Agricultural and Food Chemistry.G. This whole field is currently the subject of a major European collaborative research study co-ordinated by the Centre for Food Science and Technology at the University of Leuven in Belgium. 219-30. UK. and Wong. Labuza (ed.Case Studies on Perishable Foods and Beverages.D. P.W. A.F.H. T. 1993.W. and Prusik. Process Optimisation and Minimal Processing of Foods. (1993) Advances in Process Modelling and Assessment: The Physical Mathematical Approach and Product History Indicators. De Cordt. J. Journal of Food Processing and Preservation. Hendrickx. Van Loey. L. Kramer. M. (1972) Time-temperature indicating system 'writes' status of product shelf-life.. Fields. and Shaw. 280-2.M. pp. Brown. 580. Fields. Labuza.W. 1-4 October. J. ZaIl. (1977) Time-temperature indicators in monitoring the distribution of frozen foods. E. Kim. Campden Food and Drink Research Association.H...M. (1976) Testing of time-temperature indicating and defrost devices. Raouf. 29. J. R. T. S. Agricultural Research Review. G. and Tobback. J.Byrne.R. (1987b) Refrigerated orange juice can be monitored for freshness using indicator label.P.H. (1990) Microbiological Assessment of Process Lethality Using Food/Alginate Particles. Farquhar.. K. Technology Advances in Refrigerated Storage and Transport. Spence. France. 11. and Tobback.. (1985) Computerised Freshness Monitoring System . (1983) Time-Temperature Monitoring Using Solid-State Chemical Indicators. 1. DJ. (1987a) Packaged milk.R. Elsevier Science Publishers. R. 72. Paris. (1992) A Food Industry Specification for Defining the Technical Standards and Procedures for the Evaluation of Temperature and Time-Temperature Indicators. cream and cottage cheese can be monitored for freshness using polymer indicator labels. El Gindy. De Cordt. 30(2). M. 41-87.G. S.C. A. and ZaIl. 50(4). M. Journal of Chemical Technology and Biotechnology.. Freezing. In: Proceedings of HR XVIth International Congress of Refrigeration. R.S. 402-4. Gaze. (1987) Correlation of time-temperature indicator response with microbial growth in pasteurised milk. Food Technology.P. In: Proceedings of HR Symposium. Barrett. R. S.H. Noronha. UK. Fields. In: Proceedings of IIR Symposium. 47(1). Fields. Dairy and Food Sanitation. K-I. F.. S. Charalambous (ed.C. S. 20-3 September. 59(5). Food Processing. Portugal. Hershey. R. Technical Manual No. R. (1975) Cold chain and chilled chain . (1977) Experience with T-T Indicators. Porto. In: Proceedings of Eastern Food Science Conference VI. 56-62. Kramer. 401-6.. Hu. Maesmans. Campden Food and Drink Research Association.. Pennsylvania. 85/11. (1974) Performance of frozen food indicators subjected to time variable temperatures. ASHRAE Journal.W. Chen. Chen. S.C. 281-90.L. 174-6. 839-46. Wells. Amsterdam. pp. Hendrickx. M.temperature integrity monitoring devices. Dairy and Food Sanitation. (1988) Use of remote communications to transmit product quality information from polymer-based time-temperature indicators. 117-23. 91-9. 7(8).P.E. 26(8)... and Prusik.. and Holdsworth. . LA. Journal of Food Quality.D. Y.). and El Manawaty (1972) A study on the effect of processing temperature and time on the colour loss of anthocyanin pigments in grapes. pp. S. Frozen Storage & Freeze Drying. G. Dairy and Food Sanitation. Food Technology: A View of the Future. Hayakawa.. UK. T. In: Shelf-Life Dating of Foods T. (1989) Monitoring of Product Quality Using Time-Temperature Indicators. P. H. (1986) Shelf-life estimation of beverages and food products using bar coded time-temperature indicator labels. 35. A. Proc. J. Chipping Campden. Glos. 193-9. Grisius. 59. J.). 16(4). Institute Refrigeration. P. (1994) Convenience of immobilised Bacillus licheniformis a-amylase as time-temperature indicator. Food Technology. and Farquhar. and Goodenough. A. Food Technology. 50-6. In: The Shelf-Life of Food and Beverages... 7(6). J.R. Food and Nutrition Press Inc. Maesmans. Chipping Campden. and Farquhar. G. George. (1993) Intrinsic chemical markers for aseptic processing of particulate foods. J. 44—8. M.-J. Trumbull. and Singh. 47-58.E.H. and ZaIl. (1982) Scientific evaluation of shelf-life. R.. 119-23. In: Proceedings of Workshop. Willocx. 309-24.C. 77/1. Cook. and Prusik. Technical Memorandum No. Glos. 8(4). J. (1990) Chill check. T. Krai. and Taub. 39(12). 782-8. Food Technology International Europe. Paris. J. 26(10).X. Meat Processing. In: Proceedings of HR Symposium. Food Chemistry. (1985b) Application of time-temperature indicators in food storage and distribution. J. and Wells. 14. 147-50. R. 49. 25(5). (1988) Time-temperature indicators: do they work? Food Manufacture. M. 9(38). 46(1).. pp. 85/11.V. Food Manufacture.L. Cheftel and C. A. J. (1994) High-tech labels help colour your judgement.P. (1972) Defrost indicators. National Consumer Council. Packaging Week. Singh. (1992) Intelligent Packaging.P. pp. Hendrickx. Pidgeon. London. London. Fisheries and Food (1991) Time-temperature Indicators: Research into Consumer Attitudes and Behaviour. (1987) Monitoring quality changes in stored frozen strawberries with time-temperature indicators. Centre for Exploitation of Science and Technology. De Cordt. CH. 14-19. J.H. Risman.H. and Kosikowski. F. 43. Manske. R. J. F. V. C . Food Technology. Olley. Olsson. P. and Wells. (1985) Experience with Monitormark product temperature exposure indicators. Selman. 296-300.some experiments in the freezer chain. Selman. (1985a) Use of time-temperature indicators to monitor quality of frozen hamburger. Florida.M.O. Singh. and Ballantyne.I.M. R. temperature integrators. (1993) Microwave oven loads for power measurements. (1984) TT integrators . M. (1990) Time-temperature indicators in food inventory management. Germany. Elsevier Applied Science.H. J. P. 17. R. 124-30. 407-23. and temperature function generators to the food spoilage chain. 36-8. In: HR Commissions C1/C2 77-1. In: HR Annex Bulletin 76-1. and Wells. J. Schubert. France. Singh. Marin. 52-7. UK. J. and Sanz. 18. Food Technology.. 15-131. (1988) Monitoring fresh food shelf-life with IfT labels.D. 10(5). pp. USA. . International Journal of Refrigeration. 797-804.P.P. 65(8). P. (1983) Thermal Indicators for Frozen Foods. Monoprix. Ministry of Agriculture. In: Thermal Processing and Quality of Foods.how they work. B. WJ. (1983) Use of time-temperature indicators as quality control devices for market milk. WJ.H. Singh. pp. France. 369-89.. Manske. Morris. (1977) Criteria for the application of T-T indicators to quality control of deep frozen food products. and Byrne. 588-592. H. In: Proceedings of HR XVIth International Congress of Refrigeration. S. (1994) Theoretical considerations on design of multi-component time-temperature integrators in evaluation of thermal processes. Zeuthen. R. L. Microwave World.D. 63(12). 81-6. 481-97. and Wells. J. Monoprix (1990) La Plaisir du Frais: Monoprix Lance Ia Puce Fraicheur. R. M. G. 42-50. J. pp.H. H. International Journal of Refrigeration. 60(4). (1992) Study of the effect of heat (treatments) on meat protein denaturation as determined by ELISA. (1978) Current status of the theory of the application of temperature indicators. Casas. Journal of Food Processing and Preservation. Ettlingen. (1983) The Application of Controlled Fluid Migration to Temperature Limit and Time-Temperature Integrators. Cambero. (1990) The effect of internal thermal gradients on the reliability of surface mounted full-history time-temperature indicators.V. In: Proceedings of HR XVIth International Congress of Refrigeration. London. (1976) Temperature indicators. P. Journal of Food Protection. 14(1). Technology Advances in Refrigerated Storage and Transport. Singh. and Tobback. Paris. temperature function integrators and the food spoilage chain.C. Schoen. Olley. temperature integrators. (1986) Keeping track of time and temperature. Orlando. Malcata. H. 283-6. pp. 46-7. In: UR Annex Bulletin 85-5.. Summers. Sterling Publications Ltd. Paris. (1990) Time-temperature indicators . Journal of Food Processing and Preservation. 52-7. Schoen. 41-2. France. Food Engineering. 311-17. Eriksson (eds). 1(2). and Wells. 30-4.P. CE.Maesmans. 46-50. Mistry. London. (1985) Performance evaluation of time-temperature indicators for frozen food transport. Journal of Food Science. In Chilled Foods: A Comprehensive Guide. 54(4). Revue Generale du Froid. J. Dennis and M. Taoukis. 369-71. Varshney. Singh. 148-52. 52(2). A. 53(1). J.P. Wells. Wells. 261-74. P. Journal of Food Processing and Preservation. 1866-71. Woolfe. (1988c) Response characteristics of full-history time-temperature indicators suitable for perishable food handling. Journal of Food Science. 74(6). Journal of Food Science. (1990) Use of specific polyclonal antibodies to detect heat treatment of ovalbumin in mushrooms. 6(7). R. 783-8. (1992) Temperature monitoring and measurement. ZaIl. R.C. 285-90. 789-92. Wells.C. and Nobel.P. (1986) Evaluation of automated time-temperature monitoring system in measuring freshness of UHT milk. C. P. Stringer (eds). R. and Singh. 156. and Labuza. J. R.H..C. Journal of Food Science. 1893. (1988b) A kinetic approach to food quality prediction using fullhistory time-temperature indicators. T.P. London.P. J.H. and Singh. Ulrich. 337-41 US Patent (1989) Indicator device for indicating the time integral of a monitored parameter. Ellis Horwood. Wells. 53(6).S. and Labuza. (1987) A graphical interpretation of timetemperature related quality changes in frozen food. and Fields. and Singh. R. Journal Science of Food and Agriculture. US Patent 4804275. 436-41.S. (1988a) Application of time-temperature indicators in monitoring changes in quality attributes of perishable and semi-perishable foods.H. 378. 50.P. T. S. Wells. Journal of Food Science. Journal of Food Science. Chen. J. and Paraf. and Singh. 77-109. G. (1984) Indicators and integrators of time-temperature and frozen products. (1989a) Applicability of time-temperature indicators as shelflife monitors of food products. A. pp. 52(2). (1989b) Reliability of time-temperature indicators as food quality monitors under non-isothermal conditions.P. R. Dairy and Food Sanitation.H.H. M. ..Taoukis. 54(4).L. 207-18. J. R. 12(3).P. 1 Introduction Ever since Appert discovered that heating food in sealed glass jars produced a stable product. Such packaging interacts directly with the food and the environment to extend shelf-life and/or improve quality. The success of the metal can over the last 150 years is due to its ability to withstand thermal processing and provide a barrier against chemical and biological contamination. The use of packaging to safely protect and preserve foods has remained a central focus of packaging development. current research is shifting to the development of packaging which actively contributes to the preservation and safety of foods (Labuza and Breene. The major advances in food packaging over the last two decades have been the development of new materials. 1992). A scientific understanding of the relationship between shelf-life. safety. and containers with specific technical and economic benefits (Downes. It would be of little benefit to process food if there was no way to prevent recontamination. These factors are important in the health and nutritional aspects of foods. and packaging began to evolve in the late 180Os as the theoretical basis for the thermal inactivation of pathogenic spores was developed (Goldblith. 11. HOTCHKISS 11. processing/storage conditions.H. The primary roles of packaging in food safety have traditionally been to withstand thermal processing conditions and to act as a barrier to contamination. Most of these new materials and containers are inactive technologies in that they act primarily as passive barriers which separate the product from its environment. .11 Safety considerations in active packaging J. 1989).2 Packaging and food safety Packaging has often been thought of as a source of risk for foods and seldom as a technology which could be used to enhance food safety (Wolf. However. 1989). combinations of materials. a major goal of packaging has been to safely preserve foods for extended periods. Modern food packaging can also influence the nutritional and quality attributes of foods and ensure the year-round availability of many foods. 1989). This understanding is still evolving. etc.1 Types of food safety problems associated with packaging Examples Microbial contamination Loss of integrity Anaerobiosis Consequences Seal rupture. active packaging can directly enhance food safety. Can lead to toxin formation by anaerobic pathogenic microorganisms Transfer of package components to foods Environmental toxicants can permeate films Examples include preservatives used in wooden pallets. recycling. incomplete glass finishes allow contamination by pathogenic m. Table 11. Examples of 'active' packaging which improves food safety include antimicrobial polymers and films which inhibit the growth of pathogenic and spoilage microorganisms. Low oxygen environment resulting from product or microbial respiration.Certainly.o. when packaging fails to preform its protective functions the result is an unsafe product (Downes. These and other types of active packaging which improve safety and quality are areas of current research and commercial interest (Ishitani. Active packaging can not only prevent contamination but it can also improve food safety in several other ways. diesel exhaust Contamination of post-consumer packaging is transferred to foods after recycling Some insects can bore through many common packaging materials Glass shards. safety may be compromised when package components migrate to a food or when there is a loss of integrity resulting in contamination by pathogenic microorganisms. Table 11. CFCs Aroma and nutrient sorption by polymers Malicious and innocuous Underprocessing can lead to food poisoning Loss of integrity or insufficient sterilization of packaging can lead to food poisoning Chemical contamination Migration Environmental contamination Recycled packaging Insect contamination Post packaging Foreign objects Injury Exploding pressurized containers Broken containers Environmental impact Loss of nutritional and sensory quality Tamper evidency Inadequate processing Conventional Aseptic . metal pieces Soft drinks. For example. Cuts. packages which react with toxins and indicate their presence. lacerations Disposal. 1993). and packages which indicate if packages are leaking. beer in glass. packaging materials which prevent the migration of contaminant. 1994). leaking cans. However.1 lists several general ways in which packaging can detract from safety. 3. absolute barriers. Research has been undertaken in an attempt to improve the testing of integrity of polymer-based packages. Strength and integrity have become important issues because foods are transported further and stored for extended periods. With glass and metal food packaging. Post-packaging microbial contamination of foods is now not only a function of closure integrity and material integrity (Downes et a/. holes. 1991).. No currently available method is entirely satisfactory for all situations.1 Barriers to contamination The major safety and quality function of packaging is to act as a barrier between food and the environment. making a container sealed in this way one of the safest available. The barrier properties of these polymeric materials has been the central focus of packaging development in recent years. flexible materials can contain minute pinholes which allow entry to microorganisms yet still not show signs of leakage (Chen et aL.11. Flexible materials are also more prone to failure during transport and storage. 1985). Polymers which are high barriers to both oxygen and water vapor are now available. The canning industry has had considerable experience with double seam closure for metal cans. in the material or the seal. The economic and functional disadvantages of metal and glass have led to the development of polymeric packaging materials. tears. As the change to polymeric packaging has occurred. etc. which are. Completeness means that there are no gaps. concern for the integrity of the container has increased. Gnanasekharan and Floros (1994) have reviewed methodology for detecting leaks in flexible food packaging. Very recent efforts have focused on improved aroma/flavor barriers. preventing contamination is usually a function of closure integrity. The purpose is to prevent contamination (or re-contamination after processing) of the food from both environmental chemicals and pathogenic microorganisms. Flexible packaging can also develop pin holes during shipping. The lack of such long-term experience with the heat seal as a means of closure has raised safety concerns.3 Passive safety interactions 11. Considerable experience with such closures has resulted in a remarkably low risk packaging system. and foods which are hermetically sealed in polymer-based containers can absorb environmental . Increased potential for chemical contamination has become a concern because polymers are permeable to organic vapors. for practical purposes. There are two aspects of package integrity: strength and completeness. In some cases. Strength implies that the closure or seal is sufficiently strong to withstand the rigors of distribution without failure. A seal or material can be strong yet incomplete or can be complete yet have insufficient strength for distribution. The second problem is the potential contamination of food grade polymeric packages by consumers (gasoline and pesticides are commonly mentioned as potential contaminants). as well as organic toxicants such as vinyl chloride monomer which is a known human carcinogen. Considerable research has been conducted into the migration of packaging materials to foods (Crosby. Nutrients and organoleptic properties can be adversely affected in several ways. At least two potential problems exist.3. nutrients can be destroyed when oxygen or light enters a package or when the product is exposed to excessive heat. It is likely that in some cases potentially pathogenic spores could be transferred to foods from recycled materials. These additives or monomers could then migrate to foods. primarily lead from soldered cans. The transfer to foods of potentially toxic compounds used to preserve wooden shipping pallets and wooden container floors has been reported and is exacerbated by the increase in long-distance shipment of foods (Whitfield et al. Both the theoretical and empirical aspects of migration have been studied in detail and in most cases the process is scientifically understood.. Packaging also protects the nutritional and organoleptic quality of foods. become a health issue. Concern over migration has been recently heightened because of the use of recycled materials or refillable containers for food and beverage packaging (Begley and Hollifield.2 Prevention of migration The second major safety function of packaging is to limit the transfer (i. 11.e. concern over microbiological contamination of fiber based packaging materials has also increased (Klungness et al. Sorption of nutrients by the packaging material is also a mechanism of loss. migration) of packaging components to foods.. Migrants include inorganic toxicants. As the pace in the use of recycled materials has gained momentum. 1994). . These contaminants could then migrate to foods packaged in containers made from recycled materials. 1981). many environmental organic compounds which permeate films impart undesirable odors to foods. The paper making process inactivates most vegetative cells but does not inactivate microbial spores. 1993). 1994). One is that non-food grade plastics which may contain additives or monomers that are not intended for human food use will enter the recycle stream. 1990). Foods packaged in recycled materials have the potential to have acquired high spore loads from the packaging (Vaisanen et al. While not directly safety issues. For example.contaminants. foods which have lost their nutritional attributes or are not consumed because of poor taste or appearance. The loss 'of vitamin C in orange juice when stored in low barrier packaging is a prominent example. In addition to toxicological concerns. While there is concern that some active packaging systems will detract from safety there also is the possibility that new active systems can enhance safety. food polymer-based containers were designed to store products at ambient or sub-ambient temperatures. The major question is. The second effect is that elevated temperature can cause degradation of the polymer and additives which can result in migration of the breakdown products. most laboratory work on migration was undertaken at room temperature or lower over extended periods. A second recent packaging migration safety concern has resulted from the use of polymer-based packaging as containers for food during heating such as in processing low acid foods in a retort or heating foods in microwave ovens. Any contaminants would be removed during this processing. Heating plastics has two effects on migration. Initially. Migration is also affected by the chemical and physical nature of the migrant. First is the use of equipment to detect contaminated containers prior to refilling. Commercial sniffers are available and in use. . How effective is this virgin layer at preventing migration? Other treatments of polymers such as cross-linking can retard migration. The second solution is to chemically break down the polymeric structure and subsequently reform the basic polymer. migration in general follows Arrhenius-type kinetics and increasing temperature increases migration rates in an exponential fashion. The third solution is to construct containers in which the recycled polymer is separated from the product by a functional barrier. 11.Several solutions to the post-consumer contamination of recyclable plastics have been proposed. Combining virgin and recycled PET by co-extrusion into a PET bottle has been commercially undertaken. Active packaging materials which can minimize or eliminate migration would be of substantial interest as the concern over the environmental cost of packaging increases. The virgin PET is expected to be a functional barrier to potential contaminants in the recycled layer.4 Active safety interactions Active packaging systems face similar barrier and migration safety issues as conventional packaging. Thus. First. These are commonly referred to as 'sniffers' and are designed to sample the air inside the container and determine if volatile organic compounds such as might be found in gasoline are present. Each of these issues has been addressed by several regulatory agencies in the USA and Europe. Materials and containers are being developed specifically to reduce food safety risks. The advent of the microwave oven has meant that foods are heated in plastic vessels and on plastic surfaces. Such functional barriers are intended to prevent the migration of contaminants from recycled polymers to products. as well as some additional issues. 1 Emitters and sorbers One the earliest and most successful active packaging concepts was to incorporate a material which either absorbed or emitted vapors or gases inside a package after closure. The addition of antimicrobial metal ions to food contact surfaces . 1994). 1981). This might be as simple as water vapor absorbers which are designed to control relative humidity. the governmental regulatory and health issues will be similar to those related to migration of residual monomers or other polymer components (Crosby.4. There is also the concern that the components making up the absorber/ emitter will migrate to the food. 1994). However.2 Active packaging and migration Many active packaging systems incorporate functional additives in food contact materials.4. absorbers/emitters were contained inside packets which were added to the package along with the product. For those active packaging systems which indirectly add components to foods. More recent technologies have incorporated the sorber/emitter into the film or container wall. The safety implications of such changes are the same as those for conventional MAP. In some cases. Particularly desirable types of sorbers are those that remove both residual and ingress oxygen after the package has been sealed (Rooney. Initially.11. Oxygen absorbers which remove oxygen from the headspace of bottled beer. For example. the potential for and consequences of migration need to be assessed. or emit ethanol to control molds in bakery products. toxicological testing may be required. there has been some reluctance in some parts of the world to allow the use of ethanol emitters in foods which will be consumed without further cooking or processing. in most cases active components and additives will not be common food additives and potential toxicological concerns will need to be addressed. In each case. absorb undesirable odors from foods. 11. 1994). as discussed below. These may be as simple as iron oxides which absorb O2 or as complex as systems which react with singlet oxygen (Rooney. would likely be of little regulatory or safety concern if incorporated into antimicrobial films (Giese. Laboratory investigations will be required to determine the potential for migration and to quantify the amount of migration. The residual ethanol might be considered a food additive and thus be required to undergo the rigors of complete toxicological testing. or more complex substances which absorb ethylene from produce. This reduces the likelihood of accidental ingestion. For example. benzoic. approved antimycotic agents such as sorbic. active packaging systems may involve migrants for which there is little concern in food systems. have been successfully tested commercially. for example. These absorbers are a form of modified atmosphere packaging and can change the microbiology of foods. or propionic acids. If the amount of additive migrating is considered of potential significance. 4. 11. active packaging systems must fulfill the safety requirement of acting as a barrier to microbial and chemical contamination. Incorporating absorbers or scavengers into the adhesives used to bind layers of inert film as a means of 'burying' the additive is an example.4. In some cases. The regulatory consequences of intentional addition of even low amounts of metals will need addressing. For example. In some cases. 1993). the metals may be classified as food additives and require rigorous toxicological testing. Incorporation of active ingredients directly into the packaging rather than as sachets seems prudent. This will result in a change in the microbial ecology of the food.9 1992). This change in microbiology will indirectly influence safety. For example.is likely to result in the migration of small amounts of the metals to foods (Ishitani. 11. The addition of packets or sachets to packages of food raises concern that they will be inadvertently ingested. caution about adding nonedible items to packages should be taken. While sachets and packets have been in use for several years without apparent problems. While these metal ions may be of low toxicity. 1994). the addition of inorganic compounds such as metal-coated zeolites. Such failures become safety concerns if they allow for contamination by pathogenic microorganisms or toxic chemicals. safety may be enhanced such as when carbon dioxide is added to high pH cheeses such as cottage cheese (Chen and Hotchkiss. packaging which absorbs oxygen from inside a package with the goal of reducing deteriorative affects will affect both the types and growth rate of the microorganisms in products. In other cases. The addition of active ingredients to films could decrease their mechanical properties resulting in a higher failure rate during transport.4 Indirect effects on safety Active packaging often has indirect as well as direct effects on food safety. safety may be compromised as when the growth of Clostridium botulinum is favored. The inclusion of antimicrobial agents in the contact layer of a packaging material may have similar effects.3 Barrier to contamination In addition to migration. or oxygen scavengers will likely reduce the mechanical properties of films raising the possibility that the contamination barrier will be reduced. The type of microorganisms present on a product will thus be different from the same product packaged in a conventional manner. The effect of such changes in the microbial ecology of foods has not been investigated in detail and only a few reports on changes in microbial ecology have been published (Reddy et al. desiccants. Smith and co-workers have . the use of functional barriers to prevent migration of the active components will be required. They could also be used to determine if a food had been properly pasteurized or contained enzyme activity. food processing. but just as importantly. One example is the use of packaging which shows or in some way indicates the condition or history of a product. detect the presence of bacterial toxins in packaged foods. for example. it may be possible to incorporate these or similar biosensors . It is likely that this occurred because the aerobic Pseudomonas grew rapidly and consumed the oxygen rapidly leaving a highly anaerobic environment for the Clostridia. to the conditions. MAP in high carbon dioxide atmospheres inhibited the Pseudomonas inoculum and left traces of unconsumed O2 which inhibited the Clostridia.e. Somewhat surprisingly. Time-temperature indicators can be used on individual packages to warn consumers that a product has been exposed to a combination of time and temperature which may compromise safety or they may be used on shipping cartons to alert store personnel of potential quality/safety problems or allow stock rotations based on both time and temperature. such as temperature. Immunologically based sensors coupled to packaging could find applications in food safety. toxin was produced most rapidly in samples packaged in air (i. Biosensors which combine electronics with biological specificity and sensitivity may find use in packaging as monitors of safety and quality (Deshpande and Rocco. Such devices would be especially useful when combined with other shelf-life technologies such as MAP or sub-sterilization radiation. The next generation of safety/quality indicators may be more specific than integrating time and temperature. Such sensors could. One currently available technology is time-temperature indicators. 1994).5 Indicators of safety/spoilage In addition to decreasing the safety of food. In the future it may be possible to directly detect the presence of specific toxins in packaged foods using biosensors. 11. active packaging holds the promise of reducing risks from certain foods compared to conventional packaging. 20% O2). Shelf-life is related not only to how long a product is stored.investigated the effects of MAP on the microbiology and toxin production by Clostridium botulinum in meats (Lambert et al9 1991). pasteurized milk will last weeks at O0C but only a few hours at 35°C.4. This confirms an earlier observation we had made in cooked beef inoculated with both Pseudomonas and Clostridia spp.. These devices integrate the time and temperature history of a product and give a visual indication if the combination has exceeded some standard or desirable amount (Taoukis et al9 1991). In time. under which the product is stored. and detection of adulteration (Deshpande. These results point out that large changes in microbial populations can result indirectly from altering the gases inside a package. These changes can both detract from safety but can also improve safety. 1994). For example. The number and type of microorganisms present on a food is governed by five general variables: time. must be stated on the label. More recently. and gas atmosphere. Several simple and complex tamper-evident packaging systems have been developed and a few implemented for foods. Reportedly. Such systems could eventually be incorporated directly into food packaging. substrate (food) composition. Two general approaches. The most successful alternative to canning or the direct addition of antimicrobial agents has been modified atmosphere packaging (MAP). 1983). foods are sealed in a package and the combined productpackage thermally processed.7 Modified atmosphere packaging Recently. packaging should provide a margin of safety against tampering. The use of these additives is regulated and their use. This approach usually does not inhibit all growth but is selective for certain types of microbial growth.6 Direct inhibition of microbial growth Microbial contamination and growth are the major factors in food spoilage and responsible for food-borne disease outbreaks. microbial load (type and number). In conventional thermal processing. This is the basis of the canning industry.4. alteration of the gas atmosphere surrounding the product is the most accessible method of inhibiting microbial growth. The presence of specific pesticides or other environmental contaminants could be detected with immunological-based systems (Deshpande. the development of alternative methods of inhibiting microbial growth has resulted from a consumer desire for fresher and more natural foods. Foods can also be dried to reduce microbial growth. 1994).into food packaging systems for which the risk of toxin formation exists.. in most cases. Lastly. have been used to eliminate or minimize microbial growth. temperature. In general (although there are exceptions) Gram-negative rods are . heat sterilization and direct addition of antimicrobial additives. 11. inhibition is not uniform for all types of microbes. 11. molds for example.4. methods to quantify the presence of microorganisms on fresh meats are near commercialization (Bsat et #/. It may likewise be possible to detect the presence of toxic chemicals using similar technologies. This is known as aseptic packaging. Another method to reduce microbial growth is to add antimicrobial additives directly to foods. For a given food product which must be held above freezing. However. Tamper-indicating packaging has been discussed in detail since several malicious incidents of tampering with drugs and foods have occurred (Hotchkiss. 1994). the process of the package and the product being sterilized separately then filled and sealed aseptically has been used. respiration rates will increase and the O2 content of the package may approach zero. cause organoleptic changes in foods. It was presumed that the Pseudomonas . The combination of product respiration rate (i. The effect that this change in microbiology might have on the risk of food-borne disease has been debated (Gormley and Zeuthen. In each case. 1991). a specific gas mixture can be directly introduced into the package after removal of the air and before sealing. Thus.e. Farber. the change in atmosphere will affect both the growth rate and type of microorganisms present. organisms which cause disease (i.e. Alternatively. will reduce senescence and extend shelf-life. A third method is to use an additional material contained in a sachet or incorporated into the film which will alter the gas composition after sealing.e.. 1990). the major safety concern with MAP and controlled atmosphere packaging or other technologies which selectively change the microbiology of a food is that suppression of organoleptic spoilage (i. However. 1992).. extension of shelf-life) will decrease competitive growth pressure and provide sufficient time for slow growing pathogenic organisms to become toxic or reach infectious numbers (Hotchkiss and Banco. pathogens) do not. were present along with the Clostridium botulinum inoculum. At the same time the growth rate of pathogenic microorganisms substantially increases with the increase in temperature. 1990.inhibited by a modified atmosphere containing more than 10% CO2 while Gram-positive organisms are not inhibited and their growth can be promoted. Increasing the shelf-life by suppressing spoilage organisms might allow for the growth of pathogenic organisms without development of the normal organoleptic cues of spoilage that warn consumers that a product may not be wholesome (Farber et ai. The major goal of MAP is to reduce the growth rate of microorganisms which cause the product to become organoleptically unacceptable. Lambert et al (1991) have shown that toxigenesis occurs more rapidly in aerobically packaged pork samples compared to anaerobically packaged samples when Pseudomonas spp. If the product is stored at an elevated temperature. One is the use of selective or engineered barriers which are used for respiring products such as fruits and vegetables. rate OfCO2 formation and O2 consumption) and CO2 egress and O2 ingress results in the formation of an equilibrium concentration of gases which.. However. in many cases. temperature will affect the respiration rate to a much greater extent than the permeability. This could allow for the growth of anaerobic pathogens such as Clostridium botulinum. There are several methods of creating a modified atmosphere inside a package. if properly designed. 1990). For example. The knowledge gained over the last decade about pathogenic microorganisms which are capable of surviving and growing at common refrigeration temperatures increases concern about the safety of refrigerated extended shelf-life foods (Gormley and Zeuthen. Antimicrobial films can be divided into two types: those containing an antimicrobial agent which migrates to the surface of the food and those that are effective against surface growth without migration of the active agent(s) to the food. More recently. Several other synthetic and naturally occurring compounds have been proposed and/or tested for antimicrobial activity in packaging (Table 11. imazalil.. These results agreed with earlier results of Hintlian and Hotchkiss (1987) who made a similar observation.8 Antimicrobial films Packaging may directly affect the microbiology of foods in ways other than changing atmosphere. the idea of incorporating antimicrobial agents directly into packaging films which would come into contact with the surface of the food has been developed. antifungal) agent. fruits. lysozyme Conalbumin Allylisothiocyanate Imazalil Benomyl EDTA Silver Heptylparaben . microbial growth occurs primarily at the surface. Antimycotic agents are commonly incorporated into waxes and other edible coatings used for produce items (Peleg.2). benzoic. Only a few scientific descriptions of the effectiveness of this material have appeared and the regulatory status of the deliberate addition of silver to foods has not been clarified in the US or in Europe. The purpose of the zeolite apparently is allow for the slow release of silver ions to the food. botulinum to become toxic. 1985).e. the antimycotic (i. p-cymene Allicin Peroxidase.2 Some antimicrobial agents of potential use in food packaging Class Organic acids Bacteriocins Spice extracts Thiosulfinates Enzymes Proteins Isothiocyanates Antibiotics Fungicides Chelating agents Metals Parabens Examples Propionic. and vegetables is widely practised. This zeolite is incorporated directly into a food-contact film. is effective when incorporated into LDPE for wrapping fruits and vegetables (Miller et Table 11. For example.4.rapidly consumed the oxygen allowing the C. primarily in Japan. Silver can be antimicrobial under certain situations. Several commercial antimicrobial films have been introduced. In solid or semi-solid foods. 11. Surface treatment by spraying or dusting with antimicrobial agents for products such as cheeses. sorbic Nisin Thymol. One widely discussed product is a synthetic zeolite which has had a portion of its sodium ions replaced with silver ions. 1993). Whether or not such bound bacteriocins would be effective remains unclear. this work established that antimycotic films could be effective for control of surface molds in foods. We have demonstrated that the same compound is effective at preventing mold growth on cheese surfaces when incorporated into LDPE films (Weng and Hotchkiss. nisin. Hydrolysis leads to formation of the free acid which in turn leads to migration from the surface of the polymer to the food where the free acids can be effective antimycotics. Films were constructed of cellose derivatives and fatty acids in order to control the release of sorbic acid and potassium sorbate. which are proteins derived from microorganisms in much the same way as penicillin is derived from mold. Although imazalil is not approved for cheese. This incompatibility is likely to be due to differences in polarity. benzoic. We have spectroscopically demonstrated that propionic acid. It is unlikely that benomyl would be approved for food use for toxicological reasons. Cellulose films are not heat sealable are not good barriers in high humidity situations. and sorbic acids to polymers such as LDPE was unsuccessful because of lack of compatibility between the acid and the nonpolar film. The activity is initiated by the moisture in the food. which is a common approved food antimycotic agent. 1993). Anhydrides are stable when dry and relatively thermally stable yet become hydrolysed in aqueous environments such as foods. 1992). be attached to the surface of food-contact films. the active ingredient remains in the film until the film comes into contact with a food. theoretically. which is commonly used as a fungicide. Halek and Garg (1989) chemically coupled the antifungal agent benomyl.al. This is an example of 'switched on' packaging. These films would seem to have the greatest application as fruit and vegetable coatings. While not directly addressed by the authors. could be coupled to ionomeric films but that antimycotic activity could not be demonstrated on rigorous testing (Weng. Future work in antimicrobial films may focus on the use of biologically derived antimicrobial materials that are bound or incorporated into films and do not need to migrate to the food to be effective. Hale et al. Direct addition of simple antimycotic acids such as propionic. We have solved this problem by first forming the anhydride of the acid which removes the ionized acid function and decreases polarity (Weng and Hotchkiss. Bacteriocins are effective against organisms such as Clostridium botulinum and one such compound. to ionomer film and demonstrated inhibition of microbial growth in defined media. 1990). For example. Reports have appeared which demonstrate the effectiveness of adding common food-grade antimycotic agents to cellulose-based edible films (Vojdani and Torres. . the method used to determine inhibition of growth indicated that the benomyl migrated from the film to the growth media. a group of substances known as bacteriocins. 1992). 1984. have been described in the literature (Hoover and Steenson. These peptides could. has been approved for food use.> 1986). This may adversely affect safety.) to be effective.9 Rational functional barriers As pointed out. A third possibility for antmicrobial films is to incorporate radiationemitting materials into films. the Japanese have developed a material which emits long-wavelengt IR. • • • • Each of these questions need addressing before the safety consequences of antimicrobial packaging can be understood. for example. are effective only at acid pH while others might require certain product compositions (e. if any. including those dealing with safety. such as glucose oxidase which forms hydrogen peroxide. These enzymes would produce microbial toxins. etc. are the toxicological and regulatory concerns? What is the effect of food product composition? Some antimicrobial agents. aw9 protein. the concept of rational design or engineering of film permeability has evolved. What is the effect of the antimicrobial additives on the mechanical and physical properties of the film? It is likely. This is thought to be effective against microorganisms without the risks associated with higher energy radiation. Several such enzymes exist. for example. several questions. 11. Films are frequently selected for food use based on the highest degree of oxygen and/or water vapor barrier at the lowest cost. should be considered in developing antmicrobial films: • What is the spectrum of organisms against which the film will be effective? Films which may inhibit spoilage without affecting the growth of pathogens will raise safety questions similar to those of technologies such as a MAP. In general. However.Antimicrobial enzymes might also be bound to the inner surface of foodcontact films. Packaged foods can be exposed to contaminants from environmental sources . that effective levels of antimicrobial agents will reduce seal strength. Is the antimicrobial activity a reduction in growth rate (yet still a positive increase in cell numbers) or does it cause cell death (decline in cell numbers)? To what extent does the antimicrobial agent migrate to the food and what. The first is to act as a barrier to permeation of contaminants. These so-called 'smart' films have barrier properties which are designed to adapt or change permeabilities according to conditions such as a change in gas composition or temperature. Reportedly.g. glucose. These engineered barriers have at least two important safety-related applications.4. little direct evidence for the efficacy of this technology has been published in the scientific literature. More recently. one major safety function of packaging is to act as a chemical and biological barrier. the rate of gas change will determine the type of microorganisms on the products and. Thus. on the other hand. Common environmental sources of toxic permeants include chemicals used to treat shipping containers and pollutants. This equilibrium results from the consumption of O2 and evolution of CO2 by the food product at the same time that O2 is permeating into the package and CO2 is permeating out at a given temperature. However. This might occur if products were stored at a higher than expected temperature.or from the use of recycled plastics in food packaging. Several mathematical models have been developed which predict the proper permeation rates given by a specific product respiration rate (Mannapperuma et ai9 1991). Engineered films which can independently select CO2 and O2 permeation rates as well as films that change permeation at the same rate that fruits and vegetables change respiration rate with temperature. Common environmental pollutants such as diesel exhaust and industrial solvents used in printing also permeate many common food-packaging films. would be desirable. We have recently devised equations for achieving optimum atmosphere concentrations for extending the shelf-life of fresh corn on the cob and head lettuce. Chlorinated wood preservatives readily permeate through common films and cause taint in foods (Whitfield et al. MAP products such as lettuce and corn or other vegetables could become safety concerns if the atmosphere were to become anaerobic. The first is that respiration rates of most produce items vary widely. permeation rates will have to be tailored for each individual product item. Sweet corn. The second use of engineered barriers is in passive MAP systems in which an equilibrium in the gas mixture is achieved through the combination of product respiration and package permeability. 1994a). There are two difficulties with this concept. During this time considerable deterioration can occur. about 90 hours are required for establishment of a suitable atmosphere (Morales-Castro et al. each of which illustrates some of the problems with engineered barriers. As pointed out above. 1991). The second problem is that CO2 permeation rates for common packaging films is 2-A fold or more higher than for O2. making the atmosphere anaerobic. 1994b). probably. At some point these respiration and permeation rates will reach an equilibrium concentration. Head lettuce respires relatively slowly and films which will allow a passive modified atmosphere to be established are commercially available. respires rapidly and the establishment of a desirable steady-state atmosphere is not possible with normal films because the permeabilities are too low even for very low barrier films (Morales-Castro et aL. even within the same type of item. This means that CO2 may egress at a faster rate than O2 will enter. the safety of such foods. Selection of a film with the proper permeability will result in the desired gas mixture. This would cause an increase in respiration beyond that expected and the oxygen . A few examples of such combinations have appeared in the literature. Antimicrobial films are a .10 Combined systems The most successful active packaging materials are likely to combine different technologies. Recycled materials for food packaging is another. Fu and Labuza (1992) have suggested that MAP might be combined with time-temperature indicators as a means of extending the shelf-life of perishable foods while at the same time minimizing food-borne disease risks. This will inhibit the introduction of some active systems. Other combinations such as antimicrobial films combined with MAP or oxygen absorbers combined with antimicrobial films may find commercial uses.4. Lambert et al (1992) have demonstrated a substantial increase in the shelf-life of fresh pork treated with both irradiation and MAP. or reduce environmental impact will also be required to maintain a high level of safety. Those active packaging systems which reduce the risks associated with foods may find niche markets for products at the highest risk of deterioration.5 Conclusions It can be expected that safety will continue to be an important attribute for foods. Active packaging systems will not be an exception. MAP would reduce the deterioration of food while the time-temperature indicator would insure that the product was stored and handled within the time and temperature window for which the product was designed. Low dose irradiation and MAP have been combined to extend shelf-life (Thayer. 11. Active packaging systems which provide benefits for foods will have to adhere to governmental regulatory standards in most of the world. This would leave open the possibility of growth of anaerobic pathogens such as Clostridium botulinum. 11.might be substantially depleted. New packaging technologies which improve quality. Labuza et al (1992) have suggested that predictive microbiology should be used to evaluate the safety of MAP foods. For example. to insure safety. Zeitoun and Debevere (1991) have suggested that combining a simple lactic acid dip combined with MAP would enhance the shelf-life of fresh poultry. MAP of non-sterile foods is one example where additional safety measures such as use of microbial inhibitors or indicators of temperature abuse would be useful. usefulness. 1993). Irradiation reduces the numbers of spoilage and pathogenic vegetative organisms while a modified atmosphere reduces the likelihood that those not destroyed will grow significantly in number. 54(8). 58-70. JJ.H. Food Technology.. 146-50. (1981) Food Packaging Materials.S. . 286. et al (1994) Food safety applications of nucleic acidbased assays. G. 102-10. Farber. (1989) 50 years of progress in food science and technology: From art based on experience to technology based on science. food. Giese. T. 327-34. P. T. and Floros. D. J. 48(6). 47(11). (1994) Antimicrobials: Assuring food safety. 7(4).H.H. S. 45(1). (1992) Influence of new packaging technologies on the growth of microorganisms in produce. 50.W. Aseptipak '85: Proceedings of the Third International Conference and Exhibition on Aseptic Packaging. Food packaging in the IFT era: Five decades of unprecedented growth and chance. P. Fu. et al. Halek. Deshpande. J. 48(6). Journal of Food Protection. J. Czajka. 228-40. Applied Science Publishers Ltd. Downes. J. Harte.. and Garg. and Hollifield. and Rocco. (1991) Assessment of package integrity using a spray cabinet technique.. J. Food Microbiology. (1994) Biosensors and their potential use in food quality control. R.W. Warburton.. (1989). Miller. 218-23. N. Journal of Food Distribution Research. M.M. A. Bsat.W..W.A. 66-7. C. J. V. and Banco. T. and Hotchkiss. and Hotchkiss. Downes. 142-5.S. (1994) Immunodiagnostics in agricultural. S. Packaging Technology Engineering. Food Technology. Tropical Science. pp.R. Farber. 48(6).D. L. Hoover. Goff. 9. Journal of Dairy Science. Journal of Food Protection. (1987) Comparative growth of spoilage and pathogenic organisms in modified atmosphere packaged cooked beef. Food Technology. H. 815-20. Chen.P. 109-12. 643-7.M. G. Goldblith. 67-71. Deshpande. 972-7. 215-22. J.C. T. L. Crosby. 111-14. Arndt. CB. 9-17. Wiedmann.W.T. Journal of Food Safety. and Steenson. 152(10).W. London and New York. (eds) (1990) Chilled Foods: The Ongoing Debate. et al (1990) Microbiological quality of foods packaged under modified atmospheres.H. Gnanasekharan.G.R. B. and Smoot. Hintlian. J. 76. (1993) Recycled polymers in food packaging: Migration considerations. 363-401. Academic Press. 23(1). S. Downes. J. 43(9).M. 67-72. J. San Diego. Hotchkiss. N. (1983) Tamper evident packaging for foods: Current technology. Proceedings Prepared Foods.H. Journal of Food Protection. Food Technology. Elsevier Applied Science. T. (1993) Bacteriocins of Lactic Acid Bacteria. 26. 88-107. (1993) Growth of Listeria monocytogenes and Clostridium sporogenes in cottage cheese in modified atmosphere packaging. London. Food Technology.R and Zeuthen.. Food Technology. Developers of such materials should understand the safety and regulatory implications of their work early in the process if they expect to be successful. Activities Report of the R & D Association.. (1989) Fungal inhibition by a fungicide coupled to an ionomeric film. 43(9). 3(7). D. Hotchkiss. (1986) Evaluation of a heat-shrinkable copolymer film coated with imazalil for decay control of Florida grapefruit.. C. 136-41. References Begley. J. 54(1). Food Technology. Hale. (1994) Package integrity evaluation: Criteria for selecting a method. 48(6). 55(10). and Labuza..prime example. et al (1985) Factors Affecting Seal Integrity of Aseptic PaperboaraVFoil Packages. B. and environmental quality control. MJ. (1993) Packaging safety issues. Aspects of Analysis and Migration of Contaminants. Gour. W. (1991) Microbiological aspects of modified-atmosphere packaging technology review. T. Gormley. Chen. Lai.H.W.. Journal of Food Protection. (1992) Considerations for the application of time-temperature integrators in food distribution. 8-12. 29-37. .. P. 21-5. J. Mannapperuma. Risse. Ly-Nguyen T. 55(9). 55(3). Abs. (1994b) Modified atmosphere packaging of head lettuce.P. T. Lambert. J.B. R.-M. O. Westport. and Torres. Journal of Food Protection. (1994a) Modified atmosphere packaging of sweet corn on cob.B. J.E. (1990) Contaminant removal from recycled wastepaper pulps. (1994) Active Packaging for Foods in Japan. J.. Ithaca. et al. (1991) Simultaneous gas diffusion and chemical reaction in foods stored in modified atmosphere. Reddy.M... 56(10).P. and Montero..P. B. Lund University and SIK. 846.A. (1991) Effect of relative humidity and chlorophenol content on the fungal conversion of chlorophenols to chloroanisoles in fibreboard cartons containing dried fruits. K. (1989) Application of active packaging technologies for the improvement of shelf-life and nutritional quality of fresh and extended shelf-life foods. Hotchkiss. 1-69.S. J. and Hotchkiss. Vojdani. and Last.P. et al (1984) The effects of an imazalil-impregnated film with chlorine and imazalil to control decay of bell peppers. AVI Publishing Company. Whitfield. 595-604. Fu. et al (1992) Shelf-life extension and safety concerns about fresh fishery products packaged under modified atmospheres: A review. Smith. 14(3).Ishitani. 70-82.. (1994) Oxygen-Scavenging Plastics Activated for Fresh and Processed Foods. Journal of Food Protection.L. (1992) Development and Application of Food Packaging Films Containing Antimicrobial Agents. IFT Annual Meeting Technical Program: Book of Abstracts. W. B. 13(1). and Dodds.. J. W. 45(10).R.. (1991) Effect of initial O2 and CO2 and low-dose irradiation on toxin production by Clostridium botulinum in MAP fresh pork. Morales-Castro. N. 108-11.A. Rhodehamel. T. S. Lambert. Inc.-H. Vaisanen. Rao.A. T.J. Hotchkiss. Packaging and Distribution. Singh. M.R. Abstracts. 87-118.L. Taoukis.H. 167-83.H.P. Journal of Food Processing and Preservation. (1992) Microbiological changes and shelf-life of MAP. K. EJ. 12(2).P. L.D. M. Klungness.. Shaw.H. 6. and Rowlands. Food Microbiology. M.H.W. J. et al. (1991) Time-temperature indicators.H. Rooney. 97.. Rao.. Food Technology. (1990) Potassium sorbate permeability of methylcellulose and hydroxypropyl methylcellulose coatings: Effect of fatty acids. 831-3. Journal of Food Engineering. A. K. J. Participants. 1. Weng. 231-44. J. 123-8.Food Packaging Material.E. 741-50. CT. K. and Labuza. 401-7. (1993) Extending shelf-life of poultry and red meat by irradiation processing. Y. P. Spalding. Lambert.H. M. 18.. Information..E.. and Breene. 9. sponsored by The Lund Institute of Technology. No. Armstrong. and Taoukis.. F. The Swedish Institute for Food Research. Y. J. 279-93. F. Journal of Food Science.. 54(12). 35. D. et al (1994) Freight containers: Major sources of chloroanisoles and chlorophenols in foodstuffs. Gothenburg.A.H. et al. PhD dissertation.H. Fu. International Symposium.. D.L. Journal of Food Protection. Journal of Food Safety. Interaction: Foods . Journal of the Science of Food and Agriculture. Programme. (1992) Prediction for shelf-life and safety of minimally processed CAP/MAP chilled foods: A review. 60(2).. 295-304. Journal of Food Processing and Preservation.J. p. Thayer. Weng. Applied and Environmental Microbiology. Labuza. NY.. Lin. Labuza. A. Smith. and Hotchkiss. Peleg.D.S. R. J. et al. Florida State Horticultural Society.-H. D. (1992) Inhibition of surface molds on cheese by polyethylene film containing the antimycotic Imazalil. Journal of Food Processing Preservation.A. Dodds. 52. 641-53. 9(3). irradiated fresh pork. Miller. Proc. Nurmiaho-Lassila. EX.. Packaging Technology and Science. 841-6. CH. 18. T. Cornell University. Whitfield. Morales-Castro.D. J. F. Marmo. 939-44. (1994) Structure and composition of biological slimes on paper and board machines. 54(4). Y. Pulping Conference Proceedings.. Developments in Food Science. (1993) Anhydrides as antimycotic agents added to polyethylene films for food packaging. Weng. Journal of Food Protection. D. (1985) Produce Handling. 1991-2000. Food Technology. and Debevere. 64-70. A.A. J. International Journal of Food Microbiology. 14(2).Wolf. survival and growth of Listeria monocytogenes on poultry as influenced by buffered lactic acid treatment and modified atmosphere packaging. (1992) Critical issues in food safety. (1991) Inhibition.M. I. . Zeitoun.M.D. 46(1). 161-9. 256 .Index Index terms A absorbers food constituents free oxygen see oxygen absorbents odours and taints activation energy permeation respiration model active packaging chemical composite definition do-it-yourself economic benefit future potential history horticultural limitations literature multiple effects origins physical reasons for regulatory considerations reviews 21 8 1 17 76 32 4 9 31 10 9 3 20 3 33 10 252 252 2 143 203 24 68 65 100 213 99 100 Links This page has been reformatted by Knovel to provide easier navigation. 257 Index terms active packaging (Continued) scope terminology whole packages active packaging plastics and safety combined effect commercial use effects on foods environmental considerations migration from regulations Ageless and aw capacity chemistry types aldehydes almonds rancidity and oxygen absorbent amines anaerobic respiration antimicrobials enzymic silver zeolite antimycotics ascorbic acid and oxygen absorbent Aspergillus spp 154 159 155 100 68 243 250 248 249 150 150 149 149 100 243 82 106 74 107 243 106 12 1 29 Links 10 106 244 248 This page has been reformatted by Knovel to provide easier navigation. . 258 Index terms B bacteriocins bakery products and oxygen absorbent ethanol releasing sachets mould growth barriers functional beer commercial oxygen scavenger closures oxygen concentration in oxygen ingress blueberry broccoli 198 194 195 65 65 250 156 166 159 249 Links 169 160 196 69 C calcium carbonate as filler cans tinplate carbon dioxide permeability carnauba wax carrots packaging condensation control cauliflower casein films sorbic acid in 128 98 65 123 132 238 69 This page has been reformatted by Knovel to provide easier navigation. . 259 Index terms cheese antimycotic films for Clostridium botulinum Clostridium sporogenes effect of Ageless closure beer bottles benefits beverage bottles oxygen scavenging with ascorbic acid with sodium sulfite composite films sorbic acid barrier consumer resistance to sachets contamination barriers to controlled atmosphere (CA) corn gas atmospheres for crusty rolls and oxygen absorbents 159 251 240 55 130 162 198 168 193 199 193 163 249 244 Links 244 D deoxidisers see oxygen scavengers desiccant retorting 75 79 This page has been reformatted by Knovel to provide easier navigation. . .260 Index terms E edible coatings see edible films edible films as active packaging as food bilayer composite food surface modification formation gas exchange with moisture barrier multilayer permeability plasticisation energy transfer environment enzymes active packaging antimicrobial binding function history oxygen scavenging release equilibrium modified atmosphere (EMA) see also passive modified atmosphere packaging Clostridium botulinum in generation packaging Pseudomonas spp in 247 56 2 247 176 186 105 174 178 174 105 247 113 112 117 111 126 112 121 114 117 114 120 90 107 Links 117 177 251 9 55 66 This page has been reformatted by Knovel to provide easier navigation. 261 Index terms ethanol oxidase ethanol vapour absorption antimicrobial effects and aw in bakery products and food spoilage and food poisoning generators advantages aw effects disadvantages required sizes types uses ethylene adsorption chemistry degradation effects interaction with other gases sources synthesis ethylene scavengers activated carbon activated earth novel approaches potassium permanganate 47 48 50 46 40 38 39 41 44 45 38 171 166 171 166 166 168 167 165 165 165 171 171 186 Links 171 46 39 This page has been reformatted by Knovel to provide easier navigation. . .262 Index terms F films antimicrobial ceramic filled condensation control controlled diameter holes to humidity buffering for MAP microporous moisture control perforated temperature-compensating with oxygen absorbents fish products and oxygen absorbents flavour scalping foods oxygen absorbents for Freshilizer and aw reaction speed types FreshMax Fresh Pax and aw reaction speed types uses fruits edible coatings gas atmosphere for 126 57 151 152 152 211 151 151 151 212 155 157 99 248 70 98 96 67 68 94 68 70 92 Links 153 This page has been reformatted by Knovel to provide easier navigation. .263 Index terms functional barriers 250 Links G gelatin films sorbic acid retention tannic acid crosslinked tocopherol retention glucose oxidase gluten films with beeswax green pepper 124 65 128 128 128 181 H hydrogen oxidation hydrogen peroxide hydroxypropyl methylcellulose 84 86 130 I IMF and Staphylococcus aureus casein-coated microbiological stability papaya cubes with sorbic acid indicator bacterial toxins oxygen concentration safety spoilage temperature 245 2 245 245 209 134 132 132 132 132 This page has been reformatted by Knovel to provide easier navigation. 264 Index terms indicator (Continued) time-temperature see Time-Temperature Indicators interactive packaging see active packaging intermediate moisture food see IMF Links L lettuce gas atmosphere for limonin Listeria monocytogenes ethanol vapour effect 251 99 163 171 M mathematical modelling limitations parameters steady state unsteady state variables meat colour and oxygen absorbents meat packaging oxygen scavenging methylcellulose with palmitic acid microbiological stability carrageenan effect lactic acid effect surface pH effect microencapsulation 134 133 133 85 158 130 132 160 251 64 71 66 65 66 70 This page has been reformatted by Knovel to provide easier navigation. . 265 Index terms microwave susceptors field intensifiers reflectors microwaveable bottle migration from active packaging from heated plastics from recycled plastics of preservatives prevention of modified atmosphere packaging (MAP) active and Clostridium botulinum definition and ethanol vapour experimentation for film selection gas concentration boundaries gas tolerance limits feasibility study films for flow chart and irradiation literature review optimisation passive pathogens in and Pseudomonas quality criteria regulation of 55 245 143 170 60 66 58 61 59 67 56 252 57 60 55 246 247 59 252 243 242 242 127 241 203 206 206 209 Links 247 67 This page has been reformatted by Knovel to provide easier navigation. . 266 Index terms modified atmosphere packaging (MAP) (Continued) and Time-Temperature Indicators moisture transfer ice cream-wafer mould growth on bakery products on cheese mozarella cheese and oxygen absorbents mushrooms 160 69 75 75 121 252 Links O odours from oxygen scavengers organic acids Ox-Bar oxygen concentration measurement permeability of closure liners oxygen absorbents see also oxygen scavengers advantages and aflatoxins and mould growth applications choice of classification CO2 producing definition disadvantages dual effect 161 164 159 148 152 145 146 144 161 146 150 151 193 195 194 82 243 82 91 This page has been reformatted by Knovel to provide easier navigation. . 267 Index terms oxygen absorbents (Continued) function history in Japan in USA market statistics reaction speed reactions in requirements for research with oxygen absorbers see oxygen absorbents. oxygen scavengers oxygen permeation aw effect chemical barrier edible films oxygen scavengers see also oxygen absorbents Advanced Oxygen Technologies. ascorbic acid ascorbic acid plus sodium sulfite beer bottle closures future beer flavour and bottle closures chemistry of closure liner theory composite systems erythorbic acid 198 211 198 85 86 200 199 213 83 197 8 198 124 92 123 1 148 4 144 155 144 146 145 145 159 Links 153 159 185 198 This page has been reformatted by Knovel to provide easier navigation. . Ageless Aquanautics Corp. Inc. novel designs Ox-Bar OxyBan patent applications plastics vs.268 Index terms oxygen scavengers (Continued) fatty acids food applications FreshMax Fresh Pax history hydrogen/catalyst iron see oxygen absorbents Mitsubishi Gas and Chemical Co Multiform Desiccants Inc. sachets PureSeal release of carbon dioxide rubbers and odours SmartCap sulfite oxidation oxygen scavenging activation see triggering and aflatoxin production and microbial growth by autoxidation enzymic peroxide formation purposes oxygen scavenging packaging forms of 76 164 163 91 179 86 75 211 211 7 83 181 5 81 199 89 82 199 85 82 212 212 211 4 84 Links 91 90 91 86 198 81 This page has been reformatted by Knovel to provide easier navigation. . .269 Index terms oxygen scavenging plastics forms of history light-energised light triggered metal-catalysed photosensitised MXD-6 nylon permeability effects photoreduction-reoxidation photosensitised potential applications singlet oxygen mechanism oxygen scavenging sachets see oxygen absorbents Oya Stone broccoli packaging and Evert-Fresh Bag 209 210 209 77 76 80 80 91 91 83 99 92 87 75 87 Links 81 P package integrity packaging active constituent impact on antimicrobial intelligent interactive modelling modified atmosphere safety problems tamper evident with oxygen scavengers 27 243 2 2 64 2 239 246 92 153 246 244 215 246 216 240 This page has been reformatted by Knovel to provide easier navigation. .270 Index terms patents oxygen scavenging pectin films Penicillium spp perforated films computer simulation permeability activation energy composite films edible films effect on oxygen scavenging humidity effect modification ratio smoke table temperature effect to ethanol to water vapour peroxide value and oxygen absorbent photosensitisation Pichit pizzas and oxygen absorbents plastics definition for oxygen scavenging functional barrier 74 77 242 160 154 87 97 68 118 114 78 79 105 67 105 68 123 120 169 115 69 5 128 159 Links 81 89 71 78 124 130 125 116 169 117 This page has been reformatted by Knovel to provide easier navigation. 3-butadiene) polydimethylbutadiene polyethylene antimycotics in polyisoprene potassium sorbate processed foods and oxygen absorbents produce packaging propionic acid propionic anhydride 158 9 249 249 248 89 127 78 242 77 89 89 Links 80 91 46 55 209 Q Q10 62 R radiation far infra-red regulation release antimicrobial agents antioxidants butylated hydroxytoluene enzymes ethanol vapour 102 103 104 105 165 179 181 70 106 250 242 243 252 This page has been reformatted by Knovel to provide easier navigation.2-butadiene) poly(1.271 Index terms plastics (Continued) iron in recycled poly(1. . 272 Index terms release (Continued) flavours food ingredients fumigants hinokitiol Maillard reaction products permethrin silver ions sorbic acid removal aldehydes amines cholesterol lactose styrene respiration rate circulation closed system flow-through measurement temperature effect respiratory quotient retortable packaging 62 63 61 62 61 61 3 100 100 190 189 101 103 102 104 102 104 104 248 126 Links 63 79 S Saccharomyces cerevisiae ethanol vapour effect sachets combined effect consumer resistance 146 162 150 151 152 170 This page has been reformatted by Knovel to provide easier navigation. . 273 Index terms sachets (Continued) ethanol releasing ethylene-removing oxygen scavenging see oxygen absorbents and public health safety with safety active interactions and packaging indirect effects on passive interactions scalping sheets drip-absorbent shelf life with oxygen absorbents silica as filler silicone film smart films sodium chloride sorbic acid diffusivity permeability Staphylococcus aureus strawberries sulfites superabsorbent polymers 69 69 1 98 126 129 129 163 69 79 96 153 95 242 238 244 240 99 163 244 165 46 Links 250 This page has been reformatted by Knovel to provide easier navigation. . .274 Index terms T taints see also odours Time-Temperature Indicator (TTI) activation bar code classification of consumer attitudes definitions enzymic operating principles reasons for requirements of specifications thermal process validation with validation tests toxicology triggering chain reaction of propionic acid oxygen scavenging plastics photoreduction 91 249 83 92 228 222 233 229 215 188 217 216 217 229 230 224 243 99 Links 251 245 V vegetables gas atmospheres for vitamin C see ascorbic acid 59 This page has been reformatted by Knovel to provide easier navigation. .275 Index terms W water activity (aw) and ethanol generators 68 Links Y yeast growth ethanol effect oxygen absorber 4 4 170 Z zein films lactic acid retention 128 134 This page has been reformatted by Knovel to provide easier navigation. Documents Similar To Active Food PackagingSkip carouselcarousel previouscarousel nextFood Packaging#Sustainable Plastic and Food Packaging 20070411Food PackagingGrowth Strategies in Bakery and CerealsNew+Packaging+DesignPolymer ElectronicsHandbook of Postharvest Technology02 Trends of Food Packaging & Packaging Technologies in Japan and the WorldPackaging FilmsThe_power_of_packagingFood Packaging Food packagingeFood PackagingMateri Food Packaging TechnologyPackaging FoodFood Packaging GuidanceAntibiotic Stewardship IDSA 2010Cadbury.packaging InnovationCleanroom Concept and Regulatory Requirements_bibekDocumentation Non Conformancesfilmes antimicrobianoFOOD_PACKAGING_1Quality EngineerHandbook of Plastic FilmsAnalytical Method ValidationThe Difference Between ISO and GMP Quality SystemsGMP - SOP SamplePackage of Organic Practices for Cotton, Rice, Red gram, Sugarcane and WheatHFS Book1 Module130692975 Food Additives 2edMenú del pie de páginaVolver arribaAcerca deAcerca de ScribdPrensaNuestro blog¡Únase a nuestro equipo!ContáctenosRegístrese hoyInvitar amigosObsequiosLegalTérminosPrivacidadCopyrightAsistenciaAyuda / Preguntas frecuentesAccesibilidadAyuda de compraAdChoicesEditoresRedes socialesCopyright © 2018 Scribd Inc. .Buscar libros.Directorio del sitio.Idioma del sitio: English中文EspañolالعربيةPortuguês日本語DeutschFrançaisTurkceРусский языкTiếng việtJęzyk polskiBahasa indonesiaSign up to vote on this titleUsefulNot usefulUsted está leyendo una previsualización gratuita.DescargarCerrar diálogo¿Está seguro?This action might not be possible to undo. Are you sure you want to continue?CANCELARAceptar