Food PreservationFood preservation usually involves preventing the growth of bacteria, fungi (such as yeasts), and other micro-organisms (although some methods work by introducing benign bacteria, or fungi to the food), as well as retarding the oxidation of fats that cause rancidity. Food preservation can also include processes that inhibit visual deterioration, such as the enzymatic browning reaction in apples after they are cut, which can occur during food preparation. Many processes designed to preserve food will involve a number of food preservation methods. Preserving fruit by turning it into jam, for example, involves boiling (to reduce the fruit’s moisture content and to kill bacteria, yeasts, etc.), sugaring (to prevent their re-growth) and sealing within an airtight jar (to prevent recontamination). There are many traditional methods of preserving food that limit the energy inputs and reduce carbon footprint. Maintaining or creating nutritional value, texture and flavour is an important aspect of food preservation, although, historically, some methods drastically altered the character of the food being preserved. In many cases these changes have come to be seen as desirable qualities – cheese, yoghurt and pickled onions being common examples. 1. Methods of Food Preservation 1.1. Pasteurization is a process for preservation of liquid food. It was originally applied to combat the souring of young local wines. Nowadays it is prominently applied to milk. In this method, milk is heated at about 70°C for 15 to 30 seconds to kill the bacteria present in it and cooling it quickly to 10°C to prevent the remaining bacteria from growing. The milk is then stored in sterilized bottles or pouches in cold places. This method was invented by Louis Pasteur in 1862. 1.2. Refrigeration preserve foods by slowing down the growth and reproduction of micro-organisms and the action of enzymes that cause food to rot. The introduction of commercial and domestic refrigerators drastically improved the diets of many in the Western world by allowing foods such as fresh fruit, salads, and dairy products to be stored safely for longer periods, particularly during warm weather. 1.3. Freezing is also one of the most commonly used processes commercially and domestically for preserving a very wide range of food including prepared food stuffs that would not have required freezing in their unprepared state. For example, potato waffles are stored in the freezer, but potatoes themselves require only a cool dark place to ensure many months' storage. Cold stores provide large-volume, long-term storage for strategic food stocks held in case of national emergency in many countries. 11. Lutefisk uses lye in its preparation. In chemical pickling. usually in an air-tight bag or bottle. and ingredients for making drinks such as malt and tea leaves are also smoked.Sodium hydroxide (lye) makes food too alkaline for bacterial growth. Sugar is used to preserve fruits. angelica and ginger. peppers. either in syrup with fruit such as apples. typically by a process that produces lactic acid. 1.1. which will change its flavor and texture. Many chemical pickling processes also involve heating or boiling so that the food being preserved becomes saturated with the pickling agent. which reduces water activity sufficiently to prevent bacterial growth.6. apricots. Common chemically pickled foods include cucumbers. Typical pickling agents include brine (high in salt). vinegar. Oil and Vinegar prevent the growth of food-spoiling microorganisms. surströmming. Drying is one of the most ancient food preservation techniques. and curtido. and eggs. 1. which probably arose after the development of cooking with fire. as well as inhibition of Clostridium botulinum. . Fruits and vegetables like paprika. pears. Fruits and Vegetables are often preserved by this method. peaches. Fermented pickles include sauerkraut. Modern recipes for century eggs also call for lye. cheeses. Some pickled cucumbers are also fermented. Salting or curing draws moisture from the meat through a process of osmosis. but mainly for cooking or flavoring them. 1. Pickling can be broadly categorized into two categories: chemical pickling and fermentation pickling. Lye will saponify fats in the food.8. as do some olive recipes. 1. 1. This method is used for the skins of citrus fruit (candied peel). The vacuum environment strips bacteria of oxygen needed for survival. plums or in crystallized form where the preserved material is cooked in sugar to the point of crystallisation and the resultant product is then stored dry.9. Most commonly subjected to this method of food preservation are meats and fish that have undergone curing. alcohol.5. Vacuum-packing is commonly used for storing nuts to reduce loss of flavour from oxidation. or a combination of the two. kimchi.10. Nitrates and nitrites are also often used to cure meat and contribute the characteristic pink color. the food is placed in an edible liquid that inhibits or kills bacteria and other micro-organisms. spices. the food itself produces the preservation agent. This effect is achieved by exposing the food to smoke from burning plant materials such as wood. slowing spoiling. especially olive oil but also many other oils. Lye. 1. It is one of the oldest food preservation methods. Smoking is used to lengthen the shelf life of perishable food items.4. herring. 1.7. Pickling is a method of preserving food in an edible anti-microbial liquid. corned beef. Vacuum-packing stores food in a vacuum environment. and vegetable oil. Meat is cured with salt or sugar. as well as mixed vegetables such as piccalilli. nukazuke. In fermentation pickling. and boiling the containers to kill or weaken any remaining bacteria as a form of sterilization. can support the growth of Staphylococcus aureus. Jugging. whereas marginal fruits such as tomatoes require longer boiling and addition of other acidic elements. Potted meats in aspic. where they are eaten with mashed potatoes. Irradiation of food is the exposure of food to ionizing radiation. Jellied eels are a delicacy in the East End of London. Jugging was a popular method of preserving meat up until the middle of the 20th century. agar. This organism produces no gas or obvious taste and remains undetected by taste or smell. However. Jelly. which produces a toxin that is not destroyed by canning or subsequent reheating. and arrowroot flour. including killing bacteria. sealing it in sterile cans or jars.Meat can be preserved by jugging. . 1.14. Canning involves cooking food. leading to severe illness or death. Some foods naturally form a protein gel when cooked such as eels and elvers. which are a delicacy in Xiamen in Fujian province of the People's Republic of China. maize flour. Its toxin is denatured by cooking. 1.Food may be preserved by cooking in a material that solidifies to form a gel. which produces an acute toxin within the food. Red wine and/or the animal's own blood is sometimes added to the cooking liquid. Food preserved by canning or bottling is at immediate risk of spoilage once the can or bottle has been opened. and at higher doses inducing sterility. and sipunculid worms.12. The animal to be jugged is usually cut into pieces.15. 1. such as vegetables and meats require pressure canning. either highenergy electrons or X-rays from accelerators gamma rays (emitted from radioactive sources as Cobalt-60 or Caesium-137). Low acid foods. molds. It was invented by Nicolas Appert. and insect pests. (a gel made from gelatine and clarified meat broth) were a common way of serving meat off-cuts in the UK until the 1950s. Cooked mushrooms. there have been examples of poor manufacture (underprocessing) and poor hygiene allowing contamination of canned food by the obligate anaerobe Clostridium botulinum. handled poorly and then canned. The treatment has a range of effects. the process of stewing the meat (commonly game or fish) in a covered earthenware jug or casserole. reducing the ripening and spoiling of fruits. Lack of quality control in the canning process may allow ingress of water or microorganisms. Most such failures are rapidly detected as decomposition within the can causes gas production and the can will swell or burst. Such materials include gelatine. and stewed. Many jugged meats are also jellied.13. placed into a tightly-sealed jug with brine or gravy. High-acid fruits like strawberries require no preservatives to can and only a short boiling cycle. however.1. Foods have varying degrees of natural protection against spoilage and may require that the final step occur in a pressure cooker. PEF for food processing is a developing technology still being researched. The electric field enlarges the pores of the cell membranes. mold and oxidation from damaging the grain. PEF holds potential as a type of lowtemperature alternative pasteurization process for sterilizing food products. There have been limited industrial applications of PEF processing for the pasteurization of fruit juices. This causes micro-organisms to die off on the surface. In PEF processing. although salad vegetables retain their appearance and texture in such conditions. However. it is sometimes called 'cold pasteurization'. whereas in heat treatment the observation of a minimum temperature and minimum duration of exposure ensures the elimination of the microorganisms under consideration.17. this method of preservation may not retain nutrients.The technology may be compared to pasteurization. which kills the cells and releases their contents. Carbon dioxide prevents insects and. 1. Pulsed electric field (PEF) electroporation is a method for processing cells by means of brief pulses of a strong electric field. a substance is placed between two electrodes.16. 1. as the product is not heated. 1. There is concern that. as it reduces the microbial load by incremental (logarithmic) steps. . Salad crops that are notoriously difficult to preserve are now being packaged in sealed bags with an atmosphere modified to reduce the oxygen (O 2) concentration and increase the carbon dioxide (CO2) concentration. then the pulsed electric field is applied. depending on concentration. it is fundamentally different from pasteurization. especially vitamins. Non-Thermal PlasmaThis process subjects the surface of food to a 'flame' of ionised gas molecules such as helium or nitrogen.18. Modifying atmosphere is a way to preserve food by operating on the atmosphere around it. Grain stored in this way can remain edible for five years. Grains may be preserved using carbon dioxide by one of two methods: Either a block of dry ice is placed in the bottom and the can is filled with grain or the container is purged from the bottom by gaseous carbon dioxide from a cylinder or bulk supply vessel. Some LABs produce the antimicrobial nisin. salt. and can inhibit the activities of a wide spectrum of organisms.20.Some foods such as many cheeses. Beneficial bacteria or the fermentation products produced by these bacteria are used in biopreservation to control spoilage and render pathogens inactive in food. Of special interest are lactic acid bacteria (LAB. wines. . LAB bacteriocins are used as an integral part of hurdle technology. including inherently resistant Gram-negative bacteria. When LABs compete for nutrients. Biopreservation is the use of natural or controlled microbiota or antimicrobials as a way of preserving food and extending its shelf life. 1. High-pressure food preservation or Pascalization refers to the use of a food preservation technique that makes use of high pressure. and peptide bacteriocins. lack of oxygen. Ground Burial. These days. and beers will keep for a long time because their production uses specific microorganisms that combat spoilage from other less-benign organisms. hops. It is a benign ecological approach which is gaining increasing attention. "Pressed inside a vessel exerting 70. hydrogen peroxide.1. These microorganisms keep pathogens in check by creating an environment toxic for themselves and other micro-organisms by producing acid or alcohol. Controlled Use on Micro-Organisms. their metabolites often include active antimicrobials such as lactic and acetic acid.Burial of food can preserve it due to a variety of factors: lack of light. Lactobacillus). controlled (usually low) levels of oxygen and/or other methods are used to create the specific controlled conditions that will support the desirable organisms that produce food fit for human consumption 1. Using them in combination with other preservative techniques can effectively control spoilage bacteria and other pathogens.21.19. pH level.22.000 pounds per square inch (480 MPa) or more. texture and nutrients while disabling harmful microorganisms and slowing spoilage. or desiccants in the soil. Most foods can be preserved in soil that is very dry and salty (thus a desiccant). Starter micro-organisms. 1. which is a particularly effective preservative. Burial may be combined with other methods such as salting or fermentation. cool temperatures. Lactic acid bacteria have antagonistic properties that make them particularly useful as biopreservatives. the process was being used for products ranging from orange juice to guacamole to deli meats and widely sold. food can be processed so that it retains its fresh appearance." By 2005. flavour. controlled (usually cool) temperatures. or soil that is frozen. Class I preservatives refers to those preservatives which are naturally occurring. The right combination of hurdles can ensure all pathogens are eliminated or rendered harmless in the final product. which inhibit the growth of bacteria or fungi. sodium nitrate. sulfites (sulfur dioxide. sodium nitrite.23. biological samples. everyday substances. which inhibit the oxidation of food constituents. wood.Preservative food additives can be antimicrobial. glutaraldehyde (kills insects). etc. to prevent decomposition by microbial growth or by undesirable chemical changes. Fig. or antioxidant. Hurdle Technology Basics 1. . etc. including mold. honey and wood smoke. Hurdle technology is a method of ensuring that pathogens in food products can be eliminated or controlled by combining more than one approach. Artificial Food Additives. These approaches can be thought of as "hurdles" the pathogen has to overcome if it is to remain active in the food.1. ethanol. What is a Preservative? A preservative is a naturally occurring or synthetically produced substance that is added to products such as foods. Antioxidants include BHA and BHT. and methylchloroisothiazolinone. such as oxygen absorbers. Common antimicrobial preservatives include calcium propionate. paints. depending on their origin. potassium hydrogen sulfite. Class II preservatives refer to preservatives which are synthetically manufactured. 2. sodium bisulfite. pharmaceuticals. Preservatives can be divided into two types.) and disodium EDTA.24. Other preservatives include formaldehyde (usually in solution). Examples include salt. Other preservatives include ethanol and methyl-chloro-isothiazolinone. This inhibits spoilage of the food item by microbial growth. BHT. For example sulfites are commonly used in wines and some dried fruits or vegetables and are known as possible irritants to people with asthma. 5. Another group of preservatives targets enzymes in fruits and vegetables that start to metabolize after they are cut. sodium bisulfite. Vitamin C and Vitamin E are also sometimes used as preservatives. sugar. The basic approach is to eliminate microorganisms from the food and prevent their regrowth. or to retain their nutritional value and/or flavor for a longer period. Certain processes such as freezing. salt. calcium propionate. Antioxidants include BHA. Common antimicrobial preservatives include sorbic acid and its salts. children exhibited increased hyperactivity after consuming drinks containing sodium benzoate or artificial food color and additives. or reducing the water content. sulfites (sulfur dioxide. including mold or they can be antioxidants such as oxygen absorbers. hops. FDA standards do not currently require fruit and vegetable product labels to reflect the type of chemical preservative(s) used on the produce. In one study. toxicology. This is achieved by methods such as a high concentration of salt. 4. vinegar. Prior studies were however inconclusive. the naturally occurring citric and ascorbic acids in lemon or other citrus juice can inhibit the action of the enzyme phenolase which turns surfaces of cut apples and potatoes brown if a small amount of the juice is applied to the freshly cut produce. Preservatives in foods Preservatives are often added to food to prevent their spoilage. TBHQ and propyl gallate. which inhibit the growth of bacteria or fungi. alcohol. benzoic acid and its salts.3. etc. Natural food preservation Naturally occurring substances such as rosemary extract. potassium hydrogen sulfite. The benefits and safety of many artificial food additives (including preservatives) are the subject of debate among academics and regulators specializing in food science. diatomaceous earth and castor oil are also used as traditional preservatives. sodium nitrite. which inhibit the oxidation of food constituents. pickling. smoking and salting can also be used to preserve food.) and disodium EDTA. . Preservatives may be antimicrobial preservatives. Health Concerns Some modern synthetic preservatives have been shown to cause respiratory or other health problems. and biology. For instance. R36. 470 K.S45 LD50 2340 mg/kg-1 . S26. R38 S-phrases (S1/2). Information Table for KHSO3 IUPAC name Potassium hydrogen sulfite Identifiers CAS number 7646-93-7 PubChem 516920 EC number 231-594-1 UN number 2509 RTECS number TS7200000 Properties Molecular formula KHSO3 Molar mass 136.245 g/cm3 Melting point 197 °C. R37. 6. It is used during the production of alcoholic beverages as a sterilizing agent. It is made by the reaction of sulfur dioxide and potassium carbonate. Potassium Bisulphite (KHSO3) Potassium hydrogen sulfite or potassium bisulfite is a chemical compound with the chemical formula KHSO3. The solution is concentrated and then allowed to crystallize. > 300 °C Solubility in water 490 g/L Hazards MSDS External MSDS EU Index 016-056-00-4 EU classification Corrosive (C) R-phrases R34. 387 °F Boiling point Dec. The sulfur dioxide is passed through a solution of the potassium carbonate until no more carbon dioxide is given off. This additive is classified as E number E228 under the current EU approved food additive. S36/37/39.6.169 g/mol Density 2. It is soluble in water and hence easily mixes with food constituents. Sulphur Dioxide (or Sodium Benzoate) (or Potassium Bisulphite) Benzoic Acid or its sodium salt is commonly used for the preservation of food materials.Conical Flasks (100 mL). AIM OF EXPERIMENT The aim of this project is to study the effects on Potassium Bisulphite as a food preservative under various conditions likeAt different temperatures At different concentrations For different intervals of time REQUIREMENTS Apparatus. which are added to food materials to prevent their spoilage are called chemical preservatives. For preservation of fruits. Potassium Bisulphite Other aids.Experiment on KHSO4 INTRODUCTION Growth of Microorganisms in a food material can be inhibited by adding certain chemical substances for safety. two chemical preservatives. In India. Potassium Bisulphite on reaction with the acid of the juice produces SO2 which is very effective in killing microbes present in food and thus prevents it from getting spoiled. fruit juices. Potassium Bisulphite is used for preservation of colourless food materials like fruit juices. squashes and jams. which are permitted to use are1. squashes. these chemical substances should not be harmful to human beings. Such chemical substances. Benzoic Acid 2. no harmful material stays in food. a sharp knife Chemicals. This is not used for coloured food materials as the Sulphur Dioxide released in its action serve as a bleaching agent.Apples . apples and raw mango chutney. glass rod. However. Since the effective product is a gas.Sugar. 23 0.5 g 0.00 0.98 2.00 0.1 g B 50 g C 50 g 5 days 10 days 15 days 0 5 C 0.00 0.00 0.03 At Different Temperatures Microbial Growth (%) Sample Amount of Jam Amount of Potassium Bisulphite Temperature Range A 50 g 0. their growth increases with the passage of time. The preservation of jam was maximum at low temperature. kept at room temperature (25C).09 0.08 0.2 g 0.01 0.00 0.1 g 0.13 0.01 0.5 g 60 70 C 0.07 0.06 0.08 0.02 0.01 0. The growth of micro-organisms occur earliest in flask.35 0.42 0.49 0. the growth of micro-organisms appear after more days (longer period).44 D 50 g 1.2 g 25 30 C 0.0 g 0.21 0.00 0.32 B 50 g 0.00 0.OBSERVATION TABLE Under Different Concentrations of KHSO3 Sample Amount of Jam Amount of Potassium Bisulphite Growth of Micro-Organisms (%) 1 day 2 days 3 days 4 days 5 days 6 days A 50 g 0. The minimum concentration of KHSO3 required for preserving jam is approximately 1%. Once the micro-organisms appear.80 C 50 g 0.00 0.09 0.01 0. .47 RESULTS & INFERENCE As the concentration of KHSO3 is increased.00 0.59 1. Bibliography Resources and Partners Books for Reference .
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