Food Chemistry 127 (2011) 641–644Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem Short communication Quality attributes of starfruit (Averrhoa carambola L.) juice treated with ultraviolet radiation Rajeev Bhat a,⇑, Suhaida Binti Ameran a, Han Ching Voon a, A.A. Karim a, Liong Min Tze b a b Food Technology Division, School of Industrial Technology, Universiti Sains Malaysia, Penang 11800, Malaysia Bioprocess Technology Division, School of Industrial Technology, Universiti Sains Malaysia, Penang 11800, Malaysia a r t i c l e i n f o a b s t r a c t Starfruit juice were exposed to ultraviolet (UV-C) light for 0, 30 and 60 min at room temperature (25 ± 1 °C). On exposure, the titratable acidity significantly decreased, while the decrease in °Brix and pH were not significant. With regard to colorimetric parameters, L⁄ value increased significantly with a subsequent decrease in a⁄ and b⁄ values corresponding to UV treatment time. Except for the ascorbic acid, other antioxidants measured (% DPPH inhibition, total phenols, flavonols, flavonoids and antioxidant capacity) showed enhancement on expsoure to UV (significant at 60 min). Microbial studies showed reduction in APC, yeasts and mould counts by 2-log cycle on UV treatments. These results supports the application of UV as a measure of non-thermal and physical food preservation technique for starfruit juice that can be explored commercially to benefit both the producers and consumers. Ó 2011 Elsevier Ltd. All rights reserved. Article history: Received 27 September 2010 Received in revised form 29 November 2010 Accepted 11 January 2011 Available online 18 January 2011 Keywords: Ultraviolet treatment Non-thermal processing Starfruit juice Antioxidants Microorganisms Safety 1. Introduction Epidemiological studies have indicated that regular consumption of fruits and vegetables can reduce the risk of cardiovascular disease, ageing, cancer, etc. (Alothman, Bhat, & Karim, 2009a). Presently, consumer’s demand for safer and high quality foods with extendable shelflife and with minimal quantity of chemical residues has increased tremendously. Application of short wave length ultraviolet light rays (UV-C) for decontamination and shelflife improvement of fruits or their products is one of the emerging novel technologies the food industry can rely on. The lethal germicidal effect of UV-C on bacteria, yeasts and moulds have been used as an effective means for microbial inactivation and for preservation of overall quality of fruits or their products (Alothman, Bhat, & Karim, 2009b). Starfruit is a popular tropical fruit, which is consumed either fresh or made into juice to be served as a cooling beverage. The mature fruit is star-shaped, sweet and juicy and golden-yellow in appearance. Starfruits are used for preparing fruit salads or made into jellies and preserves (Macleod & Ames, 1990). In Malaysia, starfruits are mixed with apples and stewed with sugar and cloves or is cooked along with seafood or meat. In Ayurvedic medicine, starfruits or their juices are recommended to relieve pain from indigestion and bleeding haemorrhoids, and to reduce fever (Khare, 2004). ⇑ Corresponding author. Tel.: +60 4653 5212; fax: +60 4657 3678. E-mail address:
[email protected] (R. Bhat). 0308-8146/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2011.01.042 To our knowledge, ultraviolet (UV-C) radiation has not been applied for starfruits or their juices. Hence, the purpose of this study was to evaluate the effectiveness of UV on the physico-chemical parameters, antioxidant activities and on the microbiological quality of starfruit juices. It is envisaged that the baseline information generated will be useful for the successful implementation of UV technology on a pilot scale, to benefit health conscious consumers as well as being useful in implementing the hazard analysis and critical control point (HACCP) approach for preservation and shelf life improvement of starfruit and their juice. 2. Material and methods 2.1. Plant material Locally grown, fresh, matured ‘Arkin’ cultivar of starfruits (Averrhoa carambola L. Family: Oxalidaceae) (average weight, 168.0 ± 0.1 g; 11–12 mm length and 73–75 mm in cross section) were purchased from the local supermarket (Jusco, Penang, Malaysia). After transporting to the laboratory under sterile conditions, the fruits were washed in distilled water and selected for healthy fruits with uniformity in size, shape and peel colour. 2.2. Juice preparation and UV treatment Starfruits cut into identical cubes were blended in a kitchen mixer (3 min) followed by filtration (Whatman filter paper No. 1) to obtain clear juice. This juice was poured into sterile disposable 1-diphenyl-2-picrylhydrazyl) assay based on the method described by Blois (1958) and the radical scavenging activity was calculated as: à %DPPH inhibition ¼ ½ðAo À A1 =Ao Þ Â 100 where. until further analysis. Total phenolics content. germicidal fluorescent lamp with a peak emission of 254 nm. each of the exposed samples received a UV radiation dose of 2. Further. Venskutonis.1). one millilitre of decimal dilution of the sample was pipetted into Petri dish and the total plate counts were enumerated using the pour plate method. Missouri. and Okada (2005) was employed and the results were expressed as mg of (+)-catechin equivalent per gramme of extract.1. 10 mm depth) and exposed under the UV lamp (pre-calibrated for 1 h. On an average. and Aguilar (1999) was adapted to measure the antioxidant capacity and the results were expressed relative to that of ascorbic acid (mg/ml). 2. The total flavonols content was estimated by adapting the method described by Miliauskas. USA). and Van Beek (2004) with slight modifications and the content was expressed as mg quercetin equivalent per gramme of extract. antioxidant capacity. JENWAY Ltd. Statistical analyses were conducted by using SPSS 12. Germany). Deutschland. Bhat et al. maintained at a distance of 30 cm.4. Germany) and R&M Chemicals (Essex. 2. DPPH radical scavenging activity The free radical scavenging activity of the juice was measured by DPPH (1. 10% tartaric acid was added into PDA agar (final pH 3. Seelze. total soluble solids and titratable acidity The results on pH.05. For titratable acidity. 1965) and the results expressed as milligrammes of gallic acid equivalents per gramme of sample. USA) and stored at 4 °C. Switzerland). The plates were incubated at 37 ± 1 °C for 48 h. 2. Microbial analysis (aerobic plate count. The total yeast and moulds were enumerated by pour plate method using potato dextrose agar (PDA) media.7. 3. yeast and mould counts) UV treated and non-treated juice were analysed for the status of aerobic plate count (APC). yeast and mould counts.2 ± 0. Physico-chemical analysis (pH. Ao is the absorbance of the control and A1 is the absorbance of the extracts. plate count agar (PCA) and potato dextrose agar (PDA) were procured from MERCK (Darmstadt. Sample preparation Fruit samples (control and UV treated) cut into equal sized cubes (2  4 cm) were blended in a kitchen mixer (3 min) followed by extraction with the solvent (methanol. IL. Obara.5–3.. Colour appearance was taken as L⁄. Ascorbic acid (Vitamin C) content were determined based on the 2. Statistical analysis The results obtained in the present study are represented as mean values of three individual replicates ± standard deviation (SD). The results were expressed as log colony-forming units (cfus) per millilitre of juice (n = 5).9. Malaysia) for 30 and 60 min separately.8. Pineda. . This was freeze dried (LABCONCO. One drop of the juice was placed inside the refractometer ATAGO HSR-500 (Japan) and the results were expressed in °Brix. Antioxidant assays 2. Staffordshire. Kansas City. flavonoids. and b⁄ was a measure of yellowness when positive and blueness for negative. The plates were incubated at 25 °C for 5– 7 days in the incubator.. The pH and acidity are important criteria during ½ðLà À Lo Þ2 þ ðaà À ao Þ2 þ ðb À bo Þ2 1=2 where.642 R. Selangor. A series of decimal dilutions (10À1–10À5) was prepared with 0. total soluble solids and titratable acidity are shown in Table 1. 30926. 1 g of sample was titrated with 0. ao and bo are colour values of untreated juice. The extract was filtered through Whatman filter paper (No. V is titre volume of NaOH and m is the weight of starfruit juice (g). The total colour difference (TCD) or DE was measured by following equation: Ascorbic acid ðmg=100 g or mlÞ ¼ ðTitre  dye factor  concentration  100Þ =ðExtract aliquot used for estimation  volume of sample use for estimationÞ: 2.5. ESCO Airstream laminar flow cabinet. Lo. flavonols and ascorbic acid The total phenolics content was determined using the Folin–Ciocalteu (FC) reagent method (Singleton & Rossi. The total acidity was calculated using the following equation. Tachibana. 1).1% (w/v) peptone water. A corresponding control was maintained under same experimental conditions (25 ± 1 °C) (n = 3). and Luh (1983). pH 8. UK) at 1100 rpm for 3 h (25 ± 1 °C). Chicago. 1:10) with continuous magnetic stirring on a hot plate stirrer (JENWAY 1000 hot plate and stirrer. a⁄ and b⁄ values. UK). with reference to citric acid: 2.6-dichloroindophenol titrimetric method (AOAC.158 J/m2 (digital radiometer). / Food Chemistry 127 (2011) 641–644 Petri dishes (15  100 mm. Peptone water (buffer). 1995). Japan).10. Germany) and the supernatant obtained was concentrated (50 °C) using a rotary evaporator (Buchi Rotavapor R-215 Postfach Flawil. L⁄ was a measure of lightness and varied from 100 for perfect white to zero for black.5. The method described by Prieto. To determine total flavonoids. pH. the method described by Sakanaka. Analysis of variance (one way-ANOVA) was performed and the significant differences between mean values were determined by Tukey’s pair-wise comparison test at a significance level of p < 0. centrifuged (3000g. Solvents and reagents All the solvents and reagents used in the present study were procured from Sigma Aldrich (Laborchemikalien GmbH. 2. while a⁄ measured the redness when positive and greenness when negative. 2.1.7). Colour analysis The colour of the samples was measured using Minolta Spectrophotometer (Model: CM-3500D).1 N sodium hydroxide (NaOH) to the phenolphthalein end-point (1%.6. The total soluble solids content was determined according to the method described by Matsumoto.3. Results and discussion 3. To inhibit the growth of others microbes. 15 min) (SIGMA Laborzentrifugen 6-10. 2. Free Zone 6 Liter. Results were expressed as milligrammes of ascorbic acid per 100 ml sample and the results calculated as: TAð%Þ ¼ ½V  ð0:1 N NaOHÞ Â ð0:067Þ Â ð100Þ m where. titratable acidity and total soluble solids content) The pH of the fruit juice was determined using a pH Meter (HORIBA F-21.01 software (SPSS Inc. Values followed by the same letter within the same column are not significantly different from each other (p > 0. 3.2. UV treatments showed significant decrease in the acidity.2) 33.06a 0.0 ± 0. respectively.. respectively). Previously.3 ± 0.02b (6. respectively. 6.02b (6. ..1 and 6.7) a Total flavonoids (mg CE/g) 0. Antioxidant assays The results on the effect of UV on antioxidants in starfruits extracted with methanol are shown in Table 3. CE.13 ± 0. parameters a⁄ and b⁄ showed a decreasing trend corresponding to UV time of exposure. 2006).54% and 6. gallic acid equivalents. With the increase in UV time. The DPPH assay involves reaction of specific antioxidant with a stable free radical 2. delivered dose.37 ± 0. which ranged between 6. Table 3 Effect of UV treatment on antioxidant assays in starfruits extracted in methanol (n = 3 ± SD).08 ± 0. respectively) occurred.98 ± 0.23 ± 0.13a 26. methanol was used as an extracting solvent as it has been shown to exhibit potentially high antioxidant activities (Khattak.74% up to 87. solvents used and the basic raw material (Alothman et al. not detected.47 mg QE/100 g at 0 and 60 min. Treatment time (min) 0 30 60 pH 4. °Brix and titratable acidity content of freshly prepared star fruit juices (n = 3 ± SD). Our results are on par with previous reports on fruits exposed to UV radiation treatments (Alothman et al. flavonoids (0. Additionally.7 and 6. & Wang.. no significant changes were observed in the pH and °Brix on UV treatments. With regard to flavonols.77 ± 0.0 ± 2. Treatment time (min) APC 1.77 ± 0.57 ± 0.02 (3.06a 1.4 at 30 and 60 min.9 and 3.01a 0.01a 4. which was attributed to the destruction of the coloured polymeric compounds and to the enhancement in the browning degree of the fruit juice.15a 24. lemon juice) wherein decrease in a⁄ and b⁄ was observed.12a 8.24 ± 0.69 mg GAE/g at 0 and 60 min.7) 0.36a 87. 3.27 ± 0. * Values are mean of triplicate determination (n = 5 ± SD).06a 1. while for antioxidant capacity it was 1.08c (3.01 ± 0. AA.3.01b Table 1 Effects of UV treatment on pH.31 ± 0. 2008). ascorbic acid.23 8.36 ± 0.07a 2. the percentage change in total phenols after UV exposure was 3. peach.4) b Ascorbic Acid (mg/100 ml) 27. which are entirely dependent on the exposure time.2a 32.03 (1. A non-significant increase in the percent inhibition of DPPH was recorded after UV treatments. flavonols (2.00b ND Yeast and mould counts (log cfu/ml) 2.4) 0.07b a⁄ 2.01 4.0) 21. a⁄ and b⁄ of freshly prepared star fruit juices (n = 3 ± SD).08% in control and UV treated samples for 30 and 60 min. Additionally.06b 0 30 60 Values followed by the same letter within the same column are not significantly different from each other (p > 0.28 (1.27 ± 0. 2008. colony-forming units. In this study. With regard to ascorbic acid. Ibarz.58a 1. Whereas. DE representing the total colour difference (magnitude of colour change) showed a significant increase after UV treatments.2 at 30 and 60 min.39 to 4.1) ab Antioxidant capacity (mg/ml AA) 31. ND.87 in control and UV treated samples.27 ± 0.2-diphenyl-1-picrylhydrazyl wherein a reduction in the DPPH concentration caused by the antioxidant decreases the optical absorbance of DPPH. & Ihasnullah.39 ± 0.02 ± 0. Colour analysis Significant differences in the colour parameters were recorded in starfruit juice after UV treatments (Table 2).05).13a 77. while for flavonoids it was 17.09b b⁄ 26.R. the percent change recorded was 1. respectively. GAE.65–0. catechin equivalent.77a (2. 2009).4) 2.73%.23–0. a corresponding increase in the levels of total phenols (0. / Food Chemistry 127 (2011) 641–644 643 fruit juice processing as they can prolong the shelflife of the product and can be used as one of the most reliable indicator to evaluate the overall qualities. flavonoids and flavonols might be advantageous for health conscious consumers as these compounds are known to be potential antioxidants and active free radical scavengers (Alothman et al.74 ± 0. 2009b. Overall. considering 0 time as 100%. Pagan. Simpson. Ndhlala et al.05). The increase might be attributed to the accumulation of phenolic compounds or their products as a means of defence against UV treatments.73 ± 0. The pH ranged from 4.06a 78. respectively) and antioxidant capacity (31. & Samman. An increase in the lightness (L⁄) value was recorded corresponding to increased UV treatment time.43 ± 0.31 up to 24.93–33.11a 25. The increase recorded was from 85. and Garza (2005) have made similar observations in fruit juices (apple. cfus.12a a % Acidity 6.57 and 21. respectively.87 ± 0.03a 6.01 mg/ml AA at 0 and 60 min.8) a Total phenols (mg GAE/g) 0. QE.61 ± 0. 2009a).23 ± 0.43b (-10.0 ± 1.32 ± 0. the increase can be attributed to the enhanced phenylalanine ammonia-lyase and the polyphenol oxidase enzyme activities.21 (1.0b (17.77 mg/ Table 4 Effect of UV exposure time on the survival of microorganisms in freshly prepared star fruit juices*.05b 6.01 (17.9) b Total flavonols (mg QE/100 g) 2.3) 88.67 ± 0. the °Brix can be used for measuring the amount of sugars present in fruits and their juices.23 ± 0.13b DE – 0. respectively.71 ± 0. Sundram. Application of UV can either enhance or decrease the antioxidants. In the present study. Balasundram. Panades.05). making the juice more transparent.01a a Brix 9.02c Values followed by the same letter within the same column are not significantly different from each other (p > 0.42 ± 0.93 ± 0.65 ± 0. a significant decrease was recorded which ranged between 27. Wang.15b 1. 2009a.37 ± 0.47 ± 0. Bhat et al.01a 2.27 mg CE/g at 0 and 60 min.32–2.93 ± 0.48 ± 0.37 and the °Brix between 9. Treatment time (min) 0 30 60 L⁄ 77. Treatment time (min) 0 30 60 DPPH (%) 85..69 ± 0.5) Values in parenthesis indicate per cent change after UV exposure over control (0 min taken as 100%). Chen.24% in control and UV treated samples (30 and 60 min). This increase might be attributed to the degradation of the coloured compounds formed previously due to UV treatment.54c (-20. Table 2 Effects of UV treatment on colorimetric parameters L⁄.0 ± 0.54 ± 0.4 at 30 and 60 min of UV exposure time.13 and 8. 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