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Journal of Food, Agriculture & Environment Vol.11 (2): 243-248. 2013
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Combined effect of hot water dipping treatment, N-acetylcysteine and calcium on quality retention and enzymatic activity of fresh-cut apple Martha López-López, Analí Vega-Espinoza, Lidia Ayón-Reyna, José López-Valenzuela and Misael Vega-García* Maestría en Ciencia y Tecnología de Alimentos, Facultad de Ciencias Químico-Biológicas, Universidad Autónoma de Sinaloa, Cd. Universitaria, Av. de las Américas y Josefa Ortiz S/N, Culiacán, Sinaloa, México 80010. e-mail:
[email protected],
[email protected],
[email protected],
[email protected],
[email protected] Received 20 January 2013, accepted 29 April 2013.
Abstract Apple is the most popular template fruit consumed all over the world. However, the susceptibility of apples and their products to enzymatic browning and fruit softening during processing operations and storage reduces the overall quality and limits its shelf life and marketability. Actually, numerous research efforts pursue the development of new ways of preventing browning in fresh-cut fruits. In this sense, the combination of hot water treatment with dipping additives could be an effective alternative with great potential to be used commercially. Therefore, the aim of this study was to evaluate the effect of hot water treatment, N-acetylcysteine and calcium chloride dips on quality retention and enzymatic activity of fresh-cut Red Delicious apple. Whole fruits were dipped in water at ambient temperature (25°C, 10 min) (AWD) or subjected to hot water dipping treatment (HWD) at 45ºC for 10 min. After immersions, fruits were minimally processed and dipped for 3 min in N-acetylcysteine (NAC), calcium chloride (CaCl2) or their combination and stored at 4°C for 25 days. External colour changes, firmness, polyphenol oxidase (PPO) and peroxidase (POD) activities and sensory analysis were evaluated. The results obtained showed that HWD+NAC-CaCl2 treatment retained firmness, delayed colour changes and browning of fresh-cut apple during 25 days of storage compared with the other treatments. In addition, this combination effectively inhibited PPO and POD activities in the apple slices. Sensory results indicated that HWD+NAC-CaCl2 treatment did not adversely affect the attributes of fresh-cut apple, therefore can be considered a good alternative to improve the quality of fresh-cut Red Delicious apples. Key words: Malus domestica, fresh-cut apple, hot water treatment, calcium chloride, N-acetylcysteine, enzymatic browning, polyphenol oxidase, peroxidase, firmness, sensory evaluation, quality maintenance.
Introduction Increased consumers’ demand for natural products that claim health benefits and modern lifestyles have stimulated a rise for production and consumption of fresh-cut fruit and vegetables 1. Fresh-cut apple has emerged as a popular snack in food service establishments, school lunch programs and for family consumption2. This fruit is well appreciated for its crispness, taste, flavour, and juiciness, but mechanical operations during minimal processing damage the tissues and their sensory properties decrease due to an increase in metabolic activities 3 and enzymatic reactions, leading to changes in colour, flavour, and softening that can result in the consumer rejection 4. In this sense, enzymatic browning has a significant impact on the appearance and organoleptic properties of fresh-cut apples and it is usually associated with oxidation of phenolic compounds to o-quinones by polyphenol oxidase (PPO; EC 1.14.18.1), with subsequent reactions leading to the formation of brown pigments (melanins)5. The contribution of peroxidase (POD; EC 1.11.1.7) may also be relevant 6; this enzyme can oxidize both mono- and diphenols in the presence of small amounts of hydrogen peroxide 7. Also, PPO and POD may act synergistically. It has been suggested that PPO could be the promoter of POD activity because hydrogen peroxide is generated during the oxidation of phenolic compounds in the PPO-catalyzed reaction 8, 9. Journal of Food, Agriculture & Environment, Vol.11 (2), April 2013
Hot water treatment has been reported as a good alternative to reduce browning 10 and to inhibit the action of cell wall degrading enzymes 11. Koukounaras et al. 12 reported that heat treatment (50°C, 10 min) of intact peach before cutting controlled browning and retained firmness of peach slices. Also, heat treatments have been shown to reduce browning development in fresh-cut celery 13 and lettuce 14. For fresh-cut apples, respiration rate and softening were reduced and the shelf life was increased when the fruit received a heat treatment at 38°C before slicing 15. A combination of heat treatments followed by calcium dips has also been found to maintain or improve the firmness of fresh-cut lettuce (50°C, 1 min) 16, fresh-cut carrot (50°C, 1 min) 17, and fresh-cut melons (60°C, 1 min) 18. A dip treatment after peeling and/or cutting in a solution containing antibrowning compounds is the most common way to control browning in fresh-cut fruit. Various dipping treatments composed mainly of ascorbic acid, a calcium salt and an organic acid have been applied to fresh-cut apple to inhibit browning and to extend the postcut shelf life 19, 20. However, most of these chemicals have limited success because their inhibitory action is only temporary 21, 22. An alternative treatment with different antibrowning agents may improve the appearance and shelf life of fresh-cut apples. A recently investigated antibrowning 243
compound is the natural additive N-acetylcysteine (NAC), which was shown to be effective in reducing enzymatic browning in fresh-cut apple 4, 23. This compound reacts with quinones formed during the initial phase of enzymatic browning reactions to yield the colourless addition products or to reduce o-quinones to odiphenols 24. Oms-Oliu et al. 4 and Rojas-Graü et al. 25 reported that NAC inhibited browning in fresh-cut apples and pears. Also, the incorporation of NAC into some coatings resulted effective in preventing browning of fresh-cut pears 26. On the other hand, calcium salts, particularly CaCl2, are used as firming agents in a wide variety of fresh-cut fruits 10, 27. Calcium treatments improve firmness retention and product shelf life 28, but high concentrations of CaCl2 might have a detrimental effect on flavor 29. Nowadays, numerous research efforts pursue the development of new ways of preventing browning in fresh-cut fruits 21. The combination of heat treatment with NAC and CaCl2 could be an effective alternative for the prevention of enzymatic browning with great potential to be used commercially. However, current research has focused on the individual effect of heat treatments and NAC immersion or the combined effect of heat treatments and calcium salts on the quality of fresh-cut apples. Therefore, the objective of this work was to evaluate the effect of hot water treatment combined with NAC and CaCl2 on colour changes, firmness retention and the activity of related enzymes (PPO, POD) in fresh-cut Red Delicious apple. Sensory quality after storage at 4°C was also evaluated. Materials and Methods Fruit processing: Apple (Malus domestica Borkh) fruit cv. Red Delicious (mean fruit mass 180 g) was obtained from a local retail store in Culiacán, Sinaloa, México. Fruits, containers, utensils and surfaces in contact with the fruit during processing were washed and sanitized with 200 ppm NaClO. Whole fruits were randomly divided into two groups; one group was dipped in water at ambient temperature (25°C) for 10 min (AWD), while the second group received a heat treatment by immersing fruit in a water bath, set at 45°C, for a period of 10 min (HWD). Both groups were then cooled in water at 21°C for 5 min. Under aseptic conditions, unpeeled apples were hand-cut into one cm thick slices, parallel to the longitudinal axis, and manually cored using stainless steel sharp knives. Subsequently, apple slices were mixed together and randomly dipped for 3 min at 4°C in different solutions containing distilled water, NAC (0.05 M), CaCl2 (0.5%), or the combination of NAC-CaCl2. The excess solution was drained and 8 slices (90-120 g samples) were packaged into 0.250 L polypropylene trays (Nutrigo, S.A. de C.V., México) and stored up to 25 days at 4+1°C. From this storage, two trays were randomly removed for each treatment at 5 day intervals for analysis. Evaluation of external colour: Colour was evaluated on the surface of cut apple with a Minolta colorimeter CR 200 (Minolta, Osaka, Japan) using the CIE L* and a* coordinates, two parameters frequently used to monitor browning of cut apple surfaces. Pulsed xenon arc lamp, 2º observation, illuminant C and 8 mm diameter measuring area were used. Measurements were performed at the centre of each slice and eight slices per treatment were evaluated. Determination of firmness: A digital penetrometer (Chatillon DFE 100, AMETEK Inc, Largo, FL) fitted with an 11 mm diameter probe 244
was used to evaluate firmness. The pericarp at the centre of each slice was penetrated (5 mm depth) with a constant speed of 50 mm/min. Results were expressed in Newtons (N) and four replicates were tested for each treatment. Determination of PPO activity: Enzyme extracts were obtained homogenizing 5 g of mixed apple slices with 5 mL of 0.05 M K2HPO4 buffer (pH 7.0) containing 40 g/L polyvinylpolypyrrolidone (PVPP) and then centrifuged at 14,000 x g for 1 min (4°C); the supernatant was dialyzed against two changes of the same buffer over a period of 24 h at 4°C. PPO activity was determined according to GonzálezAguilar et al. 30. The reaction was started by adding 900 µL of K2HPO4 buffer (0.05 M, pH 7.0) plus 500 µL of 0.2 M catechol in sodium citrate buffer (0.1 M, pH 4.0), and 100 µL of enzymatic extract to a quartz cuvette. Changes in absorbance at 400 nm were recorded every 10 s up to 5 min using a spectrophotometer (UNICO SQ 2800, NJ, USA). One unit of activity (UA) was defined as a change in absorbance of 0.001 units/min. Protein concentration was determined according to Bradford 31 using bovine serum albumin (BSA) as a calibration standard at 595 nm. Results were expressed as UA/mg protein and obtained by triplicate. Determination of POD activity: Ten grams of apple slices were homogenized with 20 mL of 0.05 M Na2HPO4 buffer (pH 7.0) containing 100 g/L PVPP. The mixture was homogenized for 1 min and allowed to stand for 2 h in the dark at 4°C, then filtered and centrifuged at 11,000 x g for 25 min at 4°C (Eppendorf 5804-R, Hamburg, Germany). The supernatant was saturated at 70% with (NH4)2SO4 and centrifuged again. The pellet was dissolved in 20 mL of 0.05 M Na2HPO4 buffer (pH 7.0) and dialyzed against two changes of the same buffer over a period of 24 h at 4°C. POD activity was assayed spectrophotometrically 32 by adding 2700 µL of Na2HPO4 buffer (0.2 M, pH 6.5), 100 µL of H2O2 (10 g/L), 150 µL of guaiacol (40 g/L), and 150 µL of enzymatic extract. Changes in absorbance at 470 nm were measured every 10 s for 3 min. One unit of activity (UA) was defined as the change in absorbance of 0.001 units/min. Protein content was evaluated according to Bradford 31. Activity was expressed as UA/mg protein and measured by triplicate. Sensory evaluation: Apple slices from control (non-treated fruit) and the two best treatments (based on colour, firmness and enzymatic activity) were minimally processed and assessed after 20 days of storage at 4°C. Fifty one panellists (20-40 years old, 26 females and 25 males) who frequently consume apple fruit, but had no previous experience in sensory evaluation, were recruited among students and personnel of the Faculty of Chemical and Biological Sciences at the Autonomous University of Sinaloa, Mexico. Samples were kept and served at room temperature (22°C) and analyzed under normal lighting conditions. Samples were served in random order, coded with three-digit numbers. Each panellist received an instruction/score sheet with instructions for sample evaluation. Panellist were provided with water to cleanse the palate and minimize any residual effect of samples. They were asked to evaluate the acceptability of the samples for appearance, texture, taste and overall appreciation using a hedonic scale (1-9), where 1= poor and 9 = excellent. A poor (1) rating indicated dark appearance, very soft texture, or strong off-flavor taste. Excellent (9) rating corresponded to fruit with fresh, very crunchy texture, Journal of Food, Agriculture & Environment, Vol.11 (2), April 2013
or very sweet/flavourful taste 33. The limit of marketability was 5. Statistical analysis: A completely randomized experimental design was used. Statistical analyses of data were performed through multiple analysis of variance (ANOVA) using Statgraphics Plus 5.1 and the means were compared using Fisher’s least significant difference (LSD) test (P = 0.05). The means with the corresponding LSD for each level were plotted using Sigma Plot 7.0. Results and Discussion Colour parameters: The effects of treatments on L* value during storage are shown in Figs. 1A-B. This parameter tended to decrease during storage, especially in AWD and HWD treatments followed by AWD+CaCl2 and HWD+CaCl2 samples, indicating a loss of brightness associated with browning 21. AWD treatment showed significantly lower L* values compared to the other treatments after day 5; however, HWD seemed to prevent enzymatic browning of fresh-cut apple during the first 15 days. These results are not in agreement with the observations of Steiner et al. 34, who found that treating peaches at 40°C for 70 min before cutting had no significant effect on lightness when compared to the control. However, the positive effect of heat treatments appears to result from a combination of several factors that include time and temperature, as observed for peach slices 12, apples 35 and freshcut pear 36. AWD+NAC and AWD+NAC-CaCl2 prevented the reduction of lightness of fresh-cut apple during the storage period evaluated, but this reduction was more successfully decreased by HWD+NAC and HWD+NAC-CaCl 2, without showing significant differences in L* values between them. The combination of HWD and NAC could have exerted an additive effect that reduced the activity of oxidative enzymes and the colour changes in the tissue. In the CIE L* a* b* dimensional coordinate system, the a*
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Figure 1. Changes in colour (L* and a* values) (A-D) and firmness retention (E, F) during storage at 4°C of fresh-cut apples dipped in N-acetylcysteine (NAC) and/or calcium chloride (CaCl2). Each point represents the mean of eight (colour) and four (firmness) replications. Vertical bars indicate LSD. Journal of Food, Agriculture & Environment, Vol.11 (2), April 2013
value indicates the colour change from green (negative values) to red (positive values). High a* values have been used to indicate browning of samples 37. Our results showed that this parameter tended to increase during storage for all AWD treatments (Fig. 1C) suggesting they underwent browning. AWD and AWD+CaCl2 observed the largest increase followed by AWD+NAC and AWD+NAC-CaCl2. In the case of HWD treatments (Fig. 1D), HWD and HWD+CaCl2 fresh-cut apples showed higher values and significant differences with respect to the others after 10 days of storage at 4°C. The initial a* value (-4.8) of HWD+NAC and HWD+NAC-CaCl2 treated apples remained relatively unchanged, indicating that these combinations were effective to preserve the initial colour and to inhibit browning. Moreover, these treatments were more effective than the corresponding AWD treatments. Some authors have reported that heat treatment before cutting effectively controlled browning in several fresh-cut fruits 12, 35, 36; however, the results of this study indicate that this effect was observed only during the initial days. The a* values obtained were consistent with those of the L* parameter, corroborating the positive effect of the combination of HWD+NAC and HWD+NACCaCl2 in the control of enzymatic browning. Fruit firmness: Firmness changes of fresh-cut apples during storage are shown in Fig. 1E-F. In general, a continuous loss of the initial firmness (AWD = 43.7 N; HWD = 40.7 N) was observed for all treated fresh-cut fruit. Individual AWD and its combination with NAC showed a rapid decrease during the first 15 days of storage to finish with values around 17 N at day 25, while AWD+CaCl2 observed the greatest firmness retention with end values near 24 N, which represents a softening of about 45%. From day 15 until the end of storage, HWD+NAC apple slices showed the lowest firmness value (about 18.6 N) followed by HWD which showed a less pronounced decrease with end values around 20.8 N. On the other hand, HWD+CaCl2 effectively retained firmness showing a final value of 26.7 N, which represents a softening of about 35%, while HWD+NAC-CaCl2 resulted in similar firmness values at days 20 and 25. Some researchers have reported a synergistic effect when combining heat treatment with calcium salts in shredded carrots 17 and fresh-cut melons 28, 38. According to Shalom et al. 39, inhibition of the solubilisation of carbonate-soluble pectin fractions is one of the main factors contributing to the firmness retention in heat-treated apple. In addition to the effect that calcium confers to the cellular tissue, the application of hot water treatment inactivates enzymes such as pectinmethylesterase and polygalacturonase that hydrolyze methyl ester groups of the pectic material, resulting in a firmer texture and structure of the product 40. Polyphenol oxidase activity: PPO activity showed a rapid increase during the first 15 days of storage for AWD and AWD+CaCl2 apple slices with initial values near 270 UA/mg protein and final values around 1300 and 1000 UA/mg protein, respectively (Fig. 2A). After this time, PPO activity decreased in both treatments. AWD+NAC observed a slight increase in PPO activity from day 5 to day 15 reaching values near 500 UA/mg protein, while AWD+NAC-CaCl2 showed a gradual increase from day 5 until the end of storage with similar values. This indicates that these last treatments were more effective to reduce the PPO activity. This behaviour coincides with previous reports for apple slices 21 and 245
Specific activity of POD (UA/min-mg protein)
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Figure 2. PPO (A, B) and POD (C, D) activities of fresh-cut apples treated with N-acetylcysteine (NAC) and/or calcium chloride (CaCl2) during storage at 4°C. Each point represents the mean of three replications. Vertical bars indicate LSD.
could be attributed to the fact that NAC reduces o-quinones back to their o-diphenol precursors, preventing the formation of pigments or reacting with o-quinones to yield colorless compounds. For HWD treatments (Fig. 2B), it was observed that after 10 days of storage PPO activity increased sharply in HWD and HWD+CaCl2 fresh-cut fruit, reaching values of 1400 UA/mg protein, while no significant changes in PPO activity (about 200 UA/mg protein) were observed during storage of apple slices treated with HWD+NAC and HWD+NAC-CaCl2 indicating an enzymatic inhibition even higher than that observed for AWD treatments. Abreu et al. 36 proposed that the beneficial effect of heat treatment on the oxidative browning of fresh-cut pear was related to a reduction in PPO activity; this enzyme is not stable at temperatures above 40°C 10. However, in our study, the HWD treatment (45°C, 10 min) was only effective in preventing an increase in PPO activity during the first 10 days of storage and the fresh-cut apples showed the highest activity values from day 15 and up, suggesting that the enzyme was not completely inhibited by the heat treatment. In addition, there were significant differences among HWD and HWD+CaCl2 compared to HWD+NAC and HWD+NAC-CaCl2 from day 15 to the end of storage; thus, our results suggest that browning inhibition was more related to the use of NAC than to the heat application. According to RichardForget et al. 41 and Billaud et al. 42; sulphur-containing antibrowning agents do not inhibit PPO by themselves, although they have some inhibitory activity due to their ability to conjugate with primary oxidation products formed during the browning reaction. However, our results suggest an active role of NAC on the inhibition of PPO activity, as proposed by Rojas-Graü et al. 21. All of these results were consistent with the changes in colour expressed as L* and a* values. Peroxidase activity: Although PPO is more frequently related to surface browning in fresh-cut apples 21, the contribution of POD to total browning may also be relevant. For AWD apple slices, no significant differences between all treatments were observed during the first 10 days. The highest activities were obtained after 15 days of storage for AWD and AWD+CaCl2 with values close to 246
110 and 100 UA/mg protein, respectively (Fig. 2C). In contrast, lower activities were found for AWD+NAC-CaCl2 with about 48 UA/mg protein. At the end of storage, AWD+NAC and AWD+NAC-CaCl2 resulted with similar and non significant values (about 60 UA/mg protein), while the rest of treatments finished with values near 100 UA/mg protein. The positive effect of NAC in reducing enzymatic activity has been attributed to a lack of substrate due to reaction of the antibrowning agent with hydrogen peroxide 21. In general, hot water treatment of Red Delicious apple did not result in a regular pattern of variation in POD activity (Fig. 2D) as that observed for PPO. POD activity for HWD apple slices showed the highest values at day 15 (101.2 UA/mg protein), decreasing later; while in HWD+CaCl2 this activity decreased during the first 10 days, then increased after 15 days and decreased again at day 20. After 25 days, POD activity in HWD+CaCl2 treated apple slices was significantly higher than those of apple slices from the other treatments. This result agreed with that reported by Lamikanra and Watson 28 for fresh-cut cantaloupe melon heated at 60°C for 60 min before processing and dipping in calcium lactate solution. These authors found that the combination of heat and calcium favored an increase in POD activity when compared to non-calcium heat-treated fruit. POD activity of HWD+NAC treated sample increased from 38 to 93 UA/mg protein after 10 days and decreased until it reached approximately 55 UA/mg protein. The smaller variation in POD activity was observed for the HWD+NACCaCl2 treatment, which only showed a slight increase at day 15 and ended the storage period with an activity close the initial value. Despite the fact that the POD role in enzymatic browning has remained questionable 27, the production of H2O2 during oxidation of some phenolic compounds catalyzed by PPO might suggest a possible synergistic action between PPO and POD, which implies the involvement of POD in browning processes 9. According to this, our results showed that the activities of both enzymes were higher at day 15 in those treatments that showed evidence of browning (AWD, AWD+CaCl2, HWD and HWD+CaCl2), low lightness and high a* values, which was corroborated visually (data not shown). Sensory evaluation: According to the results of colour, firmness and enzymatic activity, HWD+NAC and HWD+NAC-CaCl2 were the best treatments; fresh-cut slices from these treatments and the control (non-treated apple slices) were subjected to sensory evaluation (Fig. 3). The external appearance of fresh-cut apple slices showed differences between HWD treatments and the control (Fig. 3A). The highest score (6.6) corresponded to HWD+NAC-CaCl2 treatment while the lowest score (2.3) was for control apple slices. HWD+NAC fresh-cut fruit received an intermediate value. Only HWD+NAC-CaCl2-treated apple slices were considered with acceptable appearance for consumption. Texture results were significantly different among treatments during sensory evaluation (Fig. 3B). The highest score (8.0) corresponded to HWD+NAC-CaCl2 followed by HWD+NAC (6.1), both were still above the limit of marketability (5). The lowest texture score was for control apple slices (4.7). The results for texture from the sensory evaluation were consistent with those for firmness. The taste parameter did not differ among HWD+NAC and HWD+NACCaCl2 apple slices (Fig. 3C). After 20 days of storage at 4°C, both treatments maintained the flavor since they received the highest Journal of Food, Agriculture & Environment, Vol.11 (2), April 2013
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References
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Ferrante, A., Incrocci, L. and Serra, G. 2008. Quality changes during storage of fresh-cut or intact Swiss chard leafy vegetables. Journal of Food, Agriculture & Environment 6(3&4):60-62. 2 Gorny, J. R. 2003. New opportunities for fresh-cut apples. Fresh Cut 11:14-15. 3 Zhan, L. J., Fontana, E., Tibaldi, G. and Nicola, S. 2009. Qualitative and physiological response of minimally processed garden cress (Lepidium sativum L.) to harvest handling and storage conditions. Journal of Food, Agriculture & Environment 7(3&4):43-50. 4 Oms-Oliu, G., Aguiló-Aguayo, I. and Martín-Belloso, O. 2006. Inhibition of browning on fresh-cut pear wedges by natural compounds. J. Food Sci. 71:216-224. 5 Apintanapong, M., Cheachumluang, K., Suansawang, P. and Thongprasert, N. 2007. Effect of antibrowning agents on banana slices and vacuum-fried slices. Journal of Food, Agriculture & Environment 5(3&4):151-157. 6 Jung, S. K. and Watkins, C. B. 2011. Involvement of ethylene in browning development of controlled atmosphere-stored Empire apple fruit. Postharvest Biol. and Technol. 59:219-226. 7 Degl’Innocenti, E., Guidi, L., Pardossi, A. and Tognoni, F. 2005. Biochemical study of leaf browning in minimally processed leaves of lettuce (Lactuca sativa L. var. acephala). J. Agric. Food Chem. 53:99809984. 8 Richard-Forget, F. C. and Gaulliard, F. A. 1997. Oxidation of chlorogenic acid, catechins and 4-methylcatechol in model solutions by combinations of pear (Pyrus communis cv. Williams) polyphenol oxidase and peroxidase: A possible involvement of peroxidase in enzymatic browning. J. Agric. Food Chem. 45:2472-2476. 9 Subramanian, N., Venkatesh, P., Ganguli, S. and Sinkar, V. P. 1999. Role of polyphenol oxidase and peroxidase in the generation of black tea theaflavins. J. Agric. Food Chem. 47:2571-2578. 10 Garcia, E. and Barrett, D. M. 2002. Preservative treatments for freshcut fruits and vegetables. In Laminkara, O. (ed). Fresh-cut Fruits and Vegetables: Science, Technology and Market. CRC Press, Boca Raton, FL, pp. 267-303. 11 Paul, R. E. and Chen, N. J. 2000. Heat treatment and fruit ripening. Postharvest Biol. and Technol. 21:21-38. 12 Koukounaras, A., Diamanditis, G. and Sfakiotakis, E. 2008. The effect of heat treatment on quality retention of fresh-cut peach. Postharvest Biol. and Technol. 48:30-36. 13 Viña, S. Z. and Chaves, A. R. 2008. Effect of heat treatment and refrigerated storage on antioxidant properties of pre-cut celery (Apium graveolens L.). Int. J. Food Sci. Technol. 43:44-51. 14 Loaiza-Velarde, J. G. and Saltveit, M. E. 2001. Heat shocks applied either before or after wounding reduce browning of lettuce leaf tissue. J. Amer. Soc. Hort. Sci. 126:227-234. 15 Bai, J., Baldwin, E., Fortuny, R., Mattheis, J., Stanley, R., Perera, C. and Brecht, J. 2004. Effect of pre-treatment of intact ‘Gala’ apple with ethanol vapour, heat, or 1-methylcyclopropene on quality and shelf life of fresh-cut slices. J. Amer. Soc. Hort. Sci. 129:583-593. 16 Martin-Diana, A. B., Rico, D., Mulcahy, J., Frías, J. M., Henehan, G. T. M. and Barry-Ryan, C. 2006. Effect of calcium lactate and heatshock on texture in fresh-cut lettuce during storage. J. Food Eng. 77:1069-1077. 17 Rico, D., Martin-Diana, A. B., Frias, J., Barat, J. M, Henehan, G. T. M. and Barry-Ryan, C. 2007. Improvement in texture using calcium lactate and heat shock treatments for stored ready-to-eat carrots. J. Food Eng. 79:1196-1206. 18 Aguayo, E., Escalona, V. H. and Artés, F. 2008. Effect of hot water treatment and various calcium salts on quality of fresh-cut Amarillo melon. Postharvest Biol. and Technol. 47:397-406. 19 Son, S. M., Moon, K. D. and Lee, C. Y. 2001. Inhibitory effects of various antibrowning agents on apple slices. Food Chem. 73:23-30. 20 Fan, X., Niemera, B. A., Mattheis, J. P., Zhuang, H. and Olson, D. W. 2005. Quality of fresh-cut apple slices as affected by low-dose ionizing
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Figure 3. Sensory evaluation of fresh-cut apples after 20 days of storage at 4°C. Hedonic scale of 9 points from 1 (least favorable) to 9 (most favorable). Vertical bars indicate LSD, n = 51.
scores. This indicates that the low CaCl2 concentration used did not have a detrimental effect on flavor. Control apple slices were rated as unacceptable for consumption, perhaps as a consequence of sugar loss, which was used as respiratory substrate. Judges scored the overall appreciation taking into account the sensory parameters previously evaluated. This parameter showed significant differences among treatments (Fig. 3D). The lowest value (3.9) corresponded to control apple slices, which was under the limit of acceptability. The other treatments were rated as acceptable, but HWD+NAC-CaCl2 resulted with the highest scores. All sensory results indicate that HWD+NAC-CaCl2 treatment did not adversely affect the sensory attributes of freshcut Red Delicious apple. Conclusions Hot water treatment (45°C, 10 min) of intact apple followed by cutting and dipping in a solution containing N-acetylcysteine and CaCl2, effectively controlled browning, retained firmness and maintained the overall quality of fresh-cut Red Delicious apple up to 25 days at 4°C. The individual application of HWD did not provide a positive effect on quality attributes, and the combination of HWD+CaCl2 was only effective on firmness retention. The use of HWD+NAC promoted firmness loss but was an effective inhibitor of PPO and POD activities. The positive effect of HWD+NAC-CaCl2 on browning control and firmness retention of apple slices was corroborated by enzymatic inhibition (PPO and POD), and L* and a* results. In terms of consumer acceptability, this treatment was preferred by the panellists. These results suggest that hot water dipping treatment combined with Nacetylcysteine and calcium chloride can be considered a good alternative to improve the quality of fresh-cut Red Delicious apples. Acknowledgements This study was supported by a grant to author Vega-García from Universidad Autónoma de Sinaloa (PROFAPI2010/137). MELL received a scholarship from CONACyT (Natl. Research and Technology Council, México). Journal of Food, Agriculture & Environment, Vol.11 (2), April 2013
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Journal of Food, Agriculture & Environment, Vol.11 (2), April 2013
