Food Sci. Biotechnol. 22(5): 1229-1236 (2013) DOI 10.1007/s10068-013-0206-6
RESEARCH ARTICLE
Nutritional Quality Changes of Fresh-cut Tomato during Shelf Life Maria D.C. Antunes, Daniela Rodrigues, Vasilios Pantazis, Ana M. Cavaco, Anastasios S. Siomos, and Graça Miguel
Received: 4 January 2012 / Revised: 8 March 2013 / Accepted: 27 March 2013 / Published Online: 31 October 2013 © KoSFoST and Springer 2013
Abstract Effects of dip treatments on nutritional quality preservation during the shelf life of fresh-cut tomato (Licopersicum esculentum Mill.) cv. Eufrates were investigated. Fresh-cut tomatoes were dipped in solutions of 2% ascorbic acid, citric acid, and calcium lactate for 2 min, then stored at 4ºC for 20 days. Color (L*, a*, and b*), firmness, ºBrix, phenolics, ascorbic acid content, antioxidant activity (DPPH), and sugars were measured during storage. Pathogen development was monitored, and a sensory evaluation was performed. Ascorbic acid was better in maintaining firmness. No treatments significantly affected ºBrix, color, or sugars. Ascorbic acid maintained a higher antioxidant capacity, phenolics, and ascorbic acid content, and was better at reducing bacterial growth, while citric acid treatment was better at prevention of yeast and molds proliferation. Fresh-cut tomatoes showed good quality after 10 days of shelf life, except for flavor with the calcium lactate treatment. Ascorbic acid treatment better preserved the general and nutritional quality parameters. Keywords: citric acid, ascorbic acid, antioxidant capacity, calcium lactate, dip treatment
Maria D.C. Antunes (), Daniela Rodrigues, Graça Miguel Faculdade de Ciências e Tecnologia, Universidade do Algarve, IBB, Centro de Biotecnologia Vegetal, Ed. 8, Campus de Gabelas, 8005-139 Faro, Portugal Tel: +351289800900; Fax: +351289818419 E-mail:
[email protected] Vasilios Pantazis, Anastasios S. Siomos Department of Horticulture, Aristotle University, 54124 Thessaloniki, Greece Ana M. Cavaco CEOT, Universidade do Algarve, Ed. 2 da FCT, Campus de Gambelas, 8005-139 Faro, Portugal
Introduction Tomato (Lycopersicon esculentum Mill.) is a major fresh commodity that requires suitable maturation attributes and rheological characteristics at harvest to allow for proper post-harvest handling and industrial processing (1). Tomatoes are a good source of vitamins, carotenoids, and phenolics, which are all recognized as highly beneficial for human health (2). However, to maintain the quality of this fruit for a reasonable shelf life is difficult owing to the rapid rate of ripening and senescense (3). Therefore, maintaining the quality of fresh-cut tomatoes is even more challenging, because slices are susceptible to water loss and fast softening associated with an increase in the ethylene production (4). Peeling, cutting, shredding, and slicing greatly increase tissue respiration, biochemical deterioration, browning, texture breakdown, loss of flavour, and risk of microbial contamination (5). The quality of fresh-cut tomatoes is affected by the type of cut, packaging, temperature, and storage time (6). To maintain the quality of fresh-cut tomatoes, three important factors are 1) a suitable tomato cultivar that has a low sensitivity to chilling, 2) fruit with an adherent placenta and, 3) optimal maturity stage at harvest. Mencarelli and Saltveit (7) reported that sliced mature green tomato fruit ripened normally and attained a quality for eating comparable to fruit that was sliced when ripe. Dipping fruit pieces into aqueous solutions containing antimicrobial agents, antioxidants, calcium salts, or minerals and vitamins (or combinations) is a widely practiced method to improve the quality of fresh-cut fruit (8-10). For tomato, the effect of calcium chloride dipping on the texture, colour, overall appearance, soluble solid content, and acidity has been reported (11). Also, Ayala-Zavala et al. (5) studied the effects of methyl jasmonate, ethanol, tea tree oil, and garlic oil on reduction of microbial growth in fresh-cut tomatoes with no detriment to the general quality
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of the fruit and contained bioactive compounds reported, and best results achieved using methyl jasmonate. The acceptability of the dip treatments usually applied to fresh-cut produce for maintenance of freshness and acceptance by consumers has been, up to now, based mainly on sensorial attributes. However, the nutritional and antioxidant properties of fresh-cut fruit must be preserved from harvest to consumption. Dip treatments can have different effects depending on plant species and cultivar. Moreover, the use of GRAS (generally recognized as safe) environmental friendly dip treatments for fresh-cut produce is an increasingly important issue. Some types of treatment can be harmful to consumer health or the environment, or cause organoleptic or physico-chemical damages in freshcut produce. It is important to concentrate on environmentally friendly GRAS treatments for application to fresh-cut produce. Although several studies have been done on the effect of aqueous solutions containing antimicrobial agents, antioxidants, and calcium salts to improve the quality of fresh-cut fruit, few studies have investigated the treatment effects on nutritional quality preservation. The objective of this study was to determine the effect of GRAS dip treatments using ascorbic acid, citric acid, and calcium lactate, on fresh-cut produce. Preservation of freshness and nutritional quality, including antioxidant properties, were investigated from cutting, through shelf-life, to consumption.
Materials and Methods Fruit and treatments Tomato cv. Eufrates fruits were harvested from a local greenhouse in Algarve, Portugal at the red stage of ripening. Fruits were immediately transported to the Postharvest Laboratory at the University of Algarve and analysis began on the same day. Treatments consisted of washing fruit under tap water and gently drying with blotting paper. Then, fruit was cut longitudinally in quarters using sharp knives and dipped in solutions of 2% citric acid (Citric), 2% ascorbic acid (Asc), 2% calcium lactate (CaLact), and distilled water (control) for 2 min. All reagents were of analytical grade (SigmaAldrich Co., St. Louis, MO, USA). After dipping, 4 tomato quarters per replicate were randomly selected and gently dried in blotting paper and placed in plastic trays of 11 cm diameter and 5 cm height covered with a 10 µm thick polyvinyl chloride film with the following permeability characteristics: O2, 6,000 mL/m2 ·d·atm; CO2, 45,000 mL/ m2 ·d·atm; water vapour, 157 g/m2·d·atm. All treatments were performed at room temperature of 18ºC. Trays were then put in a storage chamber at 4ºC with a relative humidity of 90-95%. After 5, 10, 15, and 20 days four trays per treatment were randomly removed from storage and
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used for analysis. Each tray was considered as a replicate. Samples for 0 days storage were analyzed within 2 h of cutting. All others were analyzed after removal from storage at each sampling time. Color, firmness, and soluble solids content (SSC) Fruit surface color was determined at 3 points around the cut tomato using a Chroma meter CR-300 series (Konica Minolta, Osaka, Japan) in the CIE L*a*b* color space. Firmness was determined using a Chatillon Force TCD 200 and Digital Force Gauge DFIS 50 (John Chatillon & Sons, Inc., Largo, FL, USA), by measuring the force required for a 6.5 mm diameter probe (conical for the last 3 mm) to penetrate a tomato quarter to a depth of 7 mm through the skin. The remaining fruit tissue was ground using an UltraTurrax mixer-T18D (IKA, Staufen, Germany), and juice was extracted by squeezing the fruit mixture through cheesecloth and immediately collecting in 20 mL vials. The vials were then frozen in liquid nitrogen and stored at −20ºC until use. Before storage, a juice aliquot was used after filtration for determination of the soluble solids content (SSC) or ºBx using a digital refractometer PR1Atago Co. Ltd., Tokyo, Japan. Sugar content Sucrose and hexose (glucose and fructose) amounts were determined in juice samples from fresh-cut tomato fruit during the shelf life at 4ºC. Sugar concentrations in the same samples were assayed using a Sucrose/DGlucose/D-Fructose kit for Enzymatic BioAnalysis/Food Analysis (Boehringer Mannheim/R-Biopharm, Darmstadt, Germany). The volumes of the samples and the reaction medium used with the kit were read on a Benchmark microplate reader (Bio-Rad Laboratories Lda., Hercules, CA, USA) at 340 nm. Ascorbic acid content To determine the ascorbic acid content, samples (1 mL) were centrifuged for 20 min at 16,060×g and filtered through a 0.45 µm filter (Millipore, Merck Chemicals GmbH, Schwalbach, Germany). Then, 20 µL of sample was injected into an HPLC system (Gold Blo Sep II; Beckman, S. Ramon, CA, USA) equipped with a Rheodyne injector, a UV166 detector (Beckman) and an Atlantis C18 (4.6 mm×150 mm; 5 mm particles) Waters column (Milford, MA, USA), at room temperature. Sodium dihydrophosphate (NaH2PO4, pH=2.7) was used as the mobile phase and readings were taken at 210 nm. The flow rate was 1 mL/min. Phenolics and antioxidant activity (DPPH) The amount of total soluble phenolics was determined in tomato juice using the Folin-Ciocalteau reagent method with gallic acid (0.024-0.096 mg/mL) as a standard for the
Quality of Fresh-cut Tomato during Shelf Life
calibration curve (12). The volume used for both gallic acid and samples was 250 µL, to which 1 mL of sodium carbonate (75 g/L) and 1.25 mL of Folin-Ciocalteau reagent were added to the same sample. The wavelength for readings was 765 nm using a Shimadzu spectrophotometer 160-UV (Schimadzu, Kyoto, Japan) after sample incubation at room temperature for 30 min. The free radical scavenging activity was measured using DPPH based on a modification of the method by BrandWilliams et al. (13), as described in Antunes et al. (9). Juice was diluted to 50% using double distilled water. The DPPH radical concentration was calculated using the following equation: Scavenging effect% (IA%)=(1Af/Ao)*100 where Ao is the absorbance of the control sample and Af is the absorbance in the presence of the sample (t=15 min). Results were compared with curves for several Trolox concentrations (0.024-0.096 mg/mL). Values are given as mM Trolox equivalents. Microbial evaluation Microbial analyses were performed in 25 g tissue in the Laboratory of Chemical Analysis at the University of Algarve. Bacterial counts were determined at 30ºC following the NP-1995:1982 method (14). Yeasts and moulds counts were determined at 25ºC according to the NP 3277-1: 1987 method (15). Results are expressed as log CFU/g. Sensory evaluation Sensory evaluation was performed by a panel with 20 trained members. Panel members were asked to evaluate the appearance, texture, sweetness, acidity, and flavor on a scale from 1 to 5 (1-dislike definitely; 2-dislike mildly; 3-neither like nor dislike; 4like mildly; 5-like definitely) at the beginning of the experiment and after 10 days of product storage at 4ºC. Statistical analysis A completely randomized design was used. Statistical analysis was carried out using the SPSS 16.0 software (SPSS Inc., Chicago, IL, USA). A two-way ANOVA and Duncan’s multiple-range test (p<0.05) were used for comparisons among treatments over time. Each treatment consisted of 4 replications.
Results and Discussion Firmness and color The firmness of fresh-cut tomatoes decreased with the shelf life (Table 1). The best effects for retention of firmness were attained using Citric and Calact treatments for up to 10 days. Thereafter, differences were not significant among treatments. Calcium salts have been used to reduce firmness loss in many fresh and fresh-cut
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commodities (8-10). Ascorbic and citric acid are used mainly as antioxidants for reduction of browning of freshcut produce (10,16), but, they may reduce firmness compared with other treatments, as observed for apple (16). They may also have no effect compared to controls (9,17). For fresh-cut kiwi fruit, calcium chloride is more effective than calcium lactate to maintain firmness (18). Preliminary studies done at our laboratory (shelf life up to 10 days) confirmed these results for firmness, as well as for the other quality parameters discussed below (data not shown). After cutting, fruit becomes darker and the lightness (L* value) tends to decrease (Table 1). Tissue browning is caused by oxidation, such as been reported for apples and bananas (16,19). None of the chemical dips prevented browning of fresh-cut tomato fruit as the L* value decreased for all treatments after 5 days of shelf life (Table 1). The a* parameter represents a change from green (negative values) to red (positive values) (20). For all treatments, there was a significant increase in the a* value by the 5th day of shelf life, which were maintained up to 10 days and followed by a significant decrease after 10-15 days back to values close to the original values registered at the beginning of the assay. The control significantly decreased after 5 days. The Asc treatment was exception, with no decrease and higher values for red color than the other treatments (Table 1). The b* value indicates changes from blue (negative values) to yellow (positive values) (20). An oscillating pattern was observed for all treatments after 15 days of storage with higher values for the control than for other treatments (Table 1). However, at the end of the experimental period there were no differences among treatments. Odriozola-Serrano et al. (2) have shown for some tomato cultivars stored in a modified atmosphere (MAP) at 4ºC that no significant color change occurs (L*, a* or b*) after 21 days of shelf life. However, Ayala-Zavala et al. (5) found decreasing L* and hue* values with storage for fresh-cut tomatoes treated with methyl jasmonate, ethanol+methyljasmonate, tea tree oil and garlic oil, but for ethanol values were maintained. Soluble solids and sugar content The Asc dip was better than the other treatments for preservation of the SSC up to 15 days of shelf life, after which all chemical dips had similar values (Table 2). As a general rule, fruit SSC values increase with ripening and slightly decrease with senescence. The SSC values of fresh-cut tomato started to decrease from the 5th day of shelf life onward, except for the Asc dipped slices for which the SSC value only decreased from the 15th to the 20th day of shelf life (Table 2). The SSC includes mostly soluble sugars and organic acids. Changes in the amounts of sucrose, fructose, and glucose were also determined in fresh-cut tomato fruit with
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Table 1. Firmness and color (CIE L*,a*,b*) of fresh-cut tomatoes cv. Eufrates through shelf-life at 4ºC, after dipping in 2% citric acid (Citric), ascorbic acid (Asc), calcium lactate (CaLact) or water (control) for 2 min Parameter Firmness (N)
Lightness (L*)
Color(a*)
Color (b*)
Day
Control
Citric aA
Asc
CaLact
0 5 10 15 20
aA1)
aA
13.81 06.88bB 05.53bB 05.00aB 06.20aB
13.81 09.25aB 08.60aB 05.78aC 06.30aBC
13.81 07.35bB 06.55abB 06.60aB 06.33aB
13.81aA 09.10aB 07.88abBC 05.45aC 06.35aBC
0 5 10 15 20
47.60aA 41.64aB 34.08bC 38.45aBC 37.32aC
47.60aA 41.37aB 38.49aBC 35.23bC 38.98aBC
47.60aA 38.83aB 36.40abB 37.61abB 39.94aB
47.60aA 39.37aB 39.26aB 36.44bB 38.89aB
0 5 10 15 20
07.01aAB 11.20bA 07.01bAB 05.21bB 07.47bAB
07.01aB 11.16bA 11.29aA 06.74abB 07.51bB
07.01aB 14.65aA 09.38abAB 08.98aAB 11.92aA
07.01aB 13.85abA 09.11abAB 08.98aAB 08.00bAB
0 5 10 15 20
25.82aA 26.76aA 18.29bB 25.01aA 23.97aA
25.82aA 25.13aA 22.73aA 16.84bB 23.72aA
25.82aA 22.73bAB 20.83abB 19.90abB 25.23aA
25.82aAB 26.58aA 23.35aAB 18.02bC 22.32aB
1)
Values in the same row followed by the same lower case letter, in the same column followed by the same upper case letter, and for each parameter are not significantly different using Duncan’s multiple range test (p>0.05).
Table 2. Soluble solids content (SSC), and sugars content (glucose, sucrose, and fructose) of fresh-cut tomatoes cv. Eufrates through shelf-life at 4ºC, after dipping in 2% citric acid (Citric), ascorbic acid (Asc), calcium lactate (CaLact) or water (control) for 2 min Parameter o
SSC ( Bx)
Glucose (g/100 mL)
Sucrose (g/100 mL)
Fructose (g/100 mL)
1)
Day
Control
Citric
CaLact
4.93 4.33bB 4.25bB 4.38bB 4.30aB
4.93 4.53abAB 4.18bB 4.53abAB 4.18aB
4.93 4.73aA 4.83aA 4.78aA 4.40aB
4.93aA 4.43bB 4.33bB 4.45bB 4.40aB
0 5 10 15 20
3.666aA 0.282dB 1.139aB 2.251aAB 1.550aB
3.666aB 5.675bA 0.540bD 4.350aB 2.419aC
3.666aB 7.859aA 0.270bC 1.993aBC 1.597aBC
3.666aA 0.963cAB 0.517bB 3.751aA 1.679aAB
0 5 10 15 20
0.879aAB 1.858aA 0.655aB 0.275aB 0.626aB
0.879aAB 0.341bBC 1.131aA 0.016aC 0.128aC
0.879aAB 0.781abAB 1.622aA 0.013aB 0.671aAB
0.879aA 1.247abA 0.536aAB 0.204aB 0.487aB
10.42aAB 15.60aA 11.89aA 02.26cC 04.11bBC
aA
Asc
0 5 10 15 20
0 5 10 15 20
aA1)
10.42aA 11.88aA 15.62aA 10.47bA 14.36aA
aA
10.42aA 12.35aA 16.51aA 17.51aA 15.03aA
10.42aC 15.13aBC 22.34aA 20.23aAB 10.84aC
Values in the same row followed by the same lower case letter, in the same column followed by the same upper case letter, and for each parameter, are not significantly different using Duncan’s multiple range test (p>0.05).
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shelf life at 4ºC (Table 2). Hexose is the most abundant sugar in tomato cv. Eufrates fruit at the table-ripe stage (21). The amount of sucrose was approximately 12-fold less than the amount of fructose. The amount of sucrose was unaffected by the chemical dips, but showed a minimum value by the 15th day of shelf life (Table 2). Some of the chemical dips had a significant positive effect on the hexose content with shelf life (Table 2). Asc and citric acids both promoted a significant increase in the glucose content after 5 days, but this effect disappeared afterward (Table 2). For fructose, the treatments had a positive effect only by the 15th day of shelf life (Table 2). Based on the patterns of soluble sugar content in fresh-cut tomato fruit, there is no clear and straightforward relationship between softening and the hexose (glucose and fructose) content, or the dips used with storage time (Table 1, 2) (22). The effectiveness of Asc alone and in combination with CaCl2 and Citric in slowing the degradation rates of sugars has been reported for fresh-cut pineapple slices stored for up to 14 d at 10ºC, and for fresh-cut mango cubes stored at 5ºC for 9, 12 and 21 days, depending on cultivar (23,24). In general, the complex and overlapping processes that occur in fresh-cut fruit with shelf life have been confirmed using fruits of tomato cv. Eufrates. In fact, the climacteric respiratory burst is enhanced by fresh-cut processing involving intervening compounds such as ascorbic and citric acids, and sugars, the action of which for preservation probably involves critical regulatory steps in several physiological pathways (25). Analysis of these steps will require further study. Ascorbic acid content, phenolics, and antioxidant activity In fresh-cut tomato cv. Eufrates treated with Asc the ascorbic acid content increased for 15 days and remained relatively high. It was always statistically higher than for the other treatments, followed by the citric treatment (Fig. 1A). Citric acid treatment also lead to significantly higher amounts of ascorbic acid over time, in comparison to CaLact and control treatments (Fig. 1A). The control and CaLact treatments showed decreased ascorbic acid contents until day 5, and values remained lower than for the other treatments through the end of the shelf life period. In other experiment with fresh-cut tomato, the ascorbic acid content was found to increase after methyl jasmonate, tea tree oil and garlic oil treatments, during the first 2-4 storage days, followed by stabilization thereafter. However, ethanol and control treated samples maintained constant ascorbic acid levels through storage (5). Tomato fruit contains different amounts of several antioxidant biomolecules, such as lycopene, carotenoids,
Fig. 1. Ascorbic acid content (A), phenolics (B), and DPPH (C) of fresh-cut tomato cv. Eufrates through shelf-life at 4ºC after dipping in 2% citric acid (Citric), ascorbic acid (Asc), calcium lactate (CaLact), and water (control) for 2 min. Values for each sampling date followed by the same letter are not significantly different using Duncan’s multiple range test (p>0.05).
ascorbic acid, flavonoids, tocopherols, and phenolics. The amounts depend on several factors (26). Some of these compounds, such as carotenoids, tocopherols, and phenolics, may prevent oxidation of ascorbic acid, or re-establish the reduced form of the vitamin after oxidation. This conversion is of importance because it maintains the relatively high amounts of bioactive antioxidants in fresh-cut tomato.
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Phenolics have a protective effect on ascorbic acid in freshcut tomato and probably in whole tomato fruit during postharvest storage (27). The total soluble phenolics content of fresh-cut tomato is shown in Fig. 1B. Asc treatment induced an increase in the phenolics content in kiwi fruit (approximately 2-fold) (9,18), compared to other treatments. An increase in the phenolics content of fresh-cut tomato fruit occurred during the first 10 days of storage, followed by a slight decline thereafter. The CaLact treatment prevented accumulation of phenolics up to the 15th day of storage. With the noted exceptions, the total soluble phenolics content did not change significantly during storage, similar to reports for other tomato cultivars (2) in which the total soluble phenolics content increased from 14 to 21 days. AyalaZavala et al. (5) reported an increase in phenolics content with storage time for up to 16 days at 5ºC in fresh-cut tomato treated with methyl jasmonate, ethanol, tea tree oil and garlic oil, with no change reported for a control. An increase in phenolic content is expected in fresh-cut fruit as tissue responds to wounding by activating defence mechanisms that lead to accumulation (or synthesis) of secondary metabolites (28). Ascorbic acid is a moderately strong reducing compound that is able to prevent the browning of fresh-cut fruit and vegetables. It reduces levels of o-quinones and o-diphenolics by preventing phenolic oxidization to quinones, which ultimately polymerize to produce the browning appearance (29). The higher amounts of phenolics in Asc treated samples may be partly attributed to ascorbic acid interference with the process of phenol determination. The Folin-Ciocalteu assay is one of the oldest methods to determine the total content of phenolics. It is still used for studying phenolic antioxidants because it is simple, reproducible, and convenient. However, this method is less suitable for the analysis of products containing a high ascorbic acid content because the Foli-Ciocalteu reagent is non-specific for phenolics. The reagent reacts directly with other non-phenolic compounds, such as ascorbic acid, resulting in colour changes caused by a reaction between the Folin-Ciocalteu reagent and the non-phenolic compounds and not necessarily by a reaction with phenolics (30). The antioxidant activity determined using the DPPH method allows evaluation of the capacity of samples to scavenge free radicals, such as DPPH. The ability of samples to quench this free radical is depicted in Fig. 1C for fresh-cut tomato cv. Eufrates. As reported for fresh-cut kiwi fruit (9,18), Asc treatment resulted in a significantly higher antioxidant activity than other treatments, showing a significant correlation between the total phenolic content and the ascorbic acid content (Pearson correlation coefficient of 0.557**, p<0.01). Even after three weeks (20 days) the antioxidant activity was not lost (Fig. 1C).
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Fig. 2. Bacterial counts (A) and yeast and molds counts (B) of fresh-cut tomato cv. Eufrates through shelf life at 4ºC after dipping in 2% citric acid (Citric), ascorbic acid (Asc), calcium lactate (CaLact), and water (control) for 2 min. Values for each sampling date followed by the same letter are not significantly different using Duncan’s multiple range test (p>0.05).
Odriozola-Serrano et al. (2) reported decreased free-radical scavenging of DPPH with storage time in fresh-cut tomato. Similar results were observed for fresh-cut kiwi fruit with no dip treatments (9). For fresh-cut tomato there were almost no changes in the antioxidant activity of the control, a slight increase for citric treatment, and the highest significant increase for Asc treated fresh-cut tomato fruits up to 10 days, with constant values up to 20 days. The accumulation of more phenolics in Asc treated fruits than in the other groups, and the presence of larger amounts of ascorbic acid may be responsible for these results concerning the antioxidant activity (Fig. 1). Microbial growth Cutting of fruit results in stress conditions that induce structural and metabolic changes that create conditions for browning, texture breakdown, and loss of flavor, and opportunities for contamination by microorganisms (6). Tissue damage caused by cutting and breaking of cells causes release of nutrients that are used by many microorganisms (31). Cutting, therefore, causes
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Quality of Fresh-cut Tomato during Shelf Life
which means that after 10 days shelf life at 4ºC, all freshcut tomato fruit presented an acceptable appearance. Asc treatment was the best preserver of freshness and of most nutritional quality attributes of fresh-cut tomato fruit, including antioxidant activity, through shelf life at 4ºC for up to 20 days. The citric treatment followed with a good taste evaluation after 10 days. In contrast, the CaLact treatment was limited in effectiveness in prevention of microbial growth, but was useful to maintain firmness.
Fig. 3. Score index (1-dislike definitely; 2-dislike mildly; 3neither like nor dislike; 4-like mildly; 5-like definitely) of fresh-cut tomato cv. Eufrates, at harvest and after 10 days of shelf life at 4ºC after dipping in 2% citric acid (Citric), ascorbic acid (Asc), calcium lactate (CaLact), and water (control) for 2 min. Values for each parameter followed by the same letter are not significantly different using Duncan’s multiple range test (p>0.05).
fruit microbial spoilage and a decline in quality. The bacterial and yeast and mould counts in fresh-cut tomato cv. Eufrates are shown in Fig. 2. Asc and citric acid treatments were the most effective antibiotic agents. After 10 days, Asc treatment was the most effective for prevention of bacterial growth; however, after 20 days citric acid was equally effective (Fig. 2A). The dip treatments exhibited a weaker effect on yeasts and molds. After 10 days of storage, both Asc and citric acid treatments efficiently prevented (p<0.05) contamination of fresh-cut tomato slices by yeasts and molds. By the 20th day of shelf life, all dips had lost their fungicide capacity (Fig. 2B). AyalaZavala et al. (5) reported a reduction in microbial proliferation when fresh-cut tomato was treated with methyl jasmonate, ethanol, tea tree oil, or garlic oil, with a combination of ethanol and methyl jasmonate being the most effective. Prolonging reductions in microbial populations through the shelf life of fresh-cut fruit via the use of healthy, GRAS methods is of great importance. Asc and citric acid treatments prevented microbial development and, consequently, quality loss in freshly cut tomato cv. Eufrates. Sensory evaluation In spite of a small decrease for most of the sensory attributes measured, appearance, aroma, sweetness, and acidity did not show significant differences among treatments or shelf life (Fig. 3). The acidity score decreased significantly after 10 days of shelf life for the control. The flavor of fresh-cut tomatoes deteriorated after 10 days of shelf life at 4ºC (Fig. 3) and there was a significant decrease in the flavour score index of slices dipped in calcium lactate from 0 to 10 days. The score of the overall appearance attribute was always more than 3,
Acknowledgments This research was partly financed by Portuguese Foundation for Science and Technology (FCT) through IBB-CBV.
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