THE INFLUENCE OF TEMPERATURE AND STORAGE TIME ON CANTALOUPE MELONS PHYSICOCHEMICAL QUALITY

Abstract

Cantaloupe melons [Cucumis melo L. subsp. melo var. cantadupensins Naudin) cu 'Chianti' were evaluated for quality traits during 14 days of storage at three different temperatures i.e., 2°, 10° and 18°C with 85-95% relative humidity. The weight loss of fruits slightly increased during the stored period studied, as well as insignificant differences between the temperatures. Whereas significant texture was lost more rapidly in the samples stored at 18° and 10°C than those stored at 2°C. TSS (total soluble solids) were also affected by storage time and temperature. The TSS content of fruit at 2°C increased and then remained constant over storage. At higher temperatures and at every stage of storage time TSS increased as storage time increased. The predominant carotenoid in all samples was ß-carotene. The carotenoids were increased and then decreased with the time; however, the decrease processes were delayed by low temperature. The alpha form was the predominant tocopherol fraction. The level of tocopherol isomers significantly (a-tocopherol) and gradualy (γ- and δ- tocopherol) increased during the 7 days, but after 1st week of storing for all isomers a significant decrease was measured. High temperature storage at 18°C in comparison to 10°C and 2°C promoted γ- and δ- tocopherol level. [PUBLICATION ABSTRACT]

Headnote

ABSTRACT

Cantaloupe melons [Cucumis melo L. subsp. melo var. cantadupensins Naudin) cu 'Chianti' were evaluated for quality traits during 14 days of storage at three different temperatures i.e., 2°, 10° and 18°C with 85-95% relative humidity. The weight loss of fruits slightly increased during the stored period studied, as well as insignificant differences between the temperatures. Whereas significant texture was lost more rapidly in the samples stored at 18° and 10°C than those stored at 2°C. TSS (total soluble solids) were also affected by storage time and temperature. The TSS content of fruit at 2°C increased and then remained constant over storage. At higher temperatures and at every stage of storage time TSS increased as storage time increased. The predominant carotenoid in all samples was ß-carotene. The carotenoids were increased and then decreased with the time; however, the decrease processes were delayed by low temperature. The alpha form was the predominant tocopherol fraction. The level of tocopherol isomers significantly (a-tocopherol) and gradualy (γ- and δ- tocopherol) increased during the 7 days, but after 1st week of storing for all isomers a significant decrease was measured. High temperature storage at 18°C in comparison to 10°C and 2°C promoted γ- and δ- tocopherol level.

- Keywords: Cantaloupe melons, storage, weight loss, texture, soluble solids, carotenoids, tocopherol -

INTRODUCTION

Cantaloupe melons [Cucumis meló L. subsp. melo var. cantalupensins Naudin) is one of the most important horticultural crops in the world of agriculture (NUÑEZ-PALENIUS et oL, 2008). According to BAN et oL (2011) the global consumption of these fruits are greater than that of any other species in the Cucurbitace family. Cantaloupes are a popular delicacy and exclusively consumed as fresh or minimally processed products such as fresh cut pieces of melon with rind or as cubes without rind.

Some researchers suggest that extract of cantaloupe melon may serve as a potential source of natural phytochemicals for food and nutraceutical application (LESTER, 2006). Over the last decade, there has been increased interest in plant foods that are rich in health-protecting source of minerals, vitamins and phytochemicals (VEBERIC et cd., 2009). Among these, carotenoids and tocopherols constitute important groups in human diet (LANDRUM and BONE, 2001). The protection provided by fruits and vegetables against a wide range of several degenerative diseases, including cancer, cardiovascular diseases and other chronic diseases, has been attributed to the antioxidants they contain (SANGEETHA and BASKARAN, 2010). The reasons for this relationship appear to be multi-faceted and include components in plants that are used as a free radical scavengers, singlet and triplet oxygen quenchers, detoxification agents, or as plant defense response components (PERKINS-VEAZIE et al, 2003).

One of the most important factors in the production and marketing of cantaloupes is the postharvest quality. Cantaloupe fruits in general have limited storage time and become soft and shriveled after about two weeks because the open, netted epidermis favors high transpiration rates (FALLIR et cd., 2005). The recommended storage temperature for whole cantaloupe is varied between 2 (FLORES et cd., 2007) to 18°C (RADULOVIÖ et cd., 2007).

The development of new cultivars of cantaloupe melons with high added value and which are well adapted to the Slovenian growing conditions has stimulated the interest in the commercial cantaloupes production. During the 2012 season, study was conducted to evaluate the effectiveness of holding fresh cantaloupe fruits in different storage temperatures of 2°, 10° and 18°C to extend their post harvest life and maintain fruit quality parameters. Further, research focused on the degradation of carotenoids of cantaloupe fruits, which data are missing in the literature

MATERIALS AND METHODS

Processing of samples for analyses

Cantaloupe melon cv 'Chianti' (Semenarna d.o.o., Ljubljana) was grown at the Experimental Station of the Biotechnical Faculty in Ljubljana. Standard agricultural practices were adopted uniformly according to crop requirements. Thirty of the tagged fruits per plot were harvested on the same day when they reached the horticultural maturity (i.e. at the 3/4 to full-slip stage). After harvest fruits were held overnight at about 10°-15°C and transferred the following day to the laboratory. Fruits were randomly divided into three groups, each group containing 30 fruits in four replicates. Fruits were then placed in the chambers for 14 days at 8595% relative humidity to simulate a commercial storehouse situation. The first group was stored at 2°C, the second one at 10°C and the third one at the 18°C. The fruits were analysed three times during storage from August 28th to September 10th 2012.

Determination of weight loss

Weight loss was evaluated by the difference in fruit weight on the first day of the experiment and each sampling. The weight of fruits was recorded using a Mettler balance model Toledo PB 602.

Determination of texture

Texture (firmness) was measured in the pulp, by removing 1 cm2 of the fruit skin, on opposite sides using a Chatillion penetrometer (model DFG 50), equipped with an 11 mm diameter round stainless steel probe with flat end (John Chatillion & Sons, U.S.A.). The crosshead speed during the firmness testing was 10 mm/min. Two measurements of the force needed to penetrate the mesocarp tissue were taken for each fruit, and an average was calculated as a puncture force (kg cm*2) recorded during penetration.

Chemical analyses

Total soluble solids concentration (Brix was noted in percentage) of the expressed juice was determined using a hand-held Atago PR1 refractometer (brix range 0-20% at 20°C).

When weight, texture and soluble solids measurements had been performed, sample of fruits flesh were chopped, frozen in liquid nitrogen and stored at -20°C. For detection of dry weight (DW), 2 g of the frozen sample was freeze-dried for 22 h in a Gamma 2-20 lyophilizer (Christ, Germany). Water content (%) was calculated from the difference between the masses before and after the lyophilization.

Carotenoid components and isomers' composition of tocopherols were determined using an improved method described in RACJ AN- MARS IC etal (2010). Carotenoids and isomers' composition of tocopherols were extracted from the dry fruit powder with ice-cold acetone. All extraction procedures were performed in dim light. Acetone extracts were subjected to HPLC gradient analysis (column Spherisorb S5 ODS-2 250 x 4.6 mm with precolumn S5 ODS-2 50 x 4.6 mm). Tocopherols were separated using methanol as solvent. Tocopherols were detected directly by fluorometry (excitation 295, emission 325). Carotenoids were separated using the following solvents: solvent A, acetonitrile/methanol/water (100/10/5, v/v/v); solvent B, acetone/ethyl acetate (2/1, v/v), at a flow rate of 1 mL min*1, linear gradient from 10% solvent B to 70% solvent B in 18 min was applied, run time 30 min, photometric detection at 440 nm.

Statistical evaluation

All measurements were performed in triplicates (n = 3). Statistical analysis was performed using the Statgraphics programme, version 4.0. Results were compared by Tukey HSD test

RESULTS AND DISCUSSION

Weight loss

The average weight of randomly chosen cantaloupe fruits measured after harvesting was 1,142 g. It was found that weight loss is quite uniform irrespective of storage temperatures. Effects of storage conditions on weight loss of stored fruits are listed in Fig. 1. Maximum weight loss occurred at 18°C (7.6%), while lowest loss was recorded at 10°C (0.9%), after the first week of storage, and 13.6% (at 18°C) and 3.5% (at 2°C) for fruits stored for two weeks. However, the difference was not statistically significant.

The weight loss experienced for other fruits and vegetables, during recommended storage conditions and storage period varies between 2 and 10%, due to moisture losses (ELKASHIF et cd., 1989). Minimal economical loss (weight loss) for cantaloupe melon during storage is due to the rind thickness and wax layer on the surface of the fruit, and for the cantaloupe melons are reported to show no climacteric activity (KARAKURT and HUBER, 2002).

Texture

The textural quality of fruits is influenced by flesh firmness. The development of pericarp firmness, i.e. the softening of the fruits, was significantly affected by storage time and temperature (Fig. 2). Firmness decreased notably at all temperatures during the storage period. It was observed from the present research intervention that firmness decreased as a function of storage time (POZRL et cd., 2010). However, firmness decreased slowly in fruits stored at 2°C. At the higher temperatures, the decrease in firmness was more noticeable. This was in agreement with the slow maturation expected at low temperatures (LAINEZ and KRARUP, 2008; GARCÍA et cd., 2005). A close relationship between the softening of the fruits, higher temperature and extension of storage time was described in previous studies (BEAULIEU and LEA, 2007). It was suggested by ZNIDARÖÖ et cd. (2010) that a postharvest change in texture can occur due to the loss of moisture through transpiration, as well as enzymatic changes. In addition, hemicelluloses and pectin become more soluble, which results in disruption and loosening of the cell wall structure and composition (PAUL et cd., 1999).

Total soluble solids (TSS)

TSS content is related to the balance of sugars and acids and it has a major impact on the flavor of the vegetable (GUILEN-RIOS et cd., 2007). Fig. 3 show that the storage period has a significant effect on TSS. It is clear from the obtained data that TSS has a significant rise through fruit development regardless of temperature and the maximum is observed in the end of the storage period. The gradual increase of TSS up to 21 days of storage might be due to conversion of insoluble to soluble forms of sugars and the least utilization of organic acid.

According to RATHORE et al. (2007), the increment of TSS might be due to the alteration in cell wall structure and breakdown of complex carbohydrates into simple sugars during storage.

Carotenoids

Carotenoid levels appears to vary by species, variety, cultivar, biochemical attributes, irrigation, degree of maturity at harvest, growing site, climate, soil fertilization (van den BERG et al., 2000). Some authors have observed that operation carried out during the post-harvest storage is also very important (KIDMOSEA et aL, 2006). For example, some authors (MENCARELLI and SALVEIT, 1988) mention that fruits bio synthesize carotenoids during ripening through-out the storage time. In our study, the major carotenoid found in the melon fruits was ß-carotene, making up on average 90% of the total carotenoids, ß-carotene have been widely reported as being one of the major carotenoids found in vegetables (CALVO, 2005).

Changes in carotenoid components of fruits are presented in Table 1. No significant differences in ß-carotene content were found between fruits stored at 2° and 10°C. On the contrary, ß-carotene content showed significant increase in fruits stored at 18°C. A steady loss in ß-carotene was observed during storage. Initial ß-carotene content of fruits was 90.41±28.19 mg/100 g, respectively, on dry weight basis. The lowest value was registered in fruits within three weeks of storage (51.25±3.88 mg/100 g).

In general, lutein content progressively increased with increasing temperatures. The initial level of lutein content was about 0.82±0.24 mg/100 g dry weight. During the storage the lutein content was increasing slightly in the first seven days and afterward the content of lutein started to decrease. As far as we know, there are no published works quantifying lutein content throughout storage of melon fruits.

The lycopene content was found to increase from a low value (2.74±0.16 mg/100 g) at 2°C g to a maximum (6.01±1.34 mg/100 g) at 18°C. Lycopene concentrations were also affected by storage time. Maximum lycopene accumulation (3.71±1.18 to 4.81± 1.93 mg/100 g) occurred in fruits that were 0-7 days in age, while the lowest lycopene concentration (1.91±0.52 mg/100 g) was in fruits at the end of storage.

Some authors (LEE and CHEN, 2002) are generally in agreement that lycopene remains relatively stable during typical food processing procedures, except at extreme conditions. On the other hand, TONUCCI et al. (1995) reported that lycopene content of vegetables increased by thermal process. For example, SHI et al. (1999) explained that this change might be caused by an increased release of lycopene from the cell, skin and insoluble fibre of tomato.

Tocopherols isomers

Tocopherols, collectively known as vitamin E, are one of the most important components of cellular antioxidant systems. Although tocopherols appear to be universal constituents of all higher plants (THRELFALL and WH I STANCE, 1971), to our knowledge, there have been no reports of the qualitative composition of tocopherols in cantaloupe fruits. In our study, three isomers of tocopherols were detected (a-, y- and Ô-tocopherol), and the results are shown in Table 2.

Among the tocopherols we determined after harvest (at 0 day) cx-tocopherol was predominant at the level of 4.82±0.87 mg/100 g. The contents of y- and 8-tocopherol were 1.42±0.61 mg/100 g and 0.17±0.08 mg/100 g, respectively.

During 21 days of post harvest the higher the storage temperature, the higher the content of tocopherols. Only exception is 8-tocopherol which concentration showed no substantial variations due to temperature conditions.

As shown in Table 2 content of tocopherols grew and peaked after 1st week of storage. Decrease of tocopherols after seven days was almost linear in all cases although the rate of decrease was slightly higher in a- and 8-tocopherol. According to ABRAMOVIÖ et al. (2007), the lower stability of a-tocopherol in comparison to y- and 8-tocopherol is due to the fact that tocopherols reacts faster with peroxy radicals formed in the process of autooxidation.

CONCLUSIONS

As consumers become increasingly aware of the nutritional value of foods and interersted in a healthier lifestyle, the positive nutritional information on cantaloupe melons will help consumer to make informed decision on consuming this nutrition food. The current data demonstrated the importance of not only temperature but also time of storage for the cantaloupe fruits quality parameters. To preserve fruits bioactive compounds it is recommended to keep them in storage for maximum of 7 days at 18°C.

ACKNOWLEDGEMENTS

This work is a part of the program Horticulture No. P4-00130481 funded by the Slovenian Research Agency (ARRS).

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Paper received April 17, 2013 Accepted June 13,2013