ارزیابی اثر زمان برداشت و مدت نگهداری میوه در سردخانه بر روی برخی خصوصیات کیفی میوه زغال اخته

Introduction: Evaluation of the physicochemical properties of fruits during different stages of maturity is essential for achieving high-quality product and extending shelf life. Harvest maturity and storage time are main factors that may lead to changes in sensory and nutritional qualities of cornelian cherries. Cornelian cherry fruit are frequently harvested at dark red stages, when their flavor is most desirable. Consumers do not usually eat cornelian cherry at any of the other maturation stages. Therefore, the effect of ripening and storage time on nutritional quality is a major issue. The cornelian cherry fruits which have sour and sweat tasting juice, contain a high amount of vitamin C. To optimum threshing performance, processes of pnematic conveying, storing and other processes of cornelian cherry fruits, its physical properties should be known.  
Materials and methods: This research was conducted to investigate the effect of harvest time at two stages (commercial harvest and 5 days after the first harvest) on some of the physicochemical properties of a commercial genotype of cornelian cherry fruit during the storage period. The fruit kept in cold storage at a temperature of 4 °C with relative humidity of 80-85% for 21 days. Fruit qualitative traits such as pH content, total soluble solids (TSS), titrable acidity (TA), TSS / TA ratio, vitamin C, ion leakage and ethylene production of fruits during storage at 0, 7, 14 and 21 days of storage were evaluated. Total soluble solids were determined by a hand refractometer (model Atago N, Japan) having range of 0-32 percent and the values obtained in per cent were correlated at 20ºC. Titratable acidity was determined by taking a known weight of fruit juice and making a known volume of it by adding distilled water. Then a known volume of this liquid was treated against 0.1 N sodium hydroxide at pH 8.2 as an indicator of titration using pH meter. The ascorbic acid (vitamin C) content in the aqueous supernatant of each maturity stage was determined.
 Results and discussion: The results showed that the harvest time has not a significant effect on pH and ion leakage of fruits. The delay in the harvest time increased the total solids soluble solids to total acidity ratio (TSS / TA) ratio and decreased total acidity (TA). However, there was a significant difference during storage period in all of the studied parameters. With progress in the maturity stage and fruit during the storage period, total soluble solids (TSS) and ethylene production in second harvest fruits showed an increase comparing the first harvest time. The increase in soluble solids content of fruit during storage period could be related to conversion of insoluble carbohydrates to soluble ones and decreasing of transpiration of fruit during storage period (Miaruddin et al. 2011). pH, total soluble solids to total acidity ratio (TSS / TA), and ion leakage of fruits increased, while the total acidity content decreased along with storage time. During ripening period of strawberry, the content of organic acids in fruit reduced and soluble sugars increased which led to increasing soluble solids content to total acidity ratio and sweeter fruit taste (Winardiantica et al. 2015). Foliar application of salicylic acid with high concentrations (2 mM) increased fruits phenol content, vitamin C, TA and total anthocyanin compound. Maximum amount of total antioxidant has been established in 2mM SA concentration that demonstrated 18% increase in compare with control. SA foliar application caused to decrease of total soluble solid (TSS) content but had not any significant effects on flavonoid and total carotenoid of grape berries. These results further indicated that the effects of Salicylic acid in grape is associated with induce defensive systems and increase biological performance such as antioxidant activity and different quality fields in grape (Ghohari et al. 2018). The content of vitamin C (ascorbic acid) of the first harvest had lower than second harvest and showed a declining trend for both of them during storage period. Many pre- and postharvest factors influence the vitamin C content of horticultural crops. Large genotypic variation in vitamin content, climatic conditions and cultural practices, Maturity at harvest, harvesting method, and postharvest handling conditions also affect the vitamin C content of fruits and vegetable (Gordon et al 2012). Chaudhari et al. (2017) reported that the ascorbic acid content of citrus fruit decreased during storage period which may related to chilling injury incidence of fruits. Membrane ion leakage of cornelian cherry fruit increased by the end of storage period which led to water soaked fruits. By the end of storage at cold temperature membrane leakage percent of both harvests increased. This may be caused by cold stress oxidative injury effect on fruit cells and softens their texture. Antioxidant activity was high in fruits and varied greatly among the genotypes. So cornelian cherry could be considered a good source of natural antioxidants. They can potentially be used in food and nutraceutical supplement formulations as well. Fruit weight, soluble solids content and acidity were varied significantly among genotypes.  Shewfelt and Purvis (1995) demonstrated that membrane ion leakage in plants could be an indirect signal of membrane integrity state which decreased by the chilling injury incidence in fruit during cold storage period. During storage period, ethylene production of both harvested fruit were increased as the values for first harvest were lower than second harvest. The increase in ethylene production may be related to the effect of cold temperature stress during storage period and change the fruit metabolism as pheylpropanoid pathway (Yung and Hoffman 1984). Ripening and senescence involve the last phase of molecular and biochemical changes that result in the transformation of fruits into an edible form with aesthetically superior organoleptic and nutritional qualities. These changes are initiated in response to ethylene.  
Conclusion: Generally, our results showed that with delay in harvest soluble solid content of fruit increased and total acidity of fruit decreased. Also, fruit of second harvest had more ascorbic acid content than first harvest that a good qualitative index as an antioxidant compound in cornelian cherry fuit for having a good quality fruit by the end of storage period. So the second harvest fruit was more qualitative than first harvest during storage period.