اثر زمان برداشت بر برخی از ویژگی‌های آنتی‌اکسیدانی میوه زغال‌اخته طی انبارمانی

Introduction: Cornelian cherry fruits are considered as natural antioxidant source and fruits are quite rich in anthocyanins, flavonoids, flavanols, tannins, carotenoids, vitamins, organic acids and phenolics acids. Leaves, flowers and fruits have been used in traditional medicine. Earlier investigations on physical and chemical properties of cornelian cherry fruits and flowers, their antioxidant and cytotoxic efficacy reported phenol, ascorbic acid, anthocyanin and high concentration of essential minerals (Ca, K, Mg) contents (Eyde, 1988). Consumers usually prefer attractive fruits in markets. However, serious quality losses are encountered in fresh-consumed fruits throughout the shelf life. Flesh softening, decays, deteriorate in taste, flavor and aroma are the basic problems experienced in shelves. Such losses are directly proportional to pre and post-harvest practices (maturity stage, harvest damages and storage conditions - temperature, relative humidity) (Lurie, 2003). When the fresh-consumed fruits were harvested at optimal maturity stage, less quality losses are experienced throughout the cold storage and shelf life of the fruits. Thus, postharvest quality losses increase in fruits not able to be harvested at optimal maturity. It was reported in previous studies that maturity stage had significant effects on storage or shelf life performance of litchi, sweet cherries, banana, plums, peaches and apples (Lata, 2007). Study of the antioxidant properties of fruits during different stages of maturity is essential for obtaining 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 (Gunduz et al. 2013). 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 (Soleimani et al. 2013). This research was conducted to investigate the effect of harvesting time on some physicochemical and antioxidant properties of Cornelian cherry fruits during its storage period.
Material and methods: Fruit were harvested commercially at 2 stages of harvesting time (first harvest, fruit with light red color and second with dark red) from a commercial orchard at Kalybar area of east Azerbaijan province. In each harvest time fruit picked from four direction of a cornelian cherry tree and then transferred to postharvest laboratory of department of horticulture sciences of university of Tabriz. After preliminary evaluation of harvested fruit and selection of intact fruit among them they divided to two group: one group were used to evaluate of the qualitative characteristics before storage and the other fruit were transferred to storage at a temperature of 4 °C and a relative humidity of 80-85% for 21 days. The study was carried out as a factorial experiment based on completely randomized design in order to study of various chemical properties such as total phenol, total flavonoid, soluble tannins, total anthocyanin, total carotenoids, total antioxidant capacity and malondialdehyde levels during storage (0, 7, 14 and 21 days).
Results and discussion: The results showed that with progress in fruit maturity during storage, the amount of phenolic and flavonoid compounds, anthocyanins increased significantly (P<0.01) with the increase in the storage period in the first harvest compared to the second harvest, but the antioxidant capacity of fruit had a more significant (P<0.01) decreasing trend by the storage time than second harvest fruit. Anthocyanins are the major phenolic components of soft berry fruits, and their antioxidant activity has been found to be closely related to total phenolic content (Lopiero et al. 2005). The phenolic content and composition of fruits depend on environmental factors as well as post-harvest processing conditions (Lurie, 2003). Anthocyanin is a pigment responsible for red color development. Le Piero et al. (2005) reported increased anthocyanin pigment accumulation with the progress of ripening. Thus, anthocyanin pigment accumulation went on in early harvested fruits (H1) throughout the storage. However, anthocyanin pigment degradation was observed in full-ripe fruits. The phenolic compounds use in plant defense mechanisms, to counteract reactive oxygen species, in order to survive and prevent molecular damage, and damaging by microorganisms, insects and herbivores (Hopkins, 1999). Also, the carotenoids content increased by delay in harvest time and by prolonging the storage time of fruits. During the storage period, the amount of fruit soluble tannins decreased significantly (P<0.01), while the malondialdehyde content of the fruits increased. With delay in harvest the amount of soluble tannins of fruits reduced. Total antioxidant activity of fruit increased by the progress in fruit maturity stage during storage time as it decreased by the storage time for both maturity stages. The antioxidant activity of phenolics is mainly due to their redox properties, which allow them to act as reducing agents, hydrogen donors and singlet oxygen quenchers (Lurie, 2003). Taken together, our results have suggested that OA treatment significantly enhanced the antioxidant activity of the cornelian cherry fruits. It has been reported that the DPPH• scavenging activity is mainly attributed to the phenols, flavonoids, anthocyanins as well as ascorbic acid contents in cornelian cherry fruits (Dokhanieh et al. 2013).  Lipid peroxidation as MDA content is a secondary end product of oxidative lipid degradation, has become the system of choice for estimating lipid peroxidation of fruit increased by storage period as the highest amount was observed by the end of storage period. Formation of lipid peroxides, their degradation, and the roles of these hydroperoxides may play in cellular metabolism and the most accurate approach to measure lipid peroxidation is to directly quantify the primary hydroperoxide products (Hodges et al. 1999).
Conclusion: In general, cornelian cherry fruit chemical composition and its antioxidant capacity affected by harvest maturity and storage time as fruit of the second harvest had higher amount of carotenoids and antioxidant capacity content compared to other constituents, than first harvest fruit during storage time. Progress in harvest maturity was accompanied by increased total phenol, flavonoid, anthocyanin and carotenoid contents as well as improved DPPH scavenging capacity. Our data suggested that the fruit of second harvest enhanced antioxidant potential could be due to the activation of biosynthesis of most of antioxidant compounds in fruit compared to first harvest during cold storage period.