The effects of different chitosan concentrations on storage life and postharvest quality of cornelian cherry (Cornus mass L.)

Introduction: Controlling the postharvest losses and the utilization of safe methods versus chemical compounds is a remarkable priority in the production of horticultural produce. Using techniques to preserve agricultural produce quality dates back to many decades ago (Paliath et al., 2009). This is essential to keep the visual characteristic and quality of products. In some ways, the procedures employed improve the quality and organoleptic properties of the crops. This is end goes to the reduced production charges and the higher incomes (Duan et al., 2007). Postharvest scientists are attempting to employ the materials to cover the fruits and to keep the harvest time quality or even to improve the quality and visual attributes. During the recent years, the application of edible coatings such as chitosan has been increased to reduce the postharvest loses, lowering the respiration rate, shelf life improvement, firmness keeping and for the control of microbial growth rates in fruit crops. Chitosan is an aliphatic organic polymer with a characterized antifungal (Allan and Hadwiger, 1979) property. Furthermore, chitosan coating lowers the respiration rate, prevents microbial growth and delays the fruit ripening by the control of CO₂, O₂ and ethylene exchange balance (EL Ghaouth et al., 1991). Moreover, low temperature storage intensifies the chitosan keeping qualities on stored fruits. Cornelian cherry fruits contain high amounts of ascorbic acid (vitamin C), organic acids, phenolics,taninns and some other bioactive compounds. Hence, the fruits have considerable nutritional and medicinal benefits effects (Moldovans et al., 2016). Furthermore, the fruits have precious antimicrobial properties (Asadov, 1990).
In the present study, we tried to evaluate the effects of different chitosan concentration to keep the antioxidant potential of cornelian cherry and of the quality attributes during postharvest period.
Material and methods: Cornus mass L. fruits were harvested from an orchard from northwest of Iran (Hourand country). In advance, the fruits were homogenized for the size, color and shape and were transferred to the Lab. The fruits were treated with 0.5,1 and 1.5 % chitosan solution and distilled water as control for 1 minute. The fruits let too dry at ambient temperature and were stored at 4±1°C for 21 days. TSS, TA and pH were evaluated in fruit juice soon after. Samples were taken during the first, 7, 14 and 21th days after treatment. The fruits were kept at cold storage and immediately the common measurements like pH, TSS and TA were conducted. Then after the fruits were freezed in liquid nitrogen and kept in - 40 °C for further studies. Total phenolics, Flavonoids and anthocyanin were measured by folin- ciocaltea (Gallic acid as standard), flavonoids based on catechin and total anthocyanin by the absorbance difference in divers pH ratios, respectively. DPPH method was employed for the antioxidant potential of fruits. Besides CAT, GPX, PPO and PAL enzymes were quantified as well. The data were analyzed by SAS (ver.9.2) software as CRD with three replications. Excel 2013 was employed for the tables figuration and the means were compared by the Duncan's multiple range test.
Results and discussion: ANOVA results revealed that interaction of storage time × chitosan concentration meaningfully (P <0.01) influenced pH. TA and TSS of fruits. The top pH was acquired by 0.5% chitosan at the third week. Chitosan modifies fruit surface atmosphere and hence by the variations in CO₂ and O₂ alters the TA and pH values. Maturity stage influences TSS values and with ripening progress, TSS was increased (Gunduz et al., 2012). In a similar experiment, with chitosan concentration adding up, TSS increase was slowed down seemingly due to the hydrolytic changes in the starch content and water loss during the storage period (Kays, 1997).  Interaction of time and chitosan concentration was statistically influenced (P <0.01) total phenolics, flavonoids and total anthocyanin content. Total phenolics had the highest amount with 1.5% chitosan seemingly due to CO₂ barrier induced by chitosan which reduces the phenolics oxidation.
Moreover, chitosan coating activates PAL enzyme in phenolics biosynthesis (Romanazzi et al., 2017). Total flavonoids were increased by storage time, and by 1% of chitosan treatment. Flavonoids are crucial antioxidants and besides phenolics were increased in the fruits during the storage time and with SA treatment (Dokhanieh et al., 2013). Total anthocyanins followed the same pattern as well. Antioxidant potential of fruits was also impacted by storage time and chitosan as well (P <0.05). Antioxidant potential is directly related to phenolics, flavonoids and anthocyanins content of fruits and vegetables. So that, the increased total amounts of the mentioned metabolites resulted in improved DPPH activity. There is evidence that other coatings such CaCl₂ and SA improved the metabolites and antioxidant potential (Dokhanieh et al., 2013; Soleimani-Aghdam et al., 2013).  CAT, PPO, GPX and PAL were influenced by the time× chitosan interaction as well. CAT activity was declined during the storage period. But, there was no significant difference between 0, 1 and 1.5% chitosan treatments. Chitosan application improves the selective permeability of membrane for CO₂ and O₂ exchange and hence reduce the phenolics oxidation. These all reduce the PPO activation and function (Duan et al., 2007). GPX activity was increased during the storage, So, that the highest GPX activity was belonged to the sampling at 21th days. PAL activity was responsive to the interaction of time × chitosan concentration and the enzyme activity was increased in time dependent pattern during the storage. The top data was recorded for the untreated fruits.
Conclusions: Cornelian cherry fruitsare rich in antioxidant compounds like phenolics, flavonoids, anthocyanins and ascorbic acid. During the storage period and like other horticultural products (fruits and vegetables), the nutritional and visual quality of cornelian cherry fruits reduces dramatically. Chitosan as an environment-friendly and non-chemical compound preserves the quality attributes of fruits. Over all, in the present experiment, chitosan treated fruits had more antioxidant potential and enzymatic activity than untreated ones.
Moreover, chitosan improved the total quantities for phenolics, flavonoids and anthocyanins. DPPH antioxidant potential was improved by chitosan application. Furthermore, CAT, PPO and PAL were correspondingly responded to chitosan treatment in favor of fruits quality.
In short, chitosan has a considerable potential to be considered as a good edible coating to improve the postharvest life and quality attributes of cornelian cherry fruits.