Investigating the effect of canopy position on rind phytochemical concentrations and radical scavenging activities of 'Nules Clementine' mandarins during postharvest cold storage

Rind phytochemical concentrations and radical scavenging activities of 'Nules Clementine' Mandarin could play a significant role in the appearance and susceptibility of fruit to various forms of physiological rind disorders. Hence, this study examined the effect of the fruit position within the tree canopy on the rind phytochemical concentrations and radical scavenging activities of 'Nules Clementine' Mandarin fruit flavedo and albedo tissues after harvest at week 0 and after 3, 6 and 9 weeks of postharvest cold storage at 7.5±0.5°C. Fruit from inside the canopy (IC) and outside the canopy (OC) were harvested at commercial maturity in May 2015 and 2016 from Unifruiti and Swartvelei Farms located at Eastern Cape (EC) (33°27'32"S, 25°34'79"E) and Western Cape (WC) (19°02'33.8"S, 33°41'17.24"E) provinces of South Africa, respectively. Results showed that the canopy position had significant (p<0.001) effects on the total carotenoid content, total phenolic and total flavonoid concentrations of the fruit rind. The parameters were also significantly more concentrated in the flavedo tissue than albedo of the fruit during cold storage. The study further showed that the production region influenced the carbohydrate content of OC and IC fruit rind during cold storage. For instance, the sucrose of the albedo tissue of the fruit (90.6, 161.9, 213.2, 148.8 mg g^-1 DW) were higher than the flavedo of fruit (36.5, 38.8 42.6 and 37.9 mg g^-1 DW%) during weeks 0, 3, 6 and 9. Overall, this study revealed that the position of a fruit within the tree canopy influenced the biochemical composition and antioxidant capacity of flavedo and albedo. High phytochemical concentrations and radical scavenging activities occurred in the fruit rind during postharvest cold storage and therefore, could be implicated in preventing the incidence of rind physiological disorders.