Effect of Naringin Radical Formed by Peroxidase on Chlorophyll Degradation during Storage of Citrus nagato-yuzukichi Fruit

Free radical formation from flavonoids by peroxidase action and changes in flavonoid levels and peroxidase activity during storage were determined to clarify the involvement of naringin radical in chlorophyll (Chl) degradation in stored green Nagato-yuzukichi (Citrus nagato-yuzukichi hort. ex Y. Tanaka) fruit. Chl a was degraded by peroxidase-hydrogen peroxide system not in the presence of hesperidin but with naringin. However, radical formation of both naringin and hesperidin, which were the main flavonoids in the flavedo of Nagatoyuzukichi fruit, with peroxidase-mediated oxidation was found by electron spin resonance analysis. The naringin radical, which was formed by a radical forming reagent, potassium ferricyanide, was related to the formation of 13-hydroxychlorophyll (OHChl) with Chl a degradation, whereas the hesperidin radical hardly affected OHChl a formation. In addition, superoxide dismutase did not inhibit Chl a degradation by naringin radical formed by potassium ferricyanide. In Nagato-yuzukichi fruit, Chl-degrading peroxidase activity increased considerably during storage at 20°C, with a peak value on day 6 of storage in accordance with decrease in Chl content, after which it decreased. The contents of naringin and hesperidin, especially the former, decreased during storage at 20°C, but afterwards increased slightly. These findings suggest that the naringin radical formed by peroxidase could be partly involved in Chl degradation during storage in Nagato-yuzukichi fruit.