Citrus unshiu is an economically important fruit on Jeju Island, Korea, but byproducts are a major source of agricultural waste. The aim of this study is to examine changes in phytochemical, antioxidant, and antibacterial activities of four C. unshiu byproducts: citrus flesh byproduct (CFB), fermented citrus flesh byproduct (FCFB), citrus peel byproduct (CPB), and fermented citrus peel byproduct (FCPB). Fermented citrus byproducts (FCFB and FCPB) exhibited greater inhibition effect on radical scavenging abilities of 2,2-diphenyl-1-picrylhtdrazyl, 2,2’-azinobis(3-ethylbenzothiazolin-6-sulfonic acid)-diammonium salt, and superoxide anion compared with those of CFB and CPB. Total polyphenol contents of FCFB and FCPB were significantly increased compared to those of CFB and CPB. Significant bioconversion of the flavonoid glucosides into corresponding bioactive aglycones during citrus byproduct fermentation was observed. Fermented citrus byproducts exhibited antibacterial activity against Listeria monocytogenes and Escherichia coli suggesting that FCFB and FCPB are potent antioxidant and antibacterial sources due to the remarkable contents of bioactive compounds in them.
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