The objectives of the present study were to (1) quantify individual flavonoids in citrus peels after enzymatic de-glycosylation (Viscozyme or Pectinex) and (2) elucidate the antioxidant activities of citrus peel after different enzymatic treatment times (60, 120, and 180 min). HPLC analysis showed that enzymatic de-glycosylation of citrus peel resulted in decreased flavonoid glycoside forms (narirutin and hesperidin) and increased aglycone forms (naringenin and hesperetin) as the reaction time increased. Enzymatic de-glycosylation of citrus peel induced significantly increased antioxidant activities compared to the control because of enzymatic de-glycosylation of narirutin and naringin to naringenin and of hesperidin to hesperetin, respectively. Furthermore, Viscozyme treatment of citrus peel appeared to be more effective at increasing the aglycone forms (naringenin and hesperetin) and antioxidant properties than Pectinex treatment. There were significant correlations between flavonoid aglycone contents in citrus peel and antioxidant activities. In conclusion, enzymatic de-glycosylation of citrus peels may enrich aglycones in citrus peel and provide more potent functional food materials by increasing antioxidant activities.

Keywords: citrus peel, flavonoid, enzyme treatment, enzymatic de-glycosylation, antioxidant activity