DPPH scavenging capacities, expressed as IC50s for California, Sichuan and Xinhui sources of OPEs were significantly (P < 0.05) lower than Guangxi and Zhejiang OPEs (Table 2). Xhinhui OPE also gave higher (P < 0.05) TEAC and ORAC values compared to the
other four OPEs sources. The positive correlation (P < 0.05) between TEAC and ORAC activity, and the negative correlation (P < 0.05) between TEAC and ORAC with the IC50 values of DPPH scavenging activity (Table 3) indicate that radical chain-breaking
and reducing capacity are closely related. The fact that TPC but not TFC was positively (P < 0.05) correlated with TEAC and negatively (P < 0.05) correlated with IC50 of DPPH scavenging activity indicates that the antioxidant activity of OPE reflects more accurately the TPC, rather than TFC. Fidrianny, Harnovi, & Insanu
(2014) also found that TPC in orange peels was positively
correlated with DPPH scavenging activity and ferric reducing
antioxidant power (FRAP). Heat treatment of orange peels
increased the extraction yield of flavonoid and TPC, which in turn increased antioxidant activity of OPE (Jeong et al., 2004). Our
findings indicated that OPE containing phytochemicals were
effective at donating either protons or electrons to stabilize free
radicals, thus contributing to a relevant antioxidant function.