Abstract: In this study, DPPH radical scavenging activities and reducing powers of flavonoids from 9 different varieties of citrus peel were compared. Meanwhile, the effect of macroporous resin purification on these antioxidant activities was studied. The results indicated that both DPPH radical scavenging activities and reducing powers of flavonoids differed significantly among 9 varieties of citrus peel (P < 0.05). Both crude and purified flavonoids from Nanfeng citrus peel revealed the strongest DPPH radical scavenging activity and reducing power, with median inhibitory concentrations (IC50)  of (0.38 ± 0.03) mg/mL and (0.086 ± 0.003) mg/mL for scavenging DPPH radicals, respectively and reducing powers of  for flavonoids from Nanfengju before and after purification were (0.166 ± 0.002) mg/mL and (45.69 ± 1.38)μg/mL, respectively. On the other hand, flavonoids from Fujian sweet mandarin peel revealed the weakest DPPH radical scavenging activity and reducing power. The IC50 values for DPPH radical scavenging activity of flavonids from Fujian sweet mandarin peel before and after purification were (0.88 ± 0.02) mg/mL and (0.281 ± 0.003) mg/mL, and those for reducing ferric ion before and after purification were (0.306±0.003) mg/mL and (97.80 ± 1.06)μg/mL, respectively. Therefore, macroporous resin purification could result in a significant enhancement in antioxidant activities of flavonoids from citrus peel. The DPPH radical scavenging activities of flavonoids from Xinhui mandarin peel and Jiangxi navel orange peel revealed 8.3- and 2.6-fold enhancement after purification, and the reducing powers of flavonoids from Jiangxi navel orange peel and Jiangxi Liucheng orange peel exhibited 4.5- and 2.8-fold increase after purification, respectively.

Key words: citrus, citrus peel, flavonoids, purification, antioxidation