Free radical scavenging and antioxidant activity of plant flavonoids

Several Korean medicinal plants were selected to evaluate for free radical scavenging capacities and antioxidant activities using commonly accepted assays. They were extracted with dichloromethane, methanol or ethanol, respectively and selected for the best antioxidant results. Flavonoids, such as catechin, morin, naringenin, quercetin and rutin, were included and used as standards in this study. Each sample under assay condition showed a dose-dependent free radical scavenging effect of DPPH (1,1-diphenyl-2-picryl hydrazyl radical) and a dose-dependent inhibitory effect of xanthine oxidase and lipid peroxidation. Among plant extracts, the root bark of Morus alba and the leaf of Saururus chinensis showed stronger SC50 or ID50 values than other plant extracts. They also showed a protective effect on DNA damage caused by hydroxyl radicals generated from UV-induced photolysis of hydrogen peroxide. A rapid evaluation for antioxidants using TLC screening and DPPH staining methods demonstrated each plant extract having various free radical scavenging capacity. Stained silica layer revealed a purple background with yellow spots at the location of drops, which showed radical scavenging capacity. The intensity of the yellow color depends upon the amount and nature of radical scavenger present in the samples. This antioxidant potential corresponded with the results of DPPH spectrophotometric assay.