Comparisons of in vitro antioxidant activities of storage proteins in tuber of two Dioscorea species

Dioscorin was purified by DE-52 ion exchange chromatography from two yam species, Dioscorea alata L. cv. Tainong 1 (TN1) and Dioscorea batatas Decne (imported from Japan, JP). By different in vitro antioxidant tests, including DPPH radical and hydroxyl radical scavenging activity assay, a reducing power test, an anti-lipid peroxidation test, DNA damage protection, and inhibition of dihydrorhodamine 123 oxidation by peroxynitrite, it was shown that dioscorins from the two species exhibited different scavenging activities against DPPH and hydroxyl radicals, even after heating 100°C for 5 min. Dioscorins from TN1 were hydrolyzed by pepsin for different durations and the peptic hydrolysates exhibited DPPH radical scavenging activities. Peptic hydrolysates separated by Sephadex G-50 (F) gel filtration were tested for anti-DPPH radical activity. Results showed that fractions of smaller molecular weight still have antioxidant activities.