Studies on antioxidative activity of yam (Dioscorea alata) peel and meat portion

[[abstract]]The purposes of this study were to evaluate the antioxidant abilities of ethanol and water extracts from one kind of Taiwanese yam peel and flesh, Darson (Dioscorea alata), and to evaluate the effects of blanching, drying and extraction methods on the antioxidant activities. The antioxidant measurements included total phenolic content, reducing power, and Diphenyl-pricryl-hydrazyl (DPPH) radical scavenging activity. Mouse liver cell (FL83B) and liver caner cell (Hepa 1-6) were used as the cell models to evaluate the influence of ethanol and water extracts from yam flesh and peel on the survival of the cells, the levels of hydrogen peroxide and malondialdehye (MDA), as well as the activities of antioxidant enzymes, such as catalase, Superoxide dismutase (SOD) and Glutathione peroxidase (GPx). The results showed that all the 50% ethanolic, hot water and water extracts from the peel had much higher total phenolic content, reducing power and DPPH radical scavenging activity than the extracts from the flesh. Among three extraction methods, 50% ethanolic extraction resulted in the highest antioxidant activity in the peel, while hot water extraction was more appropriate for the flesh. Blanching by immersing the peel in 85 oC water for 30 sec caused significant reductions in the antioxidant activities of all the extracts from the peel. Generally speaking, freeze-dried peel maintained higher antioxidant activities than hot-air dried peel did. In the cellular antioxidant evaluations, the ethanolic extract from the peel showed great protective ability toward FL83B and Hepa 1-6. However, the extracts from the flesh and peel did not decrease the levels of 25 and 50 mM tert-butyl hydroperoxide (t-BHP) induced hydrogen peroxide. The SNP induced lipid peroxidation in Hepa 1-6 decreased by the extracts from both yam flesh and peel, but the extract from the flesh showed higher inhibitory effect on the level of MDA in FL83B than the extract from the peel. For cellular antioxidant enzymes measurement, both ethanol and water extracts from Darson yam peel and flesh increased SOD and GPx activities in Hepa 1-6 cells, but they decreased the catalase activity. In FL83B, the ethanol extract from Darson yam peel showed the highest increase in the activities of SOD and GPx; however, all the extracts would not increase the catalase activity