Studies on the antioxidative activities of hsian-tsao (Mesona procumbens Hemsl) leaf gum

This study aimed at evaluating the antioxidative activity of crude hsian-tsao leaf gum extracted by sodium bicarbonate solutions and precipitated by 70% ethanol. The antioxidative activities, including the radical-scavenging effects, Fe2+-chelating ability, and reducing power as well as the inhibition of FeSO4-H2O2-induced malondialdehyde formation in rat tissue homogenate were studied in vitro. It was found that the antioxidative effect provided by hsian-tsao leaf gum was strongly concentration dependent. In general, the antioxidative activity increased with increasing gum concentration,-to a certain extent, and then leveled off with further increase in gum concentration. A concentrtaion-dependent kinetics for the rate of change in antioxidative activity was proposed. The antioxidative activity constant (k) and the half-inhibition concentration (IC50) for each antioxidative reaction studied were calculated. From a comparison of the IC50 values far different antioxidative reactions, it seemed that hsian-tsao leaf gum was more effective in scavenging superoxide radicals than chelating Fe2+ or scavenging alpha,alpha -diphenyl-beta -picrylhydrazyl (DPPH) radicals. As compared to the commercial antioxidants, hsian-tsao leaf gum showed less scavenging effect on the DPPH;radical and reducing power but better superoxide radical-scavenging effect and Fe2+-chelating ability than alpha -tocopherol and BHT.