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

This study aimed at evaluating the antioxidative activity of crude hsian-ts ao leaf gum extracted by sodium bicarbonate solutions and precipitated by 7 0% ethanol. The antioxidative activities, including the radical-scavenging effects, Fe2+-chelating ability, and reducing power as well as the inhibiti on 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, t he antioxidative activity increased with increasing gum concentration,-to a certain extent, and then leveled off with further increase in gum concentr ation. A concentrtaion-dependent kinetics for the rate of change in antioxi dative activity was proposed. The antioxidative activity constant (k) and t he half-inhibition concentration (IC50) for each antioxidative reaction stu died were calculated. From a comparison of the IC50 values far different an tioxidative reactions, it seemed that hsian-tsao leaf gum was more effectiv e in scavenging superoxide radicals than chelating Fe2+ or scavenging alpha ,alpha -diphenyl-beta -picrylhydrazyl (DPPH) radicals. As compared to the c ommercial antioxidants, hsian-tsao leaf gum showed less scavenging effect o n the DPPH;radical and reducing power but better superoxide radical-scaveng ing effect and Fe2+-chelating ability than alpha -tocopherol and BHT.