ANTIOXIDANT ACTIVITY OF SELECTED MEDICINAL-PLANTS

Commonly used medicinal plant extracts with standardized content of po lyphenols were investigated for their total antioxidant activity(TAA). Green tea, oligomeric procyanidins (from grape seed and pine bark), b ilberry, and ginkgo exhibited TAA in the range of 5.12-2.57 mM Trolox, thereby indicating a valuable antioxidant capacity. Witch hazel, prop olis EPID, artichoke, and hawthorn afforded lower TAA (1.54-0.44 mM Tr olox), whereas echinacea, ginseng, passionflower, sweet clover, and el euthero were rather uneffective (TAA < 0.32 mM Trolox). Excipients nor mally used to prepare the extracts did not interfere with the assay, a nd a good correlation between the content of polyphenols and the TAA w as assessed. The measured TAB was higher than those calculated from th e content and antioxidant potential of specific components, as exempli fied for green tea and ginkgo extracts. This may be attributed to the presence in these extracts of other substances with antioxidant capaci ty. On the other hand, some components (such as ginkgolides in ginkgo extract) insensitive to the TAA assay played an important antioxidant role in vivo. These results suggest that TAA determination is of inter est for a comparative evaluation of in vitro antioxidant potential, bu t it needs to be combined with in vivo data for adequate assessment of the antioxidant capacity of medicinal plant extracts.