Free radical scavenging activity of some Nigerian medicinal plant extracts

The present research evaluates the DPPH radical scavenging, total antioxidant activities, reducing power and total contents of phenolic compounds in methanolic leaf extracts of five Nigerian medicinal plants (Dalbergia saxatilis Hook.f. (Papilionacae), Ekebergia senegalensis A.Juss.(Meliaceae), Hymenocardia acida Tul. (Hymenocardiaceae), Icacina tricantha Oliv. (Icacinaceae) and Salacia pallescens Oliv.(Celastraceae). Total phenols were analysed according to the Folin-Ciocalteu method. Each sample under assay condition, showed a dose-dependent effect both on free radical scavenging 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) and also on Fe3+ reducing power. The antioxidant activity of the plant extracts with the DPPH radical scavenging and reducing power method, were in the order Hymenocardia> Ekebergia> Salacia> Icacina> Dalbergia. H. acida and E. senegalensis possess very high radical scavenging activity in both assays. Potency of H. acida extract was of the same magnitude as that of reference α-tocopherol. Total phenols in all the samples expressed as GAE (Gallic Acid Equivalent) varied from 1.83 to 15.47mg g-1 of dry plant material. Total antioxidant activities correlated with total phenols (R2 = 0.6640) an indication that 66% of the antioxidant capacity of these extracts results from contribution of phenolic compounds. A linear positive relationship existed between the reducing power and total phenolics of the tested plant extracts (R2 = 0.9564). © 2006 Asian Network for Scientific Information.