The phytochemical and antioxidant properties of Strophantus hispidus (stem and root), Voacanga africana (stem and leaf) and Thevetia neriifolia (stem and leaf) were investigated. The parts of the plants used were based on those used locally. All the plants tested positive for the presence of tannins, flavonoids and cardiac glycosides, all except S. hispidus (stem) tested positive for the presence of anthraquinone. Only V. africana (stem and leaves) and Thevetia neriifolia (leaves) tested positive for the presence of saponins, all except S. hispidus (root) tested positive for the presence of terpenoids. Only V. africana leaves and T. neriifoliatested positive for the presence of phlobatannins. The free radical scavenging activities were investigated based on the presence of flavonoids and tannins in all the plant materials. Preliminary screening of the free radical scavenging activity of the methanolic extracts of the plants with 2,2-Diphenyl-1-picrylhydrazyl (DPPH) using thin layer chromatography only tested positive for V. africana leaves. IC50values (concentration of sample required for 50% inhibition of DPPH radical scavenging activity) for the inhibition of DPPH were 0.048 and 0.054 mg/ml for V. africana and Vitamin C respectively. The phenolic content, total flavonoid content and proanthocyanidin contents of V. africana were determined as, 124, 30 and 90 mg as gallic acid, rutin and catechin equivalents per gram of extract respectively. A good correlation was observed between radical scavenging capacity of V. africanaand total phenolic, total flavonoid and proanthocyanidin content (R2 = 0.96 in all cases), showing that flavonoids are likely to be responsible for antioxidant activity.
Keywords: Antioxidants, free radicals, phenolic content, proanthocyanidin content, total flavonoid, DPPH, Strophantus hispidus, Voacanga africana, Thevetia neriifolia.
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