Antioxidant activity of some medicinal and dietary African vegetables

Seven medicinal and dietary plant species from Southern Africa were analysed for their antioxidant and total phenolic content. These were Lippia javanica, Tagetes minuta, Bidens pilosa, Vigna unguiculata, Amaranthus spinosus, Telfairia occidentalis and Corchorus olitarius. Aqueous methanol extracts were tested for free radical scavenging and anti-oxidant activity using three standard assays including 2,2′azinobis-(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS), 1,1-diphenyl-2-picrylhydrazyl (DPPH) and ferric reducing antioxidant potential (FRAP). The Folin-Ciocalteu assay was used to determine the total phenolic content with gallic acid as a standard. The antioxidant activity of the plants ranged from 0.76 to 5.77 mmol TEAC/100 g (ABTS), 16.29 to 1711.22 mmol TEAC/100 g (DPPH) and 0.58 to 6.12 mmol TEAC/100 g (FRAP). B. pilosa and C. olitarius had the best activity in all assays, while V. unguiculata and A. spinosus were the least active. The total phenolic content ranged from 19.79 to 333.56 mg gallic acid equivalent (GAE)/100 g. In general, there was a good correlation between antioxidant activity and total phenolic content. These results imply that these plant species may possess health promoting effects and might be potential sources of potent natural antioxidants