An assessment of the phenolic content, composition and antioxidant capacity of Bidens pilosa, Cleome gynandra, Corchorus olitorius, Galinsoga parviflora and Amaranthus hybridus

Indigenous vegetables are valuable sources of nutrients and they are particularly recognized for their antioxidant properties. Total phenolic contents of Bidens pilosa, Cleome gynandra, Corchorus olitorius, Galinsoga parviflora and Amaranthus hybridus were determined by the Folin Ciocalteu method and all the vegetables had high total phenolic content ranging from 10.02 to 51.10 mg g-1. The results of the Folin Ciocalteau method analysis demonstrated that these leafy vegetables had antioxidant potential, which may be attributed to their phenolic composition. The methanolic extracts had DPPH (1,1-diphenyl-2 picrylhydrazyl) radical scavenging capacity significantly higher when compared to ascorbic acid and catechin. Bidens pilosa had the highest DPPH radical scavenging capacity and Cleome gynandra had the lowest. The order of scavenging activity was Bidens pilosa>Amaranthus hybridus>Corchorous olitorius>Galinsoga parviflora>Cleome gynandra. A relationship was established between the antioxidant activity of these vegetables and the total phenolics content. The results showed that phenolics content and activity were weakly correlated (r2=0.49) and the relationship was significantly nonlinear (runs test). The vegetable extracts also showed significant reducing power and prevented the bleaching of β-carotene. In the β-carotene assay Corchorous olitorius had the highest capacity and Cleome gynandra had the lowest. The order of activity in the β-carotene assay was Corchorous olitorius>Bidens pilosa>Galinsoga parviflora>Amaranthus hybridus>Cleome gynandra. Predominant phenolic acids in the wild vegetables included gallic acid, protochatechuic acid, hydroxybenzoic acid, catechin, caffeic acid, vanillic acid, coumaric acid and ferullic acid. Heating the vegetables caused significant reduction in the types and quantity of the phenolic acids; hence people should use minimal heat to preserve them. Consequently and provided bioavailability of these micronutrients, the consumption of these vegetables may provide the indispensable antioxidants needed for good health, as indigenous vegetables in tropical Africa have been reported to have medicinal properties which include anti-bacterial, anti-rheumatic, anti-cancer and anti-malarial activity.