An Assessment of the Phenolic Content, Composition and Antioxidant Capacity of Selected Indigenous Vegetables of Zimbabwe

Indigenous vegetables are valuable sources of nutrients and they are also being recognized for their therapeutic potential due to the presence of bioactive compounds in them. Phenolic compounds are ubiquitous in foods of plant origin, and they constitute an integral part of the human diet. Interest in phenolic compounds has greatly increased recently because these phytochemicals have been implicated in suppressing rates of degenerative processes such as cardiovascular disorders and cancer. The objectives of the present study were to determine the total phenolics content and antioxidant activity of traditional vegetables consumed in Zimbabwe. Total phenolic contents of Bidens pilosa (Black jack), Cleome gynandra (Cats' whiskers), Corchorus olitorius (Bush okra), Galinsoga parviflora (Gallant soldier) and Amaranthus hybridus (Amaranth) were determined by the Folin Ciocalteu method. The antioxidant activities of the plant extracts were determined by the DPPH radical scavenging assay. The individual phenolic acids in the extracts were determined using HPLC. The reducing power and the beta-carotene assays were used as model systems. All the vegetables had high total phenolic content ranging from 10.02 to 51.10 mg/g. The methanolic extracts had DPPH radical scavenging capacity significantly higher when compared to ascorbic acid and catechin. The vegetable extracts showed significant reducing power and prevented the bleaching of beta-carotene. Predominant phenolic acids in the wild vegetables included gallic acid, protochatechuic acid, hydroxybenzoic acid, catechin, caffeic acid, vanillic acid, coumaric acid and ferullic acid. The traditional leafy vegetables, Amaranthus hybridus, Galinsoga parviflora, Corchorus olitorius, Bidens pilosa and Cleome gynandra, had high antioxidant activities and total phenolics. The results also suggest that these indigenous vegetables are good sources of phenolic acids, which can be useful for the prevention of cardiovascular and other chronic diseases. The indigenous vegetables may help remove the stigma of "starvation food" for poor people and promote them as a healthy food source.