Analysis of phenolic content and antioxidant properties of selected cowpea varieties tested in bovine peripheral blood

Cowpea is an important grain legume with a dual purpose function as a food and feed resource. Cowpea contains phenolic compounds that are beneficial to human and animal health. We evaluated the phenolic content, condensed tannin content and antioxidant capacities of methanol extracts of seed and leaf of seven varieties commonly used in food and animal feed. The total phenolic content and condensed tannins were quantified using the Folin-Ciocalteu and Vanillin-HCL method respectively. The effects of cowpea phenolic extract on total antioxidant capacity, glutathione peroxidase and superoxide dismutase activity was evaluated in vitro in bovine blood. Overall, the methanol extracts of the leaves contained high concentrations (p<0.0001) of total phenolic content (290.51±38.02 mg GAE/g) compared to seed extracts (118.10±71.96 mg GAE/g), although high antioxidant capacity was observed in both extracts. In addition, a positive correlation was found between total phenol and tannins content and antioxidant capacity of the extracts. Treatment with cowpea phenolic extract increased (p<0.0001) the total antioxidant capacity in cow blood (5.33±0.27 mM UAE) relative to controls (1.62±0.10 mM UAE). The enzymatic activities of GSH-Px and SOD were also increased. Our findings, suggest the potential of cowpea polyphenols to reduce oxidative stress in livestock production. Results of the present study showed that leaf and seeds of cowpea possess rich amounts of natural antioxidants and can be further explored for their possible use as a natural additive in food or use in pharmaceutical industries and in animal feed.