Comparative Analysis of Phenolic Composition and Antioxidant Effect of Seed Coat Extracts of Four Cowpea (<i>Vigna unguiculata</i>) Varieties on Broiler Meat

Abstract

Seed coat crude extracts of white-coloured ITA-256, white and brown-coloured TVS-716, deep brown-coloured IT-90K and light brown-coloured Ife brown cowpea varieties were analyzed for the presence and amount of total phenol, tannin and flavonoid content. Crude extracts of the cowpea varieties were analyzed for antioxidant activity using the Thiobarbituric Acid (TBA) assay. The seed coat extracts were added sepa-rately to 200 g of minced broiler meat sample at the rate of 0.05% of the weight of the meat and their effect compared to that of the synthetic antioxidant, butylated hydroxyl anisole (BHA) added to the meat at the rate of 0.05%. Each sample was divided into 16 parts of 12.5 g each. Eight of these were cooked while the other 8 parts were left raw. Antioxidant effect of the seed coat extracts was determined during refrigerated storage of raw and cooked minced broiler meat. All the cowpea varieties studied except TVS-716 contained phenol, tannin and flavonoids. TVS-716 contained only phenol and tannin. Seed coats extract from Ife brown contained higher levels of total phenol, tannin and flavonoids than the corresponding samples of IT-90K, ITA-256 and TVS-716. IT-90K had higher tannin content than ITA-256 and TVS-716 but its phenol and flavonoids content are not significantly different (P>0.05) from that of ITA-256. TBA assay shows that all the additives and BHA were able to reduce lipid oxidation in broiler meat. This was shown by lower TBARS values in broiler meat samples with added additives compared to the con-trol samples (meat without additives). Seed coat extracts of Ife brown, ITA-256 and IT-90k reduce lipid oxidation more than BHA in raw broiler meat samples but are less potent than BHA in cooked meat sam-ples. Seed coat extracts of Ife brown was more effective than other cowpea varieties in reducing lipid oxida-tion in both cooked and raw meat samples. The antioxidant potential of IT-90K was not significantly differ-ent (P>0.05) from that of ITA-256 while TVS-716 exhibited the least antioxidant potency.