EFFECT OF COOKING ON THE PROFILE OF PHENOLICS, TANNINS, PHYTATE, AMINO ACID, FATTY ACID AND MINERAL NUTRIENTS OF WHOLE‐GRAIN AND DECORTICATED VEGETABLE COWPEA (VIGNA UNGUICULATA L. WALP)

Abstract

ABSTRACT An experiment was conducted to determine the profile of phenolics, tannins, phytate, amino acid, fatty acid and mineral nutrients in whole‐grain and decorticated vegetable cowpea before and after cooking. Two cowpea varieties: C‐152‐White, having big grain and S‐1552‐White, having small grain with black eye were used for the study. Decortication of cowpea grain resulted in significant reduction (P ≤ 0.05) of total phenolics, total tannins and phytate contents of the two cowpea varieties. Comparison showed that cooking resulted in 19, 28, 28 and 37% losses in phenolics in whole‐grain C‐152, decorticated C‐152, whole‐grain S‐1552 and decorticated S‐1552, respectively. After cooking, whole‐grain and decorticated C‐152 retained 52.1 and 57.7% tannins while S‐1552 retained 59.4 and 49.5%, respectively. In the whole grain, C‐152 lost 72.2% phytate after cooking while S‐1552 lost 70.3%. For the decorticated samples, C‐152 lost 72.4% phytate after cooking while S‐1552 lost 71.2%. For the two cowpea varieties, decortication resulted in significant (P ≤ 0.05) losses of Ca, Fe, Mn, Mg, Zn, K and Cu while there was no significant effect on protein and amino acid profile. Cooking did not cause any significant change in the mineral nutrient composition of either the whole‐grain or decorticated cowpea. For the two cowpea varieties, bulk of the fat consisted of palmitic acid (23.2–27.3%) and stearic acid (53.5–59.8%) in the ratio of 1:2, approximately. Upon cooking, losses of crude protein were recorded in the whole‐grain and decorticated samples of the two cowpea varieties.PRACTICAL APPLICATIONSCowpea is an important cheap source of protein particularly for the low‐income countries, especially in Africa and Asia. However, there is the need for some pretreatments before its cooking because of the presence of some undesirable antinutrients which often cause flatulence after consumption or they can render some minerals unavailable for body assimilation. This study investigated the role that African traditional method of decortication and cooking could play in reducing the concentration of antinutritional factors. We also showed how the traditional treatments could affect the other nutritionally important component of cowpea.