Effect of soaking, dehulling and boiling on protein, polyphenolic and antinutrient content of cowpeas (Vigna unguiculata L. Walp)

Abstract

Legumes are good sources of protein and are rich in lysine and tryptophan, which are limiting amino acids in cereals. Common legumes include sugar beans, soya beans and cowpeas. Although soya beans are an important commercial legume, cowpea (Vigna unguiculata L. Walp) varieties grown by some communities in developing countries have many food and non-food uses. The objective of this study was to determine the effect of soaking, dehulling and boiling on the protein, polyphenolic and antinutrient content of cowpea varieties, namely CBC2 and CBC4. Phenols, tannins, flavonoids, alkaloids and saponins were present in the cowpea varieties. Boiling caused a significant (p≤0.05) decrease in the protein content of both cowpea varieties. Soaking for 24 hours resulted in an insignificant (p>0.05) change in the protein content of CBC2, but significantly (p≤0.05) decreased the protein content of CBC4. On the other hand, dehulling seeds soaked for 6 hours resulted in a significant increase (p≤0.05) in the protein content of both varieties. Boiling caused a significant decrease (p≤0.05) in total phenolic content (TPC), total flavonoid content (TFC), and content of condensed tannins and saponins in both cowpea varieties. Also, soaking for 6, 12, 18 and 24 hours significantly (p≤0.05) decreased the content of these phytochemicals. The greatest losses in TPC, TFC, condensed tannins and saponins for both varieties were observed in seeds soaked for 6 hours and dehulled samples. The results of this study show that boiling, soaking and dehulling reduced the protein, polyphenolic and antinutrient content of the cowpea varieties.