Protein fractions, in vitro protein digestibility and amino acid composition of select cowpea varieties grown in Ethiopia

Cowpea is a drought-tolerant legume consumed as a high-quality plant protein source in many parts of the world. In this study, crude protein contents, Osborne fractions, in vitro protein digestibility and amino acid composition of proteins of 5 different cowpea varieties (Asebot, Asrat, Bekur, TVu and WWT) were investigated. The crude protein contents varied from 28.1 to 31.8 g/100 g. Results showed that the globulin and albumin fractions were the predominant protein fractions, accounting for 38.4-49.1 and 19.6-22.5% of the total protein, respectively; followed by glutelins contributing from 6.4 to 10.4%, while prolamins were 1.0-1.14%. In vitro protein digestibility (IVPD) of cowpea flour ranged between 68.7 and 72.0%. IVPD showed a significant negative correlation with phytic acid (r = -0.673) and globulins contents (r = -0.846), and did not correlate with tannins content. The amino acid analysis showed that proteins were mainly comprised of non-essential amino acids: Glx and Asx (including Gln and Asn). Except for Ile and His, the amino acid score of the cowpea varieties was below the FAO/WHO requirement for essential amino acids for infants and preschool children. Trp was the first limiting amino acid for all varieties except for TVu, followed by the sulphur-containing amino acids. On the basis of crude protein content, digestibility and balance of essential amino acids, WWT, Bekur and TVu varieties can be recommended for value added food products and in breeding programs to develop high protein quality cowpea varieties.