Chemical composition and nutritional evaluation of a cowpea protein concentrate

Abstract

Cowpea protein concentrate was prepared by isoelectric precipitation, under optimum conditions
determined in a previous study. The concentrate contained 86.90 % of the flour total protein, and had 85.82
protein. Sugars and ash were in lower contents in the concentrate compared to the flour, while Fe and Zn
contents were not significantly (p> 0.05) different. Phytates and polyphenols were eliminated in abundance
during protein extraction and presence of trypsin and α-amylase inhibitors in the concentrate suggested
application of an adequate heat treatment before its use in food products. The concentrate in vitro protein
digestibility was high (86.81-88.74 %), and had a balanced essential amino acid composition compared to
the FAO/WHO reference pattern. Tryptophan and total sulphur amino acids were first and second limiting
amino acids. The predicted protein efficiency ratio, essential amino acids index and biological value
indicated the good quality of cowpea protein concentrate, although elimination of tryptophan and sulphurrich
proteins during protein extraction affected the chemical score and protein digestibility corrected amino
acid score.