Relationship between relative protein value and somein vitro indices of protein quality

Abstract

Besides amino acid composition of a protein, their bioavailability is an important determinant of the protein quality. In view of the observations over the last decade or two, implicating the small peptide uptake by the mammalian intestine as a major route of protein absorption, a few animal and plant proteins were subjected to sequential enzymatic digestionin vitro with pepsin, pancreatin + trypsin and erepsin and the release of amino acids as small (including dipeptides) and large peptides and free amino acids, was determined. The relative protein values of α-lactalbumin, egg whites, casein, gluten, zein and protein isolates of soyabeans and groundnuts was determined using rat growth method. It was observed that relative protein value were positively correlated with the essential amino acid index of protein, quantity of essential amino acids released as small peptides and the dipeptide content of enzymatic digests, while there was a negative correlation between relative protein value and essential amino acid content of large peptide fraction.