A Microbiological Approach to Nutritional Evaluation of Proteins

Abstract

This method employs the digestion of proteins with panereatin and subsequent testing of the growth-promoting activity of the hydrolysate for Streptococcus faecalis, in a medium devoid of the 10 essential amino acids. The nutritive value of the protein digest is detd. in a single assay by the amino acid liberated in a limiting concn. The results obtained with casein, egg albumin, gelatin, gluten, and zein are presented and their agreement with the biological values obtained by the rat growth method is suggested. The growth promoting activity (biological value) of casein and egg albumin is high and about equal; gelatin and gluten, in comparison, are much less active, 29 and 15%, respectively, and zein still less, 2%. At the limited growth level, casein is deficient in: lysine, arginine, isoleucine, and threonine. Egg albumin under comparable conditions is limited in lysine, arginine, histidine, threonine, isoleucine, leucine, and valine. Gelatin is low in tryptophan, isoleucine, leucine, methionine, and threonine. Gluten and zein are low in lysine. The suitability of the method descr. for studying imbalances of amino acids is proposed.