The Relation of the Amino Acid-Sugar Reaction to The Nutritive Value of Protein Hydrolysates

Abstract

In the presence of glucose the nutritive quality of protein hydrolysate solutions deteriorates. Extensive decreases in biological value upon drying such solutions are accompanied by “browning” of the preparations. The intensity of the color is to some degree related to the extent of deterioration of the nutritive quality. The reduced biological value results from the reaction of amino acids with glucose. Feeding experiments with pure amino acid supplements indicate that histidine, threonine, tryptophan, phenylalanine, lysine and methionine become unavailable to the animal. Leucine, isoleucine and valine were not appreciably affected. Relatively small losses in amino acids as measured by microbiological assay were associated with drastic changes in nutritive value for animals. There appears to be an important difference in the nutritional availability to animals and to microorganisms of the amino acid-glucose reaction products. It is suggested that an amino acid-glucose complex is formed which is unavailable to the rat but relatively more available to the microorganism. This raises the question of the validity with respect to nutritional problems of amino acid microbiological assay values for heat damaged proteins.