Availability of essential amino acids from proteins. I.—beef serum albumin

Abstract

Available essential amino acids from beef serum albumin were determined microbiologically, after total enzymic hydrolysis of the protein by papain, leucine aminopeptidase and prolidase. Samples of pu: e beef serum albumin of different moisture content were heat-treated with glucose at 90" or without it at 121 .In the enzymic digest of the protein, available essential amino acids were determined using Streptococcus faecalis, S. zymogenes and Lactobacillus arabinosus. The content of essential available amino acids was correlated with the degree of in virro digestibility of heat-treated albumin.The amount of lysine determined by Carpenter's method with ff uordinitrobenzene did not correspond to the values found for lysine by microbiological analysis with S. faecalis. Lysine reactive with fluordinitrobenzene was found in the non-digestible residue of the protein, so that the values obtained by the chemical method are probably higher than the actual amount of available lysine. The results for the trypsin digest of the albumin were similar by both methods. The availability of lysine as well as that of amino asids in general depended on the enzymic digestibility.