Helen A. Butts

Heat inactivation of threonine, glycine, and the acidic amino acids.

Abstract Little or no destruction of threonine, glycine, aspartic acid, and glutamic acid occurred when soybean oil meal, soybean protein, or the protein plus sucrose, glucose, dextrin, agar-agar, gum arabic, or soybean oil was autoclaved for 4 hr. at 15 lb. pressure. A portion of each of these amino acids was “inactivated” or tied up in such a manner that the biologically active amino acid could be liberated by acid but not by in vitro trypsin and erepsin digestion. Studies with soybean protein and mixtures of soybean protein and other constituents of soybean oil meal indicated that two types of inactivation occurred during autoclaving. Protein-bound threonine, glycine, and glutamic acid reacted with sucrose or glucose (glycine to some extent with dextrin or agar-agar) to form a linkage resistant to enzymatic but not to acid digestion. Protein-bound aspartic and glutamic acids reacted with some other constituent of the protein to form a linkage resistant to trypsin and erepsin digestion in vitro but hydrolyzed by acid digestion. Part of the second carboxyl groups of protein-bound aspartic and glutamic acids are combined with ammonia as the amide and part are free. It was postulated that the free carboxyl groups react with the free amino groups of lysine and arginine and with the imidazolyl group of histidine to form a peptide-type linkage resistant to enzymatic cleavage.