Polymerization of soy protein digests by microbial transglutaminase for improvement of the functional properties

The protease- and acid-treated soy proteins were polymerized by microbial transglutaminase (TGase) in order to improve their functional properties. Although the protease digests and acid hydrolysates were considerably insoluble, the soy protein digests or hydrolysates polymerized by TGase were soluble, despite being composed of higher molecular weight fractions ((11.8-99.4)x10(6)) compared to that of the native soy protein (0.48x10(6)). The surface hydrophobicity of the polymerized proteins was greatly decreased, compared to that of the protease digests and acid hydrolysates, suggesting that the exposed hydrophobic residues of the polymerized peptides were buried inside the polymerized molecules. The emulsifying properties of the polymerized soy proteins were greatly improved compared to those of the untreated, protease- or acid-treated proteins. The foaming properties of the polymerized soy proteins were also improved. The bitterness of the protease digests and acid hydrolysates of soy proteins was diminished by the polymerization with TGase treatment. (C) 1997 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd.