Improvement in the functional properties of gluten by protease digestion or acid hydrolysis followed by microbial transglutaminase treatment

Insoluble gluten was solubilized by proteases (chymotrypsin, papain, Pronase, and pepsin) or mild acid (0.05 N HCl) treatments. The digests and hydrolysate are turbid, but after transglutaminase (TGase) treatment, the turbid mixture was converted to a transparent solution, which was found to be soluble at a wide range of pH. The hydrophobicity was greatly decreased after polymerization by TGase. SDS-PAGE patterns of the digests and hydrolysate with and without TGase treatment showed that the digests (except Pronase) were polymerized by TGase. The emulsifying properties of the polymerized peptides were greatly improved compared to those of the protease digests and acid hydrolysates. The foaming properties of the polymerized digests were also greatly improved. The digests and hydrolysate were found to have a bitter taste, but after polymerization the bitterness completely disappeared.