Effect of transglutaminase treatment on the functional properties of native and chymotrypsin-digested soy protein

Native and chymotrypsin-digested soy protein were polymerized by transglutaminase (TGase). SDS-PAGE pattern of the polymerized proteins showed that TGase treatment resulted in proteins of higher molecular mass above the stacking gel. The free amino groups of the polymerized proteins were greatly reduced. The solubility of the protein polymer was greatly improved at pH 2 and pH 8–12 whereas, at pH 4 and 6, it was least soluble. The solubility of the digest polymer was significantly improved at all pH levels, except pH 4. The protein polymer started to coagulate when the heating temperature exceeded 50°C. The digest polymer, on the other hand, resisted heat-induced aggregation up to 60°C; thereafter, its solubility declined slightly. The emulsifying and foaming properties of the digest polymer were greatly improved compared to the protein polymer. The protein polymer was observed to form a harder gel than the digest polymer.