Effect of thermal treatment on whey protein polymerization by transglutaminase: Implications for functionality in processed dairy foods

The effect of thermal treatment of whey proteins (50 g/100 g) at 75, 80, 85, 90 and 95 °C before enzymatic treatment with microbial transglutaminase was evaluated by rheological measurements. Thermal denaturation of whey proteins was determined by differential scanning calorimetry (DSC); and the gel point and turbidity were also evaluated after addition of transglutaminase at different pH values in protein solutions. A significant (p < 0.05) interaction was observed between transglutaminase and thermal treatments. At temperatures higher than 85 °C the apparent viscosity measurements of whey protein solutions with transglutaminase were significantly higher than those of the control samples. DSC analysis showed that thermal denaturation occurred at temperatures close to 82 °C, and the enzymatic reaction was enhanced at higher temperatures. The gel point of whey proteins decreased with transglutaminase addition. This decrease became greater as a function of reaction time due to the formation of high weight protein polymers catalyzed by transglutaminase, which was also observed in the turbidity analysis.