Rheological Properties And Thermal Denaturation After Enzymatic Modification Of Whey Protein By TGase

Transglutaminase is a good protein cross-linking agent, and adding a small amount of transglutaminase can significantly improve the quality of dairy products and economic benifits. Whey protein cross-linking, and cross-linking of whey protein between other proteins under transglutaminase have been reported. However, there are some controversies for the conditions used in the cross-linking processing. Additionally, research on the viscosity and thermal denaturation characteristics of the crosslinked products have not been reported. Therefore, it is significant to explore and study in this area. The objectives of this thesis were to optimalize the crosslinking of whey protein isolated, crosslinking between whey protein isolated and soy protein,between whey protein isolated and casein via transglutaminase, respectively, and to measure the rheological properties of the crosslinked products. Three experiments were conducted.SDS-PAGE gel electrophoresis and imaging analysis were used for the comparison of preheated whey protein at 80℃for 15min with the products from 6% whey protein isolate crosslinking, or with soy protein or casein by transglutaminase at 80℃for 15 min after adding reducing agent (20mmoL / L) under denaturing conditions. Gel imaging analysis of changes in protein bands, mid-infrared spectroscopy and electron microscopy were used to determine the existence of cross-linked products. Based on the results of single factor experiments, 5 levels of catalytic time, catalytic temperature, pH, and enzyme / protein ratio of crosslinking were arranged with a four-factor 5 levels orthogonal regression rotation design or 4-factor 4-level orthogonal experimental design to optimalize the crosslinking conditions and measure the viscosity and differential thermal changes of the crosslinking products.The results showed that whey protein per se, whey protein and soy protein, whey protein and casein under the condition of heating at 80℃for 15min with a certain amount of reducing agent DTT (20mmoL/L) could be cross-linked and cross-linking effect is remarkable. At the catalytic time of 4h, catalytic temperature of 50℃, pH 8.0 and enzyme amount 20u / g, the whey protein crosslinked product had the highest viscosity value (4.05mPa.s). Thermal denaturation study showed that whey protein isolate without transglutaminase treatment had a maximal thermal denaturation temperature of 61.07℃, while treated with transglutaminase the products had a highest thermal denaturation temperature of 101.11℃.In another experiment, crosslinked products obtained at catalytic time of 4h, catalytic temperature is 50℃, pH8.0 and enzyme amount 10u / g had the largest viscosity value (6.19mPa. s).products of whey protein isolate and soy protein with or without the treatments of transglutaminase had a maximum thermal denaturation temperature of 87.37℃,or 114℃,respectively.The last experiment indicated that crosslinked products obtained at catalytic time of 4h, catalytic temperature of 50℃, pH8.0 and enzyme amount 10u / g, had a highest viscosity value (5.55mPa.s). The crosslinked products had a highest thermal denaturation temperature of 96.02℃while the control had a denaturation temperature of 70.28℃.These results indicated that whey protein perse, whey protein and soy protein, whey protein and casein can be cross-linked in certain conditions, and resulted in the changes of the functional properties. The research results provide a new approach for the development and utilization of whey protein.