Effect Of Transglutaminase On Gel Properties Of Wheat Protein And Soybean Protein Mixtures

This paper studied the effect of transglutaminase (TGase) on the gel properties of the mixtures of wheat proteins and soybean proteins, and analyzed the effect of thermal treatment on the functional groups and the structure of the mixed proteins. Furthermore, this method was applied to the processing of lactone tofu, and its influence of the quality of lactone tofu was studied. The main conclusions are as follows:(1) The effect of transglutaminase on the gel properties of the mixtures of wheat proteins and soybean proteins was investigated by analyzing its surface hydrophobicity, free sulfhydryl contents, thermal properties, and secondary structures. The results showed that when the mixture ratio of soybean proteins was less than 45%, the gel strength significantly increased with the increasing rate. After treating by TGase, the thermal stability of the mixed protein gels increased, while the free sulfhydryl content and the surface hydrophobicity of it decreased. Comparing with the wheat protein treated by TGase, the gel strength and the β-sheet content of the mixed protein gels containing 45% soybean proteins was increased by 62.74% and 5.70%, respectively, while the free sulfhydryl content of the mixed protein gels decreased by 47.48%.(2) The effect of reductants and the ionic strength on the separation of 11S and 7S proteins were studied, the optimized separation conditions were as follows:0.98 g/L of NaHSO4 and 0.25 M of NaCl. The results showed that, after treating by TGase, the mixture gels of wheat proteins and soybean proteins (SPI gels) had the largest gel intensity, followed by 7S protein gels and 11S protein gels in turn, which is the opposite of their surface hydrophobicities.(3) The effect of the thermal treatment on the gel properties of the T Gase-treated mixed proteins was investigated. The results showed that, comparing with the untreated mixed protein gels, the gel strength and the β-sheet content of the mixed protein gels significantly increased with the increasing proportion of soybean proteins in the mixtures, while the free sulfhydryl contents and surface hydrophobicities of the mixtures decreased. When pre-heated for 20 min, compared with the untreated mixed protein gels, the gel strength and the β-sheet content of the mixed protein gels increased by 31.09% and 6.84%, respectively, while the free sulfhydryl content of the mixtures decreased by 35.05%. The results of the scanning electron microscopy showed that the reticular structure of the mixed proteins was denser and the porosity extent of the proteins was increased after heating.(4) The influence the above pre-heated methods on the quality of lactone tofu was studied. The optimal reaction conditions was adding 0.3%(w/w) of lactone to tofu and then heated at 50℃ for 2.5 h. After adding 150 U TGase, compared with the untreated lactone tofu, the gel property of the lactone tofu reached the maximum value of 85.22%, while the adhesiveness of the lactone tofu decreased by 52.71%. And the hardness, the springiness, the chewiness and the resilience of the lactone tofu increased by 52.99%, 13.86%,57.44% and 13.64%, respectively.