Characterization of Whey Protein Isolate-Soymilk Complexes Modified by Transglutaminase and Their Application inYuba...

Transglutaminase (TGase) improves protein structure by facilitating cross-linking reactions. However, the effects of TGase on the physicochemical properties of whey protein isolate (WPI)-soymilk complexes and their applications in yuba remain unclear. Therefore, the impacts of TGase concentration on the free sulfhydryl content, free amino content, particle size, and structure of WPI-soymilk complexes and their film-forming properties were studied. The results showed that the physicochemical properties of the composite soymilk were changed by the TGase-induced cross-linking reaction of protein. Compared with the composite soymilk without TGase modification, the particle size of the WPI-soymilk complexes increased from 707.99 ± 9.47 nm to 914.41 ± 2.8 nm as the TGase concentration increased, and the complexes remained relatively stable at low TGase concentrations. TGase modification changed the tertiary structure of the WPI-soymilk complexes. The composite yuba with 0.01% and 0.03% levels of TGase had a higher β-sheet content than composite yuba without addition of TGase. The surface hydrophobicity of composite soymilk was decreased by all the addition levels of TGase. Meanwhile, the TGase-modified composite protein with 0.03% TGase had the lowest free sulfhydryl (35.92 μg/g) and amino groups (0.46). Additionally, the tensile strength of the composite yuba with 0.05% TGase addition reached a peak of 1.66 ± 0.02 MPa, which was 7.8% higher than that of the composite yuba without TGase addition. The SEM results revealed that the composite yuba with 0.01-0.03% TGase addition exhibited a dense and non-porous film structure. Moreover, all the composite yuba with TGase addition had a reduced rate of yuba cooking loss. This study contributes to enhancing the yield and mechanical properties of traditional yuba.