Gelation Properties of Transglutaminase-Induced Soy Protein Isolate and Wheat Gluten Mixture with Ultrahigh Pressure Pretreatment

In this study, we elucidated the microbial transglutaminase-induced gelation properties and thermal gelling ability of soy protein isolate (SPI) and wheat gluten (WG) mixture following ultrahigh pressure (UHP, 100-400 MPa) pretreatment. UHP treatment induced unfolding and aggregation within SPI/WG protein molecules, which led to increases in free sulfhydryl group content and surface hydrophobicity. However, the transglutaminase cross-linking reaction facilitated the formation of hydrophobic interactions and disulfide bonds and thus resulted in higher gel strength, water holding capacity, and denser and more homogeneous gel networks of transglutaminase cross-linked SPI/WG gels. Rheological measurements revealed that the addition of UHP steps might generate a higher storage modulus (G') value of MTGase-induced SPI/WG gelation during the heating-cooling cycle (25 A degrees C -> 95 A degrees C -> 25 A degrees C). Our results indicated that various chemical interactions including covalent interactions (i.e., epsilon-(gamma-glutamyl)lysine bonds and disulfide bonds) and non-covalent interactions (i.e., electrostatic forces and hydrophobic interactions) were involved in SPI/WG gel network structures. Hydrophobic interactions and disulfide bonds are significantly increased with the pressure level (100-400 MPa) compared with that of the unpressurized control. Furthermore, UHP treatment reduced the alpha-helix and beta-turn content but increased the beta-sheet and random coil structures. Thus, UHP treatment may be considered as a novel technique to expand the utilization of SPI/WG mixture in the food protein gelation industry.