Controlled thermal unfolding of soy protein isolate modulates transglutaminase-induced gelation and network structure of fish gelatin.

Mixed-protein gel systems have emerged as an effective strategy for tailoring textural and structural properties in sustainable food systems. In this study, the effects of varying ratios (1:1, 2:1, 4:1) and thermal pretreatment (75, 85, 95 °C) of soy protein isolate (SPI) on the gelation behavior of transglutaminase (TGase)-crosslinked fish gelatin (FG) were systematically investigated. The results showed that TGase-induced FG-SPI complexes exhibited strengthened intermolecular interactions. However, the globular structure of native SPI constrained the formation of a dense and continuous porous microstructure characteristic of TGase-crosslinked FG, thereby reducing the gel strength of the mixed gels. Preheating SPI at 75 °C promoted partial unfolding of the protein, generating additional TGase-accessible reactive sites and intensifying hydrophobic interactions and disulfide bonding, which collectively improved the gel strength and textural properties of the FG-SPI gels. These findings provide a robust framework for designing tunable, sustainable mixed-protein gels for diverse food applications.