Protein source-dependent effects of deamidated proteins on TGase-mediated crosslinking and thermal gelation of soy protein.

Soy protein isolate (SPI) has been used in the development of structured foods due to its nutritional and functional properties. However, a predominance of hydrophobic-driven aggregation in SPI thermal-induced gels often results in low mechanical strength and limited water-holding capacity (WHC). This study applied the deamidated proteins with different molecular properties and distinct dominant interaction mechanisms, including egg white protein, bovine serum albumin, gelatin, and casein, together with transglutaminase (TGase)-mediated crosslinking to improve SPI thermal gel properties. The impact of different types of heterologous proteins and their intermolecular interaction mode on molecular assembly, gelation behavior, and gel properties was systematically investigated. Compared with SPI alone, all TGase-treated SPI/deamidated heterologous protein combinations showed increased particle size and molecular weight. The high-molecular-weight aggregates in the samples were detected by GPC, SEC-MALLS, and SDS-PAGE, indicating the formation of TGase-mediated covalent crosslinking. TGase-crosslinked composites gelled at significantly lower temperatures and exhibited end-point elastic moduli 1-2 orders of magnitude higher than SPI, reflecting accelerated gelation and stronger networks. The texture analysis and compression tests revealed pronounced improvements in the physical properties of the gels, such as hardness, deformation resistance, and WHC, with disulfide bond-dominated protein systems exhibiting the most effective reinforcement and yielding the strongest gel networks. Intermolecular force analysis and ATR-FTIR demonstrated protein-dependent reinforcement mechanisms, while confocal microscopy corroborated dense, finely interconnected network architectures in disulfide bond-rich systems. This work provides a practical framework for improving SPI gels by selecting deamidated proteins with suitable molecular properties to produce high-performance plant-based structured foods.