Mechanisms of transglutaminase-induced crosslinking in hybrid surimi/plant protein gels: A focus on mechanical properties and microstructure.

Elucidating the distinct mechanisms between legume and cereal proteins in hybrid surimi/plant protein (HSP) gels crosslinked by transglutaminase (TG) is essential for achieving precise texture modulation. This study investigated the differential responses of legume proteins (soy and pea) and cereal proteins (wheat and rice) on the structural and functional properties of HSP-TG gels. Texture profile analysis revealed that gels prepared with legume proteins exhibited significantly higher resilience (0.58-0.59) than those with cereal proteins (0.54-0.55, p < 0.05), indicating superior elastic recovery in the former and greater rigidity in the latter. Rheological measurements showed that the legume protein systems exhibited stronger intermolecular interactions at the sol stage. Microstructural characterization indicated that the cereal protein HSP-TG gels formed coarse, porous network frameworks, whereas the legume protein gels displayed more compact aggregate structures. SAXS analysis revealed that rice protein gels exhibited features of inhomogeneous, low-density protein aggregates in the low-Q range (0.01-0.03 Å-1). Meanwhile, laser diffraction analysis demonstrated significantly increased aggregate sizes in legume protein gels (e.g., pea protein D75 increased from 170.80 μm to 236.55 μm). Molecular mechanism analysis showed that cereal proteins underwent substantial tertiary structure unfolding during the first heating stage at 40 °C, while legume proteins unfolded mainly during the second heating stage at 90 °C as revealed by UV and fluorescence spectroscopy. SDS-PAGE and HPLC-MS/MS analyses confirmed that myosin contributed more to crosslinking in cereal protein gels, forming abundant heterologous crosslinking interfaces (e.g., myosin and plant protein), whereas legume protein gels primarily featured homologous crosslinking. In summary, the rigidity of cereal protein gels stemmed from a loose, heterogeneous structure formed by TG-catalyzed heterologous crosslinking networks, while the compactness of legume protein gels resulted from densely packed intraphase aggregation dominated by homologous crosslinking. These insights establish a structure-property relationship that enables targeted textural design in hybrid gels through rational protein selection, supporting the development of tailored, reduced‑sodium surimi products.