Characterization of soybean lipophilic protein gel catalyzed by Transglutaminase/Genipin: Focusing on pH-ultrasonication modification and vitamin E/quercetin Co-encapsulation

Emulsion gel is widely used in the delivery of functional components because of its network structure and mechanical properties. In this study, to improve the structural and functional properties of emulsion gels and achieve efficient encapsulation and release of functional components, transglutaminase (TGase) and genipin were employed to crosslink pH-shifting/ultrasonication-modified soybean lipophilic protein (SLP), enabling the simultaneous encapsulation of vitamin E (VE, oil phase) and quercetin (QU, aqueous phase), thereby developing a co-encapsulated emulsion gel system. The impacts of combined modification (pH-ultrasonication) and enzymatic/chemical crosslinking on gel properties were systematically investigated through gel strength analysis, rheological characterization, intermolecular interaction profiling, microstructural observation, and in vitro digestion evaluation. Results demonstrated that pH-shifting combined with ultrasonication exposed more hydrophobic groups in SLP, thereby enhancing intermolecular hydrophobic interactions. Microstructural analysis revealed that TGase and genipin synergistically strengthened network crosslinking density, forming a more compact gel network structure under modified conditions. Furthermore, TGase/genipin crosslinking significantly improved structural characteristics and rheological performance (e.g., water-holding capacity increased by 14.97 %, hardness and viscosity improved), while concurrently enhancing encapsulation efficiencies of both VE and QU. In vitro digestion test confirmed that the maximum release rate reached 97.43 ± 1.50 % (VE) and 90.39 ± 2.43 % (QU) ( p  < 0.05). These findings elucidated the potential for constructing emulsion gels via combined modification and crosslinking strategies, providing theoretical guidance for co-encapsulation systems in functional factors delivery applications.