Effect of Lipase on Soybean Oil-Wheat Gluten Systems: Rheological Behavior and Molecular Mechanisms

This study investigated the regulatory effects of lipase on the viscoelastic behavior and microstructural evolution of soybean oil–wheat gluten (SOWG) composites in a model system. Dynamic frequency sweep and creep-recovery tests showed that lipase addition significantly influenced the viscoelastic properties of SOWG after 60 min of relaxation at 37°C, with optimal effects at 800 U/g. This dosage effectively maintained elasticity and recovery ability. Molecular-level analysis indicated enhanced hydrophobic interactions and reduced exposure of fluorescent groups, while also inhibiting covalent cross-linking (e.g., disulfide bond formation). Size exclusion chromatography revealed a broader molecular weight distribution in lipase-treated samples, suggesting a more complex network structure. FTIR analysis showed that 800 U/g lipase stabilized β-sheet content, whereas excessive addition (2000 U/g) reduced structural order and storage modulus by 43% and induced irregular macroporous regions (> 5 μm). In contrast, moderate lipase levels (800 U/g) promoted a more uniform and compact gluten network, with an optimized average pore size of 2.1 ± 0.4 μm. Correlation analysis revealed a synergistic relationship between viscoelastic parameters (e.g., network area, branch length, k and J values) and microstructural evolution, indicating that lipase enables multiscale regulation to improve the structural and rheological properties of SOWG composites.