Dose-dependent ultrasound mediated TGase catalysis: Mechanistic insights into the dynamic balance between protein unfolding and covalent cross-linking for yeast protein film modification

To enable high-value utilization of yeast-derived protein, this study developed an ultrasonication-transglutaminase (TGase) synergistic modification strategy for yeast protein film (YPF), and systematically elucidated its structure-activity regulation mechanism, addressing the research gap in synergistic modification of yeast protein-based edible films. The core innovation is the discovery of the dose-dependent threshold effect of ultrasonication, which governs the dynamic balance between protein unfolding and TGase-mediated covalent cross-linking: low power (100 W) fails to effectively unfold protein and inhibits TGase activity, while excessive power (500 W) causes protein over-unfolding and slightly disrupts preformed cross-linking bonds. The optimal 300 W ultrasound unlocks protein conformations via cavitation and shear forces, exposes Gln/Lys cross-linking sites, and promotes ε-(γ-glutamyl)-lysine covalent bond formation, thus constructing a dense network dominated by hydrophobic interactions and stabilized by hydrogen bonds. Multiscale characterizations (ATR-FTIR, AFM, TGA, etc.) confirmed that optimized YPF has maximized strong-binding water content, significantly reduced water solubility and swelling degree, comprehensively improved thermal stability and light barrier property, along with retained excellent UV shielding performance. This strategy realizes high-value conversion of yeast-derived protein, and provides a novel technical route and molecular mechanistic basis for developing high-performance eco-friendly food packaging materials, with both scientific innovation and industrial application potential.