Tremella Fuciformis Polysaccharides and Maillard Reaction Improve the Gel Properties of Whey Protein: The Changes in Gel Structures and Digestibility

Background:The application of whey protein isolate (WPI) is limited by an associated instability at low temperatures, as well as the high brittleness and shrinkage of pure WPI gels. Protein–polysaccharide interactions can effectively improve the structural integrity and stability of food systems. This study aimed to investigate the mechanism through which Tremella fuciformis polysaccharide (TPS) modifies and functionally regulates WPI gels at varying concentrations (0–10%) via the Maillard reaction.Methods:TPS–WPI composite gels with varying TPS concentrations were prepared via a thermally induced Maillard reaction, with an unheated mixture serving as the control. The extent of the Maillard reaction was characterized by the grafting degree (DG), browning intensity, and fluorescence intensity of advanced glycation end-products (AGEs). Water-holding capacity (WHC), textural properties, and rheological behavior were evaluated. Gel microstructure and intermolecular interactions were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). Gastrointestinal digestion was also simulated in vitro.Results:TPS induced structural modifications and functional enhancement in WPI gels via Maillard reaction-induced covalent cross-linking. DG, browning intensity, and AGEs fluorescence all initially increased and then decreased as TPS concentration increased, reaching peak values at 6% TPS. Cross-linking was primarily driven by disulfide bonds and hydrophobic interactions, resulting in a sponge-like porous microstructure. Higher TPS concentrations (≥6%) grafted onto WPI further improved gel WHC, hydrophilicity, the proportion of amorphous structure, and digestion resistance. The Maillard reaction promoted interactions between WPI and TPS, thereby facilitating gel formation. The resulting cross-linked network increased the overall random coil content and reduced protein digestibility by forming a dense structure.Conclusions:Maillard reaction-mediated covalent cross-linking between TPS and WPI effectively optimized the properties of WPI gels, with 6% TPS identified as the optimal concentration. This study establishes a comprehensive correlation among TPS concentration, the degree of Maillard reaction, gel structure, and digestion resistance, providing theoretical support for the functionalization of protein gels and the application of the Maillard reaction to develop swallowing-friendly gel modifiers.