Functional Evaluations of Soy Yogurt: Influence of Soy Protein Isolate‐Chitosan‐Epigallocatechin Gallate Complexed Microgels on Structure and Tribology

This work explores how soy protein isolate-chitosan-epigallocatechin gallate (SPI-CS-EGCG) ternary complexes influence the structural and functional characteristics of soy yogurt. The study particularly focuses on how these complexes interact with soy milk proteins during acid-induced gelation and how they modify the final gel matrix. The addition of SPI-CS-EGCG microgels significantly enhanced the nutritional composition of soy yogurt, increasing protein content from 3.83% to 5.22% (p < 0.05) and total phenolic content from 0.06 to 0.09 mg gallic acid equivalents per gram (p < 0.05), while significantly reducing fat content from 2.16% to 1.90% (p < 0.05). In terms of functionality, the fortified yogurts exhibited stronger textural properties, such as greater firmness, elasticity, and viscosity, as well as improved water-holding capacity. Rheological testing revealed higher apparent viscosity and shear modulus values in the fortified samples. The SPI-CS-EGCG complexes also promoted earlier aggregation of soy proteins during fermentation, initiating gelation at a higher pH (6.14) compared to the control (pH 5.61). Moreover, the modified yogurts exhibited significantly improved lubrication performance, as indicated by lower friction coefficients across the sliding speed range, particularly at speeds above 6000 µm/s compared with the control (p < 0.05), suggesting improved mouthfeel characteristics. Overall, the integration of SPI-CS-EGCG complexes effectively improved both the nutritional and structural properties of soy yogurt, offering a promising strategy for developing high-quality plant-based fermented products.