Characterization of the Hydrogel-Binding Mechanism of Phellinus linteus Polysaccharides and Polymerized Whey Protein by SR-IR Technology and Its Application in Goat Milk Yogurt

The development of natural biopolymers to improve the structural and textural defects of whey protein in acidic dairy products is of great interest. This study investigated the interaction between Phellinus linteus polysaccharides (PLPs) and heat-induced polymerized whey protein (PWP), and its application in goat milk yogurt. The physicochemical properties and interaction mechanisms of PWP-PLP composite hydrogels (with 1–4% PLP) were characterized using particle size, DSC, and synchronous rheology and Fourier transform infrared spectroscopy. The results show that PLP increased hydrogel particle size, absolute zeta potential (from −34.98 mV to −42.26 mV), and denaturation temperature (from 102.33 °C to 112.57 °C), indicating the enhanced stability. SR-IR analysis revealed intensified hydrogen bonding and protein secondary structure rearrangement. Incorporated into yogurt, the optimal composite (10% PWP with 3% PLP) significantly improved water-holding capacity (by 20–30%), storage modulus (G′), and produced a denser microstructure with superior texture. This work demonstrates that PLP is an effective natural modifier for constructing stable protein–polysaccharide hydrogels to enhance yogurt quality.