pH-governed Tannic Acid Bridging Modulates Myofibrillar Protein/κ-Carrageenan Ternary Gel Networks

Protein-polysaccharide binary gels often suffer from limited cross-linking density and insufficient control over network compactness and water immobilization. In this study, we developed a myofibrillar protein (MP)/κ-carrageenan (KC)/tannic acid (TA) ternary gel system and investigated how TA concentration and pH regulate polyphenol-mediated network assembly. MP/KC mixtures were incorporated with TA at 0.50–0.65% and the pH was adjusted accordingly. The result shows TA addition promoted MP unfolding and ternary interactions among MP, KC, and TA, resulting in a denser and more continuous gel network. Notably, pH 6.4 provided a favorable charge-balance window for TA-mediated bridging. The gel prepared with 0.60% TA at pH 6.4 exhibited the best water retention, with water holding capacity (WHC) increasing from 48% in the binary control to 73%. Meanwhile, TA addition significantly changed the zeta potential from –18.1 mV to –25.6 mV, indicating enhanced electrostatic stability. Concurrently, reactive sulfhydryl content decreased from 75.6 nmol/mg to 48.3 nmol/mg with increasing TA, while α-helix content dropped from 53 to 38%, confirming TA-induced MP unfolding. Meanwhile, gel porosity decreased from 8.4% in the control group to 2.1%, further confirming the formation of a denser network structure. However, excessive TA addition led to over-cross-linking and network contraction, which increased structural stiffness but reduced water retention. As the concentration of TA continued to increase, WHC decreased to 69%. These findings indicate that pH acts as a molecular switch controlling TA-mediated bridging in MP/KC/TA ternary gels, offering a mechanism-based strategy for designing meat protein gel systems with tunable texture, WHC and microstructure. Graphical