Tyrosinase-Catalyzed Soy Protein and Tannic Acid Interaction: Effects on Structural and Rheological Properties of Complexes.

This study investigated the structural, rheological, and microstructural properties of soy protein isolate (SPI) induced by tyrosinase-catalyzed crosslinking with tannic acid (TA) at 25 °C under neutral conditions at pH 6.5. The particle size and polydispersity index of modified SPI progressively increased with rising TA concentrations. Tyrosinase-induced polymerization significantly impacted the conformational structure of SPI, evidenced by a notable decrease in intrinsic fluorescence, a pronounced red shift, and a remarkable reduction in surface hydrophobicity. FTIR analysis further revealed that, compared to control SPI, the amide I, II, and III bands of SPI incubated with TA and tyrosinase exhibited varying degrees of red-shift or blue-shift. These observations suggested a substantial alteration in the secondary structure of SPI after incubation with TA and tyrosinase. The apparent viscosity, G', and G″ of the modified SPI increased with higher TA concentrations, indicating that the modification of SPI by TA in the presence of tyrosinase resulted in enhanced covalent crosslinking. Microstructural observations confirmed that higher TA levels promoted the formation of denser and more uniform gel-like networks. The findings demonstrated that tyrosinase-mediated crosslinking improved the functionality of SPI, making it a promising approach for food applications.