Formation and characterization of soy protein isolate-chitosan-epigallocatechin gallate ternary complexes: Molecular interactions and functional properties

In this study, ternary complexes using soy protein isolate (SPI), chitosan (CS), and epigallocatechin gallate (EGCG) were prepared, and the non-covalent interaction mechanisms between SPI-CS and EGCG were explored through multispectral techniques. The impact of varying EGCG concentrations (0.1–0.5 mg/mL, corresponding to approximately 0.22–1.09 mmol/L) on the properties of SPI-CS complexed microgels was studied under different pH (3.0–7.0) and NaCl (0–400 mM) conditions. The findings confirmed the successful formation of a new ternary complex, as shown by structural alterations in the SPI-CS binary complexes upon the addition of EGCG, as evidenced by quenched intrinsic fluorescence and a red shift in the maximum fluorescence emission peak. The secondary structure analysis revealed a reduction in β-sheet content accompanied by an increase in α-helix structures. FTIR results indicated that electrostatic interactions, hydrogen bonding, and hydrophobic interactions played key roles in the interactions between SPI-CS and EGCG. These structural changes also influenced the thermal stability of the complexes. Furthermore, EGCG increased the apparent viscosity, yield stress, and viscoelastic moduli (G′ and G″), while also improving the tribological performance of the SPI-CS systems. Overall, this study offers foundational insight into the potential utilization of SPI-CS-EGCG complexes in food applications.