Study of soybean protein isolate-tannic acid non-covalent complexes by multi-spectroscopic analysis, molecular docking, and interfacial adsorption kinetics

In this study, non-covalent complexes of soybean protein isolate (SPI) and tannic acid (TA) were prepared, and the interaction mechanism between SPI and TA was investigated by multiple methods of multi-spectroscopy and molecular docking techniques. The non-covalent binding to TA resulted in a reduction of the α-helix and β-sheet contents and a decrease in the fluorescence intensity. The fluorescence-quenching mechanism and molecular docking analysis determined that TA statically quenched the fluorescence of SPI with a binding constant of 1168 L/mol, a binding site number of 0.99, ΔG < 0, ΔH of −32.666 kJ/mol, and ΔS of −0.0466 kJ/mol, and the interaction between SPI and TA was dominated by hydrogen bonding. The interfacial adsorption kinetics study revealed that the maximum diffusion rate of the SPI-TA complex was 0.06771, which occurred at 1.0 mg/mL of TA. The emulsification activity index and emulsion stability index of the complexes under these conditions were 98 m2/g and 48.3 min, respectively. The above findings help to elucidate the mechanism of non-covalent binding of SPI with TA and promote the application of protein-polyphenol complexes in emulsions.