Binding effects of piceatannol and oxyresveratrol on the structural and functional properties of soy protein isolate

•The interactions of SPI with PIC or OXY were investigated.•The secondary structure of SPI was altered due to the binding of PIC or OXY.•The emulsifying and foaming properties of SPI were enhanced.•Synergistic antioxidant effects between PIC/OXY and SPI were observed.•PIC−SPI and OXY−SPI complexes have the stomach-protective effect. Piceatannol (PIC), oxyresveratrol (OXY), and soy protein isolate (SPI) are essential dietary molecules. This study evaluated the interaction between PIC/OXY and SPI using multiple spectroscopic techniques and molecular docking simulations. The static quenching mechanism was confirmed by steady-state fluorescence, Förster resonance energy transfer (FRET), and time-resolved fluorescence (TRF) spectroscopy. The binding affinity of PIC to SPI was stronger than that of OXY, and the interactions were spontaneous and exothermic. The subtle change in the secondary structure of SPI after the addition of PIC or OXY can be ascertained by analyzing the surface hydrophobicity, sulfhydryl group content, particle size, zeta potential, and α-helical content. The emulsifying and foaming properties of SPI were enhanced after complexing with PIC/OXY. The thermodynamic parameters and molecular docking results demonstrated that PIC and OXY bound to SPI at the same sites, and that van der Waals forces (vdW forces) and hydrogen bonding (H-bonding) were the main interaction forces. In addition, the results also showed that the encapsulation of SPI can enhance the antioxidant activity of PIC and OXY. The in vitro gastrointestinal digestion of PIC and OXY in the absence or presence of SPI was evaluated. This study can be used as a reference for further research on the digestion and absorption of SPI−PIC/OXY complexes and as a guide for healthy diets. [Display omitted]