Comparative analysis of non-covalent complexation between isomeric polyphenols and soy protein isolate: Focus on...

This study aimed to investigate the differences in interaction mechanisms between soy protein isolate (SPI) and isomeric polyphenols (quercetin, Que/morin, Mor) at varying concentrations (0-1.6 mM). It also examined the oil/water (O/W) interfacial properties and emulsion stability of the complexes (SQ/SM). Polyphenol binding equivalents (PBE) and SDS-PAGE results showed that SPI formed non-covalent complexes with Que/Mor, with PBE peaking at 0.8 mM (3.08 and 2.72 mmol/mg protein). Multispectral analysis including fourier transform infrared spectra, two-dimensional correlation spectra, ultraviolet and fluorescence spectra revealed that polyphenols bound to SPI through hydrogen bonds and hydrophobic interactions. These induced unfolding of the secondary structure (conversion of β-sheet to disordered structures) and tertiary conformational changes in the protein. Meanwhile, the particle size increased after Que/Mor complexed with SPI, and electrostatic repulsion weakened. The combined molecular docking found that Que exhibited stronger binding affinity to SPI than Mor (7S-Que/Mor, -8.5/-8.1 kcal/mol). The hydrogen bond played a crucial role in the formation of SQ. Furthermore, polyphenol-modified SPI showed a more balanced hydrophilic/hydrophobic (contact angle approaching 90°), reduced interfacial tension, and accelerated interfacial protein adsorption. The complexes stabilize the emulsion system through a networked "bridging" structure. The appropriate amount of Que/Mor reduced emulsion particle size, enhanced size distribution uniformity, and improved emulsion stability and rheological properties. SQ had superior interfacial and emulsifying properties compared to SM. This work will provide theoretical basis for studying the interaction mechanisms between isomeric polyphenols and proteins, as well as for developing highly stable soy protein functional products.