Combination and precipitation mechanism of soy protein and tea polyphenols

Non-covalent interactions of plant proteins and polyphenols is often occurred in food production and processing. However, the combination of the two may form a precipitate to reduce the aesthetic value and taste. In this study, we prepared different proportions of soy protein isolate (SPI) and catechin/epigallocatechin-3-gallate (EGCG) non-covalent complexes. The structural and conformational changes of the complex in the noncovalent interaction system were explored by multi-spectral technology, and the transition mechanism from the solution-state to the precipitation-state was analyzed. As a "bridge", polyphenols made more SPI cross-linked and aggregate, and reduce hydrophobicity. The enhancement of resonance Rayleigh scattering further confirmed the formation of macromolecular particles. SPI mainly combined with catechin/EGCG through hydrogen bonds, and more benzene rings and phenol hydroxyl structure of EGCG were conducive to the formation of a more stable complex with protein. In addition, the increase of polyphenol concentration promoted the conjugation effect (hydrophobic interaction and electrostatic interaction) with protein, resulting in insoluble high molecular weight aggregate precipitation.