Regulation of Tea Polyphenols on the Gel Properties of Soy Protein and the Action Mechanism

Effects of non-covalent interactions between tea polyphenols (TPs) and soybean protein isolate (SPI) on the structural and functional properties of soy protein gels were investigated, and the potential action mechanism was further explored. SPI was firstly non-covalent bound with TP to form the SPI-TP gel, and its structural characteristics, physicochemical properties, rheological properties, and digestion properties were determined. TP exhibited the strong capability to form hydrogen bonds and/or hydrophobic interactions with SPI, which was concentration-dependent. Moderate addition of TP could effectively regulate the strength of different interactions in gel, such as interactions of proteins and interactions between proteins and water molecules, thereby yielding gels with good gel strength and hydration capacity. With increase of addition concentration, TP showed the capability to induce protein structural unfolding and formed new non-covalent interactions with proteins, which facilitated the formation of a more robust and uniform gel network, thereby improving gel's properties. However, excessive addition of TP caused the excessive cross-linking of protein, ultimately compromising gel strength and structural stability. Additionally, during in vitro digestion, the addition of TP reduced the digestion of protein in gel but significantly enhanced the antioxidant properties of the digesta. All results suggest that TPs have the potential to effectively regulate the structure and function of SPI gels, which provides the theoretical guidance and research foundations for the application of protein-polyphenol complexes as functional food ingredients or biomaterials in food and chemical industries.