Gel properties of transglutaminase‐induced soy protein isolate–polyphenol complex: influence of epigallocatechin‐3‐gallate

Abstract BACKGROUND Traditional soy protein isolate (SPI)‐based gel products, such as tofu, are generally produced by heating and by addition of metal salt ions to adjust the hydrophobicity and electrostatic force of soybean protein to facilitate the formation of a uniform network structure. However, the gelation rate of the soy protein gel network structure is difficult to control. Theoretically, epigallocatechin‐3‐gallate (EGCG) could be used to alter the surface hydrophobicity of thermally induced SPI to improve its gelation rate and form a more uniform network structure, thus improving SPI‐based gel properties (hardness, water holding capacity and rheological properties). RESULTS An SPI‐EGCG complex (SPIE) was prepared, and properties of the resulting gel, following induction of transglutaminase (TG), were evaluated. Results showed that EGCG is bound to thermally induced SPI primarily via hydrophobic and hydrogen bonding, thus altering the secondary structure composition and reducing surface hydrophobicity of proteins in thermally induced SPI. Furthermore, the optimum amount of EGCG required to improve the gel strength, water holding capacity and rheological properties was ≤0.04:1 (SPI 1 g L −1 ; EGCG:SPI, w/w). Thermal stability analysis further indicated that EGCG in SPIE was more stable than free EGCG after heating. CONCLUSION This study demonstrated that EGCG can improve the gel properties of TG‐crosslinked SPIE, while EGCG in SPIE exhibits enhanced thermal stability. Additionally, the results of this study provide a novel strategy for the development of SPI‐based gel foods with improved gel properties and that are enriched with bioactive compounds. © 2020 Society of Chemical Industry