Theanine improves the gelation of soy protein isolate by modifying protein conformation and enhancing molecular interaction

This study systematically investigated the dose-effect relationship and regulatory mechanism of theanine on the gelling properties of soy protein isolate (SPI). The results indicated that the strength and water holding capacity of 0.10% theanine-SPI gel increased by 238.80% and 1.13% compared with pure SPI gel, respectively. Hydrogen bonds and van der Waals forces mainly promoted the binding of theanine to β-conglycinin and glycinin. This binding could further change the protein aggregation state (reducing particle size and irregular aggregation), functional groups (exposing more hydrophilic amino acid residues and sulfhydryl groups), and molecular structure (α-helix and β-turn transforming into β-sheet). Furthermore, a more uniform and dense three-dimensional gel network was formed in the composite gels, offering the structural basis for improving the performance of the SPI gel. The results will provide theoretical basis and technical support for the precise regulation of gel properties of the functional amino acid-SPI complex as well as the efficient creation of new SPI-based foods.