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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. [Display omitted] • Theanine improved gel strength and water holding capacity of soy protein isolate. • Theanine bound to 7S and 11S globulin by hydrogen bonds and van der Waals forces. • Moderate theanine changed protein conformation and enhanced molecular interaction. [ABSTRACT FROM AUTHOR]

This study aims to elucidate the changes and corresponding mechanisms of storage stability of soy protein isolate (SPI) films strengthened via wheat bran cellulose (WBC) and cellulose nanocrystals (CNC). The incorporation of WBC and CNC improved the mechanical strength, water resistance, water vapor and visible light barrier abilities of stored SPI-based films to varying degrees. Higher crystallinity and lower water mobility were observed in the composite films. WBC molecules reduced the irregular pores and cracks within the internal structure of the film through physical filling and non-covalent interactions, involving hydrogen bond and van der Waals force. In contrast, uniformly distributed CNC cross-linked with amino acid residues at specific binding sites under non-covalent forces. Furthermore, CNC induced the secondary conformation of proteins to transform from α-helix to β-sheet and enhanced the hydrophobic interaction, which promoted the establishment of a stable network structure and thus extended the storage stability of SPI-based films. [Display omitted] • Cellulose and cellulose nanocrystals improved storage stability of protein film. • Cellulose improved structural integrity by filling and non-covalent interaction. • Binding sites of cellulose chains and proteins were analyzed via molecular docking. • Nanocellulose modified protein conformation and enhanced intramolecular interaction. [ABSTRACT FROM AUTHOR]