Regulation of disulfide bond cleavage on the physicochemical and digestive properties of EGCG-gluten covalent complexes

Disulfide bond critically govern gluten structure and its covalent interactions with polyphenols, ultimately determining gluten-polyphenol complex properties. This study investigated how disulfide bond cleavage modulates gluten structure, enhances epigallocatechin gallate (EGCG)-gluten covalent binding, and regulates the physicochemical/digestive properties of their complexes. Sodium metabisulfite treatment (0–25 mM treatment) induced disulfide bonds cleavage, which promoted the structural unfolding and exposed reactive groups for covalent binding with EGCG. With analysis of particle size, fluorescence spectroscopy, fourier-transform infrared spectroscopy, and thermogravimetric analysis, disulfide bond cleavage significantly reduced the particle size (from 124.5 to 62.26 μm) of gluten, altered the secondary (α-helix decreased from 23.4 % to 15.1 %, β-sheet from 32.8 % to 23.7 %) and tertiary structures of gluten, increased its surface hydrophobicity and enhanced its binding efficiency (from 51.98 % to 62.02 %) with EGCG. With increase of disulfide bond cleavage, EGCG-gluten covalent complexes exhibited enhanced thermal, pH, and oxidation stability, along with strong antioxidant activity. In addition, the disulfide bond cleavage of gluten inhibited the premature releasing and degradation of EGCG from covalent complexes during the digestion process, which was beneficial for improving the bioaccessibility of EGCG. All results suggest that the disulfide bond cleavage of gluten improve the physicochemical and digestive properties of EGCG-gluten covalent complexes, which provides a potential approach to regulate the properties of proteins-polyphenols covalent complexes as delivery systems of active compounds for functional foods and nutraceuticals.