Effects of catechins with different structure characteristics on the structure and properties of gluten-catechin covalent complex.

Effects of catechins with different structure characteristics on the structure and properties of gluten-catechin covalent complex were investigated, and the structure-activity relationship was further explored. Catechins including epicatechin (EC), epigallocatechin (EGC), epicatechin-3-gallate (ECG), and epigallocatechin-3-gallate (EGCG) could successfully covalently bind with gluten through C-N and/or C-S bonds. The physicochemical properties of covalent complex, including particle size, thermal stability, content of free amino groups, free sulfhydryl groups and disulfide bonds, were significantly affected by different catechins, and the action order was: EGCG > ECG > EGC > EC. Multispectral analysis indicated that catechins significantly changed the tertiary and secondary structures of covalent complex, while galloylated catechins (ECG and EGCG) showed stronger capability than non-galloylated catechins (EC and EGC). Furthermore, the in vitro protein digestibility of covalent complexes reduced with all catechins, and its polyphenols release rate and antioxidant activity were improved. Combining multispectral analysis and molecular dynamics simulation, the hydroxyl group at 5th position in B ring and the galloyl group at 3rd position in C ring played an important role to affect the covalent binding of catechins and gluten, while the amount of hydroxyl groups and the molecule size of catechins both significantly affected its capability to covalently bind with gluten.