Soy protein-phlorizin conjugate prepared by tyrosinase catalysis: Identification of covalent binding sites and alterations in protein structure and functionality

Tyrosinase-catalyzed synthesis of soy 7S/11S-phlorizin conjugates was performed, and the reaction sites, conformation alterations and functional properties of complexes were evaluated using proteomic, in combination with multispectral technologies. Phlorizin was conjugated to 7S/11S primarily via residues of Lys, Cys, His and Arg residues. The phlorizin binding equivalents and decreased contents of free and total sulfhydryl groups and free amino groups confirmed the covalent interaction in the 7S/11S-phlorizin complexes. Conjugation with phlorizin promoted the conversion of alpha-helix to beta-sheet and beta-turn, with simultaneous transformation of the microenvironments around Trp and Tyr residues to hydrophilic and hydrophobic microenvironments, respec-tively, and lowering of the surface hydrophobicity of 7S/11S. The DPPH and ABTS radical scavenging abilities and alpha-glucosidase inhibitory activities of 7S/11S were increased by three-, two- and three-fold after the covalent binding of phlorizin. The study provided an ideal tyrosinase-catalyzed approach to fabricate custom-tailored nutritional soy protein-polyphenol products.