Alkaline and radical-mediated covalent bonding of zein-epicatechin gallate: mechanism analysis, structural evolution,...

The pronounced hydrophobicity and poor aqueous solubility of zein substantially limit its food applications. Zein-epicatechin gallate conjugates were prepared using alkaline (pH 7, 9, 12) and free radical-mediated methods. Multispectroscopic, physicochemical, and bioactivity analyses were employed to assess structural and functional changes. Alkaline treatment at pH 12 induced marked reddish-brown discoloration and the lowest grafting efficiency. Covalent modification quenched intrinsic fluorescence, reduced α-helix content and free sulfhydryl groups, and increased β-turn proportion. Conjugates exhibited improved solubility, thermal stability, in vitro digestibility, oil-water interfacial adsorption, and antioxidant activity. Grafting efficiency and conformational changes were key determinants of functional enhancement, with conjugates prepared under alkaline conditions at pH 9 achieving the optimal balance between structural integrity and bioactivity. This study elucidates pH-dependent covalent interaction mechanisms and associated structure-function relationships, providing a rational basis for designing tailored hydrophobic protein-based functional composites for food applications.