Covalent modification of zein with polyphenols: A feasible strategy to improve antioxidant activity and solubility

Covalent modification of protein with polyphenols is an attractive research topic, since it is an effective way to improve the properties and broaden the applications of protein. However, the majority of prolamin-polyphenol reactions were carried out in alcohol aqueous solution, and this study aimed to investigate the covalent interaction of zein and polyphenols in water. Chlorogenic acid (CGA), gallic acid (GA), and caffeic acid (CA) were used as polyphenol models. The grafting ratio revealed that zein interacted more strongly with CGA and CA than with GA, which was probably due to the larger molecular weight of CGA and the hydroxycinnamic acid structure of CA. Afterward, the differences in structural and functional properties between control zein and zein-polyphenol complexes were compared. Covalent interaction with polyphenols induced great changes in the morphology and secondary structure of zein. Compared with control zein and non-covalent complexes, covalent zein-polyphenol complexes exhibited better solubility, antioxidant activity, and thermal stability. PRACTICAL APPLICATION: Covalent modification of zein with polyphenols in water is a simple and efficient method, which can ameliorate the antioxidant activity as well as the hydrophilicity of zein and improve its application value. The findings of this research carry important implications for using zein-polyphenol complexes as novel food additives, or to design more efficient delivery systems.