Interactions between Zein and Polyphenols and Characterization of Their Complexes

This study investigated the non-covalent interactions between zein and each of three polyphenols, and the structure and antioxidant properties of zein-polyphenol complexes in ethanol-water solution using a fluorescence spectrophotometer and an ultraviolet (UV) spectrophotometer. The zein-polyphenols colloidal particles were characterized for their turbidity, particle sizes and microscopic morphology, and the effect of polyphenols on the self-assembly of zein colloidal particles was discussed. The results showed that the polyphenols could statically quench the fluorescence of zein. Zein bound to tannic acid (TA) and epigallocatechin gallate (EGCG) by hydrogen bonds, and the binding constants decreased with increasing temperature, thereby impairing the binding capacity. Zein and gallic acid (GA) were combined by hydrophobic interaction to form a complex, and increased temperature was conducive to the interaction between them. The molar binding ratios of the three polyphenols to zein were all nearly 1:1. In addition, after the combination of polyphenols and zein, the UV absorbance of the complexes was significantly increased, the mode of protein folding was changed, the hydrophobic group was buried, and the antioxidant activity and thermal stability of the non-covalently bound complexes was increased. The non-covalent interaction between zein and TA increased the particle size of the complex, and decreased the surface charge. The microstructure of the composite particles showed a regular spherical shape. TA could act as a cross-linking agent for the particles. Similarly, the surface characteristics and microstructure of the composite nanoparticles formed by zein with EGCG or GA were changed. However, the colloidal particles were not cross-linked obviously and still uniformly dispersed.