Physicochemical properties, antioxidant activities, and binding behavior of 3,5-di-O-caffeoylquinic acid with beta-lactoglobulin colloidal particles.

Milk proteins and polyphenols are increasingly being studied as functional ingredients due to the epidemiologically-proved health benefits. In this study, composite ß-lactoglobulin (ß-lg) or ß-lactoglobulin nanoparticles (ß-lgNPs)-3,5-di-O-caffeoylquinic acid (3,5diCQA) with superior physicochemical and antioxidant activity (AA) were produced using ß-lg and 3,5-di-O-caffeoylquinic acid. The main interactions between ß-lg or ß-lgNPs with 3,5diCQA were hydrogen bonding and hydrophobic effects. The 3,5diCQA caused a decrease in α-helix and ß-sheet structure with a corresponding increase in unordered structure. Compared to ß-lg alone, composite ß-lg or ß-lgNPs-3,5diCQA slightly decreased the particle size but increased their negative surface potentials especially for ß-lg or ß-lgNPs at a molar ratio of 5:1. The addition of 3,5diCQA appreciably improved the AA in a dose-dependent manner. These results shed light on the structural, physicochemical, and AA of composite ß-lg or ß-lgNPs-3,5diCQA non-covalent complexes, important for application as functional ingredients in food solutions as well as in the pharmaceutical industry.