Characterization of Non-Covalent Interactions Between Whey Protein and Tannic Acid

Whey protein and tannic acid (TA) are important functional components that have been extensively studied, but the concentration-dependent effects of TA on the physicochemical characteristics and functional properties of WPI remain insufficiently characterized. Here, whey protein isolate (WPI, 10 mg/mL) and TA at various concentrations (0–2 mg/mL) were employed to prepare WPI-TA complexes, which were studied by different analytical techniques. In comparison with WPI, WPI–TA association resulted in concentration-dependent changes in the overall UV absorption characteristics of the system. FTIR analysis further indicated changes in the spectral characteristics associated with WPI–TA interactions after TA addition, although the contribution of TA-related absorption could not be completely excluded. The results suggested that hydrogen bonding may contribute to WPI–TA association, although the involvement of other non-covalent interactions cannot be excluded. The reduced apparent free sulfhydryl content in WPI–TA complexes suggested changes in the sulfhydryl environment or the accessibility of sulfhydryl groups in WPI. Furthermore, WPI–TA interactions led to increased particle size, significantly (p < 0.05) improved emulsifying and foaming properties, and alterations in the thermal transition behavior of the protein. Therefore, this study offers an effective approach to the modification of whey protein by polyphenols to obtain functional ingredients for potential application in functional foods.