Adding functionality to milk-based protein: Preparation, and physicochemical characterization of β-lactoglobulin-phenolic conjugates

Multi-functional phenolic emulsifiers were prepared by covalently coupling beta-Lactoglobulin (beta Lg) to caffeic acid (CA) using crosslinker chemistry at different pH conditions (pH 2.5, 6.0, and 8.5). The resulting bioconjugates were characterized by MALDI-TOF MS, differential scanning calorimetry (DSC), fluorescence-quenching, infrared and circular dichroism spectroscopies. Furthermore, the emulsifying and antioxidant properties of beta Lg-CA conjugates were evaluated and compared to native beta-Lactoglobulin and the non-covalent beta-lactoglobulin/caffeic complex (beta Lg/CA). Results showed: 1) An optimal molar ratio (8: 1) of caffeic acid to beta Lg was obtained at pH 6; 2) DPPH activity of beta Lg-CA increases as the number of CA units coupled increases; 3) beta Lg-CA conjugates displayed comparable or superior water solubility than native beta Lg and beta Lg/CA. Moreover, DSC results showed that coupling of CA with beta Lg significantly increased the thermal stability of beta Lg. In summary, beta Lg-CA conjugates can act as effective antioxidant emulsifiers and stabilizers and may find application in food and cosmetic industries.