Effects of Ferulic Acid and Xanthan Gum Interaction on Structural Characteristics and Antigenicity of β-Lactoglobulin

The structural characteristics of proteins change when they are complexed with polyphenols and polysaccharides. This study investigated the synergistic effects of ferulic acid (FA), a dietary polyphenol, and xanthan gum (XG) at different mass concentrations on the structural characteristics and antigenicity of β-lactoglobulin (β-LG). The structural changes of β-LG after binding with FA and XG were analyzed using ultraviolet-visible (UV-Vis) absorption spectroscopy, intrinsic fluorescence spectroscopy, synchronous fluorescence spectroscopy, three-dimensional fluorescence spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and molecular docking simulation. The impact of β-LG-FA-XG binding on protein antigenicity was evaluated using an indirect competitive enzyme-linked immunosorbent assay. The results demonstrated significant changes in the microenvironments around tryptophan and tyrosine residues after the complexation, along with an increase in the polarity. Furthermore, the secondary structure of the protein changed; as the mass concentration of XG increased, the relative content of β-sheets first increased and then decreased, while the relative contents of α-helices and β-turns first decreased and then increased. The relative content of random coils showed no clear trend. In addition, compared with β-LG, the β-LG-FA-XG ternary complex exhibited a significantly reduced binding capacity to immunoglobulin G (IgG), indicating decreased antigenicity. The highest IgG binding capacity inhibition rate of 17.97% was observed at an XG mass concentration of 0.10 mg/mL.