pH-dependent interaction mechanisms between β-lactoglobulin and EGCG: Insights from multi-spectroscopy and molecular dynamics simulation methods

pH values have an important influence on the aggregation state of β-lactoglobulin (β-LG), which affects its ligand-binding properties. In this study, the pH-dependent interaction mechanisms between β-LG and epigallocatechin-3-gallate (EGCG) were explored by multi-spectroscopy and molecular dynamics simulation. Compared to β-LG, the increasing absorbance and blue shift of the maximum wavelength in UV–Vis spectroscopy confirmed the formation of β-LG-EGCG complexes. Fluorescence data showed that the quenching of β-LG by EGCG was mainly static quenching at different pH values, and the interaction between β-LG and EGCG was endothermic and spontaneously driven by hydrophobic interactions. Fourier transform infrared spectroscopy (FTIR) and circular dichroism (CD) studies demonstrated that the interactions between EGCG and β-LG caused slight changes to the secondary structure of β-LG. Molecular dynamics (MD) simulation elucidated that EGCG preferred to bind to the pocket of β-LG at pH 7.0 (dimer) and 5.3 (tetramer), which consisted of two I lamellae and an α-helix. However, the binding site of EGCG at pH 2.5 (monomer) was located on the outer surface of β-LG due to the closure of β-barrel structure of β-LG. Moreover, the binding free energies had a trend of pH 7.0 > pH 5.3 > pH 2.5, which was consistent with the trend of thermodynamic data. This study revealed the interaction mechanisms between EGCG and β-LG at different pH, which has great significance to further develop dairy products as EGCG delivery system.