Galloyl moieties enhance the binding of (−)-epigallocatechin-3-gallate to β-lactoglobulin: A spectroscopic analysis

The current study was designed to examine the role of galloyl moieties in the interaction of β-lactoglobulin (β-Lg) with (-)-epigallocatechin-3-gallate (EGCG) using fluorescence and CD spectroscopic methods. The interactions with β-Lg were investigated for EGCG, (-)-epigallocatechin (EGC), and the phenolic compound methyl gallate (MeG) at pH values 3.0, 5.0 and 7.4. The spectroscopic data indicated the binding constants for polyphenol complexes with β-Lg in phosphate buffer pH 7.4 to be in the order of MeG>EGCG>EGC. MeG exhibited the strongest quenching efficiency compared to EGCG and EGC, and EGC exhibited the weakest quenching efficiency. The quenching efficiency of EGCG on β-Lg fluorescence decreased with increasing pH. Polyphenols binding results in a slight secondary structural change of β-Lg, consistent with the fluorescence analysis. This study confirmed that the high binding affinity of EGCG to β-Lg is due to the galloyl functional group.