Unraveling the effects of low protein-phenol binding affinity on the structural properties of beta-lactoglobulin

Non-covalent interactions of phenolics with proteins cannot always be readily identified, often leading to con-tradictory results described in the literature. This results in uncertainties as to what extent phenolics can be added to protein solutions (for example for bioactivity studies) without affecting the protein structure. Here, we clarify which tea phenolics (epigallocatechin gallate (EGCG), epicatechin and gallic acid) interact with the whey protein ll-lactoglobulin by combining various state-of-the-art-methods. STD-NMR revealed that all rings of EGCG can interact with native ll-lactoglobulin, indicating multidentate binding, as confirmed by the small angle X-ray scattering experiments. For epicatechin, unspecific interactions were found only at higher protein:epicatechin molar ratios and only with 1H NMR shift perturbation and FTIR. For gallic acid, none of the methods found evidence for an interaction with ll-lactoglobulin. Thus, gallic acid and epicatechin can be added to native BLG, for example as antioxidants without causing modification within wide concentration ranges.

Automated summary

The non-covalent interactions between phenolics and proteins are difficult to identify, leading to contradictory results in the literature. In this study, we use advanced methods to clarify the interactions between tea phenolics (EGCG, epicatechin, and gallic acid) and whey protein ll-lactoglobulin. The results show that all rings of EGCG can interact with native ll-lactoglobulin, indicating a multidentate binding. However, specific interactions were found for epicatechin only at higher protein:epicatechin molar ratios, and no evidence of interaction was found for gallic acid. Therefore, gallic acid and epicatechin can be added to native BLG without causing modification.