Fatty Acid-Induced Modulation of Saliva Protein-Polyphenol Interactions: Molecular Signatures Underlying the Camembert Effect of Astringency

The first contact of polyphenols with the human body occurs in the mouth, where they are known to interact with proline-rich proteins (PRPs), leading to physicochemical and biochemical changes in the salivary pellicles and epithelia of the oral cavity. These interactions are important at the sensory level for the development of astringency. Organoleptic tests have also shown that astringency can be attenuated when fatty foods are consumed, a phenomenon known as the Camembert effect. Employing isothermal titration calorimetry, fluorescence, and CD spectroscopy, we investigated the binding process of the prototypical polyphenol catechin to the PRP IB9-37, also in the presence of 10 vol % ethanol, which is known to influence polyphenol interactions, and in the presence of fatty acids. Our results show that the binding of catechin to IB9-37 is characterized by weak binding, and the binding strength increases markedly in hydroalcoholic solution. The calorimetric data show that the binding process is largely enthalpy-driven, but solvent-related hydrophobic interactions are present as well in the absence of ethanol. We found that significantly higher binding affinities are observed when catechin binds to stearic and oleic acids, indicating that the interaction of the polyphenol with lipid molecules in fatty food boluses is expected to be at least an order of magnitude stronger than with salivary proteins. This clearly shows that fats can prevent the formation of irritating polyphenol-protein interactions, which is consistent with the common understanding of the Camembert effect. Remarkably, binding of the fatty acids to the PRP is also an order of magnitude stronger compared to the catechin-polypeptide interaction; therefore, it will also contribute significantly to reducing astringency. Overall, using a prototypical model system, we were able to obtain a detailed molecular picture of the binary interactions that contribute to these effects and uncover the underlying driving forces that help us to understand them.