Molecular study of mucin-procyanidin interaction by fluorescence quenching and Saturation Transfer Difference (STD)-NMR

- Procyanidins with various degrees of polymerization are able to interact with mucin.
- The procyanidins with higher polymerization degree have higher quenching ability.
- Hydrogen bonds/hydrophobic interactions governed mucin-procyanidin interaction.
- Ionic strength and pH can also influence mucin-procyanidin interaction.

Astringency is closely related to the interaction between procyanidins and salivary proteins (SP). The aim of this work was to study the interaction between mucin, a SP responsible for saliva lubricating properties, with different procyanidins (B4 dimer, tetramer (TT) and fractions of oligomeric procyanidins), and the influence of several conditions [pH, ionic strength, procyanidins' mean degree of polymerization (mDP) and different solvents (ethanol or dimethylsulfoxide)] on this interaction by fluorescence quenching and Saturation Transfer Difference (STD)-NMR.For fractions of oligomeric procyanidins, the mucin-procyanidin interaction increased with mDP; however, for pure compounds, procyanidin TT has lower affinity than dimer B4 which could be due to a lower structural flexibility imposed by its complex structure. Furthermore, EtOH and DMSO can disrupt the main driving forces of these interactions, hydrophobic interactions and hydrogen bonds, respectively, lowering significantly the binding constants.