Towards a molecular interpretation of astringency. Synthesis, 3D-structure, colloidal state and human saliva protein recognition of procyanidins

Astringency is a mouth-feel character determining red wines quality. This feeling is the result of an interaction between tannins and saliva proteins, mainly PRP, leading to the formation and precipitation of the complex. A dry, rough, and pucker sensation is then perceived in the mouth. To get an insight into astringency at a molecular level, were investigated: (i) an efficient and iterative method for 4–8 procyanidins synthesis that gives rise to all the possible procyanidins up to the tetramer with a total control of the oligomerization degree and the stereochemistry of the interflavan link. (ii) Their 3D-structure determination, which takes into account their internal movements, using 2D NMR and molecular modeling. (iii) Their self-association process in water or hydro-alcoholic solutions using Diffusion NMR spectroscopy that gives the active proportion of tannins able to fix proteins. (iv) The comprehensive description of the PRP- procyanidins complex formation to get information about stoichiometry, binding site localization and affinity constants for different procyanidins. The data collected suggest that the interactions are controlled by both procyanidins conformational and colloidal state preferences. All these results shine a new light into the molecular interpretation of tannins astringency.