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

Astringency is a sensation in the mouth used in judging the quality of red wine. The rough, dry, and puckering sensation called astringency is the result of an interaction between tannins and sali- va proteins, mainly proline-rich proteins (PRP), which leads to the formation and precipitation of a complex. A dry and rough sensation is then per- ceived in the mouth. To get an insight into astrin- gency at the molecular level we investigated: (i) An efficient and iterative method for 4-8 procya- nidin synthesis, which gives rise to all possible 4- 8 procyanidins up to the tetramer with total con- trol of degree of oligomerization and stereochem- istry. (ii) The 3D‑structural preferences, which take into account their internal movements, using 2DNMR and molecular modeling. (iii) The self-as- sociation process in water or hydroalcoholic solu- tions using diffusion NMR spectroscopy that gives the active proportion of tannins able to fix pro- teins. (iv) A comprehensive description of the PRP-procyanidin complex formation to get infor- mation about stoichiometry, binding site localiza- tion, and affinity constants for different procyani- dins. The data collected suggest that the interac- tions are controlled by both procyanidin confor- mational and colloidal state preferences. All these results provide new insights into the molecular interpretation of tannin astringency. " procyanidin l " proline rich peptide l " astringency l " NMR l " molecular dynamics