Tannins and polyphenols in grapes and products based on grapes

Grapes and wine polyphenols show a wide diversity of structures, from simple molecules (monomers, oligomers) to polymers. These lasts, usually called “tannins” because of their capacity to interact with proteins, are divided in two: condensed tannins and hydrolysable tannins.

Only condensed tannins are presents in grapes. Wine can contain hydrolysable tannins from an exogenous origin (wooden barrels, oenological tannins) as well.

Wine and grapes’ condensed tannins are analysed by thiolysis, followed by a reverse HPLC phase, and by LC-MS.

Grape seeds’ tannins are partly composed with procyanidins, while grape skins and rods contain prodelphinidines.

The average tannin’s molecular weight is higher in skin than in seeds. Wine tannin’s composition depends on grape which it has been developed with, and vinification conditions, which influences on tannin’s exctraction from the hard parts of the cluster, and their following reactions.

Thus, prodelphinidins spread quicker than procyanidins, while tannin’s molecules, which have a higher molecular weight, are extracted slower.