Use of dmaca to visualise flavan-3-ols in grape berry skins (Vitis vinifera L., CV Cabernet Franc)

Phenolic compounds are of great importance in Enology. They play a major role in the elaboration of red wines and during wine preservation, and contribute greatly to their organoleptic properties. Among them, flavonoids constitute the major group present in berry skins. Their histological study is based classically on the use of Toluidine blue O as a staining agent, which is not specific of any type of phenolics. The use of DMACA (p-dimethylaminocinnamaldehyde), which is specific of tannins (flavan-3-ols), permitted to precise the localisation of these compounds without any risk of error; it allowed also for the visualisation of tannins, stuck to the tonoplast, which had not been identified with Toluidine blue O.