Flavan-3-ol compositional changes in grape berries (Vitis vinifera L. cv Cabernet Franc) before veraison, using two complementary analytical approaches, HPLC reversed phase and histochemistry Original Research Article

Several studies have shown that the proanthocyanidins are responsible for some major flavour properties of the red wines such as colour, bitterness and astringency. Nevertheless, their synthesis and properties are still misunderstood. Some studies have suggested that the proanthocyanidin content is set before veraison. This paper describes the setting of the proanthocyanidins, until the veraison stage, and the relations that exist with the environment. The flavan-3-ol composition was monitored from the end of the berry set until mid veraison, on two plots known to induce a different behaviour of the vine. The study considered the value of the parameters for a homogeneous stage of development. The composition in proanthocyanidins in skin was determined by HPLC reversed phase, after fractionation and thiolysis. A further information about the proanthocyanidins was obtained by histochemistry. The sections, 2 μm thick, were stained according to the 4-dimethylaminocinnamaldehyde method. The interest and the limits of these approaches are described and discussed. Moreover, it is shown that the linking of these two analytical techniques which associates quantitative data and the spatializing of the tannins in cellular tissue could improve the understanding of the setting of the proanthocyanidins content. Finally, this original approach pointed out the importance of the period previous ripening in the synthesis of flavan-3-ols in the skin; the heterogeneity among berries was in relation with the stage of development but some other factors, as light exposition could also play a role.