Phenolic composition of Merlot and Cabernet-Sauvignon grapes from Bordeaux vineyard for the 2009-vintage: Comparison to 2006, 2007 and 2008 vintages

Cabernet-Sauvignon and Merlot skin and seed extracts from Bordeaux grapes were investigated to determine both grape variety and vintage effect on phenolic composition. The total content of polyphenols and tannins in Merlot seeds was higher than that of Cabernet-Sauvignon allowing to discriminate the varieties. HPLC analyses underlined significant differences in the absolute concentration of proanthocyanidins amongst the two varieties and in their composition: mean degree of polymerisation (mDP) and percentage of galloylation of seed extracts were good indicators of grape variety. The vintage effect on the phenolic composition was confirmed for 2009 in comparison to previous vintages. Low values of mDP and concentrations of proanthocyanidins and anthocyanins were found in 2009 seeds and skins. The climatic conditions of 2009 (high rainfall before flowering followed by a strong hydric stress during berries development until ripening) let us hypothesise a lower activation of flavonoid pathway.