Phenolic composition of Bordeaux grapes 2009 vintage: comparison with 2006, 2007 and 2008 vintages

Abstract

‘Cabernet sauvignon’ and ‘Merlot’ are among the most recognized red wine grape cultivars. This work is aimed at investigating the proanthocyanidin composition of skins and seeds to determine the grape variety and the vintage effects on the phenolic composition of Bordeaux grapes. ‘Cabernet sauvignon’ and ‘Merlot’ grape samples were collected from vineyards in Bordeaux. Total polyphenol and tannin contents were determined from skin and seed extracts. The proanthocyanidin monomers and oligomers were identified/quantified by HPLC-UV-Fluo. Percentages of galloylation (%G), of prodelphinidins (%P) and mean degree of polymerization (mDP) of tannins oligomers were determined by HPLC-UV-MS. Vintage and grape variety influence on these parameters were explored. The total content of polyphenols and tannins in the seed extracts of ‘Merlot’ was higher than that of ‘Cabernet sauvignon’; these data can be successfully used to discriminate the two cultivars. HPLC analysis confirmed these results and underlined important differences in the absolute concentration and composition of free flavanols and proanthocyanidins among the two varieties. The effect of the vintage on the grape phenolic composition was confirmed for 2009. In comparison to last vintages, low concentrations of proanthocyanidins were found in seed and skin extracts.