Résumé
Effect of macerating enzymes on the polyphenol and polysaccharide composition of Merlot wines after 20 months of ageing was studied over three vintages (2004, 2005, 2006). Pectinase rich enzyme preparations, by degrading grape berry cell walls, led to a modification of the molecular weight distribution of polysaccharides released into the wines. Enzyme-treated wines contained more Rhamnogalacturonan II (RG-II) and less polysaccharides rich in arabinose and galactose (PRAGs) over the three vintages. The enzyme treatment also modified wine polyphenol composition. An increase of colour intensity, of derived pigments resistant to sulphite bleaching and of proanthocyanidins (condensed tannins) was observed, modulated by vintage effect. Principal Component Analysis of all the data indicated both vintage and enzyme effects. Beside the vintage effect separating the wine samples, the impact of enzyme treatment on wines was established for each year