Résumé
Commercial pectinase preparations are applied in winemaking to improve wine processing and final quality. These preparations contain pectolytic enzyme activities such as polygalacturonases, pectin esterases, pectin lyases, and rhamnoglacturonases. These enzymes modify the polysaccharide and oligosaccharide composition of wines. The influence of various commercial enzyme preparations on wine oligosaccharide composition was studied, on Merlot wines from the Bordeaux area. Wine oligosaccharides were isolated by high-resolution size-exclusion chromatography on a Superdex-30 HR column. The glycosyl residue and glycosyl linkage compositions of the oligosaccharide fractions obtained were determined. The MS spectra of the Merlot oligosaccharide fractions from control and enzyme-treated wines were recorded on an AccuTOF mass spectrometer equipped with an electrospray ionization (ESI) source and a time-of-flight (TOF) mass analyzer. Oligosaccharides in the control wines were partly methylated homogalacturonans, corresponding to smooth regions of pectins, whereas those of the enzyme-treated wines were mostly rhamnogalacturonan-like structures linked with neutral lateral chains, arising from the hairy regions. The enzyme preparations used thus cleaved the rhamnogalacturonan backbone of the hairy zones and demethylated and hydrolyzed the smooth regions. Besides, different structures were detected, depending on the enzyme preparation used, indicating that they contained rhamnogalacturonase activities with different specificities. The oligosaccharide profiles can serve as a marker of enzymatic treatments.