Isolation of Carignan and Merlot red wine oligosaccharides and their characterization by ESI-MS

The oligosaccharides of Carignan and Merlot wines have been characterized for the first time. In a first step, this fraction was prepared after discoloration of the wines and was collected by elution on an HPSEC system. In a second step, the glycosyl composition and linkages of wine oligosaccharides were determined by several methods. High resolution MS spectra of the Carignan and Merlot oligosaccharide fractions were obtained on an AccuTOF mass spectrometer equipped with an electrospray ionization (ESI) source and a time-of-flight (TOF) mass analyser. Oligosaccharides were present at a concentration of 330 and 250 mg/L in Carignan and Merlot red wines, respectively. Glycosyl residue composition analysis showed the presence of mannose, arabinose, galactose, rhamnose, fucose, xylose, glucose, galacturonic acid, and glucuronic acid. We show that oligosaccharides are present in significant amounts in wines, that they result from the degradation of cell wall polysaccharides and that they have an extreme diversity, about 30 peaks in ESI-TOF spectra corresponding each to at least one oligosaccharidic structure. The ESI-TOF spectra in negative mode of the Carignan and Merlot oligosaccharides showed oligosaccharidic structures corresponding to oligogalacturonic acids, partially esterified by methyl group (trigalacturonic acid detected at m/z 545, m/z 559 and m/z 573) or to the repetition of the basic unit [-> 4)-alpha-D-GalAp-(1 -> 2)-alpha-L-Rhap-(1 ->] two (m/z 661), or three (m/z 983) times. These units can be substituted either by a hexose, or by a pentose, or by both, but also by deoxyhexose or uronic acid. The identification of [4-OMe-GlcA-[Xyl](2)-Xylitol] and [4-OMe-GlcA-[Xyl](3)-Xylitol] by MSn fragmentation performed on a mass spectrometer equipped with an ESI source and an ion trap mass analyser makes it possible to explain the presence of xylose in wines. (C) 2009 Elsevier Ltd. All rights reserved.