Oligosaccharides in red wines: could their structure and composition be influenced by the grape-growing

Abstract

Oligosaccharides have only recently been characterized in wine, and the information on composition and content is still limited. In wine, these molecules are mainly natural byproducts of the degradation of grape berry cell wall polysaccharides. Wine oligosaccharides present several physicochemical properties, being one relevant factor linked to the astringency perception of wines (1,2). A terroir can be defined as a grouping of homogeneous environmental units based on the typicality of the products obtained. This notion is particularly associated with wine, being the climate and the soil two of the major elements of terroir concept. Monastrell red wines, predominant varietal wines from the Southern of Spain, were elaborated with grapes from four different terroirs: Cañada Judío, Albatana, Bullas and Montealegre. Climate and soil data from different terroirs were gathered to properly distinguish them. Oligosaccharide fractions from wines were isolated, after removal of phenolic compounds, by high resolution size-exclusion chromatography. The glycosyl–linkages composition was determined by GC–MS of the partially methylated alditol acetates. Results show differences in the glycosyl–linkages composition of oligosaccharides from wines, according to their terroir. The molar percentage of glucose, rhamnose, arabinose, xylose and mannose residues exhibit marked differences depending on the terroir. The ratio of the terminal to the branched residues for Cañada Judío, Albatana, Bullas and Montealegre oligosaccharides is, respectively, 0.75, 0.85, 0.99 and 0.89. Proportions of oligosaccharides families have been calculated from glycosyl-linkage data (3,4,5). Montealegre wine clearly presents the lowest relative molar percentage for the oligosaccharides from yeasts (the sum of OligoGlucans and OligoMannans) and also for OligoXyloGlucans, whereas Bullas wine exhibits by far the lowest release of OligoRhamnogalacturonans. OligoArabinans and OligoArabiGalactans type II also show differences according to the terroir. All these data were treated by PCA to permit a best understanding. The projections on the first axis show obvious separation of Montealegre, whereas a clear separation of Albatana is observed in the projections on the second axis. The first and second principal components represent, respectively, 69% and 19% of the variability for samples. In summary, our results suggest the impact of “terroir” on the structure and the composition of wine oligosaccharide fraction, which could affect their physicochemical and sensory properties.

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