Focus on the relationships between the cell wall composition in the extraction of anthocyanins and tannins from grape berries.

Concentrations of anthocyanins and tannins after extraction from berries in wines and from skin macerations in model solutions have been studied for two grape varieties, two maturation levels and two vintages berries. Characterization of the cell wall polysaccharides has also been performed, the classical method based on the analysis of the neutral sugars after depolymerization being completed by a comprehensive microarray polymer profiling (CoMPP). Extraction was lower in model solutions than in wines, with the same ranking: non acylated anthocyanins> tannins > p-coumaroylated anthocyanins. The polysaccharidic composition suggested a role of homogalacturonans, rhamnogalacturonans and extensins in the extraction process. A global explanation of the interactions between anthocyanins, tannins and polysaccharides is proposed.

Fate of Anthocyanins and Proanthocyanidins during the Alcoholic Fermentation of Thermovinified Red Musts by Different Saccharomyces cerevisiae Strains.

UV-visible spectrophotometry, size exclusion chromatography, and UHPLC-QqQ-MS were combined to evaluate the respective impacts of chemical changes and adsorption by yeasts on both proanthocyanidins (PA) and anthocyanins during the fermentation of a thermovinified red must by four yeast strains. Results evidenced a sharp decrease in anthocyanins (∼45%) and color intensity (∼50%), along with the formation of pyranoanthocyanins and flavanol-anthocyanin dimers related to yeast metabolism. However, the latter only accounted for 10% of anthocyanin losses. Comparison of spectrophotometry and phloroglucinolysis data underlined the involvement of PAs in chemical changes, related to yeast metabolites but also to direct reactions. Color losses during fermentation in this case study were mostly related to the formation of colorless compounds and to a decrease of copigmentation. Adsorption represented only a small proportion of pigment losses (∼5%) but a major part of those corresponding to total oligomeric/polymeric species, which were specifically involved. Only small differences could be evidenced between the four studied strains.