ReviewUpdated knowledge about pyranoanthocyanins: Impact of oxygen on their contents, and contribution in the winemaking process to overall wine color

- Oxygen improves cycloaddition and enhances the formation of pyranoanthocyanins.
- Micro-oxygenated red wines are richer in Vitisin A than the control ones.
- Higher oxygen rate and lower pH values enhance flavanol-pyranoanthocyanin contents.
- Trends in Vitisin B contents depend on the varietal red wine used.
- Further data are needed to evaluate phenyl-pyranoanthocyanin contents.

BackgroundBetter knowledge of wine composition, especially that of anthocyanin-derived pigments, has helped improve wine quality over the years. The use of micro-oxygenation (MOX), which consists in adding low quantities of oxygen at different stages of the winemaking process, contributes to enhancing and stabilizing wine color through the formation of stable pigments called pyranoanthocyanins, while the cycloaddition of anthocyanins requires an oxidation step.Scope and approachThis review describes the formation kinetics and the evolution of the concentrations of the various groups of pyranoanthocyanins. Both non-oxygenated and oxygenated varietal red wine samples are compared in order to determine the impact of MOX on pyranoanthocyanin contents.Key findings and conclusionsDuring alcoholic fermentation, the concentration of vitisin A increases due to the availability of pyruvic acid and progressively decreases with aging. Higher contents are found in Port red wines. MOX can enhance the concentrations in dry red wines but the contents remain lower than those found in Port wines. The formation of vitisin B can be promoted by the oxidation of ethanol in acetaldehyde but the results depend on the varietal red wine used. Flavanol-pyranoanthocyanin contents also vary according to wine age, with a reported decreasing concentration during aging for Port and dry red wines. After MOX treatment, their concentrations increase with a more acidic pH and a higher oxygen rate. The increase of the content in pyranoanthocyanins after two years of ageing contributes to stabilize wine colour. Further studies will determine the impact of oxygen on phenyl-pyranoanthocyanins since data are still scarce on the subject.

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