Role of anthocyanins and copigmentation in flavonol solubility in red wines
Over the last years, due to climate change, several red wines, such as the Sangiovese wines, have been often subjected to loss of clarity due to the formation of deposits of fine needle-shaped crystals. This phenomenon turned out to be due to an excess of quercetin (Q) and its glycosides (Q-Gs) in wines. These compounds are synthesized to a large extent when grapes are excessively exposed to UVB radiations in vineyards. Unfortunately, it is not easy to predict the degree of Q precipitation because its solubility strongly depends on the wine and matrix composition. Surprisingly, some red wines rich in anthocyanins, even if contained high amount of Q, did not show any precipitates. Likely anthocyanins favour the solubility of Q since flavonols are among the most powerful cofactors involved in the copigmentation phenomenon. Thus, in this study, the role of anthocyanins in Q solubility was evaluated by adding known amounts of grape-derived anthocyanins into model solutions containing either Q or Q-Gs. The effects of pH and time on the Q solubility, copigmentation as well as on the hydrolysis of Q-Gs were determined. Our data showed that the solubility of Q passed from 5 mg/L to 25 mg/L when the amount of grape-derived anthocyanins added into the model solutions increased from 0 to 500 mg/L. Experimental samples were investigated over 30 days and significant changes in Q solubility, correlated to the variation in copigmentation and in anthocyanins/quercetin ratio, were observed. These results can assist wine producers to better evaluate the level of flavonol precipitation in red wines and to develop appropriate strategies in order to avoid undesired precipitations in bottle.
Acknowledgements: The authors would like to thank the Biolaffort Company for funding.
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Issue: ICGWS 2023
1 Department of Agricultural Sciences, Section of Vine and Wine Sciences, University of Napoli ″Federico II″, Viale Italia, Avellino 83100, Italy