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Keywords:

  • acetone;
  • ethanol;
  • grape;
  • proanthocyanidins;
  • ripening;
  • seed;
  • tannin

Abstract

Background and Aims: The evolution of seed tannins in three grape varieties grown in the same vineyard was followed from preveraison to harvest, to determine their pattern of accumulation. Also, to elucidate whether the use of 70% acetone as extracting solvent overestimate what will occur during fermentation, seed tannins were extracted throughout the ripening period with a method that involved a 3 days extraction with aqueous 12.5% ethanol and the results compared with the acetone extraction method.

Methods and Results: For both methods, the extracted tannins were analysed following acid-catalysis in the presence of excess of phloroglucinol. Seed tannins reached a maximum around veraison and decreased towards maturity, the mean degree of polymerization (mDP) varying only slightly during the studied period. When tannins were extracted with 12.5% ethanol, their concentration was much higher during the first part of the maturation than using acetone but was significantly lower at harvest.

Conclusions: The decrease in extractable seed tannins during ripening was observed with both solvents. The differences observed in the concentration of tannins with both solvents could be due to the histochemical changes occurring in seeds during maturation.

Significance of the Study: The differences observed in tannin concentration with the two different methods may indicate that when pulp maturity is reached before seeds are ripe, the fermenting solution will extract more tannins than the acetone method. These results point to the importance of extraction methodology when monitoring seed maturity for the prediction of seed tannins in wine.