Structural composition of polymeric polyphenols of red wine after long-term ageing: effect of vinification technology

Abstract

Aged red wines possess phenolic composition very different from young ones due to the transformations among native grape phenolics and the formation of new polymeric polyphenols during aging process. In this work, Syrah red wines were made by different winemaking technologies, i.e., traditional fermentation on skin (total 7 days of maceration), prolonged maceration with addition of extra skins at the end of traditional fermentation (total 14 days of maceration) and prolonged maceration with addition of extra stems at the end of traditional fermentation (total 14 days of maceration). After 8 years of ageing in bottle, the structural composition of polymeric polyphenols in these wines was comprehensively analysed through different degradation methods (hydrochloric acid hydrolysis, NaOH hydrolysis and Benzyl mercaptan hydrolysis), followed by HPLC-FT-ICR-MS, HPLC/UPLC-MS analysis. The results showed that the molecules of polymeric polyphenols in the aged red wines were composed of not only proanthocyanidins but also anthocyanins, amino acids and phenolic acids. The percentages of the constitutive units of the polymeric polyphenol molecules in these wines varied considerably, being catechin (7.1 – 14.9%), epicatechin (74.5 – 78.2%), epicatechin-3-O-gallate (5.8 – 12.2%), amino acids (0.7 – 1.5%), phenolic acids (0.0 – 0.9%) anthocyanins (0.1 – 0.4%) and epigallocatechin (0.7 – 4.7%),  depending on the type of the winemaking technologies. Catechin, epicatechin and epicatechin-3-O-gallate were presented as both terminal and extension units, with the latter predominant, while amino acids, phenolic acids and anthocyanins were found to be presented exclusively as terminal units and epigallocatechin was found to be presented exclusively as extension units. Comparing with the wine made by traditional fermentation on skin, the lower phenolic acids and anthocyanins units was found in the wine made by prolonged fermentation/maceration with skin and with stem. The prolonged fermentation/maceration with skin was found to have highest amino acids units. On the other hand, different vinification technologies affected the mean polymerization degrees (mDP) of polymeric polyphenols in the aged red wines, being mDP 25.2 for the control one, mDP 13.1 for the wine made by the prolonged fermentation with skin and mDP 15.7 for the prolonged fermention with stem. These results indicated that, different winemaking technologies affect significantly the structural features of polymeric polyphenols.