Ingrid Weilack,* Christina Schmitz, James F. Harbertson, and Fabian Weber
*Rheinische Friedrich-Wilhelms-Universität Bonn – Institute of Nutritional and Food Sciences, Friedrich-Hirzebruch-Allee 7, 53115 Bonn, Germany (weilack@uni-bonn.de)

Condensed tannins and polymeric pigments are essential red wine components since they contribute to color stability, taste, and mouthfeel. Due to the chemical heterogeneity of proanthocyanidin polymers, analytical tools to determine the polymers’ structural features are limited. The incorporation of anthocyanins increases the structural complexity even more and leaves it almost impossible to objectively analyze their impact on sensory attributes and quality of red wine. To better understand the structural diversity of red wine polymers, this study used FLASH-fractionation of polyphenolic wine extracts to reveal the relationship between phenolic polymers and two physicochemical properties: polarity and hydrophilicity. Red wine polyphenols were characterized regarding their polarity, octanol-water partitioning coefficient, protein precipitation assay, UHPLC-MS, and color. Tannin concentrations in wines subjected to forced aging decreased while the concentrations remained constant in the corresponding extracts, suggesting an alteration in precipitation behavior. A simultaneous increase in precipitable polymeric pigments gives rise to the assumption that incorporation of anthocyanins into tannin molecules alters interactions with red wine polysaccharides and proteins, resulting in lower tannin readings. Wines produced from differently ripe berries showed a shift in polyphenol polarity from being more polar at early harvest and less polar at the later stage of maturity. This is accompanied by an overall increase in precipitible polymeric pigments and a change in astringency perception. Finding tannins and polymeric pigments in different FLASH-fractions indicates that precipitability of polymers is affected by the physicochemical properties, which in turn depend on the degree of polymerization and degree of pigmentation. The results of this study show that red wine astringency and its sub-qualities may be related to the increase in precipitable polymeric pigments and their putative enhanced interaction with wine  polysaccharides and can help to better understand astringency mechanisms.

Funding Support: This research project was financially supported by the German Ministry of Economics and Technology (via AiF) and the FEI (Forschungskreis der Ernährungsindustrie e.V., Bonn); Project AiF 20024N