Composition and astringency of Cabernet Sauvignon red wines: Implications of polyphenol-polysaccharide interactions

Abstract

Red wine quality is based on organoleptic properties like color, color stability, and mouthfeel, among others. The specifications for these attributes vary depending on cultivar, wine style, and personal taste. Ideally, red wines should come with a well-balanced taste and mouthfeel without any unpleasant spikes of acidity, bitterness, or astringency.

The role of red wine polyphenols in these characteristics is well known, with anthocyanins providing color for young red wines, polymeric pigments stabilizing the color in the long term, and condensed tannins eliciting the mouthfeel, more precisely the astringency. However, due to the complex mechanisms behind the astringency perception and difficulties to characterize polymeric flavonoids, the exact factors influencing astringency are not yet fully understood. Furthermore, information on the impact of grape-derived pectic polysaccharides on red wine astringency is limited.

Therefore, the aims of this thesis were to develop a new approach to further characterize condensed tannins and polymeric pigments, their structural changes during red wine aging, and to examine the implications for changes in the astringency perception. Furthermore, the influence of pectic polysaccharides on the condensed tannin and polymeric pigment composition was investigated to gain knowledge about their role in the precipitability of these polymers and ultimately the astringency.

The determination of the polarity and hydrophobicity of condensed tannins and polymeric pigments visualized the complex structural transformations these polymers undergo during red wine aging. Medium sized and hydrophilic, pigmented tannins seemed to be a factor in the attenuation of astringency, which may be attributed to their higher density of positively charged flavylium cations and enhanced interactions with dissociated pectin fragments. The polymerization of these molecules resulted in their increased polarity and hydrophilicity, possibly strengthening the interactions with salivary proteins, which resulted in higher astringency ratings.

In general, the formation of polymeric pigments correlated with an age-related decrease in astringency, highlighting their role in the attenuation of astringency. However, depending on the composition of wine pectic polysaccharides, polymeric pigments did not comprise of conventional tannins that incorporated anthocyanins but rather of pigmented polysaccharide-polyphenol aggregates. Therefore, this thesis revealed that pectic polysaccharides could significantly alter the polyphenolic profile of red wines. Furthermore, they were unambiguously connected with astringency-related mouthfeel attributes, emphasizing their importance for red wine quality.