Napa Valley Cabernet Sauvignon Proanthocyanidin Changes During Fruit Ripening: A Multi-Appellation Survey
2024. James Campbell, Thibaut Scholasch, Andrew Waterhouse, James Kennedy
Journal of Agricultural and Food Chemistry
BACKGROUND
In 2015, an experiment was designed to investigate the distribution and variance of in winegrape flavonoids across the ripening phase in the Napa Valley. This Cabernet Sauvignon experiment was intended to evaluate the polyphenol differences across Napa Valley in order to understand parameters controlling “proanthocyanidin activity.” This method has shown promise in understanding proanthocyanidin (PA) astringency based on size distribution, pigmentation, conformation, and composition.
RESULTS
Results from whole berry partial extractions showed that seed PA material was driving PA activity early in the ripening phase, while the formation of the pigmented polymer led to a decrease later in the growing season. Multivariate analysis showed that the main drivers of changes across the ripening phase were the molecular masses of PAs and the amount of pigmentation.
CONCLUSION
Given the high amount of variability seen in the experiment between sites in such a small geographical area, the results suggest that manipulation of PA activity may be possible in the vineyard, perhaps explaining variations in wine mouthfeel attributes between locations. These results can be used to develop furthermore controlled experiments targeting the variables responsible for PA activity changes.
Effect of applied shading during fruit ripening on tannin structure–activity relationships of grape skin extracts
2023. James Campbell, Will Thomas, Andrew Waterhouse, James Kennedy
Journal of the Science of Food and Agriculture
BACKGROUND
Historically, the effect of wine grape shading on flavonoids has investigated the impact of light incidence on proanthocyanidin (PA), flavonol, or anthocyanin concentration. In addition to concentration, the current experiment was designed to look at changes in PA composition, size and tannin activity through ripening. Tannin activity is a methodology for assessing the impact of structure and size on the affinity of tannin towards a hydrophobic surface and is considered to be a proxy for predicted astringency descriptive quality. In 2016 a shade cloth study was imposed on Cabernet Sauvignon on Mt Veeder, within the larger Napa Valley viticultural area. A control, which was unshaded, and two treatments consisting of 40% and 80% shade were applied at the onset of veraison.
RESULTS
Results showed significant differences in the composition and concentration of anthocyanins throughout ripening. Compositional differences in PA were also observed, where shaded treatments had a significantly higher proportion of galloylated subunits. The molecular mass of the extracted tannin was significantly lower in the unshaded control than in the 80% shade treatment. These factors led to a lower measured tannin activity in extracts from exposed fruit.
CONCLUSION
This work suggests that manipulation of canopy architecture, such as artificial shading, leads to changes in berry pigmentation, tannin composition and activity. These results show that the astringency and mouthfeel characteristics of a wine may be altered by vineyard management practices. © 2023 Society of Chemical Industry.
Anthocyanin Addition Alters Tannin Extraction from Grape Skins in Model Solutions via Chemical Reactions
2021. James Campbell, Florian Grosnickel, James Kennedy, Andrew Waterhouse
Journal of Agricultural and Food Chemistry
BACKGROUND
Observations from researchers, including our previous work, suggested that anthocyanins altered the extractability of tannin during maceration. In order to probe this phenomena, model extractions were conducted with Sauvignon Blanc in the presence, or absence, of anthocyanins. Concentrations of anthocyanins inside of the model extracts (72 hours) was 0, 300, and 1000 mg/L. Samples were taken from lag phase until commercial harvest to evaluate changes in extractability.
RESULTS
Anthocyanins showed a significant impact on the extraction of flavan-3-ol material in the early stages of ripening that declined in the latter stages of ripening. Furthermore, anthocyanins significantly decreased the size of the condensed tannin extracted. These results suggest that anthocyanins are not only enhancing the extractability of condensed tannin but also readily incorporating into the polymeric material, leading to a decrease in the average molecular mass of the condensed tannin polymer. The extent of reaction in 72 h suggests that the rate of interflavan bond cleavage may be higher than previously reported and merits closer scrutiny.
CONCLUSION
This work showed that there was no clear treatment effect for the presence of higher concentrations of anthocyanins regarding the extraction of tannin. However, there were clear impacts on the increased loss of anthocyanins at higher concentrations. Furthermore, high concentrations of anthocyanins resulted in tannin with lower degrees of polymerization. This result helps confirm that anthocyanins are non-oxidatively incorporating into tannin, modifying their activity.