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Some aspects of colour and phenolic evolution in Vitis vinifera L. cv. Pinot noir wine

Bloomfield, David G.
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Red wine 'structure' is considered to be of paramount importance in the perception of wine quality. The structure of red wine is primarily the result of a group of compounds known as flavonoids and their interaction with other compounds. The influence of some hydroxycinnamic acids on colour as well as the influence of selective fining on flavonoid development in wine made from Vitis vinifera L. ca. Pinot noir was investigated with the aim of elucidating the role of copigmentation and condensation reactions in wine. Caffeic and p-coumaric acid were added to musts of Cabernet Sauvignon and Pinot noir prior to fermentation. Both acids produced a significantly larger hyperchromic shift in absorbance maxima, when added to Cabernet Sauvignon in relation to Pinot noir. Both acids produced significant hyperchromic shifts in absorbance maxima in both Cabernet Sauvignon and Pinot noir post fermentation (49 days from addition of acids) compared to the untreated wine. This hyperchromic effect diminished from day 60 (up to 120 days) in the Cabernet Sauvignon. The addition of p-coumaric acid to Pinot noir produced a hypsochromic shift in absorbance maxima throughout the time monitored. A hybrid form of intramolecular copigmentation and the production of malvidin 3-glucoside - 4-vinylphenol are presented as possible theories to explain the results. The anthocyanin - tannin (A/T) ratio of Pinot noir wine was manipulated by selective fining and the A/T ratio of a model solution containing grape seed extract and increasing concentrations of anthocyanins was examined using mDP (mean degree ofpolymerisation by thiolysis) and DmDP (differentiation of mDP by normal phase HPLC). The addition of gelatin (80mgL⁻¹) post fermentation significantly reduced mDP on all days measured (62, 90, 120 days from harvest) relative to the other treatments with all treatments showing a reduction in mDP over time. The model solutions showed a reduction in mDP with increasing concentrations of anthocyanins. The hypothesis that flavonoids develop towards an anthocyanin - tannin - anthocyanin (A-T -A) adduct is likely, and desirable, in quality red wine is postulated.
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