Influence of oxygen addition on the phenolic composition of red wine

[摘要] ENGLISH ABSTRACT: Tannins and colour components in red wine are important quality parameters. These factors canbe manipulated in the vineyard by grape growing techniques or in the cellar by different winemakingpractices. Grape seeds make a significant contribution to tannin concentration in winewhen compared to those from the skins and pulp. Tannins contribute to the ageing potential,organoleptic properties and stabilisation of red wine colour. The colour of a red wine is alsoinfluenced by malolactic fermentation, the biological process that transforms malic acid intolactic acid which normally leads to an increase in pH. The subsequent change in pH alters theanthocyanin equilibrium, the primary colour components in red wine. Oxygen contributes to thepolymerisation of anthocyanins over time to form more stable pigments that are less sensitive topH fluctuations and sulphur dioxide bleaching. Limited research has been done on the use ofoxygen after alcoholic fermentation and the impact it has on the phenolic composition of redwines. Similarly, only a few studies have examined the impact of either the addition or removalof seeds to the phenolic composition of a red wine in combination with oxygen addition.Additionally, little published data seems to exist on the effect of different pHs on red wine'sphenolic and colour development after oxygen addition.In our results we have shown that it is possible to stabilise wine colour by addingsupplementary seeds before alcoholic fermentation. This led to an increase in colour intensity incertain cases. Some red wines produced without seeds had significantly lower colour intensities.This clearly suggests that catechins and proanthocyanidins are extracted from seeds andcontribute to wine colour as they combine with other pigments to stabilise wine colour.Spectrophotometric and HPLC analyses have shown that the total phenolic content increasedwith seed concentration. However, we have observed that a wine may possibly becomesaturated with phenols when supplementary seeds are added. Anthocyanin concentrationsoften decreased when oxygen was added, while polymeric phenols and polymeric pigmentssometimes increased.When applying different oxygen dosages to a red wine on commercial scale with microoxygenation,it was found that monomeric anthocyanins decreased as more oxygen was addedand this decrease in anthocyanins led to the formation of stable polymeric pigments. Thiswas reflected in the significant increase in colour intensity for the wines receiving oxygen. Smalldifferences were detected in the total phenol and tannin concentration for the control andoxygenated wines. However, some of these phenolic and colour differences disappearedduring subsequent ageing of the wine.When making wines of different initial pHs, we observed that the colour density decreasedas the pH increased. The application of oxygen reduced the decrease in colour during MLF,especially at a lower pH. The addition of oxygen did not result in significantly different polymericpigment concentrations in the various pH treatments, although the results could have beendifferent if the wines were aged. However, pH differences in the range between 3.4 and 4.0 didnot significantly influence the phenol composition of the wines under our conditions. This studyled to a better understanding on the effect of oxygen additions under different conditions on redwine's phenolic and colour composition.

[发布机构] Stellenbosch University