| Colour, taste and aroma are important characteristics when defining wine quality, while the phenolic compounds are among the most important components of wines an d are directly related to its color, flavor and oxidative level. Major wine phenolics are anthocyanins,several anthocyanin reactions have been demonstrated in red wine, incl uding reactions involving flavanols give rise to flavanol–anthocyanin adducts, and, thro ugh condensation with acetaldehyde, to flavanol–methylmethine–anthocyanin adducts(of ten called flavanol–ethyl–anthocyanin adducts), and pyranoanthocyanin–flavanol adducts.Other pyranoanthocyanins have also been found in red wines, which result from react ion of anthocyanins with yeast metabolites such as acetaldehyde and pyruvic acid, whi ch are also major products of wine oxygenation. Many of the complex reactions invol ving phenolics during wine-making and storage are affected by oxygen exposure of wi ne, and a moderate uptake of oxygen during aging can accelerate specific reactions inf luencing wine properties, thus wines that are aged for sometime are exposed to a slo w oxygenation process which is considered important for aldehyde formation to induce aldehyde-cross linkage of polymeric tannins, production of stable pigments. The aim of this work was to investigate the influence of wine microorganisms on changes in p olyphenol and carbonyls composition induced by micro-oxygenation, and the impact of post-bottling oxygen exposure on different carbonyls and phenolic composition of Cabe rnet Sauvignon wines.1. Carbonyl compounds are produced by fermentation and chemical oxidation duri ng wine making and aging, and they are important to wine flavor and color stability, which are also an essential compound for wine chemical evolution. As wine also cont ains these compounds as α–hydroxysulfonates from the presence of sulfur dioxide, an alkaline pre-treatment requiring oxygen exclusion has been used to release these bound carbonyls for analysis of total carbonyls. To simplify the process, we have developed a modified method using acid hydrolysis where carbonyl compounds are simultaneous ly derivatized with 2, 4-dinitrophenylhydrazine(DNPH) at 65 ℃ for 15 minutes, and sulfur dioxide is added to prevent oxidation. The method was optimized for temperatu re, reaction time, and concentrations of DNPH, sulfur dioxide and acid. The hydrazones were shown to be stable for 10 hours, adequate time for chromatographic analysis. This method is demonstrated for 2-ketoglutaric acid, pyruvic acid, acetoin and acetalde hyde, wine carbonyls of very different reactivities, and it offers good specificity, high recovery and low limits of detection. This new rapid, simple method is demonstrated f or the measurement of carbonyl compounds in a range of wines with different ages a nd grape varieties.2. The presence of oxygen in red wine leads to the transformation of ethanol int o acetaldehyde, which after capturing a protonwill react with flavanols to start the pro cess of forming ethyl bridges between flavanols and between flavanols and anthocyani ns. Yest also can generate acetaldehyde through ethanol metabolism when sugar is def icient after alcoholic fermentation. Consequently, the aim of this chapter was to study how microorganismcan affect the changes of phenolics and carbonyls induced by micr o-oxygenation in Cabernet Sauvignon wines. During micro-oxygenation, the wine conta ining yeast consumed oxygen more quickly, proving yest work in this treatment. The most significant differenceamong wines with differentmicroorganism was acetaldehyde, the wine of sterile filtration with added yeat contained highest mean concentration of acetaldehyde, it is unexpected that the wine without sterile filtration had much lower a cetaldehyde than sterile wine, this result maybe induced by interaction of lactic acid b acteria and yeast. The differences between micro-oxygenated wines and their controls were, in general, greater when acetaldehyde was more.Specifically, the differences bet ween micro-oxygenated wines and their corresponding controls in terms ofcolor due to derivatives resistant to SO2 bleaching(CDR SO2), B-type vitisins, polymeric pigments, 5-hydroxy-2-methyl-1,3-dioxane and 4-hydroxymethyl-2-methyl-1,3-dioxolane were greate r at higher acetaldehyde. In contrast, the effects of micro-oxygenation when acetaldehy de was less were much lessevident and sometimes practically nonexistent. These result s demonstrate that the acetaldehydeformation has a greatinfluence on oxygen-induced c hanges of color and phenolic compounds in wine.3. The impact of moderate oxygen exposure after bottling on wine phenolic and carbonyls composition has been investigated on three Cabernet Sauvignon wines showing different acetaldehyde contents,obtained by sterile wine, sterile wine with yest and sterile wine with yestand micro oxygenation respectively.Three different oxygen transfer rate(OTR) conditions were ensured by using one screw cap and two syntheticclosures with controlled oxygen permeability.Wine phenolic and carbonyls composition weremonitored by triplicate analysis of bottles sampled at bottling(T0) and after 6 and 12 months of ageing.During ageing, the level of acetaldehyde had a much stronger impact on phenolics and acetal than oxygen exposure. The wine had more acetaldehyde, more anthocyanins were lost, and the more acetal and polymeric pigment compound were accumulated, also the more acetaldehyde was decrement. It is similar that acetal and polymeric pigment compoundincreased with oxygen exposure, and anthocyanins was decreased. Therefore, acetaldehyde is a key compound during wine chemical evolution, in another word, wine aging is a slow process of acetaldehyde generating, which induce a series of chemical changes in wine.4. Wine aging is generally limited by the amount of oxidation, and that is dependent on the amount of oxygen entering via the closure. Cabernet Sauvignon wine is well known for its high concentration of tannin, making it an ideal red wine for long time aging. The impact of closure type after five years bottle aging has been investigated on four 2007 Cabernet Sauvignon red wines showing high and low phenolic contents,obtained by PVPP treatment and no PVPP treatment(control), respectively, and processed with(Mox) or without(no Mox) micro-oxygenation. Two oxygen transfer rate(OTR) conditions(16 and 5 μg day-1) into 375 m L bottles were obtained by using different synthetic stoppers.Closure type strongly influenced color parameters involving SO2 bleaching, and some phenolics, particularly quercetin was affected, but there was little effect on carbonyls other than acetaldehyde. Low levels of phenolics afforded the wines with the lowest color density, but highest acetaldehyde. Few effects of micro-oxygenation could be detected. Therefore, oxygen exposure strongly affects sulfur dioxide levels, the primary antioxidant in wine, in aged wine, but phenolic levels substantially alter the secondary reactions of oxidative aging. |
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