Carbohydrate composition of red wines during early aging and incidence on spoilage by Brettanomyces bruxellensis.

Wine is generally considered as hostile medium in which spoilage microbes have to manage with many abiotic factors among which low nutrient content. Wines elaborated in 8 wineries were sampled during the first summer of aging over two consecutive vintages, and analysed for carbohydrate composition. This revealed the systematic presence of many carbohydrates including those useful for the spoilage yeast Brettanomyces bruxellensis. However, during the first summer of aging, the changes in wine carbohydrate composition were low and it was difficult to assess how much carbohydrate composition contributed to wine spoilage by B. bruxellensis. Subsequent laboratory experiments in inoculated wines showed that the sugars preferentially consumed in wine by the spoilage yeast are d-glucose, d-fructose, and trehalose, whatever the yeast strain considered. The addition of these sugars to red wines accelerates the yeast growth and the volatile phenols formation. Although probably not the only promoting factor, the presence of high amounts of metabolisable sugars thus really increases the risk of "brett" spoilage.

Brettanomyces bruxellensis phenotypic diversity, tolerance to wine stress and wine spoilage ability.

Brettanomyces bruxellensis is a yeast species found in many fermented matrices. A high level of genetic diversity prevails in this species and was recently connected with tolerance to sulfur dioxide, the main preservative used in wine. We therefore examine other phenotypes that may modulate the ability of the species to spoil wine, in a selection of representative strains. The species shows a fairly high homogeneity with respect to the carbohydrates that can support growth, but more diverse behaviors regarding tolerance to low pH or ethanol. Thought no clear link can be drawn with genotype, some strains appear more tolerant than the others, mainly in the AWRI1499 like genetic group. Volatile phenol production is ubiquitous within the species, independent from yeast growth profile and not affected by the nature of the growth substrate. The specific production. n rate of volatile phenol production raises in case of increased aeration. It is little affected by pH decrease until 3.0 or by ethanol concentration increase up to 12% vol, but it decreased in case of increased constraint (pH < 3.0, Ethanol ≥14% vol) or combination of constraints. All the strain studied have thus the ability to spoil wine but some outstanding dangerous strains can even spoil the wine with high level of constrainst.

Quantification of three galloylglucoside flavour precursors by liquid chromatography tandem mass spectrometry in brandies aged in oak wood barrels.

Vanillin-(6'-O-galloyl)-ß-glucopyranoside (VGG), 3,4,5-trimethoxyphenyl-(6'-O-galloyl)-ß-glucopyranoside (TMPGG), and (6R,9R)-3-oxo-α-ionol-9-O-(6'-O-galloyl)-ß-glucopyranoside (macarangioside E) were identified as aroma precursors in oak wood. An LC-MS/MS method was developed and validated to quantify these three galloylglucoside compounds in brandies aged in oak barrels. The detection system consisted of a triple quadrupole mass analyser operating in multiple reaction monitoring (MRM) mode. For the first time, vanillin-ß-d-xylopyranoside (VX) was synthesised for use as an internal standard. The detection limits (48 µg L(-1) for VGG, 52 µg L(-1) for TMPGG, and 19 µg L(-1) for macarangioside E) were low enough to quantify these aroma precursors in spirits without any sample preparation.

Quantification of megastigmatrienone, a potential contributor to tobacco aroma in spirits.

A SPME-GC-MS method was adapted and validated in order to quantify 5 megastigmatrienones and related odorous compounds from oak wood: guaiacol, cis-whisky lactone, trans-whisky lactone, γ-nonalactone, eugenol, vanillin, and acetovanillone in a single run. The five megastigmatrienone isomers (tabanones) were quantified, for the first time, in Cognac, Armagnac and rum, as contributors to tobacco-like aromas. Spirits aged in oak barrels contain higher amounts, but megastigmatrienones are also present in freshly-distilled spirits. Statistical analysis revealed that freshly-distilled and barrel-aged spirits were differentiated by their megastigma-4,7E,9-trien-3-one levels. The Armagnac and Cognac samples were distinguished by their concentrations of the megastigma-4,6Z,8E-trien-3-one isomer.

Quantitative solid phase microextraction--gas chromatography mass spectrometry analysis of five megastigmatrienone isomers in aged wine.

Megastigmatrienone is a key flavor compound in tobacco. It has also been detected in wine, where it may contribute to a tobacco/incense aroma, but its importance and concentration in wines had never previously been evaluated. A method was developed and validated for quantifying the five megastigmatrienone isomers in red and white wines. Megastigmatrienone isomers were extracted by headspace solid-phase microextraction (HS-SPME), with a 65 µm film thickness polydimethylsiloxane-divinylbenzene (PDMS-DVB) fiber and analyzed using gas chromatography-mass spectrometry (GC/MS) in selected ion monitoring mode (SIM). Several parameters affecting the length of the adsorption process (i.e., adding salt, extraction time and extraction temperature) were tested. The optimum analytical conditions were established. The LOQ were between 0.06 µg L(-1) and 0.49 µg L(-1) for white wine and 0.11 µg L(-1) and 0.98 µg L(-1) for red wine, repeatability in both types of wine was less than 10% and recovery ranged from 96% for white wine to 94% for red wine. The five isomers of megastigmatrienone were quantified in red and white wines for the first time. Concentrations ranged from 2 µg L(-1) to 41 µg L(-1) in both red and white wines. Initial results revealed a link between wine aging and megastigmatrienone levels, indicating that megastigmatrienone may be a component in wine "bouquet".

Characterization of fruity aroma modifications in red wines during malolactic fermentation.

The role of malolactic fermentation (MLF) in the fruity aroma of red wines was investigated by an analytical study on more than 60 volatile compounds in 48 red wines made in varied conditions and supplemented by a sensory study. Lactic acid bacteria (LAB) modify the fruity notes of red wines but without a specific trend. The absence, in the short term, of a lactic mask was emphasized, whereas the existence of a smoked/toasted reduction-like mask note was evoked but not characterized. Variations in the composition of the fruity aroma markers were predominant. Although LAB ß-glycosidase activities were not very involved, on the other hand, esterase seemed to play a central role that was sometimes associated with the metabolism of the sulfur-containing compounds. New insights in ester metabolism in enological LAB and the importance of wine composition on bacterial variations in metabolites and aromatic alterations were emphasized.

A survey of seasonal temperatures and vineyard altitude influences on 2-methoxy-3-isobutylpyrazine, C13-norisoprenoids, and the sensory profile of Brazilian Cabernet Sauvignon wines.

This report has investigated the seasonal temperatures influences (winter and summer) of five vineyards at different altitudes on the concentrations of 2-methoxy-3-isobutylpyrazine (MIBP), alpha- and beta-ionone, and beta-damascenone in 2004 or 2005 vintages of Cabernet Sauvignon wines from Santa Catarina State, Brazil. Sensorial analyses were also carried out on the wine samples and compared to altitude and climate. Significant regression was observed between MIBP concentrations and the vineyard's altitude. No significant relation was observed between alpha- and beta-ionone and beta-damascenone with the vineyard's altitude. Principal component analysis positively correlated wines from higher altitudes with a "bell pepper" aroma. Conversely, the wines made with grapes from lower altitudes were correlated with "red fruits" and "jam" aromas. An important relation between the bell pepper aroma and the lower winter temperature was observed. A strong negative correlation was also observed between seasonal temperatures and vineyard altitude as well as between MIBP content and seasonal temperature of growing grapevines.