Denis Dubourdieu

A new type of flavor precursors in Vitis vinifera L. cv. Sauvignon Blanc : S-Cysteine conjugates

Three flavor-active volatile thiols (4-mercapto-4-methylpentan-2-one, 4-mercapto-4-methylpentan-2-ol and 3-mercaptohexan-1-ol) involved in Vitis vinifera L. var. Sauvignon blanc wine aroma can be generated in vitro from nonvolatile must extracts by the enzyme action of a cell-free extract obtained from the gastrointestinal bacterium Eubacterium limosum. The specificity of a cysteine conjugate β-lyase (EC 4.4.1.13) which is contained in the cell-free extract, strongly suggested the existence of precursor for these volatile thiols having a structure of S-cysteine conjugate. Gas-phase chromatography analysis coupled with mass spectrometry of must extract in the form of trimethylsilylated derivatives, verified this hypothesis. The release of flavor-active volatile thiols during alcoholic fermentation of the must is shown to be due to the degradation, by yeast, of the corresponding S-cysteine conjugates. This mechanism explains the amplification of the typical Sauvignon blanc grape aroma during alcoholic ferme...

Identification of new volatile thiols in the aroma of Vitis vinifera L. var. Sauvignon blanc wines

Three new flavour-active mercapto-alcohols have been identified in Sauvignon blanc wines: 4-mercapto-4-methylpentan-2-ol, 3-mercaptohexan-1-ol and 3-mercapto-3-methylbutan-1-ol. The first two have a perception threshold of the order of 60 ng/l in an aqueous alcohol solution and their respective odours are reminiscent of citrus zest and grapefruit. The perception threshold of 3-mercapto-3-methylbutan-1-ol, with its odour of cooked leeks, is higher (1500 ng/l in the same solution). These three compounds may contribute towards the typical aroma of Sauvignon blanc wines.

Differentiation of white wines by their aromatic index

Wines from four Galician white varieties (Albariño, Loureira, Treixadura and Dona Branca) with 1992 to 1995 vintages have been analysed, in order to obtain their characterisation by the aromatic index. Monoterpenes, higher alcohols, ethyl esters, fatty acids, acetates, volatile phenols and heavy sulphur compounds were analysed by gas chromatography alone and together with mass spectrometry. Flavour compositions were similar for each wine obtained from grapes harvested in different years. Comparisons between odour unit values (OUV) from each wine variety and from these vintages were similar. However, odour profiles of Galician wines from these years were clearly differentiated. A correct differentiation could be achieved between samples elaborated with different varieties, when principal component and linear discriminant analysis were applied to the OUV data.

Association of Saccharomyces bayanus var. uvarum with some French wines: genetic analysis of yeast populations

Using genetic hybridization analysis, electrophoretic karyotyping and PCR-RFLP of the MET2 gene, we found that the yeast Saccharomyces bayanus var. uvarum is associated with certain types of wines produced in the Val de Loire, Sauternes, and Jurancon regions. The average frequency of appearance of this yeast in the three regions of France was 41, 7 and 77%, respectively. In contrast, we did not find S. bayanus var. uvarum in red wines produced in the Bordeaux area. The results of this study, as well as the findings already reported on Tokay (Slovakia), Muscat (Crimea, Ukraine) and Amarone (Italy) wines, lead us to consider that distribution of S. bayanus var. uvarum yeast is connected with low temperature climatic conditions and/or wine technologies in which must fermentation is at least partially carried out at low temperatures (10-15 degrees C).

Molecular genetic study of introgression between Saccharomyces bayanus and S. cerevisiae

The genomic constitution of different S. bayanus strains and natural interspecific Saccharomyces hybrids has been studied by genetic and molecular methods. Unlike S. bayanus var. uvarum, some S. bayanus var. bayanus strains (the type culture CBS 380, CBS 378, CBS 425, CBS 1548) harbour a number of S. cerevisiae subtelomeric sequences: Y′, pEL50, SUC, RTM and MAL. The two varieties, having 86–100% nDNA–nDNA reassociation, are partly genetically isolated from one another but completely isolated from S. cerevisiae. Genetic and molecular data support the maintaining of var. bayanus and var. uvarum strains in the species S. bayanus. Using Southern hybridization with species‐specific molecular markers, RFLP of the MET2 gene and flow cytometry analysis, we showed that the non‐S. cerevisiae parents are different in lager brewing yeasts and in wine hybrid strains. Our results suggest that S. pastorianus is a hybrid between S. cerevisiae and S. bayanus var. bayanus, while S. bayanus var. uvarum contributed to the formation of the wine hybrids S6U and CID1. According to the partial sequence of ACT1 gene and flow cytometry analysis, strain CID1 is a triple hybrid between S. cerevisiae, S. kudriavzevii and S. bayanus var. uvarum. Copyright

Impact of Oxygen Dissolved at Bottling and Transmitted through Closures on the Composition and Sensory Properties of a Sauvignon Blanc Wine during Bottle Storage

This work outlines the results from an investigation to determine the effect of the oxygen dissolved at bottling and the specific oxygen barrier properties of commercially available closures on the composition, color and sensory properties of a Bordeaux Sauvignon Blanc wine during two years of storage. The importance of oxygen for wine development after bottling was also assessed using an airtight bottle ampule. Wines were assessed for the antioxidants (SO(2) and ascorbic acid), varietal thiols (4-mercapto-4-methylpentan-2-one, 3-mercaptohexan-1-ol), hydrogen sulfide and sotolon content, and color throughout 24 months of storage. In addition, the aroma and palate properties of wines were also assessed. The combination of oxygen dissolved at bottling and the oxygen transferred through closures has a significant effect on Sauvignon Blanc development after bottling. Wines highly exposed to oxygen at bottling and those sealed with a synthetic, Nomacorc classic closure, highly permeable to oxygen, were relatively oxidized in aroma, brown in color, and low in antioxidants and volatile compounds compared to wines sealed with other closures. Conversely, wines sealed under more airtight conditions, bottle ampule and screw cap Saran-tin, have the slowest rate of browning, and displayed the greatest contents of antioxidants and varietal thiols, but also high levels of H(2)S, which were responsible for the reduced dominating character found in these wines, while wines sealed with cork stoppers and screw cap Saranex presented negligible reduced and oxidized characters.

Influence of assimilable nitrogen on volatile acidity production by Saccharomyces cerevisiae during high sugar fermentation

We analyzed the variability of volatile acidity and glycerol production by Saccharomyces cerevisiae on a large sample of high sugar musts. The production of volatile acidity was inversely correlated with the maximum cell population and the assimilable nitrogen concentration. The higher the nitrogen concentration, the less volatile acidity was produced. An approach to minimize volatile acidity production during high sugar fermentations by adjustment of assimilable nitrogen in musts was investigated in terms of both quantity and addition time. It was found that the optimal nitrogen concentration in the must is 190 mgN.l(-1). The best moment for nitrogen addition was at the beginning of fermentation. Addition at the end of the growth phase had less effect on volatile acidity reduction. We suggest that by stimulating cell growth, nitrogen addition provides NADH in the redox-equilibrating process, which in turn reduces volatile acidity formation.

An invertase fragment responsible for improving the protein stability of dry white wines

The thermoprotective effect of yeast parietal mannoproteins improves the protein stability of white wines aged on their lees (sur lie). The substance responsible for this is an N-glycosylated, 31.8 kDa mannoprotein that corresponds to a parietal invertase fragment of Saccharomyces cerevisiae. This mannoprotein is released into the wine during autolysis of the lees by the combined action of β-glucanases from the cell wall and the yeasts vacuolar protease. This mannoprotein may be obtained industrially by extracting yeast mannoproteins using enzymatic digestion of the cell wall with commercially prepared β-glucanases (GlucanexTM -Novo-Nordisk). A wines susceptibility to protein breakdown may be considerably reduced by adding this mannoprotein extract. As a result, less bentonite is needed to stabilise the wine. © 1999 Society of Chemical Industry

Structure of an exocellular β-d-glucan from Pediococcus sp., a wine lactic bacteria

Pediococcus sp. produces an exocellular slime containing exclusively D-glucose. The structure of the polysaccharide was determined by methylation analysis, Smith degradation, enzymic hydrolysis, and 13C-n.m.r. spectroscopy as having a trisaccharide repeating unit, ----3)-beta-D-Glcp-(1---- 3)-[beta-D-Glcp-(1----2)]-beta-D-Glcp-(1----.

Nitrogen catabolic repression controls the release of volatile thiols by Saccharomyces cerevisiae during wine fermentation

Volatile thiols such as 4-methyl-4-sulfanylpentan-2-one (4MSP) and 3-sulfanylhexan-1-ol (3SH) are aromatic molecules having an important organoleptic impact on white wines. These components are produced from inodorous nonvolatile cysteinylated precursors by Saccharomyces cerevisiae metabolic activity during alcoholic fermentation. Here we provide a new insight into the genetic determinism of the production of volatile thiols by yeast. Using a gene deletion approach, we investigated the role of three yeast beta-lyases and demonstrate that Irc7p, a putative cystathionine beta-lyase, is one of the main proteins catalyzing the 4MSP and 3SH release under enological conditions. Moreover, we demonstrate that Ure2p/Gln3p proteins mainly control the bioconversion of volatile thiols by the transcriptional regulation of the IRC7 gene through the general mechanism of nitrogen catabolic repression. Finally, our findings suggest that the enantiomer balance of 3SH may be modulated by activating specifically stereoselective enzymes such as Irc7p.