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International audience; The oxygen transfer rate (OTR) of closures is a well-known parameter impacting the quality of Sauvignon blanc wines (SBw) within the first years of storage, but little research has been published on its long-term effects. The chemical changes in oxidation odor intensity in three SBw sealed with natural cork and other closures that had different known OTRs, ranging from

Six new triterpenoids (1-6), two known genins (7 and 8), and five known functionalized triterpenoids (9-13) were isolated from a Quercus robur heartwood extract. The purification protocol was guided by LC-HRMS by searching for structural analogues of bartogenic acid on the basis of their putative empirical formula. The structures of the new compounds were unequivocally elucidated using HRESIMS and 1D/2D NMR experiments. Sensory analyses were performed in water and in a non-oaked white wine on the pure compounds 1-13 at 5 mg/L. All molecules were perceived as bitter in water and wine, but they were mostly reported as modifying the wine taste balance. Using LC-HRMS, compounds 1-13 were observed in oaked red wine and cognac and were semiquantified in oak wood extracts. The influence of two cooperage parameters, oak species and toasting process, on compounds 1-13 content was studied. All compounds were found in quantities significantly higher in pedunculate than in sessile oak wood. Toasting is a key step in barrel manufacture and modulates the concentration of the discussed compounds. Significantly higher quantities were observed in untoasted wood compared to medium or highly toasted wood. These findings provide new insights into the molecular origin of taste changes due to oak aging.

International audience; Eight new triterpenoids (1-8), the known genin (9), and two known functionalized triterpenoids (10 and 11) were isolated from a Quercus petraea heartwood extract. The structures of the new compounds were unequivocally elucidated using HRESIMS and 1D/2D NMR experiments. Sensory analyses were performed in a non-oaked wine on the pure compounds 1-11. Except compounds 1 and 11, all molecules exhibited a sweet taste at 5 mg/L that was particularly intense for compounds 3 and 9. Using LC-HRMS, compounds 1-11 were observed in an oak wood extract and in oaked red wine and cognac. They were also semiquantified in several samples of sessile ( Q. petraea) and pedunculate ( Q. robur) oak wood extract. All compounds were found in quantities significantly higher in sessile than in pedunculate oak wood. These results support the hypothesis of their contribution to the increase in sweetness during oak aging and show that they can be used as chemical markers to identify the species of oak used for cooperage.

International audience; Ethanol is the second major component of wine after water and exhibits important sensory properties. Previous studies suggested that its bittersweet taste varies according to the alcohol content and the matrix. However, the organoleptic impact of ethanol on wine remains largely ambiguous. Various sensory tests were carried out with a trained panel and the results were statistically analyzed. Tastings revealed that variations of ethanol content usually observed in dry wines have no direct effect on sweet taste of wine. The role of ethanol in white wine bitterness was also studied, revealing its ability to impart the perception of bitterness due to sensory interactions with other constituents. Moreover, a threshold effect was observed between 7 and 10% alc. vol.. These results underline the importance of sensory interactions in the perception of taste and illustrate the role of matrix effects.

Chardonnay wines impart a unique complex aroma characterized by its buttery, yellow stone fruit, melon, bready, and woody notes. Among the terms used in the sensory analysis of these wines, this study investigated hazelnut-like attributes. Multidimensional gas chromatography coupled to olfactometry identified five pyrroles reminiscent of hazelnut: 1-ethylpyrrole-2-carboxaldehyde, 1H-pyrrole, 2-acetyl-1H-pyrrole (first identification in wine), 1-methylpyrrole-2-carboxaldehyde, and 1H-pyrrole-2-carboxaldehyde. Quantitative analyses demonstrated their significantly higher abundance in Chardonnay wines. However, they proved irrelevant in sensory terms, given the low amounts measured in wine compared to their olfactory detection threshold. Nevertheless, the presence of methanethiol derivatives from these pyrroles was investigated in wine. 1-Methylpyrrole-2-methanethiol and 1-ethylpyrrole-2-methanethiol were identified and exhibited hazelnut-like aroma. These compounds, which have not been observed in natural products to date, are potent volatile compounds with detection thresholds of 0.7 and 1.4 ng/L, respectively, in model wine. These findings open up promising perspectives concerning the interpretation of the typical aromatic nuances of some Chardonnay wines.

Quercoresinosides A and B (1 and 2), two new lignans, were isolated from a toasted Quercus petraea heartwood extract along with a known compound, 3-methoxy-4-hydroxyphenol 1-O-β-d-(6′-O-galloyl)glucopyranoside (3). The purification protocol was based on a taste-guided approach that sought to reveal new bitter compounds released from oak wood into wines and spirits. HRMS and NMR data were used to establish that compounds 1 and 2 are lignan derivatives bearing a glucosyl unit and a galloyl unit at the same positions. Hydrolysis of these compounds showed that they could be distinguished by the absolute configuration of their respective lyoniresinol genin as determined by chiral LC-HRMS in comparison with (+)- and (−)-lyoniresinol standards. Sensory analyses were performed in a non-oaked wine on the pure compounds 1–3. The three molecules exhibited a bitter taste at 2 mg/L that was particularly intense for compounds 2 and 3. Finally, LC-HRMS demonstrated the occurrence of compounds 1–3 in oaked wine and brandy, which supports the hypothesis of their contributions to the increase in bitterness during oak aging.

International audience; Oak aging is a crucial step in winemaking during which the organoleptic properties of wine are modified. Various parameters affect the chemical composition of oak wood including botanical origin, which has been previously shown to be a determinant factor. This study focused on the development of a LC-HRMS method to assay four recently discovered taste-active triterpenes (three sweet and one bitter). The method was applied to evaluate the effect of oak species (Quercus petraea and Quercus robur) on the concentration of these molecules in wood. The results showed that sessile oak was richer in sweet triterpenes and poorer in the bitter one than pedunculate oak, with high interindividual variations within species. Furthermore, a triterpenoid index was calculated to reveal the triterpenoid composition of oak wood. This index appears to be a promising tool for the unambiguous discrimination of oak species and could offer new insights into oak wood selection by coopers and the monitoring of oak aging by winemakers.

International audience; Wine expresses its beauty by sending a sensory message to the taster through molecules coming from grapes, yeast metabolism or oak wood. Among the compounds released during barrel aging, lyoniresinol has been recently reported as a relevant contributor to wine bitterness. As this lignan contains three stereogenic carbons, this work aimed at investigating the influence of stereochemistry on wine taste by combining analytical and sensorial techniques. First, an oak wood extract was screened by Liquid Chromatography-High Resolution Mass Spectrometry to target isomers separable in a symmetric environment and a diastereoisomer called epi-lyoniresinol was isolated for the first time. Then, an original racemic resolution based on natural xylose-derivatives was carried out to obtain lyoniresinol enantiomers. Chiroptical spectroscopic measurements associated with theoretical calculations allowed the unambiguous determination of their absolute configuration. The taste properties of all these stereoisomers revealed that only one lyoniresinol enantiomer is strongly bitter whereas the other one is tasteless and the diastereoisomer is slightly sweet. The presence of these three compounds was established in an oaked Bordeaux wine by chiral and non-chiral chromatography, suggesting the significant influence of stereochemistry on wine taste.

International audience; Glutathione (GSH) is a natural tripeptide present in grapes and wines. Its antioxidant properties are particularly useful during winemaking with white varieties like Sauvignon blanc. We examined two winemaking techniques, skin contact and pressing under nitrogen, for their effect on the GSH concentration in the must and wine. GSH was originally reported in the skin (64%), but later investigations on berries showed that juice (51%) and skin (40%) were far greater reduced GSH reservoirs than pulp and seeds. Therefore, we studied the impact of skin contact and pressing on GSH concentrations in must. Climate effects greatly influenced GSH concentrations in mature grapes. Depending on grape quality, GSH increased during skin contact from 2 to 55% and its release occurred in the first hours of maceration. During pressing under nitrogen, must GSH concentrations increased, reaching 80 to 90 mg/L when low pressure was applied (

International audience; Two grape antioxidants, ascorbic acid and glutathione, and a flavan-3-ol, catechin, were analyzed and related to the production or depletion of volatile compounds (phenylacetaldehyde, methional, and sotolon) that act as markers of premature aging in dry white wines. This research assessed the impact of adding ascorbic acid (AA, 80 mg/L) and glutathione (GSH, 10 mg/L) to a Sauvignon Blanc wine sealed with two closures with different permeability to oxygen on wine flavor development over 10 years’ bottle storage. A decrease in AA was correlated with the closure’s oxygen permeability, while GSH depletion (90 % in 12 months) was associated with the dissolved oxygen content at bottling. Sensory analysis revealed significant differences in the development of wine oxidation flavors, correlated with the closure, as well as AA and GSH content. Wines spiked with AA and GSH at bottling were preferred by panelists to controls, without GSH. The sensory data were in complete agreement with analytical results, showing that these wines had the lowest sotolon content. We also demonstrated that, on the basis of analyzing the oxidation markers (sotolon, methional, and phenylacetaldehyde), high catechin levels in white wines contributed to their formation in a temperature-dependent manner.

International audience; Sweetness contributes notably to the taste-balance of dry wines and increases during oak-barrel aging owing to the release of natural sweeteners from wood. The search for such taste-active molecules, which are sometimes present at very low concentrations in wine or other complex matrixes, requires both reliable purification tools and powerful identification techniques. Here, we report the development of an original inductive method using centrifugal partition chromatography (CPC) and sensorial analysis. This method, called CPC-gustatometry, was implemented to isolate a sweet fraction with only four compounds from a complex oak wood extract. The recently developed Fourier transform mass spectrometry (FT-MS, Orbitrap analyzer) was used jointly with two-dimensional nuclear magnetic resonance (2D (1)H and (13)C NMR) to obtain the structural elucidation of the purified compounds. The tandem mass spectrometry (MS/MS) spectra obtained with resonant and nonresonant fragmentation modes were compared, thus providing complementary information about the molecular structure. Two oleanane-type triterpenoids substituted with galloyl and glucosyl moieties were identified, one of which exhibits sweet properties. We term these compounds which have never been reported, Quercotriterpenoside I and II.

International audience; Yeast autolysis during lees contact influences the organoleptic properties of wines especially by increasing their sweet taste. Although observed by winemakers, this phenomenon is poorly explained in enology. Moreover, the compounds responsible for sweetness in wine remain unidentified. This work provides new insights in this way by combining sensorial, biochemical and genetic approaches. First, we verified by sensory analysis that yeast autolysis in red wine has a significant effect on sweetness. Moderate additions of ethanol or glycerol did not have the same effect. Second, a sapid fraction was isolated from lees extracts by successive ultrafiltrations and HPLC purifications. Using nano-LC-MS/MS, peptides released by the yeast heat shock protein Hsp12p were distinctly identified in this sample. Third, we confirmed the sweet contribution of this protein by sensorial comparison of red wines incubated with two kinds of yeast strains: a wild-type strain containing the native Hsp12p and a deletion mutant strain that lacks the Hsp12p protein (Δ°HSP12 strain). Red wines incubated with wild-type strain showed a significantly higher sweetness than control wines incubated with Δ°HSP12 strains. These results demonstrated the contribution of protein Hsp12p in the sweet perception consecutive to yeast autolysis in wine.

Among Saccharomyces yeast, S. cerevisiae and S. bayanus var. uvarum are related species, sharing the same ecosystem in sympatry. The physiological and technological properties of a large collection of genetically-identified S. bayanus var. uvarum wine strains were investigated in a biometric study and their fermentation behavior was compared at 24 degrees C and 13 degrees C. The variability of the phenotypic traits was considered at both intraspecific and interspecific levels. Low ethanol tolerance at 24 degrees C and production of high levels of 2-phenylethanol and its acetate were clearly revealed as discriminative technological traits, distinguishing the S. bayanus var. uvarum strains from S. cerevisiae. Although some S. bayanus var. uvarum strains produced very small amounts of acetic acid, this was not a species-specific trait, as the distribution of values was similar in both species. Fermentation kinetics at 24 degrees C showed that S. bayanus var. uvarum maintained a high fermentation rate after Vmax, with low nitrogen requirements, but stuck fermentations were observed at later stages. In contrast, a shorter lag phase compared with S.cerevisiae, higher cell viability, and the ability to complete alcoholic fermentation at 13 degrees C confirmed the low-temperature adaptation trait of S.bayanus var. uvarum. This study produced a phenotypic characterization data set for a collection of S. bayanus var. uvarum strains, thus paving the way for industrial developments using this species as a new genetic resource.

International audience; Sotolon (3-hydroxy-4,5-dimethyl-2(5H)-furanone) is a chiral furanone, an aroma compound known to be responsible for premature-aging flavor in dry white wines. Sotolon generally results from mild oxygenation during bottle aging, and until now, its formation pathways had not been elucidated. The ability of the main precursors described in the literature under very different experimental conditions to produce sotolon was tested. In model wine solution maintained at 40 degrees C for 6 months, sotolon was produced by the oxidative degradation of ascorbic acid. By use of GC-MS, 2-ketobutyric acid, produced by the oxidative degradation of the ascorbic acid in the model wine solution, was identified as a potent precursor of sotolon in this pathway. Ascorbic acid is an exogenous compound, added before bottling, but 2-ketobutyric acid was found even in white wines that had not been supplemented. Consequently, this sotolon formation pathway is also valid in white wines with no added ascorbic acid. In addition, we showed that Saccharomyces cerevisiae strains were capable of producing variable concentrations of this ketone during alcoholic fermentation. In model wine solution, certain yeast strains released large quantities of 2-ketobutyric acid, similar to those found in oxidized dry white wines. In view of these results, the role of yeast strains in this premature-aging phenomenon of dry white wines is discussed. Finally, these investigations revealed that one chemical mechanism responsible for the low concentrations of sotolon found in prematurely aged white wines made from various grape varieties was an aldol condensation between 2-ketobutyric acid and acetaldehyde.

International audience; Wine has very rich and complex aromas but is paradoxically obtained from grape juice that has very little odour itself. This aromatic transformation is mainly due to the action of yeasts during the alcoholic fermentation. First, yeasts produce secondary metabolites that give to wines its basic 'winy' characteristic. Second, some enzymatic activities may transform non-odorous compounds of certain grape varieties into varietal aromas, giving the specific characteristics of 'cepage'. Depending on the yeast strain, the concentration of aromatic molecules is determined, modifying the organoleptic perception of wine. The enzymatic activities of yeast metabolism and their genetic control have been widely studied, allowing genetic selection approaches as well as molecular engineering for selecting more specialized commercial starters.

A Selection of papers presented at the 6th Symposium in Vino Analytica Scientia - In Vino 2009 ; International audience; Sweet wines made from botrytized grapes contain much higher concentrations of volatile thiols, especially 3-sulfanylhexan-1-ol (3SH), than dry white wines. Three new specific volatile thiols (3-sulfanylpentan-1-ol (3SP), 3-sulfanylheptan-1-ol (3SHp), and 2-methyl-3-sulfanylbutan-1-ol (2M3SB) were recently identified in Sauternes wines. Like most volatile thiols, these compounds were almost totally absent from must, mainly being formed during alcoholic fermentation. In this work, we describe the identification and quantification of three new cysteine-S-conjugate precursors in must made from Botrytis-infected grapes. S-3-(pentan-1-ol)-l-cysteine (P-3SP), S-3-(heptan-1-ol)-l-cysteine (P-3SHp), and S-3-(2-methylbutan-1-ol)-l-cysteine (P-2M3SB) were identified by direct GC–MS analysis of their derivative forms obtained by silylation of an enriched fraction, isolated from must by affinity chromatography. Concentrations were considerably higher when Botrytis cinerea had developed on the grapes. In botrytized must, the mean levels of P-3SP, P-3SHp, and P-2M3SB were in the vicinity of 700, 50, and 500 nM, respectively, whereas concentrations in healthy must ranged from 0 to 50 nM. This indicated that these three new sulfanyl alcohols, responsible for the characteristic aroma of botrytized wines, were formed by the yeast metabolism during alcoholic fermentation from the corresponding non-volatile cysteine-S-conjugate precursors. Moreover, these results highlighted the predominant role of botrytization in developing grape aroma potential.

International audience; Nelson Sauvin (NS) is a unique hop cultivar that was bred and grown in New Zealand. This hop gives a specific flavor (exotic fruit-like, white wine-like) to finished beers. However, the key compounds of this flavor have not yet been identified. We have attempted to identify the specific flavor compounds derived from NS. We focused on certain volatile thiols that are well-known to contribute to wine flavors, especially Sauvignon Blanc. The product made from NS (NS product) lost its specific flavor by contact with copper. Copper is well-known as an absorber of thiols in the field of wine flavor investigations. Therefore, it might point to the existence of thiols. We analyzed the NS product by GC-FPD, GC-olfactometry and GC-MS, and identified two new volatile thiols, 3-sulfanyl-4-methylpentan-1-ol (3S4MP), and 3-sulfanyl-4-methylpentyl acetate (3S4MPA). These compounds have a grapefruit-like and/or rhubarb-like odor, similar to that of Sauvignon Blanc. We quantified these compounds in the NS products and determined their thresholds. As a result, 3S4MP contained about 2-fold of its threshold in beers, and 3S4MPA was included below its threshold. However, it was confirmed that 3S4MP enhanced the flavors of 3S4MPA by synergy. Therefore, we concluded that both of the new volatile thiols would contribute to the specific odor of beers produced with NS.

International audience; Sulfur dioxide is now considered to be a toxic chemical by most world health authorities. However, it remains an irreplaceable additive in enology for wine conservation, combining antioxidant and antibacterial properties. Sweet white wines from botrytized grapes retain particularly high SO2 levels due to their high sulfur dioxide binding power. This paper presents a new method for reducing this binding power by removing some of the carbonyl compounds responsible, which are naturally present in these wines. The main carbonyl compounds responsible for the SO2 binding power of sweet wines were removed, that is, acetaldehyde, pyruvic acid, 2-oxoglutaric acid, and 5-oxofructose. The method retained was selective liquid-solid removal, using phenylsulfonylhydrazine as a scavenging agent. The scavenging function was grafted on different classes of porous polymer supports, and its efficiency was evaluated on sweet white wines under conditions intended to conserve their organoleptic qualities. The results obtained showed that the method was efficient for removing carbonyl compounds and significantly reduced the binding power of the wines. Sensory analysis revealed that this process did not deteriorate their organoleptic qualities.

International audience; The diastereoisomeric distribution of S-3-(hexan-1-ol)cysteine (P-3SH), the cysteinylated precursor of 3-sulfanylhexan-1-ol (3SH) in Vitis vinifera grape juice, was determined by a new method. This procedure is based on the purification of P-3SH in a small volume of must (500 μL) by affinity chromatography, followed by the separation of chiral molecules in derivative forms by gas chromatography coupled with ion trap tandem mass spectrometry (GC–MS/MS). The diastereoisomers were easily separated using heptafluorobutyric anhydride and heptafluorobutanol (HFBA and HFOH) as derivatization reagents. Method validation was conducted using samples of grape juice, synthetic must, fermenting must, and wine that were fortified with P-3SH at concentrations of 0.6 and 2.5 μM. The relative standard deviation (RSD) and limit of detection (LOD) of the GC–MS/MS method were 4.6% and 1.5 nM, respectively. P-3SH assays in Bordeaux white grape juice affected by Botrytis cinerea showed an unusually increased proportion of the RS form of the precursor (approximately RR:RS = 30:70) as compared to a diastereoisomer ratio (in the vicinity of 50:50) in healthy grape juice.

International audience; 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 β-lyases and demonstrate that Irc7p, a putative cystathionine β-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.

International audience; GC-MS in electron ionization mode (EI) was used as a simple, sensitive method for assaying sotolon [4,5-dimethyl-3-hydroxy-2(5) H-furanone] in various dry white wines. The impact of barrel-aging conditions, that is, whether yeast lees were present or not, on the formation of sotolon in dry white wines was then studied. The sotolon content was highest in dry white wines aged in new barrels without lees, often exceeding the perception threshold (8 microg/L). These results demonstrated that yeast lees were capable of minimizing the formation of sotolon in dry white wines during aging. The sotolon and oxygen contents of several bottle of the same white wine were also compared 7 years after bottling. At the range of dissolved oxygen concentrations generally measured, between 5 and 100 microg/L, the sotolon content remained below its perception threshold in wine. The perception threshold was exceeded only in wines with oxygen concentrations above 500 microg/L. The presence of dissolved oxygen in the wine samples analyzed also resulted in a decrease in their free sulfur dioxide content.

International audience; Conventional wine yeasts produce high concentrations of volatile acidity, mainly acetic acid, during high-sugar fermentation. This alcoholic fermentation by-product is highly detrimental to wine quality and, in some cases, levels may even exceed legal limits. In this study, a non-conventional species, Torulaspora delbrueckii, was used, in pure cultures and mixed with Saccharomyces cerevisiae yeast, to ferment botrytized musts. Fermentation rate, biomass growth, and the formation of volatile acidity, acetaldehyde, and glycerol were considered. This study demonstrated that T. delbrueckii, often described as a low acetic producer under standard conditions, retained this quality even in a high-sugar medium. Unlike S. cerevisiae, this species did not respond to the hyper-osmotic medium by increasing acetic production as soon as it is inoculated into the must. Nevertheless, this yeast produced low ethanol and biomass yields, and the fermentation was sluggish. As a result, T. delbrueckii fermentations do not reach the required ethanol content (14%vol.), although this species can survive at this concentration. A mixed culture of T. delbrueckii and S. cerevisiae was the best combination for improving the analytical profile of sweet wine, particularly volatile acidity and acetaldehyde production. A mixed T. delbrueckii/S. cerevisiae culture at a 20:1 ratio produced 53% less in volatile acidity and 60% less acetaldehyde than a pure culture of S. cerevisiae. Inoculating S. cerevisiae after 5 days' fermentation by T. delbrueckii had less effect on volatile acidity and acetaldehyde production and resulted in stuck fermentation. These results contribute to a better understanding of the behaviour of non-Saccharomyces and their potential application in wine industry.

International audience; Commercial Albariño wines from different subzones of Certified Brand of Origin 'Rías Baixas' (NW Spain) were analysed over four consecutive harvests. The contents of monoterpenes, volatile phenols, alcohols, sulphur compounds, acetates, fatty acids and ethyl esters were determined by gas chromatography (flame ionisation detector and flame photometric detector) and gas chromatography–mass spectrometry. These white wines presented high concentrations of free monoterpenes, volatile phenols, acetates, and ethyl esters, while the levels of sulphur compounds, known as default compounds, were very low. All the wines were elaborated from Albariño grapes, but they were produced by different enological practices, such as skin contact and by carrying out malolactic fermentation or not. No significant differences were found between wines from the same subzone and from different vintages. The results obtained, and confirmed by Principal component and linear discriminant analysis, showed a differentiation among these wines as a function of the Galician subzone of origin.

International audience; The enantiomers of sotolon, a flavor compound typical of oxidized white wines, were separated by preparative HPLC to determine their perception thresholds and distribution in wines. The enantiomeric ratios of chiral sotolon were evaluated in several dry white wines using gas chromatography and a chiral column (β-cyclodextrin) connected to a 2 m precolumn (BP20). The perception threshold of (S)-sotolon (0.8 µg/L) in model wine solution was 100 times lower than that of the (R) form (89 µg/L), indicating that (S)-sotolon contributes to the characteristic aroma of prematurely aged dry white wines. Both enantiomers are detected in white wines. Analysis of commercial dry white wines from various vintages and origins revealed three types of distribution patterns: the racemic form, an excess of R, and an excess of S. The proportions found in these wines may be partially explained by the slow racemization kinetics (20 months) of optically active sotolon.

International audience; Beta-damascenone, a C-13 norisoprenoid compound, is usually presented as an impact odorant in red wines. Its direct contribution to their aroma was investigated. Both free beta-damascenone and beta-damascenone precursors were isolated from various French red wines and then analyzed by gas chromatography-mass spectrometry, revealing concentrations in the vicinity of 1 and 2 µ*g/L for free compounds and both forms, respectively. Gas chromatography-olfactometry analyses were also performed on dilutions of both red wine extracts and pure beta-damascenone. The very low detection threshold in olfactometry for this compound explains why it is found at the highest dilution factor in aroma extract dilution analysis methods. Moreover, determination of beta-damascenone's odor thresholds confirmed the huge importance of the matrix: Beta-damascenone is characterized by a very low perception threshold in hydroalcoholic solution as compared to red wine, where it is over 1000-fold higher. In hydroalcoholic solution, beta-damascenone enhanced fruity notes of ethyl cinnamate and caproate and masked the herbaceous aroma of IBMP. Globally, these results suggested that beta-damascenone has more an indirect than a direct impact on red wine aroma.

International audience; Sweet white wines from botrytized grapes present high SO2 levels because of their high sulfur dioxide binding power. The objective of this work was to develop a new method for reducing this binding power by partially eliminating the carbonyl compounds naturally present in these wines that are responsible for this phenomenon. A selective liquid-solid removal technique was developed. Phenylsulfonylhydrazine was selected as the best candidate for removing carbonyl compounds. Its reactivity in the presence or absence of sulfur dioxide was verified in model media containing acetaldehyde, pyruvic acid, and 2-oxoglutaric acid, some of the main carbonyl compounds responsible for the SO2 binding power of sweet wines. The scavenging function was grafted on porous polymer supports, and its efficiency was evaluated in model wines. Dependent upon the supports used, different quantities of carbonyl compounds (over 90% in some cases) were removed in a few days. The presence of sulfur dioxide delayed removal without changing its quality. The results obtained showed that the method removed carbonyl compounds efficiently and was applicable to wines at any stage in winemaking.

International audience; Specific extraction of volatile thiols using sodium p-hydroxymercuribenzoate revealed the presence of three new sulfanylalcohols in wines made from Botrytis-infected grapes: 3-sulfanylpentan-1-ol (II), 3-sulfanylheptan-1-ol (III), and 2-methyl-3-sulfanylbutan-1-ol (IV). The first two have citrus aromas, whereas the third is reminiscent of raw onion. In addition, 2-methyl-3-sulfanylpentan-1-ol, which has a raw onion odor, was tentatively identified. Like 3-sulfanylhexan-1-ol (I), already reported in Sauternes wines, compounds II, III, and IV were absent from must. They were found in wine after alcoholic fermentation, and their concentrations were drastically higher when Botrytis cinerea had developed on the grapes. In the commercial botrytized wines analyzed, the mean levels of II, III, and IV were 209, 51, and 103 ng/L, respectively. Despite their low odor activity values, sensory tests showed additive effects among I, II, and III, thus confirming their olfactory impact on the overall aroma of botrytized wines.

A method to measure specific β(1,3)-glucanase activity in wines has been developed, and is based on the measurement of the kinetics of glucose release in the presence of laminarin (a β(1,3)-glucan from Laminaria digitata). The reaction time and substrate amount have been optimised to allow for measurements in wine conditions. The optimised method has been used to measure the efficiency of a commercial enzyme preparation in wines in relation to filterability. The results indicate that despite the inhibition of wine constituents, β-glucanase activities were present in all wines after enzyme addition. The filterability of the wines significantly increased after enzyme addition as measured by a standardised procedure (Vmax index).

The effects of powdery mildew (Uncinula necator) on grape yield, juice and wine quality were quantified for cultivar Cabernet Sauvignon (CSa) in 1997 and 1999, and for Sauvignon blanc (Sa) in 1999. Analyses were carried out on batches of healthy berries to which known percentages (0–50%) of diseased berries were added, and on natural clusters that were classified into four visual classes from low (C1) to high (C4) disease severity. CSa diseased berries showed an average weight reduction of 12% (1997) and 20% (1999). The direct consequence of a higher percentage of smaller, diseased berries was a reduction in yield. The accompanying loss of weight in must from C1 to C4 clusters increased from 10 to 45%. Sugar content in diseased berries was not significantly different from disease-free berries in 1997, but was 20–21% (CSa) and 14% (Sa) higher in 1999. Severely infected batches also showed a higher total acidity than healthy ones. The total anthocyanin content of CSa was decreased by 0·91% (1997) and 0·66% (1999) per percentage mildewed berries added by weight. In Sa wines the concentration of 3-mercaptohexanol, a component of varietal aroma, was decreased by powdery mildew. Multidimensional analyses, based on all the variables studied, successfully grouped batches of CSa according to disease severity. Using directional triangular tests wine experts were able to recognize CSa wines produced from berries with ≈25% of powdery mildew; the threshold for nonexperts was 50%. CSa wines obtained from samples with more than 30% of diseased berries by weight were significantly classified as the worst according to preference order criteria, but below this value the preference was not significant. Sa wines with

Benzenemethanethiol, a volatile thiol with a strong empyreumatic aroma reminiscent of smoke, has been identified in boxwood (Buxus sempervirens L.) as well as in red and white Vitis vinifera L. wines. The perception threshold in a model hydroalcoholic solution is approximately 0.3 ng/L. All of the wines analyzed for this study contained this compound in concentrations of several dozen nanograms per liter. The Chardonnay wines had 30-40 ng/L. Sensory discrimination between a wine containing 7 ng/L benzenemethanethiol and the same wine with an additional 4 ng/L is very significant; the difference in smell is described as "empyreumatic". This compound can therefore significantly contribute to the aroma of certain wines (Sauvignon Blanc, Semillon, Chardonnay, etc.) containing concentrations as high as 30-100 times higher than their perception threshold.

Geosmin (trans-1,10-dimethyl-trans-9-decalol), a well-known, highly odorous compound, has recently been identified and quantified in red and sweet white wines, as well as in grape juice before alcoholic fermentation. Geosmin is a chiral compound and the (–) form is much more odoriferous than the (+) form. Enantioselective multidimensional gas chromatography analysis of a purified Cabernet Sauvignon wine extract revealed the presence of only one enantiomer: (–) geosmin. In grape juices obtained from rotten grapes and in wines this compound can be found at concentrations much higher than its olfactory perception threshold, indicating that it contributes to their earthy aroma. (–) Geosmin is also the only enantiomer to have been identified in pure cultures of Streptomyces sp. and Penicillium sp. strains isolated from rotten grapes.

Dawn leaf water potential (dawnΨ), leaf water potential (leafΨ) and stem water potential (stemΨ) were measured on mature leaves to determine non-irrigated vine water status in vineyards during the growing season. StemΨ was the most discriminating indicator for both moderate and severe water deficits. The difference between stemΨ and leafΨ (ΔΨ) provided an indirect measurement of mean leaf transpiration which varied with soil moisture conditions and vapour pressure deficit in the atmosphere. The use of stemΨ as an indicator for grapevine management in both non-irrigated and irrigated vineyards is discussed.

The development of fractionation techniques in Sauvignon Blanc musts such as centrifugal partition chromatography and flash chromatography, permitted to identify two precursor forms of 3-sulfanylhexanol : the S-3-(hexan-1-al)-glutathione, and the S-3-glutathionyl-hydroxy hexanesulfonic acid. These results confirmed the major contribution of S-conjugates in the potential liberation of 3-sulfanylhexanol in musts. The two newly identified forms along with S-3-(hexan-1-ol)-L-cysteine and S-3-(hexan-1-ol)-glutathione, explain up to 65% of the total release of 3-sulfanylhexanol. Futhermore, we showed that all precursor forms belonged to the same assimilation pathway of yeast and the S-3-(hexan-1-ol)-L-cysteine is an essential intermediate in the metabolism of S-glutathione conjugates, which is a precursor of 3-sulfanylhexanol . Finally, the biotransformation percentage of different S-conjugates of 3-sulfanylhexanol seems directly related to their position in the metabolic flow., La mise au point de techniques de fractionnement des moûts de Sauvignon blanc par chromatographie de partage centrifuge et par chromatographie Flash, a permis de mettre en évidence la présence de deux « nouvelles » formes précurseurs du 3SH (le S-3-(hexan-1-al)-glutathion et l'acide S-3-glutathionyl-hydroxyhexanesulfonique). L’ensemble de ces résultats a permis de confirmer la contribution majeure des S-conjugués au potentiel en 3SH des moûts. Le S-3-(hexan-1-ol)-L-cystéine, le S-3-(hexan-1-ol)-glutathion ainsi que les deux nouvelles formes identifiées, permettent d’expliquer près de 65% du 3SH libéré dans les vins. Par ailleurs, nous avons montré que l’ensemble des formes précurseurs appartenait à la même voie d’assimilation de la levure et que le S-3-(hexan-1-ol)-L-cystéine est un intermédiaire indispensable à la biotransformation des S-conjugués au glutathion, précurseurs du 3-sulfanylhexanol. De plus, le pourcentage de biotransformation des différents S-conjugués en 3SH semble directement lié à leur position dans le flux métabolique.

National audience

National audience

Sweetness contributes to the balance in taste of dry wines. An increase in sweet taste isobservable during post-fermentation maceration and oak-barrel aging. We have revealed thatthese phenomena are respectively due to the release in wines of yeast peptides and nonvolatileoak wood compounds.The role of Hsp12 protein from S.cerevisae on the increase in sweetness is establishedwith both molecular biology and sensorial analysis techniques.The development of a method coupling centrifugal partition chromatography andgustatometry has enabled us to fractionate an oak-wood extract and to purify several sapidcompounds. Thanks to both the LC-FTMS and the NMR spectroscopy methods, we havehighlighted four new molecules, called quercotriterpenosides (QTT), out of which QTT Iand III are responsible for a sweet taste. The perception thresholds of QTT I and a bitterlignan, lyoniresinol, are respectively 590 μg/L and 1.52 mg/L.LC-FT/MS method has been used to develop a quantification method for these compoundsand we have demonstrated the organoleptic impact of lyoniresinol in wines.QTT I and III are likely to contribute, directly or indirectly, to the increase in sweetnessconsecutive to barrel aging in dry wines.; La saveur sucrée est à l’origine de l’équilibre gustatif des vins secs. On observe uneaugmentation de son intensité au cours de la macération post-fermentaire et de l’élevage enbarrique. Nous montrons que ces phénomènes sont respectivement liés à la libération depeptides de la levure et de composés non-volatils du bois de chêne dans les vins.Le rôle de la protéine Hsp12 de S. cerevisae sur le gain de sucrosité est établi enutilisant des techniques de biologie moléculaire et d’analyse sensorielle.Le développement d’un couplage chromatographie de partage centrifuge –gustatométrie permet de fractionner un extrait de bois de chêne et de purifier plusieurscomposés sapides. L’utilisation de la LC-FT/MS et de la RMN nous a permis d’identifierquatre nouvelles molécules, appelées quercotriterpénosides (QTT), deux d’entre elles (QTTI et III) possédant une saveur douce. Les seuils de perception du QTT I et d’un lignane amer,le lyonirésinol, sont respectivement 590 μg/L et 1.52 mg/L.La mise au point d’une méthode de quantification de ces composés en LC-FT/MS nous apermis de démontrer l’impact organoleptique du lyonirésinol dans les vins.Il est probable que les QTT I et III contribuent, directement ou indirectement, au gain desucrosité conféré par le bois de chêne.