New constituents related to 3-methyl-2,4-nonanedione identified in green tea

The volatile constituents of two exquisite green tea varieties, Kiyosawa tea from Japan and Long Jing tea from China, were investigated in order to identify new compounds responsible for the characteristic flavor of a green tea brew. The extracts were prepared by solid-phase extraction using Oasis-HLB-cartridges. Besides the common compounds of green tea chemistry, the already described compounds 3-methyl-2,4-nonanedione (1) and 3-hydroxy-3-methyl-2,4-nonanedione (2), products of degradation of furan fatty acids, as well as three new compounds related to compound 1 were identified. These were 1-methyl-2-oxopropyl hexanoate (3), 1-methyl-2-oxoheptyl acetate (4) and 2-butyl-4,5-dimethyl-3(2H)-furanone (5). Their syntheses and spectroscopic data are reported. Compound 2 increases the sweet, creamy aroma and the characteristic mouthfeel of a green tea flavor, compounds 3 and 4 contribute to its floral, juicy notes and compound 5 exhibits an interesting sweet, buttery flavor.     

Distribution and organoleptic impact of sotolon enantiomers in dry white wines

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 (beta-cyclodextrin) connected to a 2 m precolumn (BP20). The perception threshold of (S)-sotolon (0.8 microg/L) in model wine solution was 100 times lower than that of the (R) form (89 microg/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.     

Study of the formation mechanisms of some volatile compounds during the aging of sweet fortified wines.

Sweet fortified wines, traditionally aged under strong oxidation conditions, have a characteristic aroma. An experimental laboratory study investigated the aging of red and white sweet fortified wines under various conditions. The formation of various molecules, previously identified as characteristic of the aroma of this type of wine, was monitored by analysis. The development of these compounds during accelerated aging was affected by oxidation and the color of the wine. Among the molecules studied, sotolon [3-hydroxy-4, 5-dimethyl-2(5H)-furanone] was one of the few molecules present in concentrations above the perception threshold, in both red and white wines. Buildup was strongly affected by the presence of oxygen in white wine subjected to accelerated aging. (Ethoxymethyl)furfural, formed from 5-(hydroxymethyl)furfural, and furfural, derived from sugars, are also involved in the aroma of sweet fortified white wines aged in oxygen-free conditions. The substances most characteristic of accelerated aging of sweet fortified red wines were 5-(hydroxymethyl)furfural, acetylformoin, and hydroxymaltol, the formation of which is affected by oxidation, and dihydromaltol, formed in the absence of oxidation.     

Changes in color and odorant compounds during oxidative aging of Pedro Ximenez sweet wines

Pedro Ximenez sweet wines obtained following the typical criaderas and solera method for sherry wines and subjected to oxidative aging for 0, 1.3, 4.2, 7.0, or 11.5 years were studied in terms of color and aroma fraction by using the CIELab method and gas chromatography, respectively. The parameters defining the CIELab color space (a*, b*, and L*) were subjected to a multiple-range test (p<0.05) that allowed discrimination of the five wine aging levels studied into five uniform groups according to aging time. The aroma fraction was found to include 15 active odorant compounds with OAV > 1 that enriched the wines with fruity, fatty, floral, and balsamic notes during the aging process. The changes in color parameters and active odorants were not linearly related to aging time, being especially marked during the first 1.3 years and then less substantial up to the 7 years, the oldest wines exhibiting sensorial properties markedly departing from all others. For the wines aged over 1.3 years (minimum aging), 2,3-butanedione, linalool, and decanal can be used as reliable fingerprints of the older wines' quality.     

Odorous impact of volatile thiols on the aroma of young botrytized sweet wines: identification and quantification of new sulfanyl alcohols

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 novel method for quantification of 2-methyl-3-furanthiol and 2-furanmethanethiol in wines made from Vitis vinifera grape varieties

A rapid, easy method has been developed for isolating and quantifying 2-methyl-3-furanthiol (2M3F) in wines. Until now, it was not possible to quantify this highly odoriferous compound, with a smell reminiscent of cooked meat, in wine. The original aspect of this method is the specific release of volatile thiols using a cysteamine solution applied in reverse flow to sample percolation on the basis of a p-hydroxymercuribenzoate (pHMB)-volatile thiol conjugate formed by the direct addition of pHMB to 50 mL of wine. Purification of volatile thiols in wines is much faster and easier than our previous method. This method may also be used to assay 2-furanmethanethiol in wine. This thiol's strong aroma of roasted coffee has been shown to contribute to the "roast coffee" aroma of certain wines. Assaying 2M3F by this method showed that it was present in the wines analyzed (red and white Bordeaux, Loire Valley Sauvignon blanc, white Burgundy, and Champagne) at concentrations up to 100 ng/L, i.e., significantly above the olfactory perception threshold for this compound in model dilute alcohol solution.     

Contribution of benzenemethanethiol to smoky aroma of certain Vitis vinifera L. wines

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.     

Phenolic and volatile composition of wines made from Vitis vinifera cv. Muscat lefko grapes from the island of Samos

A study of the phenolic and volatile composition of wines produced from the white cultivar Muscat lefko from the island of Samos was conducted. Dry, fortified, naturally sweet wines and mistelles (aged and nonaged) have been studied. The phenolic components (flavan-3-ols, hydroxycinnamates, and flavonols) were measured by high-performance liquid chromatography after solid phase extraction (SPE). The terpenes (free and glycosidically linked) were determined by the use of gas chromatography-mass spectrometry (GC-MS) after SPE. The fermentation aroma components were analyzed by GC-MS after liquid-liquid extraction. It was found that the dry wines contained lower amounts of most of the phenolics and higher quantities of terpenes and fermentation aroma compounds than the sweet wines. The aged mistelle wines contained lower levels of coutaric and caftaric acids, higher concentrations of the free acids, and markedly fewer free and bound terpenes and fermentation aroma components compared to the other sweet wines. The naturally sweet wine contained relatively increased amounts of phenolics, 2,3-butanediol, and glycosidically linked terpenes.     

Differences in odor-active compounds of trincadeira wines obtained from five different clones

Odorant compounds of five young clonal red wines made from cv. Trincadeira, a native grape variety of Vitis vinifera L. grown in Portugal, were studied using 2001 and 2003 vintages. The study was carried out using gas chromatography-mass spectrometry (GC-MS) for compound identification and the gas chromatography-olfactometry (GC-O) posterior intensity method to detect the potentially most important aroma compounds. Forty-one odorant peaks were detected by GC-O analysis, from which 31 were identified by GC-MS. The odorant compounds with the highest odorant average intensities are 3-methylbutanoic acid, 2-phenylethanol, 2,5-dimethyl-4-hydroxy-3(2H)-furanone, and 4-vinylguaiacol. The GC-O analysis showed odor intensity differences among compounds, which was confirmed by analysis of variance (ANOVA). Principal component analysis (PCA) and hierarchical cluster analysis (HCA) showed that the five clonal wines from the 2001 vintage were more similar than those from the 2003 vintage. Moreover, stepwise linear discriminant analysis (SLDA) demonstrated that the factor vintage has influence on the Trincadeira clonal red wine odorant profile differentiation.     

Aroma chemical composition of red wines from different price categories and its relationship to quality

The aroma chemical composition of three sets of Spanish red wines belonging to three different price categories was studied by using an array of gas chromatographic methods. Significant differences were found in the levels of 72 aroma compounds. Expensive wines are richest in wood-related compounds, ethyl phenols, cysteinil-derived mercaptans, volatile sulfur compounds, ethyl esters of branched acids, methional, and phenylacetaldehyde and are poorest in linear and branched fatty acids, fusel alcohols, terpenols, norisoprenoids, fusel alcohol acetates, and ethyl esters of the linear fatty acids; inexpensive wines show exactly the opposite profile, being richest in E-2-nonenal, E-2-hexenal, Z-3-hexenol, acetoin, and ethyl lactate. Satisfactory models relating quality to odorant composition could be built exclusively for expensive and medium-price wines but not for the lower-price sample set in which in-mouth attributes had to be included. The models for quality reveal a common structure, but they are characteristic of a given sample set.     

Investigation of potent odorants and afterodor development in two Chardonnay wines using the buccal odor screening system (BOSS)

Potent odorants of two Chardonnay wines were characterized according to their specific overall aroma profiles and their intraoral release patterns after wine consumption. Therefore, aroma compounds were isolated and analyzed by means of high resolution gas chromatography-olfactometry (HRGC/O), leading to the detection of 36 odor-active compounds in both wines. All compounds were identified. Of the most potent odorants, 25 were quantified in both wines by means of stable isotope dilution assays. For the intraoral investigation of odor compounds at defined times after Chardonnay wine consumption, the recently developed buccal odor screening system was used. Significant differences in the oral persistence of characteristic odor notes were observed for both wines with mainly the characteristic barrique-notes being highly persistent, while fruity notes quickly disappeared from the oral cavity. The obtained analytical data were related to time-resolved retronasal aroma evaluation.     

Which impact for beta-damascenone on red wines aroma?

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 microg/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.     

The chemical characterization of the aroma of dessert and sparkling white wines (Pedro Ximénez, Fino, Sauternes, and Cava) by gas chromatography-olfactometry and chemical quantitative analysis

Wines from Pedro Ximénez (PX), Fino, botrytized Sauternes, and Cava were screened by gas chromatography-olfactometry (GC-O), and the most relevant aroma compounds were further quantified in six different wines of each group. The comparison of GC-O and quantitative data with similar data from white young wines has made it possible to identify the aroma compounds potentially responsible for the specific sensory characteristics of these wines. Results have shown that all these wines are relatively rich in 3-methylbutanal, phenylacetaldehyde, methional, sotolon, and the ethyl esters of 2-, 3-, and 4-methylpentanoic acids. While Cava has a less specific aroma profile halfway between these special wines and young white wines, PX is richest in 3-methylbutanal, furfural, beta-damascenone, ethyl cyclohexanoate, and sotolon; Fino in acetaldehyde, diacetyl, ethyl esters of branched aliphatic acids with four, five, or six carbon atoms, and 4-ethylguaiacol; and Sauternes in phenylacetaldehyde, 3-mercaptohexanol, and 4-methyl-4-mercaptopentanone.     

Analytical and sensorial characterization of the aroma of wines produced with sour rotten grapes using GC-O and GC-MS: identification of key aroma compounds

In the present work, the aroma profiles of wines elaborated from sound and sour rot-infected grapes as raw material have been studied by sensory analysis, gas chromatography-olfactometry (GC-O), and gas chromatography-mass spectrometry (GC-MS), with the aim of determining the odor volatiles most likely associated with this disease. The effect of sour rot was tested in monovarietal wines produced with the Portuguese red grape variety Trincadeira and in blends of Cabernet Sauvignon and sour rotten Trincadeira grapes. Wines produced from damaged berries exhibited clear honey-like notes not evoked by healthy samples. Ethyl phenylacetate (EPhA) and phenylacetic acid (PAA), both exhibiting sweet honey-like aromas, emerged as key aroma compounds of sour rotten wines. Their levels were 1 order of magnitude above those found in controls and reached 304 and 1668 μg L(-1) of EPhA and PAA, respectively, well above the corresponding odor thresholds. Levels of γ-nonalactone also increased by a factor 3 in sour rot samples. Results also suggest that sour rot exerts a great effect on the secondary metabolism of yeast, decreasing the levels of volatiles related to fatty acids and amino acid synthesis. The highest levels of γ-decalactone of up to 405 μg L(-1) were also found in all of the samples, suggesting that this could be a relevant aroma compound in Trincadeira wine aroma.     

Influence of storage conditions on the formation of some volatile compounds in white fortified wines (Vins doux naturels) during the aging process

Sweet fortified wines, traditionally aged under strong oxidation conditions, have a characteristic aroma. An experimental study investigated the aging of white sweet fortified wines under various conditions. The development of various molecules, previously identified as characteristic of the aroma of this type of wine, was monitored by analysis. The development of these compounds during accelerated aging was affected by oxidation and the color of the wine. Aging in oak containers, variable storage temperatures, and variable modes of oxidation affect the formation of many of the volatile compounds responsible for the aging aroma of vins doux naturels (fortified wines). Furfural (1), 5-ethoxymethylfurfural (2), and sotolon (3) always reach concentrations above their perception thresholds in wood-aged wines, especially when new oak is used. The isomers of methyl-gamma-octalactone (4 and 5) are reliable indicators of aging in oak. Among the many identifiable volatile phenols, only the vanillin (7) content increases with aging, particularly if the container is made of wood and there is a high degree of oxidation. This molecule frequently reaches and even exceeds its perception threshold. We show here that vanillin and isomers of methyl-gamma-octalactone have a major impact on the aromas of fortified wines.