3-Methyl-2-butene-1-thiol: identification, analysis, occurrence and sensory role of an uncommon thiol in wine.

A highly uncommon odorant, 3-methyl-2-butene-1-thiol was detected by using Gas Chromatography-Olfactometry (GC-O) and unequivocally identified for the first time in wine. A purge and trap sampling technique which provides highly representative extracts for olfactometric analysis was used for the extraction of the volatile fraction of a Spanish red wine made from Prieto Picudo grapes. The identification of the odorant was achieved by multidimensional gas chromatography analysis of the same purge and trap extract. Mass spectrum and retention indices in both polar and non-polar columns allowed knowing unequivocally the identity. To obtain quantitative data a method was validated for the analysis of the compound at ng L(-1) level with acceptable precision. This powerful odorant presented an odor threshold in wine of 0.5-1 ng L(-1) and it has been detected in several Prieto Picudo wines at concentrations slightly above the odor threshold.

Glycosidically bound aroma compounds and impact odorants of four strawberry varieties.

This paper reports the determination of glycosidically bound aroma compounds and the olfactometric analysis in four strawberry varieties (Fuentepina, Camarosa, Candonga and Sabrina). Different hydrolytic strategies were also studied. The results showed significant differences between acid and enzymatic hydrolysis. In general terms, the greater the duration of acid hydrolysis, the higher was the content of norisoprenoids, volatile phenols, benzenes, lactones, Furaneol, and mesifurane. A total of 51 aglycones were identified, 38 of them unreported in strawberry. Olfactometric analyses revealed that the odorants with higher modified frequencies were Furaneol, γ-decalactone, ethyl butanoate, ethyl hexanoate, ethyl 3-methylbutanoate, diacetyl, hexanoic acid, and (Z)-1,5-octadien-3-one. This last compound, described as geranium/green/pepper/lettuce (linear retention index = 1378), was identified for the first time. Differences with regard to fruity, sweet, floral, and green aroma characters were observed among varieties. In Candonga and Fuentepina, the green character overpowered the sweet. In the other two strawberry varieties sweet attributes were stronger than the rest.

Sensory and chemical characterisation of the aroma of Prieto Picudo rosé wines: the differential role of autochthonous yeast strains on aroma profiles.

This study evaluates the specific impact of isolated yeast strains on the aromatic profile of fermented musts from Prieto Picudo, an autochthonous Castilla y León (Spain) red grape variety with an increasing demand in the local marketplace. For this purpose, the aroma profiles of wines elaborated from Prieto Picudo grapes have been studied by sensory analysis, gas chromatography-olfactometry (GC-O) and gas chromatography-mass spectrometry (GC-MS), with the aim of determining the potential of each strain to generate distinctive varietal and fermentation-derived aromatic compounds. The results have shown that the yeast strain exerts a critical influence on the levels of some fermentative (linear and branched ethyl esters, fatty acids, ethyl phenylacetate) and varietal compounds (4-mercapto-4-methyl-2-pentanone, 3-mercaptohexylacetate, ß-damascenone), thus inducing a deep influence on the final aroma of the wine. Combination of both sensory and chemical data arises as a major tool to monitor the different patterns of aroma release and formation from selected yeast strains during the winemaking process.

Quality and aromatic sensory descriptors (mainly fresh and dry fruit character) of Spanish red wines can be predicted from their aroma-active chemical composition.

A satisfactory model explaining quality could be built in a set of 25 high quality Spanish red wines, by aroma-active chemical composition. The quality of the wines was positively correlated with the wine content in fruity esters, acids, enolones, and wood derived compounds, and negatively with phenylacetaldehyde, acetic acid, methional, and 4-ethylphenol. Wine fruitiness was demonstrated to be positively related not only to the wine content on fruity esters and enolones, but to wine volatile fatty acids. Fruitiness is strongly suppressed by 4-ethylphenol, acetic acid, phenylacetaldehyde, and methional, this involved in the perception of dry-fruit notes. Sensory effects were more intense in the presence of ß-damascenone and ß-ionone. A satisfactory model explaining animal notes could be built. Finally, the vegetal character of this set of wines could be related to the combined effect of dimethylsulfide (DMS), 1-hexanol, and methanethiol.

Modeling quality of premium spanish red wines from gas chromatography-olfactometry data.

The aroma compositions of 25 premium Spanish red wines have been screened by quantitative gas chromatography-olfactometry and have been related to the quality scores of the wines. The study has shown that up to 65 odorants can be present in the aroma profiles of those wines, 32 of which have been detected in less than half of the samples. One new odorant is reported for the first time in wine [(Z)-2-nonenal], and only 11 odorants, most of them weak and infrequent, remain unknown. Quality was not positively correlated with any single compound or with any olfactometric vector built by the summation of odorants with similar odors. However, an olfactometric vector built by the summation of the olfactometric scores of defective odorants, such as 2-methoxy-3,5-dimethylpyrazine, 4-ethylphenol, 3-ethylphenol, 2,4,6-trichloroanisole, and o-cresol was significant and negatively related to quality. Quality could be satisfactorily explained by a simple partial least-squares model (79% explained variance in cross-validation) with just three X-variables: the aforementioned defective vector, a second vector grouping 9 other compounds with negative aroma nuances, and the fruity vector, grouping 15 compounds with fruit-sweet descriptors. This result shows that the quality of these red wines is primarily related to the presence of defective or negative odorants, and secondarily to the presence of a relatively large number of fruit-sweet odorants. Remarkably, only in a few low-quality samples could defective aroma nuances be detected, which suggests that defective and negative odorants exert a strong aroma suppression effect on fruity aroma.