3-Mercapto-2-methylpentan

Tominaga, T. and D. Dubourdieu. 1997. Identification of 4-mercapto-4-methylpentan-2-one from the box tree (Buxus sempervirens L.) and broom (Sarothamnus scoparius (L.) Koch.). Flavour and Fragrance J. 12 373-376. 

Howell, K., Swiegers, J., Elsey, G., Siebert, T., Bartowski, E., Elett, G., Pretorius, I., de Barros Lopes, M. (2004). Variation in 4-mercapto-4-methylpentan-2-one release by Saccharomyces cerevisiae commercial wine strains. FEMS Microbiol. Letters, 240, 125-129. 

Darriet, Ph., Tominaga, T, Demole, E., Dubourdieu, D. (1993). Mise en evidence dans le raisin de Vitis vinifera (var. Sauvignon) d un precurseur de la 4-mercapto-4-methylpentan-2-one. C.R. Acad. Sci. Paris, Biologie et Pathologie vegetale, 316, 1332-1335. 

Darriet, R, Tominaga, T, Lavigne, V., Boidron, J.N., Dubourdieu, D. (1995). Identification of a powerful aromatic component of Vitis vinifera L. var. Sauvignon wines 4-Mercapto-4-methylpentan-2-one. Flav. Frag. J., 10, 385-392. 

Schneider, R., Charrier, R, Razungles, A., Baumes, R.(2006) Evidence for an alternative bio-genetic pathway leading to 3-mercaptohexanol and 4-mercapto-4-methylpentan-2-onein wines. 

Recently, AEDA and SHA-0 yielded 41 and 45 odor active compounds for Scheurebe and Gewurztraminer wines, respectively (P). Ethyl 2-methylbutyrate, ethyl isobutyrate, 2-phenylethanol, 3-methylbutanol, 3-hydroxy-4,5-dimethyl-2(5H)-furanone, 3-ethylphenol and one unknown compound, named wine lactone, showed high flavor dilution (FD)- factors (Table I) in Gewurztraminer and Scheurebe wines. 4-Mercapto-4-methylpentan-2-one belongs to the most potent odorants only in the variety Scheurebe whereas cis-rose oxide was perceived only in Gewurztraminer (Table I). 4-Mercapto-4-methylpentan-2-one was identified for the first time in Sauvignon blanc wines (JO). The unknown compound with coconut, woody and sweet odor quality, which has not yet been detected in wine or a food, was identified as 3a,4,5,7a-tetrahydro-3,6-dimethylbenzofuran-2(3H)-one (wine lactone) (JJ). 

A dilution experiment by SHA-0 indicated acetaldehyde, ethyl acetate, dimethylsulfide and dimethyltrisulfide as further potent odorants in Scheurebe and Gewurztraminer wines. AEDA and SHA-0 yielded the same assessment of 4-mercapto-4-methylpentan-2-one and cis-rose oxide, which are responsible for the odor difference of the two varieties, investigated in this study. It should be mentioned that only one sample of each variety was analyzed and for more generality further investigations are necessary. 

To estimate the sensory contribution of the 42 odorants to the overall flavor of the wine samples, their OAV s were calculated (Table II). To take into account the influence of ethanol, the odor threshold values of wine odorants were determined in a mixture of water/ethanol (9+1, w/w) and were used to calculate the OAV s for each compound. According to the results in Table A, 4-mercapto-4-methylpentan-2-one, ethyl octanoate, ethyl hexanoate, 3-methylbutyl acetate, ethyl isobutyrate, (E)-fi-damascenone, linalool, cis rose oxide and wine lactone showed the highest OAV s in the Scheurebe wine. With exception of 4-mercapto-4-methylpentan-2-one the above mentioned odorants also showed the highest OAV s in Gewurztraminer wine. Differences in the OAV s of ethyl octanoate, ethyl hexanoate, 3-methylbutyl acetate and ethyl isobutyrate between the two varieties are probably caused by differences in the maturity of the fruit at harvest and/or by the fermentation process. 

Calculation of OAV s indicated that significant differences in odor profiles of both varieties, investigated in this study, were mainly caused by cis-rose oxide in Gewurztraminer and 4-mercapto-4-methylpentan-2-one in Scheurebe. Investigations about the formation of 4-mercapto-4-methylpentan-2-one in wine were performed by Tominaga et al. (22), who found that the compound was released from an odorless must extract by a cysteine-fl-lyase. The authors suggested that the compound was bound in form of S-(4-methylpentan-2-one)-l-cysteine in grape must. 

Typical Scheurebe wines are characterized by a jfruity aroma, which is described as redcurrant-like, often with a grapefruit note. In 1995 Darriet et al. identified 4-mercapto-4-methylpentan-2-one (MMP), responsible for the distinctive odor of box tree and cat urine (7). The perception threshold of this compound in wine has been reported to be very low (3 ng/1). Recent studies by Guth and coworkers (2) showed that MMP also significaiitly influences the aroma of Scheurebe wines. 

The especially fresh, juicy grapefruit note is due to the presence of R(-i-)-para-menthene-8-thiol which can be detected as a trace constituent in the ppb range of grapefruit oils ]46]. Other important potent odour-active volatiles of grapefmit juice are l-penten-3-one, l-hepten-3-one, hex-anal, 4-mercapto-4-methylpentan-2-one and 4,5-epoxy-(E)-2-decenal ]47]. 

Analysis of grapefruit juice [71] gave high OAV for 4-mercapto-4-methylpentan-2-one (MMP), ethyl (S)-2-methylbutanoate, (Z)-3-hexenal, ethyl butanoate, decanal, ethyl methylpropanoate and l-p-menthen-8-thiol (MTO, probably the R-enantiomer). The aroma of a solution containing 19 odorants in the levels found in grapefmits was very similar to the natural aroma of this fmit [71 ]. 

Several other odoriferous volatile thiols have also been identified in Sauvignon Blanc wine (Figure 7.9) 3-mercaptohexan-l-ol acetate (Tominaga et al., 1996), 4-mercapto-4-methylpentan-... 

Roncoroni, M., Santiago, M., Hooks, D. O., Moroney, S., Harsch, M. J., Lee, S. A., etal. (2011). The yeast 1RC7 gene encodes a 3-lyase responsible for production of the varietal thiol 4-mercapto-4-methylpentan-2-one in wine. Food Microbiology, 28, 926-935. 

Figure 9.17 There are powerful synergies between Sauvignon Blanc grapes and yeast strains in formation of the compounds responsible for tropical fruit flavours 4-mercapto-4-methylpentan-2-one (4MMP), 3-mercaptohexan-l-ol (3MH) and 3-mercaptohexyl acetate (3MHA). Odourless cysteine and glutathione conjugates are converted to aromatic thiols by carbon-sulfur-lyase enzymes. Alcohol acetyl transferase further modifies 3MH, converting it to the more potent 3MHA.

Drying damages the aroma considerably. (Z)-Hexenal and 4-mercapto-4-methylpentan-2-one are still detectable in freeze-dried basil (Table 22.7) and the green/fresh note is still perceptible. This note is absent in an air-dried sample, and the increase in linalool (Table 22.7), possibly through the enzymatic hydrolysis of the corresponding glycosides, causes the flowery... 

---