Volatile thiols

The most striking characteristic of thiols is their appalling odor. Skunk scent, for instance, is caused primarily by the simple thiols 3-methyl-1-butanethiol and 2-butene-l-thiol. Volatile thiols such as ethanethiol are also added to natural gas and liquefied propane to serve as an easily detectable warning in case of leaks. 

A method for determination of volatile thiols consists of preparing the corresponding tributyltin mercaptides according to reaction 31. After concentrating the mercaptides they are hydrolysed with aqueous hydrochloric acid, and the salted-out thiols are determined by GC-FTD. This was applied to analysis of thiols in cigarette smoke284. 

Tominaga, T., Guimbertau, G., and Dubourdieu, D. (2003). Role of certain volatile thiols in the bouquet of aged Champagne wines. /. Agric. Food Chem. 51,1016-1020. 

It has been suggested that the disulfides may subsequently be reduced back to the volatile thiols (with lower perception thresholds) by SO2 present in the wine during bottle storage under low oxygen concentrations (Bobet et ah, 1990), or be released by hydrolysis from thioacetate esters (Rauhut et ah, 1996). 

A practical consideration in working with ethanethiol is the pervasive stench of this and other volatile thiols, especially as such thiols are used in minute concentration as odor markers for natural gas. It is not easy to perform the standard preparative procedures, during which transfer and filtration operations are performed, in a closed system, and vapors carried through a venting system are detectable at considerable distances, hr small-scale operations, it may be possible to employ a sodium hypochlorite trap to convert the thiols into nonvolatile, oxidized products. 

Dialkyl disulphides, of which (S)-cystine above is an example, may be prepared from thiols by mild oxidation, usually with iodine in the presence of alkali. A convenient synthesis of unsymmetrical analogues results when a symmetrical disulphide is heated with thiol to establish an equilibrium mixture. By careful choice of the reactants, fractional distillation then removes the more volatile thiol leaving the mixed disulphide as a residue.240... 

The sensors display no sensitivity to such typical interferents of mercury chemoresistors based on uncoated gold as volatile thiols and water. Preliminary data demonstrate a possibility to measure Hg(0) even in aqueous solutions. However, the coated sensors still have strong interference with halides and hydrogen halides. 

In 1949, C. J. Watson (W6) reported that methionine was peculiarly toxic in liver failure. Sherlock (S5) reported similar findings, and these observations led Challenger and Walshe (C3) to search for volatile thiols in the breath of patients with fetor hepaticus. The toxicity of mercaptans, presumably derived from methionine and cystine, was proposed as the cause of coma, and it was demonstrated that the breath of patients with fetor hepaticus contained methyl mercaptan. This observation, coupled with the finding of increased thiol levels in the blood of patients with hepatic disease, and a decreased ability to utilize cysteine (W4) gave some support to the proposal. The report that methionine... 

Recent studies have focused on cysteine-S-conjugates as varietal aroma precursors (see Baumes, 2009). Chemically, these odorless compounds are S-substituted derivatives of L-cysteine, differing in the attached to sulfur atom. During fermentation, extremely odorous volatile thiols are formed from these precursors (see Dubourdieu and Tominaga, 2009). One of these thiols, 3-sulfanylhexan-l-ol (3SH), is known as an important aroma... 

TABLE 6.7 Assay of volatile thiols (ng/l) in young Bordeaux wines made from grapes at different stages of noble rot, as well as in some bottled Sauternes wines. Adapted from Sarrazin et ai (2007b) and with permission from the American Chemical Society... 

The nature of the Botrytis aroma compounds has been subjected to extensive research. In addition to the older findings about the importance of hydroxy-, oxo-, and dicarboxylic acid esters, acetals, and some special y- and 8-lactones, the role of volatile thiols has recently been elucidated. Nonetheless, additional research is needed to identify odor active compounds that are specific for botrytized wines. 

Tominaga, T., Baltenweck-Guyot, R., Peyrot des Gachons, C., and Dubourdieu, D. (2000). Contribution of volatile thiols to the aromas of white wines made from several Vitis vinifera grape varieties. Am. J. Enol. Vitic. 51,178-181. 

Howell, K.S., Klein, M., Swiegers, J.H., Hayasaka, Y., Elsey, G.M., Fleet, G.H., Hpj, P.B., Preto-rius, I.S. de Barros Lopez, M.A. (2005). Genetic determinant of volatile-thiol release by Saccharomyces cerevisiae during wine fermentation. App. Environ. Microbiol., 71, 5420-54416. 

Swiegers, J.H., Capone, D.L., Pardon, K.H., Elsey, G.M., Sefton, M.A., Francis, I.L. Pretorius, I.S. (2007). Engineering volatile thiol release in Saccharomyces cerevisiae for improved wine aroma. Yeast, 24, 561-574. 

Masneuf-Pomarede, I., Mansour, C., Murat, M.L., Tominaga, T, Dubourdieu, D. (2006). Influence of fermentation temperature on volatile thiols concentrations in Sauvignon Blanc. Int. J. Food Microbiol, 108, 385-390. 

Murat, M. L., Masneuf, 1., Darriet, P., Lavigne, V., Tominaga, T., Dubourdieu, D. (2001b). Effect of Saccharomyces cerevisiae yeast strains on the liberation of volatile thiols in Sauvignon Wane wine. Am. J. Enol. Vitic., 52, 136-139. 

Sarrazin, E., Shinkaruk, S., Tominaga, T., Bennetau, B., Ererot, E., Dubourdieu, D. (2007). Odorous impact of volatile thiols on the aroma of young botrytized sweet wines identification and quantification of new sulfanyl alcohols. J. Agric. Food Chem., 55, 1437-1444. 

Tominaga, X, Murat, M.L., Dubourdieu, D. (1998a). Development of a method for analyzing the volatile thiols involved in the characteristic aroma of wines made from Vitis vinifera L. Cv. Sauvignon blanc. J. Agric. Food Chem, 46, 1044-1048. 

Tominaga, X, Blanchard, L., Darriet, R, Dubourdieu, D. (2000b). A powerful aromatic volatile thiol, 2-furanemethanethiol, exhibiting roast coffee aroma in wine made from several Vitis vinifera grape varieties. J. Agric. Food Chem., 48, 1799-1802. 

B.2 Volatile Thiols Involved in the Varietal Aromas of Wine.276... 

B.4 Other Volatile Thiols also Contribute a Variety of Aromatic Nuances to Wines. .283... 

B.5 Precursors of Volatile Thiols Derived from Cysteine. 286... 

Several other odoriferous volatile thiols were later identified in Sauvignon blanc wines 3-sulfanylhexyl acetate (3SHA XVI) (Tominaga et al. 1996), 4-methyl-4-sulfanylpentan-2-ol (4MSPOH VI), 3-sulfanyUiexan-l-ol (3SH XVII), and... 

Table 8B. 1 Volatile thiols identified in Vitis vinifera wines...

Table 8B.2 Assay of volatile thiols (ng/L) in four white Bordeaux wines made from Sauvignon blanc 1996 vintage (Tominaga et al. 1998a)...

Table 8B.4 Volatile thiol concentrations (ng/L) in wines made from several Vitis vinifera grape varieties (Tominaga et al. 2000)...

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