Volatile thiol concentration

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. 

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

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. 

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. 

Table 8.16. Impact of barrel-aging conditions on the concentration of volatile thiols characteristic of Sauvignon Blanc varietal aroma...

Methyl methanethiosulfonate (MMTS) is a small reversible blocking agent for sulfhydryl groups (Thermo Fisher, Toronto Research). It reacts with free thiols to form a dithiomethane modification with release of sulfinic acid (Figure 1.122). The sulfinic acid component decomposes into volatile products, which don t affect the disulfide formed from the MMTS reaction Alkylthiosulfonates react rapidly with thiols under mild conditions at physiological pH. The MMTS compound is a liquid at 10.6 M concentration and is conveniently added to a reaction medium by pipette. Complete thiol modifications of available cysteine residues in proteins can... 

It is well known that the secondary metabolites of grapes provide the basis of varietal character in wine. The important secondary metabolites are represented by several groups of compounds that contribute to the distinctive aroma profile of wines made from particular varieties of Vitis vinifera. They include terpenes, Ci3-norisoprenoids, aliphatics, benzene-derivatives, volatile phenols and long-chain polyfuntional thiols. While constituent aroma compounds within these groups occur in most grape varieties, it is only when one or more of these compounds occur at concentrations well above their odour threshold that a distinctive varietal aroma emerges. 

The most important Tropical Fruit Scenting Sulphur Volatiles (TFSV) in wine are 3-mercaptohexan-l-ol (3-MH), 3-mercaptohexanol acetate (3-MFLA) and 4-methyl-4-mercaptopentan-2-one (4-MPP). The main problem for quantification of TFSV is their possible very low concentration which may be only a few ng/L. Therefore, only the use of selective isolation and pre-concentration steps allows this difficulty to be overcome. Another problem occurring in thiols analysis is their possible reactivity towards oxidation induced by the working conditions (Rapp et al., 1985) and/or by some components of the matrix in analysis (Murat et al., 2003 Blanchard et al., 2004). 

Recent studies performed on white and red compounds wines treated to eliminate all sulphur volatile compounds by Ag salts addition (Fedrizzi et al., 2007a 2007b), showed the matrix strongly influences the apparent partition between the liquid phase and the fiber coatings. Data of peak areas reported in Table 5.14 show an inversely proportional dependence between the ethanol concentration and the thiols signals, mostly for 3-MHA. 

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