Volatile Sulfur Compounds in Wines

In general, DMS increases during aging (Simpson, 1979 Segurel et al., 2005), instead methyl and ethyl thioacetates hydrolyze, and there is an increase of thiols and disulfides observed (Rauhut, 1996). Another sulfur compound found in wine is bis(2-hydroxyethyl)disulfide, which was found in extracts of wines, in particular from Vitis labrusca grapes or its hybrids (Anocibar Beloqui et al., 1995). This compound is a precursor of H2S and 2-mercaptoethanol, two substances with a very strong rotten egg and unpleasant poultry-like odor, respectively. After 

TABLE 5.4. The SPME Conditions Used for Analysis of Sulfur Compounds2  

TABLE 5.5. The m/z Signals Used for GC/MS Analysis of Sulfur Compounds in Wines2  

The use of a 2-cm length fiber provides a higher sensitivity for all analytes. For most compounds, the best salting-out effect is achieved by addition of MgS04 7H20 1.0 M. A temperature of 35 °C is the best compromise between efficient sampling of less volatile compounds and reduced desorption of the higher volatile compounds. 

Recoveries also depend on the wine matrix white and red wines differ for volatiles and polyphenols, and contents of alcohol and sugars. For quantitative analysis, internal standards have to be spiked to the sample in suitable concentration, such as dimethyl sulfide-d6 (d6-DMS) 25 pg/L, dipropyl disulfide (DPDS) 25 pg/L, 4-methylthiazole (MT) lOpg/L, and 3-(methylthio)-l-hexanol (MTH) 50pg/L. A white wine matrix can be used [e.g., 10% v/v ethanol, sugar content 4g/L, and a polyphenolic content of 115mg/L expressed as (+)-catechin] for preparation of standard solutions to calculate the calibration curve for analytes, containing total S02 corrected to 100 g/L and previously treated twice with charcoal 3 g/L to remove sulfur and less polar volatile compounds (higher alcohols are not removed). 

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Park, S. K. Factors affecting formation of volatile sulfur compounds in wine. Ph.D. Thesis, 1993, University of California, Davis, CA.. 

Park, S. K., Boulton, R. B., Bartra, E., Noble, A. C. (1994). Incidence of volatile sulfur compounds in California wines. A preliminary survey. Am. J. Enol. Vitic., 45, 342-344. 

Karagiannis, S. and Lanaridis, P. (1999) The effect of various vinification parameters on the development of several volatile sulfur compounds in Greek white wines of the cultivars Batiki and Muscat of Hamburg, Am. J. Enol. Vitic., 50(3), 334-342. 

Owing to very low thresholds, volatile sulfur compounds (VSCs) usually have prime impact on food aromas they are found in lots of natural sources, including fermented foods (e.g. wine, beer, cheese), and act as both flavours and off-flavours [249, 250]. Although their biogenetic formation has been elucidated in detail, only few biotechnological processes with potential for commercial application have been reported. The sulfur-containing amino acids L-methionine and L-cysteine are the natural precursors of a wide variety of VSCs. Methanethiol is the most frequently found VSC in cheese and can be readily oxidised to other VSCs, such as dimethyl suMde and dimethyl disulfide, or... 

The anaerobic fermentation of sugars by Saccharomyces wine yeasts generates a variety of volatile metabolites that contribute to the sensory profile of wine. The important compounds include esters, higher alcohols, volatile fatty acids, carbonyls, and volatile sulfur compounds. The accumulation of these compounds in wine depends on the strain of yeast, must composition (chemical, physical and nutrient composition) and fermentation conditions. In addition, a variety of... 

Table 8D.3 Volatile sulfur compounds produced in wine by yeast metabolism ...

Rauhut, D., Kiirbel, H., MacNamara, K., Grossmann, M. (1998) Headspace GC-SCD monitoring of low volatile sulfur compounds during fermentation and in wine. Analusis, 26, 142-145. 

The presence of snlfnr derivatives in mnst and wine is always a matter of concern for winemakers, who are fully aware of the risk that they may cause unpleasant smells. Mnch research is in progress on this topic as these phenomena are not clearly understood. Indeed, nntil certain modem analysis techniques were recently perfected, it was impossible to assay these snbstances as they are only present in trace amonnts. Another reason for concern about these volatile sulfur compounds is the wide range of possible origins and the diversity of preventive actions. 

These two volatile sulfur compounds appear gradually. Indeed, for kinetics reasons, due to the very low pesticide concentration, the hydrolysis reaction is extremely slow, especially in the case of 5-methyl-0-methyl-)V-acetyl phosphoramide (acephate). Problems have been observed with wines made from vines treated with orthene... 

The ethylated equivalents of these two volatile sulfur compounds may also be formed, as well as trisulfides such as dimethyltrisulfide (DMTS), generated by an oxidation-reduction balance (Ned-jma, 1995) in two reactions coupled with copper. This is particularly likely to occur when wines are distilled in copper stills (Figure 8.26), presenting a risk of additional contamination in the brandy. 

Fourteen reductive sulfur compounds of interest, ranging from highly volatile compounds such as thiols and disulfides to less volatile compounds, S-thioesters and thioether alcohols, were included. Of note is that another highly volatile compound, methanethiol, was also successfully detected and quantified without the use of a cryotrap, together with further high and low volatile sulfur compounds, commonly reported in the wine literature. 

A simple method was employed to prepare a base wine for constructing a calibration curve for the quantification of the reductive sulfur compounds. Deodourisation of the base wine was carried out in order to remove the volatile sulfur compounds as much as possible, along with other volatile compwimds, while retaining further components of the wine to obtain a matrix effect similar to that of a wine sample. 

Seven reductive sulfur compounds, out of fourteen that could be analysed using the GC-MS procedure, were found in the Cabernet Sauvignon wine, and their concentrations were monitored at the beginning and the end of the trial. The highly volatile sulfur compounds (boiling point less than 90 °C) foimd to be present were methanethiol (MeSH) and dimethyl sulfide (DMS). The wine also contained five low volatile compounds (boiling point above 90 °C), including dimethyl disulfide (DMDS), methyl thioacetate (MTA), S-ethyl thioacetate (ETA), 2-(methylthio)-l-ethanol (MTE) and 3-(methylthio)-l-propanol (MTP) (methionol). 

Volatile sulfur compounds formed in wine and beer production originate from methionine and are by-products of the microorganism s metabolism. The compounds formed are methional (I), methionol (II) and acetic acid-3-(methylthio)-propyl ester (III, cf. Reaction 5.33). 

D Rauhut. Volatile sulfur compounds—impact on reduced sulfur flavor defects and atypical ageing in wine. In 31st Annual New York Wine Industry Workshop. T Henick-Kling, ed. Geneva New York State Agricultural Experiment Station, 2002, pp 103-109. 

In order to expand the worldwide market, considerable efforts are being devoted to improve the image of Madeira wine. Consequently, their characteristics have to be well defined. So, in order to define and describe the particular characteristics and the authenticity of the product, secondary metabolites of grape and wines mainly linked to a specific variety, must be deeply studied. In Madeira wine, these compounds are mainly included in the chemical classes of mono and sesquiterpenoids C13 norisoprenoid higher alcohols, ethyl esters, volatile fatty acids, carbonyl compounds, sulfur compounds, furanic compounds, lactones, and polyphenols. 

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