Sulfur compounds reductions

TABLE 4.5 Concentrations of reductive sulfur compounds and the varietal thiol 3MH ( tg/L) in a Cabernet Sauvignon wine in 300-L tanks after 16 weeks of MOX or storage in Flextanks (n = 3) data from Nguyen et al. (2010)... 

Application of an Automated Headspace Solid Phase Micro-Extraction for the GC-MS Detection and Quantification of Reductive Sulfur Compounds in Wines... 

Table 1 below presents some information about the perception thresholds, odour descriptions and the concentrations of the reductive sulfur compounds commonly reported in the wine literature (Spedding Raut, 1982 Mestres et al., 2002 Fang Qian, 2005 Ribereau-Gayon et al., 2006b Landaud et al, 2008). Fourteen reductive sulfur compounds, out of sixteen compoimds presented in this table, are the analytes of interest in the current study. 

Table 1. Common reductive sulfur compounds in wines...

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. 

The fourteen reductive sulfur compounds were methanethiol (MeSH) (CAS No. 74-93-1), ethanethiol (EtSH) (75-08-1), dimethyl sulfide (DMS) (75-18-3), diethyl sulfide (DES) (352-93-... 

Fig.l displays the peak separations of the internal standards and the investigated reductive sulfur compounds, obtained from an injection of a standard solution into the GC-MS system, as described in Section 2.3. 

Table 2. Retention times and ions used for the identification and quantification of the reductive sulfur compounds...

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. 

A research red wine (Cabernet Sauvignon) was used to construct the calibration curves for the reductive sulfur compounds of interest. The wine was deodourised twice using a Biichi Rotavapwr R (BUCHl Labortechnik AG, Flawil, Switzerland) sourced from Watson Victor Ltd., Australia New Zealand. An aliquot of the wine (200 mL) was put in an evaporation flask placed in a water bath and the temperature was maintained at 30 C. After the first evaporation, the wine was reconstituted with absolute ethanol and ultrapure water (Bamstead NANOpure Diamond Water Purification System) and was evaporated for a second time. The wine was then reconstituted with absolute ethanol and ultrapure water to have 13.5 % v/ v ethanol in the final reconstituted wine. 

Stock solutions of all thirteen reductive sulfur compounds, as mentioned in Section 2.1, except methanethiol, were separately prepared by introducing 50 pL of a commercial... 

In order to construct the calibration curves, a global stock mixture in absolute ethanol of all the reductive sulfur compounds of interest was prepared from the individual sulfur stock solutions already made up from commercial standards. The volume of the individual stock solutions needed was calculated so that the final concentrations of reductive sulfur compounds in the standard solutions fell in the concentration ranges for wines reported in the literature. 

Fig. 3. Effect of extraction time on the chromatographic profile of the reductive sulfur compounds (continued)...

Table 4 summarises the p>arameters obtained from the calibration graphs for all of the reductive sulfur analytes, along with the method detection and quantification limits for each compoimd. Linear regression analysis revealed that very good linearities (R > 0.992) were obtained in the calibration graphs for all of the reductive sulfur compounds. The method provided very good detection limits, which were well below the sensory thresholds (See Table 1) of the analysed sulfur compounds. 

The method reported in this chapter was then employed to investigate the reductive sulfur compounds in some New Zealand red and white wines. It was particularly applied for the quantification of reductive sulfur compounds during red wine micro-oxygenation, an oxygen management tool that aims to improve wine quality (Nguyen et ah, 2010). 

Reductive sulfur compound in some New Zealand red and white wines... 

Table 6. Concentrations of reductive sulfur compounds (pg/L) + standard deviations of the means n = 3) in ten commercial New Zealand white and red wines (SB = Sauvignon blanc, Chd = Chardonnay, Rslg = Riesling, PN = Pinot noir, Csav = Cabernet Sauvignon,...

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). 

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