Volatile Sulphur Compounds in Wines

Organic sulphur compounds usually play a considerable role in the sensory characteristics of food and beverages, as they are frequently contributors to the character of impact-scents. Examples of these products include truffle (Diaz et al., 2003 Aprea et al., 2007), garlic and onion (Yan et al., 1993 Bocchini et al., 2001), cooked meat (Hinrichsen and Pedersen, 1995 Andres et al., 2002 Carrapiso et al., 2002), coffee (Shimoda and Shibamoto, 1990 Semmelroch and Grosch, 1996), fruit juices (Winter et al., 1976 Boelens and van Gement, 1993 Hinterholzer 

In the following paragraphs, some of the most recent original results concerning the two different quoted groups of compounds, as well as relevant quantification methods, are presented and discussed. 

The first group of sulphur compounds mentioned above can be defined as common fermentative sulphur volatiles (CFSV) and includes in our presentation ethylmercaptan (EtSH), dimethyl sulphide (DMS), diethyl sulphide (DES), dimethyl disulphide (DMDS), diethyl disulphide (DEDS), methyl thioacetate (MTA), ethyl thioacetate (ETA), 2-mercaptoethanol (ME), 2-(methylthio)-l-ethanol (MTE), 3-(methylthio)-l-propanol (MTP), 4-(methylthio)-l-butanol (MTB), benzothiazole (BT) and 5-(2-hydroxyethyl)-4-methylthiazole (HMT) (see Table 5.6). 

Analyte Mean L 1) Min (z -S L 1) Max / gL h S.D. Sensory Threshold Literature values (MgL1) 

Dimethyl sulphide-dg (d6-DMS), dipropyl disulphide (DPDS), 3-(methylthio)-l-hexanol (MTH) and 4-methylthiazole (MT) have been used as internal standards for different compounds or groups of them. 

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Moreira, N., Mendes, F, Pereira, O., Guedes de Pinho, P, Hogg, X, Vasconcelos, I. (2002) Volatile sulphur compounds in wines related to yeast metabolism and nitrogen composition of grape musts. Analytica ChimicaActa, 458, 157-167. 

Mestres, M., Marti, M. P., Busto, O., and Guasch, J. (2000). Analysis of low volatility organic sulphur compounds in wines by solid phase microextraction and gas chromatography.. Chromatogr. A 881, 583-590. 

Fermentative Sulphur Volatile (CFSV) Compounds in Wine... 

Table 5.6 Sensory thresholds and levels of common fermentative sulphur volatile compounds in wines from Trentino (Northern Italy) in the international grape varieties Chardonnay and Merlot and the red berries native grape varieties Marzemino and Teroldego. Samples were from the five vintages 1998 and 2001-2004 (Fedrizzi et al., 2007a).

Several analytical approaches are employed to quantify sulphur volatiles in wine among them, the headspace procedure, such as the Purge and Trap, and solid-phase microextraction methods, combined with GC coupled to different detectors, was shown to be quite effective (Mestres et al., 2000 Rauhut et al., 1998). Recent papers suggest that the HS-SPME technique, with an improved choice of fiber coating phases, would be one of the more promising approaches for the concurrent measurement of compounds with different boiling points (Mestres et al., 2002 Fang and Qian, 2005). 

Mestres, M., Busto, O. and Gulasch, J. (2002) Application of headspace solid-phase microextraction to the determination of sulphur compounds with low volatility in wines,/. Chromatogr. A, 945(1-2), 211-219. 

Figure 5.4. The HS-SPME-GC/MS chromatograms recorded in SIM mode in the analysis of compounds reported in Table 5.5 (a) internal standards (33. d6-DMS, m/z 68 34. DPDS, m/z 108 35. MT, m/z 71 36. M ill, m/z 148), (b) analytes (37. EtSH, m/z 62 38. DMS, m/z 62 39. DES, m/z 75 40. MTA, m/z 90 41. DMDS, m/z 94 42. ETA, m/z 104 43. DEDS, m/z 122 44. ME, m/z 78 45. MTU, m/z 92 46. MTP, m/z 106 47. MTB, m/z 120 48. BT, m/z 135 49. IIMT, m/z 122).The SPME conditions are reported in Table 5.4. (Reprinted from Rapid Communications in Mass spectrometry 21, Fedrizzi et al., Concurrent quantification of light and heavy sulphur volatiles in wine by headspace sohd-phase microextraction coupled with gas chromatography/mass spectrometry, p. 710, Copyright 2007, with permission from John Whey Sons, Ltd.)...

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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