Measuring the aromatic potential of Vitis vinifera L. Cv. Sauvignon blanc grapes by assaying S-cysteine conjugates, precursors of the volatile thiols responsible for their varietal aroma

The method presented for measuring the aromatic potential of Sauvignon blanc must is based on an assay of the S-cysteine conjugate precursors of three volatile thiols involved in the characteristic aroma of wines made from this grape variety: 4-mercapto-4-methylpentan-2-one, 4-mercapto-4-methylpentan-2-ol, and 3-mercaptohexan-1-ol. These compounds were released enzymatically from their precursors by percolating the must through an immobilized tryptophanase column (EC 4.1.99.1), catalyzing an alpha, beta-elimination reaction on the S-cysteine conjugate. The volatile thiols were analyzed by GC-MS, as were the deuterated analogues that had been released from synthesized deuterated precursors and were added as internal standards. The quantities of volatile thiols released under these conditions were proportional to the S-cysteine conjugate content of the must.     

Identification and quantitation of 3-S-cysteinylglycinehexan-1-ol (Cysgly-3-MH) in Sauvignon blanc grape juice by HPLC-MS/MS

Precursors to varietal wine thiols are a key area of grape and wine research. Several such precursors, in the form of odorless conjugates, have been closely studied in recent years. A new conjugate has now been identified as 3-S-cysteinylglycinehexan-1-ol (Cysgly-3-MH), being the dipeptide intermediate between cysteine and glutathione precursors of tropical thiol 3-mercaptohexan-1-ol (3-MH). Authentic Cysgly-3-MH was produced via enzymatic transformation of the glutathione conjugate and used to verify the presence of both diastereomers of Cysgly-3-MH in Sauvignon blanc juice extracts. Cysgly-3-MH was added into our HPLC-MS/MS precursor method, and the validated method was used to quantify this new analyte in a selection of Sauvignon blanc juice extracts. Cysgly-3-MH was found in the highest concentrations (10-28.5 μg/L combined diastereomer total) in extracts from berries that had been machine-harvested and transported for 800 km in 12 h. This dipeptide conjugate was much less abundant than the glutathione and cysteine conjugates in the samples studied. On the basis of the results, the new cysteinylglycine conjugate of 3-MH seemingly has a short existence as an intermediate precursor, which may explain why it has not been identified as a natural juice component until now.     

Stereoisomeric distribution of 3-mercaptohexan-1-ol and 3-mercaptohexyl acetate in dry and sweet white wines made from Vitis vinifera (Var. Sauvignon Blanc and Semillon)

The enantiomeric distribution of 3-mercaptohexan-1-ol (3MH) and 3-mercaptohexyl acetate (3MHA) in Vitis vinifera wines was determined by combining two techniques: specific purification of volatile thiols from the wines using p-hydroxymercuribenzoate and separation of the chiral molecules by gas-phase chromatography on a cyclodextrin capillary column. The R and S enantiomer ratios of these two thiols in dry white Sauvignon blanc and Semillon wines are approximately 30:70 for A3MH and 50:50 for 3MH. However, in sweet white wines made from grapes affected by "noble rot" due to the development of Botrytis cinerea on ripe grapes, the proportion of the R and S forms of 3MH is in the vicinity of 30:70. During alcoholic fermentation, a change in the ratio of the two enantiomers of 3MH in dry white wines was observed. At the beginning of fermentation (around density 1.08), the S form represented over 60%; then, at lower density, as fermentation proceeded, the enatiomeric ratio approached 50:50. The ratio of the two 3MHA enantiomers remained constant throughout fermentation. On the contrary, the distribution of the two 3MH enantiomers changed very little during fermentation of the botrytized sweet wines. The perception thresholds for the R and S forms of 3MH in hydroalcoholic model solution are similar (50 and 60 ng/L). These two enantiomers have quite different aromas: The R form is fruitier, with a zesty aroma reminiscent of grapefruit, while the S form smells more of passion fruit. The perception thresholds of the R and S enantiomers of 3MHA are slightly different (9 and 2.5 ng/L). The less odoriferous R form is reminiscent of passion fruit, while the S form has a more herbaceous odor of boxwood.     

Assessing the aromatic potential of Cabernet Sauvignon and Merlot musts used to produce rose wine by assaying the cysteinylated precursor of 3-mercaptohexan-1-ol.

The development of a method for assaying S-3-(hexan-1-ol)-L-cysteine, the cysteinylated precursor of 3-mercaptohexan-1-ol (P-3MH), in must has made it possible to study its impact on the aromatic potential of Merlot and Cabernet Sauvignon grape varieties used to produce rose wines in Bordeaux. The original feature of this method is the purification of very small volumes of must (500 microL) containing P-3MH by affinity chromatography and gas-phase chromatography coupled with mass spectrometry of the purified precursor in trimethylsilylated derivative form. Assays of the cysteinylated precursor in Merlot and Cabernet Sauvignon grapes showed that it was mainly located in the grape skins (60%). Prolonged juice-skin contact increased the must's P-3MH content, and this phenomenon was more marked at higher temperatures. Assessment of the aromatic potential of must used to produce rose wines by chemical analysis of an S-cysteine conjugate is mentioned for the first time.     

Quantitative determination of sulfur-containing wine odorants at sub parts per billion levels. 2. Development and application of a stable isotope dilution assay

[(2)H(10)]-4-Mercapto-4-methylpentan-2-one (d(10)-1), [(2)H(2)]-3-mercaptohexan-1-ol (d(2)-2), and [(2)H(5)]-3-mercaptohex-1-yl acetate (d(5)-3), deuterated analogues of impact odorants of wines, were used to determine quantitatively the natural compounds in white wines (Muscadet, Sauvignon, and Bacchus) with a stable isotope dilution assay using gas chromatography coupled either with ion trap tandem mass spectrometry (GC-ITMS-MS) or with atomic emission detection monitored on sulfur-selective acquisition (GC-AED). The thiol compounds were recovered from wines by liquid-liquid extraction, then purified from the wine extracts by covalent chromatography, and analyzed. The quantitative determination of 4-mercapto-4-methylpentan-2-one 1 in the wines that were analyzed was performed better with GC-AED than with GC-ITMS-MS under the conditions that were used. However, the detection limit of the method was higher than the odor threshold of 4-mercapto-4-methylpentan-2-one 1 in wine (5 vs 0.8 ng/L). The levels of this compound in the Sauvignon and Bacchus wines were much higher than its odor threshold, but it was not detectable in the Muscadet wines. On the contrary, GC-ITMS-MS was much more sensitive than GC-AED for detection of 3-mercaptohexan-1-ol 2 and 3-mercaptohex-1-yl acetate 3, and the detection limits were much lower than their odor thresholds in wine. The former compound was detected in all of the Muscadet wines that were analyzed at levels always higher than its odor detection threshold, while the latter occurred at levels higher than its odor threshold in only one Muscadet wine.     

Aroma extraction dilution analysis of Sauternes wines. Key role of polyfunctional thiols

The aim of the present work was to investigate Sauternes wine aromas. In all wine extracts, polyfunctional thiols were revealed to have a huge impact. A very strong bacon-petroleum odor emerged at RI = 845 from a CP-Sil5-CB column. Two thiols proved to participate in this perception: 3-methyl-3-sulfanylbutanal and 2-methylfuran-3-thiol. A strong synergetic effect was evidenced between the two compounds. The former, never mentioned before in wines, and not found in the musts of this study, is most probably synthesized during fermentation. 3-Methylbut-2-ene-1-thiol, 3-sulfanylpropyl acetate, 3-sulfanylhexan-1-ol, and 3-sulfanylheptanal also contribute to the global aromas of Sauternes wines. Among other key odorants, the presence of a varietal aroma (alpha-terpineol), sotolon, fermentation alcohols (3-methylbutan-1-ol and 2-phenylethanol) and esters (ethyl butyrate, ethyl hexanoate, and ethyl isovalerate), carbonyls (trans-non-2-enal and beta-damascenone), and wood flavors (guaiacol, vanillin, eugenol, beta-methyl-gamma-octalactone, and Furaneol) is worth stressing.     

Sulfur aroma precursor present in S-glutathione conjugate form: identification of S-3-(hexan-1-ol)-glutathione in must from Vitis vinifera L. cv. Sauvignon blanc

When Sauvignon blanc or Gros Manseng grape must was percolated through an immobilized gamma-glutamyltranspeptidase column, there was a significant increase in the concentration of S-3-(hexan-1-ol)-L-cysteine, the precursor of 3-mercaptohexan-1-ol, a compound that contributes to the varietal aroma of wines made from these grapes. Low- and high-resolution liquid secondary ion mass sepectrometry (LSIMS) analyses established the presence of S-3-(hexan-1-ol)-glutathione in Sauvignon blanc must. The identification of this compound suggests that the S-3-(hexan-1-ol)-L-cysteine in grapes is produced by the catabolism of S-3-(hexan-1-ol)-glutathione. As is the case in other plant or animal organisms, S-glutathione conjugates may be involved in certain detoxification systems in vines.     

Coinoculated fermentations using saccharomyces yeasts affect the volatile composition and sensory properties of Vitis vinifera L. cv. sauvignon blanc wines

Alcoholic fermentation using Saccharomyces wine yeast is an effective means of modulating wine aroma. This study investigated the impact of coinoculating commercial yeast strains (Vin7, QA23, Vin13) on the volatile composition and sensory profile of Sauvignon Blanc wines. Small-scale replicated fermentations were conducted using single-strain and coinoculations of Vin7 with QA23 and with Vin13. The results showed that the chemical and sensory profiles of the coinoculated wines were different from both the single-strain wines and equal blends of the single-strain wines. Volatile thiol analysis indicated that the Vin7/QA23 coinoculated wines were highest in 3-mercaptohexan-1-ol (3MH) and 3-mercaptohexyl acetate (3MHA), although this pattern was not observed for the Vin7/Vin13 yeast combination. The negative white vinegar aroma and high volatile acidity measured in the Vin7 single-strain wines were not present in the coinoculated wines. This study demonstrates that coinoculations can modify the aroma profile of wines, when complementary yeasts are used.     

Application of a modified method for 3-mercaptohexan-1-ol determination to investigate the relationship between free thiol and related conjugates in grape juice and wine

A method has been developed for determining 3-mercaptohexan-1-ol (3-MH) in wine and grape juice using gas chromatography with conventional electron ionization (EI) mass spectrometry. The limit of quantitation of 40 ng/L was achieved with excellent precision using stable isotope dilution analysis (SIDA) combined with headspace solid-phase microextraction (SPME) of derivatized 3-MH. This method was used in combination with HPLC-MS/MS analysis of the individual diastereomers of 3-S-cysteinylhexan-1-ol (Cys-3-MH) and 3-S-glutathionylhexan-1-ol (Glut-3-MH), which are known precursors of the volatile thiol 3-MH. Commercial and small-lot winemaking trials were evaluated to determine the concentrations of precursors and free 3-MH at various stages of grape processing and winemaking. Five Sauvignon blanc clones were also assessed for precursors and free thiol during ripening, revealing the presence of 3-MH in the unfermented juices and a stark increase in precursor concentrations in the latter stage of ripening. Additionally, differences due to sample freezing and mode of juice preparation were revealed for the precursors, and a set of commercially available wines was analyzed to investigate the amounts of precursors and free 3-MH in Sauvignon blanc and other white wine varieties. There was seemingly no relationship between precursor concentrations in juice and 3-MH concentrations in wine. This was somewhat understandable, because the formation of precursors appears to be a dynamic process affected by a multitude of factors, beginning with grape ripening and continuing during vinification.     

Quantification of cysteine S-conjugate of 3-sulfanylhexan-1-ol in must and wine of petite arvine vine by stable isotope dilution analysis

Making use of a convenient synthetic approach to prepare the deuterated S-3-(hexan-1-ol)-cysteine by a Michael addition reaction, an analytical method was developed to measure the presence of the cysteine S-conjugate, precursor of 3-sulfanylhexan-1-ol (3-mercaptohexan-1-ol), in must and wine from Petite Arvine vine. The method uses a stable isotope dilution assay with a suitable one-step sample preparation and HPLC-MS detection. The method has limits of detection and quantification of 3 and 10 microg/L, respectively. A correlation between the increase of the precursor concentration and the increase of the degree of rot has been established.     

Volatile components and aroma active compounds in aqueous essence and fresh pink guava fruit puree (Psidium guajava L.) by GC-MS and multidimensional GC/GC-O

Characterization of the aromatic profile in commercial guava essence and fresh fruit puree by GC-MS yielded a total of 51 components quantified. Commercial essence was characterized to present a volatile profile rich in components with low molecular weight, especially alcohols, esters, and aldehydes, whereas in the fresh fruit puree terpenic hydrocarbons and 3-hydroxy-2-butanone were the most abundant components. In the olfactometric analyses totals of 43 and 48 aroma active components were detected by the panelists in commercial essence and fruit puree, respectively. New components were described for the first time as active aromatic constituents in pink guava fruit (3-penten-2-ol and 2-butenyl acetate). Principal differences between the aroma of the commercial guava essence and the fresh fruit puree could be related to acetic acid, 3-hydroxy-2-butanone, 3-methyl-1-butanol, 2,3-butanediol, 3-methylbutanoic acid, (Z)-3-hexen-1-ol, 6-methyl-5-hepten-2-one, limonene, octanol, ethyl octanoate, 3-phenylpropanol, cinnamyl alcohol, alpha-copaene, and an unknown component. (E)-2-Hexenal seems to be more significant to the aroma of the commercial essence than of the fresh fruit puree.     

Volatile organic sulfur-containing constituents in Poncirus trifoliata (L.) Raf. (Rutaceae)

During our screening of plant materials to find new natural fragrance and flavor ingredients, we discovered two series of 3-sulfanylalkyl alkanoates in a peel extract of fruits of wild-growing Poncirus trifoliata (L.) Raf. (Rutaceae), a species closely related to Citrus. The two series belong to alkanoates of 3-methyl-3-sulfanylbutan-1-ol and 3-sulfanylhexan-1-ol, respectively, and thus are members of a family of natural molecules having in common a 1,3-positioned O,S moiety. The alkanoate residues comprise all even-numbered saturated fatty acids from C2 (acetate) to C18 (octadecanoate). Among the 20 sulfur-containing compounds identified, 14 are described for the first time as naturally occurring in a botanical species. Several cysteine-S-conjugates were synthesized as hypothetical precursors of the new volatile sulfur-containing constituents, where after S-(3-hydroxy-1,1-dimethylpropyl)-L-cysteine, S-[3-(acetyloxy)-1,1-dimethylpropyl]-L-cysteine, and S-[1-(2-hydroxyethyl)butyl]-L-cysteine were identified in the fruit peel. No cysteine-S-conjugates were detected in the fruit juice.     

Odorous impact of volatile thiols on the aroma of young botrytized sweet wines: identification and quantification of new sulfanyl alcohols

Specific extraction of volatile thiols using sodium p-hydroxymercuribenzoate revealed the presence of three new sulfanylalcohols in wines made from Botrytis-infected grapes: 3-sulfanylpentan-1-ol (II), 3-sulfanylheptan-1-ol (III), and 2-methyl-3-sulfanylbutan-1-ol (IV). The first two have citrus aromas, whereas the third is reminiscent of raw onion. In addition, 2-methyl-3-sulfanylpentan-1-ol, which has a raw onion odor, was tentatively identified. Like 3-sulfanylhexan-1-ol (I), already reported in Sauternes wines, compounds II, III, and IV were absent from must. They were found in wine after alcoholic fermentation, and their concentrations were drastically higher when Botrytis cinerea had developed on the grapes. In the commercial botrytized wines analyzed, the mean levels of II, III, and IV were 209, 51, and 103 ng/L, respectively. Despite their low odor activity values, sensory tests showed additive effects among I, II, and III, thus confirming their olfactory impact on the overall aroma of botrytized wines.     

Occurrence of Odorant Polyfunctional Thiols in Beers Hopped with Different Cultivars. First Evidence of an S-Cysteine Conjugate in Hop ( Humulus lupulus L.)

Forty-one thiols, mainly β-sulfanylalkyl acetates, β-sulfanylalkyl alcohols, and β-sulfanylalkyl carbonyls, were recently evidenced in hop. In a beer hopped with the Tomahawk cultivar, most of them were found at higher levels than expected. The aim of the present work was to investigate the polyfunctional thiols in beers hopped with different varieties. A few thiols proved not to come only from hop (mainly 2-sulfanylethyl acetate, μg/L levels, and 1-sulfanylpentan-3-one and 1-sulfanylpentan-3-ol, ng/L levels, internal standard (IST) equivalents). The thiol profile of Saaz-hopped beer proved similar to that of the reference beer produced without hop. A high level of 3-sulfanyloctan-1-ol emerged as an indicator of the use of Tomahawk hop (140 ng/L, IST equivalents; FD (flavor dilution) = 65536). In both Cascade- and Tomahawk-hopped beers, 3-sulfanylhexan-1-ol and 3-sulfanylheptan-1-ol were smelled at high flavor dilutions, although only for the latter, significant amounts of the unreduced 3-sulfanylheptanal were found in hop. As already claimed for hop authentication, 3-sulfanyl-4-methylpentan-1-ol remains a good marker of Nelson Sauvin-hopped beers (548 ng/L, IST equivalents; FD = 65536), together with 4-sulfanyl-4-methylpentan-2-one (128 ng/L, FD = 4096). As illustrated by the huge production occurring during fermentation, accurate prediction of hop varietal impact requires quantitating thiol adducts in hop. S-3-(1-Hydroxyhexyl)cysteine was evidenced here for the first time in Cascade hop.     

Volatile chemicals identified in extracts from newly hybrid citrus,dekopon (Shiranuhi mandarin Suppl. J.)

Extracts from the peel and flesh of a citrus fruit, dekopon (Shiranuhi mandarin Suppl. J.), were obtained under reduced pressure followed by dichloromethane extraction. A total of 127 volatile chemicals were identified in the extracts using gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). They included 11 monoterpenes, 32 monoterpenoids, 9 sesquiterpenes, 5 sesquiterpenoids, 20 aliphatic alcohols, 14 aliphatic esters, 15 aliphatic aldehydes and ketones, 7 aliphatic acids, and 10 miscellaneous compounds. The major volatile constituents of the extract from the peel were d-limonene (2380.33 mg/kg), myrcene (36.54 mg/kg), bisabolene (30.03 mg/kg), sabinene (21.12 mg/kg), trans-beta-ocimene (16.96 mg/kg), valencene (12.84 mg/kg), decanal (8.14 mg/kg), beta-phellandrene (4.53 mg/kg), citronellol (4.51 mg/kg), 4-terpineol (4.50 mg/kg), linalool (4.13 mg/kg), and citronellyl acetate (3.63 mg/kg). The major volatile constituents of the extract from the flesh were ethyl acetate (21.54 mg/kg), acetoin (7.23 mg/kg), 3-methylbutanol (2.79 mg/kg), p-mentha-cis-2,8-dien-1-ol (1.01 mg/kg), 3-methylbutanoic acid (0.95 mg/kg), isobutanol (0.59 mg/kg), trans-isopiperitenol (0.58 mg/kg), p-mentha-trans-2,8-dien-1-ol, and trans-carveol (0.44 mg/kg). Compositions of volatile chemicals in peel and flesh extract were considerably different: the peel extract was rich in terpenes, whereas the flesh extract was rich in aliphatic compounds.     

Identification of odor-active 3-mercapto-3-methylbutyl acetate in volatile fraction of roasted coffee brew isolated by steam distillation under reduced pressure

In a roasted Arabica coffee brew, the potent roasty odor quality compound was identified as 3-mercapto-3-methylbutyl acetate by comparison of its Kovats gas chromatography retention index, mass spectrum, and odor quality to those of the synthetic authentic compound. 3-Mercapto-3-methylbutyl acetate has been identified for the first time in the coffee, and according to the results of the aroma extract dilution analysis, the contribution of this compound to the flavor of the roasted coffee brew varied depending on the degree of the coffee bean roasting. The concentration of this compound in the coffee brews as with 3-mercapto-3-methylbutyl formate increased with an increase in the degree of roasting. However, the slope of the amount of both esters was different, and 3-mercapto-3-methylbutyl acetate hardly increased with a low degree of roasting at more than a 21 luminosity (L)-value, but it rapidly increased when the roasting degree of the coffee beans reached the L-value of 18. These results suggested that the contribution of 3-mercapto-3-methylbutyl acetate to the overall flavor is peculiar to the flavor of the highly roasted coffee.     

Quantitation of the intense aroma compound 3-mercapto-2-methylpentan-1-ol in raw and processed onions (Allium cepa) of different origins and in other Allium varieties using a stable isotope dilution assay

A stable isotope dilution assay was developed for the quantitation of the potent onion odorant 3-mercapto-2-methylpentan-1-ol (1) using mass chromatography and synthesized [(2)H(2)]-3-mercapto-2-methylpentan-1-ol as the internal standard. Application of the newly developed method on onions from different origins revealed amounts between 8 and 32 microg/kg in raw onions, whereas 34-246 microg was found in sliced, stored (50 min), and then cooked onions. In extracts prepared by simultaneous steam distillation-extraction the highest concentrations of 1 were formed, amounting to >1200 microg/kg. The much higher content of 3-mercapto-2-methylpentan-1-ol in cooked onions suggested its formation from specific, yet unkown, precursors enzymatically formed during cutting of raw onions. 1 was for the first time identified and also quantified in other Allium species such as chives, scallions, and leek, whereas surprisingly garlic and bear's garlic did not contain the aroma compound.     

Discrimination of olive oils and fruits into cultivars and maturity stages based on phenolic and volatile compounds

Olive oil and fruit samples from six cultivars sampled at four different maturity stages were discriminated into cultivars and maturity stages. The variables-volatile and phenolic compounds-that significantly (p < 0.01) discriminated cultivars and maturity stage groups were identified. Separation by stepwise linear discriminant analysis revealed that Manzanilla olive cultivar was separated from cultivars Leccino, Barnea, Mission, Corregiola, and Paragon, whereas cultivars Corregiola and Paragon formed a cluster. The volatile compounds hexanol, hexanal, and 1-penten-3-ol were responsible for the discrimination of cultivars. All maturity stages were discriminated, with the separation of early stages attributed to oil phenolic compounds, tyrosol and oleuropein derivatives, whereas the volatile compounds (E)-2-hexenal, hexanol, 1-penten-3-ol, and (Z)-2-penten-3-ol characterized the separation of all maturity stages and in particular the late stages. Hexanol and 1-penten-3-ol characterized the separation of both cultivars and maturity stages.     

Determination and isolation of a thioesterase from passion fruit (Passiflora edulis Sims) that hydrolyzes volatile thioesters

Volatile organosulfur compounds (VOSCs) are high impact aroma chemicals characteristic of tropical fruits which are active as both free thiols and the respective thioesters. Using a simple and sensitive colorimetric enzyme assay, a thioesterase activity toward VOSCs has been identified in ripening purple passion fruit ( Passiflora edulis Sims). The assay was based on determining the release of free thiols from 2-methyl-3-furanthiol acetate using Ellman's reagent. The major thioesterase in the fruit was found to be a wall-bound protein in the mesocarp. The extracted enzyme activity was purified 150-fold and shown to be associated with a 43 kDa monomeric serine hydrolase which was selectively labeled with a fluorophosphonate suicide probe. MS-MS sequencing identified the thioesterase as a class 13 glycoside hydrolase, most similar to pectin acetylesterase, an enzyme involved in cell wall modifications in the peel of a number of fruit. Our results suggest that cell wall hydrolases in tropical fruit may have additional useful roles in biotransforming VOSCs.     

Occurrence of polyfunctional thiols in fresh lager beers

Polyfunctional thiols are known to have a strong impact on the overall aroma of many fermented foods. Surprisingly, very little data is available on their occurrence in beer. A specific extraction with p-hydroxymercuribenzoic acid was performed on four different fresh light-protected lager beers. gas chromatography-olfactometry, gas chromatography-mass spectrometry, and gas chromatography-pulsed-flame photometer detector analyses of the extracts revealed the presence of more than 10 polyfunctional thiols. All of them were absent from wort, suggesting a key role of the H(2)S excreted by yeasts. 3-Methyl-2-buten-1-thiol, 2-mercapto-3-methylbutanol, 3-mercapto-3-methylbutanol seem to be created from hop allylic alcohols via four different mechanisms: nucleophilic substitution, addition-elimination, and radical anti-Markovnikov or electrophilic Markovnikov additions. 1,4 Addition of hydrogen sulfide to wort alpha,beta-unsaturated aldehydes or ketones may explain the synthesis of 1-mercapto-3-pentanol, 3-mercaptohexanol, and 4-mercapto-4-methyl-2-pentanone through fermentation. Finally, 2-mercaptoethanol, 3-mercaptopropanol, and their corresponding acetates may derive from Ehrlich degradation of sulfur amino acids, while 2-methyl-3-furanthiol should be logically issued from Maillard reactions.