3-mercaptohexyl Acetate Research Articles

The Effect of Yeast Inoculation Methods on the Metabolite Composition of Sauvignon Blanc Wines

Evidence from the literature suggests that different inoculation strategies using either active dry yeast (ADY) or freshly prepared yeast cultures affect wine yeast performance, thus altering biomass and many primary and secondary metabolites produced during fermentation. Here, we investigated how different inoculation methods changed the fermentation behaviour and metabolism of a commercial wine yeast. Using a commercial Sauvignon blanc (SB) grape juice, fermentation was carried out with two different inoculum preparation protocols using Saccharomyces cerevisiae X5: rehydration of commercial ADY and preparation of pre-inoculum in a rich laboratory medium. We also determined the effect of different numbers of yeast cells inoculation (varying from 1 × 106 to 1 × 1012) and successive inoculation on fermentation and end-product formation. The yeast inoculation method and number of cells significantly affected the fermentation time. Principal component analysis (PCA) using 60 wine metabolites showed a separation pattern between wines produced from the two inoculation methods. Inoculation methods influenced the production of amino acids and different aroma compounds, including ethyl and acetate esters. Varietal thiols, 3-mercaptohexanol (3MH), and 4-methyl-4-mercaptopentan-2-one (4MMP) in the wines were affected by the inoculation methods and numbers of inoculated cells, while little impact was observed on 3-mercaptohexyl acetate (3MHA) production. Pathway analysis using these quantified metabolites allowed us to identify the most significant pathways, most of which were related to central carbon metabolism, particularly metabolic pathways involving nitrogen and sulphur metabolism. Altogether, these results suggest that inoculation method and number of inoculated cells should be considered in the production of different wine styles.

Characterization of key sulfur aroma compounds and enantiomer distribution in Yingjia Gongjiu

Yingjia Gongjiu (YJGJ), as a strong-aroma-type baijiu, is popular among consumers due to its unique fruity flavor. However, previous research on the aroma characteristics of YJGJ mostly focused on its main aroma components, namely the esters, therefore, the present work was the first to study the aroma characteristics of YJGJ from the perspective of sulfur-containing compounds. A total of 12 sulfur-containing compounds were identified. Among them, 4-methyl-4-mercapto-2-pentanone, 2-methyl-3-furanthiol, 3-mercaptohexyl acetate, dimethyl disulfide, dimethyl trisulfide, and methional were among the key contributors to the aroma of YJGJ. Meanwhile, 14 enantiomers were identified. Among them, (R)-(−)-3-mercaptohexyl acetate, (R)-(−)-3-mercapto-2-butanone, (R)-(−)-2-octyl butanoate, (S)-(+)-2-octyl butanoate, (R)-(−)-1-octen-3-ol, (R)-(−)-ethyl 2-methylbutanoate and (R)-(−)-phenylethyl 2-methylbutanoate made an important contribution to the aroma of YJGJ. This research may provide an important theoretical basis for the quality improvement and quality identification of YJGJ and other strong-aroma-types of baijiu.

The Sensorial and Chemical Changes in Beer Brewed with Yeast Genetically Modified to Release Polyfunctional Thiols from Malt and Hops

The biotransformation of hop aroma, particularly by the cysteine S-conjugate beta-lyase enzyme (CSL), has been a recent topic of tremendous interest among brewing scientists and within the brewing community. During a process often referred to as biotransformation, yeast-encoded enzymes convert flavorless precursor molecules found in barley and hops into volatile thiols that impart a variety of desirable flavors and aromas in beer. Two volatile thiols of particular interest are 3-mercaptohexan-1-ol (3MH) and its acetate ester, 3-mercaptohexyl acetate (3MHA), which impart guava and passionfruit flavors, respectively. In this study, a parental Saccharomyces cerevisiae brewing strain that displayed low thiol biotransformation activity was genetically manipulated (GM) to substantially increase its thiol biotransformation potential. Construction of this GM strain involved integration of a gene encoding a highly active CSL enzyme that converts thiol precursors into the volatile thiol, 3MH. Three additional strains were subsequently developed, each of which paired CSL expression with expression of an alcohol acyltransferase (AAT) gene. It was hypothesized that expression of an AAT in conjunction with CSL would increase production of 3MHA. Fermentation performance, sensory characteristics, and 3MH/3MHA production were evaluated for these four GM strains and their non-GM parent in 1.5hL fermentations using 100% barley malt wort hopped at low levels with Cascade hops. No significant deviations in fermentation performance (time to attenuation, final gravity, alcohol content, wort fermentability) or finished beer chemistry were observed between the GM strains and the parent strain with the exception of the speed of vicinal diketones reduction post-fermentation, which was quicker for the GM strains. The GM strains produced beer that had up to 73-fold and 8-fold higher 3MH and 3MHA concentrations than the parent strain, achieving concentrations that were up to 79-fold greater than their sensory detection thresholds. The beers were described as intensely tropical and fruity, and were associated with guava, passionfruit, mango, pineapple and sweaty aromas. These experiments demonstrate the potential of genetic modification to dramatically enhance yeast biotransformation ability without creating off flavors or affecting fermentation performance.

Modulation of Welschriesling wine volatiles through the selection of yeast and lactic acid bacteria

Welschriesling is a variety common to Central and Eastern European wine-producing countries; however, its aromatic composition remains poorly understood. Our study aims to determine the volatile profile of Welschriesling by analysing varietal thiols, esters, higher alcohols and monoterpene alcohols in commercial wines. In addition, the selection of commercial yeast starters and lactic acid bacteria (LAB) was used to modulate Welschriesling wine volatile composition. Both the selection of yeast and LAB had a significant impact on the compositional parameters of the wines. Yeast starter Uvaferm 228 (UVF228) was the most effective in terms of 3-mercaptohexan-1-ol (3MH) and 3-mercaptohexyl acetate (3MHA) production. For the ethyl esters of fatty acids (EEFAs), higher alcohol acetates (HAAs) and higher alcohols (HAs), no common inter-group behaviour could be observed based on yeast selection, however, as a group, EEFAs and HAs were highest in wines fermented with UVF228.Malolactic fermentation (MLF) significantly influenced varietal thiols, irrespective of the LAB strain used. Concentrations of 3MH significantly increased with MLF, 4-mercapto-4-methyl-pentan-2-one (4MMP) concentrations decreased, while 3MHA concentrations remained unaltered. This study showed the specific influence of yeast and LAB strain on selected volatile compounds. MLF appeared to be a promising tool to boost the presence of 3MH in wines, however, the results need further confirmation across a range of fermentation conditions and strain selections.

Effect of Oxygen and Nitrogen Sparging during Grape Fermentation on Volatile Sulphur Compounds

Elemental sulphur is a common fungicide applied in vineyards before harvest, and has been found toincrease the production of desirable polyfunctional mercaptans, but also H2S and unwanted reductivesulphur aroma compounds. This paper investigates the effectiveness of oxygen and nitrogen sparging,applied during fermentation, on the removal of volatile sulphur compounds in Sauvignon blanc wines.Increasing the amount of elemental sulphur added to grapes after pressing, from nil to 10 to 100 mg/L,led to an increase in the formation of 3-mercaptohexanol (3MH), of 3-mercaptohexyl acetate (3MHA) forthe 10 mg/L additions only, and of some unwanted reductive compounds. Few changes were observed inthe concentrations of aroma compounds when the juices were sparged with nitrogen during fermentation.Additions of oxygen during fermentation led to some decrease in the concentration of polyfunctionalmercaptans for the 10 mg/L sulphur additions, but did not significantly remove reductive aroma compounds.Few differences were observed in the concentration of wine phenolics or of further wine aroma familieswith any of the treatments.

Characterization of the major aroma-active compounds in peach (Prunus persica L. Batsch) by gas chromatography–olfactometry, flame photometric detection and molecular sensory science approaches

Aroma profiles and aroma-active compounds of “Yulu” peach from Fenghua (the peach known for the best flavor and quality in China) were investigated by headspace solid-phase microextraction (HS-SPME), solvent-assisted flavor evaporation (SAFE), gas chromatography–olfactometry (GC–O), gas chromatography–mass spectrometry (GC–MS), and flame photometric detection (FPD). The combination of these methods improved the analysis and identification of aroma substances compared to the combination of a single aroma extraction method and GC–MS. A total of 85 aroma-active compounds, including 10 sulfur compounds were detected. Methional, methyl 3-(methylthio)propionate, methionol, and benzothiazole were first detected in peaches. These aroma compounds cannot only supplement the database of aroma substances of peaches, but also provide data support for traceability of the origins of “Yulu” peaches. In addition, the odor activity value (OAV) was used to identify the contributions of the most important compounds. The results indicated that hexanal, 3-methylbutanal, (E)-2-hexen-1-ol, 3-mercaptohexyl acetate, (E,E)-2,4-decadienal, 2-methylpropanal, γ-decalactone, 2-methylbutanal, theaspirane, and δ-decalactone were the key aroma-active compounds. The key characteristic aroma components were further ascertained by aroma reconstitution and omission experiments, which showed that the fruity, floral, sulfur, and sour notes could be well simulated. Finally, the perceptual interactions between different sulfur compounds and fruity recombination (FR) were explored. 3-mercaptohexanol and 4-methyl-4-mercaptopentan-2-one could significantly decrease the threshold of FR. The possible reason was that these two sulfur compounds had synergistic effects with the aroma compounds in FR, with the U model confirming the results of these synergistic effects. The perceptual interactions provide a basis for the regulation of characteristic fruity aroma of peach products.

Aroma and Sensory Profiles of Sauvignon Blanc Wines from Commercially Produced Free Run and Pressed Juices

Sauvignon blanc is the most important grape cultivar within the New Zealand wine industry, and wines from the Marlborough region are renowned for their intense aromas including tropical, passionfruit, and green capsicum. Quality Sauvignon blanc wines are usually made from free run juice, although press fractions can be included. The chemical aroma composition and sensory profiles of two wine sets made from three press fractions (free run, light press and heavy press) were compared. The compounds 3-mercaptohexan-1-ol and 3-mercaptohexyl acetate were found to decrease between free run and heavily pressed wines while hexyl acetate, hexanol, and benzyl alcohol increased. The accompanying sensory analysis showed that free run wines were marked by aromas of Passionfruit/sweaty, Boxwood and Fresh green capsicum, while the heavy pressed wines were described by French vanilla/bourbon, Floral and Banana lolly attributes, consistent with the aroma chemical composition.

Interpretations of key food odorant dose-olfactory response curves using statistical physics method

In this work, statistical physics treatment has been employed to understand the olfaction mechanism through the study of the dose-olfactory response of putative adsorption process of key food odorants onto the human olfactory receptor OR2W1. This is in order to obtain new steric and energetic characterizations at the molecular level of this chemical sense system. Three models have been proposed: a monolayer, a double layer and a three layers model. The monolayer model with identical and independent receptor sites has been chosen as an appropriate one to present a good correlation with the experimental dose-response curves. Indeed, the numerical values of the three fitted parameters (RM, n, C1/2) are used to characterize the size of the human olfactory receptor binding sites and the interactions between eight key food odorants i.e., (R)-(−)-carvone, (S)-(−)-limonene, (R)-(+)-limonene, 2-phenylethanthiol, 3-mercaptohexyl acetate, methyl cinnamate, cinnamyl acetate and 2-phenylethyl acetate and OR2W1 through the receptor site size distribution (RSD) and to determine an olfactory band of these odorants through the determination of the adsorption energy values and the adsorption energy distributions (AEDs).

Isolation and Identification of Indigenous Wine Yeasts and Their Use in Alcoholic Fermentation.

SUMMARYResearch backgroundIn our study, spontaneous alcoholic fermentations were carried out to isolate non-Saccharomyces and Saccharomyces yeasts from grape must from different vine-growing regions in Slovenia. Additionally, the diversity of native Saccharomyces cerevisiae strains was evaluated during the process.Experimental approachDuring spontaneous alcoholic fermentations the yeast population of non-Saccharomyces and Saccharomyces yeasts was sampled. We used eleven microsatellite markers to determine the genetic diversity of S. cerevisiae strains. In addition, different ratios of the indigenous strains of S. cerevisiae, Hanseniaspora uvarum and Starmerella bacillaris were tested for their possible use in alcoholic fermentation with inoculated yeasts by monitoring its course and measuring the concentration of aroma compounds in wine.Results and conclusionsSequencing of the internal transcribed spacer (ITS) regions of ribosomal DNA showed that of 64 isolates, 46 strains represent S. cerevisiae and 18 strains belong to non-Saccharomyces yeasts. The identified non-Saccharomyces yeast species were H. uvarum, Pichia kudriavzevii, Saturnispora diversa and S. bacillaris. The dendrogram grouped S. cerevisiae strains into 14 groups. The number of S. cervisiae strains isolated from the musts was 10 (Posavje), 11 (Podravje) and 25 (Primorska vine-growing region). On the other hand, the alcoholic fermentation with inoculated yeasts, in which the native S. cerevisiae strain predominated over H. uvarum and S. bacillaris, gave the most promising result due to the highest alcoholvolume fraction, the lowest acetic acid concentration and significantly higher concentrations of volatile thiols 3-mercaptohexyl acetate (3MHA) and 3-mercaptohexan-1-ol (3MH), 2-methylpropanol, 2-methylbutanol, 3-methylbutanol and 2-phenylethanol) in the produced wine.Novelty and scientific contributionWe confirmed the potential use of indigenous S. cerevisiae and non-Saccharomyces yeasts in alcoholic fermentation with inoculated yeasts, which allows the positive properties of the yeast strains to be expressed and good quality wines to be produced. Thus, the results are encouraging for winemakers to create different wine styles associated with a particular terroir using indigenous yeasts.

Matrix effects influencing the perception of 3-mercaptohexan-1-ol (3MH) and 3-mercaptohexyl acetate (3MHA) in different Chenin Blanc wines by Projective Mapping (PM) with Ultra Flash profiling (UFP) intensity ratings

Interaction studies are used in sensory evaluation to elucidate the complex influences (additive, masking, synergistic) that various compounds have on the perception of wine aroma. To these, the interactions between the matrix and the compounds of interest add another layer of complexity. Unlike previous interaction studies, the current work used a rapid method, Projective Mapping (PM) coupled with intensity of attributes, to evaluate the interaction effects two thiols (3-mercaptohexan-1-ol, 3MH, and 3-mercaptohexyl acetate, 3MHA) have in various matrices. The matrices used were increasingly complex, from model wine to partially dearomatized neutral Chenin Blanc to commercial wines. The results reflected the effect of the thiols interaction with the matrix more than that between compounds. The methodology proposed for the data handling highlighted possible advantages and shortcomings of the Projective Mapping with intensity approach. The choice of base matrix as well as the sensory method are relevant when studying interaction effects, and are dependent on the desired outcome of the experiment.

Characterization of Odor-Active Volatiles in Hawthorn Puree Using Thermal Desorption System Coupled to Gas Chromatography-Mass Spectrometry-Olfactometry and GC-Flame Photometric Detector.

The volatile compounds in hawthorn puree obtained from three cultivars (Y1, Crataegus pinnatifida Bunge cv. "Waibahong", Y2, Crataegus pinnatifida Bunge cv. "Damianqiu", and Y3, Crataegus pinnatifida Bunge cv. "Dajinxing") were analyzed by the thermal desorption system coupled to gas chromatography-mass spectrometry-olfactometry and GC-flame photometric detector. In the samples of Y1, Y2, and Y3, 40, 42, and 42 odor-active compounds were, respectively, identified by olfactometry. Methyl 2-methylbutanoate, methyl hexanoate, hexyl isobutanoate, methional, heptanal, and ( Z)-3-hexenyl acetate contributed largely to the characteristic aroma of the three samples. Additionally, the odor activity value (OAV) was used to determine the main compounds and 3-mercaptohexyl acetate (OAV: 10-18), 3-mercapto-2-methylpentanal (OAV: 4-7), methyl 2-methylbutanoate (OAV: 9-21), methyl hexanoate (OAV: 8-16), and 2-pentyl acetate (OAV: 5-12) were considered as the important contributors to the aroma of hawthorn samples.

Investigation of Thiol Levels in Young Commercial South African Sauvignon blanc and Chenin blanc Wines Using Propiolate Derivatization and GC-MS/MS

In this work, the ethyl propiolate method for analysing thiols in white wine by GC-MS, originally proposed by Herbst-Johnstone et al.) (2013), has been adapted to GC-MS/MS and has been validated. The method performance has shown improvement in terms of sensitivity (limit of detection, LOD) and of the number of compounds measured. In addition to 3-mercaptohexanol (3MH), 3-mercaptohexyl acetate (3MHA), and 4-mercapto-4-methylpentan-2-one (4MMP), the adapted method can also measure 2-furanmethanethiol (FMT) and makes use of a commercially-available internal standard (IS), 4-methoxy-2-methyl-2-butanethiol (4M2M2B, IS). The proposed method was applied to determine thiol levels in young commercial South African Sauvignon and Chenin Blanc wines. The samples (n=20 for each cultivar) were chosen according to a high frequency of the typical descriptors associated with this class of impact compounds. 3MH was found at 178-904 ng/L and 99-1124 ng/L, and 3MHA at 23-151 ng/L and 5-253 ng/L in Sauvignon and Chenin Blanc respectively. 4MMP was present in Sauvignon Blanc in concentrations up to 21.9 ng/L, but in none of the Chenin Blanc samples.

Lipids modulate acetic acid and thiol final concentrations in wine during fermentation by Saccharomyces cerevisiae\u2009\xd7\u2009Saccharomyces kudriavzevii hybrids

Saccharomyces cerevisiae × Saccharomyces kudriavzevii hybrids are typically used for white wine fermentation because of their cryotolerance. One group of these hybrids presents a unique ability to release thiol varietal aroma products as well as excessive amounts of acetic acid under specific conditions, which is detrimental for wine organoleptic quality. The aim of this work is to better assess the effects of lipids, sugar concentrations and temperature on the production of acetic acid and thiols during wine fermentation. To this end, we used a Box–Behnken experimental design and response surface modeling on the production of acetic acid and thiols in S. cerevisiae × S. kudriavzevii hybrids from the Eg8 family during fermentation of a synthetic must. We showed that these hybrids produced lower levels of acetic acid when the initial lipid concentration was increased, whereas they produced greater levels when the initial sugar concentration was high. Moreover, we found that lipids had a positive impact on the final concentrations of 4-methyl-4-mercaptopentan-2-one and 3-mercaptohexan-1-ol (3MH), giving box tree and citrus flavors, respectively. The increase of 3MH was concomitant with a decrease of 3-mercaptohexyl acetate (3MHA) characterized by a passion fruit aroma, indicating that lipid addition reduces the rate of 3MH acetylation into 3MHA. These results highlight the key role of lipid management in acetic acid metabolism and thiol release by S. cerevisiae × S. kudriavzevii hybrids and underline its technological interest in alcoholic fermentation to avoid the overproduction of volatile acidity while favoring the release of volatile thiols.

Effect of free fatty acids and lipolysis on Sauvignon Blanc fermentation

Background and Aims The volatile thiols, such as 3-mercaptohexanol, 3-mercaptohexyl acetate and 4-mercapto-4-methylpentan-2-one, are major aroma compounds responsible for the distinctive tropical notes (passionfruit and grapefruit) in New Zealand Sauvignon Blanc wines. Previously, it was observed that traces of linoleic acid in grape juice can significantly affect the development of these volatile thiols and other aroma compounds in wine. Here, we examined the effect of the fatty acids commonly found in Sauvignon Blanc grape juice as well as juice lipid lipolysis on the development of aroma compounds in the resulting wines. Methods and Results Experiments were performed to increase the total free fatty acid concentration in grape juice through juice treatment with acidic lipase from Aspergillus niger and through co-cultured fermentations with non-Saccharomyces lipase-secreting yeasts. We observed a significant reduction in the production of 3-mercaptohexyl acetate in fermented wines upon supplementation with linoleic acid and lipase. Supplementation with lipase increased the concentration of 3-mercaptohexanol and all ethyl esters detected, while reducing the development of acetate esters. Co-cultured fermentations also affected the development of many classes of aroma compounds. Conclusions This study demonstrated that the aroma profile of wines could be effectively manipulated by altering the amount of free unsaturated fatty acids in grape juice through lipolytic enzyme supplementation or co-fermentation with non-Saccharomyces lipolytic yeast species. Significance of the Study The key findings of this study may lead to new winemaking strategies through the manipulation of the lipid component of grape juice.

Revisiting the evaluation strategy of varietal thiol biogenesis

The varietal thiols 3-mercaptohexan-1-ol (3MH), 3-mercaptohexyl acetate (3MHA), and 4-mercapto-4-methylpentan-2-one (4MMP) are key aroma compounds in wine due to the tropical notes they impart. They are released by yeast during alcoholic fermentation from different precursors. However, a large part of 3MH origin remains unknown. In this study, we focused on dipeptide forms arising from glutathione S-conjugates to 3MH and 4MMP. Using labelled tracers, we showed in spiked must the release of varietal thiols from 4 different compounds. We highlighted the interconversion between different forms of precursors under defined enological conditions. Cysteinyl-glycine S-conjugates are partially degraded into cysteine S-conjugates, contrary to γ-glutamyl-cysteine S-conjugates. Glutathione S-conjugate to 3MH can be partially degraded to γ-glutamyl-cysteine S-conjugate to 3MH. For the first time, all these labeled forms of precursors were found to release 3MH or 4MMP between 0.17 and 1% molar conversion yield. Two different yeasts were compared without any significant difference.

Characterization of the Major Odor-Active Compounds in Dry Jujube Cultivars by Application of Gas Chromatography-Olfactometry and Odor Activity Value.

The volatile compounds of jujube ( Ziziphus jujube Mill.) puree obtained from three cultivars, 'Jinsixiaozao' (Y1), 'Youzao' (Y2), and 'Yuzao' (Y3), were analyzed by gas chromatography-olfactometry (GC-O), gas chromatography-mass spectrometry, gas chromatography-flame photometric detection, and a nitrogen phosphorus detector. The results showed that a total of 37, 37, and 35 odor-active compounds were identified by GC-O in samples of Y1, Y2, and Y3, respectively. In addition, the odor activity value (OAV) was used to determine the important compounds. The results demonstrated that hexanal (OAV of 39-85), ( E)-2-octenal (OAV of 32-70), β-damascenone (OAV of 14-49), ethyl hexanoate (OAV of 22-39), 3-mercaptohexyl acetate (OAV of 17-24), and 2,5-dimethylpyrazine (OAV of 17-22) were key odor-active compounds. It is of great significance to develop high-grade jujube food by determining key odor-active compounds. Furthermore, four volatiles (hexanal, 1-octen-3-ol, 3-mercapohexyl acetate, and benzaldehyde) reduced the overall threshold value by 2.36, 1.01, 1.34, and 1.19, respectively.

Characterization of the key aroma compounds in mulberry fruits by application of gas chromatography–olfactometry (GC-O), odor activity value (OAV), gas chromatography-mass spectrometry (GC–MS) and flame photometric detection (FPD)

The volatile compounds of mulberries obtained from three cultivars (M. nigra, Y1, M. Macroura, Y2 and M. Alba, Y3) were investigated by gas chromatography–olfactometry (GC-O), odor activity value (OAV), gas chromatography-mass spectrometry (GC–MS) and flame photometric detection (FPD). The results showed that 41, 37 and 41 compounds were detected in Y1, Y2 and Y3 samples, respectively. In addition, 12, 11, and 12 sulfur compounds were identified in three samples by FPD, respectively. Quantitative analysis showed 2-(methylthio)ethanol, methionol, dimethyl sulfide, methional and 3-ethylthiophene were present in relatively high amounts in each of the three samples. Furthermore, benzaldehyde, ethyl butanoate, (E)-2-nonenal, 1-hexanol, hexanal, methional, 3-mercaptohexyl acetate and 3-mercaptohexanol were present with much higher OAVs than other compounds. Finally, four compounds (pentanal, ethyl acetate, acetic acid, methionol) were selected to investigate possible effects on six descriptors, which indicated that the volatile compounds at sub-threshold concentrations are likely to contribute to overall aroma.

Indigenous yeasts perform alcoholic fermentation and produce aroma compounds in wine

The spontaneous alcoholic fermentations of Moscato Bianco and Welschriesling must were carried out to retrieve indigenous yeasts. We confirmed that those fermentations, conducted with non-Saccharomyces and indigenous Saccharomyces cerevisiae yeasts, can generate high amounts of aroma compounds in wines. Consequently, two of the S. cerevisiae isolates were randomly chosen and further examined in Welschriesling and Sauvignon Blanc must for their ability and efficiency in performing alcoholic fermentation. Alcoholic fermentation with a commercial yeast strain was carried out for comparison. Indigenous isolates showed acceptable fermentation ability and efficiency. Moreover, Sauvignon Blanc produced with indigenous isolates contained significantly higher amounts of 3-mercaptohexyl acetate, linalool, geraniol and 2-phenylethanol and a significantly lower amount of 3-mercaptohexan-1-ol. Differences in Welschriesling wine were less striking but in this case indigenous isolates produced lower amounts of 3-mercaptohexan-1-ol and α-terpineol. Taken together, our results confirm that a suitable aromatic profile of wine can be produced with indigenous S. cerevisiae strains.

Study of the influence of varietal amino acid profiles on the polyfunctional mercaptans released from their precursors

Polyfunctional mercaptans such as 4-mercapto-4-methyl-2-pentanone, 3-mercaptohexanol and 3-mercaptohexyl acetate contribute strongly to the varietal aroma of wines. These compounds are released during alcoholic fermentation from their precursors and their concentration is strongly linked to the grape variety. The aim of this work was to determine the effect of nine different amino acid profiles of grape varieties on the release of these polyfunctional mercaptans and on the consumption of their precursors as well as to determine which are the preferred precursors. A set-up of fermentations of synthetic must was prepared, which simulated the amino acid profiles of nine different grape varieties, containing known amounts of polyfunctional mercaptan precursors as well as the elements necessary for the yeast metabolism. The yeast assimilable nitrogen was adjusted in percentage to reach 150mgN/L in all the fermentations. Polyfunctional mercaptans and their precursors were analyzed in the final wine by gas chromatography coupled to mass spectrometry with negative chemical ionization and ultrahigh liquid performance chromatography coupled to mass spectrometry, respectively. The results showed significant differences in the release of these polyfunctional mercaptans as well as in the consumption of their precursors according to the amino acid profile. Moreover, it was observed that the preferred precursor of 4-mercapto-4-methyl-2-pentanone was its cysteinylated precursor. These results suggest that the amount of the amino acids as well as the ratio between them could modify the amount of polyfunctional mercaptans released. This could be a tool for the wine industry to vary the aromatic profile of wines by increasing or decreasing these volatile thiols.

The role of potent thiols in Chardonnay wine aroma

Background and Aims Polyfunctional thiols are key aroma compounds in many Sauvignon Blanc wines, but their role in other white cultivars is not clear. Methods and Results A survey of 106 commercial Australian Chardonnay wines found a high concentration of 3-mercaptohexan-1-ol, 3-mercaptohexyl acetate, benzyl mercaptan and 4-mercapto-4-methylpentan-2-one, with nearly all wines having a concentration of all compounds well above their reported sensory detection threshold, and some having a concentration comparable to that found in highly fruity Sauvignon Blanc wines. Wines were made on a research scale from a set of Chardonnay juices sourced from 16 vineyards across Australia. Sensory descriptive analysis combined with quantitative aroma volatile data revealed that several aroma and flavour attributes were related to the concentration of the thiols. Conclusions This study provided evidence that substantial flavour in Chardonnay can be contributed by these thiols. Additionally, consumer acceptance data showed that wines with a higher thiol concentration were liked by most consumers. Significance of the Study This study revealed the importance of polyfunctional thiols in Chardonnay wine.