•Novel GCMS/MS method for the concurrent quantification of 10 sesquiterpenes in grape must.•First SIDA quantitative study of sesquiterpenes.•Suitable for low concentration-sesquiterpene analysis in ...grape products.•Method successfully applied to variety of several grape musts.
Sesquiterpenes are a widespread class of compounds of increasing interest found in grapes and wines, amongst many other natural sources. Due to a lack of standards and the complexity of the mass spectra fragmentation, accurate quantification of these low concentration compounds had not previously been accomplished.
The current paper presents a new method for the concurrent quantification of several sesquiterpenes. The multivariate method optimisation is presented. Synthesised isotopic standards were utilised in conjunction with solid phase microextraction (SPME) and gas chromatography-tandem mass spectrometry (GC–MS/MS) to perform a standard isotope dilution assay (SIDA). The method was successfully applied to several grape must samples of four different cultivar. To the best of our knowledge this was the first time some of these sesquiterpenes were quantified in grape.
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.
•Ultra-violet (UV) light irradiation can alter wine aroma compound concentrations.•After cold settling, no differences in juice thiol precursors between UV treatments.•Lower 3-mercaptohexyl acetate ...wine levels for damaged grapes exposed to UV light.•Lower hexan-1-ol wine levels for whole grape bunches exposed to UV light.
Sauvignon blanc grapes were exposed to an ultra-violet (UV) light source post-hand harvest (whole bunches) or post-machine harvest. The thiol precursors S-3-(hexan-1-ol)-l-cysteine (Cys-3MH) and S-3-(hexan-1-ol)-l-glutathione (GSH-3MH) were quantified in the juices before and after UV treatment. Results showed that irradiation of the grapes with UV light had little to no effect on the thiol precursors. Wines were fermented from the corresponding juices and 18 aroma compounds were quantified. Differences were found between UV treatments of the wines for 3-mercaptohexanol, hexan-1-ol, ethyl butanoate, ethyl hexanoate, ethyl octanoate and phenylethyl alcohol. However, these changes were not significant (p < 0.05) for both grape media trialled. Future studies involving larger sample sizes and replicate numbers should be completed in order to ascertain any changes in aroma chemistry as a result of UV light application to grapes postharvest.
•The first in vivo study of VSCs linked to H2S formation during winemaking.•Ethanethiol, S-ethyl thioacetate and diethyl disulfide rise in wine fermented with H2S.•34S-labeled sulfate was ...incorporated into these same VSCs by H2S-producing yeast.
Hydrogen sulfide (H2S) is produced by yeast during winemaking and possesses off-flavors reminiscent of rotten eggs. The production of H2S during fermentation has also been associated in the finished wine with the rise of additional volatile sulfur compounds (VSCs) with strong aromas of cooked onions and vegetables. To characterize these more complex VSCs produced from H2S, we performed fermentations in synthetic grape juice. H2S production was manipulated experimentally by feeding increasing concentrations of sulfate to mutant strains that are unable to incorporate H2S efficiently as part of the sulfur assimilation pathway. In finished wines from these mutants, three VSCs – ethanethiol, S-ethyl thioacetate and diethyl disulfide – increased proportionally to H2S. 34S-labeled sulfate fed to the MET17-deleted strain was incorporated into same three VSCs, demonstrating that they are formed directly from H2S.
The effects of two cluster thinning regimes (low and moderate) with Vitis vinifera cv. Pinot noir, in vineyards located in Central Otago, New Zealand, on wine composition, were studied across three ...consecutive seasons. There were strong correlations between the extent of cluster thinning and pH and bunch weights, and the concentrations of the C13-norisoprenoids, monoterpenes, fatty acids, cinnamic esters, β-phenylethyl alcohol, and all polyphenols. The sensory terms herbaceous and acidic consistently received the highest ranking in the control wines without cluster thinning. The thinning treatments produced wines with higher marks in the descriptors fruity, spice, sweet, and body. Cluster thinning also had a measurable effect on timing of harvest, in addition to effects on chemical composition and wine sensory, which demonstrate benefits to wine quality that can be expected with cluster thinning of Pinot noir.
•For the first time ethyl propiolate was successfully used to analyse wine varietal thiols.•For the first time ethyl propiolate adducts were reported to be quantifiable via GC–MS.•New ethyl ...propiolate-based method shows detection limits suitable for wine analysis.•Novel ethyl propiolate-based method shows agreement with p-HMB-based method.
Varietal thiols 3-mercaptohexan-1-ol (3MH), 3-mercaptohexyl acetate (3MHA) and 4-mercapto-4-methylpentan-2-one (4MMP) have been extensively studied in the recent literature. Nonetheless the hardest obstacle for research focussing on this class of compounds is the lack of quick, user-friendly and sensitive analytical methods. The current paper presents the use of ethyl propriolate (ETP) as a novel derivatising agent to quantify varietal thiols and the first time quantification of the thiol–ETP adducts via gas chromatography–mass spectrometry. Method optimisation including choice of the best SPE cartridge, derivatisation pH and adducts stability is presented. Validation of the method via stable isotope dilution was carried out. Detection limits in both model wine (4MMP 7.2ng/L, 3MHA 40.0ng/L and 3MH 91.2ng/L) and white wine (4MMP 24.5ng/L, 3MHA 120.9ng/L and 3MH 194.6ng/L) for the novel ETP-based method were lower than those obtained with the p-HMB method. Finally, 14 New Zealand Sauvignon blanc were analysed with both the new method and the organo-mercury based procure: good correlations were obtained for 3MH and 3MHA. Detection limits obtained with the new methods, its rapidity and reproducibility make this protocol perfectly suitable for oenological purposes.
•Pre-fermentation fining outcomes can be altered by vineyard site and press fraction.•Lower linalool for wines fined pre-fermentation by activated carbon.•PVPP juice fining gave a decrease in IBMP ...concentration when compared to control.
In the wine industry, fining agents are commonly used with many choices now commercially available. Here the influence of pre-fermentation fining on wine aroma chemistry has been explored. Free run and press fraction Sauvignon blanc juices from two vineyards were fined using gelatin, activated carbon, polyvinylpolypyrrolidone (PVPP) and a combination agent which included bentonite, PVPP and isinglass. Over thirty aroma compounds were quantified in the experimental wines. Results showed that activated carbon fining led to a significant (p<0.05) concentration decrease of hexan-1-ol and linalool in the experimental wines when compared to a control, consistent across all vineyard and fraction combinations. Other aroma compounds were also influenced by fining agent, even if vineyards and press fractions played a crucial role. This study confirmed that fining agents used pre-fermentation can influence wine aroma profiles and therefore needs specific tailoring addressing style and origin of grape.
Volatile sulfur compounds (VSCs) play a significant role in the aroma of foods and beverages. With very low sensory thresholds and strong unpleasant aromas, most VSCs are considered to have a ...negative impact on wine quality. In this study, headspace solid phase microextraction coupled with gas chromatography–mass spectrometry (HS-SPME/GC-MS) was used to analyze the time course of the biosynthesis of 12 VSCs formed during wine fermentation. Two different strains of Saccharomyces cerevisiae, the laboratory strain BY4743 and a commercial strain, F15, were assessed using two media: synthetic grape media and Sauvignon Blanc juice. Seven VSCs were detected above background, with three rising above their sensory thresholds. The data revealed remarkable differences in the timing and evolution of production during fermentation, with a transient spike in methanethiol production early during anaerobic growth. Heavier VSCs such as benzothiazole and S-ethyl thioacetate were produced at a steady rate throughout grape juice fermentation, whereas others, such as diethyl sulfide, appear toward the very end of the winemaking process. The results also demonstrate significant differences between yeast strains and fermentation media.
Press fraction juice is generally considered to be of a lower quality than free run and due to excess skin and oxygen contact may result in wines with harsh phenolic profiles. In this situation, ...fining agents may be used to aid the removal of certain polyphenols. During this study, commercial fining agents were employed to fine two sets of Marlborough press fraction juice in industrial sized trials. The concentrations of 23 aroma compounds were determined for the resulting experimental wines, along with a simple sensory analysis. Results showed that both juice and fining agent choice had the ability to influence the wines aroma chemistry. For instance, the Wairau valley juices fined with activated carbon gave an average 3-mercaptohexanol level of 262 ng/L, less than the corresponding control (415 ng/L) which received no fining agent addition. 3-Mercaptohexyl acetate was also lower in these activated samples at an average level of 180 ng/L, compared to 268 ng/L for the control. Reductions of linalool and β-citronellol by activated carbon fining were also observed during this trial. Ethyl (dihydro)cinnamate increased with the use of gelatin from 0.51 and 0.42 μg/L in the control wines to 1.18 and 1.38 μg/L for each juice set, respectively.
•Juice fining can influence the aroma profiles of press fraction wines.•Activated carbon juice fining leads to decreases in varietal wine thiols.•Gelatin juice fining may lead to a rise in ethyl (dihydro)cinnamate levels.
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