Measuring elemental sulfur in grape juice in relation to varietal thiol formation in Sauvignon Blanc wines
Bahareh, Sarmadi, School of Chemical Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand
Paul A., Kilmartin, School of Chemical Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand
Brandt P., Bastow, School of Chemical Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand
Email contact: bsar724[@]aucklanduni.ac.nz
Aim: Sauvignon Blanc displays a range of styles that can include prominent tropical and passionfruit aromas. Both sensory evaluation and chemical analysis have confirmed the above-average presence of 'varietal thiols' in the Sauvignon Blanc wines from Marlborough, New Zealand.1 The varietal thiols are released from cleavage of non-volatile sulfur-containing precursors or an interaction between a sulfur donor and a C6-compound.2 Machine-harvesting is the most common harvesting practice used in New Zealand, by which, there is a higher probability to add some leaves to the must. Leaves and grapes can contain elemental sulfur (S0), which is commonly sprayed in the fields to protect berries against powdery mildew. S0 is known to cause unwanted reductive aromas, including H2S, in certain wines unless remediation steps are undertaken during winemaking. Also, it was shown that extra S0 addition to the crushed grapes could lead to more varietal thiol formation in wines.3 Despite the clear effects of residual S0 present in the must on the final wine quality and aroma4, its measurement is not a regular practice undertaken in wineries due to the lack of easy and applicable methods.
Methods: We have optimized a sulfide sensor for S0 measurement in grape juice samples and investigated the correlation between S0 concentration in grape juice and varietal thiols concentration in final wines. A simple apparatus was designed to reduce S0 to sulfide using dithiothreitol (under acidic conditions, as H2S), followed by an ion-selective electrode (ISE) to measure sulfide concentrations (under alkaline conditions as S2-). GC-MS is being used to analyze thiol concentrations in wine samples to allow comparisons to be made with juice S0 concentrations.
Results: The semi-log calibration curve plotted based on the ISE data showed very good linearity. The results also showed that the reduction process was successful, and the apparatus is working well with both standard and juice samples. The ISE was confirmed to be able to detect the reduced sulfur at concentrations as low as 0.01 ppm.
Conclusion: The methodology allows action between the concentration of S0 residues and the concentration of varietal thiols in the final wines to be investigated. The analysis is applicable in a winery setting to evaluate the potential of grape juices to form varietal thiols and/or reductive compounds in wines.
1. Lund, C. M.; Thompson, M. K.; Benkwitz, F.; Wohler, M. W.; Triggs, C. M.; Gardner, R.; Heymann, H.; Nicolau, L. American Journal of Enology and Viticulture 2009, 60, 1.
2. Harsch, M. J.; Benkwitz, F.; Frost, A.; Colonna-Ceccaldi, B.; Gardner, R. C.; Salmon, J.-M. Journal of agricultural and food chemistry 2013, 61, 3703-3713.
3. Lyu, X.; Dias Araujo, L.; Quek, S.-Y.; Kilmartin, P. A. Food Chemistry 2021, 346, 128914.
4. Araujo, L. D.; Vannevel, S.; Buica, A.; Callerot, S.; Fedrizzi, B.; Kilmartin, P. A.; du Toit, W. J. Food Research International 2017, 98, 79-86.
Alternative fate of varietal thiols in wine: identification, formation, and enantiomeric distribution of novel 1,3-oxathianes
Xingchen, WANG, Department of Wine Science and Waite Research Institute, The University of Adelaide (UA), PMB 1, Glen Osmond, SA 5064, Australia
Liang, CHEN, Universite´ de Bordeaux, Unite´ de Recherche Œnologie, EA 4577, USC 1366 INRAE, Institut des Sciences de la Vigne et du Vin, 33882, Villenave d’Ornon cedex, France
Dimitra L., CAPONE, Department of Wine Science and Waite Research Institute, Australian Research Council Training Centre for Innovative Wine Production, UA, PMB 1, Glen Osmond, SA 5064, Australia
Aurélie, ROLAND, SPO, Univ Montpellier, INRAE, Institut Agro, Montpellier, France
David W., JEFFERY, Department of Wine Science and Waite Research Institute, Australian Research Council Training Centre for Innovative Wine Production, UA, PMB 1, Glen Osmond, SA 5064, Australia
Email contact: xingchen.wang[@]adelaide.edu.au
AIM: This study aimed to explore an alternative fate of varietal thiols by identifying and characterising cis-2-methyl-4-propyl-1,3-oxathiane (cis-2-MPO) and cis-2,4,4,6-tetramethyl-1,3-oxathiane (cis-TTMO) in wine. Elucidating these new pathways could aid in explaining the loss of varietal thiols and would further our understanding of the stereochemical relationships between oxathianes and varietal thiols.
METHODS: GC-MS was used to identify cis-2-MPO,1 and a stable isotope dilution assay (SIDA) was developed to quantify its enantiomers after separation with a chiral β-cyclodextrin GC column.2 Varietal thiols and their enantiomers were analysed by SIDA with HPLC-MS/MS to determine their relationship with cis-2-MPO. Production of cis-2-MPO and its correlation with 3-SH, 3-SHA, and acetaldehyde was studied by profiling the evolution of these volatiles during alcoholic fermentation (AF) of Sauvignon blanc (SB) juice fermented with J7, VIN13, and their co-inoculum.3
RESULTS: cis-2-MPO, derived from 3-SH and acetaldehyde, was identified and then measured at up to 460 ng/L (equivalent to 385 ng/L of 3-SH) in a set of wines. Analysis of (2R,4S)-2-MPO and (2S,4R)-2-MPO, arising from thiol enantiomers (3S)-3-SH and (3R)-3-SH, showed respective concentrations of up to 250 and 303 ng/L. The enantiomeric ratio of (2R,4S)-/(2S,4R)-2-MPO was 43:57 whereas that of (3S)-/(3R)-3-SH in the same wines was 51:49.2 Strong correlations were revealed for both 3-SH and cis-2-MPO and their related enantiomeric pairs.
The AF study showed cis-2-MPO was produced from an early stage of AF and reached a peak of 847 ng/L (VIN13 ferment) before gradually declining to 50-65 ng/L. Its evolution profile was identical to that of acetaldehyde and 3-SHA, with moderate to strong correlations found for the analytes.
Additionally, cis-TTMO, derived from 4-MSPOH and acetaldehyde, was identified in wine as a single enantiomer at concentrations of up to 28 ng/L (equivalent to 23 ng/L of 4-MSPOH). An aroma detection threshold of 14.9 µg/L was determined for cis-TTMO, and this new volatile was described as ‘citrus’, ‘green’, ‘sweet/caramel’, and ‘mango’, shifting toward ‘onion/sweaty’ and ‘sulfurous’ at higher concentrations.2
CONCLUSIONS: The knowledge gained helps rationalise the fate of varietal thiols via the production of oxathianes in wine, and reveals the stereochemical links between these related compounds. A chemical formation pathway to oxathianes was verified and may also apply to other thiols bearing the 1,3-sulfanylalkanol substitution through the reaction with acetaldehyde.
1. Chen, L.; Capone, D. L.; Jeffery, D. W., Identification and quantitative analysis of 2-methyl-4-propyl-1,3-oxathiane in wine. J. Agric. Food Chem. 2018, 66 (41), 10808-10815.
2. Wang, X.; Capone, D. L.; Roland, A.; Jeffery, D. W., Chiral analysis of cis-2-methyl-4-propyl-1,3-oxathiane and identification of cis-2,4,4,6-tetramethyl-1,3-oxathiane in wine. Food Chem. 2021, 129406.
3. Wang, X.; Chen, L.; Capone, D. L.; Roland, A.; Jeffery, D. W., Evolution and correlation of cis-2-methyl-4-propyl-1,3-oxathiane, varietal thiols, and acetaldehyde during fermentation of Sauvignon blanc juice. J. Agric. Food Chem. 2020, 68 (32), 8676-8687.
Chemical and biochemical formation of polysulfides in synthetic and real wines using UHPLC-HRMS
Susanne Dekker, Edmund Mach Foundation
Tiziana Nardin, Edmund Mach Foundation
Mirko Mattana, Edmund Mach Foundation
Igor Fochi, Thermo Fisher Scientific SpA
Roberto Larcher, Edmund Mach Foundation
Katryna van Leeuwen, University of Auckland
Bruno Fedrizzi, University of Auckland
Cinzia Dell'Anna, Edmund Mach Foundation
Email contact: susanne.dekker[@]fmach.it
AIM: Sulfur compounds in wine have been studied for several years due to their impact on wine flavour, but the role of polysulfides is a recent topic. Polysulfides in wine are formed when two sulfhydryl groups oxidize, especially in presence of elemental sulfur or metal catalysts from field treatment residues (Ugliano et al. 2011). These compounds are odourless, but can degrade during storage and affect the wine quality. The mechanism of their formation is still largely unknown but different chemical and biochemical pathways have been suggested. Disulfides from cysteine (Cys) and glutathione (GSH) have been revealed in model wines (Kreitman et al. 2016) and more recently also higher polymerized forms in real wines (Van Leeuwen et al. 2020). Volatile varietal thiols like 3-mercaptohexanol (3MH) and 4-mercaptopentanone (4MMP) - flavour compounds with tropical or fruity notes - could undergo similar reactions, also with Cys and GSH, subsequently losing their flavour property (fate). Even more concerning is the possible release of H2S from polysulfides during storage, leading to undesired off-flavours (Sarrazin et al. 2010). In the present work polysulfides from varietal thiols 4MMP and 3MH were identified for the first time in synthetic and real wines. Additionally, the evolution of glutathionyl and cysteinyl polysulfides was followed during fermentation.
METHODS: For the study of thiolated polysulfides, synthetic standards, musts and wines and commercial SB wines were supplemented with copper sulfate and wettable sulfur to induce condensation reactions. For the evolution study, synthetic must and Chardonnay juice were supplemented with elemental sulfur, CuSO4, both, or nothing (control) and subsequently fermented until sugar dryness was reached (after 18 days). All samples were analysed using ultra-high-performance liquid chromatography (UHPLC) coupled to hybrid quadrupole/high-resolution mass spectrometry (HRMS, Q-Orbitrap).
RESULTS: Thiolated polysulfides with up to 4 sulfur atoms were successfully recovered from the synthetic standards, musts and wines and characterized using Compound Discoverer. The evolution study showed different patterns of polysulfide formation for the different fermenting musts, which were assigned to the difference in matrix composition and matrix complexity. Moreover, significant differences in accumulation were revealed between the differently treated musts.
CONCLUSIONS: The UHPLC/HRMS method used in both studies was successfully applied to detect polysulfides in different spiked synthetic and real wines. Differences between treatments and matrices proved the influence of known and unknown compounds playing an important role in polysulfide formation. The present method can be applied to perform ongoing polysulfide studies.
Ugliano, M., Kwiatkowski, M., Vidal, S., Capone, D., Siebert, T., Dieval, J. B., ... & Waters, E. J. (2011). Evolution of 3-mercaptohexanol, hydrogen sulfide, and methyl mercaptan during bottle storage of Sauvignon blanc wines. Effect of glutathione, copper, oxygen exposure, and closure-derived oxygen. Journal of Agricultural and Food Chemistry, 59(6), 2564-2572.
Kreitman, G. Y., Danilewicz, J. C., Jeffery, D. W., & Elias, R. J. (2016). Reaction mechanisms of metals with hydrogen sulfide and thiols in model wine. Part 2: Iron-and copper-catalyzed oxidation. Journal of agricultural and food chemistry, 64(20), 4105-4113.
van Leeuwen, K. A., Nardin, T., Barker, D., Fedrizzi, B., Nicolini, G., & Larcher, R. (2020). A novel LC-HRMS method reveals cysteinyl and glutathionyl polysulfides in wine. Talanta, 218, 121105.
Sarrazin, E., Shinkaruk, S., Pons, M., Thibon, C., Bennetau, B., & Darriet, P. (2010). Elucidation of the 1, 3-sulfanylalcohol oxidation mechanism: An unusual identification of the disulfide of 3-sulfanylhexanol in Sauternes botrytized wines. Journal of agricultural and food chemistry, 58(19), 10606-10613.