Evolution of Volatile Sulfur Compounds during Wine Fermentation

Harnessing the potential of Cupriavidus necator for CO2 capture from alcoholic fermentation and its bioconversion into poly(3-hydroxybutyrate)

The fermentation process in alcoholic beverage production converts sugars into ethanol and CO2, releasing significant amounts of greenhouse gases. Here, Cupriavidus necator DSM 545 was grown autotrophically using gas derived from alcoholic fermentation, using a fed-batch bottle system. Nutrient starvation was applied to induce intracellular accumulation of poly(3-hydroxybutyrate) (PHB), a bioplastic polymer, for bioconversion of CO2-rich waste gas into PHB. Grape marc, another by-product of wine production, was evaluated as a low-cost carbon source for the heterotrophic growth of C. necator, which was subsequently used as an inoculum for autotrophic cultures. The effect of agitation, CO2 headspace composition, and nitrogen concentration was tested, obtaining a maximum PHB concentration of 0.69 g/L, with an average CO2 uptake rate of 1.14 ± 0.41 mmol CO2 L-1h-1 and 65 % efficiency of CO2 consumption. These findings lay the groundwork for developing carbon mitigation strategies in alcoholic fermentation processes coupled with sustainable biopolymer production.

To be or not to be required: Yeast vitaminic requirements in winemaking

Although vitamins are prime actors in yeast metabolism, the nature and the extent of their requirement in Saccharomyces cerevisiae in winemaking remains little understood. To fill this gap, the evolution of 8 water-soluble vitamins and their diverse vitamers during its alcoholic fermentation in a synthetic must medium was monitored, providing the first evidence of the consumption of vitamers by five commercial S. cerevisiae strains, and highlighting the existence of preferential vitameric sources for its nutrition. The vitamins required by the yeast, B1, B5, and B8, were then identified, and the nature of their requirement characterized, strongly asserting the required trait of B1 for fermentation, B8 for growth, and B5 for both processes. The extent of the requirement for B5, that with the most impact of the three vitamins, was then quantified in three S. cerevisiae strains, resulting in the conclusion that 750 μg.L-1 should prove sufficient to cover the yeast's requirements. This investigation offers the first insight into S. cerevisiae vitaminic requirements for winemaking.

Effect of DAP and glutamine supplementation on sulfur-containing volatiles and sensory properties of Chardonnay wine fermented with Saccharomyces cerevisiae yeast

Volatile compounds in wine have a critical impact on the consumers' senses. In this study, the effect of diammonium phosphate (DAP) and glutamine on sulfur-containing volatiles and sensory properties of Chardonnay wine fermented with Saccharomyces cerevisiae yeast were evaluated. Fermentation kinetics was determined by monitoring reducing sugar consumption rates during fermentation. The volatile profile of wines was analyzed by headspace solid phase microextraction (HS-SPME) coupled with gas-chromatography-mass spectrometry (GC-MS). The volatile sulfur compounds (VSCs) were analyzed by HS-SPME-GC-MS/MS. Flavor attributes of wines were assessed by a sensory panel with quantitative descriptive analysis. A total of 53 volatiles, including 6 VSCs, were identified and quantified in the Chardonnay wine. The results suggested that glutamine supplementation at the beginning of fermentation could help to initiate fermentation earlier and promote the formation of isoamyl acetate, phenethyl acetate, ethyl nonanoate, methyl decanoate, diethyl succinate and phenethyl alcohol, isobutanol, while DAP supplementation had no obvious effect on the volatile composition of the resulting wine and fermentation kinetics. PRACTICAL APPLICATION: Suitable nitrogen source is helpful to a healthy fermentation, and can also prevent the off-flavor and regulate aroma profile of wine. This study provides insights on the volatile and sensory characteristics of Chardonnay wines affected by different nitrogen source addition.

Hydrogen sulfide production during early yeast fermentation correlates with volatile sulfur compound biogenesis but not thiol release

Yeasts undergo intensive metabolic changes during the early stages of fermentation. Previous reports suggest the early production of hydrogen sulfide (H2S) is associated with the release of a range of volatile sulfur compounds (VSCs), as well as the production of varietal thiol compounds 3-sulfanylhexan-1-ol (3SH) and 3-sulfanylhexyl acetate (3SHA) from six-carbon precursors, including (E)-hex-2-enal. In this study, we investigated the early H2S potential, VSCs/thiol output, and precursor metabolism of 11 commonly used laboratory and commercial Saccharomyces cerevisiae strains in chemically defined synthetic grape medium (SGM) within 12 h after inoculation. Considerable variability in early H2S potential was observed among the strains surveyed. Chemical profiling suggested that early H2S production correlates with the production of dimethyl disulfide, 2-mercaptoethanol, and diethyl sulfide, but not with 3SH or 3SHA. All strains were capable of metabolizing (E)-hex-2-enal, while the F15 strain showed significantly higher residue at 12 h. Early production of 3SH, but not 3SHA, can be detected in the presence of exogenous (E)-hex-2-enal and H2S. Therefore, the natural variability of early yeast H2S production contributes to the early output of selected VSCs, but the threshold of which is likely not high enough to contribute substantially to free varietal thiols in SGM.

Reciprocal hemizygosity analysis reveals that the Saccharomyces cerevisiae CGI121 gene affects lag time duration in synthetic grape must

It is standard practice to ferment white wines at low temperatures (10–18°C). However, low temperatures increase fermentation duration and risk of problem ferments, leading to significant costs. The lag duration at fermentation initiation is heavily impacted by temperature; therefore, identification of Saccharomyces cerevisiae genes influencing fermentation kinetics is of interest for winemaking. We selected 28 S. cerevisiae BY4743 single deletants, from a prior list of open reading frames (ORFs) mapped to quantitative trait loci (QTLs) on Chr. VII and XIII, influencing the duration of fermentative lag time. Five BY4743 deletants, Δapt1, Δcgi121, Δclb6, Δrps17a, and Δvma21, differed significantly in their fermentative lag duration compared to BY4743 in synthetic grape must (SGM) at 15 °C, over 72 h. Fermentation at 12.5°C for 528 h confirmed the longer lag times of BY4743 Δcgi121, Δrps17a, and Δvma21. These three candidates ORFs were deleted in S. cerevisiae RM11-1a and S288C to perform single reciprocal hemizygosity analysis (RHA). RHA hybrids and single deletants of RM11-1a and S288C were fermented at 12.5°C in SGM and lag time measurements confirmed that the S288C allele of CGI121 on Chr. XIII, encoding a component of the EKC/KEOPS complex, increased fermentative lag phase duration. Nucleotide sequences of RM11-1a and S288C CGI121 alleles differed by only one synonymous nucleotide, suggesting that intron splicing, codon bias, or positional effects might be responsible for the impact on lag phase duration. This research demonstrates a new role of CGI121 and highlights the applicability of QTL analysis for investigating complex phenotypic traits in yeast.

Inter-regional survey of the New Zealand Pinot noir fermentative sulfur compounds profile

BACKGROUND

New Zealand Pinot noir is gaining increasing attention both in New Zealand and internationally, becoming the second largest grape variety for both plantings and export. Despite the growing furore around this variety, the current coverage of the volatile chemical profile remains limited, with a lack of information on the fermentative sulfur compounds content in New Zealand Pinot noir wines.

RESULTS

Thirty-five Pinot noir wines from three different vintages (i.e. 2016, 2017 and 2018) form five different grape growing regions were analysed for their fermentative sulfur compounds contents. Six fermentative sulfur compounds (i.e. methanethiol, ethanethiol, dimethyl sulfide, carbon disulfide, methionol and benzothiazol) were detected and measured for the first time in New Zealand Pinot noir wines. Their concentrations were compared against previously measured Pinot noir wines from other countries, and some preliminary evidence about inter-regional and ageing effects was obtained.

CONCLUSION

The present study reports the first survey of the inter-regional differences in fermentative sulfur compounds contents in 35 New Zealand Pinot noir wines. Preliminary inter-regional and vintage trends prompt further research on the role of these molecules on this wine variety. © 2020 Society of Chemical Industry.

Construction of a synthetic microbial community for the biosynthesis of volatile sulfur compound by multi-module division of labor

3-(Methylthio)-1-propanol, reminiscent of cauliflower and cooked vegetable aroma, is an important sulfur compound in Baijiu. It is important to develop a method to increase 3-(methylthio)-1-propanol content to improve flavor quality of products. In this study, a synthetic microbial community was employed to enhance the content of 3-(methylthio)-1-propanol by multi-module division of labor approach. Firstly, the synthetic pathway of 3-(methylthio)-1-propanol was reconstructed and classified into three modules. Later, the hyper producers in each module were isolated and negative interaction between the members was relieved. Finally, a synthetic microbial community was constructed using three species containing one hyper producer from each module. Furthermore, the transcription characteristics of the species in each module were validated by metatranscriptomic analysis. The constructed synthetic microbial community can be used to biosynthesize 3-(methylthio)-1-propanol for Baijiu. This work provided a novel and workable strategy to design synthetic microbial community to enhance the flavor feature of other fermented foods.

Effect of salt concentration on microbial communities, physicochemical properties and metabolite profile during spontaneous fermentation of Chinese northeast sauerkraut

AIM

The aim of this study was to study the effects of salt concentrations on the microbial communities, physicochemical properties, metabolome profiles and sensory characteristics during the fermentation of traditional northeast sauerkraut.

METHODS AND RESULTS

Northeast sauerkraut was spontaneously fermented under four salt concentrations (0·5, 1·5, 2·5 and 3·5%, w/w). The result of microbiological analysis showed that the population of lactic acid bacteria in 2·5%-salted sauerkraut was significantly higher than that in the other samples. Correspondingly, the speed of decrease in pH and accumulation of acids were the highest in 2·5%-salted sauerkraut. The glucose (analysed by HPLC) in 2·5%-salted sauerkraut was consumed more completely to produce higher levels of organic acids compared to those in the other samples. Principle component analysis showed clear differences in the metabolites of sauerkraut according to different salt concentrations. A higher level of volatiles (detected by HS-SPME/GC-MS) was identified in 2·5%-salted sauerkraut, and sensory evaluation demonstrated that 2·5%-salted sauerkraut had the best sensory characteristics.

CONCLUSION

The best quality of sauerkraut was obtained from fermented under 2·5% salt concentration.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study facilitated the understanding of the effects of salt on the sauerkraut fermentation and may be useful for developing the quality of sauerkraut.

Adaptive Laboratory Evolution of Ale and Lager Yeasts for Improved Brewing Efficiency and Beer Quality

Yeasts directly impact the efficiency of brewery fermentations as well as the character of the beers produced. In recent years, there has been renewed interest in yeast selection and development inspired by the demand to utilize resources more efficiently and the need to differentiate beers in a competitive market. Reviewed here are the different, non-genetically modified (GM) approaches that have been considered, including bioprospecting, hybridization, and adaptive laboratory evolution (ALE). Particular emphasis is placed on the latter, which represents an extension of the processes that have led to the domestication of strains already used in commercial breweries. ALE can be used to accentuate the positive traits of brewing yeast as well as temper some of the traits that are less desirable from a modern brewer's perspective. This method has the added advantage of being non-GM and therefore suitable for food and beverage production.

Comparison of Volatile Composition between Alcoholic Bilberry Beverages Fermented with Non-Saccharomyces Yeasts and Dynamic Changes in Volatile Compounds during Fermentation

The profile of volatile compounds was investigated using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS) during bilberry juice fermentation with nine non-Saccharomyces yeasts, including Pachysolen tannophilus, Metschnikowia pulcherrima, Hanseniaspora uvarum, Torulaspora delbrueckii, Zygosaccharomyces bailii, Schizosaccharomyces pombe, Lachancea thermotolerans, Issatchenkia orientalis, and Saccharomycodes ludwigii. Dynamic changes in volatile compounds were determined simultaneously with the development of ethanol concentration during fermentation. H. uvarum or I. orientalis produced more ethyl acetate than other yeast strains throughout fermentation, while fermentation with M. pulcherrima resulted in high accumulation of higher alcohols. S. pombe was associated with high productions of pentane-2,3-dione, 3-hydroxybutan-2-one, 2-methylbutanal, and 3-methylbutanal. Among the 59 volatile compounds detected, generally, higher alcohols and monoterpenes accumulated constantly and reached the maximum concentration at the middle or later fermentation stage, whereas aldehydes, ketones, and acetals accumulated first followed by a significant drop. The production and accumulation dynamics of metabolites were highly dependent on the yeast species and the developing ethanol content.

A new analytical method to measure S-methyl-l-methionine in grape juice reveals the influence of yeast on dimethyl sulfide production during fermentation

BACKGROUND

Dimethyl sulfide (DMS) is a small sulfur-containing impact odorant, imparting distinctive positive and / or negative characters to food and beverages. In white wine, the presence of DMS at perception threshold is considered to be a fault, contributing strong odors reminiscent of asparagus, cooked cabbage, and creamed corn. The source of DMS in wine has long been associated with S-methyl-l-methionine (SMM), a derivative of the amino acid methionine, which is thought to break down into DMS through chemical degradation, particularly during wine ageing.

RESULTS

We developed and validated a new liquid chromatography-tandem mass spectrometry (LC-MS/MS) method with a stable isotope dilution assay (SIDA) to measure SMM in grape juice and wine. The application of this new method for quantitating SMM, followed by the quantitation of DMS using headspace-solid phase micro-extraction coupled with gas chromatography-mass spectrometry (HS-SPME/GC-MS), confirmed that DMS can be produced in wine via the chemical breakdown of SMM to DMS, with greater degradation observed at 28 °C than at 14 °C. Further investigation into the role of grape juice and yeast strain on DMS formation revealed that the DMS produced from three different Sauvignon blanc grape juices, either from the SMM naturally present or SMM spiked at 50 mmol L^-1 , was modulated depending on each of the four strains of Saccharomyces cerevisiae wine yeast used for fermentation.

CONCLUSION

This study confirms the existence of a chemical pathway to the formation of DMS and reveals a yeast-mediated mechanism towards the formation of DMS from SMM during alcoholic fermentation. © 2019 Society of Chemical Industry.

The role of yeast ARO8, ARO9 and ARO10 genes in the biosynthesis of 3-(methylthio)-1-propanol from L-methionine during fermentation in synthetic grape medium

3-(methylthio)-1-propanol (methionol), produced by yeast as an end-product of L-methionine (L-Met) catabolism, imparts off-odours reminiscent of cauliflower and potato to wine. Saccharomyces cerevisiae ARO genes, including transaminases Aro8p and Aro9p, and decarboxylase Aro10p, catalyse two key steps forming methionol via the Ehrlich pathway. We compared methionol concentrations in wines fermented by single Δaro8, Δaro9 and Δaro10 deletants in lab strain BY4743 versus wine strain Zymaflore F15, and F15 double- and triple-aro deletants versus single-aro deletants, using headspace-solid phase microextraction coupled with gas chromatography-mass spectrometry.Deletion of two or more aro genes increased growth lag phase, with the greatest delay exhibited by F15 Δaro8 Δaro9. The single Δaro8 deletion decreased methionol by 44% in BY4743 and 92% in F15, while the Δaro9 deletion increased methionol by 46% in F15 but not BY4743. Single deletion of Δaro10 had no effect on methionol.Unexpectedly, F15 Δaro8 Δaro9 and F15 Δaro8 Δaro9 Δaro10 produced more methionol than F15 Δaro8. In the absence of Aro8p and Aro9p, other transaminases may compensate or an alternative pathway may convert methanethiol to methionol. Our results confirm that Ehrlich pathway genes differ greatly between lab and wine yeast strains, impacting downstream products such as methionol.

Influence of oxygen exposure on fermentation process and sensory qualities of Sichuan pickle (paocai)

The physicochemical and microbial changes, volatile profile, texture and appearance were investigated in three groups of Sichuan pickles differing in oxygen exposure during a 64 day fermentation process.

Volatile Profiles of Sparkling Wines Produced by the Traditional Method from a Semi-Arid Region

São Francisco Valley (SFV) is located in Northeastern Brazil, in a tropical semi-arid region where one vine can produce two harvests per year, due to high temperatures, solar radiation rates, and irrigation throughout the year. This is the main characteristic differing this from other winegrowing region in the world. The objective of this study was to characterize volatile profiles of sparkling wines produced by the traditional method, using Chenin Blanc and Syrah grapes, the two main varieties used for white and red wines, respectively, grown in the region. The sparkling wines remained on lees for six months maturing. The sparkling wines were characterized by the parameters density, pH, total titratable and volatile acidities, residual sugars, dry extract, alcohol content, total phenolic compounds, in vitro antioxidant activity and volatile fraction. The volatile fraction extraction was performed by the HS-SPME technique and tentative identification of the volatile compounds was carried out with GC-MS using the scan mode. A total of 33 volatile compounds were identified, among them 11 alcohols, 13 esters, five carboxylic acids, and four different chemical classes. The volatile profile of Chenin Blanc sparkling wine was associated mainly to 2,3-butanediol, 3-ethoxypropan-1-ol, diethyl succinate, and ethyl decanoate, while Syrah sparkling wine was characterized by benzaldehyde, butyric acid, and some acetates. This study reported for the first time volatile profiles of traditional sparkling wines from SFV, as new products, contributing to better understand the quality potential of these beverages for a tropical semi-arid region.

Recent Developments on the Origin and Nature of Reductive Sulfurous Off-Odours in Wine

Reductive sulfurous off-odors are still one of the main reasons for rejecting wines by consumers. In 2008 at the International Wine Challenge in London, approximately 6% of the more than 10,000 wines presented were described as faulty. Twenty-eight percent were described as faulty because they presented “reduced characters” similar to those presented by “cork taint” and in nearly the same portion. Reductive off-odors are caused by low volatile sulfurous compounds. Their origin may be traced back to the metabolism of the microorganisms (yeasts and lactic acid bacteria) involved in the fermentation steps during wine making, often followed by chemical conversions. The main source of volatile sulfur compounds (VSCs) are precursors from the sulfate assimilation pathway (SAP, sometimes named as the “sulfate reduction pathway” SRP), used by yeast to assimilate sulfur from the environment and incorporate it into the essential sulfur-containing amino acids methionine and cysteine. Reductive off-odors became of increasing interest within the last few years, and the method to remove them by treatment with copper (II) salts (sulfate or citrate) is more and more questioned: The effectiveness is doubted, and after prolonged bottle storage, they reappear quite often. Numerous reports within the last few years and an ongoing flood of publications dealing with this matter reflect the importance of this problem. In a recent detailed review, almost all relevant aspects were discussed on a scientific data basis, and a “decision tree” was formulated to support winemakers handling this problem. Since we are dealing with a very complicated matter with a multitude of black spots still remaining, these advices can only be realized using specific equipment and special chemicals, not necessarily found in small wineries. The main problem in dealing with sulfurous compounds arises from the high variability of their reactivities. Sulfur is a metalloid with a large valence span across eight electron transformations from S (−II) up to S (+VI). This allows it to participate in an array of oxidation, reduction and disproportionation reactions, both abiotic and linked to microbial metabolism. In addition, sulfur is the element with the most allotropes and a high tendency to form chains and rings, with different stabilities of defined species and a high interconvertibility among each other. We suppose, there is simply a lack of knowledge of what is transferred during filling into bottles after fermentation and fining procedures. The treatment with copper (II) salts to remove sulfurous off-odors before filling rather increases instead of solving the problem. This paper picks up the abundant knowledge from recent literature and tries to add some aspects and observations, based on the assumption that the formation of polythionates, hitherto not taken into consideration, may explain some of the mystery of the re-appearance of reductive off-odors.

What's in wine? A clinician's perspective<sup/>

Alcoholic beverages, specifically wine, have been consumed for many years. Wine is postulated to play an important role in the improvement of cardiovascular risk factors. Most epidemiological studies have found sustained consumption at light-to-moderate amounts to increase HDL cholesterol, reduce platelet aggregation, and promote fibrinolysis. Wine consumption has been inversely associated with ischemic heart disease, and the alcohol-blood pressure association, in most studies, follows a J-shaped curve. These outcomes have been attributed to the molecular constituents of wine, namely ethanol and polyphenols. Due to the continued interest in wine as a biological beverage, we review the chemistry of wine as clinicians, including its chemical composition, viticulture and enological practices, and other chemical factors that influence the bioactive components of wine. We also outline the biological effects of wine components and directions for future research.

Photo-biocatalytic One-Pot Cascades for the Enantioselective Synthesis of 1,3-Mercaptoalkanol Volatile Sulfur Compounds

The synthesis of enantiomerically pure 1,3-mercaptoalkanol volatile sulfur compounds through a one-pot photo-biocatalytic cascade reaction is described. Two new KRED biocatalysts with opposite enantioselectivity were discovered and proved to be efficient on a wide range of substrates. The one-pot cascade reaction combining photocatalytic thio-Michael addition with biocatalytic ketoreduction in an aqueous medium provides a green and sustainable approach to enantiomerically pure 1,3-mercaptoalkanols in high yields with excellent enantioselectivity.

Headspace solid-phase microextraction and gas chromatographic analysis of low-molecular-weight sulfur volatiles with pulsed flame photometric detection and quantification by a stable isotope dilution assay

Low-molecular-weight volatile sulfur compounds such as thiols, sulfides, disulfides as well as thioacetates cause a sulfidic off-flavor in wines even at low concentration levels. The proposed analytical method for quantification of these compounds in wine is based on headspace solid-phase microextraction, followed by gas chromatographic analysis with sulfur-specific detection using a pulsed flame photometric detector. Robust quantification was achieved via a stable isotope dilution assay using commercial and synthesized deuterated isotopic standards. The necessary chromatographic separation of analytes and isotopic standards benefits from the inverse isotope effect realized on an apolar polydimethylsiloxane stationary phase of increased film thickness. Interferences with sulfur-specific detection in wine caused by sulfur dioxide were minimized by addition of propanal. The method provides adequate validation data, with good repeatability and limits of detection and quantification. It suits the requirements of wine quality management, allowing the control of oenological treatments to counteract an eventual formation of excessively high concentration of such malodorous compounds.

The GLO1 Gene Is Required for Full Activity of O-Acetyl Homoserine Sulfhydrylase Encoded by MET17

During glycolysis, yeast generates methylglyoxal (MG), a toxic metabolite that affects growth. Detoxification can occur when glyoxylase I (GLO1) and glyoxylase II (GLO2) convert MG to lactic acid. We have identified an additional, previously unrecognized role for GLO1 in sulfur assimilation in the yeast Saccharomyces cerevisiae. During a screening for putative carbon-sulfur lyases, the glo1 deletion strain showed significant production of H₂S during fermentation. The glo1 strain also assimilated sulfate inefficiently but grew normally on cysteine. These phenotypes are consistent with reduced activity of the O-acetyl homoserine sulfhydrylase, Met17p. Overexpression of Glo1p gave a dominant negative phenotype that mimicked the glo1 and met17 deletion strain phenotypes. Western analysis revealed reduced expression of Met17p in the glo1 deletion, but there was no indication of an altered conformation of Met17p or any direct interaction between the two proteins. Unravelling a novel function in sulfur assimilation and H₂S generation in yeast for a gene never connected with this pathway provides new opportunities for the study of this molecule in cell signaling, as well as the potential regulation of its accumulation in the wine and beer industry.

Microbial Contribution to Wine Aroma and Its Intended Use for Wine Quality Improvement

Wine is a complex matrix that includes components with different chemical natures, the volatile compounds being responsible for wine aroma quality. The microbial ecosystem of grapes and wine, including Saccharomyces and non-Saccharomyces yeasts, as well as lactic acid bacteria, is considered by winemakers and oenologists as a decisive factor influencing wine aroma and consumer's preferences. The challenges and opportunities emanating from the contribution of wine microbiome to the production of high quality wines are astounding. This review focuses on the current knowledge about the impact of microorganisms in wine aroma and flavour, and the biochemical reactions and pathways in which they participate, therefore contributing to both the quality and acceptability of wine. In this context, an overview of genetic and transcriptional studies to explain and interpret these effects is included, and new directions are proposed. It also considers the contribution of human oral microbiota to wine aroma conversion and perception during wine consumption. The potential use of wine yeasts and lactic acid bacteria as biological tools to enhance wine quality and the advent of promising advice allowed by pioneering -omics technologies on wine research are also discussed.

Multiple roles of lactic acid bacteria microflora in the formation of marker flavour compounds in traditional chinese paocai

Traditional paocai brine (PB), which is continuously propagated by back-slopping and contains multiple species of lactic acid bacteria (LAB), is critical for the flavour of paocai.