Formation of Hydrogen Sulfide in Wine: Interactions between Copper and Sulfur Dioxide

Analysis of the Effect of Mixed Fermentation on the Quality of Distilled Jujube Liquor by Gas Chromatography-Ion Mobility Spectrometry and Flavor Sensory Description

Distilled jujube liquor is an alcoholic beverage made from jujube, which has a unique flavor and a sweet taste. The purpose of this study was to explore the effect of mixed fermentation on the quality of distilled jujube liquor by comparing the performance of mixed fermentation between S. cerevisiae, Pichia pastoris and Lactobacillus. The results showed that there were significant differences in the quality of the jujube liquor between the combined strains. Moreover, Lactobacillus increased and P. pastoris reduced the total acid content. The results from an E-nose showed that the contents of methyl, alcohol, aldehyde, and ketone substances in the test bottle decreased significantly after decanting, while the contents of inorganic sulfide and organic sulfide increased. Fifty flavor compounds were detected, including nineteen esters, twelve alcohols, seven ketones, six aldehydes, three alkenes, one furan, one pyridine, and one acid. There were no significant differences in the type or content of flavor compounds. However, PLS-DA showed differences among the samples. Eighteen volatile organic compounds with variable importance in projection values > 1 were obtained. There were sensory differences among the four samples. Compared with the sample fermented with only S. cerevisiae, the samples co-fermented with Lactobacillus or with P. pastoris had an obvious bitter taste and mellow taste, respectively. The sample fermented by all three strains had a prominent fruity flavor. Except for the sample fermented with only S. cerevisiae, the jujube flavor was weakened to varying degrees in all samples. Co-fermentation could be a valuable method to improve the flavor quality of distilled jujube liquor. This study revealed the effects of different mixed fermentation modes on the sensory flavor of distilled jujube liquor and provided a theoretical basis for the establishment of special mixed fermentation agents for distilled jujube liquor in the future.

Surface nanoengineering technology for the removal of sulfur compounds associated with negative attributes in wines

Volatile sulfur compounds (VSCs), such as hydrogen sulfide, methanethiol, and ethanethiol, are associated with 'reductive' aromas in wine and contribute to approximately 30% of all wine faults. These compounds can have a significant impact on wine aroma and perceived quality, and subsequently, consumer preference. In this communication, we report a method for the removal of VSC compounds based on nanoengineered surfaces that incorporate immobilized gold nanoparticles.

Novel 2-Benzo[d]thiazolyl-4-quinolinylphenol Skeleton-Based Turn-on Fluorescent Probe for H2S Detection and its Multiple Applications in Water Environment, Foodstuffs, and Living Organisms

Hydrogen sulfide (H₂S) has comprehensive contributions to maintaining the normal operation and stability of organisms, and it also occurs in the wastewater environment and is related to the deterioration of foodstuffs. Therefore, developing high-sensitive detection techniques for tracing H₂S is promising and meaningful. Inspired by this, a novel nopinone-based fluorescent probe NPS for the recognition of H₂S was designed and synthesized with excellent sensitivity, low limit of detection (79 nM), good selectivity, and wide pH range (5-9). NPS could emit strong yellow fluorescence and its emission intensity showed a remarkable augmentation at 520 nm upon the supplement of H₂S. Furthermore, the recognition mechanism of NPS for H₂S was verified by the HRMS analysis, ¹H NMR spectra titration, and DFT computation. What is more, NPS also had broad applications in the monitoring of real water samples, red wine, beer, and eggs samples, which showed its development prospect and value in environmental pollution, foodstuffs quality analysis fields. NPS also was applied to monitor trace exogenous H₂S and bioimaging in living cells and zebrafish.

Wine Faults: State of Knowledge in Reductive Aromas, Oxidation and Atypical Aging, Prevention, and Correction Methods

The review summarizes the latest scientific findings and recommendations for the prevention of three very common wine faults of non-microbial origin. The first group, presented by the reductive aromas, is caused mainly by excessive H₂S and other volatile sulfur compounds with a negative impact on wine quality. The most efficient prevention of undesirable reductive aromas in wine lies in creating optimal conditions for yeast and controlling the chemistry of sulfur compounds, and the pros and cons of correction methods are discussed. The second is browning which is associated especially with the enzymatic and non-enzymatic reaction of polyphenols and the prevention of this fault is connected with decreasing the polyphenol content in must, lowering oxygen access during handling, the use of antioxidants, and correction stands for the use of fining agents. The third fault, atypical aging, mostly occurs in the agrotechnics of the entire green land cover in the vineyard and the associated stress from lack of nutrients and moisture. Typical fox tones, naphthalene, or wet towel off-odors, especially in white wines are possible to prevent by proper moisture and grassland cover and alternating greenery combined with harmonious nutrition, while the correction is possible only partially with an application of fresh yeast. With the current knowledge, the mistakes in wines of non-microbial origin can be reliably prevented. Prevention is essential because corrective solutions for the faults are difficult and never perfect.

Suppression of reductive characters in white wine by Cu fractions: Efficiency and duration of protection during bottle aging

Cu in wine can suppress sulfidic-odours, but the active forms and duration of protection are uncertain. Additions of 0, 0.3 or 0.6 mg/L Cu(II) were made to Chardonnay and Pinot Grigio at bottling. Throughout a 12- or 14-month storage period, Cu fractions were determined by colorimetry, and sulfhydryl compounds by gas chromatography with sulfur chemiluminescence detection. After Cu(II) addition, the dominant Cu fractions were associated with Cu(II)-organic acids (fraction I) and Cu(I)-thiol complexes (fraction II), and over 8-months their concentrations gradually fell below 0.015 mg/L. During this time, a fraction of Cu, predominantly attributed to sulfide-bound Cu, increased in concentration. Suppression of free hydrogen sulfide was assured when the combined Cu fractions I and II concentrations were above 0.015 mg/L, while free methanethiol suppression required Cu fraction I concentration above 0.035 mg/L. Decay rates for Cu fractions demonstrated that the duration that Cu can actively suppress sulfidic odours is wine-dependent.

Ensuring the preservation of the quality of wine during storage

The article presents the necessity for a detailed approach to the choice of packaging for wine, as well as assessing their quality level. It has been established that the transformation of the component composition of wine proceeds with different intensity depending on the type of packaging and leads to different consequences, mainly due to the occurrence of redox reactions, as well as the degree of gas exchange during storage. Complex packaging "package in a box" can become a source of premature oxidation of wines and the appearance of foreign synthetic inclusions in them.

Brine-Releasable Hydrogen Sulfide in Wine: Mechanism of Release from Copper Complexes and Effects of Glutathione

Copper-sulfhydryl complexes in wine can be disrupted by addition of brine to release free hydrogen sulfide (H₂S), and the resulting "brine-releasable H₂S" is reported to correlate with formation of H₂S during bottle storage. However, both the mechanism of the brine-release assay and factors affecting the stability of copper sulfhydryls under brine-release conditions are not well understood. By varying brine composition and concentration, it is shown that release of copper-complexed H₂S requires the presence of a halide (Cl^- and Br^-) and is not due to a general "salting-out" effect. Release of copper-complexed H₂S by the brine dilution assay is highly temperature-dependent. When H₂S and Cu(II) are added to a model wine, brine-releasable H₂S decreases markedly (∼10-fold) after a 20 min incubation period prior to performing the brine-release assay. In commercial wines, the fraction of added H₂S recovered through the brine-release assay was correlated with the initial glutathione (GSH) concentration (r² = 0.58) but not with initial Cu. Negligible additional release of H₂S from organopolysulfanes was observed following addition of a disulfide-reducing agent (tris(2-carboxyethyl)phosphine). As previous studies have reported a correlation between H₂S formed under brine-release conditions and normal storage, these results suggest that the susceptibility of a wine to form latent copper-sulfhydryl precursors of H₂S following copper addition is dependent on the concentration of sulfhydryls like GSH.

The study of the processes of influence of auxiliary agents on grape processing products

The study of the processes of the influence of capping and packaging on the quality of finished products during storage is an important component of maintaining the stable quality of wines. It has been found that packaging has a significant impact on the evolution of wine during storage. It was found that the variation in the content of total sulfur dioxide and dissolved oxygen depending on the type of packing has an inverse relationship. The dissolved oxygen content was higher in wines bottled in glass bottles and PET (polyethylene terephthalate) bottles compared to products in composite packaging. These results are metrics to consider when choosing the packaging depending on the intended distribution and marketing method. The closures are the source of a variety of microbiological and chemical substances in wine. The nomenclature depends on the kind and the type of used plugs. Natural cork, in most cases, enriches the wine with substances of microbiological origin, as well as their waste products. Synthetic closures introduce chemical components that are not inherent in the nature of wine, thereby disrupting the aroma and color of the product.

Mitochondria-Targeted Red-Emission Fluorescent Probe for Ultrafast Detection of H2S in Food and Its Bioimaging Application

Hydrogen sulfide (H₂S) contributes to human health and prolongs the storage time of postharvest fruits and vegetables. At the same time, H₂S can cause a negative impact on some foodstuffs and beverages, so an efficient probe to detect H₂S is needed. Herein, a fluorescent turn-on responding probe SPy-DNs for H₂S detection has been designed and synthesized. SPy-DNs exhibited a red emission (608 nm), large Stokes shift (111 nm), and a detection limit of a nanomolar level (356 nM) in a dimethylformamide/phosphate-buffered saline (DMF/PBS) (1:1, v/v, 10 mM, pH 7.4) solution. SPy-DNs can detect H₂S with ultrafast response within 4 s, which is faster than the response of other reported probes. In addition, the applicability of SPy-DNs to detect H₂S has been determined in the actual water samples, targeted mitochondria, and imaged H₂S in living cells. Moreover, SPy-DNs was successfully used as a tool to judge H₂S levels in beer, which indicates that SPy-DNs possesses the advantage of rapid detection of H₂S in foodstuffs.

The recent advance of organic fluorescent probe rapid detection for common substances in beverages

The beverage industry is confronted with tremendous challenges in terms of quality assurance. The allowed contents of common ingredients such as copper ions, hydrogen sulfide, cysteine and caffeine are stipulated by various governing bodies, and the beverage industry must ensure that it meets these requirements. Due to its unique advantages of high sensitivity, low cost and relatively low toxicity over high-performance liquid chromatography, atomic absorption spectrometry and nanomaterials, the use of organic fluorescent probes for the rapid detection of beverage contents has become a hot research topic. This review summarizes the detection of common substances in wine, tea, mineral water, milk and other beverages. Furthermore, the preparation of test paper and simple colour comparison are discussed to display the rapid qualitative capability of designed probes. To improve the current state of beverage safety, future trends and strategies for fast organic fluorescent probe detection in the beverage industry are also discussed.

Bottle Aging and Storage of Wines: A Review

Wine is perhaps the most ancient and popular alcoholic beverage worldwide. Winemaking practices involve careful vineyard management alongside controlled alcoholic fermentation and potential aging of the wine in barrels. Afterwards, the wine is placed in bottles and stored or distributed in retail. Yet, it is considered that wine achieves its optimum properties after a certain storage time in the bottle. The main outcome of bottle storage is a decrease of astringency and bitterness, improvement of aroma and a lighter and more stable color. This is due to a series of complex chemical changes of its components revolving around the minimized and controlled passage of oxygen into the bottle. For this matter, antioxidants like sulfur oxide are added to avoid excessive oxidation and consequent degradation of the wine. In the same sense, bottles must be closed with appropriate stoppers and stored in adequate, stable conditions, as the wine may develop unappealing color, aromas and flavors otherwise. In this review, features of bottle aging, relevance of stoppers, involved chemical reactions and storage conditions affecting wine quality will be addressed.

Sulfide-binding to Cu(II) in wine: Impact on oxygen consumption rates

This study investigates the relationship between the two main forms of Cu in wine and their impact on the rate of oxygen consumption. The Cu forms were differentiated by medium exchange constant current stripping potentiometry, which classified the Cu as either bound to sulfide or not. Oxygen consumption rates were determined in red, white and model wines after saturation with oxygen. The results for white wines showed that the oxygen consumption was sensitive to the non-sulfide-bound Cu concentration when ascorbic acid was present, and the first order rates ranged from 0.02 to 0.11 h^-1. However, the same was not true for wines without added ascorbic acid that showed little influence of Cu form on oxygen decay rates. Cu forms were also found to significantly change in some wines during the oxygen decay experiment. Ascorbic acid is critical in enabling the form of Cu to significantly influence the oxygen reaction rate in wine.

A colorimetric and near-infrared fluorescent probe for detection of hydrogen sulfide and its real multiple applications

A novel colorimetric and near-infrared fluorescent probe (L) with D-π-A structure derived from 4-diethylaminosalicylaldehyde and 2-(3-cyano-4,5,5-trimethylfuran-2(5H)-ylidene)malononitrile has been developed. Probe L displays highly selective and sensitive recognition for H₂S over various anions with a large Stokes shift (96 nm) in DMF/H₂O (3/7, v/v, PBS-HCl 10 mM, pH = 7.4). A naked-eye observable color change of L solution from colorless to bluish-purple occurred on treatment with H₂S. The potential applications of probe L were evaluated and the results show that probe L can detect H₂S vapor and H₂S in real water, red wine and living cells.

A novel coumarin-based fluorescent probe for sensitive detection of copper(II) in wine

A novel coumarin-based fluorescent probe (probe 1) for the detection of copper(II) was developed. The fluorescence intensity of probe 1 showed a linear relationship with the concentration of copper(II) in the range 0-16 μM (0-1.02 mg/L) and the limit of detection was 62 nM (3.94 µg/L). The luminescence of probe 1 at the maximum allowable amounts of copper(II) in wine and water could be observed with the naked eye under a 365-nm ultraviolet lamp. Moreover, probe 1 was successfully used for the qualitative and quantitative detection of copper(II) in wine.

Liberation of Hydrogen Sulfide from Dicysteinyl Polysulfanes in Model Wine

Diorganopolysulfanes can be generated when hydrogen sulfide (H₂S) and thiols are oxidized in the presence of Cu(II) under conditions usually aimed at removing H₂S from wine. This work sought to understand if polysulfanes could act as latent sources of H₂S during postbottling storage. The stability of the polysulfanes formed in situ in model wine containing cysteine, H₂S, and transition metals was dependent both on the number of sulfur linking atoms (S_n) and on the presence of a reducing agent, such as sulfur dioxide or ascorbic acid. A polysulfane containing three linking sulfur atoms was the most stable, with 84% of the relative initial amount remaining in solution after six months, compared to polysulfanes containing four or more linking sulfur atoms that decomposed rapidly, with 26% remaining after six months. Importantly, sulfur dioxide was associated with the rapid degradation of polysulfanes and subsequent liberation of H₂S. Three cysteine- S-sulfonates were also tentatively identified, which gives insight into the possible release mechanisms involved with H₂S reappearance.

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.

Copper(II)-Mediated Hydrogen Sulfide and Thiol Oxidation to Disulfides and Organic Polysulfanes and Their Reductive Cleavage in Wine: Mechanistic Elucidation and Potential Applications

Fermentation-derived volatile sulfur compounds (VSCs) are undesirable in wine and are often remediated in a process known as copper fining. In the present study, the addition of Cu(II) to model and real wine systems containing hydrogen sulfide (H₂S) and thiols provided evidence for the generation of disulfides (disulfanes) and organic polysulfanes. Cu(II) fining of a white wine spiked with glutathione, H₂S, and methanethiol (MeSH) resulted in the generation of MeSH-glutathione disulfide and trisulfane. In the present study, the mechanisms underlying the interaction of H₂S and thiols with Cu(II) is discussed, and a prospective diagnostic test for releasing volatile sulfur compounds from their nonvolatile forms in wine is investigated. This test utilized a combination of reducing agents, metal chelators, and low-oxygen conditions to promote the release of H₂S and MeSH, at levels above their reported sensory thresholds, from red and white wines that were otherwise free of sulfidic off-odors at the time of addition.

The impact of aging wine in high and low oxygen conditions on the fractionation of Cu and Fe in Chardonnay wine

Solid-phase extraction has previously been used to fractionate copper and iron into hydrophobic, cationic and residual forms. This study showed the change in fractionated copper and iron in Chardonnay wines with 1-year of bottle aging under variable oxygen and protein concentrations. Wines containing protein in low oxygen conditions induced a decrease (20-50%) in total copper and increased the proportion of the hydrophobic copper fraction, associated with copper(I) sulfide. In contrast, protein stabilised wines showed a lower proportion of the hydrophobic copper fraction after 1-year of aging. In oxidative storage conditions, the total iron decreased by 60% when at high concentration, and the concentration of the residual fraction of both copper and iron increased. The results show that oxidative storage increases the most oxidative catalytic form of the metal, whilst changes during reductive storage depend on the extent of protein stabilisation of the wine.