Survey of SO2 binding carbonyls in 237 red and white table wines

Novel insight into the role of sulfur dioxide in fruits and vegetables: Chemical interactions, biological activity, metabolism, applications, and safety

Sulfur dioxide (SO₂) are a category of chemical compounds widely used as additives in food industry. So far, the use of SO₂ in fruit and vegetable industry has been indispensable although its safety concerns have been controversial. This article comprehensively reviews the chemical interactions of SO₂ with the components of fruit and vegetable products, elaborates its mechanism of antimicrobial, anti-browning, and antioxidation, discusses its roles in regulation of sulfur metabolism, reactive oxygen species (ROS)/redox, resistance induction, and quality maintenance in fruits and vegetables, summarizes the application technology of SO₂ and its safety in human (absorption, metabolism, toxicity, regulation), and emphasizes the intrinsic metabolism of SO₂ and its consequences for the postharvest physiology and safety of fresh fruits and vegetables. In order to fully understand the benefits and risks of SO₂, more research is needed to evaluate the molecular mechanisms of SO₂ metabolism in the cells and tissues of fruits and vegetables, and to uncover the interaction mechanisms between SO₂ and the components of fruits and vegetables as well as the efficacy and safety of bound SO₂. This review has important guiding significance for adjusting an applicable definition of maximum residue limit of SO₂ in food.

Derivatization Strategies in Flavor Analysis: An Overview over the Wine and Beer Scenario

Wine and beer are the most appreciated and consumed beverages in the world. This success is mainly due to their characteristic taste, smell, and aroma, which can delight consumer’s palates. These olfactory characteristics are produced from specific classes of volatile compounds called “volatile odor-active compounds” linked to different factors such as age and production. Given the vast market of drinking beverages, the characterization of these odor compounds is increasingly important. However, the chemical complexity of these beverages has led the scientific community to develop several analytical techniques for extracting and quantifying these molecules. Even though the recent “green-oriented” trend is directed towards direct preparation-free procedures, for some class of analytes a conventional step like derivatization is unavoidable. This review is a snapshot of the most used derivatization strategies developed in the last 15 years for VOAs’ determination in wine and beer, the most consumed fermented beverages worldwide and among the most complex ones. A comprehensive overview is provided for every method, whereas pros and cons are critically analyzed and discussed. Emphasis was given to miniaturized methods which are more consistent with the principles of “green analytical chemistry”.

Impact of the Acetaldehyde-Mediated Condensation on the Phenolic Composition and Antioxidant Activity of Vitis vinifera L. Cv. Merlot Wine

Acetaldehyde is a critical reactant on modifying the phenolic profile during red wine aging, suggesting that the acetaldehyde-mediated condensation can be responsible for the variation of antioxidant activity during the aging of this beverage. The present study employs exogenous acetaldehyde at six levels of treatment (7.86 ± 0.10–259.02 ± 4.95 mg/L) before the bottle aging of Merlot wines to encourage phenolic modification. Acetaldehyde and antioxidant activity of wine were evaluated at 0, 15, 30, 45, 60 and 75 days of storage, while monomeric and polymeric phenolics were analyzed at 0, 30 and 75 days of storage. The loss of acetaldehyde was fitted to a first-order reaction model, the rate constant (k) demonstrated that different chemical reaction happened in wines containing a different initial acetaldehyde. The disappearance of monomeric phenolics and the formation of polymeric phenolics induced by acetaldehyde could be divided into two phases, the antioxidant activity of wine did not alter significantly in the first phase, although most monomeric phenolics vanished, but the second phase would dramatically reduce the antioxidant activity of wine. Furthermore, a higher level of acetaldehyde could shorten the reaction time of the first phase. These results indicate that careful vinification handling aiming at controlling the acetaldehyde allows one to maintain prolonged biological activity during wine aging.

Sulfonation Reactions behind the Fate of White Wine’s Shelf-Life

White wine’s oxidative stability after several years of bottle aging is synonymous to its organoleptic quality. In order to gain control over the cascade of chemical reactions that are implicated in that phenomenon, fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS)-based metabolomics and sensory evaluation were combined for the analysis of a vertical series of white wines from different vineyard plots. Data mining using supervised cluster analysis allowed the extraction of known and unknown sulfur- and nitrogen-containing molecular features, with oxidative stability molecular markers presenting an increased number of S and O atoms in their formulas. In their majority, S-containing molecular features possessed between 4 to ~12 O atoms, indicating the relatively higher importance of sulfonation reactions as opposed to dimerization reactions. Molecular networking, based on sulfonation reaction transformations, evidences the importance of hitherto unknown and/or minor sulfur dioxide binders (peptides, aldehydes, and polyphenols) on wine’s oxidative stability.

Direct NMR evidence for the dissociation of sulfur-dioxide-bound acetaldehyde under acidic conditions: Impact on wines oxidative stability

SO₂ reaction with electrophilic species present in wine, including in particular carbonyl compounds, is responsible for the reduction of its protective effect during wine aging. In the present study, direct ¹H NMR profiling was used to monitor the reactivity of SO₂ with acetaldehyde under wine-like oxidation conditions. The dissociation of acetaldehyde bound SO₂ was evidenced suggesting that released free SO₂ can further act as an antioxidant. EPR and DPPH assays showed an increasing antioxidant capacity of wine with the increase in the concentration of acetaldehyde sulfonate. The presence of acetaldehyde sulfonate in wines was correlated with the overall antioxidant activity of wines. The first evidence of acetaldehyde bound SO₂ dissociation provides a completely new representation of the long-term protection efficiency of SO₂ during bottle aging.

Observation of Residues Content after Application of a Medium-Chain Fatty Acids Mixture at the End of Alcoholic Fermentation

This study focused on applying a patented medium-chain fatty acids (MCFAs) mixture at the end of alcoholic fermentation and monitoring its residues. MCFAs are a promising agent that has the potential to increase the efficiency of sulfur dioxide and ultimately minimize its doses, which is one of the important goals of wine research today. Detailed octanoic, decanoic, and dodecanoic acid contents were observed during the experiment. The MCFA mixture was applied at doses of 0, 10, 20, and 60 mg/L. GC–MS determined the content of individual fatty acids. The results showed that the use of the investigated mixture of fatty acids at doses of 10 and 20 mg/L did not cause an increase in the content of individual fatty acids residues. The octanoic acid content after application of the 20 mg/L MCFA mixture was 8.24 mg/L after 744 h, while the untreated control variant showed a value of 7.71 mg/L. The performed sensory analysis also did not show a negative effect of MCFA application on the sensory properties of wine. Therefore, applying an MCFA mixture at 10 and 20 mg/L can be recommended as a safe alternative following alcoholic fermentation. However, the results obtained can also serve as a valuable basis for permitting the use of MCFA in the proceeding OIV approval process. The research thus opens the possibility of expanding a new oenological agent capable of reducing SO2 doses.

Responses on Must and Wine Composition of Vitis vinifera L. cvs. Riesling and Cabernet Sauvignon under a Free Air CO2 Enrichment (FACE)

Challenges of climate change on the future grape and wine production are widely discussed in science and in the wine industry with the goal to maintain a consistent must and wine quality in the future. Therefore, the effect of elevated CO2 (eCO2)-as one of the relevant greenhouse gases jointly responsible for a changing climate-was investigated concerning the composition of must and wine made of two grapevine cultivars V. vinifera L. cvs. Riesling and Cabernet Sauvignon within the established VineyardFACE (Free-Air Carbon dioxide Enrichment) experiment. Must and wine analysis were conducted in three consecutive years (2014-2016) by analyzing standard must and wine parameters, e.g., total soluble solids (TSS), pH, total acidity (TA), organic acids (e.g., tartaric acid, malic acid, shikimic acid, citric acid, volatile acid and gluconic acid) or total phenolics (TP). Also, for both cultivars CIELab coordinates (L* for lightness, a* as green/red and b* as blue/yellow components) were used to test colour in young white and red wines. Additionally, total anthocyanins and monomeric indices were analyzed for young wines of the red cultivar Cabernet Sauvignon. With marginal differences between CO2 treatments, the composition of must and young wines was not found to be negatively influenced by an eCO2 concentration.

Comparison of MCFA and Other Methods of Terminating Alcohol Fermentation and Their Influence on the Content of Carbonyl Compounds in Wine

This study deals with the effects of the use of a mixture of medium-chain fatty acids (MCFA) at the end of the alcohol fermentation process on the content of carbonyl compounds in wine. During the experiment, the effects of the addition of MCFA at doses of 10 and 20 mg/L were compared to the termination of alcohol fermentation using cross-flow filtration and chilling treatments. Individual carbonyl compounds were determined by HPLC analysis. The experiment showed that the addition of MCFA caused a reduction of the acetaldehyde content compared to the chilling process, and a reduction of the diacetyl content compared to cross-flow filtration. Throughout the experiment, a lower level of total carbonyl compounds was observed after the addition of MCFA.

Study of carbonyl compounds in white wine production

Carbonyl compounds, especially acetaldehyde in white wines which have a detrimental effect on the aroma and overall stability of wine, were studied.. Seven wine samples of Grüner Veltliner were produced of one input raw material of grapes, all with different dosage of SO2. The sulfur dioxide was maintained at a fixed level during the maturation process and sampled at six months. The grapes were processed, fermented, aged for three months in stainless steel tanks, prepared for bottling, bottled, and then aged in the bottle. In the samples taken, the volume of acetaldehyde, pyruvate, 2-oxoglutarate, diacetyl, and acetoin was determined by HPLC with diode array detection. Individual forms of SO2 were determined by iodometric titration. The wine that was matured on the lees and without the addition of SO2 (variant (0/0/0)) contained the lowest amount of all compounds measured. For example, the volume of acetaldehyde for this wine was 2.7 mg/L at the end of the experiment. The results of the sensory analysis showed that such wine could compete with wines with higher SO2 content without any problems.

Wine Consumption and Oral Cavity Cancer: Friend or Foe, Two Faces of Janus

The health benefits of moderate wine consumption have been extensively studied during the last few decades. Some studies have demonstrated protective associations between moderate drinking and several diseases including oral cavity cancer (OCC). However, due to the various adverse effects related to ethanol content, the recommendation of moderate wine consumption has been controversial. The polyphenolic components of wine contribute to its beneficial effects with different biological pathways, including antioxidant, lipid regulating and anti-inflammatory effects. On the other hand, in the oral cavity, ethanol is oxidized to form acetaldehyde, a metabolite with genotoxic properties. This review is a critical compilation of both the beneficial and the detrimental effects of wine consumption on OCC.

Chitosan as an antioxidant alternative to sulphites in oenology: EPR investigation of inhibitory mechanisms

The efficacy against oxidative degradation in model and sulphite-free white wines of two commercial, insoluble chitosans (one being approved for winemaking) were investigated by electron paramagnetic resonance (EPR). Both compounds at various doses significantly inhibited the formation of α-(4-pyridyl-1-oxide)-N-t-butylnitrone (4-POBN)-1-hydroxyethyl adducts under normal wine storage conditions. Pre-incubation with 2 g/L chitosan followed by filtration had a better effect than adding 50 mg/L sulphur dioxide to the experimental Chardonnay wine on the release of 4-POBN adducts after 6 days of incubation with 100 μM iron(II). In a relevant photooxidative system acetaldehyde formation was significantly reduced after 6 days of incubation. Parallel EPR tests were performed to assess the importance of metal chelation (iron and copper) versus direct scavenging of hydroxyl radicals on the effect of chitosan. The present data support the potentiality of using biocompatible chitosan as a healthier complement and/or alternative to sulphur dioxide against white wine oxidative spoilage.

Sulfur free red wines through the use of grapevine shoots: Impact on the wine quality

Following a preliminary study to determine the possibility of using a grapevine shoot extract (VIN) as a sustainable alternative to sulfur dioxide (SO₂), in this study, the chromatic features, phenolic composition, and sensory analysis of wines treated with VIN at two concentrations were studied during storage in bottle for the first time. The highest differences were found in phenolic compounds after 12months of storage in bottle. The VIN wines had a low content of free anthocyanins and were high in vinyl-pyranoanthocyanins, and B-type vitisins. Consequently, they showed better chromatic characteristics. Moreover VIN, especially at high dose, preserved non-anthocyanin phenolic compounds better than SO₂. However, at this high dose some organoleptic properties were affected. VIN, when used at a low dose, is able to preserve wine composition without loss of quality.

Improved Sensitivity of Acetaldehyde Biosensor by Detecting ADH Reverse Reaction-Mediated NADH Fluoro-Quenching for Wine Evaluation

Acetaldehyde (AcH) is found in ambient air, foods, and the living body. This toxic substance is also contained in wine and known as an important ingredient affecting the quality of wine. Herein, we constructed and evaluated two different fiber-optic biosensors for measurement of AcH in the liquid phase (AcH biosensor) using aldehyde dehydrogenase (ALDH) or alcohol dehydrogenase (ADH). The AcH biosensor measured a concentration of AcH using fluorescence intensity of a reduced form of nicotinamide adenine dinucleotide (NADH) that was produced or consumed via catalytic reaction of the respective enzyme. In the AcH measurement system, an ultraviolet light emitting diode (UV-LED) and photomultiplier tube (PMT) were connected to a bifurcated optical fiber and were used to excite and detect NADH. A sensing region was developed using an optical fiber probe and an enzyme-immobilized membrane, buffer pH, and concentrations of a coenzyme in buffer solution for ALDH forward reaction and ADH reverse reaction were optimized, and the dynamic ranges were compared. ADH-mediated AcH biosensor showed higher sensitivity, wider dynamic range (1-500 μM), and capability of rapid measurement (less than 3 min) than ALDH-mediated AcH biosensor (5-200 μM). ADH biosensor also presented a high selectivity and allowed measurement of AcH in 9 different wine samples (5 red and 4 white wines). The determined concentrations were comparable to those measured by NADH absorbance method, which validated the accuracy of the ADH biosensor in AcH measurement.

Acetaldehyde kinetics of enological yeast during alcoholic fermentation in grape must

Acetaldehyde strongly binds to the wine preservative SO2 and, on average, causes 50–70 mg l−1 of bound SO2 in red and white wines, respectively. Therefore, a reduction of bound and total SO2 concentrations necessitates knowledge of the factors that affect final acetaldehyde concentrations in wines. This study provides a comprehensive analysis of the acetaldehyde production and degradation kinetics of 26 yeast strains of oenological relevance during alcoholic fermentation in must under controlled anaerobic conditions. Saccharomyces cerevisiae and non-Saccharomyces strains displayed similar metabolic kinetics where acetaldehyde reached an initial peak value at the beginning of fermentations followed by partial reutilization. Quantitatively, the range of values obtained for non-Saccharomyces strains greatly exceeded the variability among the S. cerevisiae strains tested. Non-Saccharomyces strains of the species C. vini, H. anomala, H. uvarum, and M. pulcherrima led to low acetaldehyde residues (<10 mg l−1), while C. stellata, Z. bailii, and, especially, a S. pombe strain led to large residues (24–48 mg l−1). Acetaldehyde residues in S. cerevisiae cultures were intermediate and less dispersed (14–34 mg l−1). Addition of SO2 to Chardonnay must triggered significant increases in acetaldehyde formation and residual acetaldehyde. On average, 0.33 mg of residual acetaldehyde remained per mg of SO2 added to must, corresponding to an increase of 0.47 mg of bound SO2 per mg of SO2 added. This research demonstrates that certain non-Saccharomyces strains display acetaldehyde kinetics that would be suitable to reduce residual acetaldehyde, and hence, bound-SO2 levels in grape wines. The acetaldehyde formation potential may be included as strain selection argument in view of reducing preservative SO2 concentrations.

Chemical and Sensory Study on the Evolution of Aromatic and Nonaromatic Compounds during the Progressive Oxidative Storage of a Sauvignon blanc Wine

The effect of repetitive controlled oxidation on the chemical and sensory composition of a fresh and fruity style Sauvignon blanc wine was investigated. Chemical analyses were conducted together with extensive sensory profiling. A decrease in volatile thiols responsible for the fruity nuances and an increase in oxidation-related compounds, such as acetaldehyde, during the course of the oxidation was observed. The wine evolved from a fresh and fruity one to one with slight oxidation and then developed extreme oxidative characteristics. The control samples (no oxygen added) developed a "cooked" character that could indicate the formation of "reductive" compounds in these wines. Conversely, the wines that received a single dose of oxygen did not develop this flavor and were perceived to be fresher and fruitier than the control samples. The color of the wine evolved before the disappearance of the pleasant aroma.

Perceived minerality in sauvignon blanc wine: Chemical reality or cultural construct?

The study aimed to determine the relationship between perceived mineral character in wine and wine chemical composition. We investigated the sensory properties and chemical composition of sauvignon blanc wines from two major sauvignon-producing countries, New Zealand and France. Sensory experiments employing 16 wines (8 French, 8 New Zealand) were conducted in Marlborough, New Zealand and in three regions of France, namely Bordeaux, Burgundy, and the Sancerre/Loire region. Wine professionals (31 New Zealanders and 32 French professionals) sensorially characterised the 16 wines under three conditions, bouquet only (ortho-nasal olfaction), palate only (nose clip condition), and full tasting (global condition: ortho-nasal olfaction, retronasal olfaction, taste, trigeminal stimulation). Sensory data from the global condition only are reported in this article. Physical and chemical analyses conducted on all wines included wine standard parameters, elemental composition, volatile aroma composition, and measures of organic acids. Major results demonstrate that (i) on average French and New Zealand wines were perceived similarly in intensity of mineral character, although judgments to individual wines differed as a function of participant culture; (ii) French and NZ participants drew on different information to make their sensory judgments; and (iii) several aspects of wine composition associated positively with perception of mineral character while others associated negatively, the significant associations differing as a function of participant culture.

Direct Analysis of Free and Sulfite-Bound Carbonyl Compounds in Wine by Two-Dimensional Quantitative Proton and Carbon Nuclear Magnetic Resonance Spectroscopy

Recent developments that have accelerated 2D NMR methods and improved quantitation have made these methods accessible analytical procedures, and the large signal dispersion allows for the analysis of complex samples. Few natural samples are as complex as wine, so the application to challenges in wine analysis look promising. The analysis of carbonyl compounds in wine, key oxidation products, is complicated by a multitude of kinetically reversible adducts, such as acetals and sulfonates, so that sample preparation steps can generate complex interferences. These challenges could be overcome if the compounds could be quantified in situ. Here, two-dimensional ((1)H-(1)H) homonuclear and heteronuclear ((13)C-(1)H) single quantum correlations (correlation spectroscopy, COSY, and heteronuclear single quantum coherence, HSQC) nuclear magnetic resonance spectra of undiluted wine samples were observed at natural abundance. These techniques achieve simultaneous direct identification and quantitation of acetaldehyde, pyruvic acid, acetoin, methylglyoxal, and α-ketoglutaric acid in wine with only a small addition of D2O. It was also possible to observe and sometimes quantify the sulfite, hydrate, and acetal forms of the carbonyl compounds. The accuracy of the method was tested in wine samples by spiking with a mixture of all analytes at different concentrations. The method was applied to 15 wine samples of various vintages and grape varieties. The application of this method could provide a powerful tool to better understand the development, evolution, and perception of wine oxidation and insight into the impact of these sulfite bound carbonyls on antimicrobial and antioxidant action by SO2.

Development of a liquid chromatography-tandem mass spectrometry method for the determination of sulfite in food

Sulfites are widely used food preservatives that can cause severe reactions in sensitive individuals. As a result, the U.S. FDA requires that sulfites be listed on the label of any food product containing >10 mg/kg (ppm) sulfite (measured as sulfur dioxide). Currently, the optimized Monier-Williams (MW) method (AOAC Official Method 990.28) is the most common approach for determining sulfite concentrations in food samples. However, this method is time-consuming and lacks specificity in certain matrices. An improved rapid, sensitive, and selective method has been developed using electrospray ionization (ESI) high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the determination of sulfite in various food matrices. A total of 12 different types of foods were evaluated. These included dried fruits and vegetables, frozen seafood, sweeteners, and juices. The matrix is extracted with a buffered formaldehyde solution, converting free and reversibly bound sulfite to the stable formaldehyde adduct, hydroxymethylsulfonate (HMS). Extracts are prepared for injection using a C18 SPE cartridge to remove any lipophilic compounds. HMS is then separated from other matrix components using hydrophilic interaction chromatography (HILIC) and detected using multiple reaction monitoring (MRM). The method was validated at 5 concentrations in 12 food matrices. Accuracy data showed spiked recoveries ranging from 84 to 115% in representative foods. Six commercially available sulfited products were analyzed using the LC-MS/MS method, as well as the MW method, to determine if differences exist.

Implications of new research and technologies for malolactic fermentation in wine

The initial conversion of grape must to wine is an alcoholic fermentation (AF) largely carried out by one or more strains of yeast, typically Saccharomyces cerevisiae. After the AF, a secondary or malolactic fermentation (MLF) which is carried out by lactic acid bacteria (LAB) is often undertaken. The MLF involves the bioconversion of malic acid to lactic acid and carbon dioxide. The ability to metabolise L-malic acid is strain specific, and both individual Oenococcus oeni strains and other LAB strains vary in their ability to efficiently carry out MLF. Aside from impacts on acidity, LAB can also metabolise other precursors present in wine during fermentation and, therefore, alter the chemical composition of the wine resulting in an increased complexity of wine aroma and flavour. Recent research has focused on three main areas: enzymatic changes during MLF, safety of the final product and mechanisms of stress resistance. This review summarises the latest research and technological advances in the rapidly evolving study of MLF and investigates the directions that future research may take.