Identification of a sotolon pathway in dry white wines

Key Odorants Forming Aroma of Polish Mead: Influence of the Raw Material and Manufacturing Processes

Mead was analyzed by using the concept of molecular sensory science for the identification of key odorants. A total of 29 odor-active compounds were identified in mead by using gas chromatography olfactometry (GCO). Flavor dilution (FD) factors of identified compounds ranged from 1 to 16,384, compounds with FD factors ≥32 were quantitated by using stable isotopically substituted odorants as internal standards or external standard method, and odor activity values (OAVs) were calculated. Fifteen compounds showed OAVs ≥1: aldehydes (2-phenylacetaldehyde, 3-(methylsulfanyl)propanal), 4-hydroxy-3-methoxybenzaldehyde), esters (ethyl 3-methylbutanoate, ethyl propanoate, ethyl octanoate), alcohols (2-phenylethan-1-ol, 3- and 2-methylbutan-1-ol, 3-(methylsulyfanyl)propan-1-ol), furanons (4-hydroxy-2,5-dimethylfuran-3(2H)-one, 3-hydroxy-4,5-dimethylfuran-2(5H)-one), acids (3- and 2-methylbutanoic acid, acetic acid), 1,1-diethoxyethane, and 4-methylphenol. 2-Phenylacetaldehyde (OAV, 3100) was suggested as the compound with the biggest influence on the aroma of mead, followed by 4-hydroxy-2,5-dimethylfuran-3(2H)-one (OAV, 1900), 3-(methylsulfanyl)propanal (OAV, 890), and 2-phenylethan-1-ol (OAV, 680). Quantitative olfactory profile analysis revealed strong honey, malty, and alcoholic impressions. Omission experiments revealed that 3-(methylsulfanyl)propanal, 2-phenylethan-1-ol, 4-hydroxy-2,5-dimethylfuran-3(2H)-one, ethyl propanoate, ethyl 3-methylbutanoate, 2-phenylacetaldehyde, 3- and 2-methylbutanoic acid, 3-hydroxy-4,5-dimethylfuran-2(5H)-one, and 4-hydroxy-3-methoxybenzaldehyde were the key odorants in the mead. Determining concentrations of key odorants in important production steps showed that the fermentation and maturation stages had the strongest effect on the formation of mead aroma.

Characterization of Key Aging Aroma Compounds in Aged Jiangxiangxing Baijiu and Their Formation Influencing Factors during the Storge Process

Long-term storage Baijiu has an appealing sensory property, yet the chemical makeup is rarely reported. This study investigated a 30-year-old Jiangxiangxing (JXX) Baijiu and recognized and measured 69 aroma compounds. 3-Methyl-2,4-nonanedione (2.76 μg/L), 2,5-dimethyl-4-hydroxy-3(2H)-furanone (HDMF, 46.2 μg/L), 2-ethyl-4-hydroxy-5-methyl-3(2H)-furanone (HEMF, 61.7 μg/L), and piperitone (3.66 μg/L) were detected for the first time in Baijiu. Compared with 3-year-old JXX Baijiu, 24 compounds were significantly higher in the 30-year-old, mainly including furans, pyrazines, and aromatics. Notably, 4,5-dimethyl-3-hydroxy-2(5H)-furanone (sotolon), HDMF, HEMF, vanillin, acetovanillone, and alkyl pyrazines in 30-year-old JXX Baijiu were 2-7 times higher than those of a 3-year-old, and they increased steadily during aging for 3, 15, and 30 years, assumed to be associated with the aging aroma. Following 24 months of storing JXX Baijiu under different conditions, the pottery significantly promoted the synthesis of sotolon, HDMF, HEMF, and alkyl pyrazines. These findings suggest that pottery is a potential catalyst for enhancing aged Baijiu.

Comparative study on key odorants of Jiujiang Fenggang Huangjiu and their succession regularities during aging using sensory-directed flavor analysis

Huangjiu was a Chinese national alcohol with a unique flavor. The key odorants in Jiujiang Fenggang Huangjiu (JJFG) and their succession regularities during aging were systematically researched by a sensomics analysis approach. The volatiles of JJFG were isolated by solvent-assisted flavor evaporation, 77 odorants were identified using gas chromatography-olfactometry-mass spectrometry combined with odor-specific magnitude estimation. Three aroma recombinants, prepared using odorants with odor activity values ≥ 1, all showed good similarities with their corresponding samples (92.1%∼97.5%). After omission/addition tests, 7 new key aroma compounds were found in JJFG, including 1-octen-3-one, 1-pentanol, guaiacol, ethyl 2-hydroxy-4-methylpentanoate, 2-phenethyl acetate, ethyl butanoate, and (E,Z)-2,6-nonadienal. Using orthogonal partial least squares-discriminant analysis, 20 compounds with VIP ≥ 1 were found to be important indicators during aging of JJFG. Among them, sotolon, 3-methylsulfanylpropanal, et al. increased with aging. The improved solid-phase extraction can effectively quantify sotolon, with a recovery rate of 80.96%∼91.75%.

Sotolon and (2E,4E,6Z)-Nona-2,4,6-trienal Are the Key Compounds in the Aroma of Walnuts

Fresh kernels of the walnut tree (Juglans regia L.) show a characteristic and pleasant aroma, the molecular basis of which was unknown. The application of an aroma extract dilution analysis resulted in 50 odor-active compounds. Among them, 37 had not been reported as fresh walnut kernel volatiles before, including the two odorants with the highest flavor dilution factors, namely, fenugreek-like smelling 3-hydroxy-4,5-dimethylfuran-2(5H)-one (sotolon) and oatmeal-like smelling (2E,4E,6Z)-nona-2,4,6-trienal. Quantitations revealed 17 odorants with concentrations in the walnuts that exceeded their odor threshold concentrations. Aroma reconstitution and omission experiments finally showed that the characteristic aroma of fresh walnuts is best represented by a binary mixture of sotolon and (2E,4E,6Z)-nona-2,4,6-trienal. Of both, the natural concentration was ∼10 μg/kg. Further sensory studies showed that the walnut character is intensified when their concentrations are in parallel increased to ∼100 μg/kg. This finding may guide the future breeding of new walnut cultivars with improved aroma.

Characterization of key aroma compounds in aged Qingxiangxing baijiu by Comparative Aroma Extract Dilution Analysis, Quantitative Measurements, Aroma Recombination, and Omission Studies

Aging aroma is an intriguing but an understudied phenomenon in baijiu. The aromatic characteristics of Qingxiangxing (QXX) baijiu stored for 45 years (aged) were investigated using the sensomics approach and were compared with those of young baijiu (0 year-old). Aroma extract dilution analysis revealed 59 odorants, with many long-retained components exhibiting greater flavor dilution values in the aged than the young sample. The analysis of variance of the quantitative data showed significant differences between the young and aged baijiu for 26 compounds. Based on the variations in the content of these compounds, QXX baijiu aged for 0, 5, 15, 20, and 45 years was analyzed and twelve compounds were significantly correlated with aging duration. Finally, eight positively correlated compounds were omitted from the recombinant model, and sotolon, methional, vanillin, dimethyl trisulfide, benzaldehyde, and 3-hydroxy-2-butanone were confirmed to primarily contribute toward the aging aroma of QXX baijiu.

Flavor of tea (Camellia sinensis): A review on odorants and analytical techniques

Tea is among the most consumed nonalcoholic beverages worldwide. Understanding tea flavor, in terms of both sensory aspects and chemical properties, is essential for manufacturers and consumers to maintain high quality of tea products and to correctly distinguish acceptable or unacceptable products. This article gives a comprehensive review on the aroma and off-flavor characteristics associated with 184 odorants. Although many efforts have been made toward the characterization of flavor compounds in different types of tea, modern flavor analytical techniques that affect the results of flavor analysis have not been compared and summarized systematically up to now. Thus, the overview mainly provides the instrumental flavor analytical techniques for both aroma and taste of tea (i.e., extraction and enrichment, qualitative, quantitative, and chemometric approaches) as well as descriptive sensory analytical methodologies for tea, which is helpful for tea flavor researchers. Flavor developments of tea evolved toward time-saving, portability, real-time monitoring, and visualization are also prospected to get a deeper insight into the influences of different processing techniques on the formation and changes of flavor compounds, especially desired flavor compounds and off-flavor substances present at (ultra)trace amounts in tea and tea products.

Cork, a Natural Choice to Wine?

This review presents the most recent data on the state-of-the-art of the main compounds present in cork, their interaction with wine, and the impact that natural stoppers may have on wines’ physical-chemical and sensory properties. According to the recent scientific literature, the chemical composition of cork and the scientific relevance of the compounds extract from cork to wine over time are reviewed. Furthermore, the effect of cork compounds transfer into wines during post-bottling is also discussed, as well as their impact on the organoleptic (colour and taste) of wines. This knowledge is essential for the decision-making process undertaken by wine producers to select the stopper most suitable for their wines. In addition, sustainability is also a topic addressed since it is a natural product that generates some waste as well as the way in which this industry is adapting to the closure of the waste cycle.

Determination of 2-Pentanol Enantiomers via Chiral GC-MS and Its Sensory Evaluation in Baijiu

The enantiomeric contents of 2-pentanol of Baijiu were analyzed by liquid-liquid extraction (LLE) coupled with gas chromatography-mass spectrometry (GC-MS) using β-cyclodextrin as a chiral stationary phase. In this study, the average enantiomeric ratios R:S were 72:28, 64:36, and 94:6 in soy sauce aroma-type Baijiu (SSB), strong aroma-type Baijiu (STB), and light aroma-type Baijiu (LTB), respectively, and only (R)- configuration was found in rice aroma-type Baijiu (RTB). The highest enantiomeric concentration of 2-pentanol was found in STB. (R)-2-pentanol dominated in 48 Baijiu studied, and the concentration of (R)-2-pentanol was higher than that of the (S)-configuration. The results showed that the enantiomers of 2-pentanol were discrepant in different aroma types of Baijiu, and it may be the result of differences in raw materials, environment, and production processes. The 2-pentanol enantiomers had different odor characteristics, with different olfactory thresholds in pure water and 46% ethanol solutions by sensory analysis. (R)-2-pentanol was described as paint, rubber, grease, while the (S)-form had mint, plastic, and pungent notes. The olfactory thresholds of (R)- and (S)-form were 163.30 mg/L and 78.58 mg/L in 46% ethanol and 12.62 mg/L and 3.03 mg/L in pure water, respectively. The different enantiomeric distribution and aroma characteristics of the 2-pentanol enantiomers in Baijiu could be a potential marker for determining adulteration.

Impact of Closure OTR on the Volatile Compound Composition and Oxidation Aroma Intensity of Sauvignon Blanc Wines during and after 10 Years of Bottle Storage

The oxygen transfer rate (OTR) of closures is a well-known parameter impacting the quality of Sauvignon blanc wines (SBw) within the first years of storage, but little research has been published on its long-term effects. The chemical changes in oxidation odor intensity in three SBw sealed with natural cork and other closures that had different known OTRs, ranging from <0.1 to 4.6 mg/year, were monitored over a 10 year period. During aging, free SO₂ and 3-sulfanylhexanol loss, concomitant with increases in dissolved O₂, OD₄₂₀, and sotolon, were correlated with closure OTR levels. After 10 years of aging, sensory analysis was conducted, supported by additional chemical analysis of aroma impact markers, including methional, phenylacetaldehyde, 2-furanmethanthiol, 4-methyl-4-sulfanylpentan-2-one, ethyl-2-sulfanylacetate, and hydrogen sulfide, as well as total SO₂ and dissolved CO₂. These analyses revealed that selected SBw were protected from oxidation over a 10 year aging period, provided that the closure OTR did not exceed 0.3 mg/year.

How acetaldehyde reacts with low molecular weight phenolics in white and red wines

Acetaldehyde is a key compound in determining wine color evolution and sensory properties. Major wine metabolites reactive to acetaldehyde are phenolic compounds, mainly flavan-3-ols and anthocyanins. Many studies have been conducted with the purpose of investigating acetaldehyde reactivity in model solutions, but very poor are the reports of its fate in real wines. By means of LC-HRESIMS and UV/Vis HPLC, red and white wines exposed to an excess of acetaldehyde were analyzed with a specific focus on low molecular weight phenolics. The chemical behavior of acetaldehyde turned out to be different in white and red wines. In white wines, it mainly mediated the formation of vinyl-flavan-3-ol derivatives, while in red wines it led to the formation of ethylidene-bridged red pigments. These latter positively enhanced the color properties of red wines. Conversely, in white wines, the formation of compounds, such as xanthylium ions, causing the undesired browning effects were not detected.

Flavor of rapeseed oil: An overview of odorants, analytical techniques, and impact of treatment

As one of the three major vegetable oils in the world, rapeseed oil is appreciated for its high nutritional value and characteristic flavor. Flavor is an essential attribute, determining rapeseed oil quality and consumer acceptance. The present manuscript provides a systematic literature review of recent advances and knowledge on the flavor of rapeseed oil, which focuses on aroma-active as well as off-flavor compounds, flavor analysis techniques (i.e., extraction, qualitative, quantitative, sensory, and chemometric methods), and effects of treatments (storage, dehulling, roasting, microwave, flavoring with herbs, refining, and oil heating) on flavor from sensory and molecular perspectives. One hundred thirty-seven odorants found in rapeseed oil from literature are listed and possible formation pathways of some key aroma-active compounds are also proposed. Future flavor analysis techniques will evolve toward time-saving, portability, real-time monitoring, and visualization, which aims to obtain a "complete" flavor profile of rapeseed oil. The changes of volatile compounds in rapeseed oil under different treatments are summarized in this view. Studies to elucidate the influence of different treatments on the formation of aroma-active compounds are needed to get a deeper understanding of factors leading to the variations of rapeseed oil flavor.

An accurate single-step LLE method using keeper solvent for quantification of trace amounts of sotolon in Port and white table wines by HPLC-DAD

Sotolon has been reported to play an important role in the typical aroma of aged Port wines. A simple and cheap single-step liquid-liquid extraction (LLE) using glycerol as a keeper for liquid chromatography/ultra-violet absorption quantification of sotolon in Port wines is proposed in this work. The glycerol plays a protective role during the concentration of the extracts increasing the sotolon recovery as well the method repeatability. The proposed method yields chromatograms without interfering compounds and a forty-fold enrichment of sotolon. The detection and quantification limits were far below the sotolon odour threshold in Port wine (19 μg/L). The method was also validated for dry white table wines with good validation parameters. The methodology was successfully applied to selected commercial Tawny, Ruby, and White Port wines, being reported the presence of sotolon in young Ruby and White Port wines for the first time, although below the olfactory detection threshold.

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.

Oxygen-induced faults in bottled white wine: A review of technological and chemical characteristics

Several changes can take place in wine after blotting. Some of them lead to the desired evolution of wine being more complex, round and pleasant. However, unexpected changes can also occur ascribable to the premature wine oxidation (PremOx) arising when a wine, presumably with aging potential, results oxidized and often undrinkable. The complexity of PremOx, where aromas are also involved, makes difficult to identify all the oxidation products, and to predict its occurrence in wines. Despite most studies have been focused on the effect of time after wine bottling on PremOx as well as pinking phenomena, identification of pinking markers, reliable methods for their detection in wine, and correlations between markers and the wine-bottle-closure system are still unknown. This review aimed to highlight aspects PremOx-related, including wine-bottle-closure system, color change, with particular emphasis on pinking, and aroma decay based on the current knowledge becoming the bases for future perspectives.

Novel biotechnological glucosylation of high-impact aroma chemicals, 3(2H)- and 2(5H)-furanones

Glucosyltransferases are versatile biocatalysts to chemically modify small molecules and thus enhance their water solubility and structural stability. Although the genomes of all organisms harbor a multitude of glucosyltransferase genes, their functional characterization is hampered by the lack of high-throughput in-vivo systems to rapidly test the versatility of the encoded proteins. We have developed and applied a high-throughput whole cell biotransformation system to screen a plant glucosyltransferase library. As proof of principle, we identified 25, 24, 15, and 18 biocatalysts transferring D-glucose to sotolone, maple furanone, furaneol and homofuraneol, four highly appreciated flavor compounds, respectively. Although these 3(2H)- and 2(5H)-furanones have extremely low odor thresholds their glucosides were odorless. Upscaling of the biotechnological process yielded titers of 5.3 and 7.2 g/L for the new to nature β-D-glucopyranosides of sotolone and maple furanone, respectively. Consequently, plant glucosyltransferase show stunning catalytic activities, which enable the economical production of novel and unexplored chemicals with exciting new functionalities by whole-cell biotransformation.

Characterization of the Key Aroma Compounds in Aged Chinese Rice Wine by Comparative Aroma Extract Dilution Analysis, Quantitative Measurements, Aroma Recombination, and Omission Studies

The aroma compounds in young and aged Chinese rice wines (rice wines) with a clear difference in their overall aroma profiles were analyzed by comparative aroma extract dilution analysis (cAEDA). In AEDA, more aroma-active regions with flavor dilution (FD) factors of ≥64 were detected in the aged rice wine than in the young rice wine. A total of 43 odorants were further identified and quantitated. The odor activity values (OAVs) revealed 33 aroma compounds with OAVs of ≥1 in young or aged rice wine. Among these aroma compounds with relatively higher OAVs, 3-methylbutanoic acid, 1,1-diethoxyethane, vanillin, 3-methylbutanal, sotolon, benzaldehyde, 4-vinylguaiacol, methional, and 2,3-butanedione showed significant differences between young and aged rice wines. This difference was confirmed through a quantitative analysis of 34 rice wine samples with ages of 0-15 years. Then, the aroma profile of the aged rice wine was successfully simulated through an aroma recombination model. Omission models suggested that sotolon, vanillin, 3-methylbutanal, and benzaldehyde played key roles in the overall aroma of aged rice wine.

Rapid Determination of Sotolon in Fortified Wines Using a Miniaturized Liquid-Liquid Extraction Followed by LC-MS/MS Analysis

Sotolon (4,5-dimethyl-3-hydroxy-2,5-dihydrofuran-2-one) is a powerful odorant usually pointed out as being responsible not only for the characteristic curry notes of the finest fortified wines but also for the off-flavour notes in prematurely oxidized white wines. Most methods reported in literature for quantifying sotolon in wines are quite laborious and use large volumes of organic solvents. Thus, in the present study, the development of a simple, fast, and environment-friendly method for the quantification of sotolon in fortified wine is herein presented. The proposed method uses a single-step liquid-liquid extraction followed by RP-LC-MS/MS and was optimized using a full factorial design. The method showed good linearity (R ² = 0.9999), intra- and interday precision lower than 10% RSD, recovery of about 95%, and high sensitivity (LOQ of 0.04 μg/L). The method was applied to analyse 44 fortified wines from different styles (from dry to sweet wines) and ages (3-115 years old), and it was found that it covers the concentration range usually found for this compound in this kind of alcoholic beverages, which was found to be within 6.3-810 μg/L. Thus, it can be concluded that this method can be used as an accurate tool for the rapid analysis of sotolon, since the early stages of its formation up to long ageing periods.

Characterization of Key Odorants Causing a Fusty/Musty Off-Flavor in Native Cold-Pressed Rapeseed Oil by Means of the Sensomics Approach

The sensomics approach was used to clarify the formation of the fusty/musty off-flavor of native cold-pressed rapeseed oil. A "positive control" (PC) showing the desired sensory attributes and an oil eliciting a fusty/musty off-flavor (OF) were analyzed. Comparative aroma extract dilution analysis (cAEDA), identification experiments, quantitation by stable isotope dilution assays (SIDAs), calculation of odor activity values (OAVs), and aroma recombination resulted in 11 odorants with an OAV ≥ 1 in PC. Main differences between both oils were obtained for compounds caused by microbial influence revealing significantly higher concentrations in OF, e.g., for ethyl 2-methylbutanoate, 2-methoxyphenol, 3-hydroxy-4,5-dimethylfuran-2(5H)-one (sotolon), 2- and 3-methylbutanoic acid, and 4-methylphenol. Comparison of the key odorants in OF with those of the rapeseeds (OFS), from which it was pressed, showed the same 18 compounds proving that the grade of the seeds and their storage conditions are important criteria for the quality of the final oil. Finally, a further 7 native cold-pressed rapeseed oils, eliciting the same sensory defect, were analyzed to confirm aroma-active marker compounds responsible for the fusty/musty off-flavor.

Occurrence of Theaspirane and its Odorant Degradation Products in Hop and Beer

In model oxidized media, six theaspirane-derived compounds were identified by gas chromatography-high resolution mass spectrometry: 4-hydroxy-7,8-dihydro-β-ionone, 6-hydroxy-7,8-dihydro-α-ionone, dihydrodehydro-β-ionone, two monoepoxides, and a derived alcohol. Only 4-hydroxy-7,8-dihydro-β-ionone and dihydrodehydro-β-ionone have been described previously in the literature. Investigation of hop revealed five of these compounds in free form together with theaspirane (especially in the Mosaic variety), while the Citra and Amarillo hop varieties emerged as very interesting for the release of theaspirane, 4-hydroxy-7,8-dihydro-β-ionone, and dihydrodehydro-β-ionone from glucoside precursors. For the first time, theaspirane, 4-hydroxy-7,8-dihydro-β-ionone, 6-hydroxy-7,8-dihydro-α-ionone, and both monoepoxides were found in a fresh commercial top fermentation beer (only theaspirane, 4-hydroxy-7,8-dihydro-β-ionone, and dihydrodehydro-β-ionone have recently been mentioned as Gueuze constituents).

How sotolon can impart a Madeira off-flavor to aged beers

4,5-Dimethyl-3-hydroxy-2(5H)-furanone or sotolon is known to impart powerful Madeira-oxidized-curry-walnut notes to various alcoholic beverages. It has been much studied in oxidized Jura flor-sherry wines, aged Roussillon sweet wines, and old Port wines, in which it contributes to the characteristic "Madeira-oxidized" aroma of these beverages. No scientific paper describes how sotolon might be involved in the Madeira off-flavor found in aged beers. The specific extraction procedure applied here allowed us to quantify this lactone in 7 special beers, at levels sometimes well above its threshold (from 5 to 42 μg/L after 6, 12, 18, and 24 months of natural aging, while unquantifiable in fresh beer). Investigation of spiked beers led us to highlight the key role of pro-oxidants and acetaldehyde. Addition of ascorbic acid without sulfites should be avoided by brewers, as the former would intensify sotolon synthesis. Acetoin, a beer fermentation byproduct, also emerged as possible precursor in beer when combined with serine.

UHPLC quantification of sotolon in white wine

Sotolon (4,5-dimethyl-3-hydroxy-2,5-dihydrofuran-2-one) is a volatile compound involved in the atypical aging of dry white wine, causing an irreversible defect when it exceeds 7-8 μg L(-1), and it might be adopted as a chemical marker of oxidative aging. An easier and sensitive ultrahigh-pressure liquid chromatography method for its determination in white wine is reported. The sample preparation is based on the liquid/liquid extraction by dichloromethane and the purification by solid phase extraction of the redissolved dry sample. This method showed good linearity and intermediate repeatability (<0.7 μg L(-1)), high recovery (>89.5%), and low detection limit (0.029 μg L(-1)). This method was usefully applied to 30 Italian sparkling and still white wine samples, where sotolon was not detected in most of them and exceeded the perception threshold only in one sparkling wine (13 μg L(-1)). The proposed method could be used to further investigate the aging/storage conditions and the chemical-physical parameters affecting its formation in wine.

Measuring protection of aromatic wine thiols from oxidation by competitive reactions vs wine preservatives with ortho-quinones

Quinones are central intermediates in wine oxidation that can degrade the quality of wine by reactions with varietal thiols, such as 3-sulfanylhexanol, decreasing desirable aroma. Protection by wine preservatives (sulphur dioxide, glutathione, ascorbic acid and model tannin, phloroglucinol) was assessed by competitive sacrificial reactions with 4-methyl-1,2-benzoquinone, quantifying products and ratios by HPLC-UV-MS. Regioselectivity was assessed by product isolation and identification by NMR spectroscopy. Nucleophilic addition reactions compete with two electron reduction of quinones by sulphur dioxide or ascorbic acid, and both routes serve as effective quenching pathways, but minor secondary products from coupled redox reactions between the products and reactants are also observed. The wine preservatives were all highly reactive and thus all very protective against 3-sulfanylhexanol loss to the quinone, but showed only additive antioxidant effects. Confirmation of these reaction rates and pathways in wine is needed to assess the actual protective action of each tested preservative.

Characterization of odor-active compounds in sweet-type Chinese rice wine by aroma extract dilution analysis with special emphasis on sotolon

The aroma characteristics of sweet-type Chinese rice wine were studied by sensory analysis, aroma extract dilution analysis (AEDA), and quantitative analysis. Sensory evaluation demonstrated that a caramel-like note was the most distinctive characteristic for sweet-type Chinese rice wine. AEDA was carried out on the extract of a typical sweet-type Chinese rice wine sample. Thirty-nine odor-active regions were detected in the sample with a flavor dilution (FD) factor ≥8, and 37 of these were further identified. Among them, sotolon and 2- and 3-methylbutanol showed the highest FD factor of 1024, followed by 2-acetyl-1-pyrroline (tentatively identified), dimethyl trisulfide, 2-phenylethanol, and vanillin with a FD factor of 512. Sotolon was identified as a key aroma compound in Chinese rice wine for the first time. AEDA results indicated that sotolon (caramel-like/seasoning-like) was the potentially key contributor to the caramel-like descriptor of sweet-type Chinese rice wine. The concentration of sotolon in Chinese rice wine was further quantitated by Lichrolut-EN solid-phase extraction coupled with microvial insert large volume injection method. The content of sotolon ranged from 35.93 to 526.17 μg/L, which was above its odor threshold (9 μg/L) for all Chinese rice wine samples. The highest concentration of sotolon was found in the sweet-type Chinese rice wine, which highlighted the important aroma role of sotolon for this particular type of Chinese rice wine.

Oxygen contribution to wine aroma evolution during bottle aging

Wine aroma undergoes major changes during bottle aging, which are deeply influenced by the degree of oxygen exposure in the bottle. This review discusses the involvement of oxygen in the main chemical transformations occurring in wine aroma composition during bottle aging, with particular emphasis on the formation of oxidative aroma compounds and formation/degradation of sulfur-containing volatile compounds. The implications for wine sensory properties are discussed, as well as some practical aspects of oxygen management during bottle aging, including the role of closure oxygen permeability.

Thermal generation of 3-amino-4,5-dimethylfuran-2(5H)-one, the postulated precursor of sotolone, from amino acid model systems containing glyoxylic and pyruvic acids

4,5-Dimethyl-3-hydroxy-2(5H)-furanone (sotolone), a naturally occurring flavor impact compound, can be isolated from various sources, especially fenugreek seeds. It can also be thermally produced from intermediates generated from the Maillard reaction such as pyruvic and ketoglutaric acids, glyoxal, and 2,3-butanedione. A naturally occurring precursor of sotolone, 3-amino-4,5-dimethyl-2(5H)-furanone, was thermally generated for the first time from pyruvic acid and glycine or from glyoxylic acid and alanine model systems. Isotope labeling studies have implicated 4,5-dimethylfuran-2,3-dione as an intermediate that can be converted into 3-amino-4,5-dimethyl-2(5H)-furanone through Strecker-like interaction with any amino acid. Furthermore, these studies have also indicated the presence of two pathways for the formation of 4,5-dimethylfuran-2,3-dione, one requiring pyruvic acid and a formaldehyde source and the other requiring glyoxylic acid and acetaldehyde. Self-aldol condensation of pyruvic acid followed by lactonization and further aldol reaction with formaldehyde can generate the same intermediate as the self-aldol addition product of acetaldehyde with glyoxylic acid followed by lactonization. The pyruvic acid pathway was found to be a more efficient route than the glyoxylic acid pathway. Furthermore, the pyruvic acid/glycine model system was able to generate sotolone in the presence of moisture, and in the presence of ammonia, commercial sotolone was converted back into 3-amino-4,5-dimethyl-2(5H)-furanone.