Wine Oxidation Research Articles

Enological tannins affect acetaldehyde evolution, colour stability and tannin reactivity during forced oxidation of red wine

SummaryThe addition of enological tannins is a practice admitted and widely used to improve wine phenolic compositions. Although wine ageing is an oxidative process involving phenolic compounds and acetaldehyde production and consumption, the effect of enological tannins on the acetaldehyde and chromatic and phenolic changes of a red wine during oxidation is still not known. In this study, three enological tannins preparations containing gallotannins GT, ellagitannins ET and condensed tannins CT were added to a young commercial Lambrusco red wine in order to obtain wines with three different phenolic compositions. Samples were then treated with hydrogen peroxide to trigger oxidation. All added tannins have determined a production of acetaldehyde greater than control. Acetaldehyde was then consumed in 30 days. The samples treated with CT and ET showed, after oxidation, an increase in colour intensity, determined as the sum of 420, 520 and 620 nm absorbances. A simultaneously increase in polymeric pigments was detected. No significant variation of the Saliva Precipitation Index (SPI), an index useful to give an indirect measure of wine astringency, was observed after 30 days of treatment of CT and ET samples. Results highlight that the addition of CT and ET can help to stabilise colour without affecting wine reactivity towards salivary proteins. A significant role of acetaldehyde has been even detected. These are the first data showing the effect of different enological tannins on the production and consumption of acetaldehyde formation during an oxidation process.

A kinetic approach to describe the time evolution of red wine as a function of packaging and storage conditions

With the aim to determine the influence of packaging in preserving the quality of wine, in this research project the chemical and sensorial evolution of a red wine stored in different packaging materials (glass bottles vs multilayer Tetrabriks®) has been evaluated over a period of 12 months. Furthermore, two different temperature levels (4 and 20 °C) for each packaging solution were maintained throughout the storage period. The results show how the characteristics of packaging could deeply affect wine quality as a function of the storage conditions used, and suggest that with their rational optimization the quality of red wine during storage can be kept and its shelf life extended. In this context, the kinetic characterization of the time evolution of some chemical compounds that can be assumed as indexes of wine oxidation rate could enhance the consumer’s enjoyment during tasting. Under the adopted experimental conditions, the rate of wine aging was higher when the storage temperature increased. Furthermore, after 12 months of storage at room temperature, the glass bottles generally better preserved red wine from oxidation than multilayer Tetrabriks®.

Effect of Pre-fermentation Maceration on the Content of Antioxidant Compounds in Grapevine Juice

Lower antioxidant capacity of white wines is caused by a lower content of phenolic compounds. In red wine, a higher content of phenolic compounds is the result of maceration. This study deals with effects of pre-fermentation maceration on contents of some selected compounds (above all antioxidants) in juices made of grapes of white varieties 'Welschriesling', 'Green Veltliner' and 'Neuburger'. The grapevine mush was macerated for 0; 2; 4; 8; 12; 24 and 48 hours. The spectrophotometry methods was used to estimate juice antioxidant activity and content of flavanols, anthocyans, catechins, hydroxycinnamic acids and flavonols. Contents of total titratable acids and pH were estimated as well. Results of this study show increasing tendency of all parameters with length of maceration. The highest content of antioxidants were found out in the variety 'Welschriesling'. Important are increasing values of hydroxycinnamic acids. However, the main role of the phenolics acids is to contribute to the anti-oxidant capacity, the tartaric esters of hydroxycinnamic acids (particularly caftaric acid) are centrally involved in oxidation and browning reactions in white wine. Their levels increased during the whole period of maceration. In 'Welschriesling', their content increased by 74 mg·L-1. Decreasing tendency show results of titratable acids. Their contents decreased within the first 12 hours of maceration and thereafter they do not change. Longer must maceration could contribute to a decrease in contents of total titratable acids and, thus, to a better harmony of produced wine.

Gas chromatography-mass spectrometry strategies for the accurate and sensitive speciation of sulfur dioxide in wine

Understanding the chemistry of wine oxidation requires the accurate and sensitive quantitative determination of the most important molecular species which SO2 can form. An analytical strategy based in three independent static headspace GC–MS determinations is proposed in order to obtain information about the total, nominally free and truly free levels of SO2. Nominally free forms are directly determined after sample acidulation, total forms require the previous incubation at 100°C, and truly free forms are determined after preconcentration of the headspace of the undisturbed sample in an alkaline solution. The two first determinations provide results equivalent to those reported by the aeration-oxidation (A-O) method, with lower limits of detection (1mgL−1) and better repeatabilities (<4.0%). Results from the analysis of different wines revealed that levels of nominally free are systematically in excess than those of truly free SO2, which suggests that free SO2 determined by any method using previous acidulation includes at least two different species of SO2, which may have different antioxidant behavior.

Quinones as Strecker degradation reagents in wine oxidation processes.

The Strecker aldehydes formed during the reaction between α-amino acids (phenylalanine or methionine) and either gallic acid, caffeic acid or (+)-catechin ortho-quinones were evaluated in wine-model systems. It was demonstrated that phenylacetaldehyde was formed by quinone intermediates at wine pH. The highest amounts of phenylacetaldehyde during the 10days of experiment (69±5µg/L/day; 7x>Control) were obtained from (+) catechin, followed by gallic acid (61±4µg/L/day; 6x>Control) and caffeic acid (41±4µg/L/day; 4x>Control). The intermediate structures delivered from the reaction of ortho-quinones with α-amino acids were demonstrated by MSn.

Evolution of pigments, tannins and acetaldehyde during forced oxidation of red wine: Effect of tannins addition

During wine-making and aging, the phenolic composition gradually changes, mainly owing to oxidation reactions, which may result in a decrease in astringency as well as in color stabilization. Anthocyanins and tannins are the main compounds involved in these changes. The influence of enological tannins on the outcome of red wine oxidation has been evaluated in this study. Oligomeric tannins were added to red wine so as to have wines with three different anthocyanin A/tannin T ratios W (ratio 1A: 0.5T) WT (ratio 1A: 1T) WTT (ratio 1A: 3T). Samples were then treated with hydrogen peroxide to trigger the Fenton reaction. Chromatic characteristics, phenolic composition and acetaldehyde were monitored during oxidation. The samples treated with a higher concentration of tannins showed a clear improvement of color intensity with oxidation mainly due to an increase in polymeric pigments. The higher the content of tannins were, the lower the production of acetaldehyde. These are the first data showing the effect of different A/T ratios on the production of acetaldehyde during an oxidation process.

(1)H NMR: A Novel Approach To Determining the Thermodynamic Properties of Acetaldehyde Condensation Reactions with Glycerol, (+)-Catechin, and Glutathione in Model Wine.

As wine oxidizes, ethanol is converted to acetaldehyde, but its accumulation is not predictable, due to poorly characterized reactions with alcohols, SO2, thiols, flavanols, and others. Measurement of these components has been thwarted by equilibria into the other forms during sample preparation. NMR spectra can be taken on intact samples and is thus ideal for this situation. Equilibria of acetaldehyde with glycerol, (+)-catechin, and glutathione were studied separately in model wine solutions at pH 3-4 by (1)H NMR and 2D ((1)H-(1)H) COSY spectra. Glycerol acetals had equilibrium constants between 1.14 ± 0.056 and 2.53 ± 0.043 M(-1), whereas ethylidene-bridged (+)-catechin dimers and glutathione thiohemiacetals had more favorable equilibria: from (3.92 ± 0.13) × 10(3) to (6.13 ± 0.32) × 10(3) M(-2) and from 10.18 ± 0.22 to 11.17 ± 0.47 M(-1), respectively. These data can be used to create accurate measures of acetaldehyde in its various forms and, consequently, offer insight into wine oxidation.

Sulfur Dioxide–Oxygen Consumption Ratio Reveals Differences in Bottled Wine Oxidation

The availability of oxygen to a wine after bottling can have both beneficial and detrimental effects over time, which may be altered by the wine’s storage history. A Chardonnay wine underwent four different aging treatments: aged in stainless steel with and without lees and aged in oak barrels with and without lees. After six mos of aging, the wines were bottled and subjected to four levels of oxygen exposure by differences in bottle closure. The wines were then monitored for dissolved, headspace, and total consumed oxygen (TCO) concentrations, SO2, aldehydes, esters, and many other standard endpoints. After bottling with substantial oxygen uptake, oxygen consumption was slow, with 0.5 mg/L dissolved oxygen persisting in some bottles after six mos. SO2 concentration decreased and absorbance at 420 nm increased in response to higher accumulated oxygen exposure, expressed as TCO. A comparison of oxygen versus SO2 consumed by the wine provided new insights into the development of oxidation products. Wines aged on yeast lees consumed more SO2 for each equivalent of oxygen consumed. As these wines also had lower levels of weak SO2-binding agents, we hypothesized that these agents interfered in SO2-mediated protection against wine oxidation. At 12 mos after bottling and using descriptive analysis, the 16 wines were rated for 13 attributes determined by 14 judges in triplicate. The aging container, consisting of either stainless steel or oak barrels, had the largest impact on the descriptive analysis followed by oxygen availability through the bottle closure. Wines with the highest TCO had noticeably oxidized characters. The ratio of SO2 versus O2 consumed may help identify wines that will become oxidized. SO2-binding agents and their role in affecting wine oxidation and SO2 analysis needs clarification.

Chemistry of Manganese and Interaction with Iron and Copper in Wine

Iron (Fe) plays a key role in wine oxidation. The reduction potential of the Fe(III)/Fe(II) redox couple in wine conditions allows Fe(II) to react with O2 and Fe(III) to react with polyphenols with the assistance of sulfite. Copper (Cu) accelerates Fe(II) oxidation and thus can greatly accelerate wine oxidation. Some studies suggest that manganese (Mn), which is present at concentrations similar to those of Fe in wine, may also participate in the catalytic process. This study was therefore undertaken to examine the possible interaction of Mn with Fe and Cu in wine. The reduction potential of the Mn(III)/Mn(II) redox couple is considerably higher than that of the Fe couple. As a result, Fe(III), H2O2, and O2 cannot oxidize Mn(II). Furthermore, Mn(III) is a stronger oxidant than Fe(III) and rapidly oxidizes tartaric acid. Thus, Mn cannot redox-cycle in the same way as the Fe couple. Despite this, Mn(II) accelerates Fe(II) oxidation in an air-saturated wine model, and it is proposed that Mn(II) reacts with an intermediate Fe(III)-superoxo complex to generate Mn(III). This accelerates the oxidation of 4-methylcatechol (4-MeC; a model polyphenol) in the presence of Fe and Cu in the model wine. Mn is a powerful catalyst of sulfite autoxidation, involving a radical chain reaction initiated by traces of Fe. As a radical scavenger, 4-MeC prevents chain propagation and, as with Fe, polyphenols prevent Mn-catalyzed sulfite autoxidation in wine. Results show that Mn accelerates the air oxidation of white wine, which is most evident at high Fe and Cu concentrations.

Reaction Mechanisms of Metals with Hydrogen Sulfide and Thiols in Model Wine. Part 2: Iron- and Copper-Catalyzed Oxidation.

Sulfidic off-odors arising during wine production are frequently removed by Cu(II) fining. In part 1 of this study ( 10.1021/acs.jafc.6b00641 ), the reaction of H2S and thiols with Cu(II) was examined; however, the interaction of iron and copper is also known to play an important synergistic role in mediating non-enzymatic wine oxidation. The interaction of these two metals in the oxidation of H2S and thiols (cysteine, 3-sulfanylhexan-1-ol, and 6-sulfanylhexan-1-ol) was therefore examined under wine-like conditions. H2S and thiols (300 μM) were reacted with Fe(III) (100 or 200 μM) alone and in combination with Cu(II) (25 or 50 μM), and concentrations of H2S and thiols, oxygen, and acetaldehyde were monitored over time. H2S and thiols were shown to be slowly oxidized in the presence of Fe(III) alone and were not bound to Fe(III) under model wine conditions. However, Cu(II) added to model wine containing Fe(III) was quickly reduced by H2S and thiols to form Cu(I) complexes, which then rapidly reduced Fe(III) to Fe(II). Oxidation of Fe(II) in the presence of oxygen regenerated Fe(III) and completed the iron redox cycle. In addition, sulfur-derived oxidation products were observed, and the formation of organic polysulfanes was demonstrated.

Quantification of the production of hydrogen peroxide H2O2 during accelerated wine oxidation

Understanding how wines react towards oxidation is of primary importance. Here, a novel approach was developed based on the quantitative determination of the key intermediate H2O2 produced during accelerated oxidation by ambient oxygen. The assay makes use of the conversion of the non-fluorescent Amplex Red substrate into a fluorescent product in presence of H2O2. The total production of H2O2 during 30min was quantified with low within-day and between-day variabilities.Polymerized pigments, but not total polyphenols, played a major role in the determination of H2O2 levels, which were lower in white wines than red wines. H2O2 amounts also increased with temperature and the addition of metal ions, but did not depend on the concentration of many other wine constituents such as SO2. H2O2 levels did not correlate with anti-oxidant properties.We believe that this novel methodology might be generically used to decipher the oxidation mechanisms in wines and food products.

Sensory effect of acetaldehyde on the perception of 3-mercaptohexan-1-ol and 3-isobutyl-2-methoxypyrazine

Background and Aims Wine aroma is influenced by complex interactions between various wine constituents. This study investigated the sensory interactive effects of Sauvignon Blanc impact compounds, 3-mercaptohexan-1-ol and 3-isobutyl-2-methoxypyrazine, with acetaldehyde that typically forms during the oxidation of wine. Methods and Results Spiked model wines were subjected to sensory descriptive analysis using a trained sensory panel. The concentration of each compound varied from below aroma threshold values to high values as reported for wine. Depending on the concentration, acetaldehyde enhanced fruity attributes at a lower concentration, whereas suppression occurred at a higher concentration. Acetaldehyde effectively suppressed the green pepper aroma attribute at certain concentration values, whereas 3-mercaptohexan-1-ol suppressed oxidised green apple associated with acetaldehyde. Changes in attributes used for aroma description also occurred because of change in concentration. Conclusions Complex sensory interactions may occur between Sauvignon Blanc impact compounds and one of the main oxidation-derived compounds, acetaldehyde. Acetaldehyde can enhance or suppress pleasant fruity characters depending on the concentration. Significance of the Study This study showed the potential positive effect of acetaldehyde on white wine aroma when present at a low concentration. Formation of this compound during winemaking and ageing should, however, be controlled because of negative sensory interactions occurring at a higher concentration. This study may also contribute to the sensory characterisation of Sauvignon Blanc wine undergoing oxidation.

Release and Formation of Oxidation-Related Aldehydes during Wine Oxidation.

Twenty-four Spanish wines were subjected to five consecutive cycles of air saturation at 25 °C. Free and bound forms of carbonyls were measured in the initial samples and after each saturation. Nonoxidized commercial wines contain important and sensory relevant amounts of oxidation-related carbonyls under the form of odorless bound forms. Models relating the contents in total aldehydes to the wine chemical composition suggest that fermentation can be a major origin for Strecker aldehydes: methional, phenylacetaldehyde, isobutyraldehyde, 2-methylbutanal, and isovaleraldehyde. Bound forms are further cleaved, releasing free aldehydes during the first steps of wine oxidation, as a consequence of equilibrium shifts caused by the depletion of SO2. At low levels of free SO2, de novo formation and aldehyde degradation are both observed. The relative importance of these phenomena depends on both the aldehyde and the wine. Models relating aldehyde formation rates to wine chemical composition suggest that amino acids are in most cases the most important precursors for de novo formation.

Fe(II):Fe(III) Ratio and Redox Status of White Wines

Iron plays a key role in wine oxidation. Polyphenols that contain catechol systems are the main reductants, and it has been proposed that the oxidation of these substances is mediated by the redox cycling of the Fe(III)/Fe(II) couple. At any time, the Fe(II):Fe(III) concentration ratio should depend on the rate of Fe(II) oxidation by oxygen relative to that of Fe(III) reduction by polyphenols. Fe(III) oxidation of polyphenols, although facilitated by sulfite, is somewhat slower than the reaction of Fe(II) with oxygen, which is strongly accelerated by Cu. Alongside this process, Fe(III) inhibits is own formation. Therefore, the Fe(II):Fe(III) concentration ratio is determined by the interplay of a number of competing reactions. However, because of the relative speed of Fe(II) oxidation, oxygen should be a major determinant of this ratio. A simple spectroscopic method involving ferrozine is used to measure Fe(II) concentration in wines collected under nitrogen with minimal disturbance so as to determine Fe(II) levels in the original wine container. However, Fe(III), which becomes a strong oxidant in the presence of ferrozine, oxidizes catechols in wine conditions. Therefore, Fe(II) concentration, which increases as a result of catechol oxidation, was monitored over time and extrapolated back to the moment of ferrozine addition. Total Fe concentration was determined by adding ascorbic acid to reduce the Fe(III). As expected, the Fe(II):Fe(III) ratio was higher in wines bottled with screw caps than in those bottled with natural cork or filled in boxes. Exposure of wines to oxygen lowered the ratio, which reached equilibrium after some days of aerial saturation. However, the ratio attained differed in the different wines, and this difference likely depends on wine constituents that alter the relative rate of Fe(II) oxidation to that of Fe(III) reduction.

Oxygen Consumption by Red Wines. Part II: Differential Effects on Color and Chemical Composition Caused by Oxygen Taken in Different Sulfur Dioxide-Related Oxidation Contexts.

Chemical changes caused by oxidation of red wines during 5 consecutive air-saturation cycles have been assessed. In order to investigate the existing relationship between the effects caused by O2 and the levels and consumption rates of wine SO2, the total oxygen consumed by the wines (16-25 mg/L) was subdivided into different nonmutually exclusive categories. The ones found most influential on chemical changes were the O2 consumed in the first saturation without equivalent SO2 consumption (O2preSO2) and the O2 consumed when levels of free SO2 were below 5 mg/L (radical forming O2). Chromatic changes were strongly related to both O2 categories, even though anthocyanidin degradation was not related to any O2 category. Radical forming O2 prevented both formation of red pigments and reduction of epigallocatechin and other proanthocyanidins, induced accumulation of phenolic acids, and caused losses of β-damascenone and whiskylactone without evidence of acetaldehyde formation. O2preSO2 seemed to play a key role in the formation of blue pigments and in the decrease of Folin index and of many important aroma compounds.

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.

Influence of the temperature and oxygen exposure in red Port wine: A kinetic approach

Although phenolics are recognized to be related with health benefits by limiting lipid oxidation, in wine, they are the primary substrates for oxidation resulting in the quinone by-products with the participation of transition metal ions. Nevertheless, high quality Port wines require a period of aging in either bottle or barrels. During this time, a modification of sensory properties of wines such as the decrease of astringency or the stabilization of color is recognized to phenolic compounds, mainly attributed to anthocyanins and derived pigments.The present work aims to illustrate the oxidation of red Port wine based on its phenolic composition by the effect of both thermal and oxygen exposures. A kinetic approach toanthocyanins degradation was also achieved. For this purpose a forced red Port wine aging protocol was performed at four different storage temperatures, respectively, 20, 30, 35 and 40°C, and two adjusted oxygen saturation levels, no oxygen addition (treatment I), and oxygen addition (treatment II). Three hydroxycinnamic esters, three hydroxycinnamic acids, three hydroxybenzoic acids, two flavan-3-ols, and six anthocyanins were quantitated weekly during 63days, along with oxygen consumption. The most relevant phenolic oxidation markers were anthocyanins and catechin-type flavonoids, which had the highest decreases during the thermal and oxidative red Port wine process. Both temperature and oxygen treatments affected the rate of phenolic degradation. In addition, temperature seems to influence mostly the phenolics kinetic degradation.

Sensory interaction between 3-mercaptohexan-1-ol, 3-isobutyl-2-methoxypyrazine and oxidation-related compounds

Background and Aims Wine aroma is influenced by complex interactions between various wine constituents. This study investigated the sensorial interactive effects of Sauvignon Blanc impact compounds, 3-mercaptohexan-1-ol, 3-isobutyl-2-methoxypyrazine with aldehydes typically originating from oxidation of white wines, methional and phenylacetaldehyde. Methods and Results Spiked model wines were subjected to sensory descriptive analysis using a trained panel. The concentration of each compound varied from below aroma threshold value to high values reported in wine. Combinations of the four compounds were also evaluated sensorially. Depending on the concentration of the compounds, methional had a strong suppressive effect on the intensity of attributes contributed by 3-mercaptohexan-1-ol, such as grapefruit and guava, whereas methional and 3-isobutyl-2-methoxypyrazine enhanced the intensity of certain attributes, which included cooked beans and cooked potato. Conclusions Complex sensory interactions may occur between Sauvignon Blanc impact compounds and compounds related to oxidation depending on concentration of the compounds. Oxidation-derived compounds such as methional can suppress pleasant aroma attributes linked to volatile thiols, while contributing negative attributes especially in the presence of 3-isobutyl-2-methoxypyrazine. Significance of the Study This study highlights the importance of preserving fresh and fruity flavours while preventing the formation of unwanted aldehydes due to interactions that can influence the overall aroma profile of the wine. This study may also contribute to the sensory characterisation of oxidised Sauvignon Blanc wine.

Rapid analysis of heterocyclic acetals in wine by stable isotope dilution gas chromatography–mass spectrometry

Heterocyclic acetals from acetaldehyde and glycerol have been proposed as markers of age and oxidation in fortified wines. Here the analysis of these acetals (cis- and trans-5-hydroxy-2-methyl-1,3-dioxane and cis- and trans-4-hydroxymethyl-2-methyl-1,3-dioxolane) by liquid–liquid extraction and gas chromatography–mass spectrometry was optimized for rapid monitoring of these compounds in aged and oxidized table wines. The method provides a wide range of linearity and reproducibility below 3.0% RSD, while the detection limits, 2.85–13.5 μg/L, were significantly lower than typical levels measured in wines. Stable isotope dilution improved the accuracy of the method. Oxidation of red wines was shown to correlate with increased levels of the acetals. The accuracy and speed of the new method will allow for quantifying oxidation in large experiments such as wine aging or micro-oxygenation trials, and to assess the potential value of these substances as markers of wine oxidation.

HPLC-DAD–MS/MS characterization of phenolic compounds in white wine stored without added sulfite

The oxidation of dihydroxybenzene and hydroxycinnamate compounds generates unstable quinones which undergo further reactions to combine nucleophilic compounds. These reactions are limited when sulfur dioxide (SO2) is used as wine preservative, as SO2 plays an important role in reducing quinones back to their phenol form. In no sulfite-added wine, oxidation chemistry undoubtedly results changed. Therefore, in this work, the phenolic profile of a white wine without adding sulfites, after twelve-month storage, was investigated by HPLC-DAD-MS/MS and compared to a control stored with sulfur dioxide. A total of twenty-six phenolics were detected including hydroxycinnamate derivatives and minor compounds resulting from oxidation processes, i.e. oxidized caffeic acid dimers, whose structures were tentatively proposed on the basis of their UV, MS, and MS/MS typical fragmentation. The experimental evidence of these latter is described for the first time in wine stored without added sulfites, and it may contribute to get new insight in the field of wine oxidation processes.