Red Wine Oxidation Characterization by Accelerated Ageing Tests and Cyclic Voltammetry

In order to obtain information on the oxidative behavior of red wines, oxygen consumption rates and electrochemical changes (cyclic voltammetry) were measured for nine red wines subject to three different accelerated ageing tests: chemical (with hydrogen peroxide), enzymatic (with laccase from Trametes versicolor), and temperature (at 60 °C). Oxidative behavior depended both on the wine sample and accelerated ageing test type. A good correlation was observed between electrochemical parameters of charges for reference/non-oxidized wines, in accordance with their antioxidant capacity, and the variation of charges after enzymatic and temperature tests, meaning that cyclic voltammetry could be used in order to predict these two oxidation tests and reflect the wine sensitivity towards respective oxidation targets. However, it was not possible to predict wine chemical oxidation test based on hydrogen peroxide from the electrochemical measurements.

Yeast stress and death caused by the synergistic effect of ethanol and SO2 during the second fermentation of sparkling wines

Problems can often arise at the beginning of the second fermentation (prise de mousse) of sparkling wines, such as no start, a long lag period or slow fermentation. These problems are generally associated with yeast stress when inoculated in a base wine with high ethanol content and low pH. However, few studies focus on sulphites, which are often added to base wines to prevent malolactic fermentation, microbiological instability, and wine oxidation. This study aimed to evaluate the joint effect of ethanol and sulfur dioxide on yeasts during the second fermentation. For this purpose, yeasts (Saccharomyces cerevisiae EC1118) were subjected to ethanol, sulfur dioxide and ethanol/sulfur dioxide at the beginning of fermentation, and their vitality and viability, as well as the accumulation of intracellular reactive oxygen species and intracellular pH, were evaluated by flow cytometry. Furthermore, the expression of genes involved in sulfur transport and metabolism was determined. The results showed high mortality, ROS accumulation and intracellular pH reduction in fermentations with both ethanol and sulfur dioxide. The negative effect of ethanol, sulfur dioxide and ethanol/sulfur dioxide on yeasts was found to be dose-dependent and high in those commonly found in some base wines. Cells treated with ethanol/sulfur dioxide showed over-expression of genes involved in sulphite transport (SUL1 and SUL2), efflux pump (SSU1 and FZF1) and metabolism of sulfur amino acids (MET14). Altogether, our data indicate that ethanol and sulfur dioxide have a synergistic effect on yeasts, which may be the root cause of the problems encountered at the beginning of the second fermentation of sparkling wines, and should thus be seriously taken into consideration by winemakers.

Unambiguous NMR Structural Determination of (+)-Catechin—Laccase Dimeric Reaction Products as Potential Markers of Grape and Wine Oxidation

(+)-Catechin—laccase oxidation dimeric standards were hemi-synthesized using laccase from Trametes versicolor in a water-ethanol solution at pH 3.6. Eight fractions corresponding to eight potential oxidation dimeric products were detected. The fractions profiles were compared with profiles obtained with two other oxidoreductases: polyphenoloxidase extracted from grapes and laccase from Botrytis cinerea. The profiles were very similar, although some minor differences suggested possible dissimilarities in the reactivity of these enzymes. Five fractions were then isolated and analyzed by 1D and 2D NMR spectroscopy. The addition of traces of cadmium nitrate in the samples solubilized in acetone-d6 led to fully resolved NMR signals of phenolic protons, allowing the unambiguous structural determination of six reaction products, one of the fractions containing two enantiomers. These products can further be used as oxidation markers to investigate their presence and evolution in wine during winemaking and wine ageing.

Sensory Relevance of Strecker Aldehydes in Wines. Preliminary Studies of Its Removal with Different Type of Resins

The orthonasal quality of two synthetic contexts of wine (young wine and oaked wine) spiked with six different levels of the Strecker aldehydes (isobutyraldehyde, 2-methylbutanal, 3-methylbutanal, methional and phenylacetaldehyde) was evaluated by a panel of wine experts. The aldehyde levels simulated the concentrations present in wines protected from oxidation during production and storage and after severe oxidation. Significant quality detriments were observed at concentrations of 13 µg/L of methional, 49 µg/L of phenylacetaldehyde, 17 µg/L of isobutyraldehyde, 12 µg/L of 2-methylbutanal and 24 µg/L of 3-methylbutanal. The presence of these levels of aldehyde concentrations induced the reduction of fruitiness in young wines and of woody notes in oaked wines as well as the appearance of the typical attributes that define wine oxidation. More than 75% of recently opened commercial wines contain total levels of Strecker aldehydes higher than those, however their effect is not always noticeable as they are forming inodorous adducts with SO2. Nevertheless, this content is a potential risk for the shelf life of the wine, as once SO2 is depleted, these aldehydes could release back into their odour-active forms. Thus, in order to reduce the presence of Strecker aldehydes, eight different resins were studied (two scavengers, four mixed-mode anion exchange and two pure anion exchange) in white wine at two levels of SO2. After 24-h contact, the mixed mode Strata X-A resin was able to significantly reduce aldehydes’ percentages: between 11% for isobutyraldehyde and 86% for phenylacetaldehyde. On the other hand, wine colour was affected and therefore the applicability of the treatment should be further studied. However, this work can be considered a starting point to solve the technological challenge involved in the elimination of aldehydes from wine.

Comparison of Three Accelerated Oxidation Tests Applied to Red Wines with Different Chemical Composition

Background: Three accelerated oxidation tests were proposed to simulate red wine oxidation thus providing information useful to correctly manage moderate oxygen exposure of wine during aging in regard to phenolic composition and wine color. Since the results of the tests have never been compared on wines with different initial composition, the aim of this study was to find a suitable method to simulate oxidation of any still red wine. Methods: Aglianico, Barbera, Gaglioppo, Magliocco, and Nerello wines were treated with (1) three cycles of air saturation, (2) the addition of hydrogen peroxide, and (3) the addition of acetaldehyde. Changes in chromatic characteristics and phenolic composition were determined by spectrophotometric and HPLC methods. Results: Important differences in the behavior of the different wines were detected: the highest formation of polymeric pigments was observed in Barbera and Aglianico wines. In contrast, Gaglioppo and Magliocco wines showed a lower variability before and after the oxidation probably due to the lower anthocyanin/tannin ratio. Among the accelerated oxidation tests applied, no significant differences in color parameters and phenolic composition were detected in samples treated with the addition of H2O2 and the air saturation method. Conclusion: The study demonstrated that H2O2 addition is a successful tool to predict the evolution of different phenolic compounds during the air saturation treatment of wines.

Red Wine Oxidation: Accelerated Ageing Tests, Possible Reaction Mechanisms and Application to Syrah Red Wines

Wine oxidation and ageing involve many complex chemical pathways and reaction mechanisms. The purpose of this study is to set up new and reproducible accelerated red wine ageing tests and identify chemical oxidation or ageing molecular markers. Three accelerated and reproducible ageing tests were developed: a heat test (60 °C); an enzymatic test (laccase test; a chemical test (hydrogen peroxide test). Depending on the test, oxygen consumption was significantly different. For a young wine (2018), the oxygen consumption rate moved from 2.40 ppm·h−1 for the heat test to 3.33 ppm·h−1 for the enzymatic test and 2.86 ppm·h−1 for the chemical test. Once applied to two other vintages (2010 and 2014) from the same winery, the tests revealed different comportments corresponding to wine natural evolution. High resolution UPLC-MS was performed on forced ageing samples and compared to naturally aged red wines. Specific oxidation or ageing ion markers were found with significant differences between tests, revealing the specificity of each test and different possible molecular pathways involved. The hydrogen peroxide test seems to be closer to natural oxidation with an important decrease in absorbance at 520 nm and similar molecular ion variations for [M+H]+ = 291, 331, 347, 493, 535, 581, 639 Da.

New insight about the functionality of oenological tannins; Main results of the working group on oenological tannins

This communication synthetize all the results obtained by the OIV working group on oenological tannins to the current date. The obtained results confirm that oenological tannins really exert a protection effect against grape juice and wine oxidation because they have antioxidant activity, they consume directly oxygen and they exert an inhibitory effect on the laccase activity. Moreover, oenological tannins also exert a copigmentation effect which can improve and protect de color of red wines.