Untargeted voltammetric approaches for characterization of oxidation patterns in white wines

Evidence of the Relationship between the Oxygen Radical Absorbance Capacity (ORAC) and the Potential Exposure of White Wines to Atypical Aging (ATA)

Atypical aging (ATA) is a well-known wine defect that leads to unacceptable off-odors of wet mop, soap, waxy, furniture varnish, and dish rag. The main compound that is responsible for these undesired scents, 2-aminoacetophenone (AAP), results from the oxidative degradation of 3-indole acetic acid. This study aimed to investigate different technological factors for a possible effect on the oxygen radical absorption capacity (ORAC) and ATA development in white wine. Oxygenation during fermentation did not result in a significant effect on the development of ORAC or ATA development. Instead, the addition of ascorbic acid after vinification led to increased ORAC and decreased AAP formation. The first evidence of a tendency toward a correlation between ORAC and potential ATA development was found, with r = 0.365. This study showed the potential of the ORAC assay for an early assessment of the possible formation of ATA during wine storage.

White wine phenolics: current methods of analysis

White wine phenolic analyses are less common in the literature than analyses of red wine phenolics. Analytical techniques for white wine phenolic analyses using spectrophotometric, chromatographic, spectroscopic, and electrochemical methods are reported. The interest of research in this area combined with the advances in technology aimed at the winemaking industry are promoting the establishment of novel approaches for identifying, quantifying, and classifying phenolic compounds in white wine. This review article provides an overview of the current research into white wine phenolics through a critical discussion of the analytical methods employed. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Comparison of a Rapid Light-Induced and Forced Test to Study the Oxidative Stability of White Wines

The oxidation processes of white wines can occur during storage and commercialization due to several factors, and these can negatively affect the color, aroma, and quality of the wine. Wineries should have faster and simpler methods that provide valuable information on oxidation stability of wines and allow fast decision-making procedures, able to trigger suitable technological interventions. Using a portable prototype instrument for light irradiations at different wavelengths and times was considered and evaluated on sensorial, spectrophotometric, and colorimetric parameters of white wines. The sensorial analysis revealed that white and light blue were the most significant, after only 1 h of irradiation. The experimental results showed that hydrogen peroxide could enhance the effect of light treatment, allowing a contemporary evaluation of the oxidation stability of wine against light and chemical stresses. As expected, a good correlation (R² > 0.89) between optical density at 420 nm and b* parameter was highlighted. The synergic effect of light and H₂O₂ was also studied on the hydrolyzable and condensed tannins' additions to white wine. The proposed methodology could be used to evaluate the oxidative stability of white wines, but also to evaluate the effect of some oenological adjuvants on wine stability.

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.

An assessment of voltammetry on disposable screen printed electrodes to predict wine chemical composition and oxygen consumption rates

The present work aimed at determining the applicability of linear sweep voltammetry coupled to disposable carbon paste electrodes to predict chemical composition and wine oxygen consumption rates (OCR) by PLS-modeling of the voltammetric signal. Voltammetric signals were acquired in a set of 16 red commercial wines. Samples were extensively characterized including SO₂, antioxidant indexes, metals and polyphenols measured by HPLC. Wine OCRs were calculated by measuring oxygen consumption under controlled oxidation conditions. PLS-Regression models were calculated to predict chemical variables and wine OCRs from first order difference voltammogram curves. A significant number of fully validated models predicting chemical variables from voltammetric signals were obtained. Interestingly, monomeric and polymerized anthocyanins can be differently predicted from the first and second wave of the first derivative of voltammograms, respectively. This fast, cheap and easy-to-use approach presents an important potential to be used in wineries for rapid wine chemical characterization.

Air saturation methodology proposal for the analysis of wine oxygen consumption kinetics

The great heterogeneity currently present when characterizing wine consumption kinetics means that a saturation method, as well as different parameters that allow comparison between wines, need to be established. The aim of this work was to establish a robust method for a wine saturation protocol and compare different fitting models to approximate the oxygen consumption kinetics. To differentiate wines, parameters extracted from the oxygen consumption curves were studied and proposed. 72 young commercial wines (red, white and rosé) from different Spanish appellations of origin, varieties and vintages were used. The results revealed that 5 min was enough to saturate wines up to the maximum level for each one at 35 °C. The inverse curve fitting model showed the best results for all wines. Oxygen at half consumption time (O_mid) and time required to consume from 90% to 10% of the oxygen initially available (Δt_{O_90_10}) were the parameters that differentiated wines the most.

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.

Electrochemical Approaches for Rapid Characterization of Oxidizable Compounds in Different Oak Alternatives

Oak alternatives (OAs) such as chips, granulates or staves, are becoming increasingly used in the wine industry. Although they are mostly considered for their contribution to wine aroma, they are also a source of phenolic compounds to be released in the wine, in particular ellagitannins contributing to wine mouthfeel and antioxidant characteristics. In the present study, we explore the potential for a rapid analytical method based on linear sweep voltammetry (LSV) combined with disposable sensors to provide a rapid measure of the oxidizable compounds present in different OAs, as well as their characterization. Strong correlations were found between the tannin content of different OAs and the total current measures during LSV analysis, allowing a rapid quantification of the oxidizable compounds present, mostly ellagitannin. Application of derivatization to raw voltammograms allowed extraction of a number of features that can be used for classification purposes, in particular with respect to OAs types (chips or staves) and degree of toasting.

Oxygen and SO2 Consumption of Different Enological Tannins in Relationship to Their Chemical and Electrochemical Characteristics

The oxidative behavior of five commercial enological tannins of different sources (tea, grape marc, grape seed, untoasted oak, and toasted oak) was investigated in model wine solutions in the presence or absence of SO2. Solutions of the tannins were also analyzed for total phenolics, methyl cellulose precipitable tannins, high-performance liquid chromatography, and linear sweep voltammetry. Tea and oak-derived tannin solutions were characterized by the highest oxygen consumption rates, with oak-derived tannins exhibiting the highest oxygen consumption rates per milligram of phenolic material present. Linear sweep and derivative voltammetry parameters were well-correlated with oxygen consumption rates, whereas total phenolics or total tannins were not. All tannins were associated with consumption of SO2 upon reaction with oxygen, with the lowest rate of SO2 lost per milligram of O2 reacted being observed for oak tannins.

Monitoring Oxidative Status in Winemaking by Untargeted Linear Sweep Voltammetry

An electrochemical portable device based on linear sweep voltammetry was evaluated for studying the redox behavior of polyphenolic compounds in industrial scale winemaking to infer the effects of selected early processing steps on the vinification trials of Pinot gris, Chardonnay, Vermentino and Sangiovese grapes. For each sample, the redox behavior showed a distinctive voltammetric signal pattern related to the processing step during winemaking, therefore being useful as a potential fingerprint for wine identification and to provide insights about the phenolic content. For instance, there was a high correlation (R² = 0.72) between the total phenolic compounds (PhenOx) and the easily oxidizable compounds (EasyOx), the latter representing approx. 30% on average of the total phenolics. Furthermore, the maceration of red grapes was concluded after 29 days based on information driven by the phenolics pattern. As expected, during alcoholic fermentation, white wines showed a lower content of phenolic compounds than those found in red wines, with an average ratio PhenOx/EasyOx of about 4.7, 5.0 and 3.6 for Chardonnay, Pinot gris and Vermentino, respectively. The portable tool with miniaturized disposable electrodes showed interesting analytical features that can be exploited for on-site and real-time quality control for monitoring change in phenolic composition during wine processing and storage, and for tailoring winemaking practices to enhance the color stability of products.

Fermentative and post-fermentative oxygenation of Corvina red wine: influence on phenolic and volatile composition, colour and wine oxidative response

BACKGROUND

During the production of red wine, moderate uptake of oxygen in the post-fermentative phase helps the stabilization of colour and the decrease of astringent tannins. However, the influence of oxygen uptake during the fermentative phase in must has not been completely investigated. In this study we evaluated the effect of controlled oxygen supply during fermentation-maceration of Corvina grapes on colour characteristics, tannins, volatile compounds, acetaldehyde production and oxidative stability of the finished wine.

RESULTS

Oxygen supply during fermentation improved the formations of stable pigments of Corvina wines due to the higher production of acetaldehyde. However, in wines treated with oxygen a lower production of fruity esters by yeasts was observed. Wines obtained from higher oxygen exposure during fermentation-maceration showed reduced ability to react with oxygen during storage.

CONCLUSIONS

Fermentative and post-fermentative oxygenation should be considered as a technological approach for modifying colour composition and stability, as well as oxidative behaviour of wine during aging. © 2020 Society of Chemical Industry.

Progress in Electrochemical (Bio)Sensors for Monitoring Wine Production

Electrochemical sensors and biosensors have been proposed as fast and cost effective analytical tools, meeting the robustness and performance requirements for industrial process monitoring. In wine production, electrochemical biosensors have proven useful for monitoring critical parameters related to alcoholic fermentation (AF), malolactic fermentation (MLF), determining the impact of the various technological steps and treatments on wine quality, or assessing the differences due to wine age, grape variety, vineyard or geographical region. This review summarizes the current information on the voltamperometric biosensors developed for monitoring wine production with a focus on sensing concepts tested in industry-like settings and on the main quality parameters such as glucose, alcohol, malic and lactic acids, phenolic compounds and allergens. Recent progress featuring nanomaterial-enabled enhancement of sensor performance and applications based on screen-printed electrodes is emphasized. A case study presents the monitoring of alcoholic fermentation based on commercial biosensors adapted with minimal method development for the detection of glucose and phenolic compounds in wine and included in an automated monitoring system. The current challenges and perspectives for the wider application of electrochemical sensors in monitoring industrial processes such as wine production are discussed.

Wine aging: a bottleneck story

The sporadic oxidation of white wines remains an open question, making wine shelf life a subjective debate. Through a multidisciplinary synoptic approach performed as a remarkable case study on aged bottles of white wine, this work unraveled a yet unexplored route for uncontrolled oxidation. By combining sensory evaluation, chemical and metabolomics analyses of the wine, and investigating oxygen transfer through the bottleneck/stopper, this work elucidates the importance of the glass/cork interface. It shows unambiguously that the transfer of oxygen at the interface between the cork stopper and the glass bottleneck must be considered a potentially significant contributor to oxidation state during the bottle aging, leading to a notable modification of a wine’s chemical signature.