Optimization and Validation of a Method to Determine Enolones and Vanillin Derivatives in Wines-Occurrence in Spanish Red Wines and Mistelles

Understanding the chemical nature of wine aroma demands accurate quantitative determinations of different odor-active compounds. Quantitative determinations of enolones (maltol, furaneol, homofuraneol, and sotolon) and vanillin derivatives (vanillin, methyl vanillate, ethyl vanillate, and acetovanillone) at low concentrations are complicated due to their high polarity. For this reason, this paper presents an improved and automated version for the accurate measure of these common trace wine polar compounds (enolones and vanillin derivatives). As a result, a faster and more user-friendly method with a reduction of organic solvents and resins was developed and validated. The optimization of some stages of the solid phase extraction (SPE) process, such as washing with an aqueous solution containing 1% NaHCO₃ at pH 8, led to cleaner extracts and solved interference problems. Due to the polarity of these type of compounds, an optimization of the large volume injection was also carried out. Finally, a programmable temperature vaporization (PTV) quartz glass inlet liner without wool was used. The injector temperature was raised to 300 °C in addition to applying a pressure pulse of 180 kPa for 4 min. Matrix effects were solved by the use of adequate internal standards, such as ethyl maltol and 3',4'-(methylenedioxy)acetophenone. Method figures of merit were highly satisfactory: good linearity (r² > 0.98), precision (relative standard deviation, RSD < 10%), high recovery (RSD > 89%), and low detection limits (<0.7 μg/L). Enolones and vanillin derivatives are associated with wine aging. For this reason, the methodology was successfully applied to the quantification of these compounds in 16 Spanish red wines and 12 mistelles. Odor activity values (OAV) indicate that furaneol should be considered an aroma impact odorant in red wines and mistelles (OAV > 1) while homofuraneol and sotolon could also produce changes in their aroma perceptions (0.1 < OAV < 1).

To fear the unknown: Covid-19 confinement, fear, and food choice

The coronavirus outbreak in December 2019 completely changed the dynamic of consumption in different sectors of industry. The food and beverage industries have been profoundly affected, from production, to modifications in consumers' choices. Among the different reasons behind those modifications is confinement, which forces consumers to stay at home for an extended period and just go out to perform essential tasks, such as going to the supermarket. We hypothesized that this new dynamic of consumption could create a situation of fear that changes food choice. To test this hypothesis, two studies were conducted in three countries with a different degree of confinement: Mexico (flexible), Spain (strict), and Peru (hard). Study one consisted of a free association task with 60 participants in each country with the inductor word "coronavirus and food". The different associations served as the basis to build a structured questionnaire, which was used in the second study focused on fear and food choice. The second study was applied to 450 participants in the same three countries. Results showed that fear can be separated into nine dimensions: social, emotional, food supply, government, basic needs, food-delivery, overeating, immunity, and family conflicts. The participants could also be clustered into four different groups that differ in their country of origin and sex, but also in their food choice. Overall, the results showed that fear influenced consumer's food choices during a confinement period.

How has COVID-19, lockdown and social distancing changed alcohol drinking patterns? A cross-cultural perspective between britons and spaniards

During the early months of 2020, the world experienced a novel, violent, and relentless pandemic era. By the end of the year more than seventy-seven million cases of COVID-19 had been reported around the globe. Due to it being a highly contagious disease, the recommended measures adopted by most nations to prevent infection include social distancing and quarantine. How did these measures affect people's relationship with alcohol consumption in cultures where alcohol plays an important social role? A questionnaire-based study, designed to follow the drinking behaviour of people before and during lockdown was applied to two different cultural groups impacted by the pandemic during the strict phase of lockdown. These are the British and Spanish populations (179 participants from each country were interviewed). Considering the frequency of consumption of the alcoholic beverages evaluated (wine, beer, cider, whisky and spirits), the results showed that a significant lockdown*country interaction was observed. Overall, Spanish participants consumed alcoholic beverages less frequently during lockdown than before, while British participants reported no change in their consumption habits. Spaniards’ decrease in alcohol consumption is related to the absence of a social contexts while Britons seems to have adapted their consumption to the modified context. Results suggest that, alcohol consumption is a central core of the British culture, while for the Spanish, socialization is more a cultural characteristic than the alcohol itself.

How the country-of-origin impacts wine traders' mental representation about wines: A study in a world wine trade fair

Using data collected at a world wine trade fair, we study how the country-of-origin impacts wine traders' mental representation about wines. In the analysis we use traditional exporters in Old (France) and New (Argentina) world wine countries in comparison to non-traditional exporters in Old (Switzerland) and New (Brazil) world wine countries. Three main findings are reported. First, the country-of-origin of wines was more important on guiding participants' representations, than the category of countries the traders came from. Second, participants' evocations were more precise and specific for traditional wine-exporting countries than for less traditional wine exporting countries. Finally, the lack of traders' knowledge of wines from non-traditional wine-exporting countries produced associations and beliefs related to the image of the country itself. Our findings have important implications for the marketing and export activities of the wine industry.

Elusive Chemistry of Hydrogen Sulfide and Mercaptans in Wine

This paper summarizes, discusses, and complements recent findings about the fate of H₂S and methanethiol (MeSH) during wine storage. Analytical assays to determine free volatile sulfur compounds (VSCs) and brine-releasable (BR-) VSCs in combination with accelerated reductive (AR) aging and micro-oxygenation (MOX) assays allow characterizing the different categories of species able to produce H₂S and MeSH and the processes of interconversion. Each wine seems to contain a specific total amount of H₂S and MeSH distributed into free, metal-complexed, and oxidized forms (di and polysulfides) interconnected through reversible redox equilibria whose external expression is wine redox potential. Oxidation transforms all mercaptans likely into nonvolatile disulfides and hydrodisulfides. In anoxia, these molecules are spontaneously and quantitatively reduced back. The concomitant accumulation of major wine thiols would provoke complex dissociation and the release of free H₂S and MeSH. Additionally, total amounts can increase due to the metal-catalyzed desulfhydration of cysteine and methionine.

Micro-oxygenation does not eliminate hydrogen sulfide and mercaptans from wine; it simply shifts redox and complex-related equilibria to reversible oxidized species and complexed forms

This work seeks to assess the effects of micro-oxygenation (MOX) on the present and potential levels of Volatile Sulfur Compounds (VSCs) of wine. With such purpose, three red wines with a tendency to develop sulfury off-odors were subjected to three different MOX conditions (4.4-20mg/L delivered at 0.05 or 0.2mg/L/day). Samples were further subjected to Accelerated Reductive aging (AR) and analyzed for free and Brine Releasable (BR) VSCs and redox potential. Although MOX induced strong decreases in the levels of all free VSCs, hardly affected the ability of the wine to release back hydrogen sulfide and other mercaptans during AR-aging. During aging BR-levels of MOX samples became in most cases similar or higher than non-oxygenated controls. BR-levels and the fractions free/BR follow characteristic sigmoid plots when represented versus redox potential suggesting that all changes are the result of reversible equilibria between free, metal-complexed and oxidized forms of VSCs.

The effects of copper fining on the wine content in sulfur off-odors and on their evolution during accelerated anoxic storage

Three different red wines with reductive character have been treated with two different doses of copper sulfate (0.06 and 0.5mg/L) and with a commercial copper-containing product at the recommended dose (0.6mg/L). Wines were in contact with copper one week, centrifuged and stored at 50°C in strict anoxia for 2weeks (up to 7 in one case). Brine-releasable (BR-) and free fractions of Volatile Sulfur Compounds were determined throughout the process. Relevant increases of BR-H₂S suggest that those wines contained other H₂S precursors non-detectable by the brine dilution method. Copper treatments had two major effects: 1) immediate decrease the levels of free H₂S and methanethiol (MeSH); 2) slow the rate at which free H₂S (not MeSH) increases during anoxic storage. After 7weeks of anoxia levels of free H₂S and MeSH were high and similar regardless of the copper treatment. Higher copper doses could induce the accumulation of BR-H₂S.

Sensory and chemical drivers of wine minerality aroma: An application to Chablis wines

The goal of this work was to evaluate the effect of vineyard position on the minerality of wines and to establish relationships between minerality scores, sensory descriptors and chemical composition. Sensory analyses included minerality rating and free description performed by wine professionals under two conditions: orthonasal olfaction alone and global tasting. Chemical characterization included analysis of major and minor volatile compounds, volatile sulphur compounds, mercaptans, metals, anions and cations. Results showed a significant effect of the river bank on wine minerality scores only in the orthonasal olfaction condition, samples from the left being more mineral than those from the right bank. Methanethiol, involved in shellfish aroma, was significantly higher in wines from the left (more mineral) than from the right bank. Contrary, copper levels, related to lower levels of free MeSH, and norisoprenoids, responsible for white fruit and floral aromas, were higher in wines from the right bank (less mineral).

Formation and Release of H2S, Methanethiol, and Dimethylsulfide during the Anoxic Storage of Wines at Room Temperature

A total of 21 different wines (13 reds, 5 whites, and 3 rosés) were kept at 25 °C in anoxia for 379 days. Free and total forms of H2S and methanethiol (MeSH) and dimethylsulfide (DMS) were measured initially and after 117, 221, and 379 days of storage. Levels of free H2S, free and total MeSH, and DMS continuously increased during storage, while levels of total H2S remained essentially unchanged. Average increases of free H2S amount to 6.2 μg/L (from 1.1 to 12.9 μg/L), those of free MeSH to 1.6 μg/L (from 0.7 to 3.5 μg/L), and those of total MeSH to 1.9 μg/L (from 1.1 to 3.0 μg/L), whereas those of DMS were 27.8 μg/L (from 11 to 69 μg/L). The fraction of H2S under free forms significantly increased, suggesting that release is a major factor explaining H2S increases. All increases can be satisfactorily predicted from data obtained at 50 °C.

Study of the effect of H2S, MeSH and DMS on the sensory profile of wine model solutions by Rate-All-That-Apply (RATA)

The effect of hydrogen sulfide (H₂S), methanethiol (MeSH) and dimethyl sulfide (DMS) on the odor properties of three wine models-WM- (young white, young red and oaked red wines) was studied. Wine models were built by mixing a pool of common wine volatile and non-volatile compounds and further spiked with eight different combinations of the three sulfur compounds present at two levels (level 0: 0μgL^-1 and level 1: 40μgL^-1 of H₂S, 12μgL^-1 of MeSH; 55μgL^-1 of DMS). For each wine matrix eight WMs were produced and further submitted to sensory description by Rate-All-That-Apply (RATA) method. Hydrogen sulfide and methanethiol were clearly involved in the formation of reductive aromas and shared the ability to act as strong suppressors of fruity and floral attributes. Specifically, hydrogen sulfide generated aromas of rotten eggs, while methanethiol generated significant increases in camembert and decreases in citrus, smoky/roasted and oxidation aromas. The simultaneous presence of hydrogen sulfide and methanethiol enhanced the intensity of the unspecific term reduction, while the specific nuances individually imparted by each of the two compounds could not be further identified. DMS did not exert any outstanding effect on the reductive character of wines and its sensory effect was matrix-dependent. It was involved in the formation of fruity notes such as cooked/candied and red/black fruits in young wines, and vegetal notes (canned vegetables) in oaked red WMs.

Reductive off-odors in wines: Formation and release of H₂S and methanethiol during the accelerated anoxic storage of wines

In order to better understand the processes involved in the development of H2S and methanethiol (MeSH) along anoxic storage of wines, 24 wines were stored in strict anoxia at 50°C for 3weeks. Free and total forms of H2S and MeSH were measured at different times. Results showed that: (1) all wines contain relevant proportions of bonded forms of H2S and MeSH (93% and 47% on average); (2) such % decreases with age; (3) levels of total forms are related to wine metal composition; (4) anoxic storage brings about an increase of free forms, a strong decrease in the percentage of bonded forms, and except for H2S in red wines, an increase in total forms. Both de novo formation and release contribute to reductive off-odors. Release is predominant for reds and H2S, while at 50°C, de novo formation dominates for whites and rosés and MeSH.

Key changes in wine aroma active compounds during bottle storage of Spanish red wines under different oxygen levels

Samples from 16 Spanish red wines have been stored for 6 months at 25 °C under different levels of oxygen (0-56 mg/L). Amino acids, metals, and phenolic compounds were analyzed and related to the production or depletion of key oxidation- and reduction-related aroma compounds. Oxidation brings about sensory-relevant increases in Strecker aldehydes, 1-octen-3-one, and vanillin. Formation of Strecker aldehydes correlates to the wine content on the corresponding amino acid precursor, Zn, and caffeic acid ethyl ester and negatively to some flavonols and anthocyanin derivatives. Formation of most carbonyls correlates to wine-combined SO2, suggesting that part of the increments are the result of the release of aldehydes forming bisulfite combinations once SO2 is oxidized. Methanethiol (MeSH) and dimethylsulfide (DMS), but not H2S levels, increase during storage. MeSH increments correlate to methionine levels and proanthocyanidins and negatively to resveratrol and aluminum. H2S, MeSH, and DMS levels all decreased with oxidation, and for the latter two, there are important effects of Mn and pH, respectively.

Quantitative analysis of free and bonded forms of volatile sulfur compouds in wine. Basic methodologies and evidences showing the existence of reversible cation-complexed forms

This paper examines first some basic aspects critical to the analysis of Volatile Sulfur Compounds (VSCs), such as the analytical characteristics of the GC-pFPD system and the stability of the different standard solutions required for a proper calibration. Following, a direct static headspace analytical method for the determination of exclusively free forms of VSCs has been developed. Method repeatability is better than 4%, detection limits for main analytes are below 0.5μgL(-1), and the method dynamic linear range (r(2)>0.99) is expanded by controlling the split ratio in the chromatographic inlet to cover the natural range of occurrence of these compounds in wines. The method gives reliable estimates of headspace concentrations but, as expected, suffers from strong matrix effects with recoveries ranging from 0 to 100% or from 60 to 100 in the cases of H2S and the other mercaptans, respectively. This demonstrates the existence of strong interactions of these compounds with different matrix components. The complexing ability of Cu(2+) and to a lower extent Fe(2+) and Zn(2+) has been experimentally checked. A previously developed method in which the wine is strongly diluted with brine and the volatiles are preconcentrated by HS-SPME, was found to give a reliable estimation of the total amount (free+complexed) of mercaptans, demonstrating that metal-mercaptan complexes are reversible. The comparative analysis of different wines by the two procedures reveals that in normal wines H2S and methanethiol can be complexed at levels above 99%, with averages around 97% for H2S and 75% for methanethiol, while thioethers such as dimethyl sulfide (DMS) are not complexed. Overall, the proposed strategy may be generalized to understand problems caused by VSCs in different matrices.