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).

A New Classification of Perceptual Interactions between Odorants to Interpret Complex Aroma Systems. Application to Model Wine Aroma.

Although perceptual interactions are usually mentioned and blamed for the difficulties in understanding the relationship between odorant composition and aromatic sensory properties, they are poorly defined and categorised. Furthermore, old classifications refer mainly to effects on the odour intensity of the mixture of dissimilar non-blending odours and do not consider odour blending, which is one of the most relevant and influential perceptual interactions. Beginning with the results from classical studies about odour interaction, a new and simple systematic is proposed in which odour interactions are classified into four categories: competitive, cooperative, destructive and creative. The first categories are most frequent and display a mild level of interaction, being characterised mostly by analytical processing. The last two are less frequent and activate (or deactivate) configurational processes of object recognition with deep effects on the quality and intensity of the perception. These interactions can be systematically applied to interpret the formation of sensory descriptors from the odorant composition, suggesting that qualitatively the system works. However, there is a lack of quantitative data to work with odour intensities reliably, and a pressing need to systematise the effects of creative interactions.

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.

Gas Chromatography Olfactometry (GC-O) for the (Semi)Quantitative Screening of Wine Aroma.

This review discusses the different approaches developed by researchers in the last 40 years for the qualitative and semi-quantitative screening of odorants, with special emphasis in wine aroma profiling. In the first part, the aims and possibilities of Gas chromatography-olfactometry (GC-O) as odour-screening and aroma profiling technique are discussed. The critical difference between approaches is whether the ranking of odorants is carried out on an extract containing all the odorants present in the product, or on an extract representative of the odorants contained in the vapour phases that cause the odour and flavour. While the second alternative is more direct and can be more efficient, it requires a good understanding of the factors affecting orthonasal olfaction, handling volatiles (purging, trapping, eluting, and separating) and about the sensory assessment of GC effluents. The review also includes an updated list compiling all the odorants detected in wine by GC-O, including retention indexes and odour descriptions with a general guideline for the identification of odorants.

Fourteen ethyl esters of wine can be replaced by simpler ester vectors without compromising quality but at the expense of increasing aroma concentration.

Aroma contribution of individual esters has been studied in complex mixtures mimicking red wine models. A mixture containing 14 ethyl esters at concentrations found in wine (V1) was prepared and kept as reference. Isointense and qualitatively similar aroma vectors with a reduced number of esters (V2-V7) were prepared. Those vectors were introduced in two reconstituted wines to assess whether simpler vectors could replace V1 without compromising wine quality. In the simpler young wine model, V1 could be replaced by a vector containing just 3 odorants (ethyl 2-methylbutyrate, ethyl butyrate and hexanoate). In the oaky model, a vector containing just ethyl 2-methylbutyrate (V7) could replace V1 without any discernible sensory change. Results also reveal that sub- or perithreshold odorants play outstanding roles on the overall odour intensity of the mixture and that aroma simplification concomitantly implies an increase in the amount of odorant required to keep the intensity of the aroma vector.

Aroma profiling of an aerated fermentation of natural grape must with selected yeast strains at pilot scale.

The use of non-Saccharomyces strains in aerated conditions has proven effective for alcohol content reduction in wine during lab-scale fermentation. The process has been scaled up to 20 L batches, in order to produce lower alcohol wines amenable to sensory analysis. Sequential instead of simultaneous inoculation was chosen to prevent oxygen exposure of Saccharomyces cerevisiae during fermentation, since previous results indicated that this would result in increased acetic acid production. In addition, an adaptation step was included to facilitate non-Saccharomyces implantation in natural must. Wines elaborated with Torulaspora delbrueckii or Metschnikowia pulcherrima in aerated conditions contained less alcohol than control wine (S. cerevisiae, non-aerated). Sensory and aroma analysis revealed that the quality of mixed fermentations was affected by the high levels of some yeast amino acid related byproducts, which suggests that further progress requires a careful selection of non-Saccharomyces strains and the use of specific N-nutrients.

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).

On the effects of higher alcohols on red wine aroma.

This work aims to assess the aromatic sensory contribution of the four most relevant wine higher alcohols (isobutanol, isoamyl alcohol, methionol and ß-phenylethanol) on red wine aroma. The four alcohols were added at two levels of concentration, within the natural range of occurrence, to eight different wine models (WM), close reconstitutions of red wines differing in levels of fruity (F), woody (W), animal (A) or humidity (H) notes. Samples were submitted to discriminant and descriptive sensory analysis. Results showed that the contribution of methionol and ß-phenylethanol to wine aroma was negligible and confirmed the sensory importance of the pair isobutanol-isoamyl alcohol. Sensory effects were only evident in WM containing intense aromas, demonstrating a strong dependence on the aromatic context. Higher alcohols significantly suppress strawberry/lactic/red fruity, coconut/wood/vanilla and humidity/TCA notes, but not the leather/animal/ink note. The spirit/alcoholic/solvent character generated by higher alcohols has been shown to be wine dependent.