Chiral Polyfunctional Thiols and Their Conjugated Precursors upon Winemaking with Five Vitis vinifera Sauvignon blanc Clones

The Influence of Grape Clone and Yeast Strain on Varietal Thiol Concentrations and Sensory Properties of Graševina Wines

Varietal thiol concentration in wine is influenced by numerous factors, of which grape variety and winemaking practices are often highlighted as the most important. Therefore, the aim of this work was to study the effects of grape clone and yeast strain (Saccharomyces and non-Saccharomyces) on the varietal thiols concentrations and sensory characteristics of Graševina (Vitis vinifera L.) white wines. Two grape clones were evaluated (OB-412 and OB-445) along with three different commercial yeast strains (Saccharomyces cerevisiae Lalvin Sensy and Sauvy, and Metschnikowia pulcherrima Flavia). The results showed that the concentration of varietal thiols in Graševina wines amounted up to a total of 226 ng/L. The clone OB-412 was characterized by its significantly higher concentrations, especially of 3-sulfanylhexanol (3SH) and 3-sulfanylhexyl acetate (3SHA). Moreover, alcoholic fermentation with pure S. cerevisiae Sauvy yeasts generally resulted in higher thiol concentrations, while sequential fermentation involving M. pulcherrima positively affected only the 4-methyl-4-sulfanyl-pentan-2-one (4MSP) concentration. Finally, sensory analysis showed that fermentation with pure S. cerevisiae Sauvy yeast also produced more desirable wines. The results suggest that clonal, and especially yeast strain, selections are important modulators of the aroma and sensory properties of wine.

Characterization and Evolution of Volatile Compounds of Cabernet Sauvignon Wines from Two Different Clones during Oak Barrel Aging

Xinjiang is a major wine-making region in China, but its hot climate in summer and intense sun exposure negatively affect the aroma quality of Cabernet Sauvignon wine. The aim of this study was to characterize and differentiate the volatile composition of Cabernet Sauvignon wines from two clones (169 and 191) in Xinjiang, and to study their aromatic profile evolution during 12-month oak barrel aging period. Results showed that before aging, clone 169 wine contained higher concentrations of several alcohols and ethyl esters, while acetate esters and furanic compounds were higher in clone 191 wine. After aging, levels of many terpenes, norisoprenoids, volatile phenols and phenolic aldehydes were significantly higher in clone 169 wine than 191 wine. Aroma series analysis revealed that clone 169 wine exhibited higher floral and roasty aromas after aging, while clone 191 wine had stronger chemical aroma. Principal component analysis indicated that aging process played a primary role in the alteration of volatile profile in these wines. Clone played a secondary role and oak barrel had a tertiary contribution to the variation. The present work indicates that clone 169 is a better choice for producing high-quality aged Cabernet Sauvignon wine with intense and elegant aroma in Xinjiang.

Chiral analysis of cis-2-methyl-4-propyl-1,3-oxathiane and identification of cis-2,4,4,6-tetramethyl-1,3-oxathiane in wine

cis-2-Methyl-4-propyl-1,3-oxathiane (cis-2-MPO), arising from 3-sulfanylhexan-1-ol (3-SH) and acetaldehyde, was recently identified in wine, but the enantiomeric distribution was unknown. Such information could reveal influences on wine aroma, given the impact of chirality on odorant molecules. Herein, a stable isotope dilution assay employing headspace solid-phase microextraction with chiral gas chromatography-mass spectrometry was developed, validated, and applied to a selection of wines. Studies with (3R)-3-SH revealed the elution order of the cis-2-MPO enantiomers and the concentrations of (2R,4S)-2-MPO and (2S,4R)-2-MPO in the studied wines ranged from undetected to 250 ng/L and 303 ng/L, respectively. Strong positive correlations were found between (3R)-3-SH and (2S,4R)-2-MPO (r = 0.654), and (3S)-3-SH and (2R,4S)-2-MPO (r = 0.860). Additionally, cis-2,4,4,6-tetramethyl-1,3-oxathiane, constituted from acetaldehyde and 4-methyl-4-sulfanylpentan-2-ol (4-MSPOH), was identified in wine for the first time. This new 1,3-oxathiane, which presents a novel fate for 4-MSPOH, was detected in wines as a single enantiomer at up to 28 ng/L.

Chirality: An Important Phenomenon Regarding Biosynthesis, Perception, and Authenticity of Flavor Compounds

Chirality plays an important role in flavor research. This will be outlined using selected examples from the key areas analysis, authenticity assessment, biogenesis, and odor perception. Developments of analytical techniques, in particular the use of chiral stationary phases in capillary gas chromatography, enabled the determination of naturally occurring configurations of chiral volatiles at trace levels. Thus, knowledge of pathways and enzymes involved in the biogenesis of chiral substances was acquired, and enantioselective analysis has become a prominent tool in the authenticity assessment of flavorings. Increasing information is also available on structure-odor relationships of chiral flavor compounds and the influence of their configurations on odor thresholds and odor properties. A substantial extension of these data sets and a further understanding of the role of chirality in the perception of aroma compounds is expected from studies on the enantioselectivity of odorant receptor systems. Developments in these areas will be put into a historical perspective, recent progress will be emphasized, and data gaps will be described.

Evolution and Correlation of cis-2-Methyl-4-propyl-1,3-oxathiane, Varietal Thiols, and Acetaldehyde during Fermentation of Sauvignon blanc Juice

cis-2-Methyl-4-propyl-1,3-oxathiane (cis-2-MPO) was recently identified in wine and proposed to arise from the reaction of 3-sulfanylhexan-1-ol (3-SH) and acetaldehyde. However, the evolution profile of cis-2-MPO during alcoholic fermentation (AF) and storage and its relationship with varietal thiols and acetaldehyde production were unknown. These aspects were investigated by fermenting Sauvignon blanc juice with J7 and/or VIN13 yeast strains and assessing the stability of cis-2-MPO during wine storage. Moderate to strong Pearson correlations verified similar evolution trends between acetaldehyde, 3-sulfanylhexyl acetate, and cis-2-MPO, with initial increases and a peak during the early to middle stages of AF before consecutive decreases until the end. Contrarily, 3-SH correlated moderately only at the end of AF. A consistent decrease observed for cis-2-MPO when spiked into Sauvignon blanc wine and assessed during 1-year storage revealed its general instability, but acetaldehyde addition (100 mg/L), pH 3.0, and storage at 4 °C all appeared to retain cis-2-MPO. These results have implications for wine aroma and the potential for cis-2-MPO to act as a sink (or source) for 3-SH in wine over time.

Identification and Quantitative Analysis of 2-Methyl-4-propyl-1,3-oxathiane in Wine

On the basis of the chemistry of wine and the co-occurrence of 3-sulfanylhexan-1-ol (3-SH) and acetaldehyde, we investigated the existence of 2-methyl-4-propyl-1,3-oxathiane (1) and identified the presence of a single detectable geometric isomer, cis-1, in wines for the first time. A stable isotope dilution assay (SIDA) using headspace-solid-phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS) was developed and validated, and used to quantitate cis-1 in a survey of wines, revealing a range from undetectable (limit of detection = 2.6 ng/L) to 460 ng/L. The odor detection threshold of 1 (using a standard comprising 85% cis-1 and 15% trans-1) in neutral white wine was determined to be 7.1 μg/L. Despite cis-1 not appearing above the determined sensory threshold in the studied wines, the findings demonstrated the presence of a new volatile sulfur compound with a strong correlation to 3-SH concentration ( r = 0.72), showing that cis-1 has potential implications for the fate of the important wine aroma compound 3-SH.