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A comprehensive review on Sauvignon Blanc aroma with a focus on certain positive volatile thiols
Abstract
Vitis vinifera L. cv. Sauvignon blanc wines have become increasingly popular as it is a cultivar that can be
influenced in the vineyard and the cellar to produce a range of wine styles. Although originally from France,
Sauvignon blanc is now widely cultivated in the wine growing regions of the world. These wines are usually
given aroma descriptors such as green pepper, grassy, asparagus; while other more tropical aromas include passion fruit and guava. Volatile thiols, specifically 4-mercapto-4-methylpentan-2-one, 3-mercaptohexan- 1-ol and 3-mercaptohexyl acetate, are a group of chemical compounds contributing to a large extent to the perception of the tropical aroma. A recent influx of new research has given insight into the precursors, development and reactions of volatile thiols in Sauvignon blanc must and wine. As there is currently much interest in these compounds, this review will focus on these volatile thiols, but will also discuss the role of other compounds that could influence the aroma of Sauvignon blanc. This paper could assist researchers and winemakers by giving a comprehensive review of Sauvignon blanc aroma, with a particular focus on certain sought after volatile thiols.
... Research conducted by Naviglio et al. [51] and Naranjo et al. [52] involved the rapid cooling of Bianchello del Metauro grapes by sparging the grapes with liquid CO 2 before crushing and destemming. The white wines produced from these treated grapes were not statistically different from the control wines in terms of alcohol, pH, titratable acidity, and volatile acidity [55,56]. This was similar to findings observed in earlier research. ...
... Key thiols present in Sauvignon blanc and responsible for its varietal aromas are 4-methyl-4-sulfanylpentan-2-one (4-MSP), 3-sulfanylhexan-1-ol (3-SH), and 3-sulfanylhexyl acetate (3-SHA) with perception thresholds of 0.8 ng L −1 , 60 ng L −1 , and 4 ng L −1 , respectively (Table 3). They are predominantly responsible for the "tropical" (gooseberry, grapefruit, and passion fruit) characteristics associated with Sauvignon blanc [56]. However, it is interesting to note that when present in excessive concentrations, they often impart less desirable strong, sweaty aromas resembling "cat urine" [54,56]. ...
... They are predominantly responsible for the "tropical" (gooseberry, grapefruit, and passion fruit) characteristics associated with Sauvignon blanc [56]. However, it is interesting to note that when present in excessive concentrations, they often impart less desirable strong, sweaty aromas resembling "cat urine" [54,56]. Furthermore, research conducted on South African (SA) Chenin blanc revealed the presence of the varietal thiols 3-SH and 3-SHA in concentrations above their aroma thresholds, indicating that these two compounds also contribute significantly to the aroma of Chenin blanc wines [65][66][67]. ...
Low-temperature treatments preceding alcoholic fermentation are becoming increasingly popular and have been used in winemaking as a tool to improve wine colour, aroma, and quality. Additionally, the pre-fermentative treatment of grapes with cryogenic agents protects the grape juice (must) from oxidation by reducing the diffusion of atmospheric oxygen into the liquid phase during the winemaking process. Resultant wines were reported to have enhanced varietal aromas, increased complexity, and higher thiol levels. Indications are that increased contact time between skin and juice improves the extraction of the compounds and/or precursors. Recently, there has been considerable interest in the production of wines with enhanced varietal aromas and improved quality by applying innovative winemaking technologies. This review aims to provide an overview of the aroma and organoleptic quality of Sauvignon blanc and Chenin blanc wines produced from grapes that were subjected to pre-fermentative cryogenic treatments including the impact aroma compounds, i.e., volatile thiols and methoxypyrazines.
... Research conducted by Naviglio et al. [51] and Naranjo et al. [52] involved the rapid cooling of Bianchello del Metauro grapes by sparging the grapes with liquid CO 2 before crushing and destemming. The white wines produced from these treated grapes were not statistically different from the control wines in terms of alcohol, pH, titratable acidity, and volatile acidity [55,56]. This was similar to findings observed in earlier research. ...
... Key thiols present in Sauvignon blanc and responsible for its varietal aromas are 4-methyl-4-sulfanylpentan-2-one (4-MSP), 3-sulfanylhexan-1-ol (3-SH), and 3-sulfanylhexyl acetate (3-SHA) with perception thresholds of 0.8 ng L −1 , 60 ng L −1 , and 4 ng L −1 , respectively (Table 3). They are predominantly responsible for the "tropical" (gooseberry, grapefruit, and passion fruit) characteristics associated with Sauvignon blanc [56]. However, it is interesting to note that when present in excessive concentrations, they often impart less desirable strong, sweaty aromas resembling "cat urine" [54,56]. ...
... They are predominantly responsible for the "tropical" (gooseberry, grapefruit, and passion fruit) characteristics associated with Sauvignon blanc [56]. However, it is interesting to note that when present in excessive concentrations, they often impart less desirable strong, sweaty aromas resembling "cat urine" [54,56]. Furthermore, research conducted on South African (SA) Chenin blanc revealed the presence of the varietal thiols 3-SH and 3-SHA in concentrations above their aroma thresholds, indicating that these two compounds also contribute significantly to the aroma of Chenin blanc wines [65][66][67]. ...
Low-temperature treatments preceding alcoholic fermentation are becoming increasingly popular and have been used in winemaking as a tool to improve wine colour, aroma, and quality. Additionally, the pre-fermentative treatment of grapes with cryogenic agents protects the grape juice (must) from oxidation by reducing the diffusion of atmospheric oxygen into the liquid phase during the winemaking process. Resultant wines were reported to have enhanced varietal aromas, increased complexity, and higher thiol levels. Indications are that increased contact time between skin and juice improves the extraction of the compounds and/or precursors. Recently, there has been considerable interest in the production of wines with enhanced varietal aromas and improved quality by applying innovative winemaking technologies. This review aims to provide an overview of the aroma and organoleptic quality of Sauvignon blanc and Chenin blanc wines produced from grapes that were subjected to pre-fermentative cryogenic treatments including the impact aroma compounds, i.e., volatile thiols and methoxypyrazines.
... On the one hand, some sulfur-containing compounds are responsible for off-flavours, such as rotten eggs ascribed to H2S produced by wine yeast [24,25], and cooked vegetables caused by thioacetic acid esters and mercaptans under low redox potential in wine [25]. On the other hand, certain sulfurcontaining compounds can contribute to positive odours such as the notes of gooseberry, passion fruit, grapefruit, and guava [3]. These compounds considered to be the impact odorants in New Zealand's Sauvignon Blanc are referred to as volatile thiols or polyfunctional mercaptans [26]. ...
... These compounds considered to be the impact odorants in New Zealand's Sauvignon Blanc are referred to as volatile thiols or polyfunctional mercaptans [26]. Volatile thiols contain one or more sulfhydryl groups with additional functional groups such as ketones, alcohols, and esters in their molecules [3], and they can be perceived by the human nose at very low concentrations [27]. ...
... Medium-chain fatty acids in wine, such as hexanoic, octanoic, and decanoic fatty acids, are found to play an essential role in the fruity notes of wine [3]. These fatty acids are believed to be produced by yeast as intermediates in the biosynthesis of long-chain fatty acids [73]. ...
Key varietal characteristics of Sauvignon Blanc, including the descriptors of ‘green’ and ‘tropical fruit’, are mostly attributed to methoxypyrazines and volatile thiols, while monoterpenes, higher alcohols, esters, fatty acids, and other volatile compounds also add complexity and fruity notes to the wines. During the winemaking and ageing period, oxidation decreases the concentrations of these compounds and diminishes the flavours derived from this aromatic grape variety. Therefore, antioxidants, such as sulfur dioxide, are commonly utilized in Sauvignon Blanc wine production for better preservation of those beneficial primary aromas. This review focuses on key varietal aromas in Sauvignon Blanc wine and how they are influenced by oxidation, and SO2 alternatives, including ascorbic acid, glutathione, and glutathione-enriched inactivated dry yeasts, that can be used in winemaking as antioxidants.
... 4MSP and 3SH are released from cysteinylated (Cys-4MSP, Cys-3SH) and glutathionylated (Glut-4MSP, Glut-3SH) precursors by the β-lyase enzyme of T. delbrueckii, M. pulcherrima, and P. kluyveri [23,[47][48][49]. 3SHA is produced by the esterification of 3SH by the alcohol acetyl transferase enzyme [50]. ...
... In addition, S. cerevisiae can metabolize both Glut-3SH and Cys-3SH. Thus, in sequential fermentations, T. delbrueckii may convert the precursor Glut-3SH into 3SH and into Cys-3SH, which, in addition to the contribution of Cys-3SH from the must, increases the availability of Cys-3SH to be metabolized later by S. cerevisiae, contributing to an increase in 3SH [23,48], as well as 3SHA, because S. cerevisiae also has increased acetylation capacity (conversion of 3SH into 3SHA by acetyltransferase alcohol) [50,52]. ...
... Finally, similar to the metabolism of terpenes [43], the conversion of thiol precursors is dependent on the absorption capacity of the yeast through its cell membrane and subsequent cleavage to the corresponding odorant thiols [50]. As such, treatments to improve this absorption capacity will contribute to improving the varietal aromatic profile of wines, both at the terpenes and thiols levels as mentioned in Section 4.1, for example, in wines produced from Verdejo grapes in which 3SH, 3SHA, and 4MSP contribute to the typicity of this grape variety [25]. ...
About 42 commercial products based on non-Saccharomyces yeasts are estimated as available on the market, being mostly pure cultures (79%), with a predominance of Torulaspora delbrueckii, Lachancea thermotolerans, and Metschnikowia pulcherrima. The others are multi-starter consortia that include non-Saccharomyces/Saccharomyces mixtures or only non-Saccharomyces species. Several commercial yeasts have shown adequate biocompatibility with S. cerevisiae in mixed fermentations, allowing an increased contribution of metabolites of oenological interest, such as glycerol, esters, higher alcohols, acids, thiols, and terpenes, among others, in addition to a lower production of acetic acid, volatile phenols, biogenic amines, or urea. Multi-starter inoculations are also reviewed here, which show adequate biocompatibility and synergy between species. In certain cases, the aromatic profile of wines based on grape varieties considered neutral is improved. In addition, several yeasts show the capacity as biocontrollers against contaminating microorganisms. The studies conducted to date demonstrate the potential of these yeasts to improve the properties of wine as an alternative and complement to the traditional S. cerevisiae.
... Volatile thiols are crucial components of 'varietal character' in some varieties and originate from precursors found in the berry. Thus, volatile thiols are generated during fermentation by yeast from these precursors present in the musts (Coetzee and Du Toit, 2012;Lin et al., 2019). The conjugated thiol precursors are produced in the grape berries, but little is known about the mechanism involved in their biosynthesis (Robinson et al., 2014a). ...
... The conjugated thiol precursors are produced in the grape berries, but little is known about the mechanism involved in their biosynthesis (Robinson et al., 2014a). In wines, the concentration of volatile thiols is related to the concentration of their precursors, but only a small proportion of these precursors release the aromatic thiol (Coetzee and Du Toit, 2012). The most important thiols are 4-mercapto-4-methylpentan-2-one (4MMP), 3-mercaptohexan-1-ol (3MH), 3-mercaptohexyl acetate (3MHA), 4mercapto-4-methylpentan-2-ol (4MMPOH). ...
... The aroma of 4MMP is described as a box tree, passionfruit, broom and black currant bud. 3MH and 3 MHA are responsible for the passionfruit, grapefruit and citrus aroma, as well as 4MMPOH, although its role is limited due to low concentrations (Coetzee and Du Toit, 2012). These compounds are important for the aroma of wines from the following grapes: 'Sauvignon Blanc', 'Gewürztraminer', 'Riesling', 'Colombard', 'Petit Manseng' (Tominaga et al., 1998;Tominaga et al., 2004), 'Chardonnay' (Kobayashi et al., 2012), 'Merlot' and 'Cabernet Sauvignon' (Bouchilloux et al., 1998). ...
Volatile compounds are secondary metabolites that play a key role in the organoleptic properties of the grapes and wine. To this day, more than 700 volatile compounds have been identified in grapes and wine. The most important groups of volatile compounds are monoterpenes, C13-norisoprenoids, sesquiterpenes, alcohols, esters, ketones, aldehydes, fatty acids, methoxypyrazines and polyfunctional thiols. All volatile compounds are contained in the pericarp and their largest proportion is in the grape skin (exocarp). In grapes, they can be present in the free form and in the form of glycosides, most often in the form of diglucosides, with glucose as a unit directly linked to a non-sugar molecule, i.e., an aglycone. The aglycones can be monoterpenes, C13-norisoprenoids and volatile phenols. They are released from the berry during grape crushing by enzymatic hydrolisis or during vinification by chemical hydrolisis, and as such, in free form give the aroma of grapes and wines. Monoterpenes and C13-norisopreinods are synthesized in plastids but stored in vacuoles in the form of glycosides, which, unlike aglycones, are stable, soluble in water and can only be stored in aqueous media. Grapevines volatile composition is determined by the variety and can be influenced by biotic and abiotic factors and by different vineyard management practices. This chapter mainly concentrates in uniting the exisitng knowledge of the biosynthesis, composition and content of volatile compounds in different berry tissue and grape varieties.
... The expression of these genes is affected by both biotic and abiotic stresses. 12,13 The formation of glutathionerelated precursors is mainly linked to VvGST3 and VvGST4, which lead to the formation of Glu-3SH, which is transformed into an intermediate called cysteinylglycine-3SH by means of a GGT (γ-glutamyl-transferase) and a carboxy-peptidase. 12,13 The up-regulation of VvGST5 in plants subjected to defoliation suggests its involvement in the synthesis of thiol precursors in Sauvignon Blanc. ...
... 12,13 The formation of glutathionerelated precursors is mainly linked to VvGST3 and VvGST4, which lead to the formation of Glu-3SH, which is transformed into an intermediate called cysteinylglycine-3SH by means of a GGT (γ-glutamyl-transferase) and a carboxy-peptidase. 12,13 The up-regulation of VvGST5 in plants subjected to defoliation suggests its involvement in the synthesis of thiol precursors in Sauvignon Blanc. 14 Helwi et al. 15 reported that the high nitrogen nutrition affects thiol precursors biosynthesis, stimulating the formation of Glu-3SH. ...
... The initially spontaneous strategies (sulfites and antimicrobial-free) and mixed strategy were characterized by the presence of fatty acid esters, including ethyl hexanoate, ethyl octanoate, and ethyl decanoate. These results align with the literature reports on Sauvignon Blanc wines fermented with Saccharomyces Cerevisiae [49]. In fact, a study evaluating the effect of SO 2 on Sauvignon Blanc must showed that the ethyl esters ethyl hexanoate, ethyl octanoate, and ethyl decanoate were produced in greater quantities in wines after adding sulfites compared to those without sulfites [49]. ...
... These results align with the literature reports on Sauvignon Blanc wines fermented with Saccharomyces Cerevisiae [49]. In fact, a study evaluating the effect of SO 2 on Sauvignon Blanc must showed that the ethyl esters ethyl hexanoate, ethyl octanoate, and ethyl decanoate were produced in greater quantities in wines after adding sulfites compared to those without sulfites [49]. ...
Studying non-Saccharomyces yeasts as bio-protectors can help find new alternatives to the chemical additive SO2 in winemaking. The present article evaluates the effect of two native yeasts, Candida oleophila and Candida boidinii, as potential bio-protectors to replace SO2 during the production of Sauvignon Blanc wine. Fermentation was conducted on simple and mixed inoculum at two concentrations, 1 × 106 and 1 × 107 cells/mL. We monitored the population of deterioration microorganisms, including lactic acid bacteria (LAB), acetic acid bacteria (AAB), and Brettanomyces bruxellensis (BB), apart from the final chemical and volatile composition of the wine. The results were compared with fermentations protected with SO2, where Candida oleophila yeast was more effective against lactic acid bacteria, whereas Candida boidinii was more effective against acetic acid bacteria and Brettanomyces bruxellensis; meanwhile, the fermentations with the initial inoculum of 1 × 107 cells/mL showed better results than those with an inoculum of 1 × 106 cells/mL. Bio-protector use did not negatively affect wine quality, equaling the effectiveness of SO2 for spoilage microorganism inhibition. This study reveals for the first time the potential of Candida oleophila and Candida boidinii yeasts as bio-protectors in microbiological wine stabilization.
... For example, Philipp et al. [19] showed that a selection of Austrian Pinot Blanc wines had higher ethyl octanoate and isobutyl acetate concentrations than other Austrian white wines. For Sauvignon Blanc, green characteristics, such as green asparagus and green pepper, are enhanced by the presence of methoxypyrazines (MPZ), in particular 2-methoxy-3-isobutylpyrazine (IBMP), while tropical fruit (citrus and passion fruit) and black currant aromas are enhanced by various fruity thiols (e.g., 3-sulfanylhexan-1-ol , 3sulfanylhexyl acetate , and 4-methyl-4-sulfanylpentan-2-one ) [20,21]. Besides these varietal aromas, other fermentation aromas such as higher alcohols, fatty acids, and esters play a supporting role for the characteristics [22]. ...
... Te aroma of Sauvignon Blanc is essentially characterised by sulphanyl compounds (thiols) and MPZ [20]. Two important sulphanyl compounds are 3-SHA, which was not signifcantly infuenced by the treatment, and 3-SH, which was signifcantly infuenced by the treatment. ...
Many varietal aromas of wine are located in the berry skin. In the present study, we evaluated four important Austrian grape varieties: Grüner Veltliner, Sauvignon Blanc, Traminer, and Pinot Blanc. We assessed whether prefermentation skin contact, fermentation with the skin (only for Grüner Veltliner), and stabulation (lees stirring; only for Sauvignon Blanc, Traminer, and Pinot Blanc) could enhance the varietal aromas of the different grape cultivars. The aim was to intensify the varietal aromas without extracting the undesirable phenols. We performed a detailed analytical characterisation of approximately 100 volatile and phenolic compounds as well as a sensory characterisation. Although mash fermentation significantly increased the spicy aromas of Grüner Veltliner, which are affected by climate change (especially the sesquiterpene rotundone), it markedly decreased the fruitiness and increased the bitterness; therefore, it cannot be recommended for this cultivar. For Sauvignon Blanc, stabulation is a possible option; the varietal aromas (thiols and methoxypyrazines) were increased in the final wines of these variants. For Pinot Blanc and Traminer, prefermentation skin contact yielded the best results: for Traminer, it produced the highest content of monoterpenes (especially z-rose oxide), and for Pinot Blanc, it produced the highest content of ethyl esters. To summarise, stabulation will not completely replace classic skin contact, and mash fermentation is certainly not an alternative for the production of standard Grüner Veltliner wine. However, additional investigations are necessary with regard to other grape varieties, terroirs, and vintages before we can make final recommendations.
... Tropical fruit aroma is an important driver for consumer acceptance in Sauvignon blanc [3,10]. The volatile thiols 3-MH, 3-MHA and 4-MMP are well known for exclusively imparting these aromas in white wines [27,28]. However, recent studies have shown the perception of tropical fruit aroma in white wines which the presence of these varietal compounds are less prominent [16,20,29,30]. ...
... While there is substantial evidence indicating that tropical fruit aroma is highly correlated to thiols and that such aroma is exclusively caused by these compounds [28], a similar outcome was clearly not observed in this study (Fig. 3). Our results showed that esters and ester-thiol combinations caused different qualities of tropical fruit aroma, including passionfruit, guava and grapefruit. ...
The assessment of different aroma families on tropical fruit aroma perception is still not well understood. This study aimed to investigate the effect of esters and volatile thiols on tropical fruit aroma perception in white wines. Four levels of thiols (none, low, medium and high) and three levels of esters (none, low, medium) were added to a dearomatized white wine base in a full factorial design. Check-All-That-Apply (CATA) was used to determine the aroma descriptors that most differentiated the wines followed by Sensory Descriptive Analysis (SDA) to evaluate the intensity of those significant aroma attributes. More than 78% of the total variance was described in the first two dimensions when using Canonical Variate Analysis. Tropical fruit aromas were associated with wines containing different levels of esters and ester-thiol combinations. Volatile thiols alone imparted earthy aroma and were grouped with the control wine. The different ester-thiol combinations altered the tropical fruit aroma quality in the wines from citrus to passionfruit, pineapple and guava. Understanding the cause of tropical fruit aroma allows for targeted processing to achieve the desired wine sensory quality.
... From a varietal point of view, VTs were observed in at least one sample of each cultivar, implying that, in the context of Italian white wines, these compounds can be considered rather ubiquitous. Quantitative variations across cultivars, as well as within the same cultivar, were rather large, reflecting the complex array of factors that can determine the VTs content of wines, such as the pedoclimatic characteristics of the vineyard, the management of the winery pre-fermentative steps, the yeast strain used in fermentation, and the levels of oxygen exposure of the wines after fermentation and after bottling (Coetzee and du Toit, 2012). These results are in strong agreement with the observations by Mateo et. ...
... 3-SH and 3-SHA are more ubiquitous than 4-MSP and have been identified in many varieties; however, Sauvignon blanc is the cultivar where these compounds reach concentrations close to 20 μg/L for 3-SH and greater than 2 μg/L for 3-SHA (Coetzee and du Toit, 2012). ...
Thanks to their low odor detection thresholds, free varietal thiols (VTs) play a key role in the primary aroma of wines, to which they confer an intense scent reminiscent of box tree, grapefruit, citrus fruits, passionfruit and cat urine odor. Excluding wines from a few VT-rich grapevine cultivars, VTs appear to be present in most cultivars at trace levels, although a comprehensive dataset is still missing. The low concentration of VTs combined with their high reactivity and matrix complexity make their determination in wines a challenging task. In this research an optimized liquid chromatography – tandem mass spectrometry (LC-MS/MS) method was validated and used for the quantification of 4-methyl-4-sulfanylpentan-2-one (4-MSP), 3-sulfanylhexan-1-ol (3-SH), 3-sulfanylhexyl acetate (3-SHA) and ethyl 3-sulfanylpropionate (E3SP) in 246 samples (vintage 2019) representative of 18 monovarietal Italian white wines. VTs were detected in all cultivars even though higher values of 3-SH were found in Lugana, Müller-Thurgau and Verdicchio cultivars. Müller-Thurgau wines showed the highest level of 4-MSP, that was mainly correlated to the odor descriptors of passionfruit and box tree/cat urine. The VTs composition of Müller-Thurgau was confirmed on a second set of 50 wines from different vintages. From a sensory perspective, the samples of Müller-Thurgau showed the best positive correlations between chemical variables and the odor descriptors thiol note, passion fruit and box tree/cat urine. These notes are significantly related to 4-MSP, suggesting that it could play a relevant olfactory role for the aroma of Müller-Thurgau wines. Sorting analysis allowed to group these wines according to their thiolic characteristics. The chemical variables and the odor descriptors attributable to the thiol notes are important for Müller-Thurgau and Lugana wines, while the contribution of thiol notes was sensorially negligible for the other wines.
... The varietal volatile thiols, 4-sulfanyl-4-methyl-2-pentanone (4MMP), 3-sulfanyl-1-hexanol (3SH) and its acetate ester, are flavour compounds present in some white and rose wines. These compounds are characterised by a low olfactory perception threshold corresponding to nanograms per litre (Darriet et al. 1995, Tominaga et al. 1998, Roland et al. 2011, Coetzee and Du Toit 2012. These compounds are released in wine as a result of the β-lyase activity of the yeast during the alcoholic fermentation. ...
... Both vine growing and winemaking practices affect the concentration of varietal thiols (VTPs) (Coetzee and Du Toit 2012, Aleixandre-Tudo et al. 2015, Olejar et al. 2015. Fermenting yeast strains, belonging to both Saccharomyces and non-Saccharomyces genera, strongly influence the release of varietal thiols Vigentini 2018, Ruiz et al. 2019). ...
Background and Aims
Varietal thiol precursors (VTPs) decrease strongly after the pre-fermentative operations. The effect of grape must extraction steps on the concentration of S-3-(hexan-1-ol)-L-glutathione (G-3SH), S-3-(hexan-1-ol)-L-cysteine (Cys-3SH) and S-3-(hexanal)-glutathione (G-3SHal) was investigated.
Methods and Results
Must produced on a commercial scale was sampled throughout the pre-fermentation steps. Must was also prepared in the laboratory for assessing the role of copper, sulfite and air. In commercial must fractions, over 95% of G-3SHal was lost because of sulfite addition, while the concentration of G-3SH and Cys-3SH increased along with must yield, and it exceeded the concentration found in berries. No Cys-3SH was found in the intact grape; instead a trace concentration of G-SHal, and a high concentration of glutathione and even cysteine was determined when sulfite was added. A large amount of G-3SHal was formed when copper was depleted.
Conclusions
Our data suggest that Cys-3SH and G-3SHal are promptly and mainly formed in grape must upon grape pressing. Sulfite and copper prevented the formation of VTPs, while settling of must led to a loss of VTPs.
Significance of the Study
Varietal thiol precursors can be preserved through the proper management of pressing with particular attention to must contact with air, extraction conditions, contact time with solids and addition of sulfite.
... A number of winemaking practices that might change white wine aroma in general have been investigated. These include oxidative and reductive winemaking as well as SO 2 and ascorbic acid must additions [3,4]. Extended skin maceration and effects of natural and different Saccharomyces and non Saccharomyces on Chenin blanc in particular have also been assessed [5,6]. ...
... Formation and later acid hydrolysis of fruit-associated compounds such as esters during barrel ageing has also been found [26]. Varietal thiols, responsible for the guava and passion fruit aromas in Chenin blanc [25], have also been reported to be sensitive towards acid hydrolyses over time [3]. These factors might all have played in a role in the changes observed in the sensory profiles of the Chenin blanc during the bottle and barrel ageing periods. ...
The sensorial evaluation of Chenin blanc wine produced with different types of oak wood treatments over time has not been investigated before. The main aim of this study was to assess the sensory profile, using a trained panel, of a South African Chenin blanc wine fermented and matured in old barrels, three types of new oak barrels, two types of oak staves as well as a stainless steel tank over time, which has not been done before. Results indicate mainly separation between the stainless-steel tank/old barrel treatments from the stave and new barrel treatments, with separation between the latter two treatments also being found. More fruity descriptors were used in the stainless-steel tank and old barrel treatments, with oak-related descriptors being used in the stave and new barrel treatments. Separation between among the new barrel and stave treatments were also noted, which was still reflected during bottle maturation. These results indicate that winemakers need to take cognizance of the sensorial differences induced by barrel and stave maturation in white wines and how these evolve over time.
... Du fait de leur faible seuil de perception (quelques ng/L), ils contribuent significativement au profil aromatique des vins. La 4MSP et le 3SH sont produits à partir des précurseurs cystéinylés et glutathionylés présents dans le moût grâce à l'action des ß-lyases des levures (Coetzee and du Toit, 2012;Darriet et al., 1995;Fedrizzi et al., 2009;Peyrot des Gachons et al., 2002;Roland et al., 2011;Subileau et al., 2008). Si elle ne produit pas de 4-methyl-4-sulfanylpentan-2-one (4MSP), d'importantes quantités de 3-sulfanylhexan-1-ol (3SH) sont retrouvés dans les vins fermentés avec T. delbrueckii (Sadoudi et al., 2012;Zott et al., 2011). ...
... Ce phénomène ne semble pas être expliqué par un mécanisme de type quorum-sensing. En effet, le quorum-sensing peut être défini comme la régulation de l'expression de certains gènes en réponse à des fluctuations de densité de population (Miller and Bassler, 2001 • Impact des cultures mixtes sur la libération des thiols volatils L'impact de ces molécules sur l'arôme des vins de plusieurs cépages, notamment du Sauvignon blanc, a été rapporté par de nombreux auteurs (Coetzee and du Toit, 2012;Darriet et al., 1995;Tominaga et al., 1998). Parmi ces composés, la 4MSP (4-méthyl-4-sulfanylpentan-2-one ; descripteur buis, genêt) et le 3SH (3-sulfanylhexan-1-ol ; descripteur pamplemousse, fruit de la passion) sont révélés par la levure à partir de précurseurs non volatils et inodores (Howell et al., 2004;Peyrot des Gachons et al., 2002;Tominaga et al., 1998 Darriet et al., 1995;Fedrizzi et al., 2009;Peyrot des Gachons et al., 2002;Roland et al., 2011;Subileau et al., 2008). ...
Les levures non-Saccharomyces, naturellement présentes dans les moûts, peuvent impacter positivement ou négativement la qualité des vins. Depuis quelques années, l’utilisation de cultures mixtes comme starters, associant une souche de Saccharomyces cerevisiae et une souche d’une autre espèce est proposée aux œnologues. C’est le cas du couple S. cerevisiae/Torulaspora delbrueckii. L’étude des interactions entre la souche T. delbrueckii Zymaflore Alpha et S. cerevisiae Zymaflore X5, de la société Laffort, a été réalisée. Les fermentations alcooliques ont été effectuées dans un réacteur à double compartiment permettant la séparation physique des levures tout en conservant l’homogénéité du milieu de culture. Les résultats ont mis en évidence que la séparation impacte la croissance des deux souches suggérant l’existence d’interactions de type cell-cell contact entre ces deux souches. Si une grande majorité de praticiens utilise désormais les levures sélectionnées, certains ont fait le choix de favoriser les populations autochtones de levures S .cerevisiae et de levures non-Saccharomyces. L’incidence de deux facteurs de l’environnement a été étudié sur un mélange de cinq espèces de non-Saccharomyces (T. delbrueckii, Metschnikowia spp., Candida zemplinina, Hanseniaspora uvarum, Pichia kluyveri) et de deux souches de S. cerevisiae (une à phase de latence courte, une à phase de latence longue) en cultures pures et en mélange. L’inoculation de la souche de S. cerevisiae à phase de latence longue dans un moût saturé en CO2 permet de stimuler les levures non-Saccharomyces d’intérêt (T. delbrueckii/P. kluyveri) tout en inhibant les espèces indésirables (H. uvarum, C. zemplinina).
... conjugate (Cys-4MMP) and glutathione conjugate (GSH-4MMP; Fedrizzi, Pardon, Sefton, Elsey, & Jeffery, 2009;Roland, Vialaret, Razungles, Rigou, & Schneider, 2010). 3MHA cysteine or glutathione precursor has not been identified yet, and this thiol is formed by esterification of 3MH by the alcohol acetyltransferase ATF1 (Coetzee & du Toit, 2012;Dubourdieu, Tominaga, Masneuf, des Gachons, and Murat, 2006). ...
... Renault et al. (2016) described a synergistic interaction between T. delbrueckii and S. cerevisiae species which caused an increased production of 3SH related with the ability of T. delbrueckii to assimilate its glutathionylated precursor. The low amounts detected for some strains could be due to the fact that under fermentation conditions, S. cerevisiae strains are able to release about 10% of the thiol precursors available in grape (Coetzee & du Toit, 2012), probably because of a low enzyme affinity for complex cysteinylated substrates and to Nitrogen Catabolism Repression , affecting both the genes responsible for the precursor assimilation (Subileau et al., 2008b) and their later cleavage (Thibon et al., 2008). ...
Volatile thiols are not present in must but are synthesized and released by wine yeasts during alcoholic fermentation. In this study, autochthonous and commercial S. cerevisiae strains were characterized for the expression of the main genes involved in thiols metabolism and their production in wine. New primer sets were developed on the basis of the S288c genome to evaluate the expression of Cys3, Cys4, MET17 and IRC7 gene. Obtained data revealed the occurrence of some thiols e.g. 4‐mercapto‐4‐methylpentan‐2‐one (4‐MMP) and 3‐mercaptohexan‐1‐ol (3‐MH) in Pecorino white wine. All genes were upregulated but only for IRC7 was found a correlation with 4‐MMP release: strains with the highest production showed the highest transcription level. IRC7 gene could be proposed as target for the selection of S. cerevisiae strains to increase thiols content in wine.
... It is assumed that it depends on the reduction rate of quinone by SO 2 . Volatile thiol is the dominant aroma because of the low odor detection threshold (0.8-60 ng/L) (Coetzee et al., 2012). Loss of thiol occurs through either Cu-mediated oxi-dation or a reaction with quinone (Kreitman et al., 2016;Ugliano, 2013). ...
Non‐enzymatic oxidation is a primary factor affecting wine quality during bottling or aging. Although red and white wines exhibit distinct responses to oxidation over time, the fundamental mechanisms driving this transformation remain remarkably uniform. Non‐enzymatic oxidation of wine commences with the intricate interplay between polyphenols and oxygen, orchestrating a delicate redox dance with iron and copper. Notably, copper emerges as an accelerant in this process. To safeguard wine integrity, sulfur dioxide (SO2) is routinely introduced to counteract the pernicious effects of oxidation by neutralizing hydrogen peroxide and quinone. In this comprehensive review, the initial stages of non‐enzymatic wine oxidation are examined. The pivotal roles played by polyphenols, oxygen, iron, copper, and SO2 in this complex oxidative process are systematically explored. Additionally, the effect of quinone formation on wine characteristics and the intricate dynamics governing oxygen availability are elucidated. The potential synergistic or additive effects of iron and copper are probed, and the precise balance between SO2 and oxygen is scrutinized. This review summarizes the mechanisms involved in the initial stages of non‐enzymatic oxidation of wine and anticipates the potential for further research.
... It is well known in the winemaking industry that a high concentration of dissolved oxygen (DO) can lead to accelerated oxidation of wines, especially white wines [1]. The wine gains oxygen throughout the winemaking process wherever it comes into contact with the air being racking the wine between tanks, as well as the materials used for racking critical points that must be taken into account to avoid large additions of oxygen before bottling [2,3]. ...
Sparging is a technique to remove an excess of dissolved oxygen from the wine with inerting gases before bottling to avoid negative consequences for its chemical and sensory properties. However, its effectiveness on these properties has not been studied in depth. This work investigates the effectiveness of different inerting gases (N 2 , CO 2 , and argon) in removing dissolved oxygen in different volumes of a model wine. The efficacy of these gases was also studied in white and red wine, as was their effect on the physicochemical characteristics. Sparging with N 2 in the model wine gave the best results in terms of cost-benefits, and with CO 2 the worst. The scaling in tanks of different sizes allowed us to establish that the N 2 expenditure ranged between 0.09 L and 0.23 L of gas per liter of model wine, establishing an index (L gas /L wine) that can be very useful for wineries to remove the dissolved oxygen. Sparging treatments in white and red wine showed very similar results to the model wine. The effect on the chemical properties of the wines was, in some cases, different for white and red wine and for each gas used. The incorporation of oxygen and the subsequent sparging produced a significant loss of some volatile compounds of sensory interest and increased the content of others that have a negative sensory effect. In addition, it had a negative effect on the chromatic properties of red wines.
... Although the exact mechanisms by which yeast convert cysteinylated and glutathionylated precursors into the corresponding volatile thiols are still not fully understood, some consensus exists regarding these mechanisms. Previous studies have reported that the uptake of cysteine-3-mercaptohexan-1-ol (3MH) adduct precursors is structurally similar to Lcysteine and is induced by amino acid transport proteins; therefore, it is suggested that furfuryl-cysteine adducts, precursors of FFT, are also induced by amino acid transporters (133,134). Thus, L-cysteine reacts with furfural to produce furfuralcysteine conjugates (129), which are subsequently transported into the cell by amino acid permeases encoded by genes MUP1, Bap2, Bap3, Gnp1, and OPT1 (encoding Mup1p, branchedchain amino acid permease, amino acid transporter, glutamine permease, oligopeptide transporter, respectively) (134)(135)(136)(137)(138). The furfuryl-cysteine adduct is cleaved in vitro or after transport into the cell by the C-S lyase encoded by the genes CYS3 and STR3 to produce FFT, pyruvate, and ammonia (129). (2) L-cysteine is transferred into cells under the action of amino acid transporters and then produced as hydrogen sulfide under the guidance of α-and β-elimination reactions or cystathionine β-synthase and cystathionine γ-cleavage enzymes encoded by genes CYS4 and CYS3, respectively (139, 140). ...
Aroma is a critical component of the flavor and quality of beverages. Among the volatile chemicals responsible for fragrance perception, sulfur compounds are unique odorants due to their extremely low odor threshold. Although trace amounts of sulfur compounds can enhance the flavor profile of beverages, they can lead to off-odors. Sulfur compounds can be formed via Maillard reaction and microbial metabolism, imparting coffee aroma and altering the flavor of beverages. In order to increase the understanding of sulfur compounds in the field of food flavor, 2-furfurylthiol (FFT) was chosen as a representative to discuss the current status of their generation, sensory impact, enrichment, analytical methods, formation mechanisms, aroma deterioration, and aroma regulation. FFT is comprehensively reviewed, and the main beverages of interest are typically baijiu, beer, wine, and coffee. Challenges and recommendations for FFT are also discussed, including analytical methods and mechanisms of formation, interactions between FFT and other compounds, and the development of specific materials to extend the duration of aroma after release.
... The esterification of 3SH with acetic acid leads to the formation of 3SHA. (Coetzee and du Toit, 2012). Varietal thiols are present in grapes at very low levels and occur mainly as precursors in the glutathionylated or S-cysteinylated forms and dipeptidic derivatives and C 6 -compounds for 3SH only (Thibon et al., 2016;Peña-Gallego et al., 2012;Capone and Jeffery, 2011). ...
The levels of varietal thiols and the role these compounds play in Colombard wine have not been investigated in detail. This study assessed the levels of the varietal thiols 4-methyl-4-sulfanylpentan-2-one (4MSP), 3-sulfanylhexyl acetate (3SHA) and 3-sulfanylhexan-1-ol (3SH) and their sensory effects in 24 young South African Colombard wines. Levels of 3SHA and 3SH were, in general, in line with those previously reported in South African Chenin blanc and Sauvignon blanc wines. Levels of 4MSP were, in general, found at a narrower range than those reported for Sauvignon blanc wines. Twelve of these wines were also sensorially analysed by a panel of wine industry experts. Aroma descriptors, such as guava, passion fruit, sweat and tomato leaf, which have previously been linked to 3SH and 3SHA, were also found, especially in the wines containing higher levels of these two compounds. Good correlations between 3SHA and sweat and guava were found. This study contributes to the knowledge of varietal thiol levels and their role played in 24 Colombard white wines. It could also lead to wine producers adapting their winemaking g practices to increase levels of varietal thiols if the aroma characteristics linked to these compounds are sought after in this single cultivar wine.
... The berry fruit response was assessed in both single-and double-stressed vines with respect to a non-stressed control. The cultivar Sauvignon Blanc, whose quality profile is significantly affected by different types of stress [45][46][47], was chosen in this study for being one of the most widespread in the world, especially in temperate areas where the above-reported climate change scenario is already impacting viticulture, and because most of the research on stress was previously carried out mainly on red grape varieties. ...
Grapevine cultivation, such as the whole horticulture, is currently challenged by several factors, among which the extreme weather events occurring under the climate change scenario are the most relevant. Within this context, the present study aims at characterizing at the berry level the physiological response of Vitis vinifera cv. Sauvignon Blanc to sequential stresses simulated under a semi controlled environment: flooding at bud-break followed by multiple summer stress (drought plus heatwave) occurring at pre-vèraison. Transcriptomic and metabolomic assessments were performed through RNASeq and NMR, respectively. A comprehensive hormone profiling was also carried out. Results pointed out a different response to the heatwave in the two situations. Flooding caused a developmental advance, determining a different physiological background in the berry, thus affecting its response to the summer stress at both transcriptional levels, with the upregulation of genes involved in oxidative stress responses, and metabolic level, with the increase in osmoprotectants, such as proline and other amino acids. In conclusion, sequential stress, including a flooding event at bud-break followed by a summer heatwave, may impact phenological development and berry ripening, with possible consequences on berry and wine quality. A berry physiological model is presented that may support the development of sustainable vineyard management solutions to improve the water use efficiency and adaptation capacity of actual viticultural systems to future scenarios.
... To increase the instrumental response towards the compounds that mainly define the typicity of Chardonnay and Sauvignon Blanc wine odours, solid-phase micro-extraction (SPME) temperature, incubation time, extraction time, and fibre composition were optimised by applying a central composite experimental design [27,28]. The optimisation was designed on three quantitative factors (extraction temperature, incubation time, and extraction time) and one qualitative factor (fiber type). ...
Monovarietal wines produced in different wine-growing areas may have completely different sensory profiles. As a result, they may be suitable for sale in different regions, depending on local preferences. Better insight into the sensory and chemical profiles of these wines can be helpful in further optimizing commercial strategies and matching supply and demand, which is the main challenge for global wine traders. The training of dedicated sensory panels, together with the correlation of the evaluated attributes with chemical parameters, followed by validation of the obtained models, may yield an improved picture of the overall features associated with products from a specific region. Eighteen samples of international Chardonnay and eighteen samples of international Sauvignon Blanc wines were collected from nine world origins (Northern Italy, Southern Italy, Chile, Argentina, New Zealand, Australia, and South Africa). The overall quality judgement (OQJ) and the sensory attributes were evaluated by a panel trained with a MRATA (Modified Rate-All-That-Apply) method. Moreover, volatile compounds were analysed by HS-SPME-GC × GC-ToF/MS and the phenolic composition, including proanthocyanidins, was determined using HPLC-QqQ/MS. The processing of the data using different multivariate analysis methods, such as multiple factor analysis (MFA), was essential to gain insight into the quality of the samples. The profile of cyclic and non-cyclic oligomeric proanthocyanidins was found to be substantially dependent on the grape variety used in the wines (varietal markers), despite the country of origin of the wine influencing it to a limited extent. The results from the same samples analysed by a sensory panel from Germany and ours were qualitatively compared, highlighting the presence of potential factors inherent to the panels themselves that could influence the different judgments and quality classification of the wines. Consequently, the combination of sensory and chemical analysis, by means of the application of multivariate statistical methods presented in this study proves to be a powerful tool for a deeper and more comprehensive understanding of the quality of the wines under investigation. Overall quality was described as a combination of the sensory attributes, according to the perception process. The attributes were in turn described based on the chemical profiles, which were determined independently by analytical techniques. Eventually, this approach can be very useful not only for basic research on wine quality but also as a tool to aid business-related decision-making activities of wineries and wine traders and to create models that can aid the refinement of marketing strategies.
... Further to this, the metabolism and conversion of precursors during fermentation have been explored under a variety of conditions, enabling the identification of additional precursors, as well as key metabolic pathways [39,70,78,79]. These studies of thiol biogenesis and precursor consumption have been thoroughly reviewed recently, and extensive discussion of these studies is outside of the scope of this work [18,20,21,80,81]. ...
Volatile polyfunctional thiol compounds, particularly 3-sulfanylhexan-1-ol (3SH) and 3-sulfanylhexyl acetate (3SHA), are key odorants contributing to the aroma profile of many wine styles, generally imparting tropical grapefruit and passionfruit aromas. 3SH and 3SHA are present in negligible concentrations in the grape berry, juice, and must, suggesting that they are released from non-volatile precursors present in the grape. The exploration of the nature and biogenesis of these precursors to 3SH and 3SHA has proven important for the elucidation of polyfunctional thiol biogenesis during alcoholic fermentation. The development and validation of appropriate analytical techniques for the analysis of 3SH precursors in enological matrices have been extensive, and this review explores the analysis and discovery of these precursor compounds. The development of analytical methods to analyze 3SH precursors, from the selection of the analytical instrument, sample preparation, and methods for standardization, will first be discussed, before highlighting how these techniques have been used in the elucidation of the biogenesis of 3SH and 3SHA in grape wines. Lastly, the future of thiol precursor analysis will be considered, with the development of new methods that greatly reduce the sample preparation time and enable multiple precursors, and the thiols themselves, to be quantitated using a single method.
... In Croatia, it is most widespread in the continental viticultural regions. This cultivar is highly valued for its distinctive aroma, described as green (vegetal, grassy, green pepper, herbaceous) and tropical (grapefruit and passion fruit) (Coetzee and du Toit, 2012). Sauvignon Blanc wines are high in proteins and they can exhibit protein haze if not clarified before bottling (Vela et al. 2017). ...
Bentonite fining is commonly used by the wine industry as a clarifying technique to remove proteins that are a potential source of haze in wines. Large amounts of added bentonite can decrease the sensory properties of wines. The aim of this research was to study the influence of the standard wine clarification process by two different types of bentonite fining agents on the basic chemical composition and aromatic profile of Sauvignon Blanc by gas chromatography-mass spectrometry (GC-MS). The general characteristic of Sauvignon Blanc wines showed no differences among treated wines independently of the type (sodium bentonite Bentogran® and sodium-activated bentonite Majorbenton C®) and the dose of bentonite. The results showed that type of bentonite regardless of the dose applied, affected the monoterpenes concentration.
... It is well known that a high concentration of dissolved oxygen can lead to oxidation, especially in white wines (Coetzee and du Toit 2012). As these effects can be undesirable, winemakers can seek to remove dissolved O 2 from white wines using inert gas sparging techniques. ...
Sparging with an inert gas is often used in the wine industry to lower the dissolved oxygen concentration in wine. It is not well known, however, if this practice affects the composition of wine, and as well as the physio‐chemical and operating factors affecting the efficacy of sparging. The main aims of this study were to assess the effect of sparging on white wine composition and to elucidate winemaking related factors affecting its efficacy. Chenin Blanc and Sauvignon Blanc white wines were exposed to several sparging regimes to evaluate the effect of gas flow rate, wine temperature, gas composition, bubble size, repeated sparging and extended sparging on sparging efficacy and wine composition. Bubble size and wine temperature were the two main factors that influenced sparging efficacy the most. Sparging with nitrogen gas does not appear to influence the chemical composition of the wine to a large extent, except in the case of dissolved CO2 concentration; however, sensory studies on its effects are required. Sparging appears to be a safe practice for wine producers to lower dissolved oxygen concentration in wine if lost dissolved CO2 can be replenished.
... When present, they contribute to the vegetal (e.g., bell pepper, peas, leafy), earthy, nutty, and/or moldy aroma of a wine [3]. MPs are key aromatic compounds in some grape cultivars, including Sauvignon blanc [4,5], Cabernet Sauvignon [6], Cabernet franc [7], Merlot [8], and Carménère [9], where low levels contribute to the varietal character of these wines. However, MPs are generally undesirable and are considered fault compounds when they are present at high levels in wines [10]. ...
Alkyl-methoxypyrazines are an important class of odor-active molecules that contribute green, ‘unripe’ characters to wine and are considered undesirable in most wine styles. They are naturally occurring grape metabolites in many cultivars, but can also be derived from some Coccinel-lidae species when these ‘ladybugs’ are inadvertently introduced into the must during harvesting operations. The projected impacts of climate change are discussed, and we conclude that these include an altered alkyl-methoxypyrazine composition in grapes and wines in many wine regions. Thus, a careful consideration of how to manage them in both the vineyard and winery is important and timely. This review brings together the relevant literatures on viticultural and oenological inter-ventions aimed at mitigating alkyl-methoxypyrazine loads, and makes recommendations on their management with an aim to maintaining wine quality under a changing and challenging climate.
... As shown in Table 1, the most important volatile thiols are 4-mercapto-4-methylpentan-2-one (4MMP), 4-mercapto-4-methylpentan-2-ol (4MMPOH), 3-mercaptohexan-1-ol (3MH), and 3-mercapto-hexylacetate (3MHA) [58]. The free thiols and their acetate are practically absent from musts, while they are liberated by the yeasts during fermentation from cysteine conjugate and glutathione conjugate precursors. ...
Climate change with rising temperatures and the unpredictability of rainy events during ripening leads to tough challenges for the winemakers in preserving the quality of white grape varieties. Grape quality is a complex concept that mainly refers to berry chemical composition, including secondary metabolites such as aroma compounds that in white berries play a key role in the identity of the wine. Terpenes, thiols, C13-norisoprenoids, methoxypyrazines, and nonterpenic alcohols are the most important aroma compounds in white grapes and several of them can be found as free volatiles or bound as glycoconjugate molecules. Agronomic practices in vineyards, such as biostimulant application, irrigation, defoliation, training systems, foliar fertilization, and bunch thinning, can have a positive effect on their concentration. This review aims to highlight the aromatic characteristics of the most utilized white grape cultivars and focus on agronomic techniques in the vineyard to enhance, implement, and intensify their aromatic characteristics. The purpose of this review paper is therefore to investigate the state of the art regarding the exaltation of aroma in white grapes in the scientific literature through sustainable agronomic techniques, but further future investigations are considered necessary given the uncertainty concerning some mechanisms of biosynthesis and their correlation with such agronomic practices.
... Under the MLF conditions in our study, 3MH concentrations increased significantly in selected commercial O. oeni strains and during spontaneous MLF. During AF only a small percentage of thiol precursors are released, so that after the end of AF wine represents an enormous pool of aromatic potential that could be explored (Coetzee and du Toit, 2012). An increase in 3MH concentration after MLF in red wine has already been observed for some commercial O. oeni strains (Antalick et al., 2012). ...
Welschriesling is a variety common to Central and Eastern European wine-producing countries; however, its aromatic composition remains poorly understood. Our study aims to determine the volatile profile of Welschriesling by analysing varietal thiols, esters, higher alcohols and monoterpene alcohols in commercial wines. In addition, the selection of commercial yeast starters and lactic acid bacteria (LAB) was used to modulate Welschriesling wine volatile composition. Both the selection of yeast and LAB had a significant impact on the compositional parameters of the wines. Yeast starter Uvaferm 228 (UVF228) was the most effective in terms of 3-mercaptohexan-1-ol (3MH) and 3-mercaptohexyl acetate (3MHA) production. For the ethyl esters of fatty acids (EEFAs), higher alcohol acetates (HAAs) and higher alcohols (HAs), no common inter-group behaviour could be observed based on yeast selection, however, as a group, EEFAs and HAs were highest in wines fermented with UVF228.
Malolactic fermentation (MLF) significantly influenced varietal thiols, irrespective of the LAB strain used. Concentrations of 3MH significantly increased with MLF, 4-mercapto-4-methyl-pentan-2-one (4MMP) concentrations decreased, while 3MHA concentrations remained unaltered. This study showed the specific influence of yeast and LAB strain on selected volatile compounds. MLF appeared to be a promising tool to boost the presence of 3MH in wines, however, the results need further confirmation across a range of fermentation conditions and strain selections.
... Fruity notes, passion fruit and grapefruit aroma are the most common descriptors of Sauvignon Blanc; these aromatic notes derive from the biogenesis of volatile thiols (Tominaga et al., 1998a). The most important volatile thiols are 4-mercapto-4-methylpentan-2-one (4MMP), responsible of passionfruit and boxtree aromas, 4-mercapto-4-methylpentan-2-ol (4MMPOH) responsible of citrus zest aromas, 3-mercaptohexan-1-ol (3MH) and 3-mercapto-hexylacetate (3MHA) which produce gooseberrie and grapefruit aromas respectively (Coetzee and du Toit, 2012). ...
Climate change has an important impact on the phenological phases of the grapevine. The consequences are directly reflected in quantitative and qualitative characteristics of the grapes. In fact, there is a decrease in the skin-to-pulp ratio (therefore a decrease in production with an excess of alcohol) and a consequent reduction in the aromatic potential of white grapes (lowering of the quality of musts). Volatile tioles are important aromatic compounds found in various foods and drinks; in particular they contribute to forming the aroma of some types of white wines as they are characterized by extremely low perception thresholds. This work aimed to evaluate the effects of water stress on ecophysiology, technological maturity and on the thiol precursors of Vitis vinifera L. cv. Sauvignon Blanc vineyards in the Tuscan region (Italy) during two seasons. To this end, three treatments were established: WW (well watered), MW (medium watered), and WS (water stress with no irrigation). During the seasons, measurements were made of single-leaf gas exchange, pre-dawn and leaf midday water potential, leaf temperature, chlorophyll fluorescence, as well chlorophyll content. In addition, the parameters of plant yield, technological maturity (° Brix, acidity, pH and berries weight) and the precursors of 3-Mercaptohexanol (3MH) were analyzed: 3-S-cysteinylhexan-1-ol (Cys-3MH) and 3-S-glutathionylhexan-1-ol (GSH-3MH). Well watered treatments (WW) showed less negative water potential, a higher rate of photosynthesis, of stomatal conductance, a lower leaf temperature (°C). Furthermore, WW showed higher levels of precursors accumulation (Cys-3MH and GSH-3MH) than the other treatments during two seasons. Technological analyses (° Brix and acidity) showed significant differences between WW and WS treatments. The lower berry weight was found in the WS treatment. Finally as a result of climate change, precision irrigation has proved to be a good technique to rebalance the gap between technological and aromatic maturity in Sauvignon Blanc grapes.
... The esterification reaction between 3MH and acetic acid is catalysed by the enzyme ester forming alcohol acetyltransferase . The precursors of volatile thiols and the volatile thiols levels are influenced by the following viticultural and oenological factors: ripening, water deficit, nitrogen level, Botrytis cinerea, machine harvest, SO 2 addition, oxygen exposure, skin contact, higher maceration temperature, pressing, fermentation, yeast strain, fermentation temperature, oxidation, copper addition and bottle aging (Coetzee and Du Toit, 2011). Fermentation aroma has an impact on Riesling wines in general, but has higher impact on young Riesling wines. ...
The influence of two yeast strains and the addition of copper sulphate on the aroma of Riesling wines was monitored. Two commercially available yeast strains, Zymaflore VL3 and X-Pure, were applied. General composition, volatile thiols, norisoprenoids, free terpenes, aroma fermentation, sulphur compounds and copper content were determined, and the sensory attributes were assessed by 22 tasters in a balanced incomplete block design (BIBD). The VL3 yeast produced a higher concentration of thiols than the X-Pure yeast. Wines treated with copper sulphate showed a higher concentration of 3MH than the wines produced without copper sulphate addition for both yeast strains. Yeast strain and copper sulphate addition both influenced the amount of β-damascenone in Riesling wines significantly, but they showed no significant influence on the level of terpenes. Five out of eight rated sensory attributes showed significant differences. Yeast strain and copper sulphate addition were decisive factors for the sensory profile of experimental wines.
... Fruity notes, passion fruit and grapefruit aroma are the most common descriptors of Sauvignon Blanc; these aromatic notes derive from the biogenesis of volatile thiols (Tominaga et al., 1998a). The most important volatile thiols are 4-mercapto-4-methylpentan-2-one (4MMP), responsible of passionfruit and boxtree aromas, 4-mercapto-4-methylpentan-2-ol (4MMPOH) responsible of citrus zest aromas, 3-mercaptohexan-1-ol (3MH) and 3-mercapto-hexylacetate (3MHA) which produce gooseberrie and grapefruit aromas respectively (Coetzee and du Toit, 2012). ...
... It limits the manipulation of the sample and avoids the use of solvent and its parameters can be tailored to detect a wide variety of analytes in wine (Azzi-Achkouty et al., 2017;Perestrelo et al., 2014). Moreover, the use of derivatizing agents has proved to enhance the detection of specific compounds such as carbonyls (Panighel and Flamini, 2014;Zapata et al., 2010), phenols (Pizarro et al., 2007) and thiols (Coetzee and du Toit, 2012;Rodr ıguez-Bencomo et al., 2009). Progress in authentication and traceability of grapes and wines by using data mining and analysis with chemometric approaches has been the subject of a recent review (Versari et al., 2014). ...
Purpose
Methods to assess the authenticity and traceability of wines have been extensively studied as enhancers of food quality, allowing producers to obtain market recognition and premium prices. Among analytical techniques, the volatilome profile attained by gas chromatography coupled with mass spectrometry is acquiring more and more attention by the scientific community, together with the use of chemometrics
Design/methodology/approach
The volatilome profile of three varieties of blanc wines from the Collio area (namely Ribolla Gialla, Malvasia and Friulano) between Italy and Slovenia, was determined by head space-solid phase micro extraction-gas chromatography-mass spectrometry, enhancing the carbonyl compounds identification with O-(2, 3, 4, 5, 6-pentafluorobenzyl)-hydroxylamine with the aim of identifying the autochthonous Friulano variety.
Findings
A two-step chemometric approach based on an unsupervised technique (PCA) followed by a supervised one (PLS-DA) allowed to identify possible markers for discriminating the Friulano Collio variety from the others, in particular two chemical classes were identified by PCA (ketones and long chain esters). PLS-DA showed 87% accuracy in classification. A correct classification (i.e. non-Friulano Collio) of a group of wines obtained from the same grape variety but produced in an extra-Collio area was obtained as well. The results confirmed the benefits of using a derivatization step prior to volatile organic compounds analysis.
Research limitations/implications
Among methods to assess the authenticity and traceability of wines, volatilome profile of wines determined by head space-solid phase micro extraction-gas chromatography-mass spectrometry, enhanced by the carbonyl compound identifications with O-(2, 3, 4, 5, 6-pentafluorobenzyl)-hydroxylamine, may have a key role in conjunction with chemometrics and, in particular with principal component analysis and partial least square discriminant analysis.
Practical implications
Among methods to assess the authenticity and traceability of Friulano wine, volatilome profile of wines determined by head space-solid phase micro extraction-gas chromatography-mass spectrometry, enhanced by the carbonyl compound identifications with O-(2, 3, 4, 5, 6-Pentafluorobenzyl)Hydroxylamine hydrochloride, may have a key role in conjunction with chemometrics.
Originality/value
Few works investigated both wine traceability with a volatilome enhancer and chemometrics of the Friulano wine variety obtaining such an improvement in this wine variety discrimination.
... No significant difference in this attribute was found for the SAB wines. In SEM and SAB wines, tropical aroma of pineapple and passionfruit notes may relate to specific esters (isoamyl acetate, ethyl hexanoate and 2-phenylethyl acetate), terpenes (nerol and geraniol) or from the volatile thiol 3-mercaptohexyl acetate (3MHA) (Coetzee & Du Toit, 2012). Tropical aroma was more pronounced in GSP treated wines than in bentonite controls (Fig. 2) and may relate to reductions of isoamyl acetate, ethyl hexanoate and 2phenylethyl acetate during bentonite fining (Lambri, Dordoni, Silva & De Faveri, 2010). ...
Grape pathogenesis-related (PR) proteins in white wine can induce haze and hinder the sale of the product. Bentonite is used to remove proteins and "heat-stabilise" wine however it is non-selective and can reduce wine quality. Grape seed powder (GSP) has previously been shown to remove PR proteins and reduce haze formation on a lab scale, however the effect on wine sensory properties was unknown and crucial to the evaluation of GSP as a bentonite alternative. Semillon (SEM) and Sauvignon Blanc (SAB) juices (20L in triplicate) were treated with GSP at two doses, Low (7.5 g/L) and High (15 g/L), prior to fermentation. GSP treatment reduced the concentration of wine PR proteins by up to 57% and 37% for SEM and SAB, respectively, and reduced the amount of haze formed in a heat test by up to 75% and 80%, respectively. Sensory analysis conducted by a trained panel showed that for both wine types the high GSP treatments were rated deeper in colour and higher in bitterness than the bentonite controls, with the low GSP treatment having a similar but less pronounced effect on these attributes. The GSP-treated SAB wine showed greater tropical fruit aroma, and pungency, compared to the bentonite control. Use of GSP can reduce the amount of bentonite needed to stabilize wines and may provide a sustainable and effective alternative to bentonite, notably for textural white wine styles.
... To our knowledge, several compounds originating from the grape berry directly contribute to the aroma characteristics, such as the 'green pepper' aroma from 3-alkyl-2methoxypyrazines (Allen et al., 1994), the 'floral' bouquet from monoterpenoids (Mateo and Jiménez, 2000), the 'passion fruit' aroma from volatile thiols (Coetzee and du Toit, 2012), and the 'peppery' and 'spicy' aroma from rotundone (Wood et al., 2008). Moreover, Dennis et al. (2012) reported that C6 compounds, octanol, and benzyl alcohol derived from the grape berry were precursors to hexyl acetate, octyl acetate, and benzyl acetate, respectively, in wine. ...
Berries of six Vitis davidii Foex (spine grape) cultivars (‘Baiputao’, ‘Gaoshan 1’, ‘Gaoshan 2’, ‘Seputao’, ‘Miputao’, and ‘Tianputao’) were harvested from a commercial vineyard in Hunan Province in China. Free and bound volatile compounds and fatty acids were analyzed by GC–MS, and amino acids were analyzed by HPLC. ‘Tianputao’ and ‘Miputao’ were characterized by relatively higher concentrations of aromatic amino acids and lower concentrations of branched-chain amino acids. The major free volatile compounds of spine grapes were hexanal, (E)-2-hexenal, 1-hexanol, (E)-2-hexenol, (E)-β-damascenone, and benzeneacetaldehyde. The major glycosidically bound volatile compounds identified were 1-hexanol, menthol, nerol, 1-butanol, 3-methyl-3-butenol, benzenemethanol, β-phenylethanol, eugenol, and guaiacol. (E)-β-damascenone, benzeneacetaldehyde, guaiacol, and eugenol had odor activity values (OAVs) > 1 in all cultivar grapes. Partial least squares discriminant analysis (PLS-DA) revealed ‘Tianputao’ to be distinct from the other cultivars due to its relatively higher concentrations of major terpenoids, norisoprenoids, higher alcohols, and aromatic amino acids.
... Recently, more and more researchers used GSH for fruit wine production or storage. GSH played an important role in preventing browning and flavor loss caused by oxidation of white wine (Coetzee and Toit 2012;Kritzinger, Bauer, and Du Toit 2013;Rodr ıguez-Bencomo et al. 2014). But only reduced GSH has the function, and GSH is easily oxidized to GSSG. ...
Grape wine is the most widely consumed fruit wine in the world. With the increasing diversification of consumers’ needs, the variety of fruit wines in the market is becoming more and more abundant. Whether it is the production of grape wine or other fruit wines these processes are inseparable from the participation of enzymes. The quality of these wines is closely related to the application of enzymes in the winemaking process. Enzymes are involved in pretreatment, fermentation, filtration, flavoring, aging and storage of fruit wines. This review systematically illustrated the role of pectinase, β-glucanase, β-glucosidase, glucose oxidase, lysozyme, protease, tannase and urease in the production of wines and their current production status and also provided a theoretical basis for better application of various enzymes in the production of various fruit wines. This knowledge could be great significance to improve the quality of fruit wines and reduce the production costs in the fruit wine industry.
... Grape and subsequently must nitrogen composition play a key role on final wine quality since yeast growth, fermentation kinetics and flavor metabolism are considerably affected by the initial nitrogen status of the must (Bell and Henschke, 2005;Garde-Cerdán and Ancín-Azpilicueta, 2008;Coetzee and du Toit, 2012;Gutiérrez-Gamboa et al., 2018c). A low nitrogen content present in the must may cause stuck or sluggish fermentations, which leads to economical and technical problems in wine production in the winery (Bisson and Butzke, 2000). ...
There is little available information about the effects of seaweed biostimulation to grapevines on grape juice and wine nitrogen content. This trial aimed to study the effects of the biostimulation through an Ascophyllum no-dosum fertilizer to Tempranillo grapevines at low (Ld: 0.25 % v v −1) and high (Hd: 0.50 % v v −1) dosages on must and wine amino acids and ammonium during two seasons. The content of these compounds in musts and wines were measured by UHPLC. The results showed that precipitations could have affected berry size and enological parameters of musts and wines. In the driest season (2017), Ld treatment increased the concentration of several amino acids in musts such as His, Arg, Ala, Gaba, Pro, Val, Met, Ile, Trp, Orn, Lys, and total amino acids. In the rainiest season (2018), the Hd treatment was the most effective, increasing the content of His, Cit + Thr, and Trp. Generally, a high yeast assimilable nitrogen (> 279.4 mg N L-1) content in the must allowed to reach a high concentration of amino acids in wines. Therefore, seaweed foliar application to grapevines allowed to improve amino acid content in musts in both seasons and its effectiveness depended of climate conditions of the season and the dosage applied.
The diversity of alcohol beverage microorganisms is of great significance for improving the brewing process and the quality of alcohol beverage products. During the process of making alcoholic beverages, a group of microorganisms, represented by yeast and lactic acid bacteria, conducts fermentation. These microorganisms have complex synergistic or competitive relationships, and the participation of different microorganisms has a major impact on the fermentation process and the flavor and aroma of the product. Strain selection is one of the key steps. Utilizing scientific breeding technology, the relationship between strains can be managed, the composition of the alcoholic beverage microbial community can be improved, and the quality and flavor of the alcoholic beverage products can be increased. Currently, research on the microbial diversity of alcohol beverages has received extensive attention. However, the selection technology for dominant bacteria in alcohol beverages has not yet been systematically summarized. To breed better-quality alcohol beverage strains and improve the quality and characteristics of wine, this paper introduces the microbial diversity characteristics of the world’s three major brewing alcohols: beer, wine, and yellow wine, as well as the breeding technologies of related strains. The application of culture selection technology in the study of microbial diversity of brewed wine was reviewed and analyzed. The strain selection technology and alcohol beverage process should be combined to explore the potential application of a diverse array of alcohol beverage strains, thereby boosting the quality and flavor of the alcohol beverage and driving the sustainable development of the alcoholic beverage industry.
A new method, based on the combination of two sorptive extraction methods, namely stir bar sorptive extraction (SBSE) and solvent-assisted stir bar sorptive extraction (SA-SBSE), was developed for the quantitative determination of ultra-trace levels of polyfunctional thiols in white wine. Extraction of 4-methyl-4-sulfanyl-pentan-2-one (4-MSP), 3-sulfanylhexan-1-ol (3-SH) and 2-furylmethanethiol (2-FMT) is performed by SA-SBSE combined with in-situ derivatization using ethylpropiolate (ETP), while 3-sulfanylhexyl acetate (3-SHA) is simultaneously extracted in parallel using SBSE, without derivatization. Analysis is performed by thermal desorption in combination with GC-MS/MS operated in selected reaction monitoring (SRM) mode. All four target solutes could be detected in a single GC-MS/MS run at levels below the odor detection threshold (ODT) of the solutes (LODs: 0.20 ng/L for 4-MSP, 2.8 ng/L for 3-SH, 0.27 ng/L for 3-SHA and 0.11 ng/L for 2-FMT). The method could be successfully applied to a set of white wine samples, showing significant differences in polyfunctional thiol concentrations between samples.
A relevant trend in winemaking is to reduce the use of chemical compounds in both the vineyard and winery. In organic productions, synthetic chemical fertilizers and pesticides must be avoided, aiming to achieve the production of a “safer wine”. Also, in line with consumer preferences and due to the effects of global climate change, new trends have emerged in wine fermentation and wine technology, namely new genetic engineering methods, such as CRISPR/Cas9, described as efficient, versatile, cheap, easy-to-use, and able to target multiple sites.
Consumers are also looking for wines with less ethanol and fruitier aromas, but with a good balance in terms of acidity and mouthfeel. An appropriate acidity, pleasant to the palate is more difficult to achieve in wines that have high acidity. Non-conventional yeasts, in the past considered spoilage yeasts, now can be used to enhance the aroma profile of wine or to modulate wine composition, namely wine acidity, reinforcing the role of non-Saccharomyces as selected strains for controlling fermentations mostly in co-fermentation with Saccharomyces cerevisiae.
The effects of ascorbic acid (VC), reduced glutathione (GSH), sulfur dioxide (SO2), chitosan and ethylenediaminetetraacetic acid disodium (EDTA‐2Na) on the color parameters of Dangshan pear wine during storage were investigated. The different addition amounts of VC and EDTA‐2Na increased the browning degree of pear wine, and chitosan had a weak inhibitory effect on the browning of pear wine. The addition of 0.01%, 0.05% and 0.10% GSH reduced the browning degree of pear wine by 8.80%, 13.82%, and 5.02%, respectively; 0.05% GSH decreased the color saturation and increased the brightness during the storage of pear wine. Adding 0.05% and 0.10% SO2 reduced the browning degree of pear wine by 14.73% and 21.05%, respectively, the inhibitory effect for browning was significant, 0.10% SO2 reduced the brightness of pear wine during storage. This result showed that GSH and SO2 were the most effective candidate inhibitors for Dangshan pear wine browning.
Climate change with rising temperatures and the unpredictability of rainy events during ripening leads to tough challenges for the winemakers in preserving the quality of white grape varieties. Grape quality is a complex concept that mainly refers to berry chemical composition, including secondary metabolites such as aroma compounds that in white berries play a key role in the identity of the wine. Terpenes, thiols, C13-norisoprenoids, methoxypyrazines, and nonterpenic alcohols are the most important aroma compounds in white grapes and several of them can be found as free volatiles or bound as glycoconjugate molecules. Agronomic practices in vineyards, such as biostimulant application, irrigation, defoliation, training systems, foliar fertilization, and bunch thinning, can have a positive effect on their concentration. This review aims to highlight the aromatic characteristics of the most utilized white grape cultivars and focus on agronomic techniques in the vineyard to enhance, implement, and intensify their aromatic characteristics. The purpose of this review paper is therefore to investigate the state of the art regarding the exaltation of aroma in white grapes in the scientific literature through sustainable agronomic techniques, but further future investigations are considered necessary given the uncertainty concerning some mechanisms of biosynthesis and their correlation with such agronomic practices.
Sauvignon Blanc represents an important grape variety. The wine made from this variety is known to have a wide range of aroma profiles from nettles to tropical fruits. Beside the raw material quality (grapes), the quality of wines can be fundamentally influenced by the technological conditions applied in the wine making process. Yeast and other microorganisms play a key role in the formation of metabolites during alcoholic fermentation. In this study, the effects of autochthonous or selected wine yeasts ( Saccharomyces cerevisiae ) and fermentation temperatures (15 °C and 19 °C) were tested on major monoterpenes contents of wines during the period 2016–2017. The obtained values show that the highest contents of linalool (24.36 μg L ⁻¹ ) and hotrienol (11.84 μg L ⁻¹ ) were determined in wine samples produced with active (selected) wine yeast at lower temperature. Sensory evaluation results indicated that monoterpenes can have a positive effect on the overall sensory quality of Sauvignon Blanc wines, despite the fact that their determined concentrations in the evaluated samples were not higher than their threshold values.
Aroma profiles and aroma-active compounds of “Yulu” peach from Fenghua (the peach known for the best flavor and quality in China) were investigated by headspace solid-phase microextraction (HS-SPME), solvent-assisted flavor evaporation (SAFE), gas chromatography-olfactometry (GC-O), gas chromatography-mass spectrometry (GC-MS), and flame photometric detection (FPD). The combination of these methods improved the analysis and identification of aroma substances compared to the combination of a single aroma extraction method and GC-MS. A total of 85 aroma-active compounds, including 10 sulfur compounds were detected. Methional, methyl 3-(methylthio)propionate, methionol, and benzothiazole were first detected in peaches. These aroma compounds cannot only supplement the database of aroma substances of peaches, but also provide data support for traceability of the origins of “Yulu” peaches. In addition, the odor activity value (OAV) was used to identify the contributions of the most important compounds. The results indicated that hexanal, 3-methylbutanal, (E)-2-hexen-1-ol, 3-mercaptohexyl acetate, (E,E)-2,4-decadienal, 2-methylpropanal, γ-decalactone, 2-methylbutanal, theaspirane, and δ-decalactone were the key aroma-active compounds. The key characteristic aroma components were further ascertained by aroma reconstitution and omission experiments, which showed that the fruity, floral, sulfur, and sour notes could be well simulated. Finally, the perceptual interactions between different sulfur compounds and fruity recombination (FR) were explored. 3-mercaptohexanol and 4-methyl-4-mercaptopentan-2-one could significantly decrease the threshold of FR. The possible reason was that these two sulfur compounds had synergistic effects with the aroma compounds in FR, with the U model confirming the results of these synergistic effects. The perceptual interactions provide a basis for the regulation of characteristic fruity aroma of peach products.
A wine fault or flaw will be detected during a structured tasting process by a trained and experienced taster. Depending upon the fault in question, it may be revealed when examining a wine's appearance, nose, palate, or a combination of these. Although individual faults have defined detection thresholds, their perception may be dependent upon the relationship between numerous components of the wine matrix. Some compounds will always constitute a wine fault, if they are detectable. Others may be desirable in some types of wine but be totally unacceptable in others. There are also structural components of wine that must be in balance, otherwise a wine may be regarded as flawed.
Background and Aims
The presence of matter other than grapes (MOG) is common in the winemaking process when sorting equipment is not utilised. Experimental wines were made to examine the effect of MOG on the sensory profile and chemical composition of wine.
Methods and Results
A Shiraz wine made without MOG was compared to fermentations with grape leaves, grape stalks (rachis) and peduncles (the stalk connecting the bunch to the vine) added at amounts at or slightly above those found in a commercial harvest bin. Fifty‐one volatile aroma compounds were quantified in the wines, and sensory descriptive analysis was applied. The wine made with leaves added was rated by the sensory panel similar to the Control and was significantly higher only in positive aromas such as ‘confectionery’ and ‘red fruit’ likely due to a higher concentration of hexanol and (Z)‐3‐hexen‐1‐ol. The addition of peduncles slightly enhanced ‘green’ aroma and flavour. The rachis treatment was high in ‘green capsicum/green stalks’ attributes, as well as astringency, and was high in methoxypyrazines.
Conclusions
The inclusion of different types of MOG during fermentation can alter the sensory profile and chemical composition of Shiraz wines in varying ways, including extraction of methoxypyrazines from the rachis, resulting in notable ‘green’ attributes.
Significance of the Study
The inclusion of MOG is unavoidable in common winemaking practices, especially with the use of mechanical harvesting. Determining the influence of MOG on the volatile composition of the finished wine is an important step in manipulating wine style.
The analytical scope of static headspace-gas chromatography-ion mobility spectrometry (SHS-GC-IMS) was applied to wine aroma analysis for the first time. The method parameters were first fine-tuned to achieve optimal analytical results, before the method stability was demonstrated, in terms of repeatability and reproducibility. Succinct qualitative identification of compounds was also realized, with the identification of several volatiles that have seldom been described previously in Sauvignon Blanc wine, such as methyl acetate, ethyl formate, and amyl acetate. Using the SHS-GC-IMS data in an untargeted approach, computer modeling of large datasets was applied to link aroma chemistry via prediction models to wine sensory quality gradings. Six machine learning models were compared, and artificial neural network (ANN) returned the most promising performance with a prediction accuracy of 95.4%. Despite its inherent complexity, the ANN model offered intriguing insights on the influential volatiles that correlated well with higher and lower sensory gradings. These findings could, in the future, guide winemakers in establishing wine quality, particularly during blending operations prior to bottling.
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.
Monoterpenes are important aroma components in grapes and wines. We analyzed the free and bound monoterpene profiles and the transcript levels of terpenoid biosynthesis genes in Vitis Vinifera cvs. Muscat Hamburg, Riesling, and Sauvignon Blanc grapes at five ripening stages. Principal component analyses revealed that the three cultivars had different free monoterpene profiles at harvest and the early stage of ripening. In all cultivars, the total bound monoterpene contents were higher than the free monoterpene contents during grape ripening. The changes in monoterpene profiles in different grape varieties were correlated with the transcript levels of some VviTPS and VviGT genes. In Riesling, the VviGT14 and VviUGT88A1L1 transcript levels were related to geraniol glucoside accumulation. In Muscat Hamburg, the VviPNLGl1, VviPNLGl2, and VviPNLGl4 transcript levels were related to linalool accumulation. Understanding the dynamic changes in monoterpene accumulation and biosynthesis will allow winemakers to devise strategies to improve grape and wine aromas.
Sulfur dioxide (SO2) is the most common additive used in winemaking for many years. This compound is important for wine producers and consumers due to its antiseptic and antioxidant properties. However, excessive sulfites caused some symptoms such as a headache, nausea, stomach irritation and respiratory distress in asthmatic patients. Additionally, excessive SO2 in winemaking process leads to organoleptic changes of final product. For these reasons, the maximum SO2 concentrations allowed in wines were gradually reduced. In the wine industry it is essential to reduce or even eliminate SO2 especially in the production of organic wines. These obstacles lead to requirements of new healthier and safety strategies for reduction of SO2. Up to know have been discussed the priorities of SO2 used in wine making. Recently some authors evaluated studies with chemical and non-thermal alternatives of SO2. Some other authors reviewed the side effects of SO2 used in wines, but none of them have comprised the effects of new techniques in grape, must, wine and pomace. This review discussed effects of different alternatives (thermal, non-thermal, chemical and natural additives) techniques demonstrated in grape, must, wine and pomace as possible alternative to SO2 in comprehensive manner. The antioxidant, antimicrobial and sensory properties of tannin, oak and vine shoot extracts are also discussed as new alternatives of SO2. The studies demonstrated that SO2 could be lowered and even changed by using the development of new methods.
The most mysterious aspect of wine is the endless variety of flavours that stem from a complex, completely non-linear system of interactions among many hundreds of compounds. In its widest sense, wine flavour refers to the overall impression of both aroma and taste components. Aroma is usually associated with odorous, volatile compounds; the bouquet of wine refers to the more complex flavour compounds which evolve as a result of fermentation, elevage and ageing. With the exception of terpenes in the aromatic grape varieties and alkoxypyrazines in the herbaceous cultivars, perceived flavour is the result of absolute amounts and specific ratios of many of these interactive compounds, rather than being attributable to a single "impact" compound. Without underestimating the complexity of these interactive effects or negating the definitive role played by the accumulated secondary grape metabolites in the varietal character of wine, this review will focus mainly on the contribution of yeast fermentation to the sensorial quality of the final product. Yeast and fermentation conditions are claimed to be the most important factors influencing the flavours in wine. Both spontaneous and inoculated wine fermentations are affected by the diversity of yeasts associated with the vineyard and winery. During the primary alcoholic fermentation of sugar, the wine yeast, Saccharomyces cerevisiae, together with other indigenous non-Saccharomyces species, produce ethanol, carbon dioxide and a number of by-products. Of these yeast-derived metabolites, the alcohols, acetates and C4-C8 1tfatty acid ethyl esters are found in the highest concentration in wine. While the volatile metabolites contribute tothe fermentation bouquet ubiquitous to all young wines, the production levels of these by-products are variable and yeast strain specific. Therefore, this article also highlights the importance of untapping the hidden wealth of indigenous yeast species present on grapes, and the selection and genetic development of yeast starter culture strains with improved flavour profiles. In the future, some winemakers may prefer to use mixtures of indigenous yeast species and tailored S. cerevisiae strains as starter cultures to reflect the biodiversity and stylistic distinctiveness of a given region. This will help winemakers to fullfil the consumer's demand for individual wines with intact local character and to ensure the survival of wine's most enthralling aspect - its endless variety.
The study focused on the production of Sauvignon blanc wines from grapes grown in sub-optimal climatic conditions. Grape temperatures of l0°C and 25°C at harvest, and fermentation with different Saccharomyces cerevisiae yeast strains, i.e. VIN 13, VIN 7, NT 116 and NT 7, were investigated over three seasons (1998, 1999 and 2000). The highest quality wines were produced from the cooler 10°C grapes. Choice of yeast strain was complicated by effects of factors such as grape temperature, grape maturity and season. In general, the highest ester concentrations and lowest higher alcohol concentrations were produced by NT 116, and the highest wine quality by NT 7. Strain VIN 7 yielded the lowest ester levels, which in some cases were preferred, since the masking effect of esters was diminished with the result that Sauvignon blanc wines with more pronounced cultivar-typical green notes and consequently higher quality could be produced. Therefore when Sauvignon blanc grapes, known to produce neutral wines, are used, factors such as low temperature at harvest and yeast strains suitable for these conditions should be considered.
Sauvignon blanc is one of the most important white wine cultivars grown in South Africa. It is well-known that climatic and viticultural factors have a major effect on Sauvignon blanc grape and wine composition and quality. Of equal importance is the effect of production factors on Sauvignon blanc wine composition and quality. The purpose of this study was to evaluate the effect of such factors. Wines were produced from grapes from two regions that were stored overnight at 0°C and 20°C. Skin contact was conducted for 15 hours at these temperatures, with as well as without S02 addition prior to fermentation. Free-run juices were used as control. Settled juices were analysed for 2-methoxy-3-isobutylpyrazine (ibMP) and monoterpenes, and the corresponding wines also for ibMP, acetate and ethyl esters, total polyphenols and total flavanoids. The wines were sensorially evaluated for fruitiness and the typical green pepper/grassy aroma of Sauvignon blanc. Grape temperature, skin contact, and oxidative and reductive conditions prior to fermentation affected some of the above-mentioned component concentrations and therefore wine quality. Generally, most component concentrations were increased by skin contact, while polyphenol and flavanoid concentrations were lower in wines produced oxidatively. It appeared that wines produced reductively from free-run as well as low temperature skin contact juices presented the highest quality.
Oxygen can play an important role during the winemaking process. It can influence the composition and quality of the must and wine. Phenolic compounds are the main substrates for oxidation in must and wine. Oxygen addition leads to colour changes and the polymerisation of phenolic molecules in wine. Oxygen can, however, also influence the flavour and microbial composition of wine drastically, with certain off-flavours being formed and spoilage micro-organisms able to grow at too high oxygen additions to wine. A state-of-the-art, up-to-date review on the effects of oxygen in must and wine has, however, not been published recently. This review focuses on the effects of oxygen in must, during alcoholic fermentation, extended lees contact and during ageing of white and red wines. The effects it has on acetic acid bacteria and Brettanomyces are also discussed, as well as micro-oxygenation, a relative new technique used in wine production.
Wine is a highly complex mixture of compounds which largely define its appearance, aroma, flavour and mouth-feel properties. The compounds responsible for those attributes have been derived in turn from three major sources, viz. grapes, microbes and, when used, wood (most commonly, oak). The grape-derived compounds provide varietal distinction in addition to giving wine its basic structure. Thus, the floral monoterpenes largely define Muscat-related wines and the fruity volatile thiols define Sauvignon-related wines; the grape acids and tannins, together with alcohol, contribute the palate and mouth-feel properties. Yeast fermentation of sugars not only produces ethanol and carbon dioxide but a range of minor but sensorially important volatile metabolites which gives wine its vinous character. These volatile metabolites, which comprise esters, higher alcohols, carbonyls, volatile fatty acids and sulfur compounds, are derived from sugar and amino acid metabolism. The malolactic fermentation, when needed, not only provides deacidification, but can enhance the flavour profile. The aroma and flavour profile of wine is the result of an almost infinite number of variations in production, whether in the vineyard or the winery. In addition to the obvious, such as the grapes selected, the winemaker employs a variety of techniques and tools to produce wines with specific flavour profiles. One of these tools is the choice of microorganism to conduct fermentation. During alcoholic fermentation, the wine yeast Saccharomyces cerevisiae brings forth the major changes between grape must and wine: modifying aroma, flavour, mouth-feel, colour and chemical complexity. The wine bacterium Oenococcus oeni adds its contribution to wines that undergo malolactic fermentation. Thus flavour-active yeasts and bacterial strains can produce desirable sensory results by helping to extract compounds from the solids in grape must, by modifying grape-derived molecules and by producing flavour-active metabolites. This article reviews some of the most important flavour compounds found in wine, and their microbiological origin.
The precise location of 2-methoxy-3-isobutylpyrazine in Cabernet Sauvignon grape bunches was identified before véraison, after véraison, and when grapes were picked. Regardless of ripeness, the compound was mainly located in stems, then in skins and seeds, while the flesh contained very little. During ripening, the proportion of 2-methoxy-3-isobutylpyrazine in stems and seeds decreased, while it increased in skins. During the winemaking process, this methoxypyrazine was easily extracted from Sauvignon blanc (at the beginning of pressing) and Cabernet Sauvignon grapes (after 24 hours in vat). The concentration in Sauvignon blanc must may be reduced by settling (decreasing by half). The 2-methoxy-3-isobutylpyrazine content of Cabernet Sauvignon wines varied relatively little during vatting, irrespective of the length of time or the number of times it was pumped over. Press wines, however, had higher concentrations of this compound than free-run wines. Although settling white must and careful addition of press wine to blends had a certain impact, the 2-methoxy-3-isobutylpyrazine content of the wine depended primarily on the composition of the grapes.
Three methoxypyrazines were identified and quantified by gas chromatography/mass spectrometry in wine and juice samples of Vitis vinifera L. cv. Sauvignon blanc. Twenty-two wines of Australian, New Zealand, and French origin were analyzed together with 16 juice samples from four Australian regions. 2-Methoxy-3-(2-methylpropyl)pyrazine was present in all wines (0.6 - 38.1 ng/L) and all juice samples (0.6 - 78.5 ng/L); it was invariably the major methoxypyrazine. 2-Methoxy-3-(1-methylethyl)pyrazine was found in 11 wines (0.9 - 5.6 ng/L) and almost all juice samples (0.2 - 6.8 ng/L). In three wines and some juice samples, small quantities of 2-methoxy-3-(1-methylpropyl)pyrazine were found (typically 0.1 - 1.0 ng/L). Methoxypyrazine levels in the New Zealand wines were significantly higher than in the Australian wines (p < 0.001). Fruit grown under cool conditions gave higher grape methoxypyrazine levels than fruit grown under hot conditions. Grape methoxypyrazine levels were relatively high at veraison but decreased markedly with ripening.
The influence of naturally occurring and added methoxypyrazines on wine aroma was assessed by sensory evaluation. Addition of 2-methoxy-3-(2-methylpropyl)pyrazine or 2-methoxy-3-(1-methylethyl)pyrazine, at 1 ng/L and 2 ng/L, respectively, significantly influenced the aroma of a methoxypyrazine-free white wine. Ranking of samples prepared by addition of 2-methoxy-3-(2-methylpropyl)pyrazine (0-32 ng/L) to the methoxypyrazine-free wine showed that the compound contributed significantly to vegetative aroma at 8 ng/L or above. A range of commercial Sauvignon blanc wines was assessed by scoring for vegetative varietal aroma intensity and methoxypyrazine aroma intensity. Comparison with the naturally occurring methoxypyrazine concentration showed that wines of high (> 26 ng/L) and low (< 12 ng/L) methoxypyrazine concentration were clearly distinguished on the basis of vegetative varietal aroma or methoxypyrazine aroma. It is concluded that methoxypyrazines do contribute to the characteristic vegetative aroma of Sauvignon blanc wines.
Vine nitrogen status influence on S-cysteine conjugate precursors of volatile thiols, glutathione and phenolic content of the berries of Vitis vinifera L. cv. Sauvignon blanc have been assessed. Despite an increase in berry weight, the increase in nitrogen supply in the vine leads to higher cysteine precursor levels in grape juice. We also show that a late addition of nitrogen at berry set leads to a lower level of phenolic compounds in white grapes and to higher glutathione levels. Therefore, in white varieties, and particularly Sauvignon blanc, improving the nitrogen supply of the vine clearly increases its aromatic potential. However, an excess of nitrogen supply would increase the grape sensitivity to Botrytis cinerea and therefore decrease its quality.
The typical cultivar aroma of Sauvignon blanc may be described as containing vegetative, grassy, herbaceous, gooseberry, asparagus and green pepper nuances. The chemical components responsible for these aromas are reviewed. The most important components are methoxypyrazines, especially 2-methoxy-3-isobutylpyrazine. Other components, such as 4-methyl-4-mercapto-pentan-2-one, monoterpenes, C13-norisoprenoids, C6-alcohols and C6-aldehydes may also contribute to the complexity of Sauvignon blanc aroma. Factors affecting methoxypyrazine levels and therefore the typical Sauvignon blanc cultivar aroma are, amongst others, origin/climate and level of grape ripeness. Methoxypyrazine concentrations decrease with grape ripening and under increased sunlight and temperature conditions. To produce Sauvignon blanc wines with typical aromas, vines should be cultivated in cool areas and wines stored in dark rooms to retain these aromas.
This paper reviews some aspects of terpenes and terpene derivatives in grapes and wines, such as the identification of these compounds, their use in the identification of and differentiation between cultivars, the effect of grape maturity and wine-making techniques on terpene concentrations and wine quality, as well as transformations of terpenes in grapes and wine.
The effect of canopy microclimate on the grape aroma composition and wine quality of Sauvignon blanc was investigated in three climatically-different regions, i.e. in the Stellenbosch (1996 and 1997 season), Robertson and Elgin regions (1997 and 1998 season). A canopy shade treatment altering microclimate in a natural way, was applied to Sauvignon blanc vineyards in the three regions. Control vines were not manipulated. The concentrations of aroma compounds in the grapes, namely monoterpenes, C 13 -norisoprenoids and 2-methoxy-3-isobutylpyrazine, were determined weekly during the respective ripening periods. Solar radiation above and within the canopies as well as temperature within the canopies were also measured continually during the ripening periods. The highest canopy solar radiation, temperature, and monoterpene and C 13 -norisoprenoid concentrations were found for the control treatments, followed by the shaded treatments. An opposite tendency was found for 2-methoxy-3-isobutylpyrazine, which is one of the most important components responsible for the typical green pepper/asparagus aroma of Sauvignon blanc. There appears to be a relationship between chemical and microclimatic data in each region and over seasons. Marked temperature and aroma component concentration differences were observed among the three regions during the cool 1997 season, which manifested in wine aroma parameters such as fruitiness and vegetative/asparagus/green pepper nuances. Two definite wine styles emerged, namely the green pepper/asparagus "cool climate" style and the "warm climate" fruity/tropical style. However, differences in 2-methoxy-3-isobutylpyrazine and C13 -norisoprenoid levels and wine characteristics between regions were not as pronounced during the warm 1998 season. The data contribute to establishing guidelines for canopy manipulation for obtaining a specific wine character and quality. The choice lies with the viticulturist and winemaker to strive for and obtain, within limits, the style that they prefer.
Glutathione and N-acetyl-cysteine were tested as inhibitors of the decline of terpene alcohols, aroma compounds in dry and sweet Muscat wines stored in open bottles at 20degreesC. The drywine contained 251.2 mug/L linalool and 216.6 mug/L alpha-terpineol, and the sweet wine 131.7 mug/L linalool and 118.0 mug/L alpha-terpineol. In both wines, the concentration of linalool and alpha-terpineol did not change with the addition of glutathione or N-acetyl-cysteine. Control samples of dry wine exhibited lower (P<0.05) concentrations of linalool and alpha-terpineol after 2 and 3 days of storage. However, samples containing glutathione or N-acetyl-cysteine exhibited statistically higher linalool and in most cases alpha-terpineol content than control samples after 2 and 3 days of storage. Samples of control sweet wine exhibited lower (P<0.05) concentrations of linalool and a similar concentration of alpha-terpineol compared to control samples after 3 days of storage. However, samples containing glutathione or N-acetyl-cysteine exhibited a statistically higher (P<0.05) concentration of linalool than control samples after 3 days of storage. while they exhibited a similar concentration of alpha-terpineol.
Glutathione (GSH) was measured in grape (Vitis vinifera L.) berries during ripening. The Thompson Seedless variety was studied during two consecutive seasons from just before the onset of sugar accumulation until the berries attained commercial maturity. The GSH content increased along with soluble solids in both years. From Julian day 173 to day 197 in 1990 (21 June to 15 July), the GSH increased from 28.8 nmoles/gFW to 319 nmoles/ gFW. The average fresh weight of the berries increased from 0.79 g/berry to 1.95 g/berry during this period, so the GSH increase on a per berry basis was 22.4 nmoles/berry to 639 nmoles/berry. An increase in GSH was also observed in berries of Perlette, another seedless table grape variety. Beauty Seedless, a red variety, showed a gain in GSH accompanying the increase in soluble solids which began with the onset of pigmentation. Pigmented berries on a turning cluster showed higher GSH than green berries on the same cluster. Likewise, a seeded wine variety (Cabernet Sauvignon) had more GSH in berries with higher soluble solids, and more in pigmented berries on a turning cluster than in green berries from the same cluster. The results show that there is an increase in glutathione at the onset of ripening in grape berries. The increase was observed in red, green, seeded and seedless varieties, so GSH accumulation may be a general feature of grape berry ripening. The source of the GSH and a possible explanation for the timing of this phenomenon is discussed. © 1993 by the American Society for Enology and Viticulture. All rights reserved.
By extracting specific volatile thiols using p-hydroxymercuribenzoate, 4-mercapto-4-methylpentan-2-one (4MMP), 4-mercapto-4-methylpentan-2-ol (4MMPOH), 3-mercapto-3-methylbutan-1-ol (3MMB), 3-mercaptohexan-1-ol (3MH), 3-mercaptohexyle acetate (3MHA), and furanmethanethiol (2FM) were identified in wines made from several Vitis vinifera white and red grape varieties. The assay of volatile thiols in certain wines made from Sauvignon blanc, Gewurztraminer, Riesling, Colombard, Petit Manseng and botrytized Semillon confirmed the contribution of 4MMP, A3MH and 3MH to their characteristic aromas reminiscent of box tree, grapefruit, and passion fruit. 2FM, exhibiting a strong roasted coffee aroma, is present in white and red wines elaborated in new oak barrel at much higher concentrations than the perception threshold. 4MMP, 4MMPOH and 3MH can be released during alcoholic fermentation from their S-cysteine conjugate precursors. 2FM is generated in white wines during barrel fermentation. The formation is due to yeast transformation of furfural released from toasted staves. (C) 2004 American Chemical Society.
The development of the aromas of certain grapes varieties during fermentation has not been greatly investigated in enology until now. Recent works on sulfur compounds that participate in the aroma of Sauvignon blanc wines offer an example of grape flavor enhancement by yeasts. Several very odorous volatile thiols have been identified as constituents of the particular aroma of Sauvignon blanc wines: 4-mercapto-4-methylpentan-2-one (4MMP), 4-mercapto-4-methylpentan-2-ol, 3-mercaptohexanol, 3-mercaptohexyl acetate. These different thiols are practically absent in grapes or musts. They appear in wines during the alcoholic fermentation. This increase in varietal flavor due to yeast metabolism can be explained by the degradation of S-cysteine conjugates in the grape, leading to the formation of corresponding volatile thiols. The ability of Saccharomyces cerevisiae strains to augment Sauvignon blanc aromas related to these sulfur-containing aroma compounds is variable. The same Sauvignon must fermented by pure cultures of different yeast strains results in wines with different levels of volatile sulfur aromas. Certain yeast strains (EG8, VL3c) which winemakers have empirically noted produce Sauvignon wines with pronounced varietal character, release the largest quantities of 4MMP. The differences in behavior between S. cerevisiae strains also appears during the fermentation of model mediums added with S-4-(4-methylpentan-2one)-L-cysteine. Comparing the S. cerevisiae strains commonly used in winemaking, certain wild varieties of Saccharomyces bayanus have been proved particularly suited to freeing the Sauvignon sulfur aromas. Such strains have been isolated in spontaneous fermentation in Sancerre. Natural hybrids between S. cerevisiae and S. bayanus var. uvarum have also been found. They may also be obtained in the laboratory by breeding. The interest in the interspecific hybrids for the vinification of certain grape varieties must be examined.
A trained sensory panel (n = 14) identified key flavors in Sauvignon blanc wines from Australia, France. New Zealand, Spain, South Africa, and the United States. Sixteen characteristics were identified and measured: sweet sweaty passion fruit, capsicum, passion fruit skin/stalk, boxwood/cat urine, grassy, mineral/ flinty, citrus, bourbon, apple lolly/candy, tropical, mint, fresh asparagus, canned asparagus, stone fruit, apple and snow pea. Principal component analysis was used to describe differences among regions and countries. Sauvignon blanc wines from Marlborough, New Zealand, were described by tropical and sweet sweaty passion fruit characteristics, while French and South African Sauvignon blanc wines were described as having flinty/mineral and bourbon-like flavors. Chemical analyses of these wines also showed that wines from Marlborough had more methoxypyrazine and thiol compounds. A consumer study (n = 105) showed that New Zealanders significantly prefer New Zealand-style Sauvignon blanc. Copyright © 2009 by the American Society for Enology and Viticulture. All rights reserved.
The rate of oxidation of SO2 was studied in a wine-model system under aerial oxygen saturation conditions to gain further insight into its mechanism of action in wine. When SO2 was studied alone, no significant oxidation was observed unless iron and copper were introduced. When these metals were added a slow oxidation was observed and bound SO2 also increased to a small but significant extent. These results are consistent with a radical chain mechanism initiated by metal catalysis, in which powerful oxidizing radicals, capable of oxidizing ethanol to acetaldehyde, are produced. This increase in bound SO2 is prevented by 4-methylcatechol (4-MeC) in keeping with the known ability of polyphenols to scavenge these intermediate radicals and thus to inhibit SO2 autoxidation, which consequently should not occur in wine. When 4-MeC was introduced at a concentration that simulated the reducing capacity of red wine, again no significant SO2 oxidation was observed without addition of iron and copper. Had the catechol been oxidized, hydrogen peroxide would have been generated and reacted with the SO2. In the presence of both metals the rate of SO2 oxidation was markedly increased compared to SO2 alone and then was dependent on the concentration of the catechol. These results demonstrate the crucial importance of metals in allowing polyphenol oxidation and that the rate of SO2 consumption is dependent on the rate of catechol oxidation. When iron and copper were added separately, only a modest increase in rate of catechol oxidation resulted. However, when combined, marked synergism was observed and the rate then became very sensitive to copper concentration. It is proposed that copper, by interacting with oxygen, facilitates redox cycling of iron. Exposure of a red wine to the conditions used in this study produced similar results regarding SO2 oxidation to those observed. Copyright © 2007 by the American Society for Enology and Viticulture. All rights reserved.
3-Mercaptohexanol formed during alcoholic fermentation from an odorless precursor present in grapes can contribute to the fruity aromas of Cabernet Sauvignon, Cabernet franc, and Merlot wines. The concentrations of this compound decreased during aging as a result of oxygen addition each time the wine was handled. 3-Mercaptohexanol decrease did not result from a direct oxidation by oxygen, as the kinetics of 3-mercaptohexanol disappearance in a red wine supplemented with oxygen was delayed compared to the kinetics of oxygen consumption. The implication of wine phenolic compounds in these mechanisms was studied in a model medium. When catechin was dissolved in the presence of oxygen, the 3-mercaptohexanol content decreased more rapidly than in a solution containing only 3-mercaptohexanol and oxygen. Anthocyanins did limit the decrease in 3-mercaptohexanol. The vital role of sulfur dioxide in protecting 3-mercaptohexanol in the model medium and in wines was shown.
The localization in the berry of S-cysteine conjugates, sulfur flavor precursors in the Sauvignon blanc grapes, was studied. The assay of the S-cysteine conjugates showed that the content of 4-mercapto-4-methylpentan-2-one and 4-mercapto-4-methylpentan-2-ol precursors (P-4MMP and P-4MMPOH) were equivalent in the juice and skin, while the concentration of 3-mercaptohexan-1-ol precursor (P-3MH) was almost eight times higher in the skin. In comparison with immediate pressing, skin contact only allowed a modest increase in the concentration of P-4MMP and P-4MMPOH, but it enriched the must considerably with P-3MH. The difference in behavior between the P-4MMP and P-4MMPOH and the P-3MH was explained by their localization within the berries.
Selective extraction of volatile mercaptans present in wines at trace levels, combined with capillary gas chromatographic (GC) analysis using flame photometric detector (FPD) revealed the presence of a previously unreported compound in Sauvignon wine. 3-mercaptohexylacetate was identified by comparison of chromatographic and mass spectrum data with those of the reference compound. This mercapto ester, recently found in passion-fruit, exhibits aroma reminiscent of box tree with grapefruit and passion fruit notes. Its perception threshold in water and model solution is around 2-4 ng/l. 3-mercaptohexylacetate may contribute to the typical varietal aroma of Sauvignon wines.
Five volatile thiols previously identified in Sauvignon blanc wines, 4-mercapto-4-methylpentan-2-one (4MMP), 4-mercapto-4-methylpentan-2-ol (4MMPOH), 3-mercapto-3-methylbutan-1-ol (3MMB), 3-mercaptohexan-1-ol (3MH) and 3-mercaptohexyl acetate (A3MH) were found to be present in wines made from several other white Vitis vinifera grape varieties. An assay of these volatile thiols showed that concentrations of 4MMP, 3MH, and A3MH were considerably higher than the perception thresholds in certain wines made from Gewurztraminer, Riesling, Colombard, Petit Manseng, and botrytized Semillon. The impact of volatile thiols on the aromas of wines made from these grape varieties was investigated for the first time.
The chemical, biochemical, and enological literature has been broadly surveyed to identify the reaction mechanisms of oxygen and of its intermediate reduction products that should apply to wine. The reduction potentials of redox couples derived from wine polyphenols and oxygen, as well as that of the Fe3+/Fe2+ couple, have been calculated for wine conditions and form the basis for discussing how these redox systems are likely to interact. Values obtained for wine quinone/catechol couples agree well with those reported for wine-model conditions. Catechol derivatives are oxidized sequentially to semiquinones and quinones, while oxygen is reduced in turn to hydroperoxyl radicals and hydrogen peroxide. The whole process is mediated by redox cycling of the Fe3+/Fe2+ couple, which is made possible by the lowering of its reduction potential by coordination of Fe3+ to hydroxy acids. Hydrogen peroxide is then further reduced by Fe2+ in the Fenton reaction to produce hydroxyl radicals, which oxidize saturated hydroxy compounds. Intermediate radicals may react with oxygen, providing an additional pathway for its reduction. Thus, both ferric and ferrous ions, which are present in wine, perform an important catalytic function. The antioxidant activity of bisulfite is largely restricted to its reaction with hydrogen peroxide. Direct reaction of sulfur dioxide with oxygen, which is a radical chain process, is prevented by the radical scavenging activity of polyphenols.
The concentrations of acetate esters in beer were reduced by up to 85% by addition of linoleic acid to the fermentation or by pitching with yeast previously enriched with this unsaturated fatty acid. Linoleic acid was rapidly incorporated into yeast lipids and was effective in reducing the rate of ethyl acetate formation within 2 h. Addition of linoleic acid altered the pattern of synthesis of fatty acids by yeast, causing a shift from medium toward long chain acids. Secondly, the amount of squalene in yeast was reduced by up to 70% whereas that of lanosterol was increased threefold. Since total yeast lipid synthesis was reduced by up to 40%, we conclude that less acetylCoA is synthesized in the presence of linoleic acid. Further, high concentrations of linoleic acid decreased the proportion of acetylCoA consumed by the synthesis of acetate esters. Therefore linoleic acid may directly decrease acetate ester synthesis in addition to its effect via reduction of acetylCoA availability.
Oxidation reactions involving phenolics might change the chemical and sensory profile of wines. While oxidation is a long-standing problem in winemaking, a definitive understanding of its chemical mechanisms is lacking, and such an understanding could allow us to better predict and control wine aging. We briefly summarize and discuss the current knowledge on the chemistry of wine phenolic oxidation and propose, along with other researchers, a new, comprehensive scheme in which the Fenton reaction and hydroxyl radicals have an essential role. This hypothesis suggests that catalytic iron converts wine's hydrogen peroxide into hydroxyl radical. This leads to a much stronger and less selective oxidant that could react with almost all wine components, in proportion to their concentration and with little selectivity for antioxidant properties. This reaction could produce many electrophilic oxidation products, mainly aldehydes and ketones, that could further modify the chemical composition and sensory perception of wine. While the brevity of this report precludes a full review of oxidation, our aim is to stimulate more study and debate on the mechanisms in wine oxidation chemistry.
Rotundone, an oxygenated sesquiterpene, is responsible for the peppery aroma in wines. We developed an effective and simple method to determine trace levels of rotundone in grapes and wines. The method uses stir bar sorptive extraction (SBSE) with heart-cutting two-dimensional gas chromatography/mass spectrometry without a pre-extraction process such as solid-phase extraction. The limits of detection and quantitation for rotundone were 2.1 and 6.5 ng/kg in grape and 2.4 and 7.2 ng/L in wine. The recoveries of rotundone from Cabernet Sauvignon grape and wine were 106% (spiked with 120 ng/kg for grape) and 96% (spiked with 120 ng/L for wine), respectively. We demonstrated that rotundone concentrations in Syrah grapes and wines from Ueda were higher (up to 2342 ng/ kg and 232 ng/L, respectively) than the maximal rotundone concentrations in Australian Syrah grapes and wines. Findings indicate that some environmental factors in Japan may promote rotundone accumulation in Syrah grapes, and underscores the importance of studying regional characteristics of rotundone accumulation in Syrah grapes.
The degradation of glutathione (GSH) in the yeast Saccharomyces cerevisiae appears to be mediated only by γ-glutamyltranspeptidase and cysteinylglycine dipeptidase. Other enzymes of the γ-glutamyl cycle, γ-glutamyl cyclotransferase and 5-oxo-l-prolinase, are not present in the yeast. In vivo transpeptidation was shown in the presence of a high intracellular level of γ-glutamyltranspeptidase, but only when the de-repressing nitrogen source was a suitable acceptor of the transferase reaction. In contrast, when the de-repressing source was not an acceptor of the transferase reaction (e.g. urea), only glutamate was detected. Intracellular GSH is virtually inert when the level of γ-glutamyltranspeptidase is low. Possible roles for in vivo transpeptidation are discussed.
This research aimed at the development and validation of an ultra-performance liquid chromatography (UPLC) method for the quantification of glutathione (GSH) in grape juice and in white wine after derivatisation with para-benzoquinone. The phenolic compounds catechin and caffeic acid that occur in white wine and have antioxidant effects, are also quantified in the same analysis. Catechin is the basic monomeric unit of grape and wine tannins and caffeic acid, when esterified with tartaric acid, plays a relevant role in Grape Reaction Product (GRP) formation.The analytical method proposed showed good linearity, repeatability and intermediate repeatability, as well as high recovery (>85%). It was applied for the quantification of GSH, catechin and caffeic acid in South African juices (12) and white wines (43).This novel method will have a large impact on the time and costs of the analyses for the wine industry through enabling rapid routine quantification of GSH, catechin and caffeic acid.
Some varieties of Vitis vinifera L. can undergo berry weight loss during later stages of ripening. This defines a third phase of development in addition to berry formation and berry expansion. Berry weight loss is due to net water loss, but the component water flows through different pathways have remained obscure. Because of the very negative osmotic potential of the cell sap, the maintenance of semipermeable membranes in the berry is required for the berry to counter xylem and apoplast tensions that may be transferred from the vine. The transfer of tension is determined by the hydraulic connection through the xylem from the berry to the vine, which changes during development. Here we assess the membrane integrity of three varieties of V. vinifera berries (cvv. Shiraz, Chardonnay and Thompson seedless) throughout development using the vitality stains, fluorescein diacetate and propidium iodide, on fresh longitudinal sections of whole berries. We also measured the xylem pressure using a pressure probe connected to the pedicel of detached berries. The wine grapes, Chardonnay and Shiraz, maintained fully vital cells after veraison and during berry expansion, but began to show cell death in the mesocarp and endocarp at or near the time that the berries attain maximum weight. This corresponded to a change in rate of accumulation of solutes in the berry and the beginning of weight loss in Shiraz, but not in Chardonnay. Continuous decline in mesocarp and endocarp cell vitality occurred for both varieties until normal harvest dates. Shiraz grapes classified as high quality and sourced from a different vineyard also showed the same death response at the same time after anthesis, but they displayed a more consistent pattern of pericarp cell death. The table grape, Thompson seedless, showed near to 100% vitality for all cells throughout development and well past normal harvest date, except for berries with noticeable berry collapse that were treated with giberellic acid. The high cell vitality in Thompson seedless berries corresponded to negative xylem pressures that contrasted to the slightly positive pressures for Shiraz and Chardonnay. We hypothesise that two variety dependent strategies exist for grapevine berries late in development: (1) programmed cell death in the pericarp and loss of osmotically competent membranes that requires concomitant reduction in the hydraulic conductance via the xylem to the vine; (2) continued cell vitality and osmotically competent membranes that can allow high hydraulic conductance to the vine.