Wine Aroma Compounds Research Articles

Impact of accentuated cut edges (ACE) technique on volatile and sensory profiles of Shiraz wines

Varietal thiols are important wine aroma compounds that are generally less abundant in red wines. Accentuated cut edges (ACE), known for accelerating phenolic extraction, was applied to Shiraz winemaking and compared with conventional crushing (NOACE) to examine the effects on varietal thiol precursor extraction and thiol formation. Water addition to grape must and skin contact time (SCT) during fermentation were also assessed. Although there was no difference for precursors in the must, ACE significantly decreased 3-S-glutathionylhexan-1-ol concentration during fermentation. 3-Sulfanylhexan-1-ol and ethyl esters were significantly influenced by crushing method and/or SCT, with NOACE or shorter SCT yielding higher concentrations. Acetates, higher alcohols, fatty acids, and isoprenoids differed according to the interaction of crushing method and SCT, with ACE and shorter SCT significantly enhancing all groups except acetates. Volatiles in Sauvignon blanc and Pinot noir wines produced at commercial scale with ACE were briefly evaluated, suggesting an impact of grape variety.

Influence of tannins, human saliva, and the interaction between them on volatility of aroma compounds in a model wine.

During wine drinking, aroma release is mainly impacted by wine matrix compositions and oral physiological parameters. Notably, tannins in wine could interact with saliva protein to form aggregates which might also affect the volatility of volatiles. To explore tannins, saliva, and the interaction between them on the volatility of volatiles, the volatility of 16 aroma compounds in the model wine mixed with the commercial tannin extracts, human saliva, or both respectively, was evaluated in vitro static condition by using HS-SPME-GC/MS. The volatility of aroma compounds with high hydrophobicity or benzene ring appeared to decrease more when increasing the tannin levels. Specifically, the volatility of ethyl octanoate, β-ionone, and guaiacol was decreased more than 20% by adding 2 g/L tannin extract. The addition of human saliva could significantly inhibit volatility of most aroma compounds in the model wine. Furthermore, the volatility of most aroma compounds in the mixture of tannins and human saliva was significantly lower than the control or the sample which were added with tannins or human saliva individually. The volatility of some aroma compounds in the mixture of the tannin and saliva was only around 50% or less, relative to the control. Two-way ANOVA analysis showed that there was a synergistic effect between tannin and saliva on decreasing the volatility of most aroma compounds (p < 0.05). Overall, understanding the effect of key factors such as tannins and saliva on volatility of volatiles could help to understand the sophisticated retronasal perceptions during wine tasting. PRACTICAL APPLICATION: The outputs of this research will be helpful in understanding the impact of tannins on retronasal aroma release during wine tasting. It might promote the control of tannins in the viticulture and brewing process to improve the retronasal perception of wine aroma.

The influence of different commercial yeasts on aroma compounds of rosé wine produced from cv. Öküzgözü grape

In this study, the effects of the use of different commercial yeasts on the aroma compounds of rosé wines produced from Öküzgözü grape grown in Turkey were investigated. For this purpose, three different wines have been produced through spontaneous fermentation and using commercial yeasts (NBY17 and Zymaflore X5). The aroma compounds were isolated using the liquid-liquid extraction method. These compounds were identified and quantified using the GC-MS-FID. The total amount of aroma compounds was found 150,749.4 µg/L in spontaneous wine, 170,681.6 µg/L in wine using NBY17, and 162,623.1 µg/L in wine using Zymaflore X5. The most dominant aroma groups in wines were higher alcohols and esters. In general, NBY17 has been found to play an important role in the formation of pleasing aromatic compounds in wine both in terms of aroma formation and sensory properties. This study provided the first data on the formation ability of aroma compounds for NBY17 yeast. Pratical applications Many wineries today use commercial yeasts because of their ability to start fermentation directly, convert sugar to alcohol greatly, and produce wine with the desired properties, as well as producing small amounts of undesirable by-products. This study which was performed using Zymaflore X5 and NBY17 among these commercial yeasts was focused on the differences in the aroma compounds of rosé wines obtained from Öküzgözü grapes. With this study, the first data on the ability of commercial wine yeast called NBY17 produced in Turkey to form aroma compounds was provided. The use of commercial yeast significantly influenced the amounts of aroma compounds in wines and the commercial yeast called NBY17 plays an important role in the formation of pleasing aroma compounds in wine.

Minty aroma compounds in red wine: Development of a novel automated HS-SPME-arrow and gas chromatography-tandem mass spectrometry quantification method

A novel automated method was developed for the quantitative determination of nine terpenoids that could contribute to the minty notes of red wine bouquet. The method couples headspace SPME-Arrow extraction with GC-MS/MS analysis. PDMS/DVB fiber was chosen for the extraction and an ionization energy of 30 eV permitted to optimize the analyte detection. The optimal sample preparation consists of a two-fold dilution of the wine sample with addition of 4 g of sodium chloride while the most suitable extraction conditions take place at 50 °C for 1 h. The method shows good linearity, intraday variations between 2 and 25%, interday variations between 7 and 23% and recoveries between 80 and 119%. The method exhibits the required low detection (between 3 and 60 ng/L) and quantification (between 6 ng/L and 200 ng/L) limits. These limits have permitted the quantification of the pool of minty terpenoids in fourteen red Bordeaux wines.

Effect of Soil Management and Training System on Negroamaro Wine Aroma.

This study aimed to assess the impact of two soil managements and training systems on yield and wine aroma compounds of Negroamaro variety grown in a warm climate region (southern Italy). Cover crop (CC) and soil tillage (ST) as soil management, whilst bilateral Guyot (BG) and monolateral Guyot (MG) as training systems were compared. Free and bound volatile fractions were evaluated by GC-MS. ST and CC as well as BG and MG significantly affected yield parameters. In particular, yield was higher in ST and BG than in CC and MG, respectively; moreover, it was found to be positively influenced by interaction between BG and ST. Regarding aroma compounds, significant interactions between soil management and training system factors were observed. In case of free volatiles, the most positive interaction was found between BG and ST, whereas, for bound volatiles, the best interaction was represented by MG with both soil tillage and cover crop. Vine leaf area and development over vine growth stages along with water stress levels played an important role in determining the aroma profile as well as yield parameters. In conclusion, the training system significantly interacted with soil management and affected most of important aroma compounds in Negroamaro wine.

Oral Release Behavior of Wine Aroma Compounds by Using In-Mouth Headspace Sorptive Extraction (HSSE) Method.

The oral release behavior of wine aroma compounds was determined by using an in-mouth headspace sorptive extraction (HSSE) procedure. For this, 32 volunteers rinsed their mouths with a red wine. Aroma release was monitored at three time points (immediately, 60 s, and 120 s) after wine expectoration. Twenty-two aroma compounds belonging to different chemical classes were identified in the mouth. Despite the large inter-individual differences, some interesting trends in oral release behavior were observed depending on the chemical family. In general, esters and linear alcohols showed rapid losses in the mouth over the three sampling times and therefore showed a low oral aroma persistence. On the contrary, terpenes, lactones, and C13 norisoprenoids showed lower variations in oral aroma release over time, thus showing a higher oral aroma persistence. Additionally, and despite their low polarity, furanic acids and guaiacol showed the highest oral aroma persistence. This work represents the first large study regarding in-mouth aroma release behavior after wine tasting, using real wines, and it confirmed that oral release behavior does not only depend on the physicochemical properties of aroma compounds but also on other features, such as the molecular structure and probably, on the characteristics and composition of the oral environment.

Potential application of CHS and 4CL genes from grape endophytic fungus in production of naringenin and resveratrol and the improvement of polyphenol profiles and flavour of wine

4-Coumaroyl-CoA ligase (Al4CL) and chalcone synthase (AlCHS) genes were found in grape endophyte Alternaria sp. MG1, but were not functional verified. A cross-validation method was used in Saccharomyces cerevisiae to identify their functions. AlCHS was identified to synthesize both naringenin and resveratrol, while Al4CL synthesized p-coumaroyl CoA. Co-culture of S. cerevisiae strains separately containing AlCHS and Al4CL resulted in the simultaneous production of naringenin (18.5 mg/L) and resveratrol (113.2 μg/L). Strain S. cerevisiae containing Al4CL was used in winemaking and the chemical and aroma compounds in wine were detected by HPLC and SPME-GC–MS. Results showed that the total contents of polyphenols, anthocyanins, flavonol, ethyl esters and fatty acids significantly increased, while the 4-vinylphenol content decreased, and the fruit and cheese flavour increased but the green aroma declined. This study indicated the potential application of Al4CL and AlCHS genes from Alternaria sp. MG1 for improvement of wine nutrients and flavour.

Effect of mixed fermentation with Pichia fermentans , Hanseniaspora uvarum, and Wickeramomyces anomala on the quality of fig ( Ficus carica L .) wines

This study aimed at evaluating the quality of fig wines that co-fermented by three non-Saccharomyces. Four suitable ratios were selected for co-fermentation, and the fermentation performance of fig wines was compared with fig juice and the pure fermentation of Saccharomyces. HPLC was used to analyze organic acids and mono-phenols in fig wines, and the amino acid analyzer was used to detect free amino acids. The results showed that fig wines fermented by non-Saccharomyces had higher contents of organic acids and mono-phenols. HS-SPME-GC/MS was used to detect 48 aroma compounds in fig wines, and the results revealed that co-fermentation by non-Saccharomyces could obtain up to 38 aroma compounds, which was superior to 30 substances obtained from fermentation by Saccharomyces. PCA was used to detect positive correlations between samples and aroma compounds. The results showed that there were significant differences in the aroma compounds in the different samples. Practical applications Non-Saccharomyces played an important role in the aroma and flavor of fruit wine, and were used as an auxiliary starter culture to improve the effect of Saccharomyces fermentation. The research on non-Saccharomyces in the literature was limited to the use of non-Saccharomyces alone for fermentation, and the fermentation performance was much worse than Saccharomyces. In this study, three non-Saccharomyces were selected for co-fermentation. The result revealed that pleasant fig wine could be obtained by co-fermentation of non-Saccharomyces without a Saccharomyces starter culture, which provided a significant reference for the subsequent research on non-Saccharomyces and fig wines.

Sensory-directed characterisation of distinctive aromas of Sauternes and Viognier wines through semi-preparative liquid chromatography and gas chromatography approaches

Gas chromatography-olfactometry-mass spectrometry (GC-O-MS) has been very useful in identifying aroma compounds from within the complex matrix of wine. Supplementary separation can be required to overcome co-elution of volatiles or other sensory-directed chromatographic strategies are needed, including multidimensional chromatography and preparative fraction collection coupled to GC. Studies investigating ‘overripe orange’ aroma in sweet Sauternes wine and the similar ‘apricot’ aroma in Viognier wine were conducted. Wines with the targeted aroma attributes were selected and concentrated wine extracts prepared. GC-O found no individual aroma compounds with the targeted aroma attribute. Semi-preparative HPLC was used to obtain less complex fractions of the wine extracts. The fractions were eluted in water/ethanol and, therefore, could be smelled directly. Fractions with the targeted aroma character were further resolved by GC-preparative fraction collection (GC-PFC). Recombinational GC-PFC demonstrated the importance of the components within a 4 min preparative GC fraction to the ‘overripe orange’ aroma of typical Bordeaux dessert wine. In Viognier wine, monoterpenes linalool, α-terpineol and geraniol as well as benzaldehyde were found to be associated with the ‘apricot’ character. Thus, several wine aroma compounds interact for these specific aromas to be perceived. This sensory-led combination of separation techniques is a powerful tool for the identification of key compounds responsible for specific aromas across the wine and beverage industries.

Influence of Triazole Pesticides on Wine Flavor and Quality Based on Multidimensional Analysis Technology.

Triazole pesticides are widely used to control grapevine diseases. In this study, we investigated the impact of three triazole pesticides—triadimefon, tebuconazole, and paclobutrazol—on the concentrations of wine aroma compounds. All three triazole pesticides significantly affected the ester and acid aroma components. Among them, paclobutrazol exhibited the greatest negative influence on the wine aroma quality through its effect on the ester and acid aroma substances, followed by tebuconazole and triadimefon. Qualitative and quantitative analysis by solid-phase micro-extraction gas chromatography coupled with mass spectrometry revealed that the triazole pesticides also changed the flower and fruit flavor component contents of the wines. This was attributed to changes in the yeast fermentation activity caused by the pesticide residues. The study reveals that triazole pesticides negatively impact on the volatile composition of wines with a potential undesirable effect on wine quality, underlining the desirability of stricter control by the food industry over pesticide residues in winemaking.

Scalable synthesis of the aroma compounds d6-β-ionone and d6-β-cyclocitral for use as internal standards in stable isotope dilution assays

C13 Norisoprenoids are important aroma compounds in wine, giving positive attributes to the overall wine aroma even when found at very low levels. β-Ionone is considered one of the most important aroma compounds giving violet, woody and raspberry aromas to wine, fruits and vegetables in which it is found. Due to its potent aroma at low levels, precise analytical methods are desired for its quantification. Stable isotope dilution assay (SIDA) is one of the most important of these methods but requires the use of isotopically labelled standards. Herein, we describe the scalable synthesis of d6-β-ionone and d6-β-cyclocitral, another aroma compound with smokey and fruity notes, starting from the relatively inexpensive deuterated starting material d6-acetone.

Recent advancements in understanding the terroir effect on aromas in grapes and wines

Terroir is about the link between wine and its origin. It has long been understood by sensory evaluation that the taste of wine from a given variety can be related to its origins. Specific organoleptic characteristics of wine are influenced by environmental factors such as soil and climate. By deconstructing the effect of measurable soil and climate parameters on grape and wine aroma compounds, the terroir effect on wine typicity can be better understood. Climate influences on vine development and grape ripening are mainly associated with temperature, radiation and rainfall, while soil influences are primarily associated with water availability and nitrogen supply. Significant advances have been made over recent years in understanding wine aromas and their molecular basis and influences of climate and soil on a wide range of molecules responsible for wine aroma expression. This article aims to review these recent research advances to obtain a more comprehensive understanding of how terroir influences wine typicity. The effect of terroir on wine quality and typicity is sometimes considered intangible and difficult to explain on a scientific basis. By combining agronomic, analytical and sensory approaches, however, this review shows that the terroir effect is mediated by measurable factors that can easily be monitored in the vineyard. Assessment of the results compiled by this review allows the suggestion that terroir expression at specific sites might be maximized by choosing appropriate plant material in relation to soil and climate, by acting on manageable parameters like vine water and nitrogen status, or by implementing canopy management to modify microclimate in the bunch zone.

Investigating the effects of two volatile phenols on aroma perception of four red wine cultivars using Projective Mapping

AbstractPerception of aroma compounds in wine is the result of complex phenomena, in which the compounds, their concentrations, the matrix, and their interactions play a role. In order to evaluate the impact of compounds and matrices on red wine aroma perception, a two‐part study was conducted. First, the work evaluated Projective Mapping (PM) and Descriptive Analysis (DA) in assessing olfactory interactions in a large (n = 18) set of red wine samples. Both methods generated a rich and comparable set of descriptors (21 and 28 for DA and PM, respectively), indicating that the rapid method was fit for purpose. Subsequently, PM was used to test the olfactory effects of 4‐ethyl phenol (4‐EP) and o‐cresol in four red cultivars by a trained panel of twelve judges. There were marked similarities in the impact of these compounds in all cultivars regarding aspects such as loss of fruitiness. However, important differences in the sensory profiles of similarly spiked samples were also observed, highlighting the importance of matrix effects.Practical ApplicationsThe results confirm that work related to wine matrices can be carried out with a trained panel using PM rather than DA. This finding suggests that limiting aspects of DA (e.g., the large number of samples generated through experimental design) can be addressed through careful choice of evaluation method, while taking into account the fine balance between gain and loss of relevant information. The study furthermore emphasizes the need to carefully consider the composition of the matrix when determining and comparing olfactory perceptual interactions in wine, and when evaluating the effects of treatments on wine aroma.

Nitrogen metabolism of branched‐chain alcohols acetates in jujube wine assessed by 13 C‐labeling

Branched-chain alcohols acetates (BCAA) are important aroma components of jujube wine. However, their presence is somewhat difficult to control during fermentation. In this regard, 13C-labeling and Gas Chromatography-Mass Spectrometer (GC-MS) were used to explore the Ehrlich pathway for the formation of BCAA. Initially, branched-chain (BC) amino acids, known to be involved in the production of BCAA, were investigated. BC amino acids, aldehydes, and alcohols were observed to gradually transform, while a small amount of alcohols was esterified to BCAA. Following the addition of 13C-BC amino acids into the jujube pulp, 13C-aldehydes, 13C-alcohols and 13C-BCAA were detected in the wine at 2, 24, and 72 hr, respectively, by mass spectrometric analysis. BC amino acids were observed to be transaminated, decarboxylated to aldehydes and then reduced to alcohols. The alcohols were subsequently esterified with acetyl CoA to form BCAA confirming a potential pathway for flavor regulation and quality improvement of jujube wine. Practical applications Jujube wine, produced by jujube fermentation with Saccharomyces cerevisiae, is a famous alcoholic beverage in Taihang Mountain districts in Hebei with Chinese characteristics. But the development of jujube wine was restricted because its flavor and quality were very unstable. Branched-chain alcohols acetates (BCAA) are the key aroma compounds of jujube wine. Understanding the formation mechanism of BCAA could provide the guide of process optimization and flavor regulation, making it become a unique brandy with Chinese characteristics, recognized, and accepting by the world.

A New Approach to the Reduction of Alcohol Content in Red Wines: The Use of High-Power Ultrasounds.

Background: To obtain wines with a lower percentage of alcohol, the simplest approach would be an earlier harvest of the grapes. However, this has implications for the wine composition and quality, due to the lack of phenolic maturity that these grapes may present. A technological innovation that could help in this situation could be the use of ultrasound in wineries. Methods: Grapes were harvested with two different ripening levels (25.4 °Brix and 29 °Brix), transported to the winery, and vinified. Also, a large-scale high-power ultrasound system was used to treat part of the less mature grapes just after crushing. These grapes were also vinified. The three different vinifications were skin-macerated for 7 days. The wine aroma compounds and physicochemical, chromatic, and sensory characteristics were analyzed at the time of bottling. Results: The wine made with the ultrasound-treated grapes showed very similar characteristics to the wine made with the more mature grapes, especially regarding total phenol and tannin content, but with an alcohol content 15% lower than the latter. Conclusions: The results indicate that this technology could be applied to grapes to favor the extraction of grape phenolic compounds, even when grape phenolic maturity is not complete, allowing the production of quality wines with a reduced alcohol content.

Interactions Among Odorants, Phenolic Compounds, and Oral Components and Their Effects on Wine Aroma Volatility.

To determine the impact of oral physiology on the volatility of typical wine aroma compounds, mixtures of a synthetic wine with oral components (centrifuged human saliva (HS), artificial saliva with mucin (AS), and buccal epithelial cells (BC)) were prepared. Each wine type was independently spiked with four relevant wine odorants (guaiacol, β-phenyl ethanol, ethyl hexanoate, and β-ionone). Additionally, the impact of four types of phenolic compounds (gallic acid, catechin, grape seed extract, and a red wine extract) on aroma volatility in the HS, AS, and BC wines was also assessed. Static headspace was measured at equilibrium by solid phase microextraction–GC/MS analysis. Results showed a significant impact of oral components on the volatility of the four tested odorants. Independently of the type of aroma compound, aroma volatility was in general, higher in wines with BC. Moreover, while guaiacol and ethyl hexanoate volatility was significantly lower in wines with HS compared to wines with AS, β-ionone showed the opposite behavior, which might be related to metabolism and retention of mucin, respectively. Phenolic compounds also showed a different effect on aroma volatility depending on the type of compound and wine. Gallic acid had little effect on polar compounds but it enhanced the volatility of the most hydrophobic ones (ethyl hexanoate and β-ionone). In general, flavonoid type polyphenols significantly reduced the volatility of both polar (guaiacol and β-phenyl ethanol) and hydrophobic compounds (β-ionone in HS and BC wines), but through different mechanisms (e.g., π–π interactions and hydrophobic binding for polar and apolar odorants respectively). On the contrary, flavonoids enhanced the volatility of ethyl hexanoate, which might be due to the inhibition exerted on some salivary enzymes (e.g., carboxyl esterase) involved in the metabolism of this odorant molecule.

Evidence of the Possible Interaction between Ultrasound and Thiol Precursors.

The effect of ultrasound (20 kHz, 153 μm) on the prefermentation extraction mechanisms in Sauvignon Blanc grapes was studied, focusing on 3-mercaptohexan-1-ol (3MH) and 4-mercapto-4-methyl-pentan-2-one (4MMP) precursors linked to glutathione (GSH) and cysteine (Cys). The treatment determined a positive extraction trend between the duration (untreated, 3 and 5 min) and the conductivity or the concentration of catechins and total phenols, significantly differentiated after 5 min. Nevertheless, the concentration of the thiol precursors in grape juice not only remained undifferentiated, but that of 3-S-glutathionyl mercaptohexan-1-ol showed a negative trend with the treatment time applied (168 ± 43, 156 ± 36, and 149 ± 32 μg/L, respectively, for control, 3 and 5 min). The divergence on the effect between families of compounds suggests an interaction between the sonication treatment and thiol precursor molecules. In order to evaluate the possible degradation properly, ultrasound was applied in a model solution spiked with 3MH and 4MMP precursors, reproducing the conditions of grapes. Except for Cys-3MH, the mean concentration (n = 5) for the rest of the precursors was significantly lower in treated samples, predominantly in those linked to glutathione (~−22% and ~18% for GSH-3MH and GSH-4MMP) rather than to cysteine (~−6%~−8% for Cys-3MH and Cys-4MMP). The degradation of precursors was associated with a significant increase of 3MH and 4MMP. The formation of volatile thiols following sonication is interesting from a technological point of view, as they are key aroma compounds of wine and potentially exploitable in the wine industry through specific vinification protocols.

Crop level vs. leaf removal: Effects on Istrian Malvasia wine aroma and phenolic acids composition

The impact of crop level and leaf removal on Istrian Malvasia (Vitis vinifera L.) white wine aroma and phenolic acids composition was studied over two vine-growing seasons. Two crop levels were combined with leaf removal or untreated control in two-factorial design. Crop level showed limited impact on aroma compounds in wine and the concentration of some esters was increased by higher crop level. In contrast, leaf removal increased the concentration of several aroma compounds and especially monoterpenes and esters. The concentration of hydroxycinnamic acids in wine was enhanced only by leaf removal, while no consistent impact of the investigated factors on hydroxybenzoic acids was observed. The obtained results suggest that in cases where environmental conditions are not limiting, increasing the crop level under adequate microclimate in fruit zone has no detrimental effects on white wine aroma and hydroxycinnamic acids composition, potentially leading to economically more sustainable grape production.

The Actual and Potential Aroma of Winemaking Grapes.

This review intends to rationalize the knowledge related to the aroma of grapes and to the aroma of wine with specific origin in molecules formed in grapes. The actual flavor of grapes is formed by the few free aroma molecules already found in the pulp and in the skin, plus by those aroma molecules quickly formed by enzymatic/catalytic reactions. The review covers key aroma components of aromatic grapes, raisins and raisinized grapes, and the aroma components responsible from green and vegetal notes. This knowledge is used to explain the flavor properties of neutral grapes. The aroma potential of grape is the consequence of five different systems/pools of specific aroma precursors that during fermentation and/or aging, release wine varietal aroma. In total, 27 relevant wine aroma compounds can be considered that proceed from grape specific precursors. Some of them are immediately formed during fermentation, while some others require long aging time to accumulate. Precursors are glycosides, glutathionyl and cysteinyl conjugates, and other non-volatile molecules.

Functional Characterization of the Grapevine γ-Glutamyl Transferase/Transpeptidase (E.C. 2.3.2.2) Gene Family Reveals a Single Functional Gene Whose Encoded Protein Product Is Not Located in Either the Vacuole or Apoplast.

γ-glutamyl transferases/transpeptidases (E.C. 2.3.2.2, GGTs) are involved in the catabolism of many compounds that are conjugated to glutathione (GSH), which have a variety of roles. GSH can act as storage and transport vehicle for reduced sulfur; it is involved in the detoxification of xenobiotics and also acts as a redox buffer by utilizing its thiol residue to protect against reactive oxygen species, which accumulate in response to biotic and abiotic stress. Furthermore, many distinctive flavor and aroma compounds in Sauvignon blanc wines originate from odorless C5- and C6-GSH conjugates or their GGT catabolized derivatives. These precursors are then processed into their volatile forms by yeast during fermentation. In many plant species, two or more isoforms of GGTs exist that target GSH-conjugates to either the apoplast or the vacuole. A bioinformatics approach identified multiple GGT candidates in grapevine (Vitis vinifera). However, only a single candidate, VvGGT3, has all the conserved residues needed for GGT activity. This is intriguing given the variety of roles of GSH and GGTs in plant cells. Characterization of VvGGT3 from cv. Sauvignon blanc was then undertaken. The VvGGT3 transcript is present in roots, leaves, inflorescences, and tendril and at equal abundance in the skin, pulp, and seed of mature berries and shows steady accumulation over the course of whole berry development. In addition, the VvGGT3 transcript in whole berries is upregulated upon Botrytis cinerea infection as well as mechanical damage to leaf tissue. VvGGT3-GFP fusion proteins transiently over-expressed in onion cells were used to study subcellular localization. To confirm VvGGT3 activity and localization in vivo, the fluorescent γ-glutamyl-7-amido-4-methylcoumarin substrate was added to Nicotiana benthamiana leaves transiently over-expressing VvGGT3. In combination, these results suggest that the functional VvGGT3 is associated with membrane-like structures. This is not consistent with its closely related functionally characterized GGTs from Arabidopsis, radish and garlic.