Insights into the Uptake, Distribution, and Metabolism of 3-Isobutyl-2-hydroxypyrazine in Grapevine Using a Stable Isotope Tracer.

Methoxypyrazines (MPs) are potent aroma compounds that have been predominately studied in grape berries but can also be detected in other vine tissues. The synthesis of MPs in berries from hydroxypyrazines by VvOMT3 is well established, but the origin of MPs in vine tissues that have negligible VvOMT3 gene expression is unknown. This research gap was addressed through the application of stable isotope tracer 3-isobutyl-2-hydroxy-[2H2]-pyrazine (d2-IBHP) to the roots of Pinot Meunier L1 microvines and high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) quantification of HPs from grapevine tissues following a novel solid-phase extraction method. Four weeks post-application, d2-IBHP and its O-methylated product 3-isobutyl-2-methoxy-[2H2]-pyrazine (d2-IBMP) were present in excised cane, berry, leaf, root, and rachis material. Translocation of d2-IBHP and d2-IBMP was investigated, but results were inconclusive. Nonetheless, knowledge that d2-IBHP, and potentially d2-IBMP, are translocated from roots to other vine organs, including the berries, could provide opportunities for controlling MP accumulation in grapevine tissues pertinent to winemaking.

Methoxypyrazine concentrations in the grape bunch rachis of Vitis vinifera L. Cv Shiraz: Influence of rootstock, region and light.

Vitis vinifera L. cv Shiraz appears unable to synthesise 3-alkyl-2-methoxypyrazines (MPs) in the berry, but can still produce significant concentrations in rachis. MPs are readily extracted from rachis during fermentation, producing Shiraz wines with uncharacteristic "green" flavours. Recently, rootstocks were shown to significantly alter MP concentrations in Cabernet Sauvignon rachis compared to own-rooted varieties, but whether Shiraz followed a similar trend required investigation. This study considered the effect of thirteen rootstocks on the concentrations of 3-isobutyl-2-methoxypyrazine (IBMP), 3-isopropyl-2-methoxypyrazine (IPMP), and 3-sec-butyl-2-methoxypyrazine (SBMP) in the rachis of Shiraz bunches sampled during multiple vintages across several Australian growing regions. Although IBMP was the most abundant, all measured MP concentrations were significantly affected by vintage, rootstock, and region. In addition, vine vigour showed positive correlations with IBMP, which were attributed to changes in canopy coverage impacting rachis light exposure. This hypothesis was explored with light exclusion trials, which significantly increased rachis IBMP concentrations.

Impact of accentuated cut edges, yeast strain, and malolactic fermentation on chemical and sensory profiles of Sauvignon blanc wine.

This pioneering investigation involved the application of accentuated cut edges (ACE) technique to Sauvignon blanc winemaking. The concentration of varietal thiol precursors in juice was significantly higher for ACE treatment compared to conventional crushing, with two-way or three-way interactions of the experimental factors, which included yeast strain and malolactic fermentation, being determined from the wine data. ACE yielded higher concentrations of 4-methyl-4-sulfanylpentan-2-one (4-MSP) and enantiomers of 3-sulfanylhexanol (3-SH) and 3-sulfanylhexyl acetate (3-SHA) in wines that were more abundant in phenolic compounds. Compared to Sauvy yeast strain, VIN13 produced greater amounts of 3-SH and 3-SHA but less 4-MSP with wines exhibiting lower intensity 'floral' and 'fruity' notes. MLF increased 3-SH and 4-MSP concentrations and led to wines that exhibited more non-fruity sensory attributes. The study revealed the potential of ACE for increasing varietal thiol concentrations in Sauvignon blanc wine and altering overall sensory profiles, with interactions involving yeast strain and MLF.

Chemical and Sensory Profiles of Sauvignon Blanc Wine Following Protein Stabilization Using a Combined Ultrafiltration/Heat/Protease Treatment.

Ultrafiltration (UF) was evaluated as a process by which proteins can be selectively removed from white wine as an alternative approach to protein stabilization than traditional bentonite fining. Unfined Sauvignon Blanc wine (50 L) was fractionated by UF and the retentate stabilized either by heat and/or protease treatment or bentonite fining before being recombined with the permeate. The heat stability of recombined wine was significantly improved when retentate was heated following protease (Aspergillopepsin) addition and subsequently stabilized by bentonite treatment. The combined UF/heat/protease treatment removed 59% of protein and reduced the quantity of bentonite needed to achieve protein stability by 72%, relative to bentonite treatment alone. This innovative approach to protein stabilization had no significant impact on wine quality or sensory characteristics, affording industry greater confidence in adopting this technology as a novel approach to achieving protein stability.

Impact of Lachancea thermotolerans on Chemical Composition and Sensory Profiles of Viognier Wines.

Viognier is a warm climate grape variety prone to loss of acidity and accumulation of excessive sugars. The yeast Lachancea thermotolerans can improve the stability and balance of such wines due to the partial conversion of sugars to lactic acid during alcoholic fermentation. This study compared the performance of five L. thermotolerans strains in co-inoculations and sequential inoculations with Saccharomyces cerevisiae in high sugar/pH Viognier fermentations. The results highlighted the dichotomy between the non-acidified and the bio-acidified L. thermotolerans treatments, with either comparable or up to 0.5 units lower pH relative to the S. cerevisiae control. Significant differences were detected in a range of flavour-active yeast volatile metabolites. The perceived acidity mirrored the modulations in wine pH/TA, as confirmed via "Rate-All-That-Apply" sensory analysis. Despite major variations in the volatile composition and acidity alike, the varietal aromatic expression (i.e., stone fruit aroma/flavour) remained conserved between the treatments.

Rootstock, Vine Vigor, and Light Mediate Methoxypyrazine Concentrations in the Grape Bunch Rachis of Vitis vinifera L. cv. Cabernet Sauvignon.

Ramsey rootstock has previously been implicated in an approximate 8-fold increase of 3-isobutyl-2-methoxypyrazine (IBMP) levels in the rachis (grape bunch stem) of Vitis vinifera L. cv. Shiraz scions over own-rooted Shiraz vines at harvest. IBMP extracted from rachis during red wine fermentation can contribute potent "green" flavors. Methoxypyrazines (MPs) are normally present in Cabernet Sauvignon grapes, rachis, and wines, but it is unknown whether rootstocks can influence the MP concentration in the rachis. This study considered the effect of eight rootstocks including Ramsey and own roots on the concentrations of IBMP, 3-isopropyl-2-methoxypyrazine (IPMP), and 3-sec-butyl-2-methoxypyrazine (SBMP) in the rachis and grapes of Cabernet Sauvignon over two seasons. IBMP predominated, and its concentration in rachis and berries at harvest was significantly affected by rootstock and growing season. In the 2020 vintage, light exclusion, vine vigor, and spatial variation in vine vigor were shown to significantly affect MP concentrations in rachis.

Consumer perspectives of wine typicity and impact of region information on the sensory perception of Cabernet Sauvignon wines.

Region of origin is used in marketing of wine and by consumers as a wine quality indicator. To better understand wine consumers' purchase decisions, sensory perception, and wine liking in connection with wine provenance, this study used regular wine consumers (n = 112) to evaluate two Cabernet Sauvignon wines from each of four wine producing regions through hedonic rating and rate-all-that-apply (RATA) testing in conjunction with pre- and post-tasting questionnaires. The majority of consumers rated the region of origin stated on the label as important for purchase intent and for deciding the price they were willing to pay for a wine. The questionnaire also revealed that consumers were familiar with the wine typicity concept, but seemed to consider it only as an extrinsic characteristic rather than an intrinsic aspect of the wine. By randomly dividing the consumers into two groups (n = 56 each), one having information on the origin of samples and the other tasting without such knowledge, it was demonstrated that origin information had a positive impact on hedonic scores. Sensory profiling revealed that origin information did not impact the sample sensory characterisation, and liking for both groups was related to 'full body', 'jammy', and 'dark fruits' attributes. Some regional profile features were apparent for the samples, such as 'minty' for Coonawarra and savoury attributes for Bordeaux. Overall, this work highlighted that consumers could differentiate wines from distinct regions on the basis of sensory characteristics.

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.

A Review of Wine Authentication Using Spectroscopic Approaches in Combination with Chemometrics.

In a global context where trading of wines involves considerable economic value, the requirement to guarantee wine authenticity can never be underestimated. With the ever-increasing advancements in analytical platforms, research into spectroscopic methods is thriving as they offer a powerful tool for rapid wine authentication. In particular, spectroscopic techniques have been identified as a user-friendly and economical alternative to traditional analyses involving more complex instrumentation that may not readily be deployable in an industry setting. Chemometrics plays an indispensable role in the interpretation and modelling of spectral data and is frequently used in conjunction with spectroscopy for sample classification. Considering the variety of available techniques under the banner of spectroscopy, this review aims to provide an update on the most popular spectroscopic approaches and chemometric data analysis procedures that are applicable to wine authentication.

Spectrofluorometric analysis combined with machine learning for geographical and varietal authentication, and prediction of phenolic compound concentrations in red wine.

Fluorescence spectroscopy is rapid, straightforward, selective, and sensitive, and can provide the molecular fingerprint of a sample based on the presence of various fluorophores. In conjunction with chemometrics, fluorescence techniques have been applied to the analysis and classification of an array of products of agricultural origin. Recognising that fluorescence spectroscopy offered a promising method for wine authentication, this study investigated the unique use of an absorbance-transmission and fluorescence excitation emission matrix (A-TEEM) technique for classification of red wines with respect to variety and geographical origin. Multi-block data analysis of A-TEEM data with extreme gradient boosting discriminant analysis yielded an unrivalled 100% and 99.7% correct class assignment for variety and region of origin, respectively. Prediction of phenolic compound concentrations with A-TEEM based on multivariate calibration models using HPLC reference data was also highly effective, and overall, the A-TEEM technique was shown to be a powerful tool for wine classification and analysis.

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

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

Authentication of the geographical origin of Australian Cabernet Sauvignon wines using spectrofluorometric and multi-element analyses with multivariate statistical modelling.

With the increased risk of wine fraud, a rapid and simple method for wine authentication has become a necessity for the global wine industry. The use of fluorescence data from an absorbance and transmission excitation-emission matrix (A-TEEM) technique for discrimination of wines according to geographical origin was investigated in comparison to inductively coupled plasma-mass spectrometry (ICP-MS). The two approaches were applied to commercial Cabernet Sauvignon wines from vintage 2015 originating from three wine regions of Australia, along with Bordeaux, France. Extreme gradient boosting discriminant analysis (XGBDA) was examined among other multivariate algorithms for classification of wines. Models were cross-validated and performance was described in terms of sensitivity, specificity, and accuracy. XGBDA classification afforded 100% correct class assignment for all tested regions using the EEM of each sample, and overall 97.7% for ICP-MS. The novel combination of A-TEEM and XGBDA was found to have great potential for accurate authentication of wines.

Sensory typicity of regional Australian Cabernet Sauvignon wines according to expert evaluations and descriptive analysis.

The concept of wine typicity has been an important tool for the international wine trade, and especially for Old World wine producing countries, where provenance criteria are regulated and act as a quality indicator. Provenance in Australia is governed by Geographical Indications, for which typicity should also be evident in terms of regional sensory profiles of wine from a given grape cultivar. Two approaches were used to identify sensory drivers for regional typicity of commercial Cabernet Sauvignon wines from three Australian regions, namely Coonawarra, Margaret River, and Yarra Valley. Cabernet Sauvignon-dominant wines from Bordeaux were also assessed for benchmarking purposes. A set of 84 wines underwent a sorting task and rate-all-that-apply (RATA) analysis of the sorted groups with an expert panel. Agglomerative hierarchical clustering of the sorting task data did not show a clear regional driver upon separating the samples into four main clusters, although certain sensory traits could be associated with the different clusters. On the other hand, canonical variate analysis (CVA) of the group-RATA results indicated several sensory drivers for the separation between the regions, such as 'mint' and 'dark fruits' being important for Coonawarra wine profiles, 'floral' and 'green pepper' for Margaret River, 'stemmy' for Yarra Valley, and 'barnyard' and 'savoury' differentiating Bordeaux wines from the other regions. A subset (n = 52) of wines was selected for further evaluation by descriptive analysis with a trained panel. Statistical evaluation with CVA revealed similar results to the expert evaluation, with Bordeaux wines showing more dissimilarity when compared to Australian regions, and having 'savoury' and 'earthy' as significant characters. The results also demonstrated that 'mint' and 'Mallee leaf' were relevant characters for Coonawarra regional sensory profile, 'violets' and 'red fruits' for Margaret River, and 'cooked vegetables' for Yarra Valley. Analysing both data sets (expert RATA and DA) revealed some agreement between the sets of results for attributes such as 'mint', 'cooked vegetables', 'floral', green-related characters, and oak characters like 'vanilla' and 'chocolate'. Overall, experts and trained panellists were able to distinguish regions based on a few characteristic sensory traits.

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

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

Sensory and Chemical Drivers of Wine Consumers' Preference for a New Shiraz Wine Product Containing Ganoderma lucidum Extract as a Novel Ingredient.

This study explored wine consumers' preferences towards a novel Australian Shiraz wine product containing Ganoderma lucidum (GL). Wine consumers (n = 124) were asked to complete a questionnaire and participate in a blind tasting of six GL wine products (differing in the amount and timing of GL extract additions). Based on individual liking scores for each GL wine product that was tasted, four hedonic clusters C1 (n = 44, preferred control and low levels of GL additions), C2 (n = 28, preferred control only), C3 (n = 26, generally preferred all GL additions) and C4 (n = 26, preferred 1 g/L additions and 4 g/L post-fermentation) were identified. Sensory attributes of the GL wine products were also profiled with rate-all-that-apply (n = 65) and the 31 sensory attributes that significantly differentiated the wines underwent principal component analysis with the hedonic clusters overlaid to explain consumers' preferences. There was a clear separation between hedonic clusters. Sensory attributes and volatile flavor compounds that significantly differentiated the wines were subjected to partial least squares regression, which indicated the important positive drivers of liking among the hedonic clusters. Pepper and jammy aroma, 3-methylbutanoic acid (linked to fruity notes) and non-fruit aftertaste positively drove C2's preference, whereas spice flavor and hexanoic acid (known for leafy and woody descriptors) drove C3's liking. There were no positive drivers for C1's liking but bitter taste, cooked vegetable, and toasty aromas drove this cluster' dislike. C4 preferred brown appearance, tobacco aroma, and jammy and cooked vegetable flavors. These findings provide the wine industry with deeper insights into consumers' liking towards new GL wine products targeted at the Australasian market.

Using Content Analysis to Characterise the Sensory Typicity and Quality Judgements of Australian Cabernet Sauvignon Wines.

Understanding the sensory attributes that explain the typicity of Australian Cabernet Sauvignon wines is essential for increasing value and growth of Australia's reputation as a fine wine producer. Content analysis of 2598 web-based wine reviews from well-known wine writers, including tasting notes and scores, was used to gather information about the regional profiles of Australian Cabernet Sauvignon wines and to create selection criteria for further wine studies. In addition, a wine expert panel evaluated 84 commercial Cabernet Sauvignon wines from Coonawarra, Margaret River, Yarra Valley and Bordeaux, using freely chosen descriptions and overall quality scores. Using content analysis software, a sensory lexicon of descriptor categories was built and frequencies of each category for each region were computed. Distinction between the sensory profiles of the regions was achieved by correspondence analysis (CA) using online review and expert panellist data. Wine quality scores obtained from reviews and experts were converted into Australian wine show medal categories. CA of assigned medal and descriptor frequencies revealed the sensory attributes that appeared to drive medal-winning wines. Multiple factor analysis of frequencies from the reviews and expert panellists indicated agreement about descriptors that were associated with wines of low and high quality, with greater alignment at the lower end of the wine quality assessment scale.

Volatile Composition and Sensory Profiles of a Shiraz Wine Product Made with Pre- and Post-Fermentation Additions of Ganoderma lucidum Extract.

Novel Shiraz red wine products enriched with Ganoderma lucidum (GL) extract, a traditional Asian medicinal mushroom, were developed and characterized. GL extract was added at different levels prior to and after primary fermentation to investigate its impact on the juice fermentation kinetics, and the chemical composition and sensory properties of the resulting wines. The fermentation kinetics of red grape juice were not significantly different between ferments. Basic chemical analyses plus headspace solid-phase micro-extraction (HS-SPME), gas chromatography‒mass spectrometry (GC-MS), and a rate-all-that-apply (RATA) (n = 65) sensory panel were used to investigate the influence of GL extract additions on wine composition and sensory characteristics. Of the 54 sensory attributes assessed, 39 significantly differentiated the wines. A clear separation between GL wine treatments was evident with PLS regression, where specific volatiles were correlated with relevant sensory attributes that dominated the wines. These products could be promising for emerging wine markets.

Analysis of Potent Odour-Active Volatile Thiols in Foods and Beverages with a Focus on Wine.

Certain volatile thiols are some of the most potent odour-active molecules that are found in nature. Thiols play significant roles in the aroma qualities of a range of foods and beverages, including wine, with extremely low odour detection thresholds (nanogram per litre range). A fundamental understanding of their formation, fate, and impact essentially depends on the development of suitable analytical methods. The analysis of volatile thiols in foods and beverages is a challenging task when considering (1) the complexity of food and beverage matrices and (2) that thiols are highly reactive, low molecular-weight volatiles that are generally present at trace to ultra-trace concentrations. For the past three decades, the analytical evaluation of volatile thiols has been intensively performed in various foods and beverages, and many novel techniques related to derivatisation, isolation, separation, and detection have been developed, particularly by wine researchers. This review aims to provide an up-to-date overview of the major analytical methodologies that are proposed for potent volatile thiol analysis in wine, foods, and other beverages. The analytical challenges for thiol analysis in foods and beverages are outlined, and the main analytical methods and recent advances in methodology are summarised and evaluated for their strengths and limitations. The key analytical aspects reviewed include derivatisation and sample preparation techniques, chromatographic separation, mass spectrometric detection, matrix effects, and quantitative analysis. In addition, future perspectives on volatile thiol research are also suggested.

Investigation of intraregional variation, grape amino acids, and pre-fermentation freezing on varietal thiols and their precursors for Vitis vinifera Sauvignon blanc.

Sauvignon blanc grape samples (n = 21) from across a single Geographical Indication of South Australia were analysed for thiol precursors and amino acids, and fermented in an identical laboratory-scale fermentation trial to investigate the intraregional pattern of varietal thiols in the wines. Precursors and thiols exhibited obvious intraregional diversity, and notably, stronger correlations were observed between a number of amino acids and thiol precursors (especially with glutamic acid, r ≤ -0.73) rather than free thiols. Additionally, pre-fermentation freezing (-20 °C, 1 month) was applied to five selected fresh grape samples and their juices, followed by identical fermentation. In comparison to wines from fresh grapes or frozen juices, significant elevation of varietal thiols (up to 10-fold) occurred in the wines derived from frozen grapes, with parallel increases of precursors (up to 19-fold) in juices from frozen berries. These novel results may lead to new strategies for thiol enhancement during winemaking.

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

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