Within-Vineyard, Within-Vine, and Within-Bunch Variability of the Rotundone Concentration in Berries of Vitis vinifera L. cv. Shiraz

Assessment of Variability Sources in Grape Ripening Parameters by Using FTIR and Multivariate Modelling

The variability in grape ripening is associated with the fact that each grape berry undergoes its own biochemical processes. Traditional viticulture manages this by averaging the physicochemical values of hundreds of grapes to make decisions. However, to obtain accurate results it is necessary to evaluate the different sources of variability, so exhaustive sampling is essential. In this article, the factors "grape maturity over time" and "position of the grape" (both in the grapevine and in the bunch/cluster) were considered and studied by analyzing the grapes with a portable ATR-FTIR instrument and evaluating the spectra obtained with ANOVA-simultaneous component analysis (ASCA). Ripeness over time was the main factor affecting the characteristics of the grapes. Position in the vine and in the bunch (in that order) were also significantly important, and their effect on the grapes evolves over time. In addition, it was also possible to predict basic oenological parameters (TSS and pH with errors of 0.3 °Brix and 0.7, respectively). Finally, a quality control chart was built based on the spectra obtained in the optimal state of ripening, which could be used to decide which grapes are suitable for harvest.

Diversity and dynamics of fungi during spontaneous fermentations and association with unique aroma profiles in wine

Microbial ecology is an integral part of an agricultural ecosystem and influences the quality of agricultural commodities. Microbial activity influences grapevine health and crop production, conversion of sugar to ethanol during fermentation, thus forming wine aroma and flavour. There are regionally differentiated microbial patterns in grapevines and must but how microbial patterns contribute to wine regional distinctiveness (terroir) at small scale (<100 km) is not well defined. Here we characterise fungal communities, yeast populations, and Saccharomyces cerevisiae populations during spontaneous fermentation using metagenomics and population genetics to investigate microbial distribution and fungal contributions to the resultant wine. We found differentiation of fungi, yeasts, and S. cerevisiae between geographic origins (estate/vineyard), with influences from the grape variety. Growth and dominance of S. cerevisiae during fermentation reshaped the fungal community and showed geographic structure at the strain level. Associations between fungal microbiota diversity and wine chemicals suggest that S. cerevisiae plays a primary role in determining wine aroma profiles at a sub-regional scale. The geographic distribution at scales of less than 12 km supports that differential microbial communities, including the dominant fermentative yeast S. cerevisiae can be distinct in a local setting. These findings provide further evidence for microbial contributions to wine terroir, and perspectives for sustainable agricultural practices to maintain microbial diversity and optimise fermentation function to craft beverage quality.

The Fungal Microbiome Is an Important Component of Vineyard Ecosystems and Correlates with Regional Distinctiveness of Wine

The composition of soil has long been thought to provide wine with characteristic regional flavors. Here, we show that for vineyards in southern Australia, the soil fungal communities are of primary importance for the aromas found in wines. We propose a mechanism by which fungi can move from the soil through the vine.

The flavors of fermented plant foods and beverages are formed by microorganisms, and in the case of wine, the location and environmental features of the vineyard site also imprint the wine with distinctive aromas and flavors. Microbial growth and metabolism play an integral role in wine production, by influencing grapevine health, wine fermentation, and the flavor, aroma, and quality of finished wines. The contributions by which microbial distribution patterns drive wine metabolites are unclear, and while flavor has been correlated with fungal and bacterial composition for wine, bacterial activity provides fewer sensorially active biochemical conversions than fungi in wine fermentation. Here, we collected samples across six distinct wine-growing areas in southern Australia to investigate regional distribution patterns of fungi and bacteria and the association with wine chemical composition. Results show that both soil and must microbiota distinguish wine-growing regions. We found a relationship between microbial and wine metabolic profiles under different environmental conditions, in particular measures of soil properties and weather. Fungal communities are associated with wine regional distinctiveness. We found that the soil microbiome is a source of grape- and must-associated fungi and suggest that weather and soil could influence wine characteristics via the soil fungal community. Our report describes a comprehensive scenario of wine microbial biogeography where microbial diversity responds to the surrounding environment and correlates with wine composition and regional characteristics. These findings provide perspectives for thoughtful human practices to optimize food composition through understanding fungal activity and abundance.

IMPORTANCE The composition of soil has long been thought to provide wine with characteristic regional flavors. Here, we show that for vineyards in southern Australia, the soil fungal communities are of primary importance for the aromas found in wines. We propose a mechanism by which fungi can move from the soil through the vine.

A Digital Approach to Evaluate the Effect of Berry Cell Death on Pinot Noir Wines’ Quality Traits and Sensory Profiles Using Non-Destructive Near-Infrared Spectroscopy

Berry cell death (BCD) is linked to the development of flavors and aromas in berries and wine. The BCD pattern and rate within a growing season start at around 90–100 days after anthesis (DAA), and the rate until harvest depends on environmental factors. This study assessed the BCD effects on berry and wine composition from a boutique commercial vineyard in Victoria, Australia, using fluorescent imaging. Results showed differences in wine sensory profiles from the two blocks studied, mainly related to variations in BCD, due to differences in altitude between blocks. Furthermore, two machine learning (ML) models were constructed using near-infrared spectroscopy (NIR) measurements from full berries as inputs and living tissue (LT) and dead tissue (DT) from berries as targets (Model 1). Model 2 was developed using Brix, LT, DT from the east and west sides of canopies as inputs and using 19 sensory descriptors from wines as targets. High correlation and performances were achieved for both models without signs of overfitting (R = 0.94 and R = 0.80, respectively). These models could be used for decision-making purposes as an objective and comprehensive berry maturity assessment obtained in a non-destructive, accurate, and in a real-time fashion close to harvest, to secure specific wine styles.

Grape terpenoids: flavor importance, genetic regulation, and future potential

Terpenes significantly affect the flavor and quality of grapes and wine. This review summarizes recent research on terpenoids with regard to grape wine. Although, the grapevine terpene synthase gene family is the largest identified, genetic modifications involving terpenes to improve wine flavor have received little attention. Key enzyme modulation alters metabolite production. Over the last decade, the heterologous manipulation of grape glycosidase has been used to alter terpenoids, and cytochrome P450s may affect terpene synthesis. Metabolic and genetic engineering can further modify terpenoid metabolism, while using transgenic grapevines (trait transfer to the plant) could yield more flavorful wine. We also discuss traits involved in wine aroma quality, and the strategies that can be used to improve grapevine breeding technology.

Characterization of Guaiene Synthases from Stellera chamaejasme L. Flowers and Their Application in De novo Production of (-)-Rotundone in Yeast

Four terpene synthases for the biosynthesis of volatile terpenoids were identified from the transcriptome of Stellera chamaejasme L. flowers, including SchTPS1, SchTPS2, SchTPS3, and SchTPS4. Their functions were characterized by synthetic biology approaches in Escherichia coli and in vitro enzymatic assays. SchTPS1, SchTPS2, and SchTPS3 are guaiene synthases, while SchTPS4 is an (E,E)-geranyl linalool synthase. Next, SchTPS1 and α-guaiene 2-oxidase VvSTO2 were co-expressed in Saccharomyces cerevisiae to reconstruct the biosynthetic pathway of (-)-rotundone, which is a unique aroma compound in fruits, vegetables, and wines. This is the first report for the construction of a (-)-rotundone-producing microbial platform.

A sense of place: transcriptomics identifies environmental signatures in Cabernet Sauvignon berry skins in the late stages of ripening

BACKGROUND

Grape berry ripening is influenced by climate, the main component of the "terroir" of a place. Light and temperature are major factors in the vineyard that affect berry development and fruit metabolite composition.

RESULTS

To better understand the effect of "place" on transcript abundance during the late stages of berry ripening, Cabernet Sauvignon berries grown in Bordeaux and Reno were compared at similar sugar levels (19 to 26 °Brix (total soluble solids)). Day temperatures were warmer and night temperatures were cooler in Reno. °Brix was lower in Bordeaux berries compared to Reno at maturity levels considered optimum for harvest. RNA-Seq analysis identified 5528 differentially expressed genes between Bordeaux and Reno grape skins at 22°Brix. Weighted Gene Coexpression Network Analysis for all expressed transcripts for all four °Brix levels measured indicated that the majority (75%) of transcript expression differed significantly between the two locations. Top gene ontology categories for the common transcript sets were translation, photosynthesis, DNA metabolism and catabolism. Top gene ontology categories for the differentially expressed genes at 22°Brix involved response to stimulus, biosynthesis and response to stress. Some differentially expressed genes encoded terpene synthases, cell wall enzymes, kinases, transporters, transcription factors and photoreceptors. Most circadian clock genes had higher transcript abundance in Bordeaux. Bordeaux berries had higher transcript abundance with differentially expressed genes associated with seed dormancy, light, auxin, ethylene signaling, powdery mildew infection, phenylpropanoid, carotenoid and terpenoid metabolism, whereas Reno berries were enriched with differentially expressed genes involved in water deprivation, cold response, ABA signaling and iron homeostasis.

CONCLUSIONS

Transcript abundance profiles in the berry skins at maturity were highly dynamic. RNA-Seq analysis identified a smaller (25% of total) common core set of ripening genes that appear not to depend on rootstock, vineyard management, plant age, soil and climatic conditions. Much of the gene expression differed between the two locations and could be associated with multiple differences in environmental conditions that may have affected the berries in the two locations; some of these genes may be potentially controlled in different ways by the vinegrower to adjust final berry composition and reach a desired result.

Sesquiterpenes in grapes and wines: Occurrence, biosynthesis, functionality, and influence of winemaking processes

Grapes are an important global horticultural product, and are mainly used for winemaking. Typically, grapes and wines are rich in various phytochemicals, including phenolics, terpenes, pyrazines, and benzenoids, with different compounds responsible for different nutritional and sensory properties. Among these compounds, sesquiterpenes, a subcategory of the terpenes, are attracting increasing interest as they affect aroma and have potential health benefits. The characteristics of sesquiterpenes in grapes and wines in terms of classification, biosynthesis pathway, and active functions have not been extensively reviewed. This paper summarizes 97 different sesquiterpenes reported in grapes and wines and reviews their biosynthesis pathways and relevant bio-regulation mechanisms. This review further discusses the functionalities of these sesquiterpenes including their aroma contribution to grapes and wines and potential health benefits, as well as how winemaking processes affect sesquiterpene concentrations.

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.

Modeling the Impacts of Weather and Cultural Factors on Rotundone Concentration in Cool-Climate Noiret Wine Grapes

The sesquiterpenoid rotundone is the compound responsible for the "black pepper" aroma of many plant species, including several economically important wine grape varieties. Since its identification in wine in 2008, there has been an increased interest in understanding how individual climatic or cultural factors affect the accumulation of rotundone in grapes and subsequently the level of wine "pepperiness." However, no study has assessed climatic and viticultural factors together to identify which variables have the strongest influence on rotundone accumulation. Our study aimed to fill this knowledge gap by developing a predictive model that identified factors that explain rotundone concentrations in Noiret (Vitis sp.) grapes at harvest. Over the 2016 and 2017 seasons, we measured 21 viticultural, meso- and microclimatic variables and concentrations of rotundone in Noiret wine grapes at seven vineyards in the northeastern U.S. Vineyard growing degree days (GDD _v ) and the amount of solar radiation (cumulative solar exposure; CSE_v) accumulated from the beginning of fruit ripening to harvest were the variables best correlated (r = 0.70 and r = 0.74, respectively) with rotundone concentrations. Linear correlations between microclimatic parameters and rotundone concentrations were weaker, but overall rotundone was negatively correlated with low (<15°C) and high (>30°C) berry temperatures. Using the 2-year data set we were able to develop a four-variable model which explained more than 80% of the variation in rotundone concentration at harvest. The model included weather [growing degree days during fruit ripening (GDD _v )] and plant-related variables (concentrations of phosphorus and calcium in the leaf petiole, and crop load). The model we developed could be used by wine producers to identify sites or cultural practices that favor rotundone accumulation in Noiret grapes after performing a model validation with an additional, external data set. More broadly, the statistical approach used here could be applied to other studies that also seek to assess the effects of multiple factors on a variable of interest under varying environmental conditions.

Free terpene evolution during the berry maturation of five Vitis vinifera L. cultivars

Terpenes and their derivatives, terpenoids, are important biomarkers of grape quality as they contribute to flavor and aroma of grape and wine. The evolution of terpene and terpenoids throughout grapevine phenological development cycles is not well understood. The current study investigated the volatile profiles of free terpene and terpenoid of five widely grown Vitis vinifera L. cultivars (Shiraz, Cabernet Sauvignon, Riesling, Chardonnay and Pinot Gris), at different phenological stages from fruit-set to harvest. 17 Monoterpenoids, 3 norisoprenoid and 13 sesquiterpenoids were identified and quantified. Discriminant analysis revealed that for each grape cultivar, free terpene profiles at different E-L stages were distinctive. When integrating total sugar, total terpenes and the cumulated heat index, it could be found that flavor ripening was more consistent with sugar ripening in the warmer vintage 2016. Comparing the two red wine varieties, the overall development patterns of total monoterpenes, norisoprenoids and sesquiterpenes were similar.

Tracking polysaccharides during white winemaking using glycan microarrays reveals glycoprotein-rich sediments

Winemaking results in a significant amount of sediments that are formed in the tanks, the vats and in the bottles before and after fermentation. Little is known about the biochemical composition of these sediments apart from the fact that they are assumed to be derived in large part from the grape matrix. Glycan microarray technology offers a relatively rapid means to track the polysaccharides from their origin in the grape material and throughout the various steps in the winemaking process. In this study Comprehensive Microarray Polymer Profiling (CoMPP) was used to investigate the glycan-rich composition of particularly white grapes during winemaking and then investigate the effects of recombinant and commercial enzyme formulations on wine sediment compositions. The gross lees or sediments produced in the absence of enzymes were found to be composed of an abundance of homogalacturonans, rhamnogalacturonans, arabinans and galactans in addition to an abundance of extensins and arabinogalactan proteins. The addition of enzymes was shown to strip off the homogalacturonan and much of the rhamnogalacturonan with its side chains revealing a sediment layer composed almost exclusively of extensins and arabinogalactan proteins. The effect of winemaking techniques was shown to have an effect on the glycan-rich wine sediment compositions and holds implications for the management of gross lees in a winery environment.

Deconstructing Wine Grape Cell Walls with Enzymes During Winemaking: New Insights from Glycan Microarray Technology

Enzyme-aid maceration is carried out in most modern winemaking industries with a range of positive impacts on wine production. However, inconsistencies in enzyme efficiency are an issue complicated by unclear targets (limited information available on berry cell wall architecture of different cultivars) and the complex wine environment (i.e., fermenting must). Recent studies have been performed to develop a clearer picture of grape cell wall structures, maceration effects, and interactions between important wine compounds and grape-derived polysaccharides. This review highlights critically important recent studies on grape berry cell wall changes during ripening, the importance of enzymes during maceration (skin contact phase) and deconstruction processes that occur during alcoholic fermentation. The novelty of the Comprehensive Microarray Polymer Profiling (CoMPP) technique using cell wall probes (e.g., antibodies) as a method for following cell wall derived polymers during different biological and biotechnological processes is discussed. Recent studies, using CoMPP together with classical analytical methods, confirmed the developmental pattern of berry cell wall changes (at the polymer level) during grape ripening. This innovative technique were also used to track enzyme-assisted depectination of grape skins during wine fermentation and determine how this influence the release of wine favourable compounds. Furthermore, polysaccharides (e.g., arabinogalactan proteins) present in the final wine could be identified. Overall, CoMPP provides a much more enriched series of datasets compared to traditional approaches. Novel insights and future studies investigating grape cell wall and polyphenol interactions, and the tailoring of enzyme cocktails for consistent, effective and "customized" winemaking is advanced and discussed.

The Influence of Apical and Basal Defoliation on the Canopy Structure and Biochemical Composition of Vitis vinifera cv. Shiraz Grapes and Wine

Defoliation is a commonly used viticultural technique to balance the ratio between grapevine vegetation and fruit. Defoliation is conducted around the fruit zone to reduce the leaf photosynthetic area, and to increase sunlight exposure of grape bunches. Apical leaf removal is not commonly practiced, and therefore its influence on canopy structure and resultant wine aroma is not well-studied. This study quantified the influences of apical and basal defoliation on canopy structure parameters using canopy cover photography and computer vision algorithms. The influence of canopy structure changes on the chemical compositions of grapes and wines was investigated over two vintages (2010-2011 and 2015-2016) in Yarra Valley, Australia. The Shiraz grapevines were subjected to five different treatments: no leaf removal (Ctrl); basal (TB) and apical (TD) leaf removal at veraison and intermediate ripeness, respectively. Basal leaf removal significantly reduced the leaf area index and foliage cover and increased canopy porosity, while apical leaf removal had limited influences on canopy parameters. However, the latter tended to result in lower alcohol level in the finished wine. Statistically significant increases in pH and decreases in TA was observed in shaded grapes, while no significant changes in the color profile and volatile compounds of the resultant wine were found. These results suggest that apical leaf removal is an effective method to reduce wine alcohol concentration with minimal influences on wine composition.

Identification and Characterization of 3-epi-Rotundone, a Novel Stereoisomer of Rotundone, in Several Kinds of Fruits

A novel stereoisomer of rotundone, 3-epi-rotundone, was identified in the aroma of grapefruit, orange, apple, and mango. 3-epi-Rotundone was prepared by the isomerization of rotundone, and its structural elucidation was confirmed by comparing the 1D and 2D nuclear magnetic resonance and nuclear Overhauser effect spectroscopy spectra with those of rotundone. The odor thresholds of rotundone and 3-epi-rotundone in water were determined by a triangle test as 5 and 19100 ng/kg, respectively. The odor of 3-epi-rotundone was evaluated as woody, spicy, peppery, citrus, grapefruit-like, powdery, and celery-like, which was a greater range of odor characteristics than that for rotundone. Results of odor evaluation of 3-epi-rotundone revealed that its unique organoleptic properties, which were odor description (woody, spicy, and peppery), anosmic properties in neat form, and strong adaptation, were similar to those of rotundone. 3-epi-Rotundone might be a valuable substance to apply new types of woody, peppery, and spicy notes.

Quantitation of Rotundone in Grapefruit (Citrus paradisi) Peel and Juice by Stable Isotope Dilution Assay

Aroma extract dilution analyses of the aromas of peels and juices of white and pink grapefruits revealed that rotundone, responsible for peppery, spicy, and woody odors, was detected for the first time at high flavor dilution factors of 256-1024. In both juices, rotundone was detected at the highest flavor dilution factor of 1024. Rotundone in grapefruits was quantitated by a stable isotope dilution assay with a newly synthesized deuterium-labeled internal standard, rotundone-d_2,3: its levels were 2180 and 1920 ng/kg in white and pink grapefruit peels and 29.6 and 49.8 ng/kg in white and pink grapefruit juices, respectively. On the basis of these results, sensory analysis was performed to assess the effects of rotundone on a white grapefruit juice aroma reconstitute. This sensory analysis revealed that rotundone does not impart a woody odor or affect any of the existing attributes, but increases various attributes, thus confirming that rotundone is indispensable for the aroma of grapefruit juice.

Sunlight Modulates Fruit Metabolic Profile and Shapes the Spatial Pattern of Compound Accumulation within the Grape Cluster

Vineyards are characterized by their large spatial variability of solar irradiance (SI) and temperature, known to effectively modulate grape metabolism. To explore the role of sunlight in shaping fruit composition and cluster uniformity, we studied the spatial pattern of incoming irradiance, fruit temperature and metabolic profile within individual grape clusters under three levels of sunlight exposure. The experiment was conducted in a vineyard of Cabernet Sauvignon cv. located in the Negev Highlands, Israel, where excess SI and midday temperatures are known to degrade grape quality. Filtering SI lowered the surface temperature of exposed fruits and increased the uniformity of irradiance and temperature in the cluster zone. SI affected the overall levels and patterns of accumulation of sugars, organic acids, amino acids and phenylpropanoids, across the grape cluster. Increased exposure to sunlight was associated with lower accumulation levels of malate, aspartate, and maleate but with higher levels of valine, leucine, and serine, in addition to the stress-related proline and GABA. Flavan-3-ols metabolites showed a negative response to SI, whereas flavonols were highly induced. The overall levels of anthocyanins decreased with increased sunlight exposure; however, a hierarchical cluster analysis revealed that the members of this family were grouped into three distinct accumulation patterns, with malvidin anthocyanins and cyanidin-glucoside showing contrasting trends. The flavonol-glucosides, quercetin and kaempferol, exhibited a logarithmic response to SI, leading to improved cluster uniformity under high-light conditions. Comparing the within-cluster variability of metabolite accumulation highlighted the stability of sugars, flavan-3-ols, and cinnamic acid metabolites to SI, in contrast to the plasticity of flavonols. A correlation-based network analysis revealed that extended exposure to SI modified metabolic coordination, increasing the number of negative correlations between metabolites in both pulp and skin. This integrated study of micrometeorology and metabolomics provided insights into the grape-cluster pattern of accumulation of 70 primary and secondary metabolites as a function of spatial variations in SI. Studying compound-specific responses against an extended gradient of quantified conditions improved our knowledge regarding the modulation of berry metabolism by SI, with the aim of using sunlight regulation to accurately modulate fruit composition in warm and arid/semi-arid regions.

Distribution of Rotundone and Possible Translocation of Related Compounds Amongst Grapevine Tissues in Vitis vinifera L. cv. Shiraz

Rotundone is an attractive wine aroma compound, especially important for cool climate Shiraz. Its presence in wine is mainly from the grape skin, but can also be found in non-grape tissues, such as leaves and stems. Whether rotundone is produced independently within different grapevine tissues or transported amongst non-grape tissues and grape berries remains unclear. The current study investigated the distribution of this compound in different vine tissues during development and studied the most likely mode of rotundone translocation-via phloem-using stable isotope feeding. In addition, local production of rotundone induced by herbivore feeding was assessed. Results showed that rotundone was firstly detected in the petioles and peduncles/rachises within the development of Vitis vinifera L. cv. Shiraz. Different grapevine tissues had a similar pattern of rotundone production at different grape developmental stages. In the individual vine shoots, non-grape tissues contained higher concentrations and amounts of rotundone compared to berries, which showed that non-grape tissues were the larger pool of rotundone within the plant. This study confirmed the local production of rotundone in individual tissues and ruled out the possibility of phloem translocation of rotundone between different tissues. In addition, other terpenes, including one monoterpenoid (geraniol) and six sesquiterpenes (clovene, α-ylangene, β-copaene, α-muurolene, δ-cadinene, and cis/trans-calamenene) were, for the first time, detected in the ethylenediaminetetraacetic acid-facilitated petiole phloem exudates, with their originality unconfirmed. Unlike other herbivore-induced terpenes, herbivorous activity had limited influences on the concentration of rotundone in grapevine leaves.

Effect of Commercial Enzymes on Berry Cell Wall Deconstruction in the Context of Intravineyard Ripeness Variation under Winemaking Conditions

Significant intravineyard variation in grape berry ripening occurs within vines and between vines. However, no cell wall data are available on such variation. Here we used a checkerboard panel design to investigate ripening variation in pooled grape bunches for enzyme-assisted winemaking. The vineyard was dissected into defined panels, which were selected for winemaking with or without enzyme addition. Cell wall material was prepared and subjected to high-throughput profiling combined with multivariate data analysis. The study showed that significant ripening-related variation was present at the berry cell wall polymer level and occurred within the experimental vineyard block. Furthemore, all enzyme treatments reduced cell wall variation via depectination. Interestingly, cell wall esterification levels were unaffected by enzyme treatments. This study provides clear evidence that enzymes can positively influence the consistency of winemaking and provides a foundation for further research into the relationship between grape berry cell wall architecture and enzyme formulations.

Cytochrome P450 CYP71BE5 in grapevine (Vitis vinifera) catalyzes the formation of the spicy aroma compound (-)-rotundone

(-)-Rotundone is a potent odorant molecule with a characteristic spicy aroma existing in various plants including grapevines (Vitis vinifera). It is considered to be a significant compound in wines and grapes because of its low sensory threshold and aroma properties. (-)-Rotundone was first identified in red wine made from the grape cultivar Syrah and here we report the identification of VvSTO2 as a α-guaiene 2-oxidase which can transform α-guaiene to (-)-rotundone in the grape cultivar Syrah. It is a cytochrome P450 (CYP) enzyme belonging to the CYP 71BE subfamily, which overlaps with the very large CYP71D family and, to the best of our knowledge, this is the first functional characterization of an enzyme from this family. VvSTO2 was expressed at a higher level in the Syrah grape exocarp (skin) in accord with the localization of (-)-rotundone accumulation in grape berries. α-Guaiene was also detected in the Syrah grape exocarp at an extremely high concentration. These findings suggest that (-)-rotundone accumulation is regulated by the VvSTO2 expression along with the availability of α-guaiene as a precursor. VvSTO2 expression during grape maturation was considerably higher in Syrah grape exocarp compared to Merlot grape exocarp, consistent with the patterns of α-guaiene and (-)-rotundone accumulation. On the basis of these findings, we propose that VvSTO2 may be a key enzyme in the biosynthesis of (-)-rotundone in grapevines by acting as a α-guaiene 2-oxidase.

Understanding the Constitutive and Induced Biosynthesis of Mono- and Sesquiterpenes in Grapes (Vitis vinifera): A Key to Unlocking the Biochemical Secrets of Unique Grape Aroma Profiles

The present review integrates current knowledge on mono- and sesquiterpenes in grapes with a special focus on biochemical and physiological aspects. Recent research has impressively shown the prominence of terpenoid metabolism in grapevine (Vitis sp). The 69 putatively functional mono- and sesquiterpene synthases that were identified by the analysis of the updated 12-fold sequencing and assembly of the grapevine genome deliver the scaffolds for structural diversity and display a surprising expansion of the terpene synthase (TPS) gene family in grapevine when compared to other plants like Arabidopsis thaliana (32 TPS). While monoterpenes occur as highly functionalized compounds and are stored as their corresponding glycoconjugates in berry tissues, sesquiterpenes are mainly present as unsaturated hydrocarbons and accumulate in the epicuticular wax layer of intact berries. Interestingly, both groups of terpenes appear to be involved as volatile organic compounds in plant defense and their biosynthesis is enhanced via the jasmonic acid signaling pathway. These novel aspects will help to understand how environmental cues affect the genes and enzymes of various metabolic pathways of relevant wine aroma compounds with numerous links to enology and wine flavor chemistry.

Environmental Factors and Seasonality Affect the Concentration of Rotundone in Vitis vinifera L. cv. Shiraz Wine

Rotundone is a sesquiterpene that gives grapes and wine a desirable ‘peppery’ aroma. Previous research has reported that growing grapevines in a cool climate is an important factor that drives rotundone accumulation in grape berries and wine. This study used historical data sets to investigate which weather parameters are mostly influencing rotundone concentration in grape berries and wine. For this purpose, wines produced from 15 vintages from the same Shiraz vineyard (The Old Block, Mount Langi Ghiran, Victoria, Australia) were analysed for rotundone concentration and compared to comprehensive weather data and minimal temperature information. Degree hours were obtained by interpolating available temperature information from the vineyard site using a simple piecewise cubic hermite interpolating polynomial method (PCHIP). Results showed that the highest concentrations of rotundone were consistently found in wines from cool and wet seasons. The Principal Component Analysis (PCA) showed that the concentration of rotundone in wine was negatively correlated with daily solar exposure and grape bunch zone temperature, and positively correlated with vineyard water balance. Finally, models were constructed based on the Gompertz function to describe the dynamics of rotundone concentration in berries through the ripening process according to phenological and thermal times. This characterisation is an important step forward to potentially predict the final quality of the resultant wines based on the evolution of specific compounds in berries according to critical environmental and micrometeorological variables. The modelling techniques described in this paper were able to describe the behaviour of rotundone concentration based on seasonal weather conditions and grapevine phenological stages, and could be potentially used to predict the final rotundone concentration early in future growing seasons. This could enable the adoption of precision irrigation and canopy management strategies to effectively mitigate adverse impacts related to climate change and microclimatic variability, such as heat waves, within a vineyard on wine quality.