The free and enzyme-released volatile compounds of distinctive Vitis amurensis var. Zuoshanyi grapes in China

3-Alkyl-2-Methoxypyrazines: Overview of Their Occurrence, Biosynthesis and Distribution in Edible Plants

Pyrazines are ubiquitous in nature - biosynthesized by microorganisms, insects, and plants. Due to their great structural diversity, they own manifold biological functions. Alkyl- and alkoxypyrazines for instance play a key role as semiochemicals, but also as important aroma compounds in foods. Especially 3-alkyl-2-methoxypyrazines (MPs) have been of great research interest. MPs are associated with green and earthy attributes. They are responsible for the distinctive aroma properties of numerous vegetables. Moreover, they have a strong influence on the aroma of wines, in which they are primarily grape-derived. Over the years various methods have been developed and implemented to analyse the distribution of MPs in plants. In addition, the biosynthetic pathway of MPs has always been of particular interest. Different pathways and precursors have been proposed and controversially discussed in the literature. While the identification of genes encoding O-methyltransferases gave important insights into the last step of MP-biosynthesis, earlier biosynthetic steps and precursors remained unknown. It was not until 2022 that in vivo feeding experiments with stable isotope labeled compounds revealed l-leucine and l-serine as important precursors for IBMP. This discovery gave evidence for a metabolic interface between the MP-biosynthesis and photorespiration.

Monoterpenoids Evolution and MEP Pathway Gene Expression Profiles in Seven Table Grape Varieties

This research investigated the evolution of both monoterpenoids and expression profiles of related biosynthesis genes in the MEP pathway in seven different table grape varieties from veraison to maturity stage in two seasons, and the correlation was further evaluated between monoterpenoid accumulation and expression of these genes studied in these varieties. Results showed that linalool, trans-furan linalool oxide, geraniol, and cis-furan linalool oxide were the main compounds in the five Muscat varieties two seasons. ‘Zaomeiguixiang’ had the highest contents of geraniol and β-Citronellol. ‘Xiangfei’ had the most abundant of linalool and cis-furan linalool oxide, whereas the neutral varieties of ‘Moldova’ and ‘Christmas Rose’ had the least amount. Monoterpenoid volatiles have been grouped in three evolutionary patterns in the berry development of these varieties. ‘Zaomeiguixiang’ and ‘Xiangfei’ had distinct different pattern of terpenoids evolution profiles. Pearson’s correlation analysis showed that in the MEP pathway, the first biosynthesis gene VvDXS3 was significantly correlated to the accumulation of monoterpenoids, and appeared to be an important candidate gene for synthesis of the monoterpenoids.

Transcriptome and Metabolomics Integrated Analysis Reveals Terpene Synthesis Genes Controlling Linalool Synthesis in Grape Berries

In this study, four hybrids from the cross between "Italia" and "Tamina" grapes were chosen to investigate their distinct monoterpenoids patterns and candidate genes involved. Monoterpenoid profiles and transcriptome data were generated at four berry developmental stages. Trans-rose oxide, cis-rose oxide, citronellol, neral, nerol, nerol oxide, geraniol, geranial, geranic acid, and cis-isogeraniol were the dominant compounds in R250 hybrid, while linalool, hotrienol, linalool oxide pyranoside, and cis-furan linalool oxide were the main compounds in R77 hybrid. Six TPS-g subfamily genes were found related with the contents of linalool and its related monoterpenoids by weighted gene coexpression network analysis (WGCNA) and phylogenetic analysis. Among them, TPS59 was cloned and functionally verified by transient overexpression in the leaves of Vitis quinquangularis. Meanwhile, NAC (newGene_195), C2C2-GATA (VIT_15s0021g02510), and bHLH (VIT_14s0128g00110) were selected as candidate transcription factors (TFs) that could regulate the expression of the six TPS-b genes. These data enhanced our understanding on the regulation of monoterpenoid biosynthesis in grapes.

Comparative study of the key aromatic compounds of Cabernet Sauvignon wine from the Xinjiang region of China

To determine the differences in the characteristic volatile compounds between winemaking areas in the Xinjiang region, this study was conducted by sampling Cabernet Sauvignon grapes from four winemaking areas in Xinjiang, named Tianshanbeilu, Yili, Yanqi, and Hami. After undergoing the same alcoholic fermentation treatment, the wines from the four areas were subjected to GC-MS and sensory analysis. The results showed that fifty aromatic compounds (including higher alcohols, esters, acids, terpenes, aldehydes/ketones, et al.) were identified and quantified. Interestingly, the terpene and phenylalanine derivative contents of the wines from northern Xinjiang were higher than those from the south. Additionally, four vineyards highly contributed to the development of key volatile compounds in the Xinjiang region. Sensory analysis showed that the wines from northern Xinjiang were impressive with a flowery and fruity aroma and the wines from southern Xinjiang had a stronger wine body and astringency.

Influence of cluster positions in the canopy and row orientation on the flavonoid and volatile compound profiles in Vitis vinifera L. Cabernet franc and Chardonnay berries

Sunlight conditions around grape clusters vary with their positions, and can have a significant effect on grape berry compounds. This study investigated the influence of cluster positions in the canopy (interior and two exterior canopy sides) and vineyard row orientation (north-south and east-west) on flavonoid and volatile compound profiles of Vitis vinifera L. cvs 'Cabernet franc' (CF) and 'Chardonnay' (CH) berries in two consecutive years. The experimental vineyard was located in Jiaodong Peninsula of China, which is characterized by a temperate monsoon-type climate and relatively short sunlight duration. Clusters located in the interior of the canopy received less sunlight irradiation than the exterior positions, and the average temperature around clusters located in different positions differed slightly. The results showed that over two years, the positions of clusters in the canopy had no consistent impact on cluster weight, berry weight, juice total soluble solids or titratable acidity for either cultivar. For both cultivars, the interior clusters had lower total flavonol concentrations than the exterior clusters, while the position of clusters in the canopy had no major impacts on the composition of anthocyanins and flavan-3-ols. The volatile compounds were somewhat influenced by the positions of clusters in the canopy, while some bound norisoprenoids and terpenoids had lower levels in interior clusters than in exterior clusters. These results will help winegrowers make decisions regarding harvest strategies.

Girdling of table grapes at fruit set can divert the phenylpropanoid pathway towards accumulation of proanthocyanidins and change the volatile composition

Girdling is an important horticultural practice that allows increased yields or modulated ripening but not much is known how it affects metabolic processes. Trunk girdling was performed at fruit set using a single-blade knife on two table grape cultivar SUPERIOR SEEDLESS® and SABLE SEEDLESS®. Sampling of berries was carried out 1 or 9 weeks after girdling in 2017 from both cultivars and 7 and 9 weeks after girdling of 'Sable' in 2018. As expected, girdling resulted in consistent increase in berry size but total soluble content of mature 'Superior' berries was not affected and in 'Sable' it was slightly reduced in one of the two seasons examined. One week after girdling, abscisic acid and gibberellin content was higher in fruitlets from girdled vines and genes of the phenylpropanoid pathway were induced in both cultivars. Berry color development of 'Sable' measured both by auto-fluorescence and concentration of anthocyanins was reduced upon girdling. In contrast, flavan-3-ol and flavonol content, and total proanthcyanidins (PA) content increased 1.8-fold while the mean degree polymerization of the PA decreased from 26 to 21 upon girdling. Girdling reduced the levels of fatty acid derived volatiles in berries of 'Superior' and 'Sable'. In 'Sable', the total terpene level and the level of volatiles released after acid hydrolysis, decreased upon girdling. Overall, our study indicates that girdling can divert metabolic pathways in a manner that may have significant effect on the taste and flavor of grapes.

The accumulation profiles of terpene metabolites in three Muscat table grape cultivars through HS-SPME-GCMS

Aroma is an important parameter for table grapes and wines; terpenes are typical compounds in Muscat-type grape cultivars and can be easily perceived by humans because of their low olfactory threshold. Volatile terpenes contribute directly to the aroma character, while glycoside-bound terpenes are potential aromatic compounds and can be changed to their volatile forms via hydrolysis. With gas chromatography-mass spectrometry and a solid-phase microextraction method, an automatic data analysis platform was constructed; terpene compounds were identified and quantified from three table grape cultivars at three stages during berry development, and the raw data were deposited in MetaboLights. Terpene metabolite accumulation profiles are presented in this article for integrative analysis with the transcriptome data and phenotypic data to elucidate the important candidate genes and mechanism for terpene biosynthesis. Our method has applications in the identification and quantification of terpene compounds with very low or trace concentrations.

The genetic basis of grape and wine aroma

The grape is one of the oldest and most important horticultural crops. Grape and wine aroma has long been of cultural and scientific interest. The diverse compound classes comprising aroma result from multiple biosynthetic pathways. Only fairly recently have researchers begun to elucidate the genetic mechanisms behind the biosynthesis and metabolism of grape volatile compounds. This review summarizes current findings regarding the genetic bases of grape and wine aroma with an aim towards highlighting areas in need of further study. From the literature, we compiled a list of functionally characterized genes involved in berry aroma biosynthesis and present them with their corresponding annotation in the grape reference genome.

Transcriptome profiles of three Muscat table grape cultivars to dissect the mechanism of terpene biosynthesis

Vitis vinifera is widely grown worldwide for making wine and for use as table grapes. Of the existing cultivars, some have a floral and fruity flavour, referred to as a Muscat flavour. It is well-documented that this flavour originates from a series of terpene compounds, but the mechanism of terpene content differences among the Muscat-type cultivars remains unclear. Transcript and terpene metabolite profiles were integrated to elucidate the molecular mechanism of this phenomenon. In this research, three genotypes with different aromatic strengths were investigated by RNA sequencing. A total of 27 fruit samples from three biological replicates were sequenced on Illumina HiSeq2000 at three stages, corresponding to the veraison; berries had intermediate Brix value and were harvest-ripe. After quality assessment and data clearance, a total of 254.18 Gb of data with more than 97% Q20 bases were obtained, approximately 9.41 Gb data were generated per sample. These results will provide a valuable dataset for the discovery of the mechanism of terpene biosynthesis.

Evaluation of Volatile Metabolites Emitted In-Vivo from Cold-Hardy Grapes during Ripening Using SPME and GC-MS: A Proof-of-Concept

In this research, we propose a novel concept for a non-destructive evaluation of volatiles emitted from ripening grapes using solid-phase microextraction (SPME). This concept is novel to both the traditional vinifera grapes and the cold-hardy cultivars. Our sample models are cold-hardy varieties in the upper Midwest for which many of the basic multiyear grape flavor and wine style data is needed. Non-destructive sampling included a use of polyvinyl fluoride (PVF) chambers temporarily enclosing and concentrating volatiles emitted by a whole cluster of grapes on a vine and a modified 2 mL glass vial for a vacuum-assisted sampling of volatiles from a single grape berry. We used SPME for either sampling in the field or headspace of crushed grapes in the lab and followed with analyses on gas chromatography-mass spectrometry (GC-MS). We have shown that it is feasible to detect volatile organic compounds (VOCs) emitted in-vivo from single grape berries (39 compounds) and whole clusters (44 compounds). Over 110 VOCs were released to headspace from crushed berries. Spatial (vineyard location) and temporal variations in VOC profiles were observed for all four cultivars. However, these changes were not consistent by growing season, by location, within cultivars, or by ripening stage when analyzed by multivariate analyses such as principal component analysis (PCA) and hierarchical cluster analyses (HCA). Research into aroma compounds present in cold-hardy cultivars is essential to the continued growth of the wine industry in cold climates and diversification of agriculture in the upper Midwestern area of the U.S.

Quality Comparison of Hawthorn Wines Fermented by Saccharomyces cerevisiae with and without Pulp Contact and Pectase Treatment

This study evaluated the chemical and volatile composition of hawthorn wines fermented with Saccharomyces cerevisiae A3.12 with and without pulp contact and pectase treatment during fermentation. The results indicated that the addition of pectase was in favor of pH decrease and clarification. The pectase-treated wines had significantly higher concentrations of acetic acid, ethyl octanoate, and isoamyl acetate than the non-enzyme-treated wines. Furthermore, the nonextracted wines had significantly higher concentrations of isoamyl alcohol, phenylethyl alcohol, ethyl lactate, and isoamyl acetate than the extracted wines. The first principal component separated the wine from the nonextracted juice with pectase from other samples based on the higher concentrations of isoamyl acetate (0.14 μg/g), diethyl butanedioate (0.07 μg/g), 2-phenylethyl acetate (0.23 μg/g), and acetoin (1.47 μg/g). The wine from nonextracted pulpy juice with pectase was significantly more aromatic than the others and 26.2% of the consumers were found to be willing to purchase this product.

Using the combined analysis of transcripts and metabolites to propose key genes for differential terpene accumulation across two regions

BACKGROUND

Terpenes are of great interest to winemakers because of their extremely low perception thresholds and pleasant floral odors. Even for the same variety, terpene profile can be substantially different for grapevine growing environments. Recently a series of genes required for terpene biosynthesis were biochemically characterized in grape berries. However, the genes that dominate the differential terpene accumulation of grape berries between regions have yet to be identified.

METHODS

Free and glycosidically-bound terpenes were identified and quantified using gas chromatography-mass spectrometry (GC-MS) technique. The transcription expression profiling of the genes was obtained by RNA sequencing and part of the results were verified by quantitative real time PCR (QPCR). The gene co-expression networks were constructed with the Cytoscape software v 2.8.2 ( www.cytoscape.org).

RESULTS

'Muscat Blanc a Petits Grains' berries were collected from two wine-producing regions with strikingly different climates, Gaotai (GT) in Gansu Province and Changli (CL) in Hebei Province in China, at four developmental stages for two consecutive years. GC-MS analysis demonstrated that both free and glycosidically bound terpenes accumulated primarily after veraison and that mature grape berries from CL contained significantly higher concentrations of free and glycosidically bound terpenes than berries from GT. Transcriptome analysis revealed that some key genes involved in terpene biosynthesis were markedly up-regulated in the CL region. Particularly in the MEP pathway, the expression of VviHDR (1-hydroxy-2-methyl-2-butenyl 4-diphosphate reductase) paralleled with the accumulation of terpenes, which can promote the flow of isopentenyl diphosphate (IPP) into the terpene synthetic pathway. The glycosidically bound monoterpenes accumulated differentially along with maturation in both regions, which is synchronous with the expression of a monoterpene glucosyltransferase gene (VviUGT85A2L4 (VviGT14)). Other genes were also found to be related to the differential accumulation of terpenes and monoterpene glycosides in the grapes between regions. Transcription factors that could regulate terpene synthesis were predicted through gene co-expression network analysis. Additionally, the genes involved in abscisic acid (ABA) and ethylene signal responses were expressed at high levels earlier in GT grapes than in CL grapes.

CONCLUSIONS

Differential production of free and glycosidically-bound terpenes in grape berries across GT and CL regions should be related at least to the expression of both VviHDR and VviUGT85A2L4 (VviGT14). Considering the expression patterns of both transcription factors and mature-related genes, we infer that less rainfall and stronger sunshine in the GT region could initiate the earlier expression of ripening-related genes and accelerate the berry maturation, eventually limiting the production of terpene volatiles.

Using the combined analysis of transcripts and metabolites to propose key genes for differential terpene accumulation across two regions

BACKGROUND

Terpenes are of great interest to winemakers because of their extremely low perception thresholds and pleasant floral odors. Even for the same variety, terpene profile can be substantially different for grapevine growing environments. Recently a series of genes required for terpene biosynthesis were biochemically characterized in grape berries. However, the genes that dominate the differential terpene accumulation of grape berries between regions have yet to be identified.

METHODS

Free and glycosidically-bound terpenes were identified and quantified using gas chromatography-mass spectrometry (GC-MS) technique. The transcription expression profiling of the genes was obtained by RNA sequencing and part of the results were verified by quantitative real time PCR (QPCR). The gene co-expression networks were constructed with the Cytoscape software v 2.8.2 ( www.cytoscape.org).

RESULTS

'Muscat Blanc a Petits Grains' berries were collected from two wine-producing regions with strikingly different climates, Gaotai (GT) in Gansu Province and Changli (CL) in Hebei Province in China, at four developmental stages for two consecutive years. GC-MS analysis demonstrated that both free and glycosidically bound terpenes accumulated primarily after veraison and that mature grape berries from CL contained significantly higher concentrations of free and glycosidically bound terpenes than berries from GT. Transcriptome analysis revealed that some key genes involved in terpene biosynthesis were markedly up-regulated in the CL region. Particularly in the MEP pathway, the expression of VviHDR (1-hydroxy-2-methyl-2-butenyl 4-diphosphate reductase) paralleled with the accumulation of terpenes, which can promote the flow of isopentenyl diphosphate (IPP) into the terpene synthetic pathway. The glycosidically bound monoterpenes accumulated differentially along with maturation in both regions, which is synchronous with the expression of a monoterpene glucosyltransferase gene (VviUGT85A2L4 (VviGT14)). Other genes were also found to be related to the differential accumulation of terpenes and monoterpene glycosides in the grapes between regions. Transcription factors that could regulate terpene synthesis were predicted through gene co-expression network analysis. Additionally, the genes involved in abscisic acid (ABA) and ethylene signal responses were expressed at high levels earlier in GT grapes than in CL grapes.

CONCLUSIONS

Differential production of free and glycosidically-bound terpenes in grape berries across GT and CL regions should be related at least to the expression of both VviHDR and VviUGT85A2L4 (VviGT14). Considering the expression patterns of both transcription factors and mature-related genes, we infer that less rainfall and stronger sunshine in the GT region could initiate the earlier expression of ripening-related genes and accelerate the berry maturation, eventually limiting the production of terpene volatiles.