Direct Analysis of Glycosidic Aroma Precursors Containing Multiple Aglycone Classes in Vitis vinifera Berries

Comparison of Dip-it-DART-Orbitrap-MS With Nitrogen Plasma to HPLC/Orbitrap-MS in Profiling Aromatic Glycoconjugation in White Grapes

Direct analysis of aromatic glycosidic precursors in plants has posed an analytical challenge for decades. Traditional techniques, such as SPE-GC/MS, primarily provided information on volatile aglycones released through hydrolysis. However, the application of high-resolution mass spectrometry combined with liquid chromatography has enabled the direct analysis of intact glycosides without the need for derivatization or hydrolysis. Advances in soft ionization methods, such as DART, offer a novel approach to exploring the hidden aromatic potential in grapes without chromatographic separation. In this work, we present a novel and rapid method for screening aromatic glycosidic precursors in white grapes using high-resolution mass spectrometry (Orbitrap) combined with the soft ionization DART method with nitrogen plasma. Optimization of N2-DART ionization parameters, including grid voltage, gas temperature, and Dip-it sampler speed, performed on selected synthetic glycosidic precursors, allowed the establishment of characteristic ionization patterns and evaluation of 15 groups of glycosidic precursors. The results from the profiling analysis using the N2-DART-Orbitrap-MS method are comparable to those obtained by HPLC/Orbitrap-MS method. This new analytical approach, N2-DART-Orbitrap-MS, reduces drastically analysis time by eliminating the need for chromatographic separation when screening glycoside precursors, uses a convenient Dip-it tips for sampling. It also allows for deeper exploration of ionization using nitrogen plasma, applied for the first time in the analysis of glycoside precursors, demonstrating the applicability of this method for the rapid characterization and screening of glycosidically bound aroma compounds in plants.

β-Glucosidase Activity of Lactiplantibacillus plantarum: A Key Player in Food Fermentation and Human Health

β-glucosidases are a relevant class of enzymes in the food industry due to their role in hydrolyzing different types of glycosidic bonds. This activity allows for formation of volatile compounds and release of bioactive aglycone compounds. In addition to endogenous β-glucosidase activity present in raw material, the function of β-glucosidases in fermenting microorganisms has been progressively clarified and increasingly appreciated. In this regard, several lactic acid bacteria, including Lactiplantibacillus plantarum, showed high β-glucosidase activity, which can be considered as a valid biotechnological resource in different food sectors. Here, we reviewed the huge literature in which the β-glucosidases of L. plantarum were shown to play a role, highlighting how their action results in enhancing the nutritional, sensory, and functional properties of fermented foods. To this aim, after a brief introduction of the main functions of these enzymes in several kingdoms, we critically analyzed the involvement of L. plantarum β-glucosidases in plant-based food production, with a particular insight for soy, cassava, and olive-fermented products, as well as in the production of both alcoholic and non-alcoholic beverages. We trust that the reports summarized here can be helpful in planning future research and innovative strategies to obtain pleasing, functional, and healthy foods.

A mutant GH3 family β-glucosidase from Oenococcus oeni exhibits superior adaptation to wine stresses and potential for improving wine aroma and phenolic profiles

In this study, we conducted a comprehensive investigation into a GH3 family β-glucosidase (BGL) from the wild-type strain of Oenococcus oeni and its mutated counterpart from the acid-tolerant mutant strain. Our analysis revealed the mutant BGL's remarkable capacity to adapt to wine-related stress conditions, including heightened tolerance to low pH, elevated ethanol concentrations, and metal ions. Additionally, the mutant BGL exhibited superior hydrolytic activity towards various substrates. Through de novo modeling, we identified specific amino acid mutations responsible for its resilience to low pH and high ethanol environments. In simulated wine conditions, the mutant BGL outperformed both wild-type and commercial BGLs, efficiently releasing terpene and phenolic aglycones from glycosides in wine grapes. These findings not only expand our understanding of O. oeni BGLs but also highlight their potential in enhancing wine production. The mutant BGL's enhanced adaptation to wine stress conditions opens promising avenue for improving wine quality and flavor.

Study of Glycosidically Bound Volatile Precursors as Variety Markers to Reveal Not-Allowed Practices in White Wines Winemaking

Liquid chromatography/high-resolution mass spectrometry (LC/HRMS) can provide identification of grape metabolites which are variety markers. White grapes are poorer in polyphenolics, and the main secondary metabolites which contribute the sensorial characteristics of wines are the glycosidically bound volatile precursors and their aglycones. The profiles of three white grape juices (Pinot grigio, Garganega, and Trebbiano) were characterized by LC/HRMS, and 70 signals of putative glycosidic terpenols, norisoprenoids, and benzenoids were identified. Four signals found only in Pinot grigio corresponded to a norisoprenoid hexose-hexose, 3-oxo-α-ionol (or 3-hydroxy-β-damascone) rhamnosyl-hexoside, monoterpene-diol hexosyl-pentosyl-hexoside, and hexose-norisoprenoid; three signals were found only in Garganega (putative isopropyl alcohol pentosyl-hexoside, phenylethanol rhamnosyl-hexoside, and norisoprenoid hexose-hexose isomers), and a monoterpenol pentosyl-hexoside isomer only in Trebbiano. These variety markers were then investigated in juice blends of the three varieties. This approach can be used to develop control methods to reveal not-allowed grape varieties and practices in white wines winemaking.

High-Resolution Mass Spectrometry-Based Metabolomics for Increased Grape Juice Metabolite Coverage

The composition of the juice from grape berries is at the basis of the definition of technological ripeness before harvest, historically evaluated from global sugar and acid contents. If many studies have contributed to the identification of other primary and secondary metabolites in whole berries, deepening knowledge about the chemical composition of the sole flesh of grape berries (i.e., without considering skins and seeds) at harvest is of primary interest when studying the enological potential of widespread grape varieties producing high-added-value wines. Here, we used non-targeted DI-FT-ICR-MS and RP-UHPLC-Q-ToF-MS analyses to explore the extent of metabolite coverage of up to 290 grape juices from four Vitis vinifera grape varieties, namely Chardonnay, Pinot noir, Meunier, and Aligoté, sampled at harvest from 91 vineyards in Europe and Argentina, over three successive vintages. SPE pretreatment of samples led to the identification of more than 4500 detected C,H,O,N,S-containing elemental compositions, likely associated with tens of thousands of distinct metabolites. We further revealed that a major part of this chemical diversity appears to be common to the different juices, as exemplified by Pinot noir and Chardonnay samples. However, it was possible to build significant models for the discrimination of Chardonnay from Pinot noir grape juices, and of Chardonnay from Aligoté grape juices, regardless of the geographical origin or the vintage. Therefore, this metabolomic approach opens access to a remarkable holistic molecular description of the instantaneous composition of such a biological matrix, which is the result of complex interplays among environmental, biochemical, and vine growing practices.

Unlocking Flavor Potential Using Microbial β-Glucosidases in Food Processing

Aroma is among of the most important criteria that indicate the quality of food and beverage products. Aroma compounds can be found as free molecules or glycosides. Notably, a significant portion of aroma precursors accumulates in numerous food products as nonvolatile and flavorless glycoconjugates, termed glycosidic aroma precursors. When subjected to enzymatic hydrolysis, these seemingly inert, nonvolatile glycosides undergo transformation into fragrant volatiles or volatiles that can generate odor-active compounds during food processing. In this context, microbial β-glucosidases play a pivotal role in enhancing or compromising the development of flavors during food and beverage processing. β-glucosidases derived from bacteria and yeast can be utilized to modulate the concentration of particular aroma and taste compounds, such as bitterness, which can be decreased through hydrolysis by glycosidases. Furthermore, oral microbiota can influence flavor perception by releasing volatile compounds that can enhance or alter the perception of food products. In this review, considering the glycosidic flavor precursors present in diverse food and beverage products, we underscore the significance of glycosidases with various origins. Subsequently, we delve into emerging insights regarding the release of aroma within the human oral cavity due to the activity of oral microbial glycosidases.

The pivotal role of high-resolution mass spectrometry in the study of grape glycosidic volatile precursors for the selection of grapevines resistant to mildews

A breeding program to produce new grape varieties tolerant to main vine fungal pathogens (Plasmopara viticola and Erysiphe necator) is carrying out by crossing Vitis vinifera cv. "Glera" with resistant genotypes such as "Solaris," "Bronner," and "Kunleany." Firstly, resistance gene-based markers analyses allowed the identification of five genotypes, which have inherited the resistance loci against mildews. To select those that also inherited the phenotype as close as possible to 'Glera' suitable to be introduced in the Prosecco wine production protocols, the grape glycosidic derivatives were studied by UHPLC/QTOF mass spectrometry. Targeted identification of the metabolites was performed using a database expressly constructed by including the glycosidic volatile precursors previously identified in grape and wine. A total of 77 glycosidic derivatives including many aroma precursors and some variety markers, were identified. Original resistant genotypes had distinct metabolomic profiles and different to 'Glera', while the crossings showed varying similarity degrees to V. vinifera parent. Findings demonstrated the Glera × Bronner and Glera × Solaris crossings are more suitable to produce high-sustainable Prosecco wines. Coupling of glycosidic volatile precursors profiling to multivariate statistical analysis was effective for phenotypic characterization of grapes and to evaluate their enological potential.

Determination of Tea Aroma Precursor Glycosides: An Efficient Approach via Liquid Chromatography-Tandem Mass Spectrometry

Tea aroma components are often stored as glycosidically bound forms in the tea plant (Camellia sinensis). However, the determination of these glycosides in tea samples is far from optimal. In the present study, we developed a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method for simultaneous quantification of eight primary aroma glycosides within 10 min. After systematic optimization of multiple reaction monitoring (MRM) parameters, the proposed method was highly sensitive and accurate. Optimization of the method permitted the efficient extraction of aroma glycosides. The developed method was applied to analyze the contents of aroma glycosides in different organs of tea plants, including the bud, leaves, and stem. Contents of aroma glycosides in the harvested 'Shaancha 1' ranged from 36.1 to 40454.4 μg kg^-1. Geranyl glucoside and primeveroside mainly accumulated in young leaves, while other glycosides mainly accumulated in mature leaves. The findings document a rapid, reliable, and efficient analysis method. This method will be helpful in elucidating the biosynthesis and biotransformation mechanism of tea aroma glycosides and in promoting the development of the tea industry using advanced technological control approaches during the cultivation of tea plants and tea manufacture.

Coupling between high-resolution mass spectrometry and focalized data-analysis methods provides the identification of new putative glycosidic non-anthocyanic flavonoids in grape

INTRODUCTION

The biochemical diversity of flavonoids is based on glycosylation, methylation, acylation, and many other modifications of the flavonoid backbone. Liquid chromatography coupled to high-resolution mass spectrometry demonstrated to be a powerful approach to gain new insights into the flavonoid composition of many plant species, including grapes.

OBJECTIVES

Among different metabolomic approaches, suspect screening analysis relies on the construction of a specific database and on ultra-high performance liquid chromatography/quadrupole time-of-flight (UHPLC/QTOF) analysis to find new compounds of oenological interest.

METHODS

A homemade database containing mass data information retrieved from the literature specific for plant flavonoid derivatives (GrapeFlavMet) was constructed. Tandem mass spectrometry analysis of V. vinifera and hybrid grape extracts was performed, and MS/MS fragmentation allowed to assign the putative flavonoid chemical structure to various identification levels, as established by the Metabolomics Standard Initiative.

RESULTS

By this approach, putative flavonoid derivatives with different glycosylation and acylation patterns were identified. They include three pentoside derivatives of tetrahydroxy-flavone, tetrahydroxy-flavanone and myricetin isomers, a putative dihydrorhamnetin hexoside derivative, three cinchonain isomers (phenylpropanoid-substituted flavan-3-ols with antidiabetic properties), and two syringetin isomer derivatives (acetyl- and p-coumaroyl-hexoside). Two acetyl-hexoside derivatives of dihydrorhamnetin and pentahydroxy-methoxy-flavanone, and three derivatives of tetrahydroxy-dimethoxy-flavanone (acetyl, p-coumaroyl, and caffeoyl-hexoside) were tentatively annotated.

CONCLUSIONS

Most of the compounds were identified in grape for the first time, while two putative syringetin derivatives previously proposed in the literature were confirmed. These findings deepen the current knowledge on grape flavonoids, suggesting more connections at the biochemical level.

Free and glycosidically bound aroma compounds in fruit: biosynthesis, transformation, and practical control

Fruit aroma makes an initial flavor impression and largely determines the consumer preference and acceptance of fruit products. Free volatile organic compounds (FVOCs) directly make up the characteristic aromas of fruits. While glycosidically bound volatile compounds (GBVs) can be hydrolyzed during fruit ripening, postharvest storage, and processing, releasing the attached aglycones as free volatiles that could alter the overall aroma attributes of fruits. GBVs typically exhibit significantly higher concentrations than their free counterparts in fruits such as grapes, cherries, kiwifruits, tomatoes, and tamarillos. This review highlights the biosynthesis of FVOCs and GBVs in fruit and illustrates their biological transformations for various functional purposes such as detoxification, aroma enhancement, plant defense, and pollinator attraction. Practical applications for regulating the levels of aroma compounds emitted or accumulated in fruit are also reviewed, emphasizing the metabolic engineering of free volatile metabolites and hydrolytic technologies on aroma glycosides. Generally, enzymatic hydrolysis using AR2000 is a common strategy to enhance the sensory attributes of fruit juices/wines, while acidic hydrolysis induces the oxidation and rearrangement of aglycones, generating artifacts with off-aromas. This review associates the occurrence of free and glycosidic bound volatiles in fruit and addresses their importance in fruit flavor enhancement and industrial applications.

Identification of new glycosidic terpenols and norisoprenoids (aroma precursors) in C. arabica L. green coffee by using a high-resolution mass spectrometry database developed in grape metabolomics

Grape aroma precursors have been extensively studied and many glycosidically-bound terpenols and C₁₃-norisoprenoids were identified. Instead, these compounds were scarcely investigated in green Coffea arabica where just few glycosidic compounds were identified so far. By resorting to knowledge of glycoside aroma precursors in grape and the possibility to identify their structures using a high-resolution mass spectrometry database constructed for grape metabolomics, targeted investigation of glycoside precursors in green C. arabica from different geographical origins, was performed. High linalool hexose-pentose was found in all the investigated samples and hexosyl-pentoside derivatives of geraniol, linalooloxide and another linalool isomer, were identified. Moreover, two putative norisoprenoid glycosides were characterized. β-Damascenone was detected in the volatile fraction of the examined C. arabica coffees only after acid addition, however no signals of β-damascenone glycosides, were found. Findings suggests that this important aroma compound could form by hydrolysis and dehydration of a putative 3-hydroxy-β-damascone glycoside precursor identified for the first time in coffee. Aglycones released during the roasting process contribute to enrich the coffee aroma with their positive sensory notes and the identification of these glycosides can contribute to disclose the coffee biology including biochemical, physiological and genetic aspects.

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Glycoside aroma precursors in green C. arabica coffee are poorly known.

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A grape database was used to investigate aroma precursors in green C. arabica.

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Geraniol and linalooloxide glycosides were identified for first time in coffee.

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Linalool hexosyl-pentoside was particularly abundant in samples from Ethiopia.

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Putative 3-hydroxy-β-damascone and vomifoliol glycosides were characterized.

Grape bioactive molecules, and the potential health benefits in reducing the risk of heart diseases

Grapes are a rich source of bioactive molecules including phenolic acids, flavonoids, anthocyanins, stilbenes, and lipids. These are the compounds which contribute to the health benefits of grape and grape-derived products. They possess antioxidant, antimicrobial, anti-inflammatory, and anti-carcinogenic activities and have wide applications in food and nutraceutical industries. Use of grape extracts rich in these bioactive compounds are linked to reduced incidence of cardiovascular disease and its major risk factors including hypertension (high blood pressure); a clinical condition associated with high mortality worldwide. Therefore, considerable attention has been given to grape-based products to alleviate and treat hypertension. The aim of this review is to summarize the bioactive compounds of grapes, composition changes in different grape extracts and the potential benefits in reducing hypertension.

Characterization of Free and Bound Monoterpene Alcohols during Riesling Fermentation

The isomeric nature of monoterpenyl glycosides makes unambiguous identification of intact glycosides difficult. As a result, it is challenging to relate the changes in free monoterpenol concentrations to the corresponding glycosides during wine fermentation and storage. In this study, we isolated and identified linalool, nerol, and geraniol monoterpenyl glycosides fromVitis viniferacv. Riesling grapes through fractionation followed by acid or enzyme hydrolysis. Changes in the composition of identified monoterpenyl glycosides and their respective free volatiles were then monitored during alcoholic fermentations of Riesling juice with four different yeast strains across two successive years. The relative concentrations of the volatiles were monitored by solid-phase microextraction gas chromatography mass spectrometry, while ultrahigh-performance liquid chromatography quadrupole time-of-flight mass spectrometry was used for intact glycosides. Glycoside hydrolysis during fermentation could be related to relative concentrations of the corresponding free aglycones. However, other sources of free monoterpenols were also observed. Differences in glycoside hydrolysis among yeast strains and across years were observed and may be related to grape maturity and/or nutrient levels.

The Occurrence of Glycosylated Aroma Precursors in Vitis vinifera Fruit and Humulus lupulus Hop Cones and Their Roles in Wine and Beer Volatile Aroma Production

Volatile aroma compounds found in grapes and hops may be present as both free volatiles and bound glycosides. Glycosides found in the raw materials are transferred to their respective fermented beverages during production where the odorless compounds may act as a reservoir of free volatiles that may be perceived by the consumer if hydrolyzed. A review of the literature on grape and wine glycosides and the emerging literature for glycosides in hops is presented in order to demonstrate the depth of history in grape glycoside research and may help direct new research on hop glycosides. Focus is brought to the presence of glycosides in the raw materials, the effect that winemaking and brewing have on glycoside levels, and current methods for the analysis of glycosidically linked aroma compounds.

Evaluation of Variety, Maturity, and Farm on the Concentrations of Monoterpene Diglycosides and Hop Volatile/Nonvolatile Composition in Five Humulus lupulus Cultivars

Pentose-hexose monoterpene alcohol glycosides were isolated and semiquantitatively measured in dried Humulus lupulus cones using UHPLC-qTOF-MS/MS and HPLC fractionation followed by GC-MS. The samples evaluated included hop cones from five important dual-purpose cultivars (varieties) in the United States, from two locations (farms) per variety and from three distinct harvest time points (maturities) per location, as dictated by dry-matter (% w/w) at the time of harvest. Hop variety accounted for the biggest variation among the concentrations of pentose-hexose monoterpene alcohol glycosides as well as other volatile and nonvolatile chemical factors measured in the samples. This indicates that genetics plays a major role in hop flavor production. Interestingly, "maturity", or ripeness at the time of harvest, was the next most significant factor impacting the concentrations of pentose-hexose monoterpene alcohol glycosides along with most of the other volatile and nonvolatile factors (such as total oil concentration and composition). However, maturity notably had a bigger impact on some cultivars such as Sabro, Mosaic, Simcoe, and Citra. Surprisingly, farm (i.e., location, farming practices, etc.) accounted for the least amount of variation among the concentrations of the different analytical factors. These results highlight the importance of breeding/genetics as well as considering hop maturity/ripeness at the time of harvest on the production and subsequent development of analytical chemical factors associated with driving hoppy beer flavor. It is essential for future studies assessing the impact of different farming practices and locations (i.e., regionality, terroir, etc.) on the constituents in hops important for hoppy beer flavor to consider and account for the impact of hop maturity as well as genetics.

Simultaneous determination of six glycosidic aroma precursors in pomelo by ultra-high performance liquid chromatography-tandem mass spectrometry

An ultra-high performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method was established and validated for the simultaneous determination of six glycosidic aroma precursors in pomelo, including geraniol β-glucoside, geraniol β-primeveroside, linalool β-primeveroside, benzyl β-primeveroside, 2-phenylethyl β-primeveroside and nerolidol β-primeveroside. The results showed that the proposed method has the advantages of rapidity, high sensitivity, and good accuracy. Six glycosidic aroma precursors were effectively separated in a short run time (13 min), and the limit of detection, limit of quantification, recovery, and repeatability of analytes were 0.321-4.47 ng mL^-1, 1.07-14.9 ng mL^-1, 94.4-109.1%, and 5.2-14.5%, respectively. The developed method was applied to analyze the contents of glycosidic aroma precursors in different organs of pomelo plant, including leaves, flowers and fruits. The analytical result showed that glycosidic aroma precursor contents in plant leaves, flowers and fruits were in the range of 0-5964.9 μg kg^-1, and more glycosidic aroma precursors were found in flowers than in leaves or fruits. It is envisioned that the proposed UPLC-MS/MS method have promising application in qualifying and quantifying these six glycosidic aroma precursors in pomelo.

Qualitative profiling of mono- and sesquiterpenols in aglycon libraries from Vitis vinifera L. Gewürztraminer using multidimensional gas chromatography–mass spectrometry

In grape berries (Vitis vinifera L.), sesquiterpenes are mainly accumulated as hydrocarbons in the epicuticular wax layer of grapes, whereas monoterpenes, which are predominantly present as alcohols, are glycosylated and are stored as glycosides in the vacuoles of grape berry cells. In this study, extensive analysis of grape berry hydrolysates by means of comprehensive two-dimensional gas chromatography–time-of-flight–mass spectrometry demonstrated that glycosylated sesquiterpene alcohols show very little structural diversity when compared to the sesquiterpene hydrocarbon fraction in the cuticle and are glycosylated to a rather low extent when compared to monoterpenols. Twenty-four enzymatically released terpenols were found in hydrolysates of the aromatic white wine variety Gewürztraminer (V. vinifera subsp. vinifera) after previous solid-phase extraction and headspace solid-phase microextraction. The detection of only three sesquiterpene alcohols, namely farnesol, nerolidol and drimenol, shows that most sesquiterpene hydrocarbons do not have a related hydroxylated structure in grapes. Nevertheless, the presence of the acyclic aglycone farnesol and nerolidol may be of importance for the wine aroma, since these structural isomers can be converted into numerous sesquiterpenes by nonenzymatic acid-catalyzed reactions during wine production. Grape-derived glycosidically bound sesquiterpene alcohols, therefore, represent, in addition to free sesquiterpene hydrocarbons, another pool of compounds that may influence the aroma profile of wines.

Influence of Non-Saccharomyces on Wine Chemistry: A Focus on Aroma-Related Compounds

Wine fermentation processes are driven by complex microbial systems, which comprise eukaryotic and prokaryotic microorganisms that participate in several biochemical interactions with the must and wine chemicals and modulate the organoleptic properties of wine. Among these, yeasts play a fundamental role, since they carry out the alcoholic fermentation (AF), converting sugars to ethanol and CO₂ together with a wide range of volatile organic compounds. The contribution of Saccharomyces cerevisiae, the reference organism associated with AF, has been extensively studied. However, in the last decade, selected non-Saccharomyces strains received considerable commercial and oenological interest due to their specific pro-technological aptitudes and the positive influence on sensory quality. This review aims to highlight the inter-specific variability within the heterogeneous class of non-Saccharomyces in terms of synthesis and release of volatile organic compounds during controlled AF in wine. In particular, we reported findings on the presence of model non-Saccharomyces organisms, including Torulaspora delbrueckii, Hanseniaspora spp,Lachancea thermotolerans, Metschnikowia pulcherrima, Pichia spp. and Candida zemplinina, in combination with S. cerevisiae. The evidence is discussed from both basic and applicative scientific perspective. In particular, the oenological significance in different kind of wines has been underlined.

Analysis of Intact Glycosidic Aroma Precursors in Grapes by High-Performance Liquid Chromatography with a Diode Array Detector

Nowadays, the techniques for the analysis of glycosidic precursors in grapes involve changes in the glycoside structure or it is necessary the use of very expensive analytical techniques. In this study, we describe for the first time an approach to analyse intact glycosidic aroma precursors in grapes by high-performance liquid chromatography with a diode array detector (HPLC-DAD), a simple and cheap analytical technique that could be used in wineries. Briefly, the skin of Muscat of Alexandria grapes was extracted using a microwave and purified using solid-phase extraction combining Oasis MCX and LiChrolut EN cartridges. In total, 20 compounds were selected by HPLC-DAD at 195 nm and taking as a reference the spectrum of phenyl β-D-glucopyranoside, whose DAD spectrum showed a first shoulder from 190 to 230 nm and a second around 200-360 nm. After that, these glycosidic compounds were identified by High-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (HPLC-qTOF-MS). Disaccharides hexose pentose were the most abundant group observed with respect to the sugars and monoterpendiols the main aglycones found.

Comparative Analysis of Glycosidic Aroma Compound Profiling in Three Vitis vinifera Varieties by Using Ultra-High-Performance Liquid Chromatography Quadrupole-Time-of-Flight Mass Spectrometry

Glycosidic aroma compounds are the important precursors of volatile aroma in grapes, and they can be added with odorous aglycones via enzyme- or acid-catalyzed hydrolysis during wine fermentation and storage. Developing an analytical method for intact glycosides can provide the possibility to study the accumulation of these aroma precursors in grape berries. For this purpose, a Tandem Mass Spectrometry (MS/MS). database based on ultra-high-performance liquid chromatography quadrupole-time-of-flight mass spectrometry was built, covering multiple aglycone classes. Subsequently, the profiles of glycosidic aroma compounds in Vitis vinifera L. cv. Muscat Blanc, Riesling, and Chardonnay berries during maturation were investigated. Pentosyl-hexosides were the most abundant glycosides in all three varieties. Both composition and concentration of glycosidic aroma compounds varied obviously among grape varieties. Except for monoterpenol pentosyl-hexosides, most glycosides were kept almost stable in their concentrations during berry maturation. This research provides an approach to understand the variation of glycosidic aroma components from the perspective of aglycones and glycosides.

UPLC-QTof-MSE Metabolomics Reveals Changes in Leaf Primary and Secondary Metabolism of Hop (Humulus lupulus L.) Plants under Drought Stress

The hop (Humulus lupulus L.) is an important specialty crop used in beer production. Untargeted UPLC-QTof-MS^E metabolomics was used to determine metabolite changes in the leaves of hop plants under varying degrees of drought stress. Principal component analysis revealed that drought treatments produced qualitatively distinct changes in the overall chemical composition of three out of four genotypes tested (i.e., Cascade, Sultana, and a wild var. neomexicanus accession but not Aurora), although differences among treatments were smaller than differences among genotypes. A total of 14 compounds consistently increased or decreased in response to drought stress, and this effect was generally progressive as the severity of drought increased. A total of 10 of these marker compounds were tentatively identified as follows: five glycerolipids, glutaric acid, pheophorbide A, abscisic acid, roseoside, and dihydromyricetin. Some of the observed metabolite changes likely occur across all plants under drought conditions, while others may be specific to hops or to the type of drought treatments performed.