Fractionation of glycoside precursors of aroma in grapes and wine

From Fruit to Beverage: Investigating Actinidia Species for Characteristics and Potential in Alcoholic Drink Production

There is a growing interest in various types of kiwifruits, such as the "yellow" kiwifruit (Actinidia chinensis var. chinensis) and the "baby" kiwifruit of Actinidia arguta. These fruits are rich in bioactive compounds, which contribute to their nutraceutical properties, but they nevertheless have a shorter shelf life, resulting in economic losses. This study aims to chemically characterize kiwifruit juices from SunGold and baby kiwifruit varieties (Hortgem Rua and Hortgem Tahi) to improve knowledge and explore the suitability of these products for producing low-alcohol beverages using non-Saccharomyces strains, with the purpose of reducing waste and generating value-added processing. Total soluble solids, acidity, hardness, dry matter, total phenolic content, and antioxidant capacity were used as indicators of fruit quality. Chemical characterization of fresh kiwifruit juices revealed distinct profiles among varieties, with SunGold juice exhibiting higher sugar content and acidity. Citric acid was the predominant organic acid, while, as expected, tartaric was not detected. Kiwifruit juice fermentations by T. delbrueckii UMY196 were always completed regardless of the type of juice used, producing beverages with ethanol content ranging from 6.46 to 8.85% (v/v). The analysis of volatile organic compounds highlighted the presence of several molecules, contributing to aroma profiles with relevant differences among the three kiwifruit-based drinks. In particular, the total concentration of esters in the beverages reached 8.2 mg/L, 9.2 mg/L, and 8.6 mg/L in the Tahi, Rua, and SunGold beverages, respectively. The qualitative and quantitative profiles of the kiwifruit drinks revealed a pronounced perception of acidity and fruity traits, with significant differences observed by Principal Component Analysis (PCA) in aroma descriptors among the proposed beverages. The possibility of using unsold, overripe, or waste fruits to prepare new products with an increase in the sustainability of this supply chain is set.

Aroma precursors of Grignolino grapes (Vitis vinifera L.) and their modulation by vintage in a climate change scenario

Current climatic conditions may cause significant changes in grapevine phenology and maturity dynamics linked often with changes to ecoclimatic indicators. The influence exerted by different meteorological conditions during four consecutive years on the aromatic potential of Grignolino grapes was investigated for the first time. The samples were collected from three vineyards characterized by different microclimatic conditions mainly related to the vineyard exposure and by a different age of the plants. Important differences as far as temperature and rainfall patterns are concerned during ripening were observed among the 4 years. Grape responses to abiotic stress, with particular emphasis on aromatic precursors, were evaluated using gas chromatography coupled to mass spectrometry. The results highlighted significant differences among the vintages for each vineyard in terms of the berry weight and the aromatic precursor concentration. For the grapes of the younger-vine vineyard, the content of aroma compounds showed a different variability among the vintages if compared to the old-vine vineyards. Optimal conditions in terms of temperature and rainfall during the green phase followed by a warm and dry post-veraison period until harvest favored all classes of compounds especially terpenoids mainly in the grapes of the old vines. High-temperature (>30°C) and low-rainfall pattern before veraison led to high benzenoid contents and increased differences among vineyards such as berry weight, whereas cooler conditions favored the terpenoid levels in grapes from southeast-oriented vineyards. In a hilly environment, lack of rainfall and high temperature that lately characterize the second part of berry development seem to favor the grape quality of Grignolino, a cultivar of medium-late ripening, by limiting the differences on bunch ripening, allowing a greater accumulation of secondary metabolites but maintaining at the same time an optimum balance sugar/acidity.

Effects of glycosidase on glycoside-bound aroma compounds in grape and cherry juice

This paper reports the occurrence of six kinds of commercial enzyme hydrolysis effects for use in grape juice and cherry juice, which provide a basis for studying the bound aroma compounds in fruit juice and their application in production. Using headspace solid-phase microextraction combined with GC-MS, a reliable procedure for determining the free and glycosidic-bound volatile compounds has been established. Comparison of these free and bound aroma compounds revealed that non-volatile glycosides, known as aroma precursors, occur at high concentrations in grape and cherry juice. Using six different glycosidase enzymes, 67 volatile compounds were identified in these two juices, including terpenes, C13-norisoprenoids, higher alcohols, esters, C6-compounds, C9-compounds, and phenols. The different enzymes had significant effects on varietal aroma. Creative and AR2000 had similar hydrolysis effects, which contribute greatly to the characteristic aroma of grape juice and cherry juice, significantly enhance the floral and fruity features of fruit juice, and improve aroma complexity in the system. The Creative enzyme can be used as a new choice for studying juice-bound aroma and hydrolysis-bound aroma in fruit and wine production.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-022-05662-3.

Effects of Traditional and Modern Post-Harvest Withering Processes on the Composition of the Vitis v. Corvina Grape and the Sensory Profile of Amarone Wines

In the Valpolicella area (Verona, Italy) Vitis vinifera cv. Corvina is the main grape variety used to produce Amarone wine. Before starting the winemaking process, the Corvina grapes are stored in a withering (i.e., dehydrating) warehouse until about 30% of the berry weight is lost (WL). This practice is performed to concentrate the metabolites in the berry and enrich the Amarone wine in aroma and antioxidant compounds. In compliance with the guidelines and strict Amarone protocol set by the Consorzio of Amarone Valpolicella, withering must be carried out by setting the grapes in a suitable environment, either under controlled relative air humidity (RH) conditions and wind speed (WS)—no temperature modification is to be applied—or, following the traditional methods, in non-controlled environmental conditions. In general, the two processes have different dehydration kinetics due to the different conditions in terms of temperature, RH, and WS, which affect the accumulation of sugars and organic acids and the biosynthesis of secondary metabolites such as stilbenes and glycoside aroma precursors. For this study, the two grape-withering processes were carried out under controlled (C) and non-controlled (NC) conditions, and the final compositions of the Corvina dried grapes were compared also to evaluate the effects on the organoleptic characteristics of Amarone wine. The findings highlighted differences between the two processes mainly in terms of the secondary metabolites of the dried grapes, which affect the organoleptic characteristics of Amarone wine. Indeed, by the sensory evaluation, wines produced by adopting the NC process were found more harmonious, elegant, and balanced. Finally, we can state how using a traditional system, grapes were characterised by higher levels of VOCs (volatile compounds), whilst wines had a higher and appreciable complexity and finesse.

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.

Glycosidically bound aroma precursors in fruits: A comprehensive review

Fruit aroma is mainly contributed by free and glycosidically bound aroma compounds, in which glycosidically bound form can be converted into free form during storage and processing, thereby enhancing the overall aroma property. In recent years, the bound aroma precursors have been widely used as flavor additives in the food industry to enhance, balance and recover the flavor of products. This review summarizes the fruit-derived aroma glycosides in different aspects including chemical structures, enzymatic hydrolysis, biosynthesis and occurrence. Aroma glycosides structurally involve an aroma compound (aglycone) and a sugar moiety (glycone). They can be hydrolyzed to release free volatiles by endo- and/or exo-glucosidase, while their biosynthesis refers to glycosylation process using glycosyltransferases (GTs). So far, aroma glycosides have been found and studied in multiple fruits such as grapes, mangoes, lychees and so on. Additionally, their importance in flavor perception, their utilization in food flavor enhancement and other industrial applications are also discussed. Aroma glycosides can enhance flavor perception via hydrolyzation by β-glucosidase in human saliva. Moreover, they are able to impart product flavor by controlling the liberation of active volatiles in industrial applications. This review provides fundamental information for the future investigation on the fruit-derived aroma glycosides.

Dynamic changes in norisoprenoids and phenylalanine-derived volatiles in off-vine Vidal blanc grape during late harvest

We investigated the dynamic changes in norisoprenoids and phenylalanine derivatives in off-vine Vidal blanc. Glycosidically bound as well as free-form volatile compounds were identified by GC-MS in two vintages. Thus, off-vine grape exhibited the development of four higher alcohols (viz. linalool oxide, 2-octanol, 1-pentanol, and 1-heptanol), C13-norisoprenoids (α-ionone), phenylalanine-derivates (2-phenylethanol), whereas β-ionone and geranial showed high correlation in on-vine grape. Freeze-thaw cycles and desiccation, two exterior stress affect volatile compound development, resulted in content fluctuations during late harvest. Interestingly, the total content of higher alcohols was higher in on-vine grapes than off-vine grapes in two vintages respectively. Interestingly, the content of higher alcohols was higher in off-vine samples in the 2016 and 2017 vintages. In terms of physicochemical parameters, off-vine Vidal showed results similar to those of on-vine sample. Nevertheless, sensorial impression of the grape juice was influenced by interaction of vintages and vine treatments.

Combining liquid chromatography and tandem mass spectrometry approaches to the study of monoterpene glycosides (aroma precursors) in wine grape

Monoterpene-glycosides are important aroma precursors that, undergo hydrolysis, confer intense floral notes to the wines. Therefore, the knowledge of the nature of the sugar residues and the structure of these molecules is of great interest. In present study, liquid chromatography (LC) separation coupled with different mass spectrometry (MS) experiments for the characterization of these compounds were explored. The LC parameters were tuned to optimize the resolution between the analytes present in grape sample extracts. Twenty principal peaks with a relative abundance >1% were selected and divided in 4 classes characterized by different molecular weight. In general, positive ionization of the studied compounds displayed the [M + NH₄ ]⁺ ion as base peak. On the contrary, a distribution between [M + Cl]^- and [M + HCOO]^- species was observed in negative ion mode. However, a clear differentiation between the studied compounds was only possible by combining both LC and tandem MS (MS/MS). Indeed, by applying a series of energy resolved MS/MS experiments and monitoring both positive and negative ions, a structural characterization of the analytes was achieved. The proposed LC-MS/MS approach provided the profile of monoterpenol-diglycosides and allowed the identification of a series of isobaric terpene-diglycosides in grape. The study of their MS/MS spectra indicated the structure of geranic and/or nerolic acid aglycones. To verify the interest of studied compounds, a preliminary evaluation of the intensity of signals of these glycosides were carried out. The obtained results showed a significant difference between the grape samples collected in two different vintages.

Effect of pre-bloom leaf removal on grape aroma composition and wine sensory profile of Semillon cultivar

BACKGROUND

Early leaf removal at pre-bloom is an innovative viticultural practice for regulating yield components and improving grape quality. The effects of this technique on vine performance, grape composition and wine sensory profile of Semillon variety were assessed.

RESULTS

Pre-bloom leaf removal enhanced canopy porosity, total soluble solids in musts and reduced cluster compactness. This practice had a strong effect on glycoside aroma precursors, in particular by increasing glycoside terpenols and norisoprenoids. Metabolites of linalool were the most responsive to leaf removal. Wine produced from defoliated vines was preferred in tasting trials for its more intense fruity notes and mouthfeel attributes.

CONCLUSION

Pre-bloom leaf removal is a powerful technique for modifying canopy microclimate, vine yield, grape composition and wine quality. The increase of glycoside aroma compounds in treated grapes has potential positive effect in improving the sensory profile of the resulting wines. © 2017 Society of Chemical Industry.

Biosurfactant-Protein Interaction: Influences of Mannosylerythritol Lipids-A on β-Glucosidase

In this work, the influences of a biosurfactant, mannosylerythritol lipids-A (MEL-A) toward β-glucosidase activity and their molecular interactions were studied by using differential scanning calorimetry (DSC), circular dichroism spectroscopy (CD), isothermal titration calorimetry (ITC), and docking simulation. The enzyme inhibition kinetics data showed that MEL-A at a low concentration (< critical micelle concentration (CMC), 20.0 ± 5.0 μM) enhanced β-glucosidase activity, whereas it inhibited the enzyme activity at higher concentrations more than 20.0 μM, followed by a decreased V_max and K_m of β-glucosidase. The thermodynamics and structural data demonstrated that the midpoint temperature (T_m) and unfolding enthalpy (ΔH) of β-glucosidase was shifted to high values (76.6 °C, 126.3 J/g) in the presence of MEL-A, and the secondary structure changes of β-glucosidase, including the increased α-helix, β-turn, or random coil contents, and a decreased β-sheet content were caused by MEL-A at a CMC concentration. The further ITC and docking simulations suggested the bindings of MEL-A toward β-glucosidase were driven by weak hydrophobic interactions happened between the amino acid residues of β-glucosidase and the fatty acid residues of MEL-A, in addition to hydrogen bonds between amino acids and hydroxyl in glycosyl residues of this biosurfactant.

Influence of vineyard altitude on Glera grape ripening (Vitis vinifera L.): effects on aroma evolution and wine sensory profile

BACKGROUND

Environmental factors have been acknowledged to greatly influence grape and wine aromas. Among them, the effect of altitude on grape aroma compounds has scarcely been debated in literature available to date. In the present study, we investigated the influence of altitude on grape composition and aroma evolution during ripening of Vitis vinifera L. cultivar Glera grown in Conegliano-Valdobbiadene DOCG area (Italy).

RESULTS

The site at highest altitude (380 m above sea level) was warmer than the lowest site (200 m above sea level) and, even with differences in temperature in the range 1.5-2 °C, the impact of the cultivation site on grape ripening and aroma accumulation and preservation was significant. The lowest site demonstrated slower grape ripening, and grapes at harvest accumulated lower amounts of all of the main classes of aroma compounds typical of the Glera variety. Wines produced from the highest site were preferred in tasting trials for their more patent floral notes and elegance.

CONCLUSION

Altitude strongly influences grape ripening evolution and flavour accumulation in the Glera grape, and this result accounts for the different styles in the sparkling wines subsequently produced. Moreover, the present study shows that aroma compound biosynthesis, particularly that of benzenoides, starts before véraison in Glera. © 2016 Society of Chemical Industry.

Applications of solid-phase microextraction and gas chromatography/mass spectrometry (SPME-GC/MS) in the study of grape and wine volatile compounds

Volatile compounds are responsible for the wine "bouquet", which is perceived by sniffing the headspace of a glass, and of the aroma component (palate-aroma) of the overall flavor, which is perceived on drinking. Grape aroma compounds are transferred to the wine and undergo minimal alteration during fermentation (e.g., monoterpenes and methoxypyrazines); others are precursors of aroma compounds which form in winemaking and during wine aging (e.g., glycosidically-bound volatile compounds and C13-norisoprenoids). Headspace solid phase microextraction (HS-SPME) is a fast and simple technique which was developed for analysis of volatile compounds. This review describes some SPME methods coupled with gas chromatography/mass spectrometry (GC/MS) used to study the grape and wine volatiles.

Profiling of grape monoterpene glycosides (aroma precursors) by ultra-high performance-liquid chromatography-high resolution mass spectrometry (UHPLC/QTOF)

A 'suspect screening analysis' method for grape metabolomics by ultra-high performance-liquid chromatography (UHPLC) and high-resolution quadrupole-time of flight (QTOF) mass spectrometry was recently developed. This method was applied to study grape monoterpene glycosides, the main grape aroma precursors. Since standard compounds were not available, they were tentatively identified by overlapping various analytical approaches, in agreement with the indications recommended in mass spectrometry (MS)-based metabolomics. Accurate mass and isotopic pattern, MS/MS fragmentation, correlation between fragments observed and putative structures and between liquid chromatography coupled with mass spectrometry (LC/MS) and gas chromatography/mass spectrometry signals were studied. Seventeen monoterpene glycosides were identified without performing the hydrolytic artifacts commonly used to study these compounds which may affect sample profile. This is the first time that a detailed study of these aroma precursors has been carried out by direct LC/MS analysis.

Expression of terpene synthase genes associated with the formation of volatiles in different organs of Vitis vinifera

Plants produce a plethora of volatile organic compounds (VOCs) which are important in determining the quality and nutraceutical properties of horticultural food products, including the taste and aroma of wine. Given that some of the most prevalent grape aroma constituents are terpenoids, we investigated the possible variations in the relative expression of terpene synthase (TPS) genes that depend on the organ. We thus analysed mature leaves, young leaves, stems, young stems, roots, rachis, tendrils, peduncles, bud flowers, flowers and berries of cv Moscato bianco in terms of their VOC content and the expression of 23 TPS genes. In terms of the volatile characterization of the organs by SPME/GC-MS analysis, flower buds and open flowers appeared to be clearly distinct from all the other organs analysed in terms of their high VOC concentration. Qualitatively detected VOCs clearly separated all the vegetative organs from flowers and berries, then the roots and rachis from other vegetative organs and flowers from berries, which confirms the specialization in volatile production among different organs. Our real-time RT-PCR results revealed that the majority of TPS genes analysed exhibited detectable transcripts in all the organs investigated, while only some were found to be expressed specifically in one or just a few organs. In most cases, we found that the known products of the in vitro assay of VvTPS enzymes corresponded well to the terpenes found in the organs in which the encoding gene was expressed, as in the case of (E)-β-caryophyllene synthases, α-terpineol synthase and α-farnesene synthase. In addition, we found groups of homologous TPS genes, such as (E)-β-caryophyllene and β-ocimene synthases, expressed distinctively in the various tissues. This thus confirmed the subfunctionalization events and a specialization on the basis of the organs in which they are mostly expressed.

Analysis of the expression of terpene synthase genes in relation to aroma content in two aromatic Vitis vinifera varieties

Grape (Vitis vinifera L.) flavour management in the vineyard requires knowledge of the derivation of individual flavour and aroma characteristics. Some of the most prevalent wine grape aroma constituents are terpenoids and this study represents a wide report about grape terpene synthase (TPS) gene transcript profiling in different tissues of two aromatic grapevine varieties, particularly flowers and developing berries, correlated with the accumulation patterns of free aroma compounds. All investigated genes belonging to the TPS-a and TPS-b subfamilies reached the highest expression in accordance with the peak of accumulation of the respective compounds. In the TPS-g subfamily, only one of the genes characterised for linalool synthases showed major transcript abundance in ripening berries, whereas the only geraniol synthase had a peak of expression in green berries and at the beginning of ripening, when geraniol concentration started to increase and overcome the linalool concentration. The genes identified in this study as being mainly responsible for linalool and geraniol synthesis during berry development, and the phenological phases in which they are mostly expressed, should be of interest to viticulturists and wine makers to improve decision making along the chain of production.

Comparison of solid-phase extraction sorbents for the fractionation and determination of important free and glycosidically-bound varietal aroma compounds in wines by gas chromatography-mass spectrometry

A critical comparison was made of seven solid-phase extraction (SPE) sorbents for the fractionation and isolation of 21 important free and glycosidically-bound varietal volatile aroma compounds. The sample was subjected to SPE and the free aromatics were eluted with dichloromethane followed by elution of the glucoconjugates with methanol; after fractionation, the free fraction was analyzed directly by GC-MS while the sugar-bound fraction was enzymatically hydrolyzed to liberate the free compounds before analysis by GC-MS. The extraction efficiency for the free compounds was evaluated based on the analytes’ signal recovery and for the glycosidically-bound compounds in terms of the relative peak areas. The best results for both the free and bound fractions were obtained with the Isolute ENV+ resin. Following selection of the most efficient SPE material, a GC-MS method was validated (in terms of selectivity, linearity, limits of detection (LODs) and limits of quantification (LOQs), recovery, repeatability, within-laboratory reproducibility and uncertainty) for the quantitative determination of the free primary volatiles in white wines. Validation results are presented at 4 fortification levels (10, 50, 200 and 500 µL−1). Regarding linearity, the correlation coefficient of the matrix-matched calibration plots was ≥0.99 for all the compounds. The LOQs were in the range 0.6–17.5 µg L−1. Recoveries ranged from 61% to 120% while the% relative standard deviation of the within-laboratory reproducibility was in the range 1.3% to 17.7%. Finally, the% expanded uncertainty ranged from 3.1% to 40.3%. The method has been successfully applied to the analysis of 20 white wine samples.

Wine flavor and aroma

The perception of wine flavor and aroma is the result of a multitude of interactions between a large number of chemical compounds and sensory receptors. Compounds interact and combine and show synergistic (i.e., the presence of one compound enhances the perception of another) and antagonistic (a compound suppresses the perception of another) interactions. The chemical profile of a wine is derived from the grape, the fermentation microflora (in particular the yeast Saccharomyces cerevisiae), secondary microbial fermentations that may occur, and the aging and storage conditions. Grape composition depends on the varietal and clonal genotype of the vine and on the interaction of the genotype and its phenotype with many environmental factors which, in wine terms, are usually grouped under the concept of "terroir" (macro, meso and microclimate, soil, topography). The microflora, and in particular the yeast responsible for fermentation, contributes to wine aroma by several mechanisms: firstly by utilizing grape juice constituents and biotransforming them into aroma- or flavor-impacting components, secondly by producing enzymes that transform neutral grape compounds into flavor-active compounds, and lastly by the de novo synthesis of many flavor-active primary (e.g., ethanol, glycerol, acetic acid, and acetaldehyde) and secondary metabolites (e.g., esters, higher alcohols, fatty acids). This review aims to present an overview of the formation of wine flavor and aroma-active components, including the varietal precursor molecules present in grapes and the chemical compounds produced during alcoholic fermentation by yeast, including compounds directly related to ethanol production or secondary metabolites. The contribution of malolactic fermentation, ageing, and maturation on the aroma and flavor of wine is also discussed.

Metabolic profiling of strawberry (Fragaria x ananassa Duch.) during fruit development and maturation

Strawberry (Fragaria × ananassa Duch), a fruit of economic and nutritional importance, is also a model species for fleshy fruits and genomics in Rosaceae. Strawberry fruit quality at different harvest stages is a function of the fruit's metabolite content, which results from physiological changes during fruit growth and ripening. In order to investigate strawberry fruit development, untargeted (GC-MS) and targeted (HPLC) metabolic profiling analyses were conducted. Principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) were employed to explore the non-polar and polar metabolite profiles from fruit samples at seven developmental stages. Different cluster patterns and a broad range of metabolites that exerted influence on cluster formation of metabolite profiles were observed. Significant changes in metabolite levels were found in both fruits turning red and fruits over-ripening in comparison with red-ripening fruits. The levels of free amino acids decreased gradually before the red-ripening stage, but increased significantly in the over-ripening stage. Metabolite correlation and network analysis revealed the interdependencies of individual metabolites and metabolic pathways. Activities of several metabolic pathways, including ester biosynthesis, the tricarboxylic acid cycle, the shikimate pathway, and amino acid metabolism, shifted during fruit growth and ripening. These results not only confirmed published metabolic data but also revealed new insights into strawberry fruit composition and metabolite changes, thus demonstrating the value of metabolomics as a functional genomics tool in characterizing the mechanism of fruit quality formation, a key developmental stage in most economically important fruit crops.

Chemical characterization and enological potential of Raboso varieties by study of secondary grape metabolites

DNA studies supported by matrix-assisted laser desorption ionization-time of flight mass spectrometry analysis of seed proteins showed that the Vitis vinifera red grape variety Raboso Veronese is the progeny of a spontaneous cross between Raboso Piave (red) and Marzemina Bianca (white) varieties. In the present work, the main secondary grape metabolites of Raboso varieties were studied, and their enological potential was evaluated and compared with that of other red varieties reported in the literature. In general, Raboso grapes had high flavonoid contents and high percentages of polyphenols extractable in winemaking and substantial contents of norisoprenoid aroma precursors. Raboso Veronese stood out for its high content of cyanidin and had higher (+)-catechin and (-)-epicatechin contents than Raboso Piave and abundant quercetin glucoside, indicating substantial plant biosynthesis toward compounds dihydroxylated in the B-ring. Study of secondary grape metabolites is confirmed as an effective tool in differentiating similar varieties, in particular on the basis of polyphenol profiles.

Comparison of the suitability of different hydrolytic strategies to predict aroma potential of different grape varieties

Precursor extracts obtained from different grape varieties were submitted to harsh acid hydrolysis (pH 2.5, 100 degrees C, 1 h) and enzymatic hydrolysis (AR2000, pH 5, 40 degrees C, 16 h) and were also added to a synthetic must (200 g L(-1) glucose), which was fermented (yeast strain Stellevin NT 116), to compare the "natural hydrolysis" carried by yeast with alternative "fast" hydrolytic strategies. In all cases, released volatile compounds were extracted by SPE and determined by GC-MS. Leaving aside Muscat, differences between varieties were not relevant, although Grenache and Chardonnay presented some key peculiarities. In general, alcoholic fermentation showed the lowest potential to release volatile compounds from aromatic precursors, whereas enzymatic hydrolysis was the most efficient but also the most different. Practically, this implies that the predictive ability of this hydrolytic strategy is rather poor. In contrast, harsh acid hydrolysis can be considered to much more adequately measure the aroma potential of grapes for winemaking, which suggests that transformations taking place during fermentation include relevant chemical rearrangements in acid media that are better predicted by acid hydrolysis.

Hydrolysis and transformation of grape glycosidically bound volatile compounds during fermentation with three Saccharomyces yeast strains

The ability of three Saccharomyces wine yeasts (S. cerevisiae AWRI 838, S. cerevisiae AWRI 1537, and S. bayanus AWRI 1375) to liberate volatile compounds from sugar-bound aroma precursors was investigated using synthetic and grape glycosides under different experimental conditions. In model systems involving the incubation of yeast cells with either synthetic or grape-derived glycosides under conditions more favorable for glycosidase activities and less favorable for acid-catalyzed hydrolysis (pH 5.0 and 30 degrees C), all yeast strains studied proved to be capable of hydrolyzing glycosides, with S. bayanus AWRI 1375 displaying greater hydrolytic activity than S. cerevisiae AWRI 838 and AWRI 1537. During the fermentation of a chemically defined grape juice-like medium containing glycosidic precursors extracted from Vitis vinifera cv. White Frontignac (synonym Muscat à Petit Grains Blanc), all yeasts promoted a significant hydrolysis of different precursors, which varied according to the chemical structures of both the sugar and the aglycon moieties, as determined by GC-MS analysis of trifluoroacetylated derivatives. Hydrolysis of the White Frontignac derived glycosidic precursors during fermentation resulted in the release of monoterepene alcohols, terpene oxides, terpene diols, and 3-oxo-alpha-ionol, demonstrating the significant potential of these yeast strains to contribute to wine varietal volatile composition during alcoholic fermentation.

Study of the microbiodegradation of terpenoid resin-based varnishes from easel painting using pyrolysis–gas chromatography–mass spectrometry and gas chromatography–mass spectrometry

The alterations produced by microbiological attack on terpenoid resin-based varnishes from panel and canvas paintings have been evaluated using pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and gas chromatography-mass spectrometry (GC-MS). The proposed methods include the on-line derivatisation of drying oils and diterpenoid resins using hexamethyldisilazane during pyrolysis and the application of methyl chloroformate as a derivatisation reagent for triterpenoid resins in GC-MS. Two types of specimens, consisting of model oil medium prepared from linseed oil and model spirit varnishes prepared from colophony and mastic resins dissolved in turpentine, have been used as reference materials. For a series of specimens upon which different genera of bacteria and fungi were inoculated and encouraged to grow, analyses indicated that no mechanisms that commonly occur during the attack of enzymes on drying oils and terpenoid biodegraders were observed to occur in the oil medium and varnishes studied. Thus, the degradation pathways observed in the performed trials usually occur as consequence of natural ageing. Specific trials consisting of the application of biocides to uninoculated colophony varnish resulted in the identification of processes that produce undesirable degradation of the varnish due to interactions between the biocide and the varnish components. Finally, the studied biocides--Biotin, New-Des and Nipagine--generally exhibited good inhibiting effects on the microorganisms studied, although some interesting differences were found between them regarding the application method and type of biocide.

Optimization and evaluation of a procedure for the gas chromatographic-mass spectrometric analysis of the aromas generated by fast acid hydrolysis of flavor precursors extracted from grapes

A procedure has been developed for the GC-MS analysis of the aromas released in fast acid hydrolysis of precursor fractions from grape musts and skins. Different sorbents for the extraction of the precursors were compared. The best results were obtained with LiChrolut EN polymeric resins which displayed two and six-fold more extraction capacity than Amberlite XAD-2 resins and C18 sorbents, respectively. C18 sorbents are more suitable for selective extraction of less polar precursors. The initial version of the method was imprecise and so the imprecision of the different steps was assessed. The maceration of the solid parts and the liquid-liquid extraction of the aromas released in the acid hydrolysis proved to be the critical steps. Greater crushing of the solid parts and solid-phase extraction (SPE) instead of liquid-liquid extraction (LLE) improved reproducibility. In the method finally proposed about 100 aromatic components belonging to four large groups (lipid derivatives, shikimic acid derivatives, norisoprenoids and terpenes) were determined with good reproducibility. Important aroma compounds, such as cis-rose oxide or wine lactone were detected in non-Muscat grapes.

Enantioselective analysis of monoterpenes in different grape varieties during berry ripening using stir bar sorptive extraction- and solid phase extraction-enantioselective-multidimensional gas chromatography-mass spectrometry

The stereoisomeric ratios of various genuine metabolites of linalool (furanoid and pyranoid linalool oxides, hotrienol) and citronellol (cis- and trans-rose oxide) were determined in grape berries by means of enantioselective-multidimensional gas chromatography-mass spectrometry. Stereoisomers of the metabolites could be separated on a chiral column with a modified cyclodextrin as stationary phase. The detailed stereoselective analysis of the furanoid and pyranoid linalool oxides in the cv. Morio-Muskat during berry ripening is giving evidence that furanoid linalool oxides are generated via two different reaction pathways. Additionally, stereoselective analysis of rose oxide in different varieties that have attained commercial maturity has been performed demonstrating that cis-(2S,4R)-rose oxide is the main stereoisomer in all varieties. (3S)-Hotrienol was the main stereoisomer in all varieties with enantiomeric purities that were always higher than 90%.

Astonishing diversity of natural surfactants: 1. Glycosides of fatty acids and alcohols

Alkyl and fatty acid glycosides have become of great commercial interest in general and specifically for the pharmaceutical, cosmetic, and food industries. Natural surfactants are good sources for future chemical preparation of these glycosides. This review article shows an astonishing diversity of natural surfactants that could be used in laboratories and industry. More than 250 natural surfactants, including their chemical structures and biological activities, are described in this review article.

Hydrolysis of terpenyl glycosides in grape juice and other fruit juices: a review

The importance of monoterpenes on varietal flavour of must and other fruit juices has been reviewed. These compounds were mainly found linked to sugar moieties in grape juice and wines, showing no olfactory characteristics. In this way, analytical techniques developed to study these compounds, in both free or glycosidically forms, are discussed. Mechanisms to liberate terpenes were studied, making a comparative study between acidic and enzymic hydrolysis of terpene glycosides; as enzymic hydrolysis seems to be the most natural way to liberate terpenes, the ability to use glycosidases from grapes, yeasts, bacterial or exogenous, i.e. fungal commercial preparations, were reviewed. Re-arrangements of terpenes after acidic hydrolysis of glycoconjugated are discussed as well as potential adverse effects of enzyme preparations.

Identification of trace volatile compounds in freshly distilled Calvados and Cognac using preparative separations coupled with gas chromatography-mass spectrometry

Gas chromatography coupled with mass spectrometry (GC-MS) using both electron impact and chemical ionization detection modes led to the determination of the volatile composition of two samples of freshly distilled Cognac and two samples of freshly distilled Calvados. A total of 169 volatile compounds were directly identified in dichloromethane extracts obtained by liquid-liquid extraction. Trace compounds present in both spirits were characterized with the help of preparative separations. In a first step, groups of compounds were separated by preparative GC, and the fractions were analyzed on a polar stationary phase by GC-MS. In a second step, silica gel fractionation was used to separate them by polarity. In this study, 331 compounds, of which 162 can be considered as trace compounds, were characterized in both freshly distilled Cognac and Calvados. Of these, 39 are common to both spirits; 30 are specific to Cognac with numerous hexenyl esters and norisoprenoidic derivatives, whereas 93 are specific to Calvados with compounds such as unsaturated alcohols, phenolic derivatives, and unsaturated aldehydes.

Enantioselective analysis of free and glycosidically bound monoterpene polyols in Vitis vinifera L. cvs. Morio Muscat and Muscat Ottonel: evidence for an oxidative monoterpene metabolism in grapes

The enantiomeric ratios of various free and glycosidically bound monoterpene polyols in musts of the aromatic grapes Vitis vinifera L. cvs. Morio Muscat and Muscat Ottonel were determined by means of enantioselective multidimensional gas chromatography-mass spectrometry. Reference compounds of defined stereochemistry were synthesized and permitted the unequivocal determination of the elution order of the target compounds on chiral columns with modified cyclodextrins as stationary phases. It could be shown for the first time that the linalool-derived polyol 3,7-dimethylocta-1,7-dien-3,6-diol occurs predominately as the (3S,6S)-configured stereoisomer, providing evidence that this compound is generated by an enzymatic process in grape berries. The involvement of a cytochrome P450 monooxygenase in the oxidative metabolism of monoterpenes in grapes is dicussed.

Identification of lipid binders in paintings by gas chromatography. Influence of the pigments

The influence of the presence and the type of pigments in the lipid binding media of paintings were studied by gas chromatography with flame ionization detector. The drying oils were linseed stand oil, poppy oil and sunflower oil, and the pigments studied were cadmium red, cobalt blue, tin white, lead white, chalk and plaster of Paris, commonly used in paintings. The results indicate that the stearic/palmitic ratio and the presence of pigments are quite stable during ageing. However, some differences in the oleic acid/palmitic acid ratio were found, depending on the type of pigment present in the lipid binding media. These variations are related to the drying effect of the pigments. The proposed method has been applied to the identification of drying oils in two samples from baroque paintings in the "Basilica de la Virgen de los Desamparados" of Valencia, Spain.

First isolation of geranyl disaccharides from ginger and their relations to aroma formation

Three geraniol glycosides were isolated from immature fresh ginger rhizomes (Zingiber officinale Roscoe). Their structures were identified as geranyl 6-O-alpha-L-arabinopyranosyl-beta-D-glucopyranoside (1) geranyl 6-O-beta-D-apiofuranosyl-beta-D-glucopyranoside (2) and geranyl 6-O-beta-D-xylopyranosyl-beta-D-glucopyranoside (3) by spectrometric analyses. After incubating each glycoside with a crude enzyme solution prepared from ginger, geraniol was liberated in all of those fractions. This result indicates that the glycosides are related to the formation of geraniol-related compounds in ginger aroma.