Screening and evolution of volatile compounds during ripening of ‘Nebbiolo,’ ‘Dolcetto’ and ‘Barbera’ (Vitis vinifera L.) neutral grapes by SBSE–GC/MS

Solvent Extraction of PDMS Tubing as a New Method for the Capture of Volatile Organic Compounds from Headspace

Polydimethylsiloxane (PDMS) tubing is increasingly being used to collect volatile organic compounds (VOCs) from static biological headspace. However, analysis of VOCs collected using PDMS tubing often deploys thermal desorption, where samples are considered as 'one-offs' and cannot be used in multiple experiments. In this study, we developed a static headspace VOC collection method using PDMS tubing which is solvent-based, meaning that VOC extracts can be used multiple times and can be linked to biological activity. Using a synthetic blend containing a range of known semiochemicals (allyl isothiocyanate, (Z)-3-hexen-1-ol, 1-octen-3-one, nonanal, (E)-anethol, (S)-bornyl acetate, (E)-caryophyllene and pentadecane) with differing chemical and physicochemical properties, VOCs were collected in static headspace by exposure to PDMS tubing with differing doses, sampling times and lengths. In a second experiment, VOCs from oranges were collected using PDMS sampling of static headspace versus dynamic headspace collection. VOCs were eluted with diethyl ether and analysed using gas chromatography - flame ionization detector (GC-FID) and coupled GC - mass spectrometry. GC-FID analysis of collected samples showed that longer PDMS tubes captured significantly greater quantities of compounds than shorter tubes, and that sampling duration significantly altered the recovery of all tested compounds. Moreover, greater quantities of compounds were recovered from closed compared to open systems. Finally, analysis of orange headspace VOCs showed no qualitative differences in VOCs recovered compared to dynamic headspace collections, although quantities sampled using PDMS tubing were lower. In summary, extraction of PDMS tubing with diethyl ether solvent captures VOCs from the headspace of synthetic blends and biological samples, and the resulting extracts can be used for multiple experiments linking VOC content to biological activity.

Influence on grape aromatic compounds of natural fungicides used for the control of downy mildew

BACKGROUND

The grape volatile fraction determines to a great extent its aroma, which is one of the most important characteristics influencing wine quality and consumer preferences. Grapevine downy mildew (GDM) is one of the most important and devastating diseases of grapevines worldwide. In this study, the impact on the volatile composition of cv. Verdicchio grapes of classical copper formulations, was compared to that of alternative products. Thus, 11 treatments were foliar applied throughout one grapevine cycle.

RESULTS

Most of the volatile compounds present in the grapes were not affected by the treatments used in order to prevent GDM. In the case of the total C₁₃ norisoprenoids, some differences were found between grapes untreated control and those applied with the grapefruit seed extract. Moreover, the content of alcohols was smaller in grapes from Bordeaux mixture treatment and higher in the samples from chitosan application.

CONCLUSION

Therefore, from the qualitative point of view of the berry, treatment with tested products alternative to copper is recommended, which minimize the environmental and health problems that this heavy metal brings to the soil and in the winery, since it means that their applications did not affect the grape aroma. © 2022 Society of Chemical Industry.

Free and glycosylated aroma compounds in grapes monitored by solid-liquid extraction and dispersive liquid-liquid microextraction combined with gas chromatography-mass spectrometry

Fifteen aroma compounds have been determined in their free and glycosylated forms in grapes using dispersive liquid‐liquid microextraction with gas chromatography‐mass spectrometry. The sample treatment includes a previous solid‐liquid extraction stage and subsequent parallel microextraction approaches to preconcentrate total aroma content and the free fraction. Thus, the extraction of the total content of analytes requires previous enzymatic hydrolysis of the bound forms. For preconcentration, chloroform (250 μl) and acetonitrile (1.5 ml) were added to 10 ml of the sample extract in the presence of 0.5 g sodium chloride. The absence of matrix effect in the samples allowed quantification against aqueous external standards. Limits of detection ranged between 5 and 30 ng/g, depending on the compound. Method accuracy was studied through recovery assays, with recoveries in the 82–115% range being obtained. Relative standard deviations for repeatability studies were lower than 12%. Four different samples of grapes were analyzed, being quantified linalool in its free form at concentrations in the 359–470 ng/g range, and benzyl alcohol, 2‐phenylethanol, and linalool oxide I and II in their bound forms between 52 and 464 ng/g.

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.

Advancement in analytical techniques for the extraction of grape and wine volatile compounds

The grape and wine aroma is one of the most determining factors of quality, therefore the study of their volatile composition is a very important topic in vitiviniculture. The range of concentrations in which many of these compounds are found is quite low, in concentrations of ng/L; due to this, a sample preparation stage is necessary before doing the chromatographic analysis of the volatile compounds. In this review, the main analytical techniques used for the extraction of volatile compounds in grapes and wines are studied. The techniques presented are liquid-liquid extraction (LLE), solid phase extraction (SPE), solid phase microextraction (SPME), stir bar sorptive extraction (SBSE), and thin film solid phase microextraction (TF-SPME). For each of these techniques, a description was made, and the different characteristics were numbered, as well as their main advantages and disadvantages. Furthermore, from the second technique, a comparison is made with the previous techniques, explaining the reasons why new techniques have emerged. Throughout the review it is possible to see the different techniques that have been emerging in the past years as an improvement of the classical techniques.

The Actual and Potential Aroma of Winemaking Grapes

This review intends to rationalize the knowledge related to the aroma of grapes and to the aroma of wine with specific origin in molecules formed in grapes. The actual flavor of grapes is formed by the few free aroma molecules already found in the pulp and in the skin, plus by those aroma molecules quickly formed by enzymatic/catalytic reactions. The review covers key aroma components of aromatic grapes, raisins and raisinized grapes, and the aroma components responsible from green and vegetal notes. This knowledge is used to explain the flavor properties of neutral grapes. The aroma potential of grape is the consequence of five different systems/pools of specific aroma precursors that during fermentation and/or aging, release wine varietal aroma. In total, 27 relevant wine aroma compounds can be considered that proceed from grape specific precursors. Some of them are immediately formed during fermentation, while some others require long aging time to accumulate. Precursors are glycosides, glutathionyl and cysteinyl conjugates, and other non-volatile molecules.

Use of density sorting for the selection of aromatic grape berries with different volatile profile

The aim of the study was to investigate the application of berry density sorting as a tool for the selection of grapes with different volatile and precursor profiles. The study was carried out on Moscato giallo, Malvasia di Schierano, Malvasia nera lunga, and Brachetto aromatic grape varieties. Free and glycosidically-bound terpene compounds including linalool, geraniol, nerol, citronellol, and terpineol, as well as lipoxygenases activity-derived compounds, were evaluated using head space-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) in density sorted berries (1075-1119 kg m^-3). Total free terpenes changed with the berry density, while no significant changes were found in total glycosylated compounds, except for Malvasia nera lunga grapes where nerol, linalool, and geraniol contributed strongly to the increase of total contents with increasing berry density. Given that these variations were strongly variety-dependent, the possible use of density sorting equipment in winery for this aim may be less effective.

Characterization of volatile compounds in Cowart muscadine grape (Vitis rotundifolia) during ripening stages using GC-MS combined with principal component analysis

Muscadine grape (Vitis rotundifolia) is a popular fruit in the Southeastern United States because of its unique aroma and strong antioxidant capacity. Volatile compounds of a locally cultivated muscadine cultivar Cowart were characterized by solid-phase microextraction coupled with GC-MS. Twenty-eight volatile compounds, including fruity short-chain esters, alcohols, terpenes, and carbonyl compounds, were detected based on mass spectra and Kovats indices. Based on principal component analysis and hierarchical clustering, the grapes in stages I and II had relatively similar flavor patterns, which were different from that in stage III. Butyl-2-butenoate, hexyl acetate, propyl acetate, ethyl trans-2-butenoate, hexyl-2-butenoate, ethyl acetate, butyl acetate, 1-octanol, ethyl hexanoate, and β- citral were present as distinct volatile chemicals in stage III, while nonanal, decanal, and β-citronellol were distinct in stage II, and myrcenol, β-ocimene, and l-limonene were biomarkers in stage I. Understanding volatile compounds at each stage can assist farmers in choosing the optimal time to harvest muscadine grapes.