Identification of a new lactone contributing to overripe orange aroma in Bordeaux dessert wines via perceptual interaction phenomena

The role of oak wood in the mint and floral notes of whisky: identification of common terpenoids by aromatic fractionation

Understanding the development of the whisky aroma during maturation in oak casks provides a rational basis for improvements in product quality. While oak wood is an important contributor to the spicy, toasted, and smoky aromatic notes, limited studies have focused on its role in floral and mint notes of matured whiskies.  However, achieving consistent flavour profiles remains difficult since the odorant molecules are mostly present in low concentration. A semi-preparative ultra-high-performance liquid chromatography (UHPLC) method was applied to whisky and oak wood extracts and used to isolate fractions characterised by floral and mint aromas. To investigate the contribution of terpenoids in these floral and fresh fragrances, a similar analytical process was applied on solutions of targeted reference compounds. This approach, coupled to gas-chromatography/mass-spectrometry analyses, indicated the presence of terpenoids in the fractions of interest as well as selective separation according to chemical structure (i.e., monoterpenes, monoterpenols, ketone monoterpenes, and C13-norisoprenoids). This approach resulted in the detection of respectively, ten and seven new terpenoids in whisky and oak wood. To the best of our knowledge, piperitone, mintlactones, and

Characterization of key odor-active compounds in Chinese Dornfelder wine and its regional variations by application of molecular sensory science approaches

In this study, aroma characteristics and odor-active compounds in Dornfelder wines from three main production regions of China were comprehensively investigated for the first time. The leading features of Chinese Dornfelder wines were black fruit, violet, acacia/lilac, red fruit, spice, dried plum, honey, and hay based on check-all-that-apply. Wines from the Northern Foothills of Tianshan Mountains and Eastern Foothills of Helan Mountains were dominated by floral and fruity aromas, while wines from the Jiaodong Peninsula were characterized by mushroom/earth, hay, and medicinal material notes. Aroma profiles of Dornfelder wines in three regions were successfully reconstructed with 61 volatiles determined by AEDA-GC-O/MS and OAV. Through aroma reconstitution, omission tests, and descriptive analysis, terpenoids could be regarded as varietal characteristic compounds directly contributing to floral perception in Dornfelder wines. Guaiacol, eugenol, and isoeugenol were further revealed to have a synergistic effect with linalool and geraniol on violet, acacia/lilac, spice, and black fruit.

Qualitative Screening of Volatile Thiols in Wine by Selective Silver Ion Solid-Phase Extraction with Heart-Cutting Multidimensional Gas Chromatography Mass Spectrometry/Olfactometry

The chemical analysis of odorous volatile thiols is intrinsically challenging. Substantial progress has been made in quantitative analysis of targeted thiols at ultra-trace concentrations (ng/L), but lesser analytical attention has been given to the qualitative screening of unknown thiols. This work presents a solid-phase extraction (SPE) method using a silver ion (Ag⁺)-based sorbent to isolate volatile thiols from red wine. This proposed Ag⁺ SPE method was effective (recovery: 87-101% for four non-furan thiols and 35-49% for two furan thiols), simple, safe, and greatly reduced artifacts, testifying to its suitability as the sample preparation protocol for a qualitative screening experiment. Separation and detection were conducted using heart-cutting multidimensional gas chromatography coupled to mass spectrometry/olfactometry (H/C MDGC-MS/O). Key parameters including H/C width, main host oven temperature, and cryogenic trapping temperature were investigated for optimal instrument performance. The developed Ag⁺ SPE H/C MDGC-MS/O strategy was readily applicable for qualitative screening of odorous volatile thiols in wine, as demonstrated by two case studies.

Modifications of Grapevine Berry Composition Induced by Main Viral and Fungal Pathogens in a Climate Change Scenario

The grapevine is subject to high number of fungal and viral diseases, which are responsible for important economic losses in the global wine sector every year. These pathogens deteriorate grapevine berry quality either directly via the modulation of fruit metabolic pathways and the production of endogenous compounds associated with bad taste and/or flavor, or indirectly via their impact on vine physiology. The most common and devastating fungal diseases in viticulture are gray mold, downy mildew (DM), and powdery mildew (PM), caused, respectively by Botrytis cinerea, Plasmopara viticola, and Erysiphe necator. Whereas B. cinerea mainly infects and deteriorates the ripening fruit directly, deteriorations by DM and PM are mostly indirect via a reduction of photosynthetic leaf area. Nevertheless, mildews can also infect berries at certain developmental stages and directly alter fruit quality via the biosynthesis of unpleasant flavor compounds that impair ultimate wine quality. The grapevine is furthermore host of a wide range of viruses that reduce vine longevity, productivity and berry quality in different ways. The most widespread virus-related diseases, that are known nowadays, are Grapevine Leafroll Disease (GLRD), Grapevine Fanleaf Disease (GFLD), and the more recently characterized grapevine red blotch disease (GRBD). Future climatic conditions are creating a more favorable environment for the proliferation of most virus-insect vectors, so the spread of virus-related diseases is expected to increase in most wine-growing regions. However, the impact of climate change on the evolution of fungal disease pressure will be variable and depending on region and pathogen, with mildews remaining certainly the major phytosanitary threat in most regions because their development rate is to a large extent temperature-driven. This paper aims to provide a review of published literature on most important grapevine fungal and viral pathogens and their impact on grape berry physiology and quality. Our overview of the published literature highlights gaps in our understanding of plant-pathogen interactions, which are valuable for conceiving future research programs dealing with the different pathogens and their impacts on grapevine berry quality and metabolism.

Strategies for the identification and sensory evaluation of volatile constituents in wine

Wine aroma, which stems from complex perceptual and cognitive processes, is initially driven by a multitude of naturally occurring volatile constituents. Its interpretation depends on the characterization of relevant volatile constituents. With large numbers of volatile constituents already identified, the search for unknown volatiles in wine has become increasingly challenging. However, the opportunities to discover unknown volatile compounds contributing to the wine volatilome are still of great interest, as demonstrated by the recent identification of highly odorous trace (µg/L) to ultra-trace (ng/L) volatile compounds in wine. This review provides an overview of both existing strategies and future directions on identifying unknown volatile constituents in wine. Chemical identification, including sample extraction, fractionation, gas chromatography, olfactometry, and mass spectrometry, is comprehensively covered. In addition, this review also focuses on aspects related to sensory-guided wine selection, authentic reference standards, artifacts and interferences, and the evaluation of the sensory significance of discovered wine volatiles. Powerful key volatile odorants present at ultra-trace levels, for which these analytical approaches have been successfully applied, are discussed. Research areas where novel wine volatiles are likely to be identified are pointed out. The importance of perceptual interaction phenomena is emphasized. Finally, future avenues for the exploration of yet unknown wine volatiles by coupling analytical approaches and sensory evaluation are suggested.

Sensory-directed characterisation of distinctive aromas of Sauternes and Viognier wines through semi-preparative liquid chromatography and gas chromatography approaches

Gas chromatography-olfactometry-mass spectrometry (GC-O-MS) has been very useful in identifying aroma compounds from within the complex matrix of wine. Supplementary separation can be required to overcome co-elution of volatiles or other sensory-directed chromatographic strategies are needed, including multidimensional chromatography and preparative fraction collection coupled to GC. Studies investigating 'overripe orange' aroma in sweet Sauternes wine and the similar 'apricot' aroma in Viognier wine were conducted. Wines with the targeted aroma attributes were selected and concentrated wine extracts prepared. GC-O found no individual aroma compounds with the targeted aroma attribute. Semi-preparative HPLC was used to obtain less complex fractions of the wine extracts. The fractions were eluted in water/ethanol and, therefore, could be smelled directly. Fractions with the targeted aroma character were further resolved by GC-preparative fraction collection (GC-PFC). Recombinational GC-PFC demonstrated the importance of the components within a 4 min preparative GC fraction to the 'overripe orange' aroma of typical Bordeaux dessert wine. In Viognier wine, monoterpenes linalool, α-terpineol and geraniol as well as benzaldehyde were found to be associated with the 'apricot' character. Thus, several wine aroma compounds interact for these specific aromas to be perceived. This sensory-led combination of separation techniques is a powerful tool for the identification of key compounds responsible for specific aromas across the wine and beverage industries.

Aromatic Potential of Bordeaux Grape Cultivars: Identification and Assays on 4-Oxononanoic Acid, a γ-Nonalactone Precursor

γ-Nonalactone has been demonstrated to be a chemical marker of dried/cooked fruit nuances detected in must and wine, but little is known about its formation pathways. Therefore, on the basis of the literature, we hypothesized 4-oxononanoic acid as a potential precursor. Using dichloromethane extraction followed by gas chromatography coupled to negative chemical ionization mass spectrometry, this keto acid was identified and quantified in Merlot and Cabernet Sauvignon musts. Its concentration ranged from traces to 60 μg/L. The biotransformation of 4-oxononanoic acid into γ-nonalactone by Saccharomyces cerevisiae during alcoholic fermentation was demonstrated using labeled d₆-4-oxononanoic acid. Additional experiments shed light on the 4-oxononanoic acid role as a γ-nonalactone precursor and revealed that this biotransformation was (R)-enantioselective. Sensory and distribution studies of the enantiomers revealed that the detection threshold of R and S forms were 66 and 35 μg/L and the average ratio of R/S in grape and wine was 94:6 and 65:35.

Impact of Whisky Lactone Diastereoisomers on Red Wine Fruity Aromatic Expression in Model Solution

The impact of whisky lactone diastereoisomers on the typical fruity expression of red Bordeaux wines was evaluated by sensory analysis. The detection thresholds of cis- and trans-whisky lactone in a dilute alcohol solution (12% v/v) were 20 and 130 μg/L, respectively. Consequently, considering their average concentrations found in oak-aged red wines, cis-whisky lactone was present at supra threshold levels, whereas trans-whisky lactone was below its detection threshold. Adding these diastereoisomers to a red wine fruity aromatic reconstitution at these average concentrations led to a decrease in the perception of this last one, highlighting a masking effect. Sensory profiles of cis- and trans-whisky lactone confirmed that these compounds modified the perception of fruity aromas, decreasing the intensity of red berry fruit notes and increasing that of blackberry fruit and spicy descriptors.

Identification of key odorants in complex mixtures occurring in nature

Covering: up to 2019Soon after the birth of gas chromatography, mass spectrometry and olfactometry were used as detectors, which allowed impressive development to be achieved in the area of odorant determinations. Since the mid-80s, structured methods of gas chromatography-olfactometry have appeared, allowing the determination of which odor constituents play a key role in materials. Progressively, numerous strategies have been proposed for sample preparation from raw materials, the representativeness evaluation of extracts, the identification of odor constituents, their quantification, and subsequently, the recombination of the key odorants to mimic the initial odor. However, the multiplicity of options at each stage of the analysis leads to a confusing landscape in this field, and thus, the present review aims at critically presenting the available options. For each step, the most frequently used alternatives are described, together with their strengths and weaknesses based on theoretical and experimental justifications according to the literature. These techniques are exemplified by many applications in the literature on aromas, fragrances and essential oils, with the initial focus on wine odorants, followed by a short overview on the molecular diversity of key odorants, which illustrates most of the facets and complexities of odor studies, including the issues raised by odorant interactions such as synergies.

The Blossoming of Technology for the Analysis of Complex Aroma Bouquets-A Review on Flavour and Odorant Multidimensional and Comprehensive Gas Chromatography Applications

Multidimensional approaches in gas chromatography have been established as potent tools to (almost) attain fully resolved analyses. Flavours and odours are important application fields for these techniques since they include complex matrices, and are of interest for both scientific study and to consumers. This article is a review of the main research studies in the above theme, discussing the achievements and challenges that demonstrate a maturing of analytical separation technology.

Quantitation, Organoleptic Contribution, and Potential Origin of Diethyl Acetals Formed from Various Aldehydes in Cognac

Cognac wine distillate (WD), especially that produced during aging, is marked by complex and elegant aroma. This work aimed at expanding the knowledge on the Cognac WD aroma by a sensory-guided approach, involving a fractional-distillation technique and gas chromatography coupled to olfactometry and mass spectrometry (GC-O-MS). In doing so, a fruity-odor zone was highlighted in WD extracts that was attributed to the diethyl acetal family. Ten additional diethyl acetals were detected by GC-MS. Next, an assay method was developed and validated for seven of these diethyl acetals. Their detection thresholds were evaluated in a model solution of water/ethanol (60:40, v/v). 1,1-Diethoxy-3-methylbutane was shown to present a significant organoleptic impact because its olfactory-detection threshold (323 μg/L) is lower than its range of concentrations in WD (461 to 3337 μg/L). Given that diethyl acetals result from reactions between ethanol and aldehydes, quantitative correlations between diethyl acetals and corresponding aldehydes were considered.

Volatile Compounds Related to 'Stone Fruit' Aroma Attributes in Viognier and Chardonnay Wines

A 'stone fruit' aroma is important in many white wine varieties and styles, but little is known about the chemical basis of this wine aroma attribute. A set of Viognier and Chardonnay wines that featured 'stone fruit' aroma attributes were selected by a panel of wine experts. The selected wines were characterized by sensory descriptive analysis and detailed volatile chemical composition analyses. This comprehensive data also allowed Viognier wine to be profiled for the first time. By partial least-squares regression, several esters and fatty acids and benzaldehyde were indicated as contributing to the 'peach' attribute; however, a reconstitution sensory study was unsuccessful in mimicking this attribute. A mixture of γ-lactones, monoterpenes, and aldehydes were positively correlated to the 'apricot' aroma, which were generally higher in the Viognier wines. Reconstitution studies confirmed that the monoterpenes linalool, geraniol, and nerol were the most important compounds for the mixture being perceived as having an 'apricot' aroma.

The Induction of Noble Rot (Botrytis cinerea) Infection during Postharvest Withering Changes the Metabolome of Grapevine Berries (Vitis vinifera L., cv. Garganega)

The natural or induced development of noble rot caused by the fungus Botrytis cinerea during the late stages of grapevine (Vitis vinifera L.) berry ripening is used in some traditional viticulture areas to produce high-quality wines such as Sauternes and Tokaji. In this research, we wanted to verify if by changing the environmental conditions during post-harvest withering we could induce the noble rot development on harvested berries in order to positively change the wine produced from withered Garganega berries. Therefore, we exposed the berries to postharvest withering under normal or artificially humid conditions, the latter to induce noble rot. The presence of noble rot symptoms was associated with the development of B. cinerea in the berries maintained under humid conditions. The composition of infected and non-infected berries was investigated by untargeted metabolomics using liquid chromatography/mass spectrometry. We also explored the effects of the two withering methods on the abundance of volatile organic compounds in wine by yeast-inoculated micro-fermentation followed by targeted gas chromatography/mass spectrometry. These experiments revealed significant metabolic differences between berries withered under normal and humid conditions, indicating that noble rot affects berry metabolism and composition. As well as well-known botrytization markers, we detected two novel lipids that have not been observed before in berries infected with noble rot. Unraveling the specific metabolic profile of berries infected with noble rot may help to determine the compounds responsible for the organoleptic quality traits of botrytized Garganega wines.

Investigation of the aroma of commercial peach (Prunus persica L. Batsch) types by Proton Transfer Reaction-Mass Spectrometry (PTR-MS) and sensory analysis

The aim of this study was to investigate the aroma and sensory profiles of various types of peaches (Prunus persica L. Batsch.). Forty-three commercial cultivars comprising peaches, flat peaches, nectarines, and canning peaches (pavías) were grown over two consecutive harvest years. Fruits were assessed for chemical aroma and sensory profiles. Chemical aroma profile was obtained by proton transfer reaction-mass spectrometry (PTR-MS) and spectral masses were tentatively identified with PTR-Time of Flight-MS (PTR-Tof-MS). Sensory analysis was performed at commercial maturity considering seven aroma/flavor attributes. The four types of peaches showed both distinct chemical aroma and sensory profiles. Flat peaches and canning peaches showed most distinct patterns according to discriminant analysis. The sensory data were related to the volatile compounds by partial least square regression. γ-Hexalactone, γ-octalactone, hotrienol, acetic acid and ethyl acetate correlated positively, and benzeneacetaldehyde, trimethylbenzene and acetaldehyde negatively to the intensities of aroma and ripe fruit sensory scores.

1,8-Cineole in French Red Wines: Evidence for a Contribution Related to Its Various Origins

The aromatic descriptor "green", reflecting grape unripeness in French red wines, is frequently associated with the levels of 3-alkyl-2-methoxypyrazines, particularly 3-isobutyl-2-methoxypyrazine (IBMP), which has bell pepper nuances. Nevertheless, not all green aromatic expressions in red wines correlate with 3-alkyl-2-methoxypyrazine concentrations. This study considered sensory and chemical approaches using Cabernet Sauvignon wines obtained from grapes harvested at one-month intervals during the 2014 and 2015 vintages to investigate other volatile odoriferous compounds. Semipreparative HPLC fractionation of wine extracts revealed a fraction with specific green aromas in the early harvest wines. Its sensory impact was confirmed by omission and reconstitution tests. Then, multidimensional gas chromatography coupled with olfactometry and mass spectrometry (MDGC-O-MS/TOF) was used for molecular characterization of the aroma compounds associated with the green aromas. Surprisingly, eucalyptol (1,8-cineole), with menthol odor was highlighted and assayed at concentrations sometimes above its olfactory detection threshold in Cabernet Sauvignon and Fer Servadou wines. Sensory tests confirmed its impact at several concentrations detected in French red wines (up to 2.61 ± 0.03 μg/L) on the menthol nuance and overall green perception, particularly via an additive effect with IBMP. Quantitation of 1,8-cineole in Cabernet Sauvignon and Merlot grapes during berry development in 2015 revealed its varietal origin with abundant concentrations in unripe berries and decrease during grape maturation. Moreover, the implication of an invasive plant (Artemisia verlotiorum) growing in certain vineyards was shown to be responsible for increased 1,8-cineole concentrations in some wines.

Influence of Chirality of Lactones on the Perception of Some Typical Fruity Notes through Perceptual Interaction Phenomena in Bordeaux Dessert Wines

Recent studies concerning the aroma of noble rot dessert wines revealed the importance of a well-known phenomenon in perfumery, the perceptual blending, to create the perception of "overripe orange" nuances. Thus, compounds associated with both oak wood aging (3-methyl-4-octanolide and eugenol) and Botrytis cinerea development under the form of noble rot (2-nonen-4-olide and γ-nonalactone) contribute to a specific aroma of great noble rot dessert wines through perceptual interaction phenomena. This synthetic perception phenomenon was established from reconstitution, addition, and omission sensory experiments, using wine extract fractions supplemented with the volatile compounds previously mentioned. To better understand the sensory impact of these compounds, the goal of this research was to study the contributions of enantiomeric forms of 2-nonen-4-olide and γ-nonalactone and the diastereoisomers of 3-methyl-4-octanolide. After multidimensional chiral chromatography analysis, the relative proportions of enantiomers or diastereomeric forms were first established and then sensory experiments were carried out using the reference compounds with isolated fractions from dessert wines. A dominance of the R form was established for 2-nonen-4-olide, which was correlated with wine aging, while the S form is more dominant in young dessert wines. Furthermore, the reconstitution experiments confirmed perceptual interaction phenomena and revealed the sensory contribution of (R)-2-nonen-4-olide and cis-3-methyl-4-octanolide concerning the "overripe orange" nuances, whereas no sensory impact for the γ-nonalactone isomers was observed.

Identification of Piperitone as an Aroma Compound Contributing to the Positive Mint Nuances Perceived in Aged Red Bordeaux Wines

Although a sensory definition of the aging bouquet of red Bordeaux wines was recently established, its chemical transcription has only partially been elucidated. A multiple-step approach, combining sensory evaluations of red Bordeaux wines and aromatic reconstitutions of wine extract fractions, was used to identify the molecular markers involved. One wine with a high aging-bouquet score and a mint nuance has received particular attention. Various reconstitution and omission tests highlighted the contribution of two specific fractions to the intensity of the perception of mint aroma. Gas chromatography coupled to olfactometry and mass spectrometry was applied to the targeted fractions to identify molecular marker(s) responsible for the mint nuance in fine red Bordeaux wines. A similar analytical process was applied to selected fractions of essential oils presenting mint odors to characterize them and interpret the mass spectrometry data. This approach resulted in the detection of piperitone, a monoterpene ketone that, to the best of our knowledge, was reported for the first time as a contributor to the positive mint aroma of aged red Bordeaux wines.