Oak Lactone Research Articles

Extraction of volatile aroma compounds from toasted oak wood using pulsed electric field

The effect of pulsed electric field (PEF) on the extraction of volatile compounds from toasted oak wood chips immersed in various aqueous ethanol solutions (5%, 12%, 50%, and 70% vol/vol) was determined by Gas chromatography/mass spectrometry (GC/MS) after ultrasound-assisted extraction. PEF treatment showed the highest impact in the 5% solution, increasing vanillin, syringaldehyde, oak lactone (cis- and trans-), and furfural by 75%, 371%, 13%, and 50%, respectively. PEF was also tested on Agiorgitiko red wine and on malt and wine distillates. In wine distillate, 4-vinylguaiacol was also detected. For red wine, a PEF of 1.2 kV/cm increased the efficiency of extraction of wood aroma compounds from 5% to 200%. Differences in the extracted volatile compound concentrations between the control and PEF-treated samples were also observed in the malt and wine distillates. The sensory evaluation showed that the PEF-treated malt was similar to an aged whiskey, having nuances of toasted oak. Practical applications This work was done as a preliminary investigation for our on-going research into the application of PEF technique for the extraction of aromatic compounds from oak wood, and the acceleration of both wine and malt distillate aging. The findings suggest that PEF could be introduced in wine, brandy, and whiskey industry as a novel technology for the acceleration of the aging process.

Untargeted UHPLC-Q-TOF-HRMS based determination of discrimating compounds for oak species Quercus robur L. and Quercus petraea Liebl. identification.

Two species of oak are dominant in French forests: pedunculate oak (Quercus robur L.) and sessile oak (Quercus petraea Liebl.). Differentiating oak species is difficult, since features such as morphological characters, geographical origin and grain are not always relevant. Even if the former is generally richer in tannin compounds while the latter is often richer in aromatic compounds, the intra-species variability is high. The characterisation of the oak species remains a suitable indicator of the molecular composition and quality of the wood. The aim of this study was to determine differentiating molecules allowing oak species identification in order to assist in a suitable wood selection for a better oak tree valorisation since the selection of the oak wood to be used in the production of barrels plays an essential role in wine ageing. Oak wood samples were collected both in forests and in cooperage timber yards. An untargeted metabolomic approach using ultra-high-pressure liquid chromatography qualitative time-of-flight high-resolution mass spectrometry (UHPLC-Q-TOF-HRMS) associated to multivariate statistical analyses (hierarchical ascendant clustering and partial least squares discriminant analysis) was implemented to determine molecular markers of oak species. Heartwood was identified as the suitable wood part to distinguish oak species. Discriminating molecules did not depend on the sample set. The pedunculate species showed overexpression of bartogenic derivatives while sessile oak presented a higher content in oak lactone precursors and in quercotriterpenosids. The developed method allowed the identification of relevant compounds for oak species identification to a better wood valorisation and selection.

A Hypothesis-Free Sensor Array Discriminates Whiskies for Brand, Age, and Taste

Summary In biology, non-specific interactions are ubiquitous and important, whereas in chemistry, non-specificity or non-selectivity is suspect. We present simple tongues consisting of fluorescent polyelectrolytes or chimeric green fluorescent proteins (GFPs) to discriminating 33 different whiskies according to their country of origin (Ireland, US, or Scotland), brand, blend status (blend or single malt), age, and taste (rich or light). The mechanism of action for these tongues is differential quenching of the fluorescence of the poly(aryleneethynylene)s or the GFPs by the complex mixture of colorants (vanillin, vanillic acid, oak lactones, tannins, etc.; the interactome) extracted from the oak barrels and added caramel coloring. The differential binding and signal generation of the interactomes to the polymers and proteins result from hydrophobic and electrostatic interactions. The collected quenching data, i.e., the response patterns, were analyzed by linear discriminant analysis. Our tongues do not need any sample preparation and are equal or superior to state-of-the-art mass spectrometric methods with respect to speed, resolution, and efficiency of discrimination.

Improvement of Verdejo white wines by contact with oak chips at different winemaking stages

The effect that the addition of wood at different stages of the winemaking process has on the volatile composition and sensory characteristics of Verdejo wines has been studied. Verdejo control wine was made by the traditional winemaking process without oak chips. Oak chips (7 g/L) were added at different stages of the winemaking process: during alcoholic fermentation (OCAF) and in the young wine (OCW). Higher alcohols, ethyl acetate, hexyl acetate, isoamyl acetates and ethyl esters of straight-chain fatty acids were present at higher concentrations in wines that had contact with oak chips during alcoholic fermentation when compared to control wines. The highest concentrations of benzene compounds, oak lactones and furanic compounds were found in both wines in contact with oak chips, particularly in CW samples. Different sensorial profiles were obtained for the wines depending on the stage of the winemaking process at which the chips were added. All wines investigated in this study can provide a viable alternative to traditional Verdejo wines.

Rapid Induction of Ageing Character in Brandy Products – Part II. Influence of Type of Oak

As part of a broader study that investigated techniques for the rapid induction of the needed ageing character in brandy products, the effect of oak type on quality and chemical composition of oak wood extracts and matured and unmatured potstill brandy, is reported on. Extracts, prepared from American and French oak chips supplied by a South African cooper, and from commercially obtained oak, and representing different levels of toasting, were added to 70% (v/v) unmatured pot-still brandy and stored for eight months in glass containers (Schott bottles) at room temperature, or in the case of controls, below 0°C. Matured and unmatured (control) pot-still brandy samples were analysed for wood-derived congeners by means of HPLC and GC. Although French oak initially yielded better quality products, these effects lost prominence and, after eight months maturation, yielded similar sensory quality to American oak. French oak samples had higher concentrations of wood-derived congeners (including eugenol, the furan derivatives and aromatic aldehydes). However, the American oak generally contained higher concentrations of oak lactones than their French counterparts, with higher proportions of the more sensorially potent cis-form of lactone than its trans-isomer.

Stereodifferentiation of oak lactone by using multidimensional chromatographic techniques

This work reports for the first time the use of on-line coupling of reversed phase liquid chromatography with gas chromatography for the stereodifferentiation of oak lactone, which is considered to be one of the main constituents of the aroma of different products.

Validation of a HS-SPME-GC Method for Determining Higher Fatty Esters and Oak Lactones in White Rums

Higher fatty esters and oak lactones are the main components of white rum aroma and furthermore, they have an important sensorial impact in these distilled alcoholic beverages. A method for analyzing these volatile compounds was validated. It involves a separation and concentration step using headspace solid-phase microextraction (HS-SPME) and determination by capillary gas chromatography using flame ionization detection. The method showed a good within-day (RSD 0.99) and the limits of detection and quantification were 0.001–0.018 and 0.003–0.054 mg L−1 (12 % v/v alcohol), respectively. Good recoveries were obtained (98.6–100.3 %). The method is suitable for the quality control of higher fatty esters and oak lactones in white rums.

Real-Time Mass Spectrometry Monitoring of Oak Wood Toasting: Elucidating Aroma Development Relevant to Oak-aged Wine Quality

We introduce a real-time method to monitor the evolution of oak aromas during the oak toasting process. French and American oak wood boards were toasted in an oven at three different temperatures, while the process-gas was continuously transferred to the inlet of a proton-transfer-reaction time-of-flight mass spectrometer for online monitoring. Oak wood aroma compounds important for their sensory contribution to oak-aged wine were tentatively identified based on soft ionization and molecular mass. The time-intensity profiles revealed toasting process dynamics illustrating in real-time how different compounds evolve from the oak wood during toasting. Sufficient sensitivity was achieved to observe spikes in volatile concentrations related to cracking phenomena on the oak wood surface. The polysaccharide-derived compounds exhibited similar profiles; whilst for lignin-derived compounds eugenol formation differed from that of vanillin and guaiacol at lower toasting temperatures. Significant generation of oak lactone from precursors was evident at 225 oC. Statistical processing of the real-time aroma data showed similarities and differences between individual oak boards and oak wood sourced from the different origins. This study enriches our understanding of the oak toasting process and demonstrates a new analytical approach for research on wood volatiles.

Accumulation of Glycoconjugates of 3-Methyl-4-hydroxyoctanoic Acid in Fruits, Leaves, and Shoots of Vitis vinifera cv. Monastrell following Foliar Applications of Oak Extract or Oak Lactone

Grapevines are capable of absorbing volatile compounds present in the vineyard during the growing season, and in some cases, volatiles have been found to accumulate in fruits or leaves in glycoconjugate forms, that is, with one or more sugar moieties attached. The presence of oak lactone in wine is usually attributable to oak maturation, but oak lactone has been detected in wines made with fruit from grapevines treated with oak extract or oak lactone. This study investigated the accumulation of glycoconjugates of 3-methyl-4-hydroxyoctanoic acid (i.e., the ring-opened form of oak lactone) in the fruits, leaves, and shoots of Monastrell grapevines following foliar application of either oak extract or oak lactone at approximately 7 days postveraison. Fruits, leaves, and shoots were collected at three different time points, including at maturity. The oak lactone content of fruit was determined by gas chromatography-mass spectrometry, with declining concentrations observed in fruit from grapevines treated with oak lactone with ripening. The concentrations of a β-d-glucopyranoside of 3-methyl-4-hydroxyoctanoic acid in fruits, leaves, and shoots was determined by liquid chromatography-tandem mass spectrometry, with the highest oak lactone glucoside levels observed in leaves of grapevines treated with oak lactone. A glucose-glucose disaccharide was also tentatively identified. These results demonstrate both ring-opening and glycosylation of oak lactone occurred after experimental treatments were imposed.

Aroma potential of oak battens prepared from decommissioned oak barrels.

During barrel maturation, volatile compounds are extracted from oak wood and impart aroma and flavor to wine, enhancing its character and complexity. However, barrels contain a finite pool of extractable material, which diminishes with time. As a consequence, most barrels are decommissioned after 5 or 6 years. This study investigated whether or not decommissioned barrels can be "reclaimed" and utilized as a previously untapped source of quality oak for wine maturation. Oak battens were prepared from staves of decommissioned French and American oak barrels, and their composition analyzed before and after toasting. The oak lactone glycoconjugate content of untoasted reclaimed oak was determined by liquid chromatography-tandem mass spectrometry, while the concentrations of cis- and trans-oak lactone, guaiacol, 4-methlyguaiacol, vanillin, eugenol, furfural, and 5-methylfurfural present in toasted reclaimed oak were determined by gas chromatography-mass spectrometry. Aroma potential was then evaluated by comparing the composition of reclaimed oak with that of new oak. Comparable levels of oak lactone glycoconjugates and oak volatiles were observed, demonstrating the aroma potential of reclaimed oak and therefore its suitability as a raw material for alternative oak products, i.e., chips or battens, for the maturation of wine. The temperature profiles achieved during toasting were also measured to evaluate the viability of any yeast or bacteria present in reclaimed oak.

Chemical and sensory evaluation of wine matured in oak barrel: effect of oak species involved and toasting process

The effect of toasting method and forest origin on volatile compounds and ellagitannin concentration extracted into Merlot wine during 1-year barrel maturation is described. Sensory analysis concerning vanilla, spicy, overall woody, astringency, bitterness and sweetness is conducted in parallel. The study is realized in two different experimental designs having only a common parameter, the wine. For the first one, common toasting methods (light, medium) and specific ones (medium toast with watering, medium plus toast, medium plus toast with watering, medium toast with toasted head and Noisette) are chosen. For the second one, the oak from which barrels are made is sourced from Center, Limousin, Allier and Colbert forests in France, from Pennsylvania forest in America, and from Slavonia forest in East Europe. Wine with different characteristics is obtained from the same wine in relation to forest origin and toasting process. Watering process during toasting enhances furanic compounds vanillin and oak lactones extraction, whereas toasting barrel head pieces may lead to eugenol and ellagitannin degradation. Wine in light toast barrel is perceived as less sweet, bitter and more astringent. Ellagitannin concentration is closely correlated to astringency, reflecting the relationship between them, R = 0.599, p < 0.001. Forest origin induces important changes; wine in American barrels is differentiated from those in Slavonia and French barrels. Ellagitannin concentration in barrels from Slavonia is halfway between French and American, and ellagitannin concentration is related linearly to astringency intensity (R = 0.811, p < 0.001). Wine aged in Slavonia showed characteristics similar and intermediate to those of the same wine aged in French and American oak woods, suggesting that they are suitable for barrel production of quality wine.

Wine finish in red wine: The effect of ethanol and tannin concentration

Wine finish, the tastes and aromas that linger after swallowing wine, is a critical aspect of wine quality. The objective of this study was to use time-intensity (TI) methodology to determine whether the finish parameters of different flavors varied as a function of wine matrix composition. Trained panelists (n=10) executed TI evaluations on three flavor compounds (2-phenylethanol (floral), 3-isobutyl-2-methoxypyrazine (bell pepper), and oak lactone (coconut)), heat, and astringency in wine adjusted to varying ethanol and tannin levels. Multivariate analysis of variance indicated that elevated ethanol increased duration and intensity of the finish for floral and coconut samples (p<0.05). For floral and bell pepper, no significant differences were shown using canonical variates analysis (CVA); however, for coconut, the high ethanol samples were more associated with a higher finish intensity and longer duration of finish. Flavor interactions also affected finish duration, with coconut (oak lactone) finish duration shortened by 10.35s in the presence of 2-phenylethanol. These results showed that the wine matrix affects red wine finish and can be used by winemakers to understand how different processing techniques that alter the ethanol and tannin content of their wines, may also be affecting the sensory qualities of the wine finish.

Volatile composition of Bobal red wines subjected to alcoholic/malolactic fermentation with oak chips

The effect of wood, in the form of oak chips, on the volatile composition of Bobal red wines caused by adding oak chips at different stages of the fermentation process has been studied. Aroma compounds were isolated by solid phase extraction (SPE) for subsequent analysis by gas chromatography–mass spectrometry (GC/MS). Bobal control wine was produced according to traditional winemaking processes, without oak chips. Oak chips were added to the rest of the wines at two dose levels (3 and 6 g/L) at different stages of the winemaking process: at one week during alcoholic fermentation (AF), during malolactic fermentation (MLF) and in young, red Bobal wine. Wines fermented with oak chips during AF showed higher concentrations of the ethyl esters of straight-chain fatty acids and ethyl, hexyl and isoamyl acetates than the control wine. A similar, trend was observed for higher alcohols. Higher concentrations of benzene compounds, oak lactones and furanic compounds were found in wines in contact with oak chips during MLF followed by young Bobal oak wines. These results reveal that the point of addition during the winemaking process and the dose level of oak chips used have a significant effect on the volatile composition of Bobal red wines.

Comparative study of two aging systems for cider brandy making. Changes in chemical composition

The influence of two systems of aging (traditional and alternative) on the chemical composition of cider brandy was compared. The traditional system consisted in classical aging in barrels while the alternative method consisted in aging in stainless steel vessels with staves and micro-oxygenation. Three types of oak wood were used: American, French and Spanish. Treatment with micro-oxygenation accelerated the changes taking place in cider distillates when compared to traditional aging in barrels. Worth noting on account of its possible impact on the final product is the higher degree of oxidation in micro-oxygenated brandies, favoring the contents of benzoic derivatives and total acetaldehyde. Furthermore, micro-oxygenated spirits also showed a higher degree of hydrolysis, resulting in a higher concentration of oak lactones and gallic acid and a more pronounced decrease in the levels of 3-methyl-1-butyl acetate and 2-phenylethyl acetate.

Role of Glycoconjugates of 3-Methyl-4-hydroxyoctanoic Acid in the Evolution of Oak Lactone in Wine during Oak Maturation

Oak lactone is a natural component of oak wood, but it also exists in glycoconjugate precursor forms. This study concerned the role of glycoconjugates of 3-methyl-4-hydroxyoctanoic acid, specifically a galloylglucoside, glucoside, and rutinoside, in the evolution of oak lactone during cooperage and maturation. The glycoconjugate profiles of 10 French oak samples were obtained by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) using stable isotope dilution analysis. The galloylglucoside was found to be the predominant glycoconjugate precursor and ranged in concentration from 110 to 354 μg/g. Maturation trials indicated the galloylglucoside undergoes acid-catalyzed hydrolysis after extraction into wine; after 12 months of maturation, the glucoside was the most abundant precursor, present at between 2- and 11-fold higher concentrations than those observed for powdered oak. Thermal degradation of glycoconjugates was observed only when oak samples were heated at 200 °C for 30 min, demonstrating their thermal stability.

Impact of alternative technique to ageing using oak chips in alcoholic or in malolactic fermentation on volatile and sensory composition of red wines

This paper reports on a complete study of the effect of wood, in the form of oak chips, on the volatile composition and sensory characteristics of Moravia Agria wines added at different stages of the fermentation process. Aroma compounds were analyzed by gas chromatography-mass spectrometry (GC-MS). Sensory profile was evaluated by experienced wine-testers. Oak chips were added to wines in two dose rates at different stages of the winemaking process: during alcoholic fermentation (AF), during malolactic fermentation (MLF) and in young, red Moravia Agria wine. Wines fermented with oak chips during AF showed higher concentrations of the ethyl esters of straight-chain fatty acids, ethyl, hexyl, isoamyl acetates and superior alcohols than the control wines. The higher concentrations of benzene compound, oak lactones and furanic compounds were found in wines in contact with oak chips during MLF. The use of oak chips gives rise to a different sensorial profile of wines depending of the point of addition. Higher intensities of woody, coconut, vanilla and sweet spices descriptors were obtained when a large dose rate of chips was employed.

Characterisation of odour-active compounds in aged rum

The volatiles of rum matured in oak casks were carefully isolated by solvent extraction followed by solvent-assisted flavour evaporation. Among the 116 volatile compounds identified by GC–MS, seven of them were found for the first time in rum. Application of the aroma extract dilution analysis (AEDA) on the volatile fraction revealed 18 odour-active areas in the flavour dilution factor range of 32–1024. On the basis of the quantitative data and odour thresholds in 35% ethanol (v/v), the odour activity values (OAV; ratio of concentration to odour threshold) were calculated. Nineteen aroma compounds showed OAVs >1, among which ethanol, (E)-β-damascenone, ethyl butanoate, ethyl hexanoate, vanillin, (Z)-oak lactone, ethyl 2-methylpropanoate, 1,1-diethoxyethane, ethyl 2-methylbutanoate, 3-methylbutyl acetate, ethyl octanoate, ethyl decanoate, 2-phenylethyl acetate, 2-phenylethanol, 2-methoxyphenol, 4-ethyl-2-methoxyphenol, 4-propyl-2-methoxyphenol, γ-nonalactone, and eugenol showed the highest values and should be considered as the most odour-active compounds.

Ent-Eudesmane sesquiterpenoids, galloyl esters of the oak lactone precursor, and a 3- O-methylellagic acid glycoside from the wood of Platycarya strobilacea

ent-Eudesmane sesquiterpenoids, 8,11-dihydroxy-2,4-cycloeudesmane, 11-hydroxy-2,4-cycloeudesman-8-one and 2,4-cyclo-7(11)-eudesmen-8-one, were isolated from the wood of Platycarya strobilacea, which has been used as an aromatic tree since at least the 18th century. On charring the wood, 2,4-cyclo-7(11)-eudesmen-8-one was detected in the smoke. In the charred wood, the concentrations of ellagitannins, such as galloyl pedunculagin, dramatically decreased, whereas concentrations of pentagalloyl glucose, and other gallotannins were relatively stable. In addition, two other compounds, the 6′- O- m- and p-digalloyl oak lactone precursor and the 3- O-methylellagic acid 4′- O-(4″- O-galloyl)-xylopyranoside, were isolated from the charred wood along with m- and p-digallic acid.

Aroma substance of fragrant tree Platycarya strobilacea and change of phenolic constituents on toasting

The wood of Platycarya strobilacea (PSW) is a fragrant tree and has been used as a substitute for expensive agarwood (Aquilaria agallocha). PSW was burned when it is used as fragrant tree, and the aim of our study is characterization of the aroma substance and chemical change of the constituents during the heating. Previously, we reported that PSW contains 3-hydroxy-α-calacorene, oak lactone (syn. whisky lactone) precursor (1), gallotannins, such as pentagalloyl-β-D-glucose, and ellagitannins, such as pedunculagin, 1(β)-O-galloylpedunculagin (5)1,2.

Crotylation of (R)-2,3-O-cyclohexylideneglyceraldehyde: a simple synthesis of (+)-trans-oak lactone

Abstract Crotylations of ( R )-2,3-cyclohexylideneglyceraldehyde ( 1 ) were utilized in a simple synthesis of trans -oak lactone ( I ), a representative example of chiral β,γ-disubstituted-γ-butyrolactones. In this endeavor, crotylations of 1 in THF mediated with four low valent metals were studied. All these reactions took place efficiently producing 2 in good yields but with varied stereoselectivities. Each reaction produced the corresponding secondary alcohol adduct 2b and 2c predominantly with diastereoisomer 2a only in trace amounts. Among these four reactions, only Sn-mediated addition yielded 2b as the major products. Later, 2c was converted into 2d through oxidation–reduction. Finally, 2c was transformed into trans -oak lactone I in a few steps. Following this route, 2a , 2b , and 2d would produce other stereoisomers of oak lactone.