hrcak mascot   Srce   HID

Izvorni znanstveni članak
https://doi.org/10.17113/ftb.55.03.17.5145

Promjene u kemijskom sastavu destilata šljive pri različitim uvjetima dozrijevanja u prisutnosti hrastovih trijeski

Maria Balcerek   ORCID icon orcid.org/0000-0003-3731-8680 ; Department of Spirit and Yeast Technology, Institute of Fermentation Technology and Microbiology, Faculty of Biotechnology and Food Sciences, Lodz University of Technology, Wolczanska 171/173, PL-90-924 Lodz, Poland
Katarzyna Pielech-Przybylska   ORCID icon orcid.org/0000-0003-3107-8065 ; Department of Spirit and Yeast Technology, Institute of Fermentation Technology and Microbiology, Faculty of Biotechnology and Food Sciences, Lodz University of Technology, Wolczanska 171/173, PL-90-924 Lodz, Poland
Urszula Dziekońska-Kubczak ; Department of Spirit and Yeast Technology, Institute of Fermentation Technology and Microbiology, Faculty of Biotechnology and Food Sciences, Lodz University of Technology, Wolczanska 171/173, PL-90-924 Lodz, Poland
Piotr Patelski ; Department of Spirit and Yeast Technology, Institute of Fermentation Technology and Microbiology, Faculty of Biotechnology and Food Sciences, Lodz University of Technology, Wolczanska 171/173, PL-90-924 Lodz, Poland
Ewelina Strąk ; Department of Spirit and Yeast Technology, Institute of Fermentation Technology and Microbiology, Faculty of Biotechnology and Food Sciences, Lodz University of Technology, Wolczanska 171/173, PL-90-924 Lodz, Poland

Puni tekst: hrvatski, pdf (1 MB) str. 333-359 preuzimanja: 79* citiraj
APA 6th Edition
Balcerek, M., Pielech-Przybylska, K., Dziekońska-Kubczak, U., Patelski, P. i Strąk, E. (2017). Promjene u kemijskom sastavu destilata šljive pri različitim uvjetima dozrijevanja u prisutnosti hrastovih trijeski. Food Technology and Biotechnology, 55 (3), 333-359. https://doi.org/10.17113/ftb.55.03.17.5145
MLA 8th Edition
Balcerek, Maria, et al. "Promjene u kemijskom sastavu destilata šljive pri različitim uvjetima dozrijevanja u prisutnosti hrastovih trijeski." Food Technology and Biotechnology, vol. 55, br. 3, 2017, str. 333-359. https://doi.org/10.17113/ftb.55.03.17.5145. Citirano 22.10.2020.
Chicago 17th Edition
Balcerek, Maria, Katarzyna Pielech-Przybylska, Urszula Dziekońska-Kubczak, Piotr Patelski i Ewelina Strąk. "Promjene u kemijskom sastavu destilata šljive pri različitim uvjetima dozrijevanja u prisutnosti hrastovih trijeski." Food Technology and Biotechnology 55, br. 3 (2017): 333-359. https://doi.org/10.17113/ftb.55.03.17.5145
Harvard
Balcerek, M., et al. (2017). 'Promjene u kemijskom sastavu destilata šljive pri različitim uvjetima dozrijevanja u prisutnosti hrastovih trijeski', Food Technology and Biotechnology, 55(3), str. 333-359. https://doi.org/10.17113/ftb.55.03.17.5145
Vancouver
Balcerek M, Pielech-Przybylska K, Dziekońska-Kubczak U, Patelski P, Strąk E. Promjene u kemijskom sastavu destilata šljive pri različitim uvjetima dozrijevanja u prisutnosti hrastovih trijeski. Food Technology and Biotechnology [Internet]. 2017 [pristupljeno 22.10.2020.];55(3):333-359. https://doi.org/10.17113/ftb.55.03.17.5145
IEEE
M. Balcerek, K. Pielech-Przybylska, U. Dziekońska-Kubczak, P. Patelski i E. Strąk, "Promjene u kemijskom sastavu destilata šljive pri različitim uvjetima dozrijevanja u prisutnosti hrastovih trijeski", Food Technology and Biotechnology, vol.55, br. 3, str. 333-359, 2017. [Online]. https://doi.org/10.17113/ftb.55.03.17.5145
Puni tekst: engleski, pdf (1 MB) str. 333-359 preuzimanja: 167* citiraj
APA 6th Edition
Balcerek, M., Pielech-Przybylska, K., Dziekońska-Kubczak, U., Patelski, P. i Strąk, E. (2017). Changes in the Chemical Composition of Plum Distillate During Maturation with Oak Chips under Different Conditions. Food Technology and Biotechnology, 55 (3), 333-359. https://doi.org/10.17113/ftb.55.03.17.5145
MLA 8th Edition
Balcerek, Maria, et al. "Changes in the Chemical Composition of Plum Distillate During Maturation with Oak Chips under Different Conditions." Food Technology and Biotechnology, vol. 55, br. 3, 2017, str. 333-359. https://doi.org/10.17113/ftb.55.03.17.5145. Citirano 22.10.2020.
Chicago 17th Edition
Balcerek, Maria, Katarzyna Pielech-Przybylska, Urszula Dziekońska-Kubczak, Piotr Patelski i Ewelina Strąk. "Changes in the Chemical Composition of Plum Distillate During Maturation with Oak Chips under Different Conditions." Food Technology and Biotechnology 55, br. 3 (2017): 333-359. https://doi.org/10.17113/ftb.55.03.17.5145
Harvard
Balcerek, M., et al. (2017). 'Changes in the Chemical Composition of Plum Distillate During Maturation with Oak Chips under Different Conditions', Food Technology and Biotechnology, 55(3), str. 333-359. https://doi.org/10.17113/ftb.55.03.17.5145
Vancouver
Balcerek M, Pielech-Przybylska K, Dziekońska-Kubczak U, Patelski P, Strąk E. Changes in the Chemical Composition of Plum Distillate During Maturation with Oak Chips under Different Conditions. Food Technology and Biotechnology [Internet]. 2017 [pristupljeno 22.10.2020.];55(3):333-359. https://doi.org/10.17113/ftb.55.03.17.5145
IEEE
M. Balcerek, K. Pielech-Przybylska, U. Dziekońska-Kubczak, P. Patelski i E. Strąk, "Changes in the Chemical Composition of Plum Distillate During Maturation with Oak Chips under Different Conditions", Food Technology and Biotechnology, vol.55, br. 3, str. 333-359, 2017. [Online]. https://doi.org/10.17113/ftb.55.03.17.5145

Rad u XML formatu

Sažetak
U radu je ispitan utjecaj dozrijevanja u kontaktu s hrastovim trijeskama na sastav i koncentraciju destilata šljive. Destilatu šljive su tijekom starenja dodane lagano pržene trijeske francuskog hrasta (Quercus sessiflora i Quercus robur) ili trijeske dobivene od starih bačava u kojima je odležao konjak. Ispitan je utjecaj količine dodanih trijeski, temperature, načina dozrijevanja (statičnog ili uz cirkulaciju) te primjene ultrazvuka. Dozrijevanjem destilata šljive u prisutnosti hrastovih trijeski povećala se količina ekstraktibilnih organskih spojeva (uključujući tanine) i promijenila boja destilata, u ovisnosti o vrsti i količini dodanih trijeski te uvjetima dozrijevanja. Koncentracija se šećera, kao što su glukoza, ksiloza i arabinoza, povećala ovisno o uvjetima dozrijevanja i vrsti trijeski. Razgradnjom lignina oslobođene su određene količine sinapaldehida, siringaldehida, coniferaldehida i vanilina, u ovisnosti o uvjetima pokusa. Od hlapljivih spojeva, koncentracija se viših alkohola i alifatskih (acikiličkih) aldehida u većem broju varijanti pokusa smanjila, dok se koncentracija furanskih aldehida, ovisno o vrsti i količini trijeski te uvjetima dozrijevanja, povećala. Koncentracija se estera, poput etilacetata u većem broju varijanti pokusa smanjila, a etil-kaproata, etil-kaprilata i etil-
-kaprata postupno povećala. Neki su fenoli i laktoni pronađeni u uzorcima destilata nakon dozrijevanja, a najmanje su koncentracije tih spojeva pronađene u uzorcima destilata dozrelog u kontaktu s hrastovim trijeskama dobivenim od bačava u kojima je odležao konjak.

Ključne riječi
destilat šljive; dozrijevanje; boja destilata od šljive; hlapljivi spojevi; fenolni spojevi; laktoni

Hrčak ID: 186543

URI
https://hrcak.srce.hr/186543

▼ Article Information



Introduction

Plum brandy (slivovitz) is the spirit prepared from varieties of plum (Prunus sp.), originating from the Balkan Peninsula. This beverage is also quite well known in Central Europe (Hungary, Poland, Czech Republic, Slovakia and Romania), and similar plum brandies are produced in Germany, Austria (Zwetschgenwasser), France (eau de vie de prune), and Switzerland (Pflümli wasser). Poland also has a long tradition of making slivovitz. One of the more recognized such products is Śliwowica Łącka, which is produced by spontaneous fermentation of Węgierka Zwykła plums grown in a submontane region of Poland with specific climatic and soil conditions (1).

The quality of plum brandy is influenced by many factors, including the soil and climate, the characteristics of the used fruit varieties and the employed technological procedures (2). Plum varieties with their distinctive aromatic compounds give to the distillates the features of a local character (3).

In view of the fact that new distillates are characterized with inharmonious taste and sharp odour, the ageing in wooden casks is the most important, final step of production process of several beverages (cognac, whisky, brandy, calvados, mescal and wine). It is also common to age the plum brandies in wooden barrels (4).

Ageing, also known as maturation, is one of the most important and also costly factors that influence the quality of distilled beverages, such as cognac, whisky, brandy and calvados. While probably serving originally only as a means of storage and transportation, time spent in an oak cask is now seen as fundamental to the finished taste and aroma (5). During maturation, spirit beverages develop a distinctive aroma and flavour that are appreciated by consumers. Ageing not only improves the sensory attributes of distilled beverages, but also causes changes in the content of total polyphenols, as well as developing other important health properties, such as increased antioxidant capacity (6, 7).

The oak (Quercus sp.) is by far the most widely used wood in the manufacture of barrels for ageing wines and spirits. In Europe, the oak species Quercus petraea (syn. Quercus sessilis) and Quercus robur (syn. Quercus pedunculata) are used.

In America, the oak species Quercus alba is widely used, the wood of which is richer in lactones than the European species (8). A common practice in cooperage, regarded as the most important technological step, is toasting the oak wood. High temperatures modify the physical structure of the wood, which is crucial for facilitating the shaping of the staves. More importantly, however, its chemical composition undergoes significant changes due to thermal degradation of the oak wood polymers (4).

The type of cask and the duration of maturation are two variables equally important for quality of old plum brandies. Both parameters of ageing in production of whisky and cognac are defined according to the international or local regulation for the product name (5). According to the tradition in European countries, brandy is kept for at least two years (sometimes for several decades) in different wooden casks, but the local regulation for brandies does not define the ageing parameters. They depend a lot on the local production practice (9).

The process of ageing changes the colour and flavour of the maturing spirit and reduces both its volume and the alcoholic content. The time required for satisfactory maturation varies, depending on the characteristics of the raw distillate, the origins of the wood, the size and treatment of the cask and the environment in which the spirit is matured. Taste and aroma are influenced by changes in the composition and concentration of compounds. These changes may be caused by direct extraction of wood compounds, by decomposition of wood macromolecules and extraction of the products into the distillate, by reactions between wood components and the constituents of the raw distillate, by reactions involving only extractable wood components (10), by oxidoreductions, esterifications, Maillard reactions, polymerizations or condensations (11).

In addition to positive impact on the quality, the ageing of brandy in wooden barrels has a disadvantage, increased costs. Wooden barrels are expensive, and difficult to clean and maintain. Evaporation of ethanol from wooden barrels is higher than from stainless steel tanks. If the quality of the wood and the workmanship are poor, the quality of the spirits will be affected and evaporation losses will increase. Furthermore, barrels lose their extractable substances after a few years and must be replaced (12). Costs rise in proportion to the length of the ageing period, as a consequence of tied up capital.

Treatment with oak chips, especially charred or toasted chips, is known to speed up the process of brandy ageing. The simplest method for adding wood-derived compounds is to use oak chips. Oak chips are increasingly used in the maturation of brandies (5)..The use of oak chips is part of traditional good cellar practice, it is legally permitted and commonplace in commercial production of wines (12). Oak chips of various sizes, pre-treated in different ways, are now commercially available and are used to compensate for the low levels of extractable components in old barrels, which may nevertheless be used to provide a barrel-like environment. Alternatively, renewable stacks of planks placed in large steel maturation tanks may be used in the production of brandies (5). The use of alternative solutions to the traditional barrels, such as oak wood fragments, may be a rapid and economical method of ageing treatment (13). Nowadays, there is no legislation applied to the ageing of spirits in contact with oak wood fragments. There are some works on brandy aged in contact with wood fragments, on cider brandy, on aged rum and on Brandy de Jerez (1416). The composition of the final product is mainly influenced by the botanical and geographical origin of the used oak, but also important during accelerated ageing are: the oak fragment size, the amount of applied wood and the toasting level (light, medium or high) (17, 18).

Oak extracts or chips contain very high levels of wood--derived compounds, which may even exceed those in barrels, in particular phenolic and furanic compounds (19). However, ageing using oak chips may be considered incomplete, as the oxygen that penetrates through the staves during the long maturation period has an important influence from a chemical and sensory standpoint. Different mechanisms have been proposed, whereby oxygen plays a part in the formation of compounds such as phenolic compounds derived from lignin (20), methylketones (21) or acetaldehyde and acetic acid (22).

This study set out to evaluate the effects of the type and dose of oak chips and maturation conditions on the changes in the qualitative and quantitative composition of plum distillate, using lightly toasted French oak wood chips and oak wood chips made from barrels used for ageing cognac.

Materials and Methods

Raw material

The raw material used was a plum distillate with an alcoholic strength by volume (ASV) of 77%, produced on an industrial scale by a Polish factory, +H2O Sp. z o. o. (Chociszew near Lodz, Poland). The raw material used for the production of distillate were plums var. Węgierka Zwykła purchased from a Polish fruit processing factory (ROLFOODS, Ziewanice near Lodz, Poland). The plum pulp for alcoholic fermentation was prepared from the stoned plums (with the addition of 10%, by mass, comminuted stones), supplemented with (NH4)2HPO4 (0.2 g per kg of fruit pulp) as a nitrogen source for the yeast.

Fermentation was initiated using dry wine yeast Saccharomyces bayanus (Fermentis, Lesaffre, Marcq-en-Baroeul, France) in the mass fraction of 0.3 g per kg of plum pulp, with an alcohol tolerance of up to 18% (by volume) and a wide fermentation temperature range (10–35 °C). The fermentation was conducted at 18 °C for 10 days. The distillation was done in a one-column continuous apparatus (F.P.H.U. SPO-CHEM, Myślenice, Poland).

Maturation of plum distillate samples was performed using lightly toasted French oak chips (produced from two varieties of French oak wood, Quercus sessiflora and Quercus robur) and French oak chips made from fragments of emptied barrels used for ageing cognac (Ares Trading SA, Warsaw, Poland). The average chip size was 7.5 mm×10 mm.

Experimental design

The scope of the experiments included assessment of the following factors: the type (see above) and dose of oak chips (3, 5 or 7 g/L), the temperature of fermentation (18–20, 35 or 45 °C) and the system of ageing (static, circulatory or ultrasound treatment). The effect of treatment with ultrasound was assessed using a SONOPULS HD 2200 homogenizer (BANDELIN electronic GmbH & Co. KG, Berlin, Germany) in continuous mode, set to 50% amplitude (ultrasound power 400 W, 24 kHz).

In all experiments, the plum distillate (77%) was diluted with deionized water to ASV of 55%. Next, 1.5 L of distillate was transferred into 2-litre lab bottles (made from clear soda glass) with a wide mouth and a ground glass stopper for an air-tight seal, and different amounts of oak chips were added. The prepared samples were aged for 12 months in a dark place under various conditions.

The variants for ageing were as follows: lightly toasted French oak chips, 18–20 °C, a static system (samples were stirred for only 3 min per day, 5 days per week) (variant A), French oak chips obtained after ageing of cognac, 18–20 °C, a static system (samples were stirred for only 3 min per day, 5 days per week) (variant B), lightly toasted French oak chips, 35 °C, a static system (samples were stirred for only 3 min per day and then heated for 2 h per day, 5 days per week, for 3 months, then matured under the same conditions as variant A) (variant C), lightly toasted French oak chips, 45 °C, a static system (samples were stirred for only 3 min per day and then heated for 2 h per day, 5 days per week, for 6 months, then matured under the same conditions as variant A) (variant D), lightly toasted French oak chips, 45 °C, a circulation system (samples heated and stirred simultaneously for 2 h per day, 5 days per week, for 6 months, then matured under the same conditions as variant A) (variant E), and lightly toasted French oak chips, 20 °C with ultrasound treatment (50% amplitude for 20 min per day, 5 days per week, for 3 months, then matured under the same conditions as variant A) (variant F).

Samples were prepared in triplicate for each variant, therefore 12 bottles were prepared, i.e. 3 bottles with plum distillate were aged for 3 months, 3 bottles for 6 months, 3 bottles for 9 months and 3 bottles for 12 months. Distillates were analyzed at the start of the ageing process and after 3, 6, 9 and 12 months. The analytes were: global parameters, such as alcoholic strength by volume (ASV in %), total extract content (g/L), colour according to CIELab chromatic parameters and concentrations of phenolic compounds (mg/L), tannins as pyrogallol (mg/L), sugars (mg/L), major and minor volatiles (mg/L of absolute alcohol). The control sample for each variant was the plum distillate before ageing.

Distillation process

The preparation of matured plum distillate samples for analyses consisted of separation of ethanol and other volatiles from the extracted compounds in a digital distilling unit model Super Dee (Gibertini Elettronica S.r.l., Novate Milanese, MI, Italy). Prior to distillation, 100 mL of sample were transferred to the glass flask of the distilling apparatus and then diluted with 50 mL of deionized water. In the next step, distillation was carried out to separate ethyl alcohol, water and other volatile compounds (distillate) from nonvolatile compounds (extract). Volatile compounds (approx. 90 mL) were condensed and collected in a separate volumetric flask (100 mL) and then distilled water was added to reach the same volume as the original sample (i.e. 100 mL). This sample was used for the determination of ASV and major volatile compounds.

The distillation residue, i.e. extract fraction, was cooled and quantitatively transferred to a 100-mL flask, and then distilled water was added to reach the same volume as the original sample, i.e. 100 mL. This sample was used for the concentration determination of total extract, phenolic compounds, tannins and sugars.

Alcoholic strength by volume

Ethanol concentration (i.e. alcoholic strength by volume; ASV) was measured with a hydrometer (thermoalcoholometer, Conbest Sp. z o.o., Cracow, Poland) using the percentage scale (by volume of ethanol) at 20 °C. If the distillate temperature diverged from 20 °C, then a correction was applied, using alcoholometric tables (23).

Total extract

Total extract content in the extracted fraction obtained after separation of ethanol and other volatiles, as described above, was determined following the methodology recommended in alcohol industry (24).

Colour according to CIELab chromatic parameters

Colour measurements were made using a Chroma Meter CR-5 (Konica Minolta, Osaka, Japan). The results were expressed in Commission Internationale d´Eclairage (CIE) L*, a* and b* colour space coordinates (25). These parameters defined: L* indicates lightness (white (100) to black (0)), a* coordinate (red (+100) to green (−100)), b* coordinate (yellow (+100) to blue (−100)). These parameters were measured using the CIE 1964 Standard Observer (10° visual field) and the CIE standard illuminant D65 as references (9, 25). The total differences in colour (ΔE*) between the tested samples (after maturation) and the standard sample (before maturation) were calculated according to the following equation (26):

FTB-55-333-e1.jpg

HPLC-DAD analysis of phenolic compounds

Phenolic compounds were analyzed using a modified method described by dos Anjos et al. (27) on an Agilent 1260 Infinity Binary LC system (Agilent Technologies, Palo Alto, CA, USA), consisting of a binary pump, a vacuum degasser, an autosampler, a thermostated column compartment and a diode array detector (DAD) with a 10-mm max-light flow cell. The samples were filtered through 0.45 µm PES (polyethersulfone) membrane filters (Sigma-Aldrich, Saint Louis, MO, USA) before injection, and separations were performed using an Agilent-Zorbax Eclipse XDB-C18 (4.6 mm×250 mm, 5 µm) column connected to an Agilent-Zorbax Eclipse XDB-C18 4-Pack (4.6 mm× 12.5 mm, 5 µm) pre-column. The mobile phase consisted of 2% acetic acid in water (solvent A) and methanol/water/acetic acid 70:28:2 (solvent B). The samples were eluted according to the following gradient: 0 to 25 min 0–40% B, 25 to 40 min 40–55% B, 40 to 43 min 55–60% B, 43 to 50 min 60–100% B, 50 to 55 min 100–0% B and 55 to 60 min 0% B.

Phenolic compounds were eluted at a 0.8 mL/min flow rate and the temperature was set to 30 °C. Absorbance was measured at 280 nm and the injection volume was 20 µL. The compounds coniferaldehyde, sinapaldehyde, syringaldehyde and vanillin were identified using reference standards, while quantification was performed using external calibration curves with standards. The recovery studies for the quantified compounds were observed in the range of 80–120%. The relative standard deviations (RSDs) were less than 2.6%.

Analysis of tannins

The content of tannins was determined in matured samples (once the volatiles, including ethanol and others, had been removed) and expressed as pyrogallol in mg/L, following the methodology described in the European Pharmacopoeia 5.0 (28).

HPLC analysis of sugars

The contents of glucose, xylose and arabinose in the samples of aged plum distillate were determined in the extract (obtained as described above), using an Infinity 1260 HPLC system equipped with a refractive index detector (RID; Agilent Technologies, Palo Alto) in a Hi-Plex Ca column (7.7 mm×300 mm, 8 µm; Agilent Technologies). Column temperature was maintained at 80 °C. HPLC grade water was used as a mobile phase at a flow rate of 0.6 mL/min with a sample volume of 20 µL. Prior to analysis, all samples were filtered through 0.45-µm PES (polyethersulfone) membranes (29). The recovery studies for the quantified compounds were in the range of 92–107%. The RSDs were less than 6.2%.

GC-FID analysis of major volatile compounds

Analysis of the major volatile compounds was performed using gas chromatograph (GC) model Agilent 7890A (Agilent Technologies, Santa Clara, CA, USA), equipped with a flame-ionization detector (FID), a split/splitless injector and a capillary column (HP-Innowax, 60 m×0.32 mm inner diameter×0.50 µm film thickness; Agilent Technologies, Santa Clara). Each sample (1 µL) previously diluted with deionized water to ASV=40% was injected directly onto the GC column using an autosampler in split mode (1:45). The temperature of the injector and FID was kept at 250 °C. The oven temperature program was as follows: 40 °C initial, 6-minute hold; 2 °C/min to 80 °C; 5 °C/min to 210 °C final, 5-minute hold. The flow rate of the carrier gas (helium) through the column was 2 mL/min. The volatile compounds (acetaldehyde, ethyl acetate, methanol, propanol, isobutanol, butanol, amyl alcohols, pentanol, hexanol and 2-phenylethanol) were identified using reference GC standards and then quantified with standard calibration curves, using 4-heptanone as the internal standard. All analyses were performed in triplicate. The obtained data were analysed using MassHunter software (Agilent Technologies, Santa Clara).

SPME-GC-MS analysis of minor volatile compounds

Chromatographic analysis of the minor volatile compounds in the distillates was performed using a GC apparatus (Agilent 7890A; Agilent Technologies, Santa Clara) with a mass spectrometer (Agilent MSD 5975C; Agilent Technologies, Santa Clara). Solid phase microextraction (SPME) was used to extract the volatile compounds, with subsequent analysis using gas chromatography-mass spectrometry (GC-MS).

SMPE conditions were as follows: a 5-mL plum distillate sample (previously diluted to ASV=20%) mixed with the internal standard (4-heptanone at a concentration of 45 mg/mL of absolute alcohol) was placed in a 20-mL amber headspace vial and capped tightly. Carboxene/divinylbenzene/polydimethylsiloxane fibre (DVB/CAR/PDMS, 50/30 µm, 1 cm fibre length; Supelco, Bellefonte, PA, USA) was used in the analyses of all samples. The vial was equilibrated at 50 °C for 15 min, after which SPME fibre was introduced. Extraction was continued for 15 min at 50 °C. The compounds were then desorbed for 5 min at 250 °C in splitless mode. GC-MS analysis was performed. After each injection, the fibre was conditioned at 250 °C for 10 min. All headspace SPME extractions were performed in triplicate.

SPME-GC-MS conditions were as follows: a capillary column (VF-WAX MS, 60 m×0.32 mm i.d.×0.50 µm film thickness; Agilent Technologies, Santa Clara) was used to separate the compounds. The GC oven temperature program was as follows: 35 °C initial, 6-minute hold; 2 °C/min to 80 °C; 10 °C/min to 250 °C final, 5-minute hold. The flow rate of the carrier gas (helium) was 1.2 mL/min. The MS run parameters were as follows: ion source temperature 230 °C, transfer line temperature 260 °C, quadrupole temperature 150 °C and ionization energy 70 eV. Detection was carried out in scan mode over a range of m/z=29–289. The volatile components were identified based on a comparison of their mass spectra with those registered in the NIST MS library (NIST 98.1 and the Wiley Registry of Mass Spectral Data, 8th edition) (30). Their retention indices (RI) were also compared with reference compounds and data in the literature (31, 32).

The minor volatile compounds were quantified with an internal standard method using MassHunter software (Agilent Technologies, Santa Clara). All gas chromatography standards were purchased from Sigma-Aldrich and were of GC purity. Standard solutions were prepared using anhydrous ethanol (Sigma-Aldrich) as the solvent and stored at 4 °C.

The recovery studies for the quantified compounds were in the range of 90–107%. The determined RSDs of intra- and interday precision were lower than 20%.

Statistical analysis

For the data evaluation, three-way (major volatile compounds) and two-way (phenolic compounds, tannins, sugars and CIELab) analysis of variance (ANOVA) with a significance level p≤0.05 were used, followed by Tukey’s post-hoc test when significant effect occurred. Statistical analyses were performed using Statistica software v. 10 (Statsoft, Tulsa, OK, USA).

SPME-GC-MS data of minor volatile compounds in aged plum distillate samples were subjected to principal component analysis (PCA) using XLSTAT software v. 2017.4 (Addinsoft, New York, NY, USA).

Results and Discussion

Changes in alcoholic strength by volume and total extract content

The process of ageing of spirit beverages in oak wood barrels is associated with changes in the physical and chemical parameters of the maturing spirit (5). One such change is a decline in the volume and the alcoholic strength by volume (ASV) of a new spirit with ASV higher than approx. 50%, as a consequence of the preferential evaporation of ethanol through the oak wood. Ullage increases at higher temperatures and lower humidity, as evaporation intensifies.

In this study, plum distillate with an ASV=55% was stored in tightly closed bottles with oak wood chips. The loss of alcohol was not expected. Unfortunately, measurements taken in successive maturation periods indicated that the ASV had decreased (see Table 1). No significant effect of dose of oak chips on ethyl alcohol content was found in all maturation variants. The ethanol loss ranged from 0.48 to 0.88% (by volume) and was affected by ageing system, as well as by temperature and time of maturation. When assessing the effect of ageing temperature on the ethanol content changes, the statistically significant differences were observed (variants A, C and D). The lower volume fractions were found in distillates matured at 35 and 45 °C (variants C and D respectively) than in those aged at 18–20 °C (variant A). Moreover, time×temperature (variants A, C and D) and time×ageing system (variants D and E, and variants A and F) interactions were found. The application of agitation in the ageing systems such as ultrasound treatment and circulation may cause ethanol evaporation (Table 1). Lower ASVs could be further attributed to the penetration of ethanol into the porous structure of the oak chips during maturation.

Table 1 Changes in alcoholic strength by volume (ASV) and total extract content during maturation of plum distillate samples with oak chips
ParameterMaturation variantControl sample[m(oak chip)/V(plum distillate)]/(g/L)
357
t(maturation)/month
369123691236912
ASV/%A55.43
±0.05
55.35
±0.02
55.15
±0.02
55.05
±0.03
54.95
±0.02
55.45
±0.02
55.05
±0.02
55.00
±0.03
54.95
±0.02
55.30
±0.02
55.15
±0.02
55.05
±0.03
54.85
±0.02
B55.43
±0.05
55.32
±0.02
55.12
±0.02
54.82
±0.02
54.62
±0.02
55.22
±0.03
55.12
±0.02
54.72
±0.02
54.62
±0.02
55.12
±0.02
54.90
±0.02
54.70
±0.02
54.62
±0.02
C55.43
±0.05
55.15
±0.02
54.95
±0.02
54.75
±0.01
54.75
±0.02
55.15
±0.02
55.05
±0.02
54.85
±0.01
54.75
±0.02
55.05
±0.01
54.95
±0.02
54.80
±0.01
54.75
±0.02
D55.43
±0.05
55.12
±0.02
54.92
±0.15
54.72
±0.15
54.72
±0.15
55.15
±0.02
54.90
±0.01
54.72
±0.02
54.72
±0.01
55.05
±0.02
54.92
±0.02
54.80
±0.01
54.72
±0.02
E55.43
±0.05
55.05
±0.03
54.82
±0.02
54.62
±0.02
54.62
±0.01
55.05
±0.03
54.72
±0.02
54.65
±0.02
54.62
±0.01
54.90
±0.03
54.75
±0.02
54.65
±0.02
54.62
±0.01
F55.43
±0.05
54.85
±0.02
54.65
±0.02
54.55
±0.02
54.55
±0.02
54.85
±0.02
54.70
±0.02
54.60
±0.02
54.55
±0.02
54.78
±0.02
54.65
±0.02
54.60
±0.02
54.55
±0.02
γ(total extract)/(g/L)An.d.0.75
±0.05
1.25
±0.07
1.50
±0.05
1.55
±0.05
1.25
±0.05
1.75
±0.05
2.25
±0.05
2.35
±0.05
1.75
±0.05
2.15
±0.05
2.35
±0.05
2.50
±0.05
Bn.d.0.45
±0.02
1.15
±0.02
1.25
±0.03
1.35
±0.05
0.65
±0.05
1.35
±0.03
1.55
±0.05
1.55
±0.03
0.75
±0.03
1.35
±0.05
1.65
±0.05
1.80
±0.05
Cn.d.0.90
±0.05
1.35
±0.05
1.75
±0.05
2.00
±0.05
1.45
±0.05
1.75
±0.05
2.05
±0.05
2.65
±0.05
1.75
±0.05
2.15
±0.05
2.75
±0.05
2.94
±0.05
Dn.d.1.28
±0.05
1.55
±0.05
1.95
±0.05
2.15
±0.05
1.48
±0.05
1.95
±0.05
2.30
±0.05
2.86
±0.05
1.80
±0.05
2.28
±0.05
2.80
±0.05
2.95
±0.05
En.d.1.25
±0.05
1.60
±0.05
1.90
±0.05
2.10
±0.05
1.65
±0.05
1.85
±0.05
2.25
±0.05
2.22
±0.05
1.85
±0.05
2.35
±0.05
2.85
±0.05
3.05
±0.05
Fn.d.0.75
±0.05
1.15
±0.07
1.30
±0.05
1.60
±0.05
1.15
±0.05
1.65
±0.05
2.05
±0.05
2.25
±0.05
1.65
±0.05
2.05
±0.05
2.35
±0.05
2.40
±0.05
ParameterEffect of dose of lightly toasted French chips, temperature and time of maturation, and interaction among them (variants A, C and D, static maturation system)Effect of dose of lightly toasted French chips, ageing system with agitation and time of maturation, and interaction among them (variants D and E, maturation at 45 °C)Effect of dose and type
of oak chips and time of maturation, and interaction among them (variants A and B, static maturation system, at 20 °C)
Effect of dose of lightly toasted French chips, ageing system with agitation and time of maturation, and interaction among them (variants A and F, maturation at 20 °C)
DCTMTDC × TDC × MTT × MTDC × T × MTDCASMTDC × ASDC × MTAS × MTDC × A × MTDCTCMTDC × TCDC × MTTC × MTDC × TC × MTDCASMTDC × ASDC × MTAS × MTDC × AS × MT
ASV/%ns******nsns***nsns******ns****nsnsns***ns*****ns******nsns***ns
γ(total extract)/ (g/L)***********************************************************************ns********

A=lightly toasted French oak chips, 18–20 °C, a static system (samples were stirred for only 3 min per day, 5 days per week), B=French oak chips obtained after ageing of cognac, 18–20 °C, a static system (samples were stirred for only 3 min per day, 5 days per week), C=lightly toasted French oak chips, 35 °C, a static system (samples were stirred for only 3 min per day and then heated for 2 h per day, 5 days per week, for 3 months, then matured under the same conditions as variant A), D=lightly toasted French oak chips, 45 °C, a static system (samples were stirred for only 3 min per day and then heated for 2 h per day, 5 days per week, for 6 months, then matured under the same conditions as variant A), E=lightly toasted French oak chips, 45 °C, a circulation system (samples heated and stirred simultaneously for 2 h per day, 5 days per week, for 6 months, then matured under the same conditions as variant A), F=lightly toasted French oak chips, 20 °C with ultrasound treatment (50% amplitude for 20 min per day, 5 days per week, for 3 months, then matured under the same conditions as variant A); n.d.=not determined
DC=dose of oak chips (3, 5 and 7 g/L), T=temperature of maturation (18–20, 35 and 45 °C), MT=maturation time (0, 3, 6, 9 and 12 months), AS=ageing system with agitation (variants A and D=static, variant E=circulation, variant F=ultrasound treatment), TC=type 
of oak chips (lightly toasted French chips or French chips after ageing of cognac); ***p<0.001, **p<0.01, *p<0.05, ns=not significant

Changes in the composition of aged spirits can also be related to the extraction of wood constituents (33). In our study, the maturation of plum distillate samples with oak chips resulted in an increase in total extract content in all experiments (Table 1). During ageing experiments, the effect of five factors on extract content changes was studied, as well as interactions among them. Extract levels in tested samples of matured plum distillate were significantly affected by the dose and type of oak chips, temperature and time of maturation, and ageing system, as well as by interactions among them. Only the interaction oak chips×ageing system (variants A and F) did not significantly affect extract content. The highest dynamics of extraction took place in the initial 3 months of maturation and decreased over the subsequent months. The values for this parameter were correlated with the dose and type of oak chips, as well as with the maturation conditions. After 12 months, samples aged with oak chips from cognac barrels were characterized by up to approx. 34% lower extract content than those aged with fresh oak chips. Moreover, it was observed that higher temperatures during maturation led to higher levels of extractable organic content in the tested samples. Periodic circulation of the oak chips in the plum distillate also led to significant further increases in extract content.

CIELab chromatic parameters of aged plum distillate samples

Fresh plum distillates obtained after distillation are colourless. Changes in colour were a visible effect of ageing, resulting from the decomposition of polyphenols extracted from the oak wood chips (6). The colour of aged alcoholic beverages is very complex, and difficult to describe and compare. The CIElab method was used for more specific and objective determination of colour, measuring two colour coordinates, a* and b*, as well as a psychometric index of lightness, L* (34). The data of CIELab chromatic parameters and results of two-way ANOVA are shown in Table 2.

Table 2 CIELab chromatic parameters of plum distillate samples aged over 12 months with oak wood chips under various conditions
CIELab chromatic parameter[m(oak chip)/V(plum distillate)]/(g/L)
357
Maturation variant
ABCDEFABCDEFABCDEF
L*91.09
±0.55
94.05
±0.65
90.49
±0.48
89.64
±0.45
89.52
±0.48
90.80
±0.43
88.70
±0.45
91.05
±0.62
87.49
±0.52
86.85
±0.42
86.52
±0.40
87.80
±0.43
86.24
±0.44
88.70
±0.39
85.62
±0.40
82.65
±0.35
81.87
±0.32
85.95
±0.41
ΔL*–6.59
±–0.54
–3.63
±–0.64
–7.19
±–0.47
–8.04
±–0.45
–8.16
±–0.46
–6.88
±–0.41
–8.98
±–0.43
–6.63
±–0.62
–10.19
±–0.50
–10.83
±–0.40
–11.16
±–0.39
–9.88
±–0.41
–11.44
±–0.42
–8.98
±–0.37
–12.06
±–0.39
–15.03
±–0.34
–15.81
±–0.31
–11.73
±–0.40
a*–2.83
±–0.03
–1.47
±–0.01
–2.80
±–0.02
–2.73
±–0.02
–2.02
±–0.01
–2.53
±–0.02
–2.58
±–0.02
–1.27
±–0.02
–2.35
±–0.02
–2.22
±–0.02
–2.02
±–0.02
–2.33
±–0.02
–0.57
±–0.02
–0.58
±–0.02
0.19
±0.02
0.22
±0.02
0.24
±0.02
–0.44
±–0.03
Δa*–2.69
±–0.02
–1.33
±–0.02
–2.66
±–0.02
–2.59
±–0.02
–1.88
±–0.01
–2.39
±–0.02
–2.44
±–0.02
–1.13
±–0.02
–2.21
±–0.02
–2.08
±–0.02
–1.88
±–0.02
–2.19
±–0.02
–0.43
±–0.02
–0.44
±–0.02
0.33
±–0.02
0.36
±–0.02
0.38
±–0.02
–0.30
±–0.02
b*26.42
±0.12
11.48
±0.05
30.55
±0.08
36.64
±0.06
36.87
±0.06
27.50
±0.04
37.20
±0.05
21.48
±0.03
31.79
±0.03
36.64
±0.03
37.87
±0.04
27.50
±0.02
46.55
±0.06
37.20
±0.04
47.23
±0.05
47.66
±0.05
47.72
±0.04
45.78
±0.04
Δb*25.99
±0.12
11.05
±0.05
30.12
±0.08
36.21
±0.06
36.44
±0.06
27.07
±0.04
36.77
±0.05
21.05
±0.03
31.36
±0.03
36.21
±0.03
37.44
±0.04
27.07
±0.02
46.12
±0.06
36.77
±0.04
46.8
±0.05
47.23
±0.05
47.29
±0.04
45.35
±0.05
ΔE26.94
±0.15
11.71
±0.06
31.08
±0.09
37.18
±0.08
37.39
±0.08
28.03
±0.05
37.93
±0.07
22.10
±0.03
33.05
±0.04
37.85
±0.04
39.11
±0.06
28.89
±0.03
47.52
±0.08
37.85
±0.05
48.33
±0.06
49.57
±0.07
49.86
±0.08
46.84
±0.05
Effect of dose of lightly toasted French chips and temperature, and interaction between them (variants A, C and D, static maturation system)Effect of dose of lightly toasted French chips and ageing system with agitation, and interaction between them (variants D and E, maturation at 45 °C)Effect of dose and type of oak chips, and interaction between them (variants A and B, static maturation system, at 20 °C)Effect of dose of lightly toasted French chips and ageing system with agitation, and interaction between them (variants A and F, maturation at 20 °C)
DCTDC × TDCASDC × ASDCTCDC × TCDCASDC × AS
L********************ns****ns
ΔL**************ns******ns****ns
a*************************************
Δa*************************************
b*************************************
Δb*************************************
ΔE************************************

A–E=see Table 1, standard sample (plum distillate sample before maturation): L*standard=97.68, a*standard=–0.14, b*standard=0.43
DC=dose of oak chips (3, 5 and 7 g/L), T=temperature of maturation (18–20, 35 and 45 °C), AS=ageing system with agitation (variants A and D=static, variant E=circulation, variant F=ultrasound treatment), TC=type of oak chips (lightly toasted French chips or French chips after ageing of cognac); ***p<0.001, **p<0.01, *p<0.05, ns=not significant

The results of our study indicate that the type of oak chip (lightly toasted, not having been used previously for maturation, or made from barrels used for cognac maturation), the dose of wood chips and the conditions of ageing each had an effect on CIElab parameters. Also interactions of dose of lightly toasted French oak chips×temperature and dose of lightly toasted French oak chips×ageing system (static and circulation) combined with agitation were observed.

The values for lightness (L*) decreased with increasing doses of both lightly toasted and oak chips after ageing of cognac. Higher temperatures also resulted in lower values of L*, associated with extraction of polyphenols (9). The samples matured with cognac barrel oak chips showed higher values of L* (greater lightness) than analogous samples aged with fresh oak chips. This confirms the poorer composition of chips made from oak barrels previously used for storing cognac than lightly toasted French oak chips.

It is interesting to note that negative values of parameter a* were found in the majority of samples. Positive values of this coordinate were obtained only for samples aged with 7 g/L of lightly toasted oak chips, periodically heated to 35 or 45 °C. In contrast, parameter b* was positive in all variants, with the lowest value detected in the sample with oak chips after cognac ageing. Parameter b* showed statistically significant differences depending on a dose and type of oak chips (variants D and E). Significant effect of interaction between these two factors was also found. The addition of lightly toasted oak chips in a dose of 7 g/L of plum distillate resulted in higher value of parameter b* than of samples matured with oak chips after cognac ageing. The use of circulation as well as ultrasound treatment during maturation had a significant effect on the higher value of parameter b* than of analogous samples maturated in static system.

Treatment with ultrasound in the first 3 months of maturation had no positive effect on the colour of the plum brandy. Based on the values of a* and b*, all the samples can be described as yellow, with slight hints of green or red. The values of ΔE*, i.e. the total colour difference in relation to the control sample, were calculated using the same coordinates discussed above. All evaluated factors had significant effect on ΔE* values. The lowest ΔE* values were observed for plum brandy samples aged with 3 g/L of oak chips (especially with barrel oak chips after cognac ageing), which increased with increasing dose of oak chips. Moreover, higher values of this factor were observed in samples aged with lightly toasted fresh oak chips. Application of periodical heating and circulation during maturation also had strong effect on higher values of ΔE*. Pecić et al. (9), who tested the effect of maturation conditions on the sensory and antioxidant properties of Serbian plum brandies matured in casks for between 10 and 47 years, obtained significantly lower values of L* and higher values of parameter a*. Only the values of coordinate b* were similar to those obtained in our study.

Changes in concentrations of phenolic compounds

Oak wood tissue is mostly made of polysaccharides such as cellulose, hemicelluloses and lignin, and is impregnated with tannins and small amounts of lipids (35). The main extractive components of wood are hydrolysable tannins and volatile compounds (36). Degradation of lignin in hydroalcoholic solutions results in the liberation of benzoic (vanillin, vanillic acid, syringaldehyde and syringic acid) and cinnamic (coniferaldehyde and sinapaldehyde) derivatives, which are the important phenolics for aroma and taste in aged brandies (37). The statistically significant effect of time×type of chips interaction was found only for vanillin content (p<0.05). After 12 months of maturation, in samples aged with cognac barrel oak chips, the vanillin concentration was lower than in the analogous samples aged with lightly toasted French oak chips (Fig. 1). No significant differences were observed for other phenolic compounds in plum distillate samples maturated with the two types of oak chips (p>0.05). In turn, temperature of maturation had statistically significant effect on the contents of all determined phenolic compounds (p<0.05). The largest increase was observed of sinapaldehyde content. After 3 months of maturation its concentration reached (14.48±0.72) mg/L (in distillate aged with lightly toasted fresh oak chips, heated periodically to 45 °C). Further changes in sinapaldehyde content were much less dynamic, and after 6 months sinapaldehyde concentrations were observed to decrease as a consequence of oxidation to syringaldehyde (20).

Fig. 1 Changes in concentrations of phenolic compounds: a) coniferaldehyde, b) sinapaldehyde, c) syringaldehyde, and d) vanillin during maturation of plum distillate samples under various conditions with added oak chips (5 g/L).
Designation of maturation variants:
A=lightly toasted French oak chips, 18–20 °C, a static system (samples were stirred for only 3 min per day, 5 days per week), B=French oak chips obtained after ageing of cognac, 18–20 °C, a static system (samples were stirred for only 3 min per day, 5 days per week), C=lightly toasted French oak chips, 35 °C, a static system (samples were stirred for only 3 min per day and then heated for 2 h per day, 5 days per week, for 3 months, then matured under the same conditions as variant A), D=lightly toasted French oak chips, 45 °C, a static system (samples were stirred for only 3 min per day and then heated for 2 h per day, 5 days per week, for 6 months, then matured under the same conditions as variant A), E=lightly toasted French oak chips, 45 °C, a circulation system (samples heated and stirred simultaneously for 2 h per day, 5 days per week, for 6 months, then matured under the same conditions as variant A), F=lightly toasted French oak chips, 20 °C with ultrasound treatment (50% amplitude for 20 min per day, 5 days per week, for 3 months, then matured under the same conditions as variant A)
FTB-55-333-f1

The conditions of maturation had a significant effect on the contents of all phenolic compounds determined in the study. Periodic circulation was found to improve coniferyl aldehyde and vanillin contents, which increased (p<0.05), in comparison with samples aged in static system. Treatment with ultrasound did not result in the release of more phenolics, with the exception of sinapaldehyde. The highest sinapaldehyde content after 12 months of maturation was found in the sample treated with ultrasound, probably as a consequence of the inhibition of oxidation to syringaldehyde by the ultrasound. Use of cognac barrel oak chips resulted in significantly lower concentrations of phenolic compounds, which is indicative of natural partial wood exhaustion.

Changes in concentrations of tannins

Tannins (soluble polyphenols with a molecular mass of 500–3000 Da) are among the most abundant constituents of oak wood that are extracted into alcoholic beverages during ageing (38). Tannins can be classified according to their chemical structures into hydrolysable and condensed tannins. During ageing in oak barrels, the hydrolysable tannins extracted from oak wood due to the action of ethanol can be condensed with other compounds, such as polysaccharides and polypeptides (39).

During the maturation of plum distillate samples, increases in tannin content were observed. The increases were correlated both with the maturation time (maximum growth occurred in the first half of the year) and with the dose of added oak chips (p<0.05) (data shown only for 5 g/L of oak chips; see Fig. 2). Using so-called maderization, heating the samples to 35 °C caused an increase in tannins content (p<0.05), but further heating to 45 °C did not affect any changes (p>0.05). In samples aged with cognac barrel oak chips, the tannin concentration was approx. 50% lower than in the analogous samples aged with lightly toasted fresh oak chips (Fig. 2) (p<0.05). One of ageing systems used in our study, i.e. periodic circulation, resulted in greater extraction of tannins, with concentrations after 6 months of ageing reaching approx. 80% of the values determined after 12 months (p<0.05), while periodical treatment with ultrasound did not cause higher extraction of tannins from oak wood (p>0.05). Tao et al. (40) studied the release of oak-related compounds from oak chips during wine ageing. They used 25-kHz ultrasound waves to intensify the mass transfer of phenolics from oak chips into a model wine. Their results showed that acoustic energy density did not affect the total phenolic yield significantly, whereas increased transfer of phenolics was observed with temperature increases during sonication.

Fig. 2 Changes in the concentrations of tannins during maturation of plum distillate samples under various conditions with added oak chips (5 g/L). For designation of maturation variants A–F see Fig. 1
FTB-55-333-f2

Changes in concentrations of sugars

The thermal degradation of cellulose and hemicelluloses that occurs during the toasting of oak wood, as well as in the processes of hydrolysis or ethanolysis which take place during ageing of hydroalcoholic solutions with oak wood leads to the release of various compounds with lower molecular mass (5, 40). These include sugars such as glucose, xylose and arabinose (41). Glucose is one of the main sugars in aged whiskies (22). During the maturation of plum distillate samples, the liberation of sugars from oak wood chips was observed. The changes are presented in Fig. 3, using the results obtained from samples aged with a medium dose of oak chips as an example, i.e. 5 g/L of plum distillate. The changes in sugar content in samples aged with 3 and 7 g/L of oak chips (data not shown) were analogous to those observed with 5 g/L. The significantly different concentrations of sugars in maturated distillates were affected by all evaluated factors of maturation process (i.e. temperature, time and ageing system) as well as the interactions among them (p>0.001). During the first 3 months of maturation at 20 °C, no significant changes in glucose content were observed (p>0.05), while significant effect was found for time×temperature interaction (p<0.001). No clear differences were detected over subsequent months between the contents of sugars (p> 0.05) in the samples aged at 35 or 45 °C. After 12 months, glucose was present in the highest concentrations, of up to (41.20±2.47) mg/L, xylose concentration reached (12.70± 0.64) mg/L and the arabinose concentration was up to (5.43±0.03) mg/L. Periodical heating of aged plum distillate samples to 35 and 45 °C caused a decrease in glucose concentration, in comparison with trials maturated at room temperature. Moreover, in samples heated periodically to 45 °C (variants D and E), intense liberation of all sugars was observed (p>0.05) during maturation, but application of periodical circulation (variant E) did not cause an increase (p>0.05) in glucose, arabinose and xylose concentrations, in comparison with the same sample maturated in static system (variant D).

Fig. 3 Changes in the concentrations of sugars: a) glucose, b) xylose, c) arabinose during maturation of plum distillate samples under various conditions with added oak chips (5 g/L). For designation of maturation variants A–F see Fig. 1
FTB-55-333-f3

The type of chips and time of maturation were also used to evaluate changes of sugar content in matured distillate samples (variants A and B). With extended time of maturation, the sugar content increased (p<0.05), while differences between the types of chips were found only for arabinose (p<0.05).

Changes in concentrations of major volatile compounds

During maturation of alcoholic beverages, as well as the extraction and degradation of oak wood components, changes in the volatile compound content occur (37). Volatiles such as carbonyl compounds, esters, higher alcohols, organic acids and others (42), which are by-products of fermentation, are subjected to oxidation, reduction, esterification and transesterification during maturation (37).

Aldehydes and ketones, known as carbonyl compounds, are usually considered to have a negative influence on the quality of spirits. The concentrations of carbonyl compounds in agricultural distillates depend on the quality of the raw materials, their chemical composition, the conditions under which technological processes take place, the type of yeast species/strain involved in the fermentation (43) and the extent of microbial contamination (44). The quality of fruit distillates may also vary depending on the distillation conditions and the type of equipment used. The above-mentioned factors explain the differences in concentrations of volatile compounds (i.e. methanol, acetaldehyde, fusel alcohols and others) in the plum distillate used in our experiments when comparing with other published works (2, 9, 45).

In our study, decreases in acetaldehyde (Tables 3 and 4{ label needed for table-wrap[@id='t4'] }) were observed in all maturation variants (with the exception of the samples treated with ultrasound). These changes were affected mainly by the time, but not by the conditions of maturation. Increases in acetaldehyde content were observed in the samples treated with ultrasound, in comparison with distillate samples maturated in static system (variants A and F). These samples were also characterized by the largest decrease in ethanol content (Table 1). The lack of significant differences between the content of acetaldehyde in samples aged at 20 or 35 °C (variants A and C) can be interpreted as a consequence of the partial oxidation of ethanol at elevated temperatures (45). Mangas et al. (46) report that throughout maturation, acetaldehyde can be produced directly from ethanol, and its interaction with ethanol results in the production of acetal. This was confirmed by the results for acetaldehyde concentration revealed in our study (Table 3). Samples aged with cognac barrel oak chips had significantly higher concentrations of acetaldehyde than those aged with fresh lightly toasted oak chips, but no significant effect of the type of chips×dose of chips interaction was found (Tables 3 and 4{ label needed for table-wrap[@id='t4'] }).

Table 3 Changes in the concentrations of major carbonyl compounds during maturation of plum distillate samples with oak chips under various conditions
CompoundMaturation variantControl sample[m(oak chip)/V(plum distillate)]/(g/L)
357
t(maturation)/month
369123691236912
γ/(mg/L of absolute alcohol)
AcetaldehydeA69.37
±3.25
63.92
±1.15
57.26
±1.21
49.75
±1.32
47.96
±1.15
61.92
±1.25
56.26
±1.15
49.96
±1.22
50.16
±0.75
57.93
±1.05
53.55
±0.82
50.96
±0.76
52.81
±0.69
B69.37
±3.25
65.70
±1.05
63.70
±0.95
60.65
±1.12
61.70
±0.75
66.25
±1.15
60.70
±0.68
60.15
±1.12
60.85
±1.05
65.22
±0.85
66.70
±1.05
63.24
±0.72
60.48
±0.84
C69.37
±3.25
60.13
±1.35
60.89
±0.75
58.13
±1.35
55.13
±0.75
60.66
±1.32
57.89
±0.55
56.42
±0.85
53.22
±0.48
60.82
±0.75
58.25
±0.84
57.13
±0.66
53.22
±0.75
D69.37
±3.25
61.13
±1.26
55.13
±0.82
54.18
±0.69
51.13
±0.66
63.22
±0.85
60.13
±0.74
56.18
±0.62
53.13
±0.39
60.40
±0.66
54.22
±0.74
51.13
±0.66
50.05
±0.66
E69.37
±3.25
60.31
±0.55
62.31
±0.45
56.31
±1.12
52.31
±0.55
58.42
±0.55
53.22
±0.39
52.35
±0.26
50.26
±0.72
60.96
±0.55
54.31
±0.66
52.31
±0.55
52.31
±0.70
F69.37
±3.25
65.37
±1.42
70.37
±3.15
73.37
±1.15
75.37
±1.42
67.22
±0.72
71.53
±0.82
70.12
±1.15
72.26
±0.86
70.25
±1.33
72.37
±0.82
71.45
±1.36
72.32
±1.15
IsobutyraldehydeA5.15
±0.15
4.86
±0.07
4.24
±0.06
4.05
±0.05
3.82
±0.05
4.78
±0.07
4.22
±0.03
4.15
±0.05
4.09
±0.05
4.86
±0.07
4.24
±0.06
4.05
±0.05
3.93
±0.03
B5.15
±0.15
4.97
±0.08
4.63
±0.05
4.15
±0.05
4.04
±0.04
4.92
±0.05
4.55
±0.03
4.21
±0.05
4.16
±0.04
5.03
±0.07
4.61
±0.05
4.15
±0.05
4.04
±0.04
C5.15
±0.15
4.45
±0.04
4.05
±0.04
3.78
±0.03
3.61
±0.03
4.48
±0.04
4.07
±0.03
3.72
±0.03
3.55
±0.04
4.65
±0.04
4.15
±0.03
3.85
±0.03
3.55
±0.03
D5.15
±0.15
4.40
±0.05
4.15
±0.06
3.65
±0.04
3.50
±0.04
4.45
±0.05
4.18
±0.03
3.71
±0.03
3.43
±0.04
4.40
±0.05
4.26
±0.06
3.65
±0.04
3.50
±0.04
E5.15
±0.15
4.50
±0.05
4.17
±0.03
4.00
±0.04
3.46
±0.04
4.55
±0.05
4.26
±0.03
3.92
±0.04
3.22
±0.03
4.39
±0.04
4.16
±0.03
3.72
±0.03
3.46
±0.04
F5.15
±0.15
4.75
±0.05
4.44
±0.04
4.25
±0.05
3.88
±0.05
4.68
±0.05
4.40
±0.04
4.32
±0.03
3.82
±0.03
4.82
±0.05
4.34
±0.04
4.27
±0.05
3.83
±0.05
IsovaleraldehydeA1.22
±0.02
1.05
±0.02
1.00
±0.02
0.95
±0.02
0.87
±0.02
1.10
±0.02
0.95
±0.02
0.95
±0.02
0.92
±0.02
1.11
±0.02
0.97
±0.02
0.95
±0.02
1.00
±0.02
B1.22
±0.02
1.13
±0.02
1.02
±0.02
0.85
±0.02
0.78
±0.02
1.15
±0.02
1.05
±0.02
0.95
±0.02
0.97
±0.02
1.10
±0.02
1.05
±0.02
0.97
±0.02
0.93
±0.02
C1.22
±0.02
1.05
±0.02
0.97
±0.02
0.92
±0.02
0.83
±0.02
1.02
±0.02
0.96
±0.02
0.93
±0.02
0.85
±0.02
1.11
±0.02
0.98
±0.02
0.93
±0.02
0.85
±0.02
D1.22
±0.02
1.08
±0.02
1.02
±0.01
0.95
±0.02
0.95
±0.01
1.06
±0.02
0.97
±0.01
0.94
±0.02
0.90
±0.02
1.03
±0.02
0.92
±0.01
0.90
±0.02
0.90
±0.02
E1.22
±0.02
1.15
±0.01
1.12
±0.02
1.15
±0.02
1.17
±0.01
1.12
±0.02
1.05
±0.02
0.98
±0.01
0.95
±0.01
1.07
±0.02
0.95
±0.02
0.98
±0.01
0.95
±0.01
F1.22
±0.02
1.22
±0.02
1.24
±0.02
1.20
±0.02
1.25
±0.02
1.15
±0.02
1.10
±0.02
1.10
±0.02
1.15
±0.02
1.17
±0.02
1.15
±0.02
1.15
±0.02
1.17
±0.02
FurfuralA3.46
±0.06
3.48
±0.05
3.52
±0.06
3.55
±0.05
3.57
±0.06
3.65
±0.04
3.82
±0.04
4.25
±0.05
4.57
±0.03
4.28
±0.05
5.12
±0.04
5.55
±0.05
5.80
±0.05
B3.46
±0.06
3.48
±0.05
3.43
±0.05
3.36
±0.05
3.48
±0.04
3.58
±0.05
3.63
±0.05
3.76
±0.04
3.95
±0.03
3.55
±0.05
3.75
±0.05
3.96
±0.05
3.90
±0.05
C3.46
±0.06
3.58
±0.05
3.76
±0.04
4.06
±0.05
4.21
±0.04
3.78
±0.05
3.96
±0.04
4.26
±0.03
4.76
±0.03
4.15
±0.05
4.72
±0.04
5.23
±0.04
5.66
±0.04
D3.46
±0.06
3.66
±0.05
3.95
±0.04
4.25
±0.05
4.45
±0.05
4.05
±0.03
4.22
±0.03
4.55
±0.05
4.85
±0.04
4.36
±0.05
4.95
±0.04
5.27
±0.05
5.80
±0.05
E3.46
±0.06
3.94
±0.05
4.26
±0.05
4.55
±0.04
4.78
±0.05
4.12
±0.05
4.26
±0.05
4.60
±0.04
4.78
±0.04
4.64
±0.04
5.26
±0.05
5.72
±0.04
5.87
±0.05
F3.46
±0.06
3.45
±0.05
3.60
±0.04
3.65
±0.05
3.70
±0.05
3.55
±0.04
3.60
±0.04
3.68
±0.03
4.26
±0.05
3.95
±0.05
4.27
±0.04
4.65
±0.05
4.65
±0.03

A–E=see Table 1

{ label needed for table-wrap[@id='t4'] }
Table 4 Results of three-way ANOVA for major volatile compound content in plum distillate samples after maturation with oak chips under various conditions
CompoundEffect of dose of lightly toasted French chips, temperature and time of maturation, and interaction among them (variants A, C and D, static maturation system)Effect of dose of lightly toasted French chips, ageing system with agitation and time of maturation, and interaction among them (variants D and E, maturation at 45 °C)Effect of dose and type
of oak chips, and time
of maturation, and interaction among
them (variants A and B, static maturation system, at 20 °C)
Effect of dose of lightly toasted French chips, ageing system with agitation and time of maturation, and interaction among them (variants A and F, maturation at 20 °C)
DCTMTDC × TDC × MTT × MTDC ×T × MTDCASMTDC × ASDC × MTAS × MTDC ×AS × MTDCTCMTDC × TCDC × MTTC× MTDC ×TC × MTDCASMTDC × ASDC × MTAS × MTDC × AS × MT
Acetaldehyde************ns***ns*******ns***ns******ns********ns******nsns******
Isobutyraldehydens******nsns***nsns***********nsns******ns*****nsnsns***nsns***ns
Isovaleraldehydens*******************************************************************************
Furfural**********************************************************************************
Ethyl acetatens******nsns*nsns****nsnsnsnsnsns***nsnsnsnsns******ns*****ns
Isoamyl acetatensnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsns
Ethyl hexanoatens******nsns***nsns***************ns******nsns***********************
Ethyl octanoatensns***nsnsnsns********************nsns***nsnsnsnsns******nsns**ns
Ethyl decanoatens*******ns***nsnsns***nsnsnsnsns******nsns***ns***ns****nsns*
Methanol*****************************ns**********ns***ns*nsns************ns***ns
1-Propanol**************************ns****ns***************************************
1-Butanol***ns***ns***nsnsnsns***nsnsnsnsns******nsns***ns****************
2-Methyl-1-propanol***********************************************ns******nsnsns***********
2-Methyl-1-butanol********************ns********ns*ns******nsns*****ns*****ns******ns
3-Methyl-1-butanolns******nsns***ns***ns***ns***nsnsns********ns***ns***ns***ns***ns
Hexanolnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsns
2-Phenylethanolnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsns

DC=dose of oak chips (3, 5 and 7 g/L), T=temperature of maturation (18–20, 35 and 45 °C), MT=maturation time (0, 3, 6, 9, and 12 months), AS=ageing system with agitation (variants A and D=static, variant E=circulation, variant F=ultrasound treatment), TC=type of oak chips (lightly toasted French chips or French chips after ageing of cognac); ***p <0.001, **p<0.01, *p<0.05, ns=not significant

Concentrations of isobutyraldehyde and isovaleraldehyde decreased with different intensities depending on the conditions of ageing. The application of periodical heating accelerated the decrease in aldehyde concentrations, especially isobutyraldehyde and isovaleraldehyde. However, the statistically significant changes of isobutyraldehyde were observed only in samples heated to 45 °C compared to those heated to 35 °C. Moreover, the effect of neither the type nor the dose of oak chips on the content of aldehydes could be clearly interpreted.

One of the heterocyclic aldehydes that occur in distillates is furfural, which is mainly formed through the dehydration of pentoses at elevated temperatures (47). Furfural is produced during distillation involving Maillard reactions (48). Furanic compounds may also be produced by the degradation of sugars during the wood toasting (49). The only furanic compound detected in the fresh distillate was furfural. Periodical increase of the temperature, circulation, and in particular increasing the dose of oak wood chips resulted in higher furfural content in all of the samples (Table 3). The type of oak chips was also a significant factor. Furfural was more abundant in samples aged with lightly toasted fresh oak chips than in those aged with oak chips made from cognac barrels.

Esters form an important group of flavour compounds found in spirits, mostly comprising ethyl esters of monocarboxylic acids. Ethyl acetate is quantitatively the most important component in the ester fraction, usually accounting for over 50% of the total. Many short-chain esters, such as isobutyl acetate, ethyl 3-methylbutyrate, ethyl n-butyrate, 2-methylbutyl acetate and 3-methylbutyl acetate, have fairly strong odours (50). Ethyl esters are formed during fermentation, and their concentrations increase during ageing (51). Plum distillates also contain esters of fatty acids C6–C10 (52). Several studies on distillates aged in oak have shown variations in these compounds during ageing, with distinct processes responsible in each case, such as hydrolysis, esterification or transesterification between compounds contained in the distillate and/or wood, or directly extracted from the wood (37). In our study, the predominant ester in the analysed plum distillate was ethyl acetate. The level of ethyl acetate was found to decrease over the course of maturation affected by the maturation time and temperature, but no interaction among these factors was observed. On the other hand, in samples treated with ultrasound, ethyl acetate content increased progressively during ageing (Table 5). This was in agreement with the findings of an earlier study (37). It is noteworthy that the changes in the concentration of this ester were not associated with either the dose or type of oak chips or with the maturation conditions (variants with static and circulation ageing systems). Only in samples aged with 7 g/L of lightly toasted oak chips, elevated temperatures were observed to have an effect on lowering the concentration of ethyl acetate after 12 months of maturation. Rodríguez Madrera et al. (53) suggest that its high initial concentration in fresh distillate causes partial hydrolysis of ethyl acetate, which increases as the acetic acid concentration rises (reflected in the amount of volatile acidity). Acetic acid may be extracted from wood, as already noted, or formed through the oxidation of ethanol (22).

Table 5 Changes in the concentrations of major esters during maturation of plum distillate samples with oak chips under various conditions
CompoundMaturation variantControl
sample
[m(oak chip)/V(plum distillate)]/(g/L)
357
t(maturation)/month
369123691236912
γ/(mg/L of absolute alcohol)
Ethyl acetateA132.20
±5.25
127.20
±3.48
125.20
±3.26
116.20
±3.50
108.70
±3.33
129.20
±3.82
122.20
±3.15
114.20
±3.33
108.82
±3.12
125.20
±3.33
119.20
±3.45
116.20
±3.50
115.46
±3.65
B132.20
±5.25
130.20
±4.50
124.20
±3.35
118.20
±2.25
114.87
±3.15
132.20
±3.42
126.20
±3.15
116.20
±2.42
109.87
±3.15
127.20
±3.50
122.20
±2.78
115.48
±2.25
111.87
±3.15
C132.20
±5.25
122.20
±2.36
113.20
±3.27
107.20
±2.25
105.20
±2.68
126.20
±2.22
115.20
±2.27
110.20
±2.72
108.20
±2.48
120.20
±2.19
116.20
±3.15
109.20
±2.25
105.44
±2.85
D132.20
±5.25
124.22
±3.25
112.20
±2.25
109.20
±2.75
106.55
±2.28
120.37
±3.52
114.27
±2.29
106.20
±2.55
105.55
±2.27
124.22
±3.25
112.20
±2.42
109.20
±2.75
106.55
±2.28
E132.20
±5.25
123.51
±3.42
116.20
±3.25
111.20
±2.65
108.65
±2.77
124.55
±3.17
115.20
±3.19
114.09
±2.35
107.77
±2.77
121.42
±3.26
113.66
±3.77
110.77
±2.49
105.65
±2.48
F132.20
±5.25
184.20
±6.22
178.20
±4.66
176.20
±4.25
172.44
±5.33
180.55
±4.65
178.20
±4.15
173.20
±3.25
172.44
±3.33
164.20
±6.22
175.20
±4.82
173.45
±4.27
172.44
±5.33
Isoamyl acetateA23.71
±0.98
23.51
±0.64
23.62
±0.68
24.32
±0.74
23.70
±0.39
23.66
±0.68
23.91
±0.78
23.15
±0.47
22.95
±0.98
23.55
±0.68
24.15
±0.88
23.71
±0.72
24.34
±0.98
B23.71
±0.98
23.31
±0.58
23.54
±0.76
23.77
±0.78
24.34
±0.58
23.77
±0.68
23.56
±0.91
23.79
±0.78
24.22
±0.68
23.63
±0.66
23.51
±0.58
24.35
±0.69
24.66
±0.58
C23.71
±0.98
23.55
±0.64
23.67
±0.58
24.59
±0.68
24.66
±0.49
23.31
±0.68
23.85
±0.73
23.77
±0.68
24.39
±0.76
23.77
±0.68
23.66
±0.77
23.75
±0.85
23.82
±0.76
D23.71
±0.98
23.76
±0.68
24.15
±0.84
23.94
±0.85
23.82
±0.58
23.55
±0.77
23.76
±0.84
24.15
±0.68
23.42
±0.77
23.65
±0.88
23.94
±0.82
23.77
±0.59
23.61
±0.68
E23.71
±0.98
23.77
±0.78
24.72
±0.84
23.77
±0.69
23.61
±0.65
23.74
±0.88
24.27
±0.76
23.92
±0.94
23.54
±0.68
23.76
±0.68
24.72
±0.74
23.56
±0.69
23.39
±0.68
F23.71
±0.98
24.42
±0.88
24.33
±0.76
23.77
±0.82
23.39
±0.59
23.92
±0.94
23.76
±0.82
23.52
±0.94
23.39
±0.48
24.55
±0.93
23.97
±0.74
23.73
±0.88
23.50
±0.77
Ethyl hexanoateA16.25
±0.02
16.44
±0.02
16.57
±0.02
16.74
±0.03
16.97
±0.03
16.51
±0.02
16.59
±0.02
16.77
±0.03
16.89
±0.03
16.47
±0.02
16.66
±0.02
16.78
±0.03
16.97
±0.05
B16.25
±0.02
16.37
±0.03
16.62
±0.02
16.66
±0.02
16.79
±0.02
16.32
±0.03
16.59
±0.02
16.61
±0.02
16.82
±0.02
16.41
±0.03
16.65
±0.02
16.69
±0.02
16.79
±0.02
C16.25
±0.02
16.57
±0.03
16.78
±0.03
16.95
±0.03
17.16
±0.03
16.59
±0.03
16.84
±0.03
16.91
±0.03
17.23
±0.03
16.62
±0.03
16.85
±0.03
16.93
±0.03
17.10
±0.03
D16.25
±0.02
16.61
±0.03
16.74
±0.03
16.80
±0.02
16.96
±0.03
16.66
±0.03
16.79
±0.03
16.84
±0.02
16.89
±0.03
16.54
±0.03
16.77
±0.03
16.84
±0.02
16.92
±0.03
E16.25
±0.02
16.55
±0.02
16.75
±0.02
16.93
±0.03
16.88
±0.03
16.62
±0.02
16.71
±0.02
16.83
±0.03
16.84
±0.03
16.51
±0.02
16.77
±0.02
16.85
±0.03
16.94
±0.03
F16.25
±0.02
16.17
±0.03
16.27
±0.02
16.52
±0.03
16.73
±0.03
16.20
±0.02
16.34
±0.02
16.45
±0.02
16.70
±0.01
16.22
±0.02
16.46
±0.02
16.75
±0.02
16.73
±0.02
Ethyl octanoateA2.84
±0.03
3.15
±0.03
3.47
±0.04
3.66
±0.04
3.71
±0.04
3.05
±0.03
3.52
±0.03
3.61
±0.04
3.75
±0.04
3.22
±0.03
3.50
±0.04
3.65
±0.04
3.70
±0.04
B2.84
±0.03
3.36
±0.03
3.64
±0.04
3.84
±0.04
3.90
±0.04
3.39
±0.03
3.54
±0.04
3.77
±0.04
3.75
±0.04
3.16
±0.03
3.43
±0.04
3.74
±0.04
3.90
±0.04
C2.84
±0.03
3.44
±0.04
3.81
±0.04
3.84
±0.04
3.95
±0.04
3.49
±0.04
3.75
±0.04
3.86
±0.04
3.90
±0.04
3.34
±0.04
3.69
±0.04
3.85
±0.04
3.87
±0.04
D2.84
±0.03
3.28
±0.03
3.84
±0.04
3.91
±0.04
3.44
±0.04
3.18
±0.03
3.81
±0.04
3.96
±0.04
3.44
±0.04
3.37
±0.03
3.85
±0.04
3.91
±0.04
3.86
±0.04
E2.84
±0.03
2.98
±0.03
3.66
±0.03
3.84
±0.03
3.85
±0.03
3.08
±0.03
3.54
±0.03
3.88
±0.03
3.90
±0.03
3.28
±0.03
3.66
±0.03
3.84
±0.03
3.93
±0.03
F2.84
±0.03
2.74
±0.03
2.88
±0.03
3.14
±0.03
3.35
±0.03
2.80
±0.03
2.86
±0.03
3.25
±0.03
3.39
±0.03
2.90
±0.03
2.88
±0.03
3.26
±0.03
3.45
±0.03
Ethyl decanoateA13.30
±0.15
13.26
±0.15
13.75
±0.18
14.12
±0.22
14.29
±0.25
13.42
±0.15
13.70
±0.17
14.06
±0.16
14.15
±0.16
13.40
±0.15
13.83
±0.17
14.30
±0.25
14.79
±0.23
B13.30
±0.15
13.69
±0.17
14.30
±0.25
15.30
±0.23
15.86
±0.25
13.63
±0.15
14.34
±0.16
15.42
±0.19
15.80
±0.15
13.55
±0.15
14.72
±0.22
15.25
±0.23
15.88
±0.22
C13.30
±0.15
13.64
±0.16
13.82
±0.15
14.07
±0.18
14.18
±0.18
13.72
±0.15
13.99
±0.16
14.12
±0.18
14.20
±0.22
13.55
±0.16
13.80
±0.15
14.13
±0.18
14.18
±0.17
D13.30
±0.15
13.50
±0.15
13.87
±0.14
14.30
±0.15
14.47
±0.17
13.68
±0.15
13.96
±0.18
14.35
±0.18
14.47
±0.17
13.52
±0.15
13.83
±0.16
14.39
±0.18
14.69
±0.21
E13.30
±0.15
13.66
±0.13
14.17
±0.15
14.37
±0.16
14.52
±0.20
13.78
±0.15
13.98
±0.17
14.33
±0.16
14.57
±0.18
13.49
±0.15
13.77
±0.16
14.29
±0.19
14.58
±0.20
F13.30
±0.15
13.43
±0.16
13.89
±0.18
14.30
±0.15
14.76
±0.16
13.19
±0.15
13.47
±0.16
13.84
±0.17
14.56
±0.21
13.62
±0.17
13.94
±0.15
14.09
±0.15
14.56
±0.13

A–E=see Table 1

Isoamyl acetate was significantly less reactive than ethyl acetate. Concentrations of isoamyl acetate did not change significantly over the 12-month period of maturation. There was no significant effect of all tested factors on its concentration. Rodríguez Madrera et al. (37) compared ageing methods in stainless steel vessels with oak wood staves of different origins and traditional ageing in oak wood barrels, revealing decreases in isoamyl acetate content of up to approx. 30% in relation to control samples. The application of micro-oxygenation resulted in more intense changes than traditional ageing.

Ethyl esters of medium chain fatty acids, i.e. hexanoic, octanoic, decanoic and dodecanoic acids, are of particular interest, on account of their relatively high levels in fermented beverages and spirits and the fruity odours they give to products (37). In our study, the concentrations of ethyl caproate, ethyl caprylate and ethyl caprate were found to gradually increase in all samples. The observed changes were affected by maturation time. Significant effect was found for time×temperature interaction, for compounds such as ethyl hexanoate and ethyl decanoate (Table 4). Unfortunately, no clear correlation was found with the type or dose of oak chips, or with maturation conditions. The only exception were the samples matured with cognac barrel oak chips, in which the concentration of ethyl caprate was significantly higher than in the distillate maturated with lightly toasted oak chips. It may be supposed that the elevated concentration of this compound (described as having a ‘fruity, reminiscent of cognac’ smell) originated from the porous oak barrels, which would have been impregnated with cognac aroma compounds, which were then liberated during maturation of the plum distillate.

Methanol is an undesirable compound in spirit distillates. While methanol does not directly affect the flavour of the distillate, it is subjected to restrictive controls, owing to its high toxicity (54). In our study, the concentration of methanol was observed to decrease in the majority of samples (Tables 4 and 6{ label needed for table-wrap[@id='t6'] }), as a consequence of sorption and esterification reactions (46). Only treatment with ultrasound led to a significant increase in methanol content in the first 3 months of ageing, after which there were no significant further changes. During treatment with ultrasound, methanol may be released from oak wood chips principally by demethylation of lignin, hemicellulose or xylans (40, 55). The obtained results revealed no significant effect of the type of oak chips on methanol concentration (Table 6).

{ label needed for table-wrap[@id='t6'] }
Table 6 Changes in the concentrations of alcohols during maturation of plum distillate samples with oak chips under various conditions
CompoundMaturation variantControl sample[m(oak chip)/V(plum distillate)]/(g/L)
357
t(maturation)/month
369123691236912
γ/(mg/L of absolute alcohol)
MethanolA115.8
±1.6
114.5
±1.2
114.3
±1.2
105.9
±0.9
103.7
±0.8
115.2
±1.2
114.7
±1.2
108.9
±0.9
105.5
±0.6
115.5
±1.3
114.6
±1.1
107.9
±0.8
105.6
±0.8
B115.8
±1.6
114.5
±1.2
114.3
±1.2
105.9
±0.9
103.7
±0.8
115.2
±1.2
114.7
±1.2
108.9
±0.9
105.5
±0.6
115.5
±1.3
114.6
±1.1
107.9
±0.8
108.3
±0.8
C115.8
±1.6
110.5
±1.2
104.3
±1.2
105.9
±0.9
103.7
±0.8
111.5
±1.2
107.3
±1.2
105.6
±0.9
103.3
±0.8
110.5
±1.2
104.3
±1.2
105.9
±0.9
101.7
±0.8
D115.8
±1.6
108.5
±1.2
102.3
±1.2
98.9
±0.9
93.7
±0.8
110.5
±1.2
108.3
±1.2
103.9
±0.9
96.7
±0.8
111.5
±1.2
102.3
±1.2
98.9
±0.9
95.6
±0.8
E115.8
±1.6
108.9
±1.2
97.3
±1.2
97.9
±0.9
94.2
±0.8
110.9
±1.2
105.3
±1.2
102.9
±0.9
92.7
±0.8
108.9
±1.2
97.3
±1.2
97.9
±0.9
95.3
±0.8
F115.8
±1.6
120.5
±1.2
119.3
±1.2
120.9
±1.5
120.7
±1.8
123.2
±1.2
124.7
±1.2
124.9
±1.9
123.5
±1.6
125.2
±1.3
125.7
±1.5
124.9
±1.9
125.5
±2.6
1-PropanolA397.3
±3.4
395.9
±3.8
394.8
±4.5
356.1
±6.8
337.3
±7.2
389.7
±6.4
356.2
±3.7
340.8
±6.6
329.6
±4.7
393.5
±6.4
372.2
±6.5
350.3
±7.1
348.8
±5.4
B397.3
±3.4
398.9
±5.2
387.8
±6.1
376.1
±6.8
357.3
±6.2
390.7
±6.6
376.2
±5.5
364.8
±6.6
349.6
±5.3
383.5
±5.4
366.2
±4.3
357.3
±5.1
354.6
±4.8
C397.3
±3.4
378.9
±4.5
356.8
±4.5
349.1
±6.8
343.5
±5.2
379.7
±6.4
366.2
±5.3
352.8
±6.6
339.6
±4.7
379.5
±7.4
372.2
±6.5
350.3
±7.1
346.3
±6.3
D397.3
±3.4
375.6
±3.7
364.8
±4.5
356.1
±6.8
337.3
±7.2
382.7
±6.4
359.2
±5.7
340.8
±6.6
329.6
±4.7
393.5
±7.4
377.2
±8.2
363.3
±7.7
348.2
±5.4
E397.3
±3.4
370.9
±5.2
354.8
±4.5
346.1
±6.8
335.8
±6.7
374.9
±56.1
359.8
±4.3
343.1
±5.5
339.6
±4.4
383.5
±6.4
376.2
±6.5
350.3
±7.1
348.5
±5.9
F397.3
±3.4
390.8
±4.5
376.1
±5.4
362.3
±5.2
359.7
±5.4
393.6
±4.7
382.1
±5.8
369.3
±6.7
355.7
±7.4
392.4
±4.7
374.1
±6.3
364.8
±6.6
355.8
±5.3
1-ButanolA6.35
±0.16
6.32
±0.15
5.11
±0.13
4.86
±0.12
4.80
±0.13
6.18
±0.15
5.15
±0.13
4.96
±0.12
4.84
±0.13
6.14
±0.14
5.22
±0.11
4.96
±0.12
4.77
±0.14
B6.35
±0.16
6.21
±0.15
5.86
±0.13
5.54
±0.12
5.33
±0.14
6.30
±0.15
5.86
±0.13
5.54
±0.12
5.33
±0.14
6.18
±0.15
5.86
±0.12
5.54
±0.13
5.33
±0.12
C6.35
±0.16
5.42
±0.14
5.21
±0.13
4.77
±0.13
4.80
±0.13
5.35
±0.14
5.11
±0.12
4.91
±0.12
4.84
±0.13
5.37
±0.15
5.16
±0.13
4.76
±0.12
4.70
±0.13
D6.35
±0.16
5.29
±0.15
5.08
±0.13
4.76
±0.12
4.65
±0.13
5.34
±0.13
4.88
±0.12
4.76
±0.11
4.66
±0.11
5.49
±0.15
5.11
±0.13
4.73
±0.12
4.66
±0.11
E6.35
±0.16
5.34
±0.12
5.17
±0.10
4.72
±0.09
4.75
±0.11
5.26
±0.12
4.93
±0.12
4.76
±0.1
4.69
±0.08
5.22
±0.11
4.93
±0.09
4.81
±0.08
4.80
±0.13
F6.35
±0.16
6.12
±0.11
5.66
±0.11
4.85
±0.09
4.76
±0.11
6.32
±0.15
6.11
±0.12
5.24
±0.09
4.86
±0.08
6.14
±0.13
5.56
±0.09
5.37
±0.09
4.84
±0.09
2-Methyl-1-propanolA483.3
±5.8
475.3
±5.5
469.8
±5.6
466.7
±4.6
441.6
±5.2
478.3
±5.3
463.4
±4.8
454.4
±4.5
431.5
±5.1
477.5
±5.5
471.9
±5.2
448.4
±4.8
425.6
±5.1
B483.3
±5.8
480.3
±5.5
479.8
±4.8
476.7
±4.9
469.6
±3.5
478.3
±4.8
473.4
±3.6
464.4
±3.8
460.5
±3.3
479.5
±3.8
475.9
±3.6
463.4
±4.5
457.6
±3.8
C483.3
±5.8
465.5
±3.7
459.8
±3.8
446.7
±3.5
438.6
±3.7
463.3
±3.5
460.4
±3.8
454.4
±2.8
441.5
±2.6
472.5
±3.8
464.9
±3.5
453.4
±3.8
445.6
±3.5
D483.3
±5.8
465.3
±2.8
459.2
±3.5
456.3
±2.7
443.6
±2.7
458.7
±2.8
443.4
±2.6
434.4
±2.7
430.5
±2.5
457.5
±2.6
451.9
±3.2
448.6
±3.3
425.6
±2.7
E483.3
±5.8
478.3
±4.2
466.5
±3.5
460.9
±2.8
441.6
±3.1
468.8
±2.4
463.4
±2.7
458.4
±2.8
439.4
±3.2
479.7
±3.8
472.6
±2.4
458.4
±2.8
455.6
±4.2
F483.3
±5.8
469.3
±54.2
456.5
±3.5
457.9
±3.7
451.6
±3.4
471.8
±3.4
465.4
±3.2
456.6
±3.4
444.5
±3.2
473.7
±3.8
462.6
±2.4
455.6
±3.2
452.6
±3.2
2-Methyl-1-butanolA579.0
±6.5
570.0
±5.7
565.6
±5.5
552.2
±6.1
504.2
±4.9
572.3
±5.3
558.4
±4.7
542.8
±4.5
523.3
±4.6
571.8
±4.7
561.6
±4.6
548.8
±4.5
497.3
±5.7
B579.0
±6.5
574.0
±6.7
572.3
±6.5
562.6
±6.3
544.2
±4.9
576.0
±6.5
570.3
±5.5
566.1
±5.3
542.2
±5.4
570.0
±5.7
568.3
±6.5
562.6
±5.3
548.2
±4.9
C579.0
±6.5
564.0
±5.5
555.6
±5.5
522.1
±6.1
494.2
±4.5
554.0
±4.7
536.6
±4.2
525.1
±4.1
491.3
±4.5
560.0
±5.1
535.6
±4.5
524.1
±5.1
488.4
±4.5
D579.0
±6.5
567.6
±5.7
552.3
±5.3
531.2
±5.1
488.2
±4.5
564.2
±4.7
546.6
±4.2
532.1
±4.6
502.2
±5.5
552.0
±4.8
537.2
±4.5
529.3
±4.6
483.5
±4.5
E579.0
±6.5
564.6
±5.2
550.8
±5.2
526.3
±5.1
505.2
±5.5
552.0
±5.3
542.6
±4.8
528.6
±45.1
496.4
±4.5
566.0
±5.10
545.6
±4.5
529.1
±4.8
491.2
±4.2
F579.0
±6.5
555.0
±4.7
550.6
±4.5
542.1
±4.1
524.2
±4.9
552.3
±4.3
548.4
±3.7
536.8
±3.5
529.3
±3.1
551.8
±4.7
550.6
±4.6
548.8
±4.5
517.2
±3.7
3-Methyl-1-butanolA1573.3
±18.4
1560.3
±15.6
1545.8
±15.4
1510.2
±14.3
1507.8
±13.9
1571.2
±15.4
1495.7
±14.7
1489.3
±14.3
1461.2
±13.7
1565.8
±14.4
1532.3
±14.7
1487.9
±14.5
1488.2
±13.8
B1573.3
±18.4
1566.3
±14.7
1549.5
±13.4
1522.2
±15.4
1529.8
±18.4
1571.3
±14.7
1559.5
±14.6
1536.2
±13.5
1527.8
±13.4
1568.3
±13.7
1533.5
±13.9
1522.2
±13.4
1529.8
±12.6
C1573.3
±18.4
1549.3
±13.6
1530.8
±14.6
1518.2
±13.3
1513.8
±13.5
1521.6
±13.4
1496.5
±13.2
1477.3
±13.7
1466.8
±13.3
1549.8
±13.4
1530.8
±13.6
1482.5
±13.5
1478.5
±13.6
D1573.3
±18.4
1550.8
±13.9
1541.2
±14.6
1521.6
±13.8
1521.8
±13.7
1527.2
±13.5
1490.7
±12.7
1469.5
±12.6
1460.6
±12.5
1538.5
±12.6
1530.8
±12.3
1488.5
±12.7
1476.6
±12.6
E1573.3
±18.4
1544.3
±13.2
1538.8
±13.5
1522.7
±14.1
1525.8
±13.2
1524.3
±13.4
1488.5
±13.2
1469.6
±12.2
1455.6
±12.3
1549.2
±13.1
1535.5
±13.4
1486.5
±12.7
1480.2
±11.8
F1573.3
±18.4
1552.3
±15.4
1546.8
±15.4
1532.2
±14.3
1517.8
±13.9
1541.2
±15.4
1525.7
±14.7
1490.3
±14.3
1468.2
±13.7
1549.8
±14.6
1532.3
±14.7
1512.9
±14.5
1498.2
±13.8
1-HexanolA45.90
±2.23
45.23
±2.55
44.75
±2.48
44.36
±2.36
44.28
±2.29
45.29
±2.45
44.75
±2.33
44.36
±2.15
44.43
±2.42
45.63
±2.35
45.25
±2.28
44.62
±2.38
44.33
±2.12
B45.90
±2.23
45.72
±2.28
45.30
±2.45
45.12
±2.22
44.75
±2.55
45.72
±2.28
45.30
±2.45
45.12
±2.22
44.75
±2.55
45.72
±2.28
45.30
±2.45
45.12
±2.22
44.75
±2.55
C45.90
±2.23
45.12
±2.45
44.42
±2.28
44.06
±2.22
44.18
±2.40
44.79
±2.30
44.55
±2.30
44.36
±2.25
44.23
±2.22
44.63
±2.25
44.25
±2.30
44.12
±2.18
44.33
±2.12
D45.90
±2.23
44.66
±2.35
44.35
±2.27
44.15
±2.22
44.28
±2.33
44.69
±2.45
44.75
±2.23
44.36
±2.25
44.13
±2.12
44.63
±2.35
44.25
±2.28
44.02
±2.15
44.13
±2.12
E45.90
±2.23
44.66
±2.35
44.35
±2.27
44.15
±2.22
44.28
±2.33
44.69
±2.45
44.75
±2.23
44.36
±2.25
44.13
±2.12
44.63
±2.35
44.25
±2.28
44.02
±2.15
44.13
±2.12
F45.90
±2.23
45.13
±2.25
44.85
±2.15
44.36
±2.22
44.28
±2.29
45.19
±2.22
44.65
±2.15
44.36
±2.15
44.43
±2.42
44.83
±2.35
44.25
±2.28
44.02
±2.15
44.12
±2.12
2-Phenyl ethanolA53.75
±3.28
53.42
±2.95
53.25
±2.82
52.76
±2.22
52.67
±2.35
53.32
±2.59
53.52
±2.28
52.92
±2.41
52.76
±2.53
53.63
±2.65
53.25
±2.48
52.76
±2.22
52.33
±2.15
B53.75
±3.28
53.44
±2.66
53.45
±2.36
53.35
±2.12
52.86
±2.35
53.60
±2.42
53.54
±2.61
53.27
±2.27
52.68
±2.53
53.60
±2.42
53.15
±2.16
52.76
±2.27
52.86
±2.45
C53.75
±3.28
53.28
±2.64
53.27
±2.62
52.72
±2.33
52.63
±2.12
52.78
±2.46
53.36
±2.26
52.66
±2.23
52.63
±2.12
52.96
±2.33
53.17
±2.12
52.72
±2.22
52.67
±2.34
D53.75
±3.28
52.42
±2.35
52.25
±2.47
52.33
±2.22
52.27
±2.15
52.62
±2.27
52.34
±2.33
52.18
±2.05
52.64
±2.32
52.53
±2.41
52.36
±2.17
52.64
±2.27
52.46
±2.15
E53.75
±3.28
52.42
±2.42
52.25
±2.48
52.26
±2.35
52.12
±2.05
52.55
±2.34
52.13
±2.22
52.36
±2.15
53.12
±2.26
53.12
±2.16
52.65
±2.05
52.34
±1.95
52.17
±2.12
F53.75
±3.28
53.44
±2.76
52.81
±2.55
52.55
±2.26
52.27
±2.05
53.63
±2.67
53.42
±2.27
52.79
±2.14
52.47
±2.19
53.13
±2.33
52.81
±2.27
52.59
±2.26
52.14
±2.32

A–E=see Table 1

The higher alcohols, i.e. 1-propanol, 2-methyl-1-propanol, 2-butanol, 1-butanol, 2-propen-1-ol, 2-methyl-1- -butanol, 3-methyl-1-butanol, 1-hexanol and 2-phenylethanol are considered part of the aromatic skeleton of fruit distillates (56). A decrease in the concentration of higher alcohols was detected in the majority of samples, compared to the initial value in the fresh spirit (Table 6). The results of statistical analysis of the effect of maturation time showed that in samples aged at 20 °C, the changes in concentrations of higher alcohols were statistically insignificant during the first 6 months of the process. In the subsequent 6 months, the content of higher alcohols decreased significantly, on average by 15%, compared to the control. Samples heated periodically (both to 35 and 45 °C) showed a more regular downward trend, but overall the decrease was not significantly greater than in samples aged at 20 °C. The type of used oak had a significant effect on final higher alcohol concentration, especially on 2-methyl-1-propanol, 2-methyl-1-butanol and 3-methyl-1-butanol, which were higher in samples aged with cognac barrel oak chips (Tables 4 and 6{ label needed for table-wrap[@id='t6'] }).

Rodríguez Madrera et al. (37) list evaporation, esterification, oxidation and sorption as causes that may explain the decrease in higher alcohols during ageing. Our results suggest that sorption plays an important role in the evolution of these volatiles. Sorption is especially connected with the type of oak chips used and the different porosities of the wood. The concentrations of 1-hexanol and 2-phenyl ethanol in the plum distillate samples did not show statistically significant changes during ageing, probably as a result of the lower reactivity of alcohols with increasing molecular mass (57).

Changes in concentrations of minor volatile compounds

An analysis of minor volatiles was also performed and presented in Table 7. To enable differentiation between plum distillate samples, principal component analysis (PCA) was conducted using as variables the concentration of minor volatile compounds (Figs. 4–10{ label needed for fig[@id='f5'] }{ label needed for fig[@id='f6'] }{ label needed for fig[@id='f7'] }{ label needed for fig[@id='f8'] }{ label needed for fig[@id='f9'] }{ label needed for fig[@id='f10'] }), which were significantly different (ANOVA, p<0.05).

Table 7 Concentration of minor volatile compounds in matured plum distillate samples
Compoundγ/(mg/L of absolute alcohol)
Control sampleABCDEF
Acetate esters
Methyl thiolacetate0.007±0.0010.005±0.0010.006±0.0010.006±0.0010.006±0.0010.008±0.0010.008±0.001
Propyl acetate0.007±0.0010.004±0.0010.002±0.0010.001±0.0010.001±0.0010.001±0.0010.002±0.001
Ethyl thiolacetate0.017±0.0010.010±0.0010.017±0.0010.007±0.0010.007±0.001n.d.0.005±0.001
2-Methyl-1-butyl acetate0.202±0.0100.194±0.0100.190±0.0100.184±0.0090.184±0.0090.187±0.0090.211±0.011
Linalyl acetate0.011±0.0010.001±0.0010.005±0.0010.005±0.0010.006±0.0010.007±0.001n.d.
Nerolidyl acetate0.027±0.0010.028±0.0010.023±0.0010.028±0.0010.027±0.0010.025±0.0010.016±0.001
2,3-Dihydrofarnesyl acetate0.001±0.0010.001±0.0000.001±0.0000.001±0.0000.001±0.0000.007±0.0010.001±0.000
2-Methylpropyl acetate0.023±0.0010.030±0.0020.028±0.0010.027±0.0010.029±0.0020.031±0.0020.032±0.002
Pentyl acetate0.279±0.0140.276±0.0140.278±0.0140.283±0.0140.239±0.0120.273±0.0140.152±0.008
Octyl acetate0.004±0.0010.002±0.0010.003±0.0010.003±0.0010.003±0.0010.003±0.0010.003±0.001
2-Phenylethyl acetate0.093±0.0100.082±0.0100.070±0.0080.078±0.0080.073±0.0060.081±0.0070.212±0.011
Decyl acetate0.016±0.0010.014±0.0010.013±0.0010.013±0.0010.013±0.0010.010±0.0010.017±0.001
Dodecyl acetate0.006±0.0010.005±0.0010.004±0.0010.004±0.0010.005±0.0010.004±0.0010.007±0.001
Other esters
Ethyl propanoate0.036±0.0020.048±0.0020.038±0.0020.041±0.0020.043±0.0020.044±0.0020.045±0.002
Ethyl 2-methylpropanoate0.382±0.0190.246±0.0120.239±0.0120.289±0.0150.269±0.0140.278±0.0140.158±0.008
3-Methyl-1-butyl acetate0.002±0.0010.009±0.0010.007±0.0010.009±0.0010.009±0.0010.020±0.0010.018±0.001
Ethyl butanoate0.240±0.0120.252±0.0130.247±0.0120.260±0.0130.260±0.0130.254±0.0130.255±0.013
Ethyl 2-butenoate0.006±0.0010.008±0.0010.007±0.0010.007±0.0010.007±0.0010.011±0.0010.004±0.001
Ethyl 2-methylbutanoate0.147±0.0070.182±0.0090.178±0.0090.198±0.0100.198±0.0100.205±0.0100.184±0.009
Ethyl 3-methylbutanoate0.309±0.0150.369±0.0180.355±0.0180.400±0.0200.400±0.0200.417±0.0210.386±0.019
Ethyl pentanoate0.029±0.0020.002±0.0010.001±0.0010.002±0.0010.001±0.0010.001±0.0010.003±0.001
Methyl pentanoate0.004±0.0010.003±0.0010.002±0.0010.003±0.0010.003±0.0010.001±0.0010.002±0.001
Ethyl 2-methyllactaten.d.0.011±0.0010.010±0.0010.006±0.0010.006±0.0010.008±0.0010.008±0.001
3-Methyl-1-butyl propanoate0.020±0.0010.012±0.0010.025±0.0010.002±0.0010.001±0.0010.001±0.0010.009±0.001
3-Methyl-1-butyl isobutyrate0.021±0.0010.020±0.0010.017±0.0010.015±0.0010.018±0.0010.019±0.0010.018±0.001
2-Methyl-pentyl propanoate0.038±0.0020.004±0.0010.003±0.0010.003±0.0010.003±0.0010.004±0.0010.003±0.001
Ethyl 2-hexenoate0.001±0.0000.002±0.0010.002±0.001n.d.0.002±0.0010.003±0.0010.002±0.001
Ethyl 2-furancarboxylate0.010±0.0010.016±0.0010.025±0.0010.014±0.0010.015±0.0010.002±0.0010.002±0.001
3-Methyl-1-butyl butyrate0.014±0.0010.015±0.0010.014±0.0010.015±0.0010.015±0.0010.002±0.0010.002±0.001
Ethyl 2,4-hexadienoate0.007±0.0010.032±0.0020.104±0.0050.042±0.0020.055±0.0030.005±0.0010.013±0.001
Ethyl heptanoate0.370±0.0195.548±0.2770.387±0.0194.090±0.2053.090±0.1554.015±0.2010.453±0.023
Methyl octanoate0.006±0.0010.041±0.0020.034±0.0020.056±0.0030.046±0.0020.006±0.0010.004±0.001
Ethyl hexanoate6.351±0.3186.221±0.3116.315±0.3166.932±0.3476.932±0.3476.432±0.3226.440±0.322
Ethyl 4-hexenoate11.849±0.5935.817±0.2916.139±0.3075.915±0.2966.779±0.3395.915±0.2966.191±0.310
Ethyl 3-hexenoate0.057±0.0030.041±0.0020.042±0.0020.036±0.0020.038±0.0020.035±0.0020.037±0.002
Ethyl benzoate0.128±0.0061.026±0.0511.105±0.0551.129±0.0561.091±0.0551.139±0.0570.184±0.009
Diethyl butanedioaten.d.0.098±0.0050.085±0.0040.084±0.0040.093±0.0050.083±0.0040.051±0.003
Butyl hexanoate0.008±0.0010.008±0.0010.009±0.0010.009±0.0010.006±0.0010.008±0.0010.009±0.001
Ethyl octanoate0.097±0.1950.086±0.0010.066±0.0010.076±0.0010.083±0.2040.110±0.2060.006±0.001
4-Octenoic acid ethyl ether0.013±0.0010.009±0.0010.198±0.0100.009±0.0010.013±0.0010.012±0.0010.015±0.001
Methyl 2-hydroxybenzoate0.004±0.0010.002±0.0010.005±0.0010.004±0.0010.005±0.0010.005±0.0010.007±0.001
Phenyl octadecanoate0.002±0.0010.027±0.001n.d.0.029±0.0020.029±0.0010.027±0.0010.052±0.003
3-Methylbutyl octanoate0.045±0.0020.041±0.0020.040±0.0020.039±0.0020.041±0.0020.040±0.0020.041±0.002
Propyl octanoate0.009±0.00040.006±0.0010.006±0.0010.006±0.0010.006±0.0010.006±0.0010.006±0.001
Ethyl nonanoate22.30±1.1221.36±1.0723.46±1.1722.35±1.1223.61±1.1820.21±1.0122.16±1.11
Methyl decanoate0.015±0.0010.077±0.004n.d.0.014±0.0010.012±0.0010.010±0.0010.011±0.001
2-Methylpropyl octanoate0.075±0.0040.064±0.0030.059±0.0030.063±0.0030.062±0.0030.055±0.0030.063±0.003
2-Methylbutyl 2-furancarboxylate0.005±0.0010.069±0.003n.d.0.003±0.0010.004±0.0010.003±0.0010.002±0.001
Ethyl decanoate6.43±0.3226.109±0.3065.951±0.2985.921±0.2966.321±0.3165.885±0.2946.537±0.327
Ethyl 5-methylnonanoate0.005±0.0010.006±0.0010.005±0.0010.007±0.0010.007±0.0010.006±0.0010.008±0.001
2-Methylbutyl octanoate0.224±0.0110.191±0.0102.802±0.1400.175±0.0090.185±0.0090.153±0.0080.190±0.010
Ethyl 3-phenyl-2-propenoate0.001±0.0010.012±0.0010.001±0.0010.024±0.0010.023±0.0010.025±0.001n.d.
Propyl decanoate0.016±0.0010.013±0.0010.011±0.0010.011±0.0010.009±0.0010.009±0.0010.012±0.001
Butyl 9-decenoate0.002±0.0010.021±0.0010.016±0.0010.017±0.0010.017±0.0010.013±0.0010.002±0.001
2-Methylpropyl decanoate0.235±0.0120.187±0.0090.175±0.0090.155±0.0080.185±0.0090.147±0.0070.186±0.010
Pentyl nonanoate0.004±0.0010.022±0.0010.002±0.0010.003±0.0010.003±0.0010.002±0.0010.023±0.001
Methyl dodecanoate0.979±0.0490.066±0.0030.086±0.0040.047±0.0020.052±0.0030.049±0.0030.074±0.004
Ethyl dodecanoate3.695±0.1853.475±0.1743.395±0.1703.391±0.1703.594±0.1803.181±0.1593.783±0.189
Isopropyl dodecanoate0.004±0.0010.005±0.0010.003±0.0010.004±0.0010.005±0.0010.006±0.0010.036±0.002
Butyl 9-decenoate0.018±0.0010.025±0.0010.013±0.0010.013±0.0010.014±0.0010.014±0.0010.244±0.012
3-Methylbutyl decanoate1.061±0.0530.989±0.0500.967±0.0480.914±0.0461.014±0.0510.843±0.0421.002±0.050
1-Methylbutyl decanoate0.385±0.0190.347±0.0170.318±0.0160.298±0.0150.331±0.0170.268±0.0130.351±0.018
2-Phenylethyl hexanoate0.005±0.0010.005±0.0010.002±0.0010.003±0.0020.003±0.0010.002±0.0010.003±0.001
Propyl dodecanoate0.004±0.0010.005±0.0010.004±0.0010.004±0.0020.003±0.0010.003±0.0010.002±0.001
Ethyl tridecanoate0.004±0.0010.003±0.0010.002±0.0010.003±0.0010.002±0.0010.003±0.0010.002±0.001
Isobutyl dodecanoate0.041±0.0020.037±0.0020.030±0.0020.023±0.0010.030±0.0020.036±0.0020.029±0.001
Ethyl heptadecanoate0.001±0.0010.004±0.0010.003±0.0010.002±0.0010.001±0.0010.001±0.0010.001±0.001
Octyl octanoate0.006±0.0010.009±0.0010.005±0.0010.006±0.0010.005±0.0010.004±0.0010.003±0.001
Ethyl tetradecanoate0.647±0.0320.429±0.0220.371±0.0190.389±0.0190.399±0.0200.406±0.0200.445±0.022
Isopropyl tetradecanoate0.028±0.0010.004±0.0010.001±0.0010.002±0.0010.003±0.0010.002±0.0010.002±0.001
3-Methylbutyl dodecanoate0.109±0.0050.134±0.0070.127±0.0060.132±0.0070.125±0.0060.091±0.0050.155±0.008
2-Methylbutyl dodecanoate0.038±0.0020.040±0.0020.048±0.0020.041±0.0020.041±0.0020.029±0.0020.075±0.004
2-Phenylethyl dodecanoate0.009±0.0010.010±0.0010.008±0.0010.011±0.0010.009±0.0010.014±0.0010.011±0.001
Ethyl 9-octadecenoate0.003±0.0010.001±0.0000.002±0.0010.002±0.0010.034±0.0020.011±0.0010.003±0.001
Ethyl pentadecanoate0.010±0.0010.008±0.0010.007±0.0010.008±0.0010.008±0.0010.009±0.0010.007±0.001
Methyl hexadecanoate0.001±0.0000.001±0.0000.001±0.0000.001±0.0010.001±0.00010.308±0.0150.003±0.001
Isobutyl tetradecanoate0.001±0.0000.001±0.0000.001±0.0000.001±0.0010.001±0.0010.001±0.0010.001±0.001
Ethyl 9-hexadecenoate0.010±0.0000.007±0.0010.007±0.0010.005±0.0010.005±0.0010.006±0.0010.015±0.001
Ethyl hexadecanoate0.439±0.0220.349±0.0180.309±0.0150.316±0.0160.328±0.0160.303±0.0150.661±0.033
Isopropyl hexadecanoate0.002±0.0010.001±0.0010.001±0.0010.001±0.0010.001±0.0010.003±0.0010.004±0.001
Isoamyl dodecanoate0.001±0.0010.001±0.0010.001±0.0010.001±0.0010.001±0.0010.001±0.0010.001±0.001
Ethyl heptadecanoate0.001±0.0010.033±0.0020.003±0.0010.003±0.0010.002±0.0010.002±0.0010.013±0.001
Isooctyl dodecanoate0.001±0.0010.001±0.0010.001±0.0010.001±0.0010.001±0.0010.007±0.0010.002±0.001
Dibutyl decanedioate0.001±0.0010.018±0.0010.014±0.0010.019±0.0010.018±0.0010.030±0.0020.006±0.001
Acetals
Formaldehyde diethyl acetal0.019±0.0010.179±0.0090.229±0.0120.217±0.0120.189±0.0100.260±0.0130.140±0.007
Acetaldehyde ethyl propyl acetaln.d.0.007±0.0010.005±0.0010.011±0.0010.012±0.0010.015±0.0010.002±0.001
Isobutyraldehyde diethyl acetaln.d.0.017±0.0010.007±0.0010.015±0.0010.018±0.0010.017±0.0010.010±0.001
Valeraldehyde diethyl acetaln.d.0.012±0.0010.049±0.0030.051±0.0030.052±0.0030.047±0.0020.009±0.001
Acetaldehyde ethyl amyl acetal0.037±0.0020.041±0.0020.035±0.0020.185±0.0090.186±0.0090.277±0.0140.132±0.007
Octanal diethyl acetal0.001±0.0000.001±0.0000.001±0.0000.002±0.0000.001±0.0000.002±0.0000.010±0.001
Aldehydes
Hexanal0.025±0.0010.035±0.0020.023±0.0010.033±0.0020.034±0.0020.034±0.0020.038±0.002
Benzaldehyde0.888±0.0440.817±0.0410.114±0.0060.094±0.0050.043±0.0020.077±0.0040.126±0.006
5-Hydroxymethylfurfuraln.d.0.420±0.0210.228±0.0110.532±0.0270.568±0.0280.558±0.0280.163±0.008
Benzeneacetaldehyde0.007±0.0010.008±0.0010.005±0.0010.006±0.0010.006±0.0010.008±0.0010.006±0.001
p-Methylbenzaldehyden.d.0.022±0.0010.012±0.0010.014±0.0010.013±0.0010.011±0.001n.d.
Nonanal