Evaluation of the Essential Oil Composition of Five Thymus Species Native to Greece
by
, , and
Eleni Kakouri
1,
Dimitra Daferera
1,
Anastasia Andriopoulou
1,
Panayiotis Trigas
2 and
Petros A. Tarantilis
1,*
1
Laboratory of Chemistry, Department of Food Science and Human Nutrition, School of Food and Nutritional Sciences, Agricultural University of Athens, Iera Odos 75, 118 55 Athens, Greece
2
Laboratory of Systematic Botany, Department of Crop Science, School of Plant Sciences, Agricultural University of Athens, Iera Odos 75, 118 55 Athens, Greece
*
Author to whom correspondence should be addressed.
Chemosensors 2024, 12(1), 7; https://doi.org/10.3390/chemosensors12010007
Submission received: 31 October 2023
/
Revised: 15 December 2023
/
Accepted: 29 December 2023
/
Published: 31 December 2023
(This article belongs to the Special Issue The Second Edition of GC, MS and GC-MS Analytical Methods: Opportunities and Challenges)
Abstract
:The genus Thymus encompasses a wide array of taxa, many of which remain underexplored in terms of their phytochemical profile. In this study, we investigated the phytochemical composition of volatile compounds of five Thymus species native to Greece using gas chromatography combined with mass spectrometry. Two samples of T. parnassicus collected from Mts Parnitha and Parnassos were studied. The predominant compounds in the Parnitha sample were α-cadinol (13.53%), E-caryophyllene (11.83%) and selin-11-en-4α-ol (7.29%). The sample from Mt. Parnassos exhibited a high concentration of E-caryophyllene (35.20%) followed by β-bisabolene (10.41%). Additionally, two species, namely T. leucotrichus subsp. leucotrichus and T. atticus, were collected on Mt. Chelmos (Peloponnese). The essential oil of T. leucotrichus was rich in elemol (35.56%), α-eudesmol (11.15%) and β-eudesmol (6.11%). Thymus atticus exhibited a high concentration in linalool (63.04%) and p-cymene (25.63%). In addition, two samples of T. holosericeus collected from Kefalonia Ιsland were both rich in geraniol (89.9% and 87.7%, respectively). We also examined the volatile profile of T. laconicus, a local endemic species of SE Peloponnese (Lakonia area), which remains unexplored. Carvacrol (32.7%) and p-cymene (29.7%) were identified as the dominant compounds. Our study contributes valuable insights into the chemical profile of Thymus spp. and sheds further light on the well-known chemical polymorphism within this genus.
1. Introduction
Thymus L. (Lamiaceae) consists of 250 taxa (214 species and 36 sub-species divided into eight sections primarily distributed across the Mediterranean Basin but also in Asia and Africa [1]. Greece hosts 31 taxa (24 species and 7 subspecies), 10 of them endemic to the country [2].
Thymus spp. are valued for their medicinal and aromatic properties. They are recognized for their antimicrobial and antioxidant properties which make them beneficial in addressing respiratory, gastrointestinal disorders and various other conditions [3,4,5]. The essential oils extracted from Thymus spp. are used in the cosmetics and food industry for their aroma or for their antioxidant and/or antimicrobial properties [6,7,8].
Thymus vulgaris is the most studied species of the genus. Its phytochemistry (volatile and non-volatile metabolites) has been studied by numerous researchers [9,10,11,12,13,14], and its biological activity, attributed to its rich chemical profile, has been documented [4,5,15,16]. The chemical analysis of its volatile profile has revealed a chemotypic diversity. In France alone, six chemotypes have been reported, prominently featuring monoterpenes such as geraniol, linalool, α-terpineol, 4-thujanol, thymol and carvacrol [9]. Other researchers identified a total of 20 distinct chemotypes among 85 T. vulgaris samples, with a majority aligning with the thymol chemotype [11]. Besides T. vulgaris, other Thymus species have also been examined for their essential oil composition [17,18,19,20]. Monoterpenes, such as thymol, p-cymene, carvacrol and γ-terpinene, commonly emerge as major constituents of Thymus spp. essential oil [21] and pure or mixed chemotypes at different or even within the same species, have been identified. However, presently, only the thymol chemotype holds official recognition within the European Pharmacopoeia [22].
Essential oils are typically extracted from aerial plant parts, particularly from the inflorescences and leaves. Their complex chemical composition, mainly comprising terpenoids and phenylpropanoids, along with substantial interspecific variability in both quality and quantity of phytochemicals, renders essential oil blends intriguing for diverse industrial applications. The chemical variability of the essential oils is not solely dependent on the species but is significantly linked to environmental, genetic and developmental factors as well as soil conditions [23,24]. Thymus spp. are often covered by dense indumentum, especially on their leaves, providing resistance to cold, hot or dry conditions. They have been adapted to a wide array of environmental conditions, and as a result, different metabolites are produced affecting their chemotypes. Thymol and carvacrol commonly emerge as the dominant metabolites of Thymus spp, lending them their characteristic aroma [25,26,27].
This study investigated the essential oil composition of five Thymus species native to Greece: T. parnassicum from two distinct geographical areas (Mts. Parnitha and Parnassos), T. atticus, T. leucotrichus subsp. leucotrichus, T. laconicus and T. holosericeus from different regions in Kefalonia Ιsland (Mts. Roudi and Enos). All species belong to Thymus sect. Hyphodromi with T. holosericeus and T. laconicus classified under subsect. Thymbropsis and T. atticus, T. parnassicus, T. leucotrichus subsp. leucotrichus under subsect. Subbracteati. Thymus holosericeus and T. laconicus are Greek endemics restricted to the Ionian Ιslands and the Peloponnese, respectively. Thymus atticus, T. parnassicus and T. leucotrichus are distributed in the Balkans (including Greece) and Anatolia [28]. Notably essential oil documentation for T. laconicus is absent, while only a single study references the volatile constituents of T. holosericeus [29]. Similarly, research on the essential oil composition of T. atticus and T. parnassicus is especially scarce [30]. Our results contribute to the study of the genus Thymus by presenting new data that elucidate its chemical polymorphism.
2. Materials and Methods
2.1. Chemicals
Standard compounds, namely p-cymene, 3-octanol, aromadendrene, caryophyllene oxide, linalool, α-pinene, terpinene-4-ol, γ-terpinene, α-terpineol, neryl acetate and α-terpinene were purchased from Sigma Aldrich (Darmstadt, Germany), decanal was purchased from ThermoFisher Scientific (Loughborough, Leicestershire), and β-eudesmol, α-copaene, α-cubebene, and terpinolene were purchased from Fluka (Buchs, Switzerland). Anhydrous sodium sulfate was purchased from Acros organics (Morris Plains, NJ, USA) and diethyl ether was purchased from Chem-Lab (Zedelgem, Belgium).
2.2. Plant Material
Plant material was collected during the flowering period from mature individuals of wild populations from different localities in Greece. The specimens were deposited at the herbarium of Agricultural University of Athens (ACA). Information regarding the geographic locations of the collected plant material is given in Table 1.
2.3. Isolation of the Essential Oil
Air-dried parts (flowers and leaves) of the collected plant material underwent hydrodistillation using a Clevenger type apparatus for 3 h. Tymus laconicus, essential oil, was directly collected from the Clevenger apparatus, while for the other samples, liquid–liquid extraction followed using diethyl ether, for collecting the volatile compounds. The organic phase was then dried using anhydrous sodium sulfate, filtered and stored at −20 °C at a fixed volume, until further analysis.
2.4. GC-MS Analysis Conditions
Chromatographic analysis was performed using a Bruker chromatograph 436-GC coupled to a mass spectrometer. A capillary column Rxi-5Sil MS (30 m, 0.25 mm ID, 0.25 μm) was used for the separation of compounds. The injector and detector temperature was set to 220 °C and 230 °C, respectively. Helium was the carrier gas at a flow rate of 1.0 mL/min. The oven temperature was held at 60 °C for 3 min and then increased to 250 °C with a rate of 3 °C/min. Injection volume was 1 μL at the splitless mode. MS detector was operated in EI mode at 70 eV. Mass range was set to 45–400 m/z.
Identification was based on authentic standard solutions and/or on comparison of compounds’ mass spectrum and Relative Retention Index (Arithmetic index, A.I) with those from NIST and ADAMS libraries. The standard compounds, namely p-cymene, 3-octanol, decanal, neryl acetate, β-eudesmol, α-copaene, α-cubebene, aromadendrene, caryophyllene oxide, terpinolene, linalool, α-pinene, terpinene-4-ol, γ-terpinene, α-terpineol and α-terpinene, were analyzed under the same experimental conditions. A mixture of n-alkanes solution (C8–C24, Sigma Aldrich) was also analyzed under the same experimental conditions for the calculation of the Relative Retention Index, according to Equation (1). Compound concentration was calculated as % content (Table 2 and Table 3). Principal Component Analysis (PCA) of the data was implemented using GraphPad prism ver. 9.5.1 and cluster analysis (CA) using IBM SPSS statistics ver. 23. The variables used to perform the analysis are highlighted in bold (Table 2 and Table 3) [31].
where tn and tn + 1 are retention time of n-alkanes that elute before and after the unknown compound (x) and tx is the retention time of the unknown compound.
A.Ix = 100n + 100(tx − tn)/(tn + 1 − tn)
3. Results
The yield (% v/w) and chemical composition of the essential oils extracted from the aerial parts of the studied Thymus species are presented in Table 2 (subsect. Subbracteati) and Table 3 (subsect. Thymbropsis). The compounds in both tables are arranged according to their Relative Retention Index (R.R.I.) values. Seventy-six compounds were identified in the essential oil of T. parnassicus (Mt. Parnitha), representing the 94.22% of the oil and 54 in T. parnassicus (Mt. Parnassos), representing 94.83% of the oil. For T. atticus, 19 compounds accounting for 99.24% of the oil were detected. Additionally, 35 compounds were identified in the essential oil of T. leucotrichus subsp. leucotrichus, representing 88.94% of the essential oil. Within subsect. Thymbropsis, 20 compounds were identified in the oil of T. holosericeus (Mt. Roudi), constituting 97.8% of the oil and 24 compounds accounting for 97.2% were detected in the plants from Mt. Enos. Finally, for T. laconicus, 99.2% of the oil’s composition was identified comprising 25 compounds. GC-MS chromatograms of the studied species are given as Supplementary Material (Figures S1–S7).
More precisely, the major compound found in the sample of T. parnassicus from Mt. Parnitha is α-cadinol (13.53%), followed by E-caryophyllene (11.83%). In the sample from Mt. Parnassos, E-caryophyllene is in abundance (35.20%), followed by β-bisabolene (10.41%). Thymus atticus is characterized by the prevalence of linalool (63.04%). For T. leucotrichus subsp. leucotrichus, the primary compound is elemol (35.56%), followed by α-eudesmol (11.15%) (Table 2). Concerning the species of subsect. Thymbropsis, both samples of T. holosericeus from Kefalonia Island are rich in geraniol (89.9% from Mt. Roudi and 87.7% from Mt. Enos). For T. laconicus, the dominant compounds are carvacrol (32.7%), and p-cymene (29.7%) (Table 3).
Two principal components were chosen for PCA analysis which explain the 56.72% of the total variance (Figure 1).
The first principal component (PC1) accounts for 34.19% of the total variance, displayed positive associations with γ-terpinene, carvacrol, p-cymene, thymol and borneol. The second component (PC2) contributes 22.5% of the total variance, positively correlated δ-cadinene, selin-11-en-4α-ol, α-cadinol, β-bisabolene and E-caryophyllene, while it was negatively correlated to α-eudesmol, β-eudesmol and elemol (Figure 2).
Therefore, the studied samples can be grouped as follows: Group 1 consists of T. holosericeus rich in geraniol, an oxygenated monoterpene, while Group 2 is divided into four sub-groups (Figure 3). Thymus leucotrichus subsp. leucotrichus, T. laconicus and T. atticus, each form a distinct cluster. Both samples of T. parnassicus were clustered together probably because of their high sesquiterpene content.
4. Discussion
The genus Thymus comprises a significant number of taxa that largely remain unexplored in terms of their phytochemistry. One such example is T. laconicus, for which we present the volatile profile data for the first time. In addition to this unexplored species, others like T. parnassicus, T. holosericeus and T. atticus have received limited research attention and have also been included in our study. Chemical polymorphism, a common trait in many medicinal and aromatic plants, has also been reported in various Thymus species [32,33,34]. These diverse profiles of both main and secondary metabolites highlight the need for further investigation of their chemical composition. Each species may contribute “uniquely” potentially offering distinct modes of action and therefore differing biological activities.
Plants synthesize secondary metabolites in response to external stimuli and their production is affected by multiple factors [35]. Biosynthetic pathways as well as specific enzymes responsible for their production may vary between plant species and they also depend on environmental factors and developmental stage of the plant. Therefore, it is necessary to understand how metabolism pathways and related enzymes vary in response to different exogenous and endogenous factors, to which a plant has been adapted.
As depicted in Table 2 and Table 3, the investigated species exhibit distinct chemotypes. Their qualitative and quantitative differences confirm the already-known patterns of chemical polymorphism within Thymus, a genus rich in secondary metabolites. Our results demonstrate that nearly all studied Thymus species, excluding T. holosericeus, display a mixed chemotype. Both thymol and carvacrol are present in almost all species; however, their proportions vary considerably among them. Especially noteworthy is the high chemical variability observed in T. parnassicus collected from two distinct geographical areas. The plants from Mt. Parnitha are rich in oxygenated sesquiterpenes followed by sesquiterpenes hydrocarbons. They present a mixed chemotype of α-cadinol (13.53%), E-caryophyllene (11.83%), selin-11-en-4α-ol (7.29%), δ-cadinene (6.54%), epi-α-muurolol (6.49%) and β-bisabolene (4.77%). These compounds constitute 50.45% of the total essential oil. One study was found to examine the chemical composition of T. parnassicus collected from three distinct geographic areas, including Mt. Parnitha [31]. The main compounds identified in this study were E-caryophyllene (8.5%), linalool acetate (8.2%), γ-terpinene (8.0%) and myrcene (5.3%). The chemical composition of T. parnassicus collected from Mt. Parnassos reveals a mixed chemotype primarily comprised E-caryophyllene (35.20%), β-bisabolene (10.41%) and elemol (6.92%) accounting 52.53% of the total constituents. In this sample, sesquiterpene hydrocarbons prevail, followed by oxygenated monoterpenes. The observation by Tzakou and Constantinidis [30] indicating the stability of the volatile profile of T. parnassicus across different origins where sesquiterpene hydrocarbons and oxygenated sesquiterpenes dominate with consistent quantities is not fully supported by our results. Our findings are partially consistent with the results of Tzakou and Constantinidis [30], since T. parnassicus from Mt. Parnitha has a similar chemical profile, with sesquiterpenes (hydrocarbons and oxygenated) being in abundance. However, significant % quantitative differences were observed among these groups of compounds (32.84% for sesquiterpenes hydrocarbons and 45.49% for oxygenated sesquiterpenes). On the other hand, the sample collected from Mt. Parnassos, albeit rich in sesquiterpenes hydrocarbons (49.57%), deviates from this trend since the second most abundant group is oxygenated monoterpenes accounting for 23.76%. Nevertheless, the combined quantity of sesquiterpenes outweighs that of monoterpenes. For a more precise characterization of the T. parnassicus samples included in this study, a comparison of their overall fingerprint is essential. Apart from α-cadinol, selin-11-en-4α-ol and epi-α-muurolol exclusively present in the Parnitha sample, other marker compounds, despite their minor % concentration, warrant attention. These include the compounds 2, 9, 29, 30, 32, 37, 62, 77, 94, 98 and 104 (Table 2) that are present only in the Parnassos sample. These differences, qualitative and quantitative, should not be neglected, as they contribute to the chemical polymorphism of T. parnassicus.
Regarding T. leucotrichus subsp. leucotrichus, elemol is the characteristic compound (35.56%), followed by α-eudesmol (11.15%) and β-eudesmol (6.11%), indicating a mixed chemotype for this taxon. Interestingly, a different chemotype was identified in [36], which examined T. leucotrichus collected in Bulgaria. The examined sample exhibited mixed chemotype, predominantly featuring β-caryophyllene (23.10%) and elemol (9.8%). β-caryophyllene was not among the compounds detected in our study. Greek samples of this species have been assessed in previous studies [37,38]. The initial study [37] did not specify identification to the infraspecific rank, whereas the subsequent study [38] focused on examining T. leucotrichus var. creticus. Diverse chemotypes were identified among the studied samples, namely β-caryophyllene/1.8 cineole and β-caryophyllene/linalool in the former study, while the latter revealed a p-cymene/γ-terpinene chemotype. Likewise, T. leucotricus of unidentified subspecies collected in Turkey showed a high percentage of p-cymene (21.55%) and thymol (31.01%) with monoterpenes being in abundance. Indeed, their % quantity far exceeded that of sesquiterpenes [39]. This is opposed to our results, since we observed the quantity of oxygenated sesquiterpenes to be five-fold that of oxygenated monoterpenes. According to our knowledge, studies regarding T. leucotricus are few. Our results, alongside the studies mentioned herein, demonstrate the importance of the accurate description of the plant, which contributes important information regarding its phytochemistry [40]. Nevertheless, all these results strengthen previous evidence of the enormous chemical variability within Thymus spp.
For T. atticus, the abundance in linalool (63.04%) and p-cymene (25.63%) detected in our samples significantly differs from previously reported values by [30], [36] and [41]. Both p-cymene and linalool were identified in all studies; however, in our study, these compounds were found in significantly higher quantities. According to [42], p-cymene production is favored by soil conditions, specifically a soil rich in carbohydrates, rather than environmental factors. Furthermore, δ-germacrene and (E)-nerolidol, which were detected in considerable quantities by [30], were not found in our study.
In T. holosericeus from Kefalonia Island, a well-defined chemotype was observed consisting of geraniol (89.9% from Mt. Roudi and 87.7% from Mt. Enos), along with its stereoisomer nerol. Neral, an oxidation product of geraniol was present in both samples, while geranial, another oxidation product was only detected in the plants collected from Mt. Roudi. A previous examination of T. holosericeus on the same island had identified a mixed chemotype specifically the carvacrol/geraniol chemotype [29]. Constituents, such as borneol, linalool and thymol, were present in significant quantities, similarly to our sample. Other geraniol chemotypes of Thymus spp. have been detected across the Baltic countries [43].
Thymus laconicus is classified as a mixed chemotype containing carvacrol (32.7%) and p-cymene (29.7%). To our knowledge, no previous studies have been conducted on this species. Notably, among the studied species, only in T. laconicus was carvacrol found in abundance. The presence of both thymol and carvacrol in the T. laconicus sample aligns with the biosynthetic pathway described by [44]. Terpinene-4-ol is an intermediate that converts γ-terpinene to p-cymene [45], which through oxidation and dehydrogenation reactions, respectively, leads to the formation of thymol and carvacrol. Similarly, in T. atticus, the metabolic pathway moves one step forward with the hydroxylation of thymol and carvacrol resulting in the formation of thymohydroquinone, which either spontaneously or via enzymatic reaction converts to thymoquinone, a compound found exclusively in T. atticus essential oil [44]. A high quantity of γ-terpinene is usually required to produce thymol or carvacrol [46]. Considering all our data, γ-terpinene is prominently present in T. laconicus essential oil (6.8%) and in a lower quantity in T. atticus (1.36%), while both T. parnassicus samples are poor in this compound. This observation partially explains the higher percentage of carvacrol found in T. laconicus compared to the other species. However, the genetic background of each species, which activates distinct enzymes in combination with variable environments conditions which can influence the expression of specific genes, may clarify the abundance of either carvacrol or linalool in T. laconicus and T. atticus, respectively.
The relationships between the samples were investigated by PCA and CA. Thymus parnassicus samples were grouped together due to the abundance of sesquiterpenes and were negatively correlated with that of T. atticus, a sample rich in oxygenated monoterpenes, primarily linalool and secondarily p-cymene. T. leucotricus subsp. leucotricus was not correlated with any of the samples of subsection Subbracteati and formed a distinct group, due to the high percentage of elemol. Regarding plants of the Thymbropsis subsection, T. holosericeus samples were grouped together apparently due to the remarkable percentage of geraniol. Thymus laconicus was isolated from the other samples due to the presence of thymol and carvacrol, which far exceeded that of the other samples. A cluster analysis was performed using the same data as for the PCA analysis and revealed five distinct chemotypes. The geraniol chemotype was attributed to T. holosericeus plants, E-caryophyllene/β-bisabolene chemotype accounted for T. parnassicus plants, with the elemol chemotype for T. leucotricus subsp. leucotricus, carvacrol/p-cymene chemotype for T. laconicus and linalool/p-cymene chemotype for T. atticus.
A chemotype is defined “as same species/subspecies/varieties of an organism containing different secondary metabolites with different quantities” [47]. Each species has a unique profile which is attributed both to qualitative and quantitative differences. Compounds that dominate in the essential oil of the species, such as p-cymene, linalool, geraniol, E-caryophyllene, elemol and others, each possess a biological or other activity [48,49,50,51,52]. However, the presence of other compounds, even in minor quantity, may indicate possible synergistic effect. Therefore, in vitro and in vivo experiments are required to explore new perspectives for different applications of Thymus spp. in the food, cosmetic and pharmaceutical industry.
5. Conclusions
This study unveils the chemical composition of unexplored (T. laconicus) or less studied (T. parnassicus, T. atticus, T. leucotrichus subsp. leucotrichus and T. holocericeus) Thymus species native to Greece. Thymus parnassicus samples were rich in sesquiterpenes, both hydrocarbons and oxygenated. Thymus atticus presented oxygenated monoterpenes in abundance, while for T. leucotricus subsp. leucotricus, oxygenated sesquiterpenes constitute more than 50% of the total essential oil. Additionally, the members of subsection Thymbropsis are all rich in oxygenated monoterpenes, while for T. laconicus, a species endemic to Greece and studied herein for the first time, monoterpene hydrocarbons are also found in considerable quantity. According to PCA and cluster analysis, samples were classified into five groups based both on qualitative and quantitative differences of their total content in monoterpenes (samples that belong to subsect. Thymbropsis and the sample of T. atticus) and sesquiterpenes (both samples of T. parnassicus and T. leucotrichus subsp. leucotrichus). The determination of a plant chemotype is crucial not only for plant chemotaxonomy but also for understanding its biological activities. Research interest should extend beyond the dominant compounds of the essential oils. Even minor compounds in quantity deserve attention since they could contribute to the species identification and provenance and may also significantly contribute to the biological activity exhibited by each species.
Supplementary Materials
The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/chemosensors12010007/s1, Figure S1: GC-MS chromatogram of T. parnassicus (Mt. Parnitha); Figure S2: GC-MS chromatogram of T. parnassicus (Mt. Parnassos); Figure S3: GC-MS chromatogram of T. atticus (Mt. Chelmos); Figure S4: GC-MS chromatogram of T. leucotricus subsp. leucotricus (Mt. Chelmos); Figure S5: GC-MS chromatogram of T. holosericeus (Mt. Roudi); Figure S6: GC-MS chromatogram of T. holosericeus (Mt. Enos); Figure S7: GC-MS chromatogram of T. laconicus (Geraki Lakonias).
Author Contributions
Conceptualization, E.K., P.T. and P.A.T.; methodology, E.K. and D.D.; investigation, E.K., D.D. and A.A.; data curation, E.K., D.D. and A.A.; writing—original draft preparation, E.K.; writing—review and editing, E.K., D.D., P.T. and P.A.T.; supervision, P.A.T. All authors have read and agreed to the published version of the manuscript.
Funding
This research received no external funding.
Institutional Review Board Statement
Not applicable.
Informed Consent Statement
Not applicable.
Data Availability Statement
The data used to support the findings of this study are included within the article.
Conflicts of Interest
The authors declare no conflicts of interest.
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Figure 1.
Proportion of variance explained by each principal component.
Figure 2.
(A) Correlation between the variables and the principal components; (B) Dimension reduction achieved by PCA; (C) Biplot of PCA analysis. Eigenvalues greater than one were chosen to perform the analysis.
Figure 2.
(A) Correlation between the variables and the principal components; (B) Dimension reduction achieved by PCA; (C) Biplot of PCA analysis. Eigenvalues greater than one were chosen to perform the analysis.
Figure 3.
Chemical polymorphism of Thymus species represented by a dendrogram obtained by cluster analysis using Ward’s method.
Figure 3.
Chemical polymorphism of Thymus species represented by a dendrogram obtained by cluster analysis using Ward’s method.
Table 1.
Collection data of the studied Thymus species.
| Taxon | Collection Site | Latitude | Longitude | Elevation (m) |
|---|---|---|---|---|
| T.parnassicus | Mt. Parnitha | 38°10′23″ | 23°43′41″ Ε | 1300 |
| T.parnassicus | Mt. Parnassos | 38°33′39″ | 22°34′26″ Ε | 1700 |
| T. atticus | Mt. Chelmos | 38°05′14″ | 22°10′30″ | 950 |
| T. leucotrichus subsp. leucotrichus | Mt. Chelmos | 37°59′20″ | 22°11′25″ | 2150 |
| T. holosericeus | Κephalonia (Mt. Roudi) | 38°10′31″ | 20°36′41″ | 870 |
| T. holosericeus | Κephalonia (Mt. Enos) | 38°07′35″ | 20°42′04″ | 1110 |
| T. laconicus | Peloponnese (Geraki Lakonias) | 36°58′53″ | 22°44′26″ | 340 |
Table 2.
Chemical composition of Thymus species (subsect. Subbracteati).
| Subsect. Subbracteati | ||||||||
|---|---|---|---|---|---|---|---|---|
| % Composition | ||||||||
| No | Classification [a] | Compound Identification | A.I Experimental | A.I Literature | T. parnassicus (Mt. Parnitha) | T. parnassicus (Mt. Parnassos) | T. atticus (Mt. Chelmos) | T. leucotrichus subsp. leucotrichus (Mt. Chelmos) |
| 1 | MH | α-pinene [b] | 931 | 932 | 0.63 | 1.89 | - [c] | - |
| 2 | MH | camphene | 947 | 946 | - | 0.08 | - | - |
| 3 | others | benzaldehyde | 955 | 952 | - | - | - | 0.22 |
| 4 | AL | 1-octen-3-ol | 974 | 974 | 0.13 | 0.42 | 0.68 | 0.72 |
| 5 | AL | 6-methyl-5-hepten-2-one | 979 | 981 | tr. * | - | - | - |
| 6 | MH | myrcene | 986 | 988 | 0.11 | tr. | - | - |
| 7 | AL | 3-octanol [b] | 991 | 988 | tr. | 0.26 | tr. | - |
| 8 | AL | (2E, 4E)-Heptadienal | 1006 | 1005 | - | - | - | 0.11 |
| 9 | MH | α-terpinene [b] | 1015 | 1014 | - | tr. | 0.25 | - |
| 10 | MH | p-cymene [b] [d] | 1022 | 1020 | 0.15 | tr. | 25.63 | - |
| 11 | MH | limonene | 1027 | 1024 | 0.22 | 1.10 | 0.08 | - |
| 12 | OM | eucalyptol | 1029 | 1026 | 0.84 | 3.91 | - | - |
| 13 | others | benzylalcohol | 1034 | 1026 | - | - | - | 0.44 |
| 14 | others | benzene acetaldehyde | 1038 | 1036 | tr. | 0.08 | - | 2.22 |
| 15 | MH | (Ε)-β-ocimene | 1042 | 1044 | tr. | -- | - | - |
| 16 | MH | γ-terpinene [b] | 1055 | 1054 | 0.21 | 0.21 | 1.36 | - |
| 17 | OM | cis-sabinene hydrate | 1065 | 1064 | - | - | 0.30 | - |
| 18 | OM | cis-linalool oxide | 1067 | 1067 | tr. | tr. | 0.39 | - |
| 19 | OM | trans-linalool oxide | 1083 | 1084 | tr. | - | 0.37 | - |
| 20 | OM | linalool [b] | 1097 | 1095 | 3.11 | 5.30 | 63.04 | 4.04 |
| 21 | AL | 1-octen-1-ol, acetate | 1105 | 1112 | 0.10 | tr. | - | - |
| 22 | others | 2,6-dimethyl-cyclohexanol | 1108 | - | - | - | - | 0.15 |
| 23 | PHP | phenyl ethyl alcohol | 1114 | 1106 | - | - | - | 0.15 |
| 24 | OM | camphor | 1143 | 1141 | 2.02 | 3.53 | - | 0.08 |
| 25 | OM | lavandulol | 1163 | 1165 | - | - | 0.13 | - |
| 26 | OM | borneol | 1168 | 1165 | 2.73 | 2.80 | - | - |
| 27 | OM | terpinen-4-ol [b] | 1177 | 1174 | 0.69 | 2.52 | 0.30 | 0.28 |
| 28 | OM | α-terpineol [b] | 1191 | 1186 | 2.06 | 1.74 | 0.19 | 0.22 |
| 29 | OM | cis-dihydrocarvone | 1194 | 1191 | - | 0.20 | - | - |
| 30 | OM | trans-dihydrocarvone | 1200 | 1200 | - | 0.31 | - | - |
| 31 | AL | decanal | 1203 | 1201 | tr. | tr. | - | - |
| 32 | OM | trans-carveol | 1215 | 1215 | - | tr. | - | - |
| 33 | others | 2,3-dihydro-benzofuran | 1218 | - | - | - | - | 0.60 |
| 34 | OM | citronellol | 1222 | 1223 | tr. | - | - | - |
| 35 | OM | nerol | 1225 | 1227 | tr. | - | - | tr. |
| 36 | OM | thymol methyl ether | 1226 | 1232 | tr. | tr. | - | - |
| 37 | OM | pulegone | 1234 | 1233 | - | tr. | - | - |
| 38 | OM | carvone | 1239 | 1239 | tr. | 1.09 | - | - |
| 39 | OM | thymoquinone | 1242 | 1248 | - | - | 0.26 | - |
| 40 | OM | geraniol | 1247 | 1249 | 0.38 | - | - | 2.45 |
| 41 | OM | geranial | 1264 | 1264 | tr. | - | - | 0.09 |
| 42 | OM | bornyl acetate | 1280 | 1284 | 0.64 | 1.99 | - | - |
| 43 | OM | thymol | 1287 | 1289 | 0.42 | - | 0.11 | 0.82 |
| 44 | OM | carvacrol | 1295 | 1298 | 0.21 | 0.11 | 5.82 | 3.27 |
| 45 | OM | 2-methoxy-4-vinylphenol | 1305 | 1309 | tr. | - | - | 0.77 |
| 46 | SEH | δ-elemene | 1329 | 1335 | tr. | - | - | - |
| 47 | SEH | α-cubebene | 1344 | 1348 | 0.12 | tr. | - | - |
| 48 | OM | eugenol | 1356 | 1356 | - | - | - | 0.05 |
| 49 | OM | neryl acetate | 1355 | 1359 | 0.32 | tr. | - | - |
| 50 | OM | carvacrol acetate | 1366 | 1370 | - | - | 0.62 | - |
| 51 | SEH | α-copaene | 1372 | 1374 | 0.98 | 0.10 | - | - |
| 52 | OM | geranyl acetate | 1374 | 1379 | 0.92 | 0.17 | - | - |
| 53 | SEH | β-bourbonene | 1379 | 1387 | 0.22 | 0.16 | - | - |
| 54 | SEH | β-elemene | 1385 | 1389 | 0.86 | 0.17 | - | - |
| 55 | SEH | (Z)-caryophyllene | 1400 | 1408 | tr. | 0.10 | - | - |
| 56 | SEH | α-gurjunene | 1403 | 1409 | tr. | - | - | - |
| 57 | SEH | E-caryophyllene [b] | 1415 | 1417 | 11.83 | 35.20 | 0.16 | - |
| 58 | SEH | β-copaene | 1425 | 1430 | 0.07 | tr. | - | - |
| 59 | SEH | trans-α-bergamotene | 1429 | 1432 | tr. | tr. | - | - |
| 60 | SEH | aromadendrene | 1433 | 1439 | tr. | - | - | - |
| 61 | SEH | cis-β-farnesene | 1437 | 1440 | tr. | - | - | - |
| 62 | SEH | α-humulene | 1450 | 1452 | 1.09 | 1.85 | - | - |
| 63 | OM | E-geranylacetone | 1443 | 1453 | - | 0.09 | - | - |
| 64 | SEH | allo-aromadendrene | 1455 | 1458 | 0.61 | - | - | - |
| 65 | SEH | Dauca-5,8-diene | 1467 | 1471 | 0.16 | - | - | - |
| 66 | SEH | γ-muurolene | 1470 | 1478 | 0.24 | tr. | - | - |
| 67 | SEH | δ-germacrene | 1475 | 1480 | 2.08 | 1.20 | - | - |
| 68 | SEH | β-selinene | 1483 | 1489 | tr. | - | - | - |
| 69 | SEH | γ-amorphene | 1485 | 1495 | 0.45 | - | - | - |
| 70 | OM | 5,6-epoxy-β-ionone | 1490 | - | - | - | - | 0.12 |
| 71 | SEH | bicyclogermacrene | 1490 | 1500 | 1.09 | - | - | - |
| 72 | SEH | α-muurolene | 1494 | 1500 | 0.66 | - | - | - |
| 73 | SEH | β-bisabolene | 1504 | 1505 | 4.77 | 10.41 | - | - |
| 74 | SEH | γ-cadinene | 1507 | 1513 | 0.64 | - | - | - |
| 75 | SEH | δ-cadinene | 1513 | 1522 | 6.54 | 0.24 | - | - |
| 76 | SEH | zonarene | 1518 | 1528 | 0.21 | - | - | - |
| 77 | SEH | β-sesquiphellandrene | 1519 | 1521 | - | 0.14 | - | - |
| 78 | SEH | α-cadinene | 1531 | 1537 | 0.13 | - | - | - |
| 79 | SEH | α-calacorene | 1535 | 1544 | 0.09 | - | - | - |
| 80 | others | 5,6,7,7α-tetrahydro-4,4,7α-trimethyl-2(4H)-benzo-furanone | 1538 | - | - | - | - | 0.18 |
| 81 | SEO | elemol | 1543 | 1548 | 2.36 | 6.92 | - | 35.56 |
| 82 | SEO | (E)-nerolidol | 1557 | 1561 | 0.12 | 1.90 | - | - |
| 83 | AL | dodecanoic acid | 1574 | 1565 | - | - | - | 0.55 |
| 84 | SEO | palustrol | 1563 | 1567 | 0.12 | - | - | - |
| 85 | SEO | spathulenol | 1570 | 1577 | 0.94 | - | - | 0.77 |
| 86 | SEO | caryophyllene oxide [b] | 1575 | 1582 | 3.21 | 1.72 | 0.17 | 0.59 |
| 87 | SEO | viridiflorol | 1587 | 1592 | 0.23 | - | - | - |
| 88 | SEO | 1,10-di-epi-Cubenol | 1621 | 1618 | - | - | - | 0.25 |
| 89 | SEO | 1-epi-cubenol | 1621 | 1627 | 0.71 | - | - | |
| 90 | SEO | γ-eudesmol | 1625 | 1630 | 0.77 | 1.32 | - | 2.42 |
| 91 | SEO | caryophylla-4(12),8(13)-dien-5-ol | 1632 | 1639 | 0.49 | - | - | - |
| 92 | SEO | epi-α-muurolol | 1637 | 1640 | 6.49 | - | - | - |
| 93 | SEO | α-muurolol | 1640 | 1644 | 0.94 | - | - | - |
| 94 | SEO | β-eudesmol | 1648 | 1649 | - | 2.87 | - | 6.11 |
| 95 | SEO | α-cadinol | 1649 | 1652 | 13.53 | - | - | 5.82 |
| 96 | SEO | selin-11-en-4α-ol | 1656 | 1658 | 7.29 | - | - | - |
| 97 | SEO | α-eudesmol | 1666 | 1652 | - | - | - | 11.15 |
| 98 | SEO | α-bisabolol | 1679 | 1685 | - | tr. | - | - |
| 99 | SEO | shyobunol | 1703 | 1688 | - | - | - | 3.16 |
| 100 | SEO | (2E, 6Z)-farnesal | 1703 | 1713 | 1.02 | 0.10 | - | - |
| 101 | SEO | (2E, 6Z)-farnesol | 1714 | 1714 | 3.34 | 2.16 | - | - |
| 102 | SEO | (2Z, 6E)-farnesol | 1725 | 1722 | - | - | - | 0.26 |
| 103 | SEO | (2E, 6E)-farnesal | 1730 | 1740 | 1.8 | 0.47 | - | - |
| 104 | others | benzyl benzoate | 1756 | 1759 | - | tr. | - | - |
| 105 | AL | tetradecanoic acid | 1769 | - | - | - | - | 0.92 |
| 106 | SEO | cryptomeridiol | 1820 | 1813 | - | - | - | 0.27 |
| 107 | SEO | (2Z, 6E)-farnesyl acetate | 1828 | 1821 | 2.13 | - | - | - |
| 108 | AL | hexadecanoic acid | 1975 | 1959 | - | - | - | 4.13 |
| %Yield (mL/100 g of dry plant material) | 0.35 | 0.32 | 0.3 | 0.5 | ||||
| AL | Aliphatic compounds | 0.23 | 0.68 | 0.68 | 6.43 | |||
| MH | Monoterpene hydrocarbons | 1.32 | 3.28 | 27.32 | - | |||
| OM | Oxygenated monoterpenes | 14.34 | 23.76 | 71.53 | 12.19 | |||
| SEH | Sesquiterpenes hydrocarbons | 32.84 | 49.57 | 0.16 | - | |||
| SEO | Sesquiterpenes oxygenated | 46.43 | 17.46 | 0.17 | 66.36 | |||
| others | - | 0.08 | - | 3.96 | ||||
| TOTAL | 95.51 | 94.83 | 99.24 | 88.94 | ||||
* tr.: traces (% concentration ≤ 0.06%); [a] AL: aliphatic compounds; MH: monoterpene hydrocarbons; OM: oxygenated monoterpenes; SEH: sesquiterpene hydrocarbons; SEO: oxygenated sesquiterpenes; [b] identification based on standard compounds; [c] not detected; [d] The variables used to perform PCA and CA are highlighted in bold.
Table 3.
Chemical composition of Thymus species (subsect. Thymbropsis).
| Subsect. Thymbropsis | |||||||
|---|---|---|---|---|---|---|---|
| % Composition | |||||||
| No | Classification [a] | Compound Identification | A.Ι Experimental | A.Ι Literature | T. holosericeus (Mt. Roudi) | T.holosericeus (Mt. Enos) | T. laconicus Peloponnesse (Geraki Laconias) |
| 1 | MH | α-thujene | 925 | 924 | - [c] | - | 0.3 |
| 2 | MH | α-pinene [b] | 932 | 932 | - | - | 1.1 |
| 3 | MH | camphene | 948 | 946 | - | - | 2.0 |
| 4 | AL | 1-octen-3-ol | 976 | 974 | - | - | 1.1 |
| 5 | MH | myrcene | 989 | 988 | - | 0.1 | 0.4 |
| 6 | MH | α-phellandrene | 1005 | 1002 | - | - | tr.* |
| 7 | MH | α-terpinene | 1017 | 1014 | - | - | 0.7 |
| 8 | MH | p-cymene [b][d] | 1029 | 1020 | - | - | 29.7 |
| 9 | others | benzene acetaldehyde | 1037 | 1036 | tr. | - | - |
| 10 | MH | (E)-β-ocimene | 1049 | 1044 | - | tr. | - |
| 11 | MH | γ-terpinene [b] | 1060 | 1054 | - | - | 6.8 |
| 12 | OM | cis-linalool oxide | 1070 | 1067 | 0.1 | - | - |
| 13 | OM | trans-linalool oxide | 1083 | 1084 | tr. | - | - |
| 14 | MH | terpinolene | 1089 | 1086 | - | - | tr. |
| 15 | MH | p-cymenene | 1089 | 1089 | - | - | 0.3 |
| 16 | OM | Linalool [b] | 1100 | 1095 | 0.4 | 0.5 | 1.0 |
| 17 | OM | camphor | 1145 | 1141 | - | - | 0.1 |
| 18 | OM | borneol | 1171 | 1165 | 1.2 | 0.2 | 8.2 |
| 19 | OM | terpinen-4-ol [b] | 1181 | 1174 | - | tr. | 2.1 |
| 20 | OM | p-cymen-8-ol | 1185 | 1179 | - | - | 0.2 |
| 21 | OM | α-terpineol [b] | 1192 | 1186 | - | - | 0.1 |
| 22 | OM | verbenone | 1207 | 1204 | 0.1 | - | - |
| 23 | OM | nerol | 1227 | 1227 | 0.5 | 0.4 | - |
| 24 | OM | neral | 1238 | 1235 | tr. | 0.6 | - |
| 25 | OM | geraniol | 1247 | 1249 | 89.9 | 87.7 | - |
| 26 | OM | geranial | 1275 | 1264 | 1.1 | - | - |
| 27 | OM | bornyl acetate | 1287 | 1284 | - | - | 0.3 |
| 28 | OM | lavandulyl acetate | 1299 | 1288 | - | 0.1 | - |
| 29 | OM | thymol | 1303 | 1289 | tr. | 1.7 | 7.9 |
| 30 | OM | carvacrol | 1311 | 1298 | - | 0.4 | 32.7 |
| 31 | OM | ethyl nerolate | 1361 | 1351 | - | tr. | - |
| 32 | OM | carvacrol acetate | 1366 | 1370 | - | - | tr. |
| 33 | OM | geranyl acetate | 1385 | 1379 | 0.7 | 0.2 | - |
| 34 | SEH | β-bourbonene | 1389 | 1387 | 0.2 | - | - |
| 35 | SEH | E-caryophyllene [b] | 1424 | 1417 | 0.7 | 2.0 | 2.8 |
| 36 | SEH | α-humulene | 1460 | 1452 | - | 0.1 | tr. |
| 37 | OM | geranyl propanoate | 1474 | 1476 | - | 0.1 | - |
| 38 | SEH | δ-germacrene | 1487 | 1480 | 0.2 | tr. | - |
| 39 | SEH | bicyclogermacrene | 1502 | 1500 | 0.4 | 0.1 | - |
| 40 | SEH | δ-Cadinene | 1527 | 1522 | 0.1 | -- | - |
| 41 | OM | geranyl butanoate | 1562 | 1562 | - | 1.2 | - |
| 42 | SEO | spathulenol | 1586 | 1577 | 0.8 | 0.1 | - |
| 43 | SEO | caryophyllene oxide [b] | 1592 | 1582 | 1.0 | 1.1 | 1.4 |
| 44 | OM | geranyl isovalerate | 1603 | 1606 | - | 0.5 | - |
| 45 | SEO | caryophylla-4(12),8(13)-dien-5-ol | 1645 | 1639 | - | 0.1 | tr. |
| 46 | OM | geranyl valerate | 1656 | 1655 | - | tr. | - |
| 47 | SEO | epi-β-bisabolol | 1672 | 1670 | 0.4 | - | - |
| % Yield (mL/100 g of dry plant material) | 2 | 3.3 | 2 | ||||
| AL | Aliphatic compounds | - | - | 1.1 | |||
| MH | Monoterpene hydrocarbons | - | 0.1 | 41.3 | |||
| OM | Oxygenated monoterpene | 94 | 93.6 | 52.6 | |||
| SEH | Sesquiterpenes hydrocarbons | 1.6 | 2.2 | 2.8 | |||
| SEO | Sesquiterpenes oxygenated | 2.2 | 1.3 | 1.4 | |||
| TOTAL | 97.8 | 97.2 | 99.2 | ||||
* tr.: traces (% concentration ≤ 0.06%); [a] AL: aliphatic compounds; MH: monoterpene hydrocarbons; OM: oxygenated monoterpenes; PHP: phenylpropanoid compounds; SEH: sesquiterpene hydrocarbons; SEO: oxygenated sesquiterpenes; [b] identification based on standard solutions; [c] not detected; [d] The variables used to perform PCA and CA are highlighted in bold.
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Kakouri, E.; Daferera, D.; Andriopoulou, A.; Trigas, P.; Tarantilis, P.A. Evaluation of the Essential Oil Composition of Five Thymus Species Native to Greece. Chemosensors 2024, 12, 7. https://doi.org/10.3390/chemosensors12010007
AMA Style
Kakouri E, Daferera D, Andriopoulou A, Trigas P, Tarantilis PA. Evaluation of the Essential Oil Composition of Five Thymus Species Native to Greece. Chemosensors. 2024; 12(1):7. https://doi.org/10.3390/chemosensors12010007
Chicago/Turabian StyleKakouri, Eleni, Dimitra Daferera, Anastasia Andriopoulou, Panayiotis Trigas, and Petros A. Tarantilis. 2024. "Evaluation of the Essential Oil Composition of Five Thymus Species Native to Greece" Chemosensors 12, no. 1: 7. https://doi.org/10.3390/chemosensors12010007
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