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Progress in Essential Oils: Thymol-rich Thymus vulgaris oils – Part 1

Oct 20th, 2017

Brian M. Lawrence, Consultant

It is well-known that various chemical forms or chemotypes are found in the oils of Thymus vulgaris L. However, the most commonly encountered oil form is that which is rich in thymol.

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It is well-known that various chemical forms or chemotypes are found in the oils of Thymus vulgaris L. However, the most commonly encountered oil form is that which is rich in thymol.

The composition of the oils of one of the clonal stock lines (a thymol-rich clone) of T. vulgaris grown in Sainte Fey (Quebec, Canada) was analyzed using GC/MS only by Bhaskara Reddy et al. (1998), and found to be as follows:

α-pinene (2.6%)

α-thujene (0.9%)

α-camphene (0.4%)

β-pinene (0.2%)

sabinene (0.1%)

δ-3-carene (7.1%)

myrcene (0.9%)

α-terpinene (0.4%)

limonene (1.2%)

1,8-cineole (1.1%)

γ-terpinene (0.2%)

p-cymene (20.8%)

terpinolene (0.2%)

p-cymenene (0.1%)

1-octen-3-ol (0.4%)

α-copaene (0.3%)

camphor (0.3%)

cis-p-menth-1-en-1-ol (0.2%)

linalool (13.3%)

β-caryophyllene (1.4%)

bornyl acetate (0.5%)

terpinen-4-ol (5.1%)

trans-p-menth-2-en-1-ol (0.2%)

isoborneol (0.4%)

verbenol^* (0.5%)

α-terpineol (2.5%)

α-muurolene (0.2%)

δ-cadinene (0.7%)

anethole^†(0.1%)

caryophyllene oxide (1.1%)

cumin alcohol^† (0.1%)

thymol (18.1%)

carvacrol (8.9%)

^*correct isomer not identified

^†incorrect identification or oil contaminant

Two commercial samples of thyme oil (T. vulgaris) that were purchased in Greece were found by Manou et al. (1998) to contain the following major constituents:

α-pinene (2.0–2.4%)

myrcene (1.2–1.5%)

p-cymene (23.1–28.7%)

γ-terpinene (5.9–9.1%)

linalool (5.1–5.8%)

thymol (38.6–43.0%)

carvacro l (2.2–9.8%)

β-caryophyllene (1.5–1.6%)

A number of oils obtained from T. vulgaris that were collected from different habitats in the Languedoc region (France) were determined by Thompson et al. (2003) to possess the following range of major constituents:

1,8-cineole (0–3.8%)

p-cymene (0–29.0%)

γ-terpinene (0–23.5%)

linalool (0.1–13.4%)

sabinene hydrate (0–3.3%)

terpinen-4-ol (0.1–5.0%)

α-terpineol (0–6.1%)

myrcen-8-ol (0–1.7%)

geraniol (0–8.9%)

thymol (21.4–72.9%)

carvacrol (0.8–26.8%)

β-caryophyllene (0.2–7.8%)

The thymol-rich chemotype of T. vulgaris that was collected in full flower from an experimental garden in Campinas (Brazil) was screened for its antimicrobial activity by Sartoratto et al. (2004). Analysis of this oil (produced in 0.56% yield) using GC-FID and GC/MS revealed that it possessed the following composition:

1-octen-3-ol (0.8%)

p-cymene (3.3%)

γ-terpinene (2.6%)

linalool (1.6%)

borneol (2.3%)

terpinen-4-ol (1.2%)

methyl thymol (0.8%)

thymol (79.2%)

carvacrol (4.6%)

β-caryophyllene (2.3%)

germacrene D (0.4%)

Seven commercially available thyme oils (T. vulgaris) from France and Italy were analyzed by GC-FID for known constituents. The constituents were found by Zamborelli et al. (2004) to quantitatively range as follows:

α-pinene (0.9–2.9%)

camphene (0.3–1.3%)

β-pinene (0.7–2.2%)

myrcene (1.2–2.4%)

δ-3-carene (0.5–2.0%)

p-cymene (21.5–44.9%)

limonene (0.5–1.3%)

γ-terpinene (0–17.3%)

linalool (1.9–3.7%)

borneol (0.6–2.2%)

terpinen-4-ol (0.6–4.5%)

thymol (22.1–38.5%)

carvacrol (1.1–1.9%)

β-caryophyllene (1.9–5.6%)

Dried thyme leaves (ex T. vulgaris) were purchased locally at a market in Davis (Northern California) and subjected to steam distillation under pressure for 3 hr. The oil, which was analyzed by a combination of GC-FID and GC/MS by Lee et al. (2005), was found to contain the following constituents:

α-terpinene (0.1%)

1,8-cineole (2.5%)

γ-terpinene (0.1%)

3-methyl-3-buten-1-ol^†(0.1%)

3-octanone (0.1%)

p-cymene (0.1%)

hexanol (0.2%)

(Z)-3-hexenol (0.1%)

cis-linalool oxide^f (0.2%)

1-octen-3-ol (0.5%)

trans-sabinene hydrate (0.3%)

trans-linalool oxide^f (0.2%)

camphor (1.5%)

linalool (4.8%)

terpinen-4-ol (1.1%)

menthol^† (0.1%)

trans-pinocarveol (0.1%)

δ-terpineol (0.4%)

trans-verbenol (0.1%)

α-terpineol (2.9%)

borneol (2.4%)

verbenone (0.9%)

dihydrocarveol (0.1%)

carvone (0.9%)

cis-linalool oxide^P (0.1%)

citronellol (0.1%)

p-methyl acetophenone^† (0.1%)

cumin aldehyde (0.1%)

myrtenol (0.1%)

(E)-anethole^† (0.3%)

trans-carveol (0.1%)

p-cymen-8-ol (0.5%)

geraniol (0.3%)

guaiacol^† (0.1%)

2-phenethyl alcohol^†(0.2%)

caryophyllene oxide (0.4%)

1,1-dimethyl-2-phenethyl alcohol^† (1.6%)

(E)-cinnamaldehyde^† (0.2%)

elemol^† (0.1%)

cuminyl alcohol^† (0.2%)

spathulenol (0.4%)

eugenol (0.9%)

thymol (85.5%)

carvacrol (6.8%)

α-eudesmol (0.1%)

δ-selinene^† (0.1%)

methyl jasmone^† (0.1%)

caryophylla-4(12), 8(13)-dien-5β-ol (0.1%)

dihydroactinodiolide^† (0.1%)

caryophylla-3, 8(13)-dien-5-ol^* (0.1%)

^*collect isomer not identified

^†incorrect identification or oil contaminant

^f = furanoid form

^P = pyranoid form

In addition, trace amounts (20.05%) of 1-penten-3-ol, (E)-2-hexenal, (E,Z)-2,4-heptadienal, (E,E)-2,4-heptadienal, methyl 2-methylbutyrate, 5,6-epoxy-(E)-β-ionone, butyric acid, octanoic acid, decanoic acid, terpinolene, trans-p-menth-2-en-1-ol, bornyl acetate, methyl carvacrol, exo-methylcamphenilol, cis-dihydrocarvone, terpinen-1-ol, lavandulol, p-mentha-1,8-dien-4-ol, exo-2-hydroxy-1,8-cineole, trans-piperitol, trans-linalool oxide pyranoid form, piperitenone, perillyl alcohol, viridiflorol, T-muurolol, isospathulenol, methyl eugenol, p-cresol, 5-isopropyl-3-methylphenol and dillapiole were also listed as being found in this oil. Many of these trace constituents listed by the authors have never been previously found in a thymol-rich T. vulgaris oil so their purported characterization requires corroboration.

Ground thyme leaves that were purchased from a Spanish market were homogenized and subjected either to simultaneous distillation-extraction using methylene chloride as the solvent, or supercritical fluid CO₂ extraction (for 25 mins at 40°C, 120 bar and CO₂ density of 0.72 g/mL). Both the oil and extract were analyzed using GC/MS and GC-FID by Diaz-Maroto et al. (2005). The respective compositions of the oil and extract can be seen in T-1.

An oil of Thymus vulgaris produced from Italian grown plants was analyzed by Tognolini et al. (2006) using GC-FID and GC/MS. It was found to possess the following composition:

tricyclene (0.1%)

α-thujene (0.6%)

α-pinene (2.3%)

camphene (1.8%)

β-pinene (0.6%)

3-octanone (0.6%)

3-octanol (0.3%)

myrcene (1.6%)

α-phellandrene (0.2%)

α-terpinene (1.6%)

p-cymene (15.3%)

limonene (2.0%)

1,8-cineole (1.9%)

(Z)-β-ocimene (0.1%)

(E)-β-ocimene (0.2%)

γ-terpinene (5.6%)

cis-sabinene hydrate (0.7%)

terpinolene (1.0%)

trans-sabinene hydrate (0.1%)

α-thujone^† (7.3%)

allo-ocimene^* (0.1%)

β-thujone^† (0.7%)

camphor (3.1%)

borneol (2.7%)

terpinen-4-ol (1.3%)

p-cymen-8-ol (0.1%)

α-terpineol (1.3%)

cis-dihydrocarvone (0.1%)

trans-dihydrocarvone (0.1%)

methyl thymol (0.6%)

methyl carvacrol (1.5%)

geraniol (8.3%)

geranial (0.6%)

bornyl acetate (0.8%)

thymol (6.8%)

carvacrol (8.0%)

α-terpinyl acetate (1.1%)

piperitenone oxide^† (0.1%)

geranyl acetate (3.9%)

β-bourbonene (0.1%)

isocaryophyllene^† (0.1%)

α-gurjunene^† (0.1%)

β-caryophyllene (3.2%)

β-humulene^† (1.5%)

allo-aromadendrene (0.2%)

γ-amorphene^† (0.3%)

viridiflorene^† (0.3%)

β-bisabolene (1.4%)

δ-amorphene^† (0.3%)

spathulenol (0.1%)

caryophyllene oxide (0.4%)

^†incorrect identification

Thymus vulgaris that was grown in the Botanic Garden of the University of Pécs (Pécs, Hungary) was harvested, air-dried and treated to hydrodistillation to produce an oil in 0.49% yield. Using GC-FID and GC/MS Horváth et al. (2006) determined that the oil possessed the following composition:

α-pinene (0.7%)

camphene (0.2%)

β-pinene (0.1%)

limonene (0.3%)

p-cymene (32.2%)

γ-terpinene (1.3%)

cis-linalool oxide^f (0.9%)

linalool (1.9%)

borneol (1.6%)

β-caryophyllene (0.7%)

thymol (45.6%)

carvacrol (4.6%)

caryophyllenol^* (1.2%)

^f = furanoid form

^*correct isomer not identified

An oil produced from Thymus vulgaris L. grown in Serbia was determined by Bozin et al. (2006) to possess the following composition:

α-pinene (0.2%)

camphene (0.4%)

β-pinene (0.2%)

p-cymene (0.8%)

limonene (0.2%)

1,8-cineole (1.9%)

γ-terpinene (8.3%)

2-nonanone (0.8%)

linalool (2.2%)

α-thujone (1.0%)

β-thujone (0.2%)

camphor (1.7%)

menthone (2.2%)

borneol (2.6%)

neomenthol (2.8%)

menthol (1.3%)

terpinen-4-ol (1.0%)

α-terpineol (0.6%)

pulegone (1.1%)

methyl thymol (0.3%)

piperitone (1.4%)

bornyl acetate (0.4%)

thymol (47.9%)

carvacrol (5.9%)

geranyl acetate (0.2%)

β-cubebene (3.4%)

β-caryophyllene (0.7%)

α-seliinene (0.3%)

γ-cadinene (0.5%)

myristicin^† (0.7%)

cis-calamenene (0.7%)

ledol(1.4%)

spathulenol (1.0%)

cadalene (1.8%)

apiole (0.4%)

^†incorrect identification or oil contaminant

As shown above,it would appear to this reviewer that the characterization of 2-nonanone, α-thujone, β-thujone, menthone, neomenthol, menthol, pulegone, piperitone, myristicin, ledol, cadalene and apiole may have arisen from some cross contamination either with the plant material or the oil as these are not normal constituents of thymol-rich oils of T. vulgaris.

Pavela (2007) screened the housefly against thyme oil. The oil used in this study possessed the following main components:

α-pinene (0.3%)

p-cymene (12.7%)

γ-terpinene (1.0%)

trans-sabinene hydrate (<0.1%)

linalool (4.3%)

α-terpineol (0.2%)

thymol (77.7%)

carvacrol (3.2%)

He found that thymol-rich T. vulgaris oil decreased the longevity of adult-flies and their larvae, as well as having a marked negative effect on the fecundity of both sexes. This means that the oil affected the reproduction cycle of adult flies and their larvae which would lead to a reduction of offspring when the oil was used.

An oil of T. vulgaris that was screened against two rice fungi by Nguefach et al. (2007) was determined to possess the following composition:

α-thujene (1.2%)

α-pinene (1.0%)

camphene (1.2%)

sabinene (0.4%)

β-pinene (0.3%)

myrcene (1.7%)

α-phellandrene (0.2%)

p-cymene (23.6%)

limonene (1.5%)

γ-terpinene (22.7%)

trans-sabinene hydrate (1.0%)

linalool (5.2%)

camphor (1.9%)

terpinen-4-ol (1.3%)

α-terpineol (0.3%)

thymol (27.2%)

carvacrol (3.3%)

β-caryophyllene (3.5%)

germacrene D (0.6%)

δ-cadinene (0.3%)

caryophyllene oxide (0.6%)

T-muurolol (0.4%)

T-cadinol (0.1%)

An oil of a thymol-rich clone of T. vulgaris produced from plants collected in Serbia was screened for its antibacterial activity (Sokovic et al. 2007) and antifungal activity (Sokovic et al. 2009). The oil was found to possess the following composition:

α-thujene (1.8%)

α-pinene (1.2%)

camphene (0.8%)

sabinene (0.6%)

β-pinene (0.4%)

myrcene (1.1%)

α-terpinene (0.7%)

p-cymene (19.0%)

limonene (0.5%)

1,8-cineole (0.7%)

(E)-β-ocimene (1.3%)

γ-terpinene (4.1%)

linalool (0.7%)

camphor (0.2%)

borneol (1.7%)

terpinen-4-ol (1.8%)

methyl thymol (0.2%)

methyl carvacrol (1.7%)

thymol (48.9%)

carvacrol (3.5%)

β-caryophyllene (3.5%)

α-humulene (0.3%)

germacrene D (0.3%)

α-cadinene (2.2%)

A sample of ground thyme (T. vulgaris) that was purchased in Poland was subjected to hydrodistillation to produce an oil that was analyzed using GC-FID and GC/MS by Kowalski and Wawrzkowski (2008). The constituents characterized in this oil were as follows:

α-pinene (0.8%)

camphene (0.6%)

sabinene (<0.1%)

myrcene (0.7%)

α-terpinene (0.8%)

p-cymene (22.3%)

1,8-cineole (0.7%)

γ-terpinene (3.6%)

linalool (2.5%)

camphor (0.5%)

borneol (1.5%)

terpinen-4-ol (0.7%)

methyl thymol (1.2%)

methyl carvacrol (0.8%)

piperitone (0.1%)

thymol (44.3%)

carvacrol (3.6%)

β-bourbonene (0.1%)

β-caryophyllene (2.2%)

(Z)-β-farnesene (<0.1%)

α-humulene (0.1%)

spathulenol (0.1%)

caryophyllene oxide (0.9%)

viridiflorol (0.3%)

humulene epoxide II (0.1%)

α-bisabolol oxide B^† (0.2%)

α-bisabolol oxide A^† (0.1%)

^†contaminant not a constituent of T. vulgaris oil

A thymol-rich commercial oil of T. vulgaris that was obtained in Germany which was analyzed by GC-FID and GC/MS, was determined by Stoilova et al. (2008) to contain the following constituents:

α-thujene (2.0%)

α-pinene (2.1%)

camphene (0.9%)

1-octen-3-ol (0.1%)

β-pinene (0.4%)

myrcene (1.7%)

α-phellandrene (0.2%)

p-cymene (16.4%)

α-terpinene (1.5%)

limonene (0.7%)

β-phellandrene (0.6%)

1,8-cineole (0.4%)

γ-terpinene (8.0%)

cis-sabinene hydrate (0.1%)

terpinolene (0.1%)

trans-sabinene hydrate (0.3%)

linalool (4.6%)

terpinen-4-ol (1.1%)

α-terpineol (0.5%)

methyl carvacrol (0.5%)

thymol (49.6%)

carvacrol (4.0%)

β-caryophyllene (0.1%)

α-humulene (0.1%)

δ-cadinene (0.1%)

caryophyllene oxide (0.1%)

spathulenol (0.1%)

In addition trace amounts (<0.05%) of 3-octanol, carvone and thymol acetate were also characterized in this oil.

An oil produced from the fresh leaves of T. vulgaris that was produced from plants collected in Petrópolis (Rio de Janeiro, Brazil) was the subject of analysis by Porte and Godoy (2008). The constituents characterized in this oil were:

1,3-octadiene^† (0.3%)

1,7-octadiene^† (0.1%)

2,4-dimethyl-2,4-heptadiene^† (1.5%)

α-pinene (0.8%)

camphene (0.3%)

sabinene (0.1%)

p-menth-1-ene^† (1.8%)

p-menth-3-ene^† (0.1%)

myrcene (2.4%)

α-phellandrene (0.3%)

α-terpinene (1.8%)

p-cymene (18.6%)

limonene (0.8%)

(Z)-β-ocimene (0.1%)

(E)-β-ocimene (0.1%)

γ-terpinene (16.5%)

p-mentha-3,8-diene^† (0.4%)

terpinolene (0.2%)

p-cymenene (0.1%)

borneol (0.5%)

trans-dihydrocarvone (0.2%)

methyl thymol (0.1%)

thymol (44.7%)

carvacrol (2.4%)

β-caryophyllene (0.8%)

δ-cadinene (0.1%)

^†incorrect identification or oil contaminant

Trace amounts of carvacrol and an isomer of calamenene were also found in this oil.

Thyme leaves ex T. vulgaris (presumed to be rich in thymol) were found by Wood et al. (2008) to contain 5 µg/kg of rotundone, a spicy compound with a low threshold.

A sample of thyme oil that was produced in the laboratory from commercially available thyme leaves (ex T. vulgaris) was examined by GC-FID and GC/MS (Chizzola et al. 2008). It was found to possess the following composition:

α-pinene (0.6%)

camphene (0.2%)

sabinene (0.2%)

β-pinene (0.5%)

myrcene (0.7%)

α-terpinene (1.1%)

p-cymene (13.1%)

limonene (0.4%)

1,8-cineole (0.6%)

γ-terpinene (5.6%)

cis-sabinene hydrate (0.5%)

linalool (2.2%)