THYME ‘LINALOOL’ Thymus vulgaris L.

What do Najar et al. (2021) document about the ‘linalool’ chemotype of thyme?

In the World Checklist of Vascular Plants (WCVP, Kew), extract read on 21/09/2026, Thymus vulgaris L. is a name of rank “Species” with the status “Accepted”, in the family Lamiaceae (identifier 205645). Najar et al. (2021) carried out a three-year field experiment (2017–2019) on an experimental field in the inland hilly area of the Pisa Province, “southern Tuscany”, Italy (Santa Luce, 43°28′42″ N, 10°32′42″ E; 160 m above sea level, slope 15 %). In the essential oil of the ‘linalool’ chemotype obtained by hydrodistillation in 2017, they measure a relative abundance of Linalool of 75.9 ± 0.96 %. In the same oil, the class “Oxygenated Monoterpenes” accounts for 90.2 ± 0.45 %.

How was the thyme grown in the study?

According to the authors, the study is part of a larger project carried out in an organic farm, where aromatic crops (lavender, lavandin, oregano and thyme) are produced according to the biodynamic production method, “subject to Regulation EC n. 834/2007 and Regulation EC n. 848/2018”; the experimental site was converted to organic production management in 2015. The plants were purchased from a local nursery specialising in aromatic and medicinal plants, with organic certification: well-rooted plantlets (10 cm high) obtained from stem cuttings “to avoid plant genetic variability […]”, planted with an inter-row spacing of 1.70 m and an intra-row spacing of 0.20 m. The thyme was planted in November 2016 with a semi-automatic transplanter, and the source writes: “The area was divided in two plots of 2300 m2 for each chemotype.” The plants of the ‘linalool’ chemotype were harvested at the full flowering stage (75 % of inflorescences open) on 11 May 2017, 24 April 2018 and 31 May 2019, the 1st, 2nd and 3rd years after planting.

What did the authors measure on the plants?

The parameters evaluated were the percentage of flowering plants, plant height (cm), the fresh and dry yield of above-ground biomass (Mg ha−1) and the essential oil content (%); dry weight was measured after drying the samples in a ventilated oven at 40 °C until constant weight. In the 1st year (harvest of 11 May 2017), Table 1 gives for the ‘linalool’ chemotype (mean ± SD) a plant density of 2.72 ± 0.15 plants m−2, a plant height of 11.20 ± 0.15 cm, and a total above-ground biomass of 0.23 ± 0.01 Mg FW ha−1 (fresh weight) and 0.07 ± 0.01 Mg DW ha−1 (dry weight). In the 2nd year (harvest of 24 April 2018), the same table gives a plant density of 2.16 ± 0.45 plants m−2, a plant height of 17.15 ± 2.92 cm, and a total above-ground biomass of 1.24 ± 0.39 Mg FW ha−1 and 0.45 ± 0.04 Mg DW ha−1. In the 3rd year (harvest of 31 May 2019), it gives a plant density of 2.94 ± 0.01 plants m−2, a plant height of 22.2 ± 0.69 cm, and a total above-ground biomass of 6.11 ± 0.55 Mg FW ha−1 and 2.94 ± 0.22 Mg DW ha−1.

How were the essential oils obtained?

Hydrodistillation (HD), 2017 to 2019

The essential oils were obtained by hydrodistillation (HD) in a Clevenger apparatus: 50 g of the dried aerial parts of each chemotype were hydrodistilled for 2 h at 100 °C according to the method reported in the European Pharmacopoeia, in triplicate for each of the three years of collection. The essential oil yield was determined as the ratio between the weight of oil obtained and the weight of plant material used; the oil was dehydrated over anhydrous sodium sulphate and, in the words of the source, “stored in a small opaque flask at 4 °C in freezer at 4 °C and far from light sources until their analyses”. For the ‘linalool’ chemotype, Table 1 gives an essential oil content of 2.80 ± 0.23 % on dry weight in the 1st year (2017), a value the authors place under hydrodistillation. In the 2nd year (2018), the same table gives 1.20 ± 0.08 % on dry weight, also under hydrodistillation.

Steam distillation (SD), 2018 and 2019

Steam distillation (SD) was performed in 2018 and 2019 from all the aerial parts of the two chemotypes, slightly dried outdoors under cover, each distillation lasting 2 h; according to the authors, it was not possible in 2017, given the low quantity of plant material in the first year and the unavailability of the stainless-steel distiller, purchased in the second year of the project.

How were the oils analysed?

The oils were analysed by gas chromatography–electron ionisation mass spectrometry (GC–EIMS) with an ion-trap mass detector: oven programmed from 60 °C to 240 °C at 3 °C/min, injector at 220 °C, transfer line at 240 °C, helium carrier gas at 1 mL/min, injection of 1 μL (5 % n-hexane solution), split ratio 1:30, full scan from 35 to 400 amu. The constituents were identified by comparing their retention times with those of authentic samples, and their linear retention indices (relative to the series of n-alkanes) and mass spectra with those of commercial libraries and of a laboratory-built library.

Which compounds does the ‘linalool’ oil contain?

The values below come from Table 5 of the study, “Essential oil composition of the Thymus vulgaris ‘linalool’ chemotype”: relative abundance (%), by procedure and by year.

Linalool and Linalyl acetate

Najar et al. (2021) measure a relative abundance of Linalool of 75.9 ± 0.96 % by hydrodistillation in 2017, 75.0 ± 1.20 % by hydrodistillation in 2018 and 70.2 ± 2.30 % by hydrodistillation in 2019, and of 64.0 ± 1.02 % by steam distillation in 2018 and 71.4 ± 1.27 % by steam distillation in 2019. They measure a relative abundance of Linalyl acetate of 9.3 ± 0.64 % by hydrodistillation in 2017, 6.5 ± 1.04 % by hydrodistillation in 2018 and 10.3 ± 1.70 % by hydrodistillation in 2019, and of 11.5 ± 0.70 % by steam distillation in 2018 and 10.2 ± 1.58 % by steam distillation in 2019.

Other oxygenated monoterpenes

The relative abundance of Camphor is 2.7 ± 0.45 % by hydrodistillation in 2018 and 2.6 ± 0.06 % by hydrodistillation in 2019, and 2.2 ± 0.08 % by steam distillation in 2018 and 2.5 ± 0.09 % by steam distillation in 2019.

The relative abundance of α-Terpineol is 1.7 ± 0.19 % by hydrodistillation in 2017, 1.4 ± 0.03 % by hydrodistillation in 2018 and 2.0 ± 0.16 % by hydrodistillation in 2019, and 2.0 ± 0.18 % by steam distillation in 2019.

The relative abundance of Borneol is 1.2 ± 0.20 % by hydrodistillation in 2018 and 1.0 ± 0.08 % by steam distillation in 2018.

The relative abundance of Geranyl acetate is 1.1 ± 0.09 % by hydrodistillation in 2017 and 1.3 ± 0.06 % by hydrodistillation in 2019, and 1.3 ± 0.08 % by steam distillation in 2019.

Thymol, Carvacrol and Carvacrol acetate

In the oil obtained by steam distillation in 2018, the relative abundance of Thymol is 4.1 ± 0.14 %; the table shows “-” in the other four columns. In the same oil (steam distillation, 2018), the relative abundance of Carvacrol is 1.5 ± 0.14 %. In that oil (steam distillation, 2018), the relative abundance of Carvacrol acetate is 1.6 ± 0.07 %.

Camphene, β-Caryophyllene, Germacrene D and Caryophyllene oxide

The relative abundance of Camphene is 1.0 ± 0.07 % by hydrodistillation in 2019, and 1.1 ± 0.07 % by steam distillation in 2018 and 1.0 ± 0.05 % by steam distillation in 2019.

The relative abundance of β-Caryophyllene is 3.7 ± 0.25 % by hydrodistillation in 2017, 3.2 ± 0.53 % by hydrodistillation in 2018 and 3.7 ± 0.31 % by hydrodistillation in 2019, and 4.7 ± 0.30 % by steam distillation in 2018 and 2.8 ± 0.26 % by steam distillation in 2019. The relative abundance of Germacrene D is 1.5 ± 0.11 % by hydrodistillation in 2017 and 1.8 ± 0.23 % by steam distillation in 2018.

The relative abundance of Caryophyllene oxide is 1.4 ± 0.10 % by hydrodistillation in 2019 and 1.2 ± 0.13 % by steam distillation in 2019.

How do the classes of compounds compare across procedures and years?

In the oil obtained by hydrodistillation in 2017, the authors count 26 identified “picks”; Monoterpene Hydrocarbons account for 2.3 ± 0.10 %, Oxygenated Monoterpenes for 90.2 ± 0.45 %, Sesquiterpene Hydrocarbons for 5.3 ± 0.38 %, Oxygenated Sesquiterpenes for 1.2 ± 0.20 % and Non-terpene derivatives for 0.4 ± 0.01 %, for a total identified of 99.4 ± 0.60 % (relative abundance). In the oil obtained by hydrodistillation in 2018, they count 28 identified “picks”; Monoterpene Hydrocarbons account for 3.6 ± 0.50 %, Oxygenated Monoterpenes for 89.3 ± 0.76 %, Sesquiterpene Hydrocarbons for 4.4 ± 1.04 %, Oxygenated Sesquiterpenes for 1.4 ± 0.63 % and Non-terpene derivatives for 0.6 ± 0.04 %, for a total identified of 99.3 ± 0.70 %. In the oil obtained by hydrodistillation in 2019, they count 29 identified “picks”; Monoterpene Hydrocarbons account for 2.1 ± 0.09 %, Oxygenated Monoterpenes for 90.0 ± 0.96 %, Sesquiterpene Hydrocarbons for 4.8 ± 0.65 %, Oxygenated Sesquiterpenes for 2.3 ± 0.13 % and Non-terpene derivatives for 0.8 ± 0.20 %, for a total identified of 99.4 ± 0.60 %. In the oil obtained by steam distillation in 2018, they count 30 identified “picks”; Monoterpene Hydrocarbons account for 3.2 ± 0.27 %, Oxygenated Monoterpenes for 88.2 ± 1.14 %, Sesquiterpene Hydrocarbons for 6.9 ± 0.06 %, Oxygenated Sesquiterpenes for 0.9 ± 0.08 % and Non-terpene derivatives for 0.7 ± 0.03 %, for a total identified of 99.9 ± 0.10 %. In the oil obtained by steam distillation in 2019, they count 24 identified “picks”; Monoterpene Hydrocarbons account for 2.0 ± 0.12 %, Oxygenated Monoterpenes for 90.6 ± 0.29 %, Sesquiterpene Hydrocarbons for 3.6 ± 0.37 %, Oxygenated Sesquiterpenes for 1.9 ± 0.03 % and Non-terpene derivatives for 0.7 ± 0.07 %, for a total identified of 98.8 ± 1.20 %.

Where is the ‘thymol’ chemotype covered?

The ‘thymol’ chemotype has its own page: ‘thymol’ chemotype.

⚠️ Important Precautions

Precautions for this plant are being verified against sources; their absence here does not mean there are none.

References

• Govaerts R. (ed.), World Checklist of Vascular Plants (WCVP), Royal Botanic Gardens, Kew — https://sftp.kew.org/pub/data-repositories/WCVP/wcvp.zip
• Najar B., Pistelli L., Ferri B., Angelini L.G., Tavarini S., « Crop Yield and Essential Oil Composition of Two Thymus vulgaris Chemotypes along Three Years of Organic Cultivation in a Hilly Area of Central Italy », Molecules 2021;26(16):5109, doi:10.3390/molecules26165109 — https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pmc&id=8398316