Origanum vulgare: drying, oregano oil yield and carvacrol

Origanum vulgare L. is a name of rank “Species” with status “Accepted” in the World Checklist of Vascular Plants (WCVP, Kew), placed in the family Lamiaceae (identifier 143954), in the extract read on 27/10/2026.

According to the Plants of the World Online (POWO, Kew) entry for the taxon “Origanum vulgare L.”, the native range of the species is “Macaronesia to China”. The same entry describes Origanum vulgare as “a perennial” that grows “primarily in the temperate biome”.

Which oregano material did Caputo et al. (2022) study?

According to Caputo et al. (2022), the aerial parts of “O. vulgare L.” studied (20 kg; WCVP accepted name: Origanum vulgare L.) were collected in July 2020. The species was identified by Prof. V. De Feo, and a voucher specimen labelled DF/2020/311 was deposited in the herbarium of the Medical Botany Chair of the University of Salerno.

How was the oregano dried in Caputo et al. (2022)?

The collected plant material was divided into several parts: one was characterized as fresh material (control), and the others were dried by convective methods (shade drying, CONV1; hot-air convective drying, CONV2), by assisted microwave heating at different operating conditions (MW1, MW2, MW3) and by osmotic treatment (semi-dry technique, OT). In Table 2, CONV1 is shade drying in a shady room for 5 days; CONV2, hot-air drying in a static oven at 50 °C for 24 h; MW1, MW2 and MW3, assisted microwave heating at 2300 W for 10 min, 1150 W for 15 min and 460 W for 35 min; OT, osmotic treatment; the untreated aerial parts are the fresh material. For shade drying (CONV1), the aerial parts, covered with filter paper (aerated shady conditions), were laid on a flat surface as a batch a few centimetres thick and left to dry at room temperature (25 ± 5 °C) for 5 days. Microwave drying of the oregano was performed at an operating frequency of 2450 MHz. The maximum temperatures reached on the oregano surface, measured during microwave irradiation, were in the range 55–70 °C (hot-spot values); the sentence that gives this range does not distinguish MW1, MW2 and MW3. For the osmotic treatment (OT), ten kilograms of aerial parts were washed by 15 s immersion in a chloride solution (100 ppm), rinsed and dried by centrifugation at 700 rpm, then cut, mixed with a solution of 20% sodium chloride and 1.2% citric acid, and macerated for 20 min at room temperature.

What moisture content did the oregano have before and after drying?

According to Caputo et al. (2022), the fresh oregano had a moisture content of approximately 70% (w/w). The shade-dried (CONV1) and hot-air-dried (CONV2) batches had residual humidity values of 37 and 5.3% (w/w), after 5 days at room temperature and 24 h at 50 °C respectively. In the batches heated by microwave at 2300 W for 10 min (MW1), 1150 W for 15 min (MW2) and 460 W for 35 min (MW3), the water contents were 8.6, 7.5 and 12.3% respectively. The residual moisture content after the osmotic treatment was 48.5%.

How was the oregano oil obtained, and what yields did Caputo et al. (2022) report?

The fresh and treated aerial parts of “O. vulgare L.” were ground and then hydrodistilled according to the standard procedure of the European Pharmacopoeia, until no significant increase in the volume of essential oil collected was observed (3 h). In Table 1, the yield (“Yield”), in %, is 0.2 ± 0.0 for the fresh material, 0.7 ± 0.0 (CONV1), 0.4 ± 0.0 (CONV2), 0.1 ± 0.0 (MW1), 0.2 ± 0.0 (MW2), 2.2 ± 0.0 (MW3) and 0.0 ± 0.0 (OT).

How were the oregano oils analysed, and how many constituents were identified?

The oils were analysed by GC-FID and GC–MS. Altogether, 39 constituents were identified across the essential oils of the fresh material and of the six dried samples. Only 15 components were found in the essential oil obtained from the fresh sample.

How much carvacrol did the oregano oils contain in Caputo et al. (2022)?

In Table 1, “Carvacrol” is given, as mean percentage ± standard deviation of three determinations, at 67.8 ± 0.5 (fresh), 73.9 ± 0.6 (CONV1), 76.1 ± 0.6 (CONV2), 68.6 ± 0.4 (MW1), 81.4 ± 0.6 (MW2), 74.5 ± 0.4 (MW3) and 56.2 ± 0.3 (OT). According to the authors, carvacrol (56.2 to 81.4%) was the main constituent in all samples. Compared with the fresh sample, carvacrol increased with all drying methods (p < 0.0001) except OT, where a significant decrease (p < 0.0001) was observed; the values compared are percentages in the oil.

How did p-cymene, γ-terpinene and the pinenes vary between the oregano oils?

In Table 1, as mean percentage ± standard deviation of three determinations, “p-Cymene” reads 17.7 ± 0.2 (fresh), 14.1 ± 0.2 (CONV1), 10.2 ± 0.1 (CONV2), 16.9 ± 0.1 (MW1), 1.6 ± 0.2 (MW2), 6.1 ± 0.3 (MW3) and 6.5 ± 0.3 (OT). On the same basis, “γ-Terpinene” reads 5.8 ± 0.1 (fresh), 2.8 ± 0.1 (CONV1), 1.1 ± 0.2 (CONV2), 3.7 ± 0.3 (MW1), 0.8 ± 0.0 (MW2), 2.4 ± 0.09 (MW3) and 14.2 ± 0.3 (OT). “α-Pinene” reads 2.1 ± 0.1 (fresh), 1.4 ± 0.2 (CONV1), 0.5 ± 0.0 (CONV2), 0.9 ± 0.0 (MW1), 0.1 ± 0.0 (MW2), 0.2 ± 0.0 (MW3) and 1.1 ± 0.1 (OT). “β-Pinene” reads 0.7 ± 0.0 (fresh), 0.4 ± 0.0 (CONV1), 0.3 ± 0.0 (CONV2), 0.4 ± 0.0 (MW1), 0.1 ± 0.0 (MW2), 0.3 ± 0.0 (MW3) and 2.1 ± 0.2 (OT). According to the authors, the major differences between fresh and dried samples concern α-pinene (0.1–2.1%), p-cymene (1.6–17.7%) and γ-terpinene (0.8–14.2%), present in lower percentages in almost all dried samples than in the fresh material (p < 0.0001); γ-terpinene, on the other hand, was present in higher amounts after osmotic treatment (OT) than in the fresh sample (p < 0.0001).

Which other compounds did Table 1 of Caputo et al. (2022) report in the oregano oils?

In Table 1, as mean percentage ± standard deviation of three determinations, “δ-2-Carene” reads 1.1 ± 0.1 (fresh), 0.7 ± 0.0 (CONV1), “t” (trace, < 0.1%) (CONV2), 0.6 ± 0.1 (MW1), 0.1 ± 0.0 (MW2), 0.5 ± 0.0 (MW3) and 2.0 ± 0.1 (OT). On the same basis, the compound the table writes “Thymol, methyl ether” (the abstract writes “thymol methyl ether”) reads 0.6 ± 0.0 (fresh), 0.4 ± 0.0 (CONV1), 0.5 ± 0.1 (CONV2), 0.9 ± 0.1 (MW1), 1.8 ± 0.3 (MW2), 1.2 ± 0.1 (MW3) and 0.9 ± 0.1 (OT). “Caryophyllene”, as the table writes it, reads 1.3 ± 0.2 (fresh), 1.3 ± 0.2 (CONV1), 1.5 ± 0.4 (CONV2), “–” (not detected) (MW1), 1.3 ± 0.0 (MW2), 2.2 ± 0.2 (MW3) and 2.3 ± 0.1 (OT). The compound the table writes “Isocaryophillene” (the text of the article writes “iso-caryophyllene”) reads “–” (not detected) (fresh), 0.1 ± 0.0 (CONV1), 0.1 ± 0.0 (CONV2), 2.4 ± 0.3 (MW1), 1.4 ± 0.1 (MW2), 0.1 ± 0.0 (MW3) and 1.2 ± 0.1 (OT). The compound the table writes “Aromandrene” (the text of the article writes “aromadendrene”) reads “–” (not detected) (fresh), 0.6 ± 0.1 (CONV1), 0.7 ± 0.0 (CONV2), 0.2 ± 0.0 (MW1), 1.4 ± 0.1 (MW2), 1.0 ± 0.1 (MW3) and 1.7 ± 0.1 (OT). “1,8-Cineole” is marked “–” (not detected) in the fresh, CONV1, CONV2 and MW1 samples, and reads 0.2 ± 0.0 (MW2), 0.5 ± 0.0 (MW3) and 1.1 ± 0.1 (OT). According to the authors, isoborneol was present in higher amounts in the shade-dried and hot-air-dried samples (CONV1 and CONV2) than in the fresh sample (p < 0.0001 for CONV1 and p < 0.01 for CONV2).

References

• Govaerts R. (ed.), World Checklist of Vascular Plants (WCVP), Royal Botanic Gardens, Kew — https://sftp.kew.org/pub/data-repositories/WCVP/wcvp.zip
• Caputo L., Amato G., de Bartolomeis P., De Martino L., Manna F., Nazzaro F., De Feo V., Barba A.A., « Impact of drying methods on the yield and chemistry of Origanum vulgare L. essential oil », Scientific Reports 2022;12:3845, doi:10.1038/s41598-022-07841-w — https://www.ebi.ac.uk/europepmc/webservices/rest/PMC8907181/fullTextXML
• Plants of the World Online (POWO), Royal Botanic Gardens, Kew, taxon page « Origanum vulgare L. », archived copy of 18/10/2026 (Internet Archive) — https://web.archive.org/web/20261018213555id_/https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:453395-1