Studies of Mediterranean Oregano Populations IX: Chemical Composition of Essential Oils of Seven Species of Oregano of Various Origins

Journal of Essential Oil Research: JEOR, Jul/Aug 2006 by Figuérédo, Gilles, Chalchat, Jean-Claude, Pasquier, Bernard

Abstract

The essential oils of seven species of oregano (Origanum vulgare L. ssp. gracile (Koch), Origanum acutidens (Hand.-Mazz.) Ietswaart, Origanum hypericifolium O. Schwarz et P.H. Davis, Origanum bargyli Mouterde, Origanum saccatum P.H. Davis, Origanum solymicum P.H. Davis, and Origanum leptocladum Boiss.) were studied by GC and GC/MS. Eighty-five constituents were identified. The discriminant components of these oils were p-cymene, γ-terpinene, cis- and trans-sabinene hydrate, borneol, terpinen-4-ol, α-terpineol, thymol, and carvacrol. Some of the species were similar to those described in the literature, and new chemotypes are reported.

Key Word Index

Origanum vulgare ssp. gracile, Origanum acutidens, Origanum hypericifolium, Origanum bargyli, Origanum saccatum, Origanum solymicum, Origanum leptocladum, essential oil composition, sabinene, p-cymene, γ-terpinene, cis-sabinene hydrate, trans-sabinene hydrate, bomeol, terpinen-4-ol, α-terpineol, thymol, carvacrol, chemotypes.

Introduction

The study concerns seven species of oregano of Mediterranean origin grown at the CNPPMAI facility (Forest of Fontainebleau) from seeds collected in identified populations. They had all been studied before (2-11) and can be grouped in the classification of letswaart (1).

The seven species were:

Origenum vulgare ssp.gracile of group C (Origanum section), originating from Munzu Dag (Turkey). This species, obtained from Turkey or conservatory-grown, was studied by Sezik et al. (2), Chalchat and Pasquier (3) and Melegari et al. (4). The oils examined by the first two authors were rich in hydrocarbons such as β-caryophyllene and germacrene D (2) or sabinene, (Z)-β-ocimene and germacrene D (3). The extract analyzed by Melegari et al. (4) was a thymol chemotype.

The six other species belonged to group A:

Origanum hypericifolium (Anatolicon section) harvested near Honaz Dag (Turkey). The oil of this species was studied by Baser et al. (5). It was found to contain mainly γ-terpinene, p-cymene and carvacrol, this last in large amounts (64.3%) before flowering, and in smaller amounts (33.9%) when in full flowering.

Origanum solymicum and Origanum saccatum (Amaracus section) came from Tahtali and Alanya (Turkey). Their oils, analyzed by Tümen et al. (6,7), were composed mainly of p-cymene (53.1% and 83.7%) along with borneol (7.2%) and thymol (9.3%) in O. solymicum.

Origanum leptoclatum, O. acutidens and O. bargyli (Brevifilamentum section) were studied by Baser (8-10). The oils of O. leptoclatum (8) and O. acutidens (9) contained mainly γ-terpinene (4.8-12.9%), p-cymene (48-20.7%), α-terpineol (10.8%) or borneol (9.5%), thymol (14.6%) orcarvacrol (14.7%). The oils of O. bargyli contained mainly p-cymene (14%) and carvacrol (66.3%). The taxa that we studied were from Ermenek, Erznacan and Osmaniye (Turkey).

Experimental

Plant material: The seeds were collected between 1997 and 1999 from their natural locations. They were planted and grown at the CNPPMAI facility, Milly-la-Forêt in March 1999. The plants were harvested when in full bloom. The plant material was dried at ambient temperature in the shade in a ventilated room, and separately isolated by water distillation using a Clevenger-type apparatus for 3 h. A voucher specimen of each taxon was conserved in the CNPPMAI Herbarium.

GC: The gas phase chromatography analysis was carried out on a Delsi DI 200 instrument equipped with a flame ionization detector and a DB-5 column (25 m x 0.25 mm, df: 0.25 µm) with a split flow rate of 60 mL/min, nitrogen as carrier gas and temperature programming (5 min at 50°C and 3°C/min up to 220°C, injector temperature 220°C and detector temperature 235°C.

GC/MS: The oils were analyzed using a Hewlett-Packard gas chromatograph Model 6890 coupled to a Hewlett-Packard MS Model 5873 equipped with an HP-5 column (30 m x 0.25 mm, df: 0.25 µm) programmed from 50°C (5 min) to 300°C at 5°C/min, and 5 min hold. The carrier gas was helium (1.0 mL/min), injection in split mode (1/10); injector and detector temperatures 250°C and 280°C, respectively. The MS ran in electron impact mode at 70 eV, electron multiplier 2200 V, ion source temperature 230°C. Mass spectral data were acquired in the scan mode in the m/z range 33-450.

Identification was carried out by calculating retention indices and comparing mass spectra with those in data banks: personal, Adams (12), Mc Lafferty and Stauffer (13).

Results and Discussion

The yields of oils ranged from 0.2-1.6% according to the species (Table I). In all, 85 compounds were identified by GC and GC/MS.

Oil of Origanum vulgare ssp. gracile was composed mainly of carvacrol (73.8%). Thymol was present in only trace amounts (0.6%). The most abundant minor constituents were p-cymene and γ-terpinene (5.4% and 4.6%). Of the remainder, only myrcene, methyl carvacrol and β-caryophyllene exceeded 1% (1.5%, 2.4% and 1.6 %, respectively). The oil analyzed differed from all the others described by the authors (2-4), in which the carvacrol levels ranged from 0.4-9.7%.