A Study of the Mediterranean Oregano Populations: Chemical Composition of Essential Oils of Origanum cordifolium Monbret et Aucher from Two Populations in Cyprus
Abstract
The seeds of two populations of oregano (O. cordifolium) harvested in Cyprus were sown at a research station in France. The resulting plants were planted in triplicate in a Fischer block design. The oils, which were produced by hydrodistillation, were analyzed by GC and GC/MS. The oils were found to be rich in α-terpineol (45.9-55.7%) of homogeneous composition irrespective of their origin or replicate.
Key Word Index
Origanum cordifolium, Lamiaceae, essential oil composition, α-terpineol, carvacrol, γ-terpinene.
Introduction
Ietswaart (1) drew up a detailed botanical classification of oregano species. The chemical compositions of several of Origanum species have been determined, e.g., Baser and Duman (2-9), Skoula et al. (10), Turnen et al. (11), Valentini et al. (12), Arnold et al. (13), Ravid and Putievsky (14), Akgiil and Bayrak (15), Fischer et al. (16), Vera and Chane-Ming (17), Pino et al. (18), Melegari et al. (19), Chalchat and Pasquier (20).
Origanum cordifolium is a very rare oregano found in a few parts of a mountainous massif in the west of Cyprus. It grows on stony soils in ravines, gorges and pinewood understories at altitudes between 500 m and 1500 m. In the wild it can reach a very large size but grows very slowly in the nursery. It is a prostrate creeper and is fragile, being prone to rot. In temperate climates it is sensitive to even mild winter conditions. It is weakly scented and finds use as an ornamental pot plant appreciated for its long drooping leafy stems ending in very lone inflorescences with large colored bracts.
Origanum cordifolium Monbret et Aucher was classified by letswaart (1) in the Amaracus section of Group A. The chemical composition of its oil was studied by Valentini et al. (12), who found α-terpineol, γ-terpinene and p-cymene as the main constituents. Other species belonging to the same sections and group have been studied: O. calcaratum L. and O. dictamnus L. by Skoula et al. (10), O. silymicum Davis and O. saccatum Davis by Turnen (11), and O. boissieri letswaart by Baser and Duman (2). In the oils of these species, p-cymene was present in large amounts (20-45%).
Here we report on the chemical composition of oils of O. cordifolium of Cypriot plant origin.
Experimental
Plant material: The seeds were harvested in the west of Cyprus near Roudia and Panagia in 1998. They were sown at the CNPPMAI botanical facility at Milly-la-Foret in March 1999, in three replicates in a Fischer block design. The plants were harvested in full flower, dried in the dark at ambient temperature in a ventilated room. A specimen was conserved in the CNPPMAI Herbarium.
Oil isolation: The isolation of oils was carried out at the CNPPMAI facility by use of a Clevenger-type hydrodistillation system for 3 h. The amount of material processed per distillation corresponded to a single plant when in sufficient quantity: if not, then the whole plant material of all the repeats or all the population was pooled.
GC: The gas phase chromatography analysis was carried out on a Delsi DI 200 instrument equipped with a flame ionization detector and a DBS 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. Quantitative data were obtained from FID areapercents without the use of correction factors.
GC/MS: The oils were analyzed on a Hewlett-Packard gas Chromatograph model 6890 coupled to a Hewlett-Packard MS model 5873 equipped with an HP5 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 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 (21), Mc Lafferty and Stauffer (22).
Results and Discussion
The yields of oils ranged from 2.1-3.4% of dry plant matter; their density and refractive index were approximately 0.950 g/mL and 1.486 g/mL, respectively. The analytical results are given in Table I. Seventy constituents were identified: 32 were quantified (greater than or equal to 0.1%), while the others were found only in trace amounts.
The oils produced from plants from the two locations, and corresponding to five replicates, had similar chemical compositions that showed the plants to be α-terpineol-type with α-terpineol content in the range 45.9-55.6%. Three other major constituents were carvacrol, γ-terpinene and p-cymene (6.2-13.8%, 6.0-9.0% and 3.2-5.8%, respectively). All the other constituents were present in very small amounts. The most abundant included monoterpenes, α-pinene (1.8-3.1%), camphene (2.6-4.2%), sabinene (1.5-2.1%), myrcene (1.2-2.0%) and limonene (1.5-2.1%), and monoterpenols, borneol (5.1-8.2%) and terpinen-4-ol (0.7-3.4%). The only quantifiable sesquiterpenes were β-caryophyllene and its oxide, and germacrene D. The proportions of the two most abundant components showed the oils to be of fairly uniform composition, with a slight predominance of carvacrol in batch 98-007-010 and of γ-terpinene in batch 98-006-007. Generally, α-terpineol was present in small amounts and in few species, e.g., O. majorana (0.6%) (6) and O. vulgare (0.1%) (19) and at slightly higher levels in O. majorana ssp. tennuifolium (7.1%) (23) and O. vulgare (9.3%) (24). However, it can be found in much larger amounts in O. vulgare and O. ramonense at 68% (19) and 42% (25), respectively. The combined presence of carvacrol, γ-terpinene and p-cymene is not surprising as they are linked by their biosynthetic pathways as studied by Croteau in Thymus vulgaris (26) and observed in O. gratissimum by Yayi (27).
This study reveals a marked uniformity in chemical composition in the two populations of O.cordifolium found in Cyprus. They are both rich in α-terpineol, but this feature is not specific as it is shared by O. vulgare and O. ramonense.
References
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