Composition of the Essential Oils from Portuguese Thymus albicans Collected at Different Regions of Ria Formosa (Algarve)

Journal of Essential Oil Research: JEOR, Jul/Aug 2004 by Miguel, Maria G, Duarte, Fernanda, Venancio, Florencia, Tavares, Regina

Abstract

The chemical composition of the essential oils from the leaves and the flowers of Thymus albicans Hoffm. et Link collected at three regions of Algarve, south of Portugal, was analyzed by GC and GC/MS. The oils isolated from the flowers and the leaves were obtained in similar yields, 4.3% (v/w) and 4.2% (v/w), in the samples from Quinta do Lago, and 3.5% and 3.6%, in the samples from Ancao, respectively. In contrast, the oil yields from Gambelas ranged from 5.7%, in the leaf oils, to 9.2%, in the flower oils. The oils isolated from all samples of leaves and flowers were dominated by the oxygenated monoterpene 1,8-cineole (42.1-67.9%). In the samples collected at Quinta do Lago, high levels of linalool were also found (30.3-36.9%). The major monoterpene hydrocarbons in all samples were [alpha]-pinene (1.7-4.3%), sabinene (1.6-3.4%) and [beta]-pinene (2.6-4.9%). The concentrations of [alpha]-pinene (1.7-1.8%), camphene (0.2%) and [beta]-pinene (2.6-2.9%) in the samples from Quinta do Lago were in lower amounts than in the remaining samples. The most representative sesquiterpene hydrocarbons were [beta]-elemene (0.2-0.7%), [beta]-caryophyllene (0.1-0.8%) and [gamma]-cadinene (0.2-0.5%). The oxygenated sesquiterpene that was always present in higher amounts in the leaf oils than in the respective flower oils was viridiflorol (0.4-1.0%), the most important compound belonging to this fraction. The previous separation of the leaves and the flowers from this species evidenced the existence of quantitative differences in some components according to the plant part used. Still, for the same chemotype there were quantitative differences in some components, showing the existence of some variability demanding a more careful study to explain it.

Key Word Index

Thymus albicans, Lamiaceae, essential oil composition, 1,8-cineole, linalool.

Introduction

Thymus albicans Hoffm. et Link is an undershrub that grows up to 80 cm tall and generally blossoms from April to june. In Portugal, this aromatic plant is only found in a restricted area of Algarve, near the sea, in sandy soils, generally in open pinewoods. The chemical composition of Portuguese oils of T. albicans was described for the first time by Palhinha (1946) (1). It has subsequently been studied by other authors (2) who established the existence of several chemotypes according to the major components present in the oils. These authors all determined the oil composition from the whole aerial parts of the plant collected during the flowering phase. In the present work, the leaves and the flowers from T. albicans collected at three areas of Algarve, all from a protected region known as Ria Formosa, were separated and the respective oils isolated by hydrodistillation. The oil composition was established by GC and GC/MS.

Experimental

Plant material: The aerial parts oIThymus albicans were randomly collected at three regions of Algarve, south of Portugal, (Gambelas, Ancao and Quinta do Lago), during the flowering phase.

Isolation procedure: The oils were isolated from both the fresh leaves (30 g) and the fresh flowers (30 g) by hydrodistillation for 4 h using a Clevenger-type apparatus.

Gas chromatography: The gas Chromatographie analyses were performed using a Hewlett Packard 5890 Series II gas Chromatograph equipped with an FID, a data handling system and an OV-IOl fused silica column (30 m � 0.25 mm, film thickness 0.25 �m). Oven temperature was held at 70�C for 5 min and then programmed to 220�C at 2�C/min. Detector and injector temperatures were set at 260�C and 250�C, respectively. The carrier gas was helium and the working flow was 1 mL/min. The percentage composition of the oils was computed from the GC peak areas without using correction factors. The data shown are mean values of two injections.

Gas chromatography/mass spectrometry: The GC/ MS analyses were performed using a Perkin Elmer 8320 gas Chromatograph, equipped with a DB-5 fused silica column (30 m � 0.25 mm, film thickness 0.25 �m) and interfaced with a Finnigan MAT 800 Ion Trap Detector (ITD; software 4.1). Oven temperature was held at 70�C and programmed to 180�C at 3�C/min. Transfer line temperature, 250�C; ion trap temperature, 220�C; carrier gas, helium adjusted to a linear velocity of 30 cm/s; splitting ratio, 1:100; ionization energy, 70 eV; ionization current, 60 �A; scan range, 30-400 amu; scan time, 1 s. The identity of the components was assigned by comparison of their retention indices, relative to C^sub 8^-C^sub 21^ n-alkanes, and mass spectra with corresponding data of components from reference oils.

Results and Discussion

The main components and the oil yields of the flower and the leaf oils from T. albicans collected at Gambelas, Ancao and Quinta do Lago are listed in Table I. The oils isolated from the flowers harvested at Gambelas were obtained in higher yields (9.2%, v/w) than those isolated from the leaves (5.7%, v/w). The oil yields of the flowers and the leaves from Ancao were 3.5% (v/w) and 3.6% (v/w), respectively, while those obtained from the flowers and the leaves derived from Quinta do Lago were 4.3% (v/w) and 4.2% (v/w), respectively.