Composition and Antioxidant Activity of the Essential Oil of Thymus dreatensis from Algeria

Abstract

Thymus genus (Lamiaceae) has been found to possess significant biological activities, including antimicrobial, antioxidant, spasmolytic, antitussive, bronchiolitis, antifungal, sedative, and rubefaciant [1–16]. Twelve species are distributed in Algeria [7], nine of them endemic. In continuation of our works on Lamiaceae essential oils [8–11], we present here the essential oil composition and the antioxidant activity of the endemic species Thymus dreatensis Batt. Extraction. The hydrodistillation in a Clenvenger-type apparatus of the aerial parts of Thymus dreatensis yielded 2.1% of a pale yellowish oil. GC Analysis. GC analysis was performed on a Hewlett Packard 6890 gas chromatograph equipped with an FID and HP-5MS capillary column (bonded and cross-linked 5% phenylmethylpolysiloxane 30 m 0.25 mm, film thickness 0.25 m). Operating conditions were as follows: carrier gas He with a flow rate of 2 mL/min; column temperature 60–275 C at a rate of 4 C/min; injector temperature 280 C; injected volume 0.1 mL of the oil; split ratio 1:50. GC/MS Analysis. The oil was analyzed by GC/MS using a Hewlett Packard 6890 mass selective detector coupled with a Hewlett Packard 6890 gas chromatograph, equipped with a FID and HP-5MS capillary column (bonded and cross-linked 5% phenylmethylpolysiloxane 30 m 0.25 mm, film thickness 0.25 m), under the same conditions as GC (column, oven temperature, flow rate of carrier gas). The MS operating parameters were as follows: ionization potential 70 eV; ion source temperature 200 C; resolution 1000. Identification of Components. Essential oil components were identified based on their retention indices (determined with reference to a homologous series of normal alkanes) and by comparison of their mass spectral fragmentation patterns with those reported in the literature [12, 13] and with authentic compounds. Thirty-five components were identified, representing 97.4% of the total oil. The major constituents of the oil were thymol (28.1%), -terpinene (18.7%), thymyl methyl ether (10.9%), p-cymene (8.8%), and linalool (5.0%). Compared with our previously reported essential oils of T. ciliatus, T. fontanesii, and Thymus numidicus [1, 14–16] which were high-thymol chemotypes, it seems that the composition of the present essential oil is different. Nevertheless, -terpinene was also mainly found in T. fontanesii oil (15.9%) [14] (Table 1). Antioxidant Activity. The antioxidant activity was evaluated using the -carotene-linoleic acid test system [17, 18]. -Carotene (0.5 mg) in 1 mL chloroform was added to 25 L of linoleic acid and 200 mg of Tween 40 emulsifier mixture. After evaporation of chloroform under vacuum, 100 mL distilled water saturated with oxygen was added, followed by vigorous shaking. Then 4.0 mL of this mixture was transferred into different tubes containing different concentrations of the sample. As soon as the emulsion was added to each tube, the zero time absorbance was measured at 470 nm using a spectrophotometer. The emulsion system was incubated for 2 h at 50 C. A blank devoid of -carotene was prepared for background subtraction. Vitamin E was used as standard.