Essential oil composition of Thymus linearis (Benth) from western Himalaya of Uttrakhand, India

Rakesh K. Joshi^1,2

¹Department of Chemistry, DSB Campus Kumaun University Nainital, India, Pin-236001

²Department of Education, Government of Uttrakhand, India

*Corresponding Author E-mail: raakeshjoshi@rediffmail.com

ABSTRACT:

The chemical constituents from leaf essential oil of Thymus linearis Benth. was analyzed GC and GC-MS. The chemical composition of the isolated oil was characterized by 40 components. The major compounds were Thymol (40.50%), p-cymene (6.50%), thymol methyl ether (5.21%), p-cymen-8-ol (4.23 %) terpinen-4-ol (2.54%), linalool, germacrene D (2.50%) α–copaene (2.40), carvacrol methyl ether (2.26%) as major compounds.

KEY WORDS: Thymus lineari, GC–MS, thymol, thymol methyl ether.

1. INTRODUCTION:

Essential oils in plant are complex volatile mixtures exist at low concentrations and are commonly found in aromatic plants [1, 2]. Essential oils extracted from fresh leaves and flowers can be used as aroma additives in food, pharmaceuticals and cosmetics [3, 4]. Thyme (Thymus linearis L.) belonging to the lamiaceae family is a pleasant smelling perennial shrub, which grows in several regions in the world [5]. The genus Thymus L. (Lamiaceae), commonly known as ‘thyme’, consists of about 215 species of herbaceous perennial and sub-shrubs [6]. Thyme also possesses various beneficial effects as antiseptic, carminative, antimicrobial and ant oxidative properties [7]. Thyme also known as creeping thyme, mountain thyme and wild thyme a small shrubby plant with a strong spicy taste and order is extensively cultivated in Europe and US for culinary use. Thymol shows spontaneous contractile activity (SCA) of smooth muscle strips (SCA) from the stomach and vena portae of guinea pigs [8].

The genus is represented by two species, namely Thymus linearis (native) and Thymus serpyllum (exotic) in India. Thymus linearis is a rather variable species, widespread in the Himalayas and reaching its western extremities in Pakistan and Afghanistan [9]. Thyme is a well-known medicinal plant having diverse pharmacological properties, such as spasmolytic, antiseptic, antitussive, expectorant and antispasmodic activities. Recent studies have shown that they have strong antibacterial, antifungal, antiviral, antiparasitic and antioxidant activities [10-13]. The antiseptic, antioxidative, insecticidal, preservative and anaesthetic properties of thyme oil are mainly due to the presence of thymol, carvacrol, geraniol and other volatile components in the species of Thymus [14].

2. EXPERIMENTAL:

2.1 Plant collection and identification

The fresh aerial parts were collected from the Munsyari (Uttarakhand, India) at an altitude of 2700 m in the month of June in 2006 at mature stage. The identification was done from Botany Department, Kumaun University, Nainital and Botanical Survey of India, Dehradun. The voucher specimens (Phyto/06/04) have been banked in the Phytochemistry lab in the Chemistry Department, Kumaun University, Nainital.

2.2 Isolation of essential oil

The fresh plant materials (1.5 kg) were subjected to steam distillation using a copper electric still, fitted with spiral glass condensers. The distillates were saturated with NaCl and extracted with n-hexane and dichloromethane. The organic phase was dried over anhydrous sodium sulfate and the solvents were distilled off in a rotary vacuum evaporator at 30^oC and the percentage oil content was computed along the basis of fresh weight of plant materials.

2.3 GC and GC-MS analysis

The oils were analyzed by using a Nucon 5765 gas chromatograph (Rtx-5 column, 30 m × 0.32 mm, FID), split ratio 1: 48, N₂ flow of 4 kg/cm2 and on Thermo Quest Trace GC 2000 interfaced with MAT Polaris Q Ion Trap Mass spectrometer fitted with a Rtx-5 (Restek Corp.) fused silica capillary column (30 m × 0.25 mm; 0.25 µm film coating). The column temperature was programmed 60⁰-210⁰C at 3⁰C/min using He as carrier gas at 1.0 mL/min. The injector temperature was 210⁰C, injection size 0.1µL prepared in hexane, split ratio 1:40. MS were taken at 70 eV with a mass range of 40-450 amu.

2.4 Identification of the components

Identification of constituents was done on the basis of Retention Index (RI, determined with reference to a homologous series of n-alkanes (C9-C24, Polyscience Corp., Niles, IL) under identical experimental condition), co-injunction with standards (Sigma and known essential oil constituents (standard isolates), MS Library search (NIST and WILEY), by comparing with the MS literature data [15]. The relative amounts of individual components were calculated based on GC peak area (FID response) without using correction factor.

Table-1 Chemical components of leaf essential oil of T. linearis from Uttrakhand Himalaya

Sr. No.	Compounds	RI	% Composition (FID)	Mode of identification
1.	a-thujene	932	2.11	a,b
2.	a-pinene	939	1.77	a,b
3.	camphene	954	1.15	a,b
4.	sabinene	978	1.87	a,b
5.	b-pinene	981	1.50	a,b
6.	b-myrcene	994	0.23	a,b
7.	a-phellandrene	1006	0.14	a,b
8.	p-cymene	1028	6.50	a,b
9.	β-phellandrene	1037	1.20	a,b
10.	1, 8-cineole	1038	1.08	a,b
11.	(E)-β-ocimene	1050	1.10	a,b
12.	γ-terpinene	1065	0.74	a,b
13.	cis-sabinene hydrate	1069	1.04	a,b
14.	trans-sabinene hydrate	1069	1.06	a,b
15.	linalool	1104	2.50	a,b
16.	cis-p-menth-2-en-1-ol	1120	0.10	a,b
17.	trans-p-menth-2-en-1-ol	1145	1.10	a,b
18.	campor	1149	1.50	a,b
19.	pinocarvone	1160	0.25	a,b
20.	terpinen-4-ol	1175	2.54	a,b
21.	p-cymen-8-ol	1177	4.23	a,b
22.	thymol methyl ether	1226	5.21	a,b
23.	carvacrol methyl ether	1245	2.26	a,b
24.	thymol	1285	40.50	a,b
25.	α-copaene	1378	2.40
26.	β-elemene	1389	0.10	a,b
27.	(Z)--farnesene	1440	0.21	a,b
28.	(E)--farnesene	1459	0.50	a,b
29.	germacrene D	1482	2.50	a,b
30.	α-selinene	1498	0.60	a,b
31.	α-muurolene	1499	0.21	a,b
32.	γ-cadinene	1524	0.44	a,b
33.	germacrene D-4-ol	1574	0.05	a,b
34.	caryophyllene oxide	1581	0.16	a,b,
35.	humulene epoxide II	1606	0.14	a,b
36.	10-epi--eudesmol	1619	0.36	a,b
37.	γ-eudesmol	1630	0.40	a,b
38	epi--cadinol	1640	0.81	a,b
39.	cubenol	1645	0.30	a,b
40.	epi--bisabolol	1674	0.16	a,b
	Total		93.05

^*Mode of identification: Retention Index (LRI, Based on homologous series of n-alkenes; C₈-C₂₄), co injection with Standards/Peak enrichment with known oil constituents, MS (GC-MS), t= trace (<0.1%); (-) = not detected, RI: Literature value (Adams, 2003)

3. RESULTS AND DISCUSSION:

The oil yield obtained from leaves of was 0.40% (v/w). The chemical constituents present in the essential oil of T. linearis were identified by GC and GC-MS. Forty (40) compounds were characterized in the oil, accounting for 93.01% of the oil (Table 1). The major compounds were Thymol (40.50%), p-cymene (6.50%), thymol methyl ether (5.21%), p-cymen-8-ol (4.23 %) terpinen-4-ol (2.54%), linalool, germacrene D (2.50%) α–copaene (2.40), carvacrol methyl ether (2.26%) as major compounds. Literature survey of T. linearis revealed that thymol (52.28–66.65%), p-cymene (1.81–21.60%) and -terpinene (1.94–12.48%) were reported from samples collected from different region of Uttrakhand [16-17]. Thymus vulgaris L. volatile oil have been comparatively investigated – steam distillation and extraction with non-polar solvents - reflected in oil quality and in the pharmacological activity. The qualitative analysis was performed by high performance thin layer chromatography (HPTLC) and the quantitative analysis by gas chromatography (GC). The antioxidant potential was determined by phosphomolybdenum reduction assay and DPPH assay. Results show that the Thymus vulgaris used for the present study belongs to thymol chemotype. Volatile oil obtained by steam distillation contains high amounts of thymol and p-cymene [18]. This study is aimed at assessing the essential oil composition, total phenolic content, and antimicrobial and antioxidant activities of Thymus vulgaris collected in five different area of the Campania Region, Southern Italy. The oils were mainly composed of phenolic compounds, and all oils belonged to the chemotype thymol. The antimicrobial activity of the five oils was assayed against ten bacterial strains. The oils showed different inhibitory activity against some Gram-positive pathogens. The total phenol content in the essential oils ranged from 77.6–165.1 mg gallic acid equivalents (GAE)/g. The results reported here may help to shed light on the complex chemotaxonomy of the genus Thymus. These oils could be used in many fields as natural preservatives of food and as nutraceuticals [19].

4. CONCLUSIONS:

In conclusion we can that the thymus species is known for rich component as thymol. The present studies also show that the species collected from Munsyari has also the similar compounds but differ in percentage of compounds and vary some other compound in small amount. This may become the ultimate source of thymol for commercial utilization form Uttrakahnd.

5. ACKNOWLEDGMENT:

The author is grateful to Head of Department Chemistry, DSB Campus Nainital for GC-MS analysis.

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Received on 29.06.2016 Accepted on 19.07.2015

© Asian Pharma Press All Right Reserved

Asian J. Pharm. Tech. 2016; 6(4): 199-201.

DOI: 10.5958/2231-5713.2016.00029.5