Chemical Composition and Antibacterial Activity of Leaf Oil of Neolitsea foliosa (Nees) Gamble var. caesia (Meisner) Gamble

Abstract

The essential oil obtained by hydrodistillation of the leaves of Neolitsea foliosa var. caesia was analyzed by GC and GC/MS. Nineteen components comprising 90.6% of the oil were identified. The major components of the oil were β-caryophyllene (35.3%), caryophyllene oxide (9.6%), elemol (8.2%) and β-elemene (6.1%). The oil showed moderate antibacterial activity against most of the tested bacteria.

Key Word Index

Neolitsea foliosa var. caesia, Lauraceae, essential oil composition, β-caryophyllene, caryophyllene oxide, antibacterial activity.

Introduction

Neolitsea foliosa (Nees) Gamble var. caesia (Meisner) Gamble, belonging to die family Lauraceae is a tree widi long petioled, long acuminate, very glaucous leaves. It is distributed in the Western Ghats, Peninsular India and Malaysia and is common along streams on hills. The flowers are dioecious, in sub-sessile umbellules, arranged in clusters with small bracts at their base. The berries are globose, fruiting perianth radier large compared with berry. Flowering and fruiting usually occurs between September and December (1-4).

Essential oils from the leaf, seed, mesocarp and fruit of Neolitsea sericea (5-8) and leaf oil of N. zeylanica (9) have been studied. In diis communication, die chemical composition and antibacterial activity of the leaf oil oí Neolitsea foliosa var. caesia is reported for the first time.

Experimental

Plant Material: Fresh leaves of N. foliosa var. caesia were collected from die trees grown at the Tropical Botanic Garden and Research Institute (TBGRI) campus, Palode, Thiruvanandiapuram, Kerala, India in July 2005. The plant was identified by E. S. Santhosh Kumar, Technical Officer, Tropical Botanic Garden and Research Institute, and a voucher specimen (No. 51850) was deposited in die Herbarium of TBGRI (TBGT).

Oil Isolation: Fresh leaves were chopped and hydrodistilled for 4 h using a Clevenger-type apparatus. The oil was collected, dried over anhydrous sodium sulphate and stored at 4°C until analyzed.

GC/FID Analysis: The oil was analyzed by GC/FID using a Nucon 5765 series gas Chromatograph fitted with SE-30 (10%) Chromosorb-W packed stainless steel column (2 m ? 2 mm) with FID detector. Nitrogen was used as the carrier gas at flow rate of 40 mL/min. Oven program: 80°-150°C (8°C/min.), 150°-230°C (5°C/min), 230°C (10 min), injector temperature 220°C, detector temperature 250°C. Relative percentages of components were calculated from the peak area-percent report of volatiles from GC/FID data (Table I).

GC/MS Analysis: GC/MS analysis of the oil was performed by splidess injection of 1.0 µL of the oil on a Hewlett Packard 6890 gas chromatograph fitted with a cross-finked 5% PH ME siloxane HP-5 MS capillary column, 30 m x 0.32 mm, 0.25 µm coating thickness, coupled with a model 5973 mass detector. GC/MS operation conditions: injector temperature 220°C; transfer line 290°C; oven temperature program 60°-246°C (3°C/min); carrier gas - He at 1.4 mL/min. Mass spectra: Electron Impact (EI+) mode 70 eV, ion source temperature 250°C. Individual components were identified by Wiley 275.L database matching and by comparison of retention times and mass spectra of constituents with published data (10). Relative retention indices (RRI) of constituents were determined using n-alkanes as standards (11).

Antibacterial Assay of the Oil: Antibacterial activity of the oil was tested by the disc agar diffusion method (12,13). Gram-positive and Gram-negative bacterial strains were obtained from the Institute of Microbial Technology (IMTECH), Chandigarh, India as Microbial Type Culture Collection (MTCC) and were used for testing. These bacteria were grown on Mueller-Hint on agar medium (pH 7.2 -7.4). Microbial suspensions were then made from the agar plates using relevant broths. The agar media were poured into the plates to uniform depth of 5 mm and allowed to solidify. Then the microbial suspensions were streaked over the surface of media using a sterile cotton swab to ensure the confluent growth of the organism. Aliquots of 10 µL at 1:1, 1:2 and 1:3 dilutions of the oil in dimethyl sulfoxide (DMSO) were impregnated on Whatman No.1 filter paper discs of 6 mm size. These discs were then aseptically applied to the surface of the agar plates at well-spaced intervals. The plates were incubated at 36°C for 24 h and observed zones of inhibition were measured. Control discs impregnated with 10 µL of DMSO and streptomycin (1 mg/mL), reference for bacteria, were used alongside the test discs in each experiment. The results are presented in Table II.

Results and Discussion

Hydrodistillation of the fresh leaves of N. foliosa var. caesia afforded a yellow colored oil with pleasant aroma, yield 0.1% (v/w), d^sup 25^ = 0.907, [α])^sup 25^ = + 4.847, nD20 = 1.5001. Nineteen components constituting 90.6% of die leaf oil have been identified. The major constituents in die leaf oil were β-caryophyllene (35.3%) followed by caryophyllene oxide (9.6%), elemol (8.2%) and β-elemene (6.1%).