Antimicrobial Activities of Essential Oils of Nepal

Journal of Essential Oil Research: JEOR, Jan/Feb 2005 by Yonzon, Minoba, Lee, Dong Jin, Yokochi, Toshihiro, Kawano, Yasuhiro, Nakahara, Toro

Abstract

The volatile components of two essential oils obtained from plants indigenous to Nepal, anthopogon (Rhododendron anthopogon) and Curcuma zedoaria oils, and four oils, chamomile (Chamomilla recutita), French basil (Ocimum basilicum), cornmint (Mentha canadensis) and palmarosa (Cymbopogon martini var. martini), which are exotic but produced in Nepal, were analyzed with GC/MS and the antimicrobial activity of all the six oils were examined using Petri plate-paper disk method. The microorganisms tested were Staphylococcus aureus (IFO14462), Corynebacterium amycolatum (IFO 15207), Escherichia coli (IFO 15034), Candida albicans (IFO 1594) and Aspergillus ochraceus (IFO 31221). Anthopogon oil contained δ-cadinene (11.4%) and Curcuma zedoaria oil contained 1,8-cineole (15.8%) and β-eudesmol (10.6%) as major volatile components. All of the examined oils indicated antimicrobial activity at similar levels to that of oils with the same designation previously reported. It was revealed that oils produced in Nepal be effectively applicable to a variety of uses in terms of antimicrobial activity,

Key Word Index

Rhododendron anthogon, Ericaceae, Curcuma zedoaria, Zingiberaceae, Chamomilla recutita, Asteraceae, Ocimum basilicum, Mentha canadensis, Lamiaceae, Cymbopogon martini var. martini, Poaceae, essential oil composition, δ-cadinene, (E)-β-farnesene, bisabol oxide A, linalool, menthone, menthol, geranyl acetate, geraniol, 1,8-cineole, β-eudesmol, antimicrobial activity.

Introduction

The Himalayan Region including Nepal is rich in diverse, traditional medical knowledge systems due to cultural and environmental diversity. It is estimated that at least 70% of the medicinal plants in the region consist of wild species. Eighty percent of the population in this mountain region still have to rely on traditional medicines for health care and treatment for several diseases. In Nepal, 30 species of indigenous Rhododendron have been found and five species including R. anthopogon extend throughout Nepal. One Rhododendron species (R. arhoreum Sm.) was designated as the national flower of Nepal in 1962 popularly known as "LaIi Guras" among Nepali. The fresh flower oilali Guras is believed to have the properties of dissolving fish-bones stuck in the throat. After establishment of Herbs Production & Processing Co. Ltd. in 1981 as an undertaking of HMG/Nepal, several companies have developed essential oils and medicinal extracts from indigenous plants like R. anthopogon and exotic conventional herbal materials like cornmint (Mentha canailensis), both of which have been well-received in the neighbouring countries and European market. Among the function of essential oils, antimicrobial activity is one of the most important properties. That is why many workers have reported the antimicrobial activities of the oils. However, such studies on Nepalese oils have been rarely reported. Thus, it is essential to study the quantitative antimicrobial activity of Nepalese oils against pathogen-related microorganisms.

The aims of present study is to measure the component of six oils produced in Nepal and evaluate the antimicrobial activity of the six oils against some microbes selected from some human and plant pathogens.

Experimental

Oil isolation and analysis: All six oils and two preparations were obtained from Herbs Production and Processing Co. Ltd. (Kathmandu, Nepal). Some of the main components like geraniol, menthol and 1,8-cineole were obtained from Wako Pure Chemical Ltd. (Tokyo, Japan).

Rhododendron anthopogon D. Don. and Curcunw zedoaria Roscoe are indigenous plants of Nepal. Anthopogon oil was obtained by steam distillation of the aerial parts of R. anthopogon. Curcuma zedoaria oil is obtained from the rhizomes of C. zedoaria through steam distillation.

The other remaining four oils are exotic varieties to Nepal. Chamomile oil was obtained from the flowers with stalks of Chamomilla recutita Rausch, through steam distillation. French basil oil was obtained by steam distillation of semi-wilted flowering tops of Ocimum bnsilicum L., a popular culinary herb. Cornmint oil was obtained by steam distillation of the aerial part of Mentha canadensis L. Palmarosa oil was obtained by steam distillation from freshly cut whole flowering plants of Cyinbopogon martinii var. martinii.

The volatile components of the six oils were analyzed by GC/MS (HP 6890/HP 5973, Hewlett-Packard, PaIo Alto, CA). EI electron impact ion source, 70 eV connected to HP-Innowax (50 m × 0.32 mm, 0.5 µm film thickness) capillary column. The samples dissolved in hexane were injected in split mode using pressure-controlled helium as carrier gas at a flow rate of 1.3 mL/min. Injection and detector temperatures were maintained at 250°C and interface temperature at 240°C, and the oven temperature was programmed at 70°-170°C at 13°C/min and 170°-230°C at 5°C/min. The components were identified with the comparison of mass spectra with library spectra and polar retention indices [Davies (1)].