Comparative study of volatile compounds from genus Ocimum

American Journal of Applied Sciences, March, 2009 by S. Raseetha Vani, S.F. Cheng, C.H. Chuah

INTRODUCTION

The genus Ocimum is ranked high among some of the astonishing herbs for having enormous medicinal potentialities. Previous studies show that there are large numbers of species and varieties falls in this genus (1-5). Several authors recognize more than 60-150 species in the genus. Characterizations of each species in this genus (family Lamiaceae) are based on the leaves and habitat (1). The shape of the leaves in Ocimum Sanctum and its close relatives varies in size of leaves, vein and petioles. The colours of the leaves vary from bright green to dark green and sometime almost black. Though the colours in the plants vary, but the reason behind it, especially in basils, are not being studied yet. Regular occurrence of the interspecific hybridization within the genus, have created taxonomic challenges, leaving very little publications on basil taxonomy which follows the International Code of Botanical nomenclature (1), (2). Due to the difficulties in identifying the species, Massimo et al. (2004) has concluded that identification can be optimized by combined analysis of morphological traits, essential oil composition and molecular markers (2).

Essential oils are fragrant, highly concentrated essences of plants which are considered to exemplify the soul or life-force of the plant. Essential oils are approximately 75-100 times more concentrated than dried herbs (6). Essential oils are generally extracted by distillation, expression, solvent extraction, cold pressing, maceration or supercritical carbon dioxide extraction (7-9). It has been reported that the quality and quantity of essential oil produced by plants depends on various factors such as seasonal variation (10), method of harvest (11), leaf development stages (12), climate (13) and soil type (6), (13). Essential oil's combined effect, which depends on the desired application, is more powerful than that of individual oil. This is commonly known as a synergistic blend. Essential oil exhibits many usages such as in medicinal application (8), (14), herbs, culinary and are used as perfume for herbal toiletries, aromatherapy treatment (14) and also in perfume industry (8), (10). Ocimum Sanctum has been extensively used in Ayurvedic system of medicine for various ailments including capability lowering plasma glucose (15). Essential oils and herbal extracts have attracted a great deal of scientific research interest due to their potential as natural flavours. A scientifically based guide has been developed to assess the safety of naturally occurring mixtures based on chemical composition, particularly essential oils, for their intended use as flavor ingredients (16). This research reports the seasonal variation of essential oil composition of Ocimum Basilicum and Ocimum Sanctum.

MATERIALS AND METHODS

Climatic Conditions: Samples were collected 60.8 m above M.S.L, 3[degrees] 06'N and 101[degrees] 39'N (station: Petaling Jaya). The average temperature during the collection of Ocimum Basilicum is 27.3[degrees]C and varies from 26.4-29.1[degrees]C, with the highest (29.1[degrees]C) in July 2003. Meanwhile the average temperature is 28.2[degrees]C when collecting Ocimum Sanctum samples.

Materials: Samples of Ocimum Basilicum were obtained from housing area at Section 17 and SS3, Petaling Jaya. Ocimum Sanctum samples were collected from an orchard along Jalan Gasing, Petaling Jaya, Malaysia.

Isolation of essential oil: Oils were isolated from fresh leaves. The leaves were cut into small pieces and soaked in n-hexane for an hour and subsequently, filtered by gravity. The extracts were then subjected to further filtration by using a short column silica gel to remove impurities. The volatile constituents extracted are quantified using Gas Chromatograph equipped with Mass Spectrometry (GC-MS).

GC-MS Analysis: GC-MS analysis of the samples were carried out using Hewlett Packard HP 6890 Series Mass Selective Detector, equipped with a cross linked methyl silicone gum phase capillary column (25m x 0.32mm). Helium was used as the carrier gas and the temperature programming was set with initial oven temperature at 40[degrees]C and held for 3 min and the final temperature of the oven was 280[degrees]C with rate at 10[degrees]C [min.sup.-1]. A 2 [mu]L sample was injected with splitless mode. Mass spectra were recorded over 35-650 amu range with electron impact ionization energy 70 eV. The total running time for a sample is 45 min.

Identification of essential oil constituents: The chemical components from the essential oil were identified by comparing the retention times of chromatographic peaks with those of authentic compounds run under identical conditions, by comparison to relative retention indices. Quantitative determinations were made by relating respective peak areas to TIC areas from the GC-MS. Qualitative and quantitative analysis were carried out to determine the concentration of the essential oils.

RESULTS AND DISCUSSION

GC-MS Analysis: The essential oils of Ocimum Sanctum and Ocimum Basilicum were subjected to detailed GC-MS analysis in order to determine the impact of the locality and seasonal variations on their volatile constituents. The yield of oils ranged from 0.4-1.7%. Exactly 15 compounds were identified in Ocimum Basilicum (Table 1) meanwhile 16 compounds were identified in Ocimum Sanctum leaves (Table 2).