Chemical Composition of the Needle-Twig Oils of Pinus brutia Ten.

Journal of Essential Oil Research: JEOR, Jul/Aug 2006 by Ghosn, Marwan W, Saliba, Najat A, Talhouk, Salma Y

Abstract

The variation in composition of the essential oils produced from different ratios of needles to terminal twigs of Pinus brutia Ten. in Lebanon was examined by GC and GC/MS. As the mass of the needles increased from 0-100% with respect to twig contents, the % oil yield decreased and the composition changed. Pure needle oil was found to be much richer in oxygenated compounds than that of pure twig oil with a corresponding reduction in amounts of monoterpene hydrocarbons. Marker compounds were chosen in order to show the chemical variation of the oils with respect to different ratio of needles to twigs distilled. By computing both physical and chemical variations, it is suggested that a fair compromise between the yield and the concentration of oxygenated compounds is the 75% needle 25% twig mixture, which appears to be the most suitable proportion of plant material for pine oil production from P. brutia.

Key Word Index

Pinus brutia, Pinaceae, essential oil composition, α-pinene, β-pinene, δ-3-carene, limonene, germacrene D.

Introduction

Pinus brutia grows naturally, abundantly and strictly in the eastern Mediterranean region extending over from Greece to Lebanon and Iraq. The chemical composition of various Pinus species oils have been the subject of numerous studies. However, work has been focused on North American and Western European species and only a restricted number of chemically oriented articles dealt with the oils of Mediterranean pine species. The chemical composition of P. hrutia oil (100% twigs or needles) has been evaluated in few places such as Greece, Italy and Morocco (1-5). Studies have pointed out the high β-pinene content of the oil of P. hrutia that characterizes it with respect to other species ( 1,2,4,6-9). This study investigates the variation of the oils from 00, 25,50, 75 and 100% w/w needles to terminal twigs of P. hrtitia in Lebanon with respect to the yield and chemical composition.

Experimental

Plant material and oil isolation: Twenty five mature samples of P. hrutia were randomly collected from a natural population located in Deir-Nbouh, North of Lebanon. Voucher specimens were identified as Pinus brutia following taxonomic verification with Herbarium specimens in the Post Herbarium the American University of Beirut, Lebanon. Information provided by the Ministry of Agriculture indicated that the age of the stand was about 30 years. An estimate of the size of the selected trees was made by measuring the DBH (diameter at breast height) that ranged from 10.8 to 25.5 cm. Needle and twig samples were taken primarily form current year flushes. Since all samples were collected in July, the effect of seasonal variation was eliminated. Ten randomly chosen samples were selected for this study. Indoor air drying of the plant material and later cutting into pieces was realized after the separation of the needles and the terminal twigs. For each sample, five different percent compositions zero, 25,50, 75 and 100% w/w needles to terminal twigs (designated zero, 25,50,75 and 100% needles (% n.)) of the raw material resulted in a total of 50 distillations. Steam distillation for3h gave pure oil samples for which physical and chemical properties were determined. As the % needles increased from O - 100%, the average % yield (%v/w) decreased by 28.0%, from 0.68% ±0.17 to 0.49% ±0.13. The sharpest decline detected in the average yield variation (13.82%) was observed in the range from 25 - 50% needles as compared to 11.07% from 75 to 100% needles.

Chemical Analysis

Analytical GC was carried out using a Hewlett-Packard 4890 gas-chromatograph equipped with an HP-5 capillary column (15.0 m x 530 µm, 1.5 µm film thickness). Nitrogen was used as the carrier gas, at a flow rate of 1.0 mL/min. The temperature program was as follows: 35°C for 2 min, ramp of 4°C/min up to 290°C, with a maximum temperature of 350°C. The injector temperature was set at 300°C. The detector was FID and the detector temperature set at 320°C.

A Hewlett-Packard HP6890 gas chromatograph equipped with an HP-5 capillary column (30.0 m x 250 µm, 0.25 µm film thickness) was used for the quantification of the oils. Oven temperature was programmed as follows: 35°C for 2.0 min and then up to 290°C at 4.0°C/min. The injector temperature was set at 300°C in a split ratio ( 100:1 ). Helium was used as the carrier gas at a flow rate of 1 mIVmin. Mass spectra were obtained using an HP-7972 series mass selective detector operating in the electron impact ionization mode (70eV).

Component Identification

Retention indices were determined by using retention times of n-alkanes injected under the same conditions. Peak identification was then accomplished by comparison of the mass spectra with databases (NIST and NBS) and confirmed by comparison of their retention indices with those reported in the literature.

Results and Discussion

An overall of 50 compounds were detected in all profiles and were quantified and characterized based on both their retention indices and mass spectra (Table I). Over 90% of the identified compounds were monoterpene and sesquiterpene hydrocarbons, while the rest consisted of oxygenated monoterpenes and sesquiterpenes and some nonterpene components. Monoterpene hydrocarbons decreased by an overall of 23.6% from pure twig to pure needle oil. However, the oxygenated monoterpenes and sesquiterpene hydrocarbons observed an opposite trend, increasing by a total of 258.6 and 134.8% from OO to 100% needles, respectively. Oxygenated sesquiterpenes and the nonterpene components followed no clear trends in the overall averaged samples.