Comparative Analysis of the Oil and Supercritical CO2 Extract of Ferula communis L.

Journal of Essential Oil Research: JEOR, Mar/Apr 2005 by Marongiu, Bruno, Piras, Alessandra, Porcedda, Silvia

Abstract

Flowerheads of Ferula communis L. were used for supercritical extraction with carbon dioxide to isolate the corresponding volatile concentrate. It was isolated by supercritical CO2 extraction coupled to a fractional separation technique. The process was carried out operating at 100 bar and 50°C in the extraction vessel, at 100 bar and below -5°C in the first separator to selectively precipitate the cuticular waxes and at a pressure between 15 and 20 bar and temperatures in the range of 15°-21°C in the second separator to recover the volatiles. GC/MS analysis of the extract allowed the identification of the volatile concentrate composition.

The main constituents in the extract were α-gurjunene, β-gurjunene, α-selinene and β-selinene. A comparison with the oil obtained by hydrodistillation is also given. The differences observed between the composition of the SFE volatile concentrate and of the hydrodistilled oil were relevant. Indeed, the HD oil had a blue color due to presence of chamazulene, whereas the volatile concentrate was pale yellow.

Key Word Index

Ferula communis, Apiaceae, essential oil composition, supercritical carbon dioxide extract composition.

Introduction

The genus Ferula belongs to the Apiaceae family, and is widespread in central Asia and in the Mediterranean region (1). The F. communis L. also grows wild in Sardinia, especially in the mountainous central region. This plant has been reported to be highly toxic to animals and to humans (2,3). In the present work we show the results concerning the obtaining of volatile concentrate from the flowerheads of F. communis by means of supercritical carbon dioxide extraction, in a single extraction stage.

Supercritical fluid extraction, SFE, is a valid alternative for the production of flavors and fragrances from natural materials. Compressed CO2 is able to solubilize hydrocarbon and oxygenated mono- and sesquiterpenes (4), the main constituents of essential oils. The separation of the extractant is easy and the volatiles are devoid of residues that pose a risk for human use. Conventional processes such as distillation, solvent extraction etc., often require additional steps such as separating the extractant, and are usually inferior to CO2 with respect to their selectivity. In addition, the lower temperature in the SFE avoids thermal degradation and the low water content limits hydrolitic process. So a volatile concentrate obtained by SFE is devoid of fatty acids, resins, waxes and coloring matters normally coextracted by conventional solvent extraction. It also possesses an aroma more similar to the starting material from which it was derived, than an essential oil obtained by steam distillation. The almost exclusive use of compressed carbon dioxide to extract volatile concentrates or aroma substances destined to human nutrition and in the pharmaceutical and perfume industries is due to its chemical and physical properties: it is safe, no toxic, non-combustible, inexpensive and its critical temperature and pressure are not high (31.06°C and 73.82 bar) (5).

Materials and Methods

Materials: Ferula communis was collected on the Gennergentu massif of Sardinia (Arzana, Nuoro). The plant was identified by Mauro Ballero, Department of Botanic Sciences, University of Cagliari, and a voucher specimen was deposited in the University's Herbarium.

The aerial parts of the plant were collected during full blossom and then air dried in the shade for several days. Before utilization the material was comminuted. CO2 (purity 99%) was supplied by SIO (Società Italiana Ossigeno, Cagliari, Italy).

SFE apparatus: Supercritical CO2 extractions were performed in a laboratory apparatus equipped with a 400 cm^sup 3^ extraction vessel, which operated in a single-pass mode by passing CO2 through the fixed bed of vegetable particles. Two fractions of the extract were recovered in two separator vessels (300 and 200 cm^sup 3^) that were connected in series. The cooling of the first separator was achieved by using a thermostatic bath (Neslab, Model CC-100II, accuracy of 0.1°C). The use of the second separator allowed the discharge of the liquid product at desired time intervals. In this section, the temperature was maintained at the desired value using two methods. First, by the utilization of a heating ribbon wrapped around the piping dividing the two separators, and secondly, by means of a water thermostatic system connected to the second separator. A high pressure diaphragm pump (Lewa, Model EL1) with a maximum capacity of 6 kg/h, pumped liquid CO2 at the desired flow rate. The CO2 was then heated to the extraction temperature in a thermostatic oven (accurate to 0.02°C). Extraction was carried out in a semi-batch mode: batch charging of vegetable matter and continuous flow solvent. The flow of CO2 was monitored by a calibrated rotameter (Sho-rate, Model 1355) positioned after the last separator. The total CO2 delivered during an extraction was measured by a dry test meter. Temperatures and pressures along the extraction apparatus were measured by thermocouple and Bourdon-tube test gauges, respectively. Pressure was regulated by high pressure valves under manual control, located on different points of the apparatus.