Extraction, separation and isolation of volatiles and dyes from Calendula officinalis L. and Aloysia triphylla (L'Her.) Britton by supercritical CO2

Journal of Essential Oil Research: JEOR, Jul/Aug 2003 by Crabas, Nicoletta, Marongiu, Bruno, Piras, Alessandra, Pivetta, Tiziana, Porcedda, Silvia

Received: February 2002

Revised: June 2002

Accepted: July 2002

Abstract

Isolation of volatile concentrate from the dried leaves of Aloysia triphylla (L'Herit.) Britton (Lemon verbena) and the dried flowers of Calendula officinalis L. were obtained by supercritical extraction with CO2. To obtain a pure volatile extract devoid of cuticular waxes, the extraction products were fractionated in two separators operating in series. A good extraction process was obtained operating at 90 bar and 50[degrees]C in the extraction vessel, at 90 bar and at -5[degrees]C in the first separator and at a pressure between 20 and 15 bar and temperatures in the range (10-20[degrees]C) in the second one.

The composition of the volatile concentrate has been analyzed by GC/MS. The volatile concentrate of A. triphylla was found to contain: phytol (11.6%), spathulenol (7.1%), caryophyllene oxide (5.6%), methyl 9,12,15-octadecatrienoate (5.6%) and [alpha]-curcumene (4.6%). The volatile concentrate of C. officinalis was found to consist of: methyl hexadecanoate (23.8%), methyl linoleate (18.6%), methyl 9,12,15-octadecatrienoate (17.2%), methyl octadecanoate (4.8%), methyl tetradecanoate (4.6%), [gamma]-cadinene and cubenol (4.0%), [delta]-cadinene (3.2%), [alpha]-cadinol (1.8%) and oplopanone (1.3%). To complete the investigation, a comparison with the hydrodistilled oil has been carried out.

On the exhausted matrix a further extraction at higher pressure (320 bar) and 50[degrees]C with a single separator was performed for the extraction of lutein from Calendula flowers, the amount of lutein obtained was determined by spectrophotometric measurements.

Key Word Index

Aloysia triphylla, Verbenaceae, Calendula officinalis, Asteraceae, essential oil composition, supercritical CO2 extract composition, phytol, spathulenol, methyl hexadecanoate, methyl linoleate, methyl linolenate.

Introduction

Extraction by means of CO2 in the supercritical state (SFE) is a good technique for the production of flavors and fragrances from vegetable matter. Generally, the oil of plants are composed of mono- and sesquiterpene hydrocarbons plus their oxygenated derivatives, mainly alcohols, ketones and aldehydes. 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 hydrolytic process. So volatile concentrates obtained by SFE are devoid of fatty acids, resins, waxes and coloring matters normally coextracted by conventional solvent extraction, and exhibit a scent more similar to the starting material from which they were derived, than those obtained by means of steam distillation. The almost exclusive use of compressed CO2 to extract volatiles or aroma substances destined to human nutrition and in the pharmaceutical and perfume industries is due to its chemical and physical properties. For examples, it is safe, non-toxic, non-combustible, inexpensive and its critical temperature and pressure are not high (31.06[degrees]C; 73.82 bar) (1). Moreover, many compounds show an appreciable solubility in supercritical CO2 at easily accessible conditions.

The extraction of cuticular waxes, typically long chain alkanes, even if not very soluble in supercritical CO2 (2,3) compared to monoterpene hydrocarbons, oxygenated monoterpenes, sesquiterpene hydrocarbons, and oxygenated sesquiterpenes (4,5), being located on the surface of vegetable matter, is unavoidable. The problem is overcome by adopting a stepwise separation (6,7) on the extracted product. Generally, two steps are adequate. In the first stage, the temperature below 0[degrees]C induces the precipitation of waxes, while in the second stage a strong reduction of pressure causes the removal of gaseous CO2 from the volatile concentrate. The objectives of this study were to produce volatile concentrates of Aloysia triphylla and Calendula officinalis, and to obtain the lutein from C. officinalis blossom by SFE. Aloysia triphylla (Lemon verbena) is a plant originating from the American tropics (8). It grows wild in South America but is cultivated in North Africa and in southern Europe (9). Its common name originates from the lemon-like smell that the leaves emit when rubbed. An infusion of its aerial parts is used as antipyretic, antispasmodic, diuretic and digestive (10). In the leaves, the oil can be found in glandular trichomes that are present on the leaves. The oil is a yellow-green liquid possessing a strong citral-like smell (11). The main compounds found in the oil by Carnat et al. (9) were neral and geranial (10-40%), limonene, 1,8-cineole, geraniol, [beta]-caryophyllene and spathulenol. This composition changes depending on the enviroment and the harvest time (12). The biosynthesis of many volatile compounds follows a seasonal rhythm in agreement with the plant growth: neral, geranial, ar-curcumene are produced until blossoming (beginning of summer), after which limonene and linalool are produced, as are [delta]-terpineol, [alpha]-terpineol, spathulenol and [alpha]-copaene during the dry season (13).