Characterization of the Portuguese-Grown Cistus ladanifer Essential Oil

Journal of Essential Oil Research: JEOR, Mar/Apr 2005 by Gomes, Paula B, Mata, Vera G, Rodrigues, A E

Abstract

The chemical composition of the cistus oil from Portuguese-grown rockrose (Cistus ladanifer) was determined using GC and GC/MS. A comparison was also made in terms of the geographical source and use of either dry or fresh plant material. The cistus oil herein obtained was richer in amber-like compounds and had a low content of monoterpenes when compared to the usual values found in the literature. Moreover, it presented a relatively high content of ambrox (amber odor), which usually is only reported in labdanum oil. The major constituents were three sesquiterpene alcohols: viridiflorol (13.6-17.4%), globulol (3.1-5.0%) and an unknown sesquiterpene alcohol (2.7-6.0%), as well as the diterpene alcohol 15-nor-labdan-8-ol (1.7-5.2%). Three samples of commercially available cistus oil were also analyzed and compared.

Key Word Index

Cistus ladanifer, Cistaceae, rockrose, essential oil composition, viridiflorol.

Introduction

Cistus ladanifer, also known as rockrose orlabdanum, is a resinous and extremely fragrant bush that grows wildly in the Mediterranean region (Portugal, Spain, France, Morocco). The plant is easily recognizable by its white flowers with a crimson spot in the base of the petals. Labdanum is a valuable raw material in perfumery as a natural fixative and for composing amber and leathery notes. It is reported to be used in 33% of all modern quality perfumes and 20% of all quality perfumes for men (1), mainly in chypre perfumes (1,2). Moreover, the isolates from C. ladanifer constitute an important alternative to ambergris, which is a rare ingredient obtained from a protected animal source (whales), and provides starting materials for manufacturing synthetic ambers (1).

Spain is the main world producer of labdanum products (3,4). The cistus oil is obtained by hydrodistillation or steam distillation of the leaves and stems, being constituted mainly by monoterpenes (3). Labdanum oil is a different product that is obtained by distillation of the gum exuded by the plant. The typical odor is due to the presence of compounds resulting from oxidative degradation of diterpenes with labdane skeleton existing in labdanum gum as the main components (3).

The main composition of cistus oil published in the literature is presented in Table I. These compositions differ significantly although it is possible to consider two groups: Group A with α-pinene as principal component and Group B with viridiflorol in higher quantity and low content of α-pinene. Group A is the most common.

Simon-Fuentes et al. (4) identified the main components by GC/MS in the neutral volatile fraction of a commercial cistus oil produced in Spain, where the highly volatile monoterpenes α-pinene, camphene and p-cymene constituted almost 50% of the composition. The norterpene 2,2,6-trimethylcyclohexanone was also the major compound (5.7%) that has been associated to the fragrance of the plant (5).

Ramalho et al. (5) studied the aromatic volatile compounds existing in the leaves of C. ladaniferus from Douro region (Portugal) that are related to the aroma quality of Porto wine by GC/MS and GC/Sniffing. In this study, the components 2,2,6-trimethylcyclohexanone (rock-rose leaf odor), acetophenone, 2-phenylethanol (floral aroma) and in small amounts 2,6,6-trimethylcyclohex-2-enone (woody balsamic-like odor) were pointed out as the most important odoriferous constituents.

Peyron et al. (6) made a detailed description on the industrial use of cistus cultivated in Corsica, including data on botanical, cultivation, extraction technologies and oil characteristics.

Mariotti et al. (7) characterized the chemical composition of cistus oil isolated from leaves and steins of C. ladaniferus of Spanish origin but grown in Corsica, using GC/FID and ^sup 13^C-NMR. The authors identified 45 components, of which the main components were pinene (39%), viridiflorol (11.8%), ledol (3.3%) and bornyl acetate (3.1%). A study of chemical variability showed that 20 samples of cistus oil displayed significant variations in their composition. They were divided in six groups, where in Group III to VI the major component was α-pinene (20.4-24.2%, 29.8-33.0%, 36.8-40.3% and 44.1-47.4%, respectively). Group I presented a considerably higher content of viridiflorol (20-22.6%) and a lower amount of α-pinene (2.1-2.5%), and the remaining Group II was intermediate between Group III and Group I with α-pinene and viridiflorol in high amount (11.1-16.4 and 9.5-10.7%, respectively).

Mrabet et al., cited by Lawrence (8), characterized the oil of two varieties of cistus grown in Morocco, which also had viridiflorol as the main constituent (12.81-20.68%) and a very low content of α-pinene (0.30-0.37%). The variety maculatus contained an unusual high level of camphor (2.92%) and a low content of 2,2,6-trimethylcyclohexanone (0.75%).

Weyerstahl et al. (9) described with great detail the composition of a commercial labdanum oil. The composition of the oil was determined by GC/MS and NMR analysis. The components found in major quantity were ledene (9.3%), viridiflorol (4.3%) and cubeban-11-ol (4.1%). The characteristic components of rockrose such as 2,2,6-trimethylcyclohexanone (1.3%) and 2,2,6-trimethylcyclohex-2-enone (0.3%) were found in smaller amounts. One of the most interesting aspects of their work was the identification of the olfactory key components for the amber scent, namely 11-nor-driman-8-ol (0.3%, powerful woody-amber), ambrox (1.4%, strong dry amber), α-ambrinol (0.2%, warm animal amber), drimenone (0.1%, tobacco, amber), 6-acetoxy-nor-drimenone (0.2%, soft warm, strong amber, woody), oxoambrox (0.1%, soft animal amber, like ambrox), sclareolide (0.2%, weak fine amber, woody-resinous tone), labdenols (weak amber-animal) labd-8(17)-en-15-ol (0.4%), labd-7-en-15-ol (0.4%) and labd-8-en-15-ol (0.3%). Sclareol oxide (0.2%) was also identified as a minor component of labdanum oil, being that component an important intermediate for the synthesis of ambergris-odorants for perfumery industry and it is usually obtained from clary sage oils (2).