Essential Oils of Nigella sativa L. and Nigella damascena L. Seed

Journal of Essential Oil Research: JEOR, May/Jun 2004 by Moretti, A, D'Antuono, L Filippo, Elementi, S

Abstract

The seed oils of three accessions of Nigella sativa and N. damascena, sown on different dates, were obtained by Likens-Nickerson hydrodistillation and analyzed by GC/MS. The main components of N. sativa oil were p-cymene (33.8 %) and thymol (26.8 %), with only small amounts of thymoquinone (3.8 %). N. damascena oil was characterized by almost 100% sesquiterpenes, of which [beta]-elemene (73.2 %) represented about three-quarters of the total amount.

Key Word Index

Nigella sativa, Nigella damascena, Ranunculaceae, essential oil composition, thymol, p-cymene, [beta]-elemene, germacrene A.

Plant Name

Nigella sauva L. and N. damascena L. (Ranunculaceae). Nigella sativa seed is called black cumin and N. damascene! is sometimes referred to as love-in-a-mist or nutmeg flower.

Source

Nigella sativa seeds were obtained from an herbal market in Rabat ( Morocco). Nigella damascena seeds were purchased from two different commercial firms in Italy. seeds of the three accessions were sown at the Ozzano experimental farm of the University of Bologna on March 3, April 9 and May 7, 1997, in a three-replication randomized block design. The identity of the two species was verified according to Flora Europaea (1), and confirmed by comparison to specimens held at the Herbarium of the Department of Evolutionary and Experimental Biology, Botany section, University of Bologna. The seeds obtained from these field trials were used for the subsequent analyses.

Previous Work

The reported oil content of N. sativa seeds ranges from about 0.1-1.5%, depending also on the isolation method and duration of distillation (2-4). The pharmaceutical properties of this species have recently been reviewed (3,5). Thymoquinone has generally been recognized as one of the more abundant components of the oil, and the one responsible for the pharmaceutical interest of the plant.

Nigella damascena is a less investigated species, with reported seed oil content of about 0.5%, and composed mainly of sesquiterpenes (3).

Present Work

Oil analysis: seed samples (20 g) from each sowing date were homogenized in 100 mL deionized water, together with 3 g of NaCl to avoid foaming, and the oil was distilled for 3 h by simultaneous distillation and extraction (SDE) in a LikensNickerson apparatus, using 50 mL of diethyl ether as the organic solvent. The extract was dried over anhydrous Na^sub 2^SO^sub 4^; the solvent was then evaporated under vacuum in a rotary evaporator. The oil content was determined gravimetrically and expressed on a dry weight basis.

The oil was analyzed by means oi a Hewlett Packard 5890 gas Chromatograph under the following conditions: BPX-5 fused silica capillary column (30 m � 0.25 mm, 0.25 �m film thickness); carrier gas, helium; injector, 240�C; detector, 280�C; temperature program: from 80�C (2 min) to 150�C (10 min) at 3�C/min, then to 240�C at 10�C/min. GC/MS analysis was carried out by means of a 3300 Variai) gas Chromatograph coupled with a Finuigan MAT ITD-40 mass spectrometer. The Chromatographie conditions were as reported above. The individual oil components were identified by means of automatic search on the computer library (NIST), and by comparison to retention indexes of pure compounds and mass spectra reported in the literature (6,7).

Results and Discussion

Essential oil yield was 0.39�0.21% and 0.39�0.08% of seed diy weight for N. sativa and N. danwscena, respectively. The higher variability of N. sativa was due to the effect of sowing date (not discussed).

The oil composition was veiy different between the two species (Table I). In fact, more than 90% of N. sativa oil was represented by monoterpenes, whereas sesquiterpenes accounted for almost 100% of N. damascena oil.

Nigfilla sauva oil was characterized by a high p-cymene content, often recognized as a typical component of the oil of this species, whereas the abundance of thymol and the low amount of thymoquinone are in contrast to what has been reported in the literature (3,4). Thymol has not been found recently in N. sativa oil (4), whereas other sources (8) report a 10:1 thymoquinone/thymol ratio as minor constituents in commercial fatty oil of N. sativa. Most of the literature refers to seeds obtained in hot diy areas of north Africa and western Asia, where temperature and water availability during seed ripening are quite different from those during these trials, which corresponded to a late-spring, higher latitude climate. Thymoquinone is easily obtained by oxidation of thymol (9). It can therefore be supposed that the ratio between the two components is determined by the different environmental factors occurring during their biosynthesis. A genetic effect cannot however be excluded. Longilolene was a typical sesquiterpene of N. natwa, being absent in N. damascena.

The presence of [alpha]-selinene and [beta]-elemene in the oil of N. damascene! is consistent with what has been reported in the literature (10). Germacrene A and 7-epi-[alpha]-selinene were two other relevant sesquiterpenes of this species.