Extraction and Composition of the Essential Oil of Ambrette (Abelmoschus moschtus) Seeds

Journal of Essential Oil Research: JEOR, Jan/Feb 2004 by Rout, P K, Rao, Y R, Jena, K S, Sahoo, D, Mishra, B C

Abstract

Selective extraction with methanol of uncrushed ambrette seeds grown in India and liquid-liquid extraction of the residue afforded a volatile concentrate in 0.33% yield free from the fatty acids and off-notes associated with a steam-distilled oil. Analysis by GC and GC/M S revealed that it contained (e) -�-farnesene (9.8%), (E,E)-[alpha]-farnesene (7.3%), decyl acetate (6%), dodecyl acetate (4.8%), (Z,E)-farnesyl acetate (3.8%), (E,E)-famesyl acetate (50.5%), 5(Z)-tetradecenolide (1.3%), 7-(Z)-hexadecenolide (9.3%) and 9-(Z)-octadecenolide (1.2%) as major components constituting 93% of the oil.

Key Word Index

Ahelmoschus moschatus, Malvaceae, extract composition, (E,E)-f'arnesyl acetate, 5-(Z)-tetradecenolide, 7-(Z)hexadecenolide, 9-(Z)-octadecenolide.

Introduction

Ahelmaschusmoschatus'L. (syn.HibiscusabelmoschusL., family Malvaceae) is a plant native to India (1). The seed oil is widely used as a fixative in fragrance formulations and is a valuable adjunct to high-grade perfume compositions to which it imparts a strong and characteristic musk note (2). It has a much smoother odor than synthetic musk compounds (3) and is noted for its rich, sweet floral-musky, distinctly wine-like odor with a bouquet and 'roundness' rarely found in other perfumery materials (4).

While the synthetic musk compounds have been shown to cause photosensitivity and dermatitis (5) in sensitive individuals, the Abelmoschus plant has been classified as 'an herb of undefined safety' by FDA and the extracts are classified as GRAS (Generally Recognized As Safe) for use in baked foods, candies and alcoholic beverages (6). Ambrettolide [7-(Z)-hexadecenolide] is reported to be non-toxic (7).

A survey of the literature reveals that Kerschbaum (8) isolated ambrettolide from ambrette seed oil by fractionation in 1927. However, the major constituent (E,E)-farnesyl acetate was reported only in 1973 (9). In a classic work by Nee et al. (10), the ambrette seeds were carefully dissected into outer and inner seed coats, endosperm and embryo; each was analyzed for the fragrance components. It was found that the oil was localized exclusively in the outer layer of the seed coat, but not in the epicuticular layer. The principal components were identified through spectroscopic studies as 2-(e) -6-(e) -farnesyI acetate (70%), 2-(Z)-G-(e) farnesyl acetate (6%), 7(Z)-hexadecen-16-olide and 9(Z)octadecen-18-olide (total 14%). Subsequently, Bernard et al. (2) obtained an oil in 0.16-0.27% yield by hydro-distillation of seeds for 6-9 h; the oil contained variable amounts of fatty acids. The researchers found that (E,E)-farnesol was present at a level of 35% while ambrettolide had decreased to 8%. The first detailed analysis of ambrette seed oil was reported by Buil et al. (11). Extracting the crushed seeds with Freon; hydrodistillation of oleoresin furnished an oil in 0.17-0.25% yield, the detailed analysis of which was reported by Cravo et al. (12,13). In another study, (e) -2,3dehydrofarnesyl acetate was reported as one of the major components in the seed oil produced from plants grown in Vietnam (14).

We extracted the uncrushed ambrette seeds with methanol and by purification of the extract through liquid-liquid extraction, have obtained a volatile concentrate in higher yields than by hydrodistillation of the seeds. We report here the comparative analysis of a hydrodistilled oil and two volatile concentrates of Indian ambrette seed.

Experimental

The ambrette seeds required for the present studies were obtained from the plants cultivated in the Aromatic & Medicinal Plants Division farm of our laboratory during 1999 and 2000. Fruits were harvested in January and February, which on dryingyielded the seeds. The seeds were dried in shade for two days before storage in cloth bags. seeds supplied by M/S Global Herbs, New Delhi, were also used. Voucher specimens were deposited in the laboratory Herbarium.

Reagent grade solvents were distilled and used for extraction or purification. Ambrette seed (1 kg) was successively extracted twice under stirring for 6 h with 4 L methanol. The combined methanol extract on concentration gave a residue, which was taken up into 2 � 75 m L pentane and the aqueous alcoholic layer discarded. Passing the pentane layer over a short column of silica gel ( 10 g), and eluting with pentane gave 3.3 g (average of six runs) of light yellow volatile concentrate. Elution was monitored on TLC and the fraction corresponding to the top nonpolar components collected. The volatile concentrate had the characteristic sweet musky odor free from any rancid notes and does not require aging before use. Distillation of 1 kg seeds using a Clevenger-type apparatus for 8 h gave 1.6 g of an oil.

GC analysis was carried out on a Shimadzu GC 17A gas Chromatograph equipped with a flame ionization detector and a 25 � 0.25 mm WCOT column coated with 0.25 �m 5% diphenyl dimethyl silicone supplied by J&W (DB-5). Helium was used as the carrier gas at a flow rate of 1.2 mL/min at a column pressure of 42 Kpa. Component separation was achieved following a linear temperature programme of 80�-280�C (4�C/min). Percentage composition was calculated using peak normalization method. The oils were analyzed using a Shimadzu QP5000 GC/MS fitted with the same column and temperature programmed as above. MS parameters: ionization voltage (EI) 70 eV, peak width 20 s, mass range 40-400 amu and detector voltage 1.5 volts. Peak identification was carried out by comparison of the mass spectra with mass spectra available on NIST-I, NIST-2 and Adams libraries. The compound identification was finally confirmed by comparison of their relative retention indices with literature data (15-17).