Essential Oil in Leaves and Inflorescences of Silphium integrifolium Michx.

Journal of Essential Oil Research: JEOR, Mar/Apr 2005 by Kowalski, Radoslaw, Wiercinski, Janusz, Mardarowicz, Marek

Abstract

The content and chemical composition of the essential oil obtained from the leaves and inflorescences of Silphium integrifolium Michx. were studied. The oil content in the leaves and inflorescences was 0.27% and 0.31% v/w, respectively. Qualitative and quantitative analyses of distilled oils were made using GC and GC/MS. It was found that the oils had similar qualitative compositions but they differed quantitative. The main constituents in the leaf and inflorescence oils were α-pinene (9.8% and 14.0%), trans-verbenol (2.7% and 6.3%), bornyl acetate (2.2% and 7.0%), allo-aromadendr-9-ene (4.3% and 6.1%) and caryophyllene oxide (8.7% and 4.7%).

Keyword Index

Silphium integrifolium, Asteraceae, essential oil composition, α-pinene.

Introduction

Essential oils as biologically active compounds are characterized with a wide spectrum of biological activity, and have special importance in medicine. Moreover, components of essential oils are used in the food and cosmetic industries. Therefore, studies aiming to evaluate the chemical composition of new raw materials of plant origin are justifiable. Thus, the North American perennial plant entire-leaf rosinweed Silphium integrifolium Michx. from Silphium L. genus (Asteraceae) is an interesting species.

It is well known that many of the popular cultivated (oil and fodder ones), vegetables, medical and ornamental plants, as well as weeds, belong to the Asteraceae family. However, Silphium L. genus is a little known plant group. Hitherto, preliminary studies upon chemical composition of some Silphium species confirmed that these plants are very interesting. According to many authors, Silphium L. is characterized with advantageous contents of mineral substances and primary metabolites such as proteins (rich in exogenous amino acids), carbohydrates (including inulin in rhizome), L-ascorbic acid and secondary metabolites: essential oil, triterpene saponins, carotenoids, phenolic acids, tannin compounds and flavonoids. This interesting composition can predispose plants of Silphium L. family for wider application, among others, as a source of foodstuff for people as invegetables or spices and animals as in silage. There are experiments on medical, fodder, meliferous, and ornamental value of S. perfoliatum L. (1-4). The aim of the present paper was to evaluate content and chemical composition of leaf and inflorescence oils of S. integrifolium.

Experimental

Plant material: The leaves and inflorescences of S. integrifolium originated from experimental cultivation of Department of the Vegetable and Medical Plants, University of Agriculture, Lublin (July 1999). The production material (the seeds of S. integrifolium) was obtained from Botanical Garden of the University of Leipzig (Germany) where a voucher specimen has been deposited.

The percentage quantity of oil was measured according to Polish Pharmacopoeia V (5). The oils were determined due to a method of distillation with water steam in a Deryng's apparatus in the presence of m-xylene. Then, the distilled oil was subjected to GC and GC/MS analysis.

GC and GC/MS: GC/MS: ITS-40 (GC/ITMS-Finnigan MAT, USA) with 30 m x 0.25 mm, DB-5 column (J&W, USA), film thickness 0.25 µm carrier gas He, injector temperature: 280°C. A temperature gradient was applied (35°C for 2 min, then increased by 4°C/min to 280°C).

GC: UNICAM 610 (Unicam, UK) with DB-5 column (J&W, USA) operated under the same conditions as GC/MS, carrier gas H^sub 2^, FID: 220°C. The qualitative analysis was carried out on the basis of MS spectra and it was compared with the spectra of the NIST library (6), the LIBR (TR) terpenes library provided by Finnigan MAT (7) and data available in literature (8). The compound's identity was confirmed by retention indexes from literature and own data (4,8-10). The quantity composition of oils was determined by GC (FID) by assuming that a total area percents of all the particular oils constituted 100%.

Results and Discussion

The mean oil content in the leaves of S. integrifolium amounted to 0.27% v/w per dry matter, while the oil content of the inflorescence was 0.31% v/w.

Table I lists the percentage composition of the two oils. Dominant components in the leaf oil were: α-pinene (9.8%), caryophyllene oxide (8.7%), humulene epoxide (5.0%), allo-aromadendr-9-ene (4.3%), gennacrene D (4.0%), camphene (3.6%), limonene (3.0%), spathulenol (2.7%), trans-verbenol (2.7%).

The most important identified components of oil obtained from the inflorescences were: α-pinene ( 14.0%), bornyl acetate (7.0%), trans-verbenol (6.3%), allo-aromadendr-9-ene (6.1%), camphene (5.7%), caryophyllene oxide (4.7%), limonene (3.9%), gennacrene D (3.5%), humulene epoxide (2.6%).

Compound R^sub I^ 1562: GC/MS, 70 eV, 220°C, m/z (rel. int.): no M^sup ^, 202(9), 187(14), 171(11), 159(32), 145(49), 131(100), 124(35), 123(75), 121(33), 120(34), 117(52), 109(76), 107(43), 105(83), 96(37), 95(31), 93(55), 91(93), 81(50), 79(69), 77(52), 67(46), 55(45), 43(91), 41(83), 39(34).

Compound R^sub I^ 1576: GC/MS, 70 eV, 220°C, m/z (rel. int.): no M^sup ^, 205(6), 177(21), 159(43), 150(15), 149(29), 133(26), 131(23), 123(72), 122(45), 121(28), 107(46), 105(37), 96(82), 95(86), 93(55), 91(55), 81(99), 79(62), 67(100), 55(42), 43(30), 41(79), 39(38).