Essential oil composition of Artemisia vulgaris harvested at different growth periods under Indo-gangetic plain conditions

Abstract

Artemisia vulgaris was cultivated under subtropical Indo-gangetic plain conditions to determine the differences in the chemical composition of its essential oil produced from plants harvested at different growth periods using a combination of GC and GC/MS. The oil yield ranged from 0.1-0.5%. The leaf oil was found to be rich in 1,8-cineole (2.2-12.2%), [alpha]-thujone (0-11.4%), camphor (15.7-23.1%) and isobomeol (9.3-20.9%). The fruit oil contained [alpha]-thujone (15.5-16.0%) and artemisia alcohol (16.3-17.7%) as major components, while camphor (38.7%) predominated in the flower oil.

Key Word Index

Artemisia vulgaris, Asteraceae, essential oil composition, camphor, artemisia alcohol, isobomeol, thujone.

Plant Name

Artemisia vulgaris L. (Asteraceae).

Source

Artemisia vulgaris was cultivated at the experimental farm of CIMAP, Lucknow. Plantlets (average height 12 cm) that grew from suckers were separated from the mother plants and were planted in the field on 16 March 2000. Fresh plant materials were collected for hydrodistillation during their early vegetative (25 April 2000, plant height 33.86 cm, maximum 39.1°C, minimum 21.5°C), late vegetative (25 June 2000, plant height 76 cm, maximum 37.2°C, minimum 26.5°C), budding (15 September 2000, plant height 155 cm, maximum 35°C, minimum 24°C), flowering (4 October 2000, plant height 162.3 cm, maximum 32.5°C, minimum 15.0°C), fruit initiation (8 November 2000, plant height 162.5 cm, maximum 33.4°C, minimum 14.7°C) and fruit maturation stages (21 November 2000, plant height 162.5 cm, maximum 29.6°C, minimum 13.6°C). At the fruiting stage, only inflorescences were collected for oil isolation since the leaves were sparse and had dried up.

Previous Work

Various reports show that the oil yield in A. vulgaris ranges from 0.2-0.5% wt/vol basis (1,2,10,11). A remarkable variation in the constituents of the oil has been observed. The major constituents of the oil from plants collected from different places were reported to be [alpha]-thujone, [beta]-caryophyllene, caryophyllene oxide, [delta]-cadinene, 1,8-cineole and camphor (3,5,6,8-10,12). However, an oil of Indian A. vulgaris had been found to contain 1,8-cineole, camphor, borneol, limonene and camphene as main constituents (2,3,11). A few other investigations were carried out in which myrcene was found to be the major component varying from 9-70% depending upon the maturity of the plant (4). The oil obtained from the flowers was reported to contain sabinene (15.9%) as the major constituent followed by myrcene (13.7%), allo-aromadendrene, [beta]-cubebene and [delta]-guaiene (7).

Present Work

Fresh plant materials (50 g each) collected at various growth stages were hydrodistilled in a Clevenger-type system for 5 h. The GC analysis was carried out on a Varian GC, model CX-3400 with an AIMIL chromatography data station. A Supelcowax-10 capillary column (Supelco, USA)-30 m x 0.3 mm, film thickness 0.25 µm-was used in this study. Oven temperature was programmed from 50°-220°C at 6°C/min with initial and final hold of 2 min and 5 min, respectively. Injector and detector temperature were maintained at 220°C and 240°C, respectively. Hydrogen was used as a carrier gas (1 mL/min) with a ratio of 1:50. The GC data were processed on an AIMIL data station. GC/MS analysis was carried out in EI mode using a Perkin Elmer AutoXL Turbomass instrument fitted with a Supelcowax-10 capillary column-30 m x 0.30 mm, film thickness 0.25 µm. The oven temperature was programmed from 50°-210°C at 5°C/min with an initial hold of 2 min. Helium was used as a carrier gas with a split ratio of 1:20. Mass spectral data were analyzed via Wiley library search and comparison with standard published data. Constituents identified in the oil of A. vulgaris from different plant parts and growth stages are listed in Table I.

The oil content in the leaves of A. vulgaris increased gradually from the early vegetative stage (0.08%) to the budding stage (0.23%) on a fresh weight basis, but it decreased when the plant commenced flowering (0.16%). During flowering, inflorescences were found to contain the maximum oil yield (0.5%); during fruiting, the yield was reduced (0.30-0.32%). Twenty-five compounds were identified in the oil obtained from the leaves and flowers. The oil from the plant when grown under Indo-gangetic plain conditions was found to be rich in a number of compounds such as camphor, artemisia alcohol, isoborneol, thujone, 1,8-cineole, [beta]-caryophyllene and [beta]-eudesmol at different growth periods. However, the major compound in the leaf oil from plants harvested in early vegetative phase was isoborneol followed by camphor, but prior to budding, camphor became the main component followed by isoborneol, 1,8-cineole and artemisia alcohol. The percentage occurrence of artemisia alcohol and camphor in the leaves of A. vulgaris was almost equal at the stage of budding, while at the flowering stage although camphor remained the major compound the next most abundant compound, was artemisia alcohol followed by isoborneol, [alpha]-thujone and [beta]-caryophyllene. At the fruiting stage, artemisia alcohol was the major compound followed by [alpha]-thujone and [beta]-eudesmol. The concentration of camphor increased gradually from the early vegetative stage to the flowering stage in leaves. Its concentration was highest in the flowers and lowest in the fruits. On the other hand, isoborneol decreased gradually from the vegetative phase onwards becoming lowest during the fruiting stage. Artemisia alcohol also exhibited a gradual increase in concentration from the early vegetative stage to the flowering stage in the leaves, but in the flowers its concentration was very low. However, it showed approximately a four-fold increase in the fruiting stage. [alpha]-Thujone, another important compound of A. vulgaris, was observed only after flowering. Its concentration during flowering was richer in the leaves than in the flowers; however, it was even more abundant in the fruits. It was of interest to note that [alpha]-terpinene, limonene, 1,8-cineole, [gamma]-terpinene and p-cymene were observed only in the vegetative stages of the plant, while [alpha]-pinene was observed from the early vegetative stage to the flowering stage until it eventually disappeared during the fruiting stage.