Abstract: The effect of various methods of drying on the content and chemical quality of the essential oil of this herb was studied. The most prominent components in the fresh, air-dried, sun-dried and oven-dried oils extracted by hydrodistillation were the monoterpenes, α-pinene (9.1, 7.4, 10.2 and 6.8%), β-pinene (3.5, 3.6, 9.6 and 7.0%), myrcene (18.7, 18.4, 22.0 and 16.4%), limonene (26.5, 26.5, 24.4 and 27.4%), cis-ocimene (2.2, 1.9, 2.8 and 2.0%), trans-ocimene (4.8, 5.6, 12.4 and 11.6%) and α-terpineol (3.4, 2.7, 2.2 and 3.2%). Methyl-eugenol, β-caryophyllene, trans-farnesene and bicyclogermacrene were the major sesquiterpenes and all were in minute quantity. Cis-lachnophyllum ester (16.2, 18.1, 19.2 and 16.1%, respectively), was the dominating non-terpenoid polyacetylinic compound. The different drying methods have no significant effect on the quality and composition of essential oil from F. muricata.
INTRODUCTION
The members of the genus Felicia are mostly perennial aromatic herbs belonging to the family Asteraceae. The genus is widely distributed in southern Africa with about 90 species of herbs and shrubs. It also extends to the northern tropical Africa as far as Nigeria and Ethiopia and indeed, Saudi Arabia (Ortiz, 2007). Among the members of this group, Felicia muricata Thunb. is one of the most commonly used for medicinal purposes. The plant is a small drought resistant perennial aromatic herb growing up 20 cm in height. The leaves are arranged in alternate fashion and are characterized by long and cylindrical non-glandular trichomes, tapering into a sharp point, all running parallel to the surface of the leaves in the direction of the leaf apex (Ashafa et al., 2008a). Its name was derived from muricate (rough, with sharp tubercles or protuberances). The species is regarded as an indicator of desertification, becoming increasingly invasive in grassland regions (Jordaan and Kruger, 1993). In the Eastern Cape of South Africa, the rural dwellers use the plant in the management of headache, pains, inflammation (Hutchings, 1989; Hutchings and Van Staden, 1994; McGaw et al., 1997), as well as stomach catarrh and cancer. According to McGaw et al. (1997), aqueous extracts from the plant showed 80-90% inhibitory activity against cyclooxygenase, which is an important enzyme in the prostaglandin biosynthesis pathway; this may be responsible for the anti-inflammatory activity of this plant. In vitro antimicrobial activity of the extracts from this herb showed strong antibacterial and antifungal activity (Ashafa et al., 2008b). Recently, its essential oil was found to be rich in limonene, α-pinene, β-pinene, myrcene and cis-lachnophyllum ester (Ashafa et al., 2008c). These compounds have been reported to exhibit strong anticancer and antimicrobial activity (Sokmen et al., 2003; Deba et al., 2008). At the beginning of this study, no information was available in the literature on the effects of drying methods on the essential oil composition of this species. This study was to investigate the effects that different drying methods could have on the yield and composition of the essential oil from Felicia muricata.
The leaves of aromatic plants are often dried before extraction to reduce moisture content. Drying is important for preserving product quality and until recently, herbs are commonly dried at 40-60 °C (Tambunan et al., 2001). It has been reported that drying plant materials before distillation could affect the yield and composition of its essential oil considerably (Díaz-Maroto et al., 2003; Omidbaigi et al., 2004; Asekun et al., 2007a). During this process, many compounds which are dragged to the leaf surfaces by the evaporating water are lost (Moyler, 1994). In this study, we report the chemical composition of the essential oils obtained from F. muricata and the effect of drying methods on the yield and quality of the oils.
MATERIALS AND METHODS
Plant material: Plants used for this study were collected in February 2008 from a single population of F. muricata growing within the premises of the Alice campus of the University of Fort Hare. A voucher specimen (AshafaMed, 2008/1) was prepared and deposited in the Giffen Herbarium of the University. The plant material was divided into three portions of about 200 g each. One portion was left to dry in the laboratory under normal air at room temperature; another portion was dried to a constant weight in the sun, while the last portion was dried in the oven at 40 °C.
Extraction and analysis of essential oils: About 150 g of the fresh and dried leaves of F. muricata were subjected to hydrodistillation for 3 h, using a Clevenger-type apparatus in accordance with the method described by Asekun et al. (2007a).
Each oil was analyzed using Hewlett Packard 6890 Gas Chromatograph linked with Hewlett Packard 5973 mass spectrometer system which was equipped with a HP5-MS capillary column (30 m x 0.25 mm, film thickness 0.25 μm, Agilent Technologies Wilmington, DE, USA). The oven temperature was programmed from 70 to 240 °C at a rate of 5 °C min-1. The ion source was set at 240 °C with ionization voltage of 70 eV. Helium was used as a carrier gas. Spectra were analyzed using the Hewlett-Packard Enhanced Chem Station G1701 programme for Windows.
The components of the oils were identified by matching their spectra and retention indices with those of the Wiley 275 library (Wiley, New York) in the computer library and literature. Percentage composition was calculated using the summation of the peak areas of the total oil composition.
RESULTS AND DISCUSSION
The yields and chemical compositions of the oils obtained from F. muricata were slightly affected by the method of moisture removal from the plant material. A total of 38, 40, 33 and 30 compounds were identified in the oils of the fresh, air-dried, sun-dried and oven-dried plant materials, respectively. In general, the dried plants yielded more essential oils than the fresh ones (Table 1). The air dried, sun-dried and oven-dried plants yielded 0.84, 0.66 and 0.59% of the essential oils, respectively, while the oil was 0.62% in the fresh plant materials.
The monoterpenoids dominated the total oil content from the fresh plant. α-pinene (9.1%), α-pinene (3.5%), myrcene (18.7%), limonene (26.5), cis-ocimene (2.2%), trans-ocimene (4.8%), 1,3,8-para-menthriene (2.7%) and α-terpineol (3.4%) were the most represented. The sesquiterpiniod content was very low with trans-farnesene (1.7%) as the most prominent while cis-lachnophyllum ester (16.2%) was the major non-terpenoid polyacetylenic compound in the fresh plant oil.
The composition of the oil from the air-dried plants followed the same pattern as in the oil from the fresh plants with monoterpenes as the most dominant group of compounds. α-pinene (7.4%), β-pinene (3.6%), myrcene (18.4%), limonene (26.5), cis-ocimene (1.9%), trans-ocimene (5.6%) and α-terpineol (2.7%) were the most represented. In the sesquiterpinenes, trans-farnesene slightly increased from 1.7% in the fresh plant to 2.1% in the air-dried plant while cis-lachnophyllum ester increased from 16.2 to 18.1%.
The sun-dried oil displayed a slight increment in the composition of major components compared to other drying methods employed in this study. α-pinene (10.2%), β-pinene (9.6%), myrcene (22.0%), limonene (24.4%), cis-ocimene (2.8%), trans-ocimene (12.4%) and α-terpineol (2.2%) were the most represented monoterpene hydrocarbons while non-terpenoid polyacetylenic compound, cis-lachnophyllum ester increased to 19.2% compared to 16.2, 18.1 and 16.1% in the fresh, air-dried and oven-dried plants.
The monoterpenes hydrocarbons, α-pinene (6.8%), β-pinene (7.0%), myrcene (16.4%), limonene (27.4%), trans-ocimene (11.6%) and α-terpineol (3.2%) remained the dominating components in the oven-dried plant materials. Trans-farnesene and cis-lahnophyllum ester were the major sesquiterpene and non-terpenoid polyacetylinic compounds.
The volatile compounds produced by plants and other biological species comprise a large number of organic substances, including isoprene and isoprenoid compounds, alkanes, alkenes, carbonyl compounds, alcohols and esters. These volatiles are responsible for various interactions between plants and other organisms, such as pollinating animals, herbivores and the predators (McCaskill and Croteau, 1998; Robles-Zepeda et al., 2006). Furthermore, because some volatile compounds have antipathogenic properties, they are produced and emitted by plants as a defence mechanism against attack by herbivores (Robles-Zepeda et al., 2006).
In general, the drying methods caused some variations in the proportions of the chemical components of the essential oils; however, there was no major or sharp difference in the composition of the main components of the oils in F. muricata which could be ascribed to the different drying methods. Similar observations have been reported by Omidbaigi et al. (2004), Veskutonis (1997), Sefidkon et al. (2006) and Asekun et al. (2007a). The results from the study suggest that the major compounds in Felicia muricata were not stored on or near the leaf surface. Compounds stored on or near leaf surfaces have been reported to be considerably affected by the drying methods (Asekun et al., 2007b).
| Table 1: | Volatile compounds hydrodistilled from the fresh, air-dried, sun-dried and oven-dried leaves of F. muricata |
| Tr: Trace amount < 0.1, -: not detected. KI: Kovat index value. %: Percentage composition | |
Limonene, which was a major component of the oil, has been shown to inhibit mammary carcinogenesis in rats (Robles-Zepeda et al., 2006). α-pinene, β-pinene and lachnophyllum esters possess strong antibacterial and antifungal activities (Sokmen et al., 2003; Deba et al., 2008). Plant essential oils and extracts have been used for thousands of years in food preservation, pharmaceuticals, alternative medicine and natural therapies (Reynolds, 1996; Lis-Balchin and Deans, 1997). They are potential sources of novel antimicrobial compounds (Meurer-Grimes et al., 1996; Rabe and Van Staden, 1997).
CONCLUSION
The oil from F. muricata could make a promising group of natural compounds for the development of safer antibacterial, antifungal, antioxidant and anticancer agents. It could also be a good candidate in the perfumery and flavouring industries. The results from the study suggest that the major compounds in F. muricata were not stored on or near the leaf surface, since the different drying methods do not have any significant effects on the major component of the essential oil.
ACKNOWLEDGMENTS
This research was supported with grants from the National Research Foundation of South Africa (grant number U1DT147) and Govan Mbeki Research and Development Centre of the University of Fort Hare.