Research Article - (2012) Volume 2, Issue 5
1Department of Horticultural Science, Science and Research Branch, IslamicAzad, University-Jahrom- Iran.
2Department of Agriculture, Payame Noor University, Tehran, Iran
The aerial parts of Lippa citriodora (Verbenaceae) were collected before flowering stage and dried by three different drying methods (sun-drying, shade-drying and oven-drying at 60 °C). The essential oils of every treatment were obtained by hydro-distillation method using Clevenger apparatus. The oils were analyzed by GC and GC—MS. The main constituents of the oils in shade method were Limonene (7.0%), 1, 8-Cineole (2.9%), (E)- β - ocimene (2.9%), Neral (24.1%), Geranial (31.9%), (E)-caryophyllene (3.1%), GermacreneD (4.8%) and bicyclogermacrene (3.4%).The analysis of variance showed that the different drying methods had a significant effect on the quantity of essential oil. Finally it could be concluded that shade drying method is suitable for highest essential oil quantity and Limonene, Neral and Geranial concentration.
Essential oil; Essential oil content; Drying methods; Shade drying; Lippa citriodora.
The genus Lippia (Verbenaceae) includes approximately 200 species of herbs, shrubs and small trees. The genus Lippia shows a rich genetic diversity, enabling it to synthesize a variety of essential oil constituents in plants grown in different parts of the world [1]; [2]. Lemon verbena Lippia citriodora is indigenous to South America and was introduced into Europe at the end of the 17th century. It is cultivated mainly due to the lemon- like aroma emitted from its leaves that are utilized for the preparation of herbal tea, which is reputed to have antispasmodic, antipyretic, sedative and digestive propertied. Lemon verbena has a long history of folk uses in treating asthma, spasms, cold, fever, flatulence, colic, diarrhea, indigestion, insomnia and anxiety [3]; [2]. Distillation (water and /or steam) is a conventional method for the extraction of essential oils from plant materials, in which the plant materials are mixed (or not) with water followed by heating or by the introduction of water system. The resulting vapors are cooled by condenser and collected in a separator and essential oil separator and essential oil separates from water. However, distillation have several disadvantages including labor intensive/time consuming, loss of target compounds due to thermal degradation, etc [4];[5], have led to search for find new benefice and efficient alternatives for isolation methods. Among several recently introduced alternative techniques, the coupling of headspace solid- phase microextrction (HS-SPME) sampling with gas chromatography mass spectrometry (GC/MS) has been shown to be very fast, has been shown to be very fast, handy, reliable and inexpensive extraction tool for organic volatiles. Theoretical bases and various applications of SPME are presented by Pawlisyzn [6] as well as in numerous puplication. The chemical composition of the essential oil from the leaves of L.citriodora has been previously reported [1]; [3]; [7]; [8]; [9]. The post-harvesting process of medicinal plants has great importance in the production chain, because of its direct influence on the quality and quantity of the active principles in the product sold [10]. A literature search was undertaken on effects of different methods on essential oil content and chemical composition of the essential oil plants, The results showed that drying method had a significant effect on oil content and composition of aromatic plants [11]; [12]; [13]; [14]; [15]; [16]. Also duration of essential oil extraction affected on the quantity and quality of essential oil. It have been reported that essential oil percentage and essential oil component of fennel and Laurus nobilis L. were affected by duration of essential oil extraction [17]; [18]. The objective of this study was evaluating the influence of drying method on essential oil yield and composition of Lippa citriodora before flowering stages.
Plant material
Samples of Lippa citriodora were collected in from greenhouse (controlled environment greenhouse at 25/13°C day/night temperature, and 65% relative humidity) in Sepidan city in Shiraz, Iran.
Drying methods
To study the effect of drying method, three methods of drying, (sun-drying, shade-drying and oven- Drying at 60°C for 24 hours) were investigated. The shade-drying occurred at room temperature.
Essential oil isolation
The dried samples of Lippa citriodora were subjected to hydro-distillation using an all glass Clevenger- type apparatus, to extract essential oils, according to the method outlined by the European Pharmacopoeia [19]. Extraction times were performed (3 hour) with three replications. The essential oils were separated from the aqueous layer, dried over anhydrous sodium sulfate and calculated average of essential oil yield. The extracted essential oils were dried over anhydrous sodium sulphate and stored in sealed vials at low temperature (4°C) before gas chromatography (GC) and gas chromatography-mass spectrometric (GC-MS) analysis. Essential oil content was defined as followed:
R (%) = (mass essential oil/mass of the dried leaves) x 100
Identification of the oil components
Analysis was carried out using an Agilent-technology chromatograph with HP-5 column (30m x0.32 mm i.d. x 0.25 m). Oven temperature was performed as follows: 60° C to 210° C at 3°/min; 210° C to 240° C at 20 °/min and hold for 8.5 min, injector temperature 280° C; detector temperature, 290° C; carrier gas, N2 (1 ml/min); split ratio of 1:50. GC-MS analysis was carried out using an Agilent 7890 operating at 70 eV ionization energy, equipped with a HP-5 MS capillary column (phenyl methyl siloxane, 30m x 0.25 mm i.dx 25μ m) with He as the carrier gas and split ratio 1:50. Retention indices were determined using retention times of n-alkanes that were injected after the essential oil under the same chromatographic conditions. The retention indices for all components were determined according to the method using n-alkanes as standard. The compounds were identified by comparison of retention indices (RRI, HP-5) with those reported in the literature and by comparison of their mass spectra with the Wiley GC/MS Library, Adams Library, MassFinder 2.1 Library data published mass spectra data [20]; [21]; [22].
Statistical analysis
Treatments were arranged in a completely randomized factorial design with three replications. Analysis of variance was performed using the Minitab software and means were separated using Tukey’s test (p < 0.05).
The effect of drying methods on essential oil content
The content of essential oil isolated from the aerial parts of Lippa citriodora which were dried under different conditions are shown in (Figure 1), result clearly shows that the oil content linked to the drying method. Indeed, in this survey the maximum mean of essential oil obtained from shade samples in 3 hours of extraction. The analysis of variance showed that the different drying methods (shade-drying, sun-drying and oven-drying) had a significant effect on the quantity of essential oil. In accordance with our results, there are similar reports from other researchers about other medicinal plants [11]; [12]; [13]; [14]; [15]; [16].
Figure l. The effect of drying method on essential oil content of Lippa citriodora.
Chemical composition of the essential oil
Thirty-seven compounds were identified in the essential oils in shade drying method and Thirty-six compounds obtained in Lippa citriodora in oven-drying method but twenty-six compounds were identified in the essential oils in sun drying method. The identified constituents with their respective percentages and RIs are summarized in (Table 1, 2 and 3). The main constituents of the oils in shade method were Limonene (7.0%), 1,8-Cineole (2.9%), (E)- β - ocimene (2.9%), Neral (24.1%), Geranial (31.9%), (E)-caryophyllene (3.1%), GermacreneD (4.8%), bicyclogermacrene (3.4%), (E)-Nerolidol (1.3%) and Caryophyllene oxide (1.9%). In our study, Limonene, Neral and Geranial were also identified at high percentages .These results are in agreement with previous reports [23]. Therefore, we investigated Limonene, Neral and Geranial in three drying methods. Results showed that maximum Limonene, Neral and Geranial percentage was obtained in shade and oven, and minimum Limonene, Neral and Geranial percentage was shown in other method of drying (sun), changed considerably for Limonene, Geranial and Neral decreasing from 7.0% to 3.8% , 31.9% to 19.1% and from 24.1% to 16.8%, respectively. All other components remained more or less unchanged. These results are in agreement with the previous reports about Roman chamomile [15]. Yuan Zhang and Zhezhi Wang [24] reported that in Glechoma longituba different drying methods caused some variation of the relative proportion of the components and the higher amount of Germacrene D (19.0%) was obtained by shade-drying.
Table 1. The effect of shade drying method on essential oil content of Lippa citriodora.
Table 2. The effect of sun drying method on essential oil content of Lippa citriodora.
Table 3. The effect of oven drying method on essential oil content of Lippa citriodora.
Finally it could be concluded that shade drying method is suitable for highest essential oil quantity and Limonene, Neral and Geranial concentration.
RI- Retention Indices
GC/MS- Gas chromatography- mass spectrometry,
HD- Hydro Distillation
We would like to thanks Dr. Vahid Rowshan for his help and his permission to use the laboratory facilities.
