Abstract
A proposed method for citronella oil extraction was developed with the application of ohmic heated hydro-distillation. The objective was to compare the performance of three different extraction methods, viz. ohmic heated hydro-distillation, hydro-distillation, and steam distillation. The maximum amount of extracted oil yield by ohmic heated hydro-distillation was 7.64 mL/kWh as compared to hydro-distillation and steam distillation methods that resulted oil yields of 3.87 mL/kWh and 1.69 mL/kWh, respectively. The kinetics of extraction followed a second-order model. Gas chromatography-mass spectrometry analysis found that the major constituents of citronella oil (GC-MS) for the different extraction methods were citronellal, citronellol, and geraniol. Scanning electron microscopy (SEM) of citronella grass provided evidence that the lignocellulosic sources of the extracted citronella oil were schizogenous cavities and cellular lignin. The citronella that had undergone ohmic-heated hydro-distillation and steam distillation showed some microfractures and less cell wall degradation than hydro-distillation. The cell walls were less rigid using ohmic-heated hydro-distillation compared to steam distillation. However, the cell walls of the hydro-distillation sample were less dense and exhibited pronounced swelling, but did not show any microfractures.
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Comparison of Citronella Oil Extraction Methods from Cymbopogon nardus Grass by Ohmic-heated Hydro-distillation, Hydro-Distillation, and Steam Distillation
Muhammad Hazwan Hamzah,a,* Hasfalina Che Man,a Zurina Zainal Abidin,b and Hishamuddin Jamaludin c
A proposed method for citronella oil extraction was developed with the application of ohmic heated hydro-distillation. The objective was to compare the performance of three different extraction methods, viz. ohmic heated hydro-distillation, hydro-distillation, and steam distillation. The maximum amount of extracted oil yield by ohmic heated hydro-distillation was 7.64 mL/kWh as compared to hydro-distillation and steam distillation methods that resulted oil yields of 3.87 mL/kWh and 1.69 mL/kWh, respectively. The kinetics of extraction followed a second-order model. Gas chromatography-mass spectrometry analysis found that the major constituents of citronella oil (GC-MS) for the different extraction methods were citronellal, citronellol, and geraniol. Scanning electron microscopy (SEM) of citronella grass provided evidence that the lignocellulosic sources of the extracted citronella oil were schizogenous cavities and cellular lignin. The citronella that had undergone ohmic-heated hydro-distillation and steam distillation showed some microfractures and less cell wall degradation than hydro-distillation. The cell walls were less rigid using ohmic-heated hydro-distillation compared to steam distillation. However, the cell walls of the hydro-distillation sample were less dense and exhibited pronounced swelling, but did not show any microfractures.
Keywords: Kinetics; Ohmic-heated hydro-distillation; Extraction; Citronella structural changes
Contact information: a: Department of Biological and Agricultural Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia; b: Department of Chemical and Environmental Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia; c: Food Technology Section, Universiti Kuala Lumpur, Malaysian Institute of Chemical and Bioengineering Technology (MICET), Lot 1988, Bandar Vendor Taboh Naning, 78000 Alor Gajah, Melaka, Malaysia; *Corresponding author: hazwanhamzah@upm.edu.my
INTRODUCTION
Cymbopogon nardus, also known as serai wangi or citronella grass, is native to South India and Sri Lanka. It can also be found growing wild in most tropical Asian countries, Central America, and Africa. Recently, this plant has been planted commercially by entrepreneurs for essential oil extraction (Abdul Rahman Azmil et al. 2005). Citronella oil is considered one of the 20 most important essential oils that are traded globally (Lawrence 1993). Nowadays, world production of citronella oil is approximately 5000 tonnes, the bulk of which is produced in Taiwan, Guatemala, Malaysia, Brazil, Ceylon, India, Argentina, Ecuador, Madagascar, Mexico, and the West Indies (Skaria et al. 2007). Due to the market potential of citronella oil, its production can realise rural-sector participation in the citronella oil and aromatherapy industry (Coronel et al.1984; Torres and Tio 2001). On the other hand, the citronella oil has been in comparatively high demand because of its wide usage in the perfume, soap manufacturing, cosmetics, and flavouring industries, and is effective as an insect repellent (Duke and du Cellier 1993; Pandey 2010; Silva et al. 2011).
In addition, citronella grass is a non-woody plant and has lignocellulosic fiber characteristics (Kaur et al. 2010). The cell wall is made of three major lignocellulosic constituents: cellulose, hemicelluloses, and lignin (Wan Aizan et al. 2008). The cell wall is low in pectin and glycoproteins (Moerschbacher and Mendgen 2001). Citronella is classified as a monocotyledon and has a less complex system of fibers and associated botanical components than dicotyledons. Furthermore, less lignin is found in this lignocellulosic grass than in wood (Kaur and Dutt (2013).
Hydro-distillation and steam distillation are the most common or conventional methods for extracting oil from citronella (Brugnera et al. 2003; Abena et al. 2007; Mahalwal and Ali 2003; Nakahara et al. 2003; Cassel and Vargas 2006; Chungsamarnyart and Jiwajinda 1992). Although the process is very simple, it can induce thermal degradation, hydrolysis, and water solubility of some fragrance constituents (Reverchon and Marco 2006). Supercritical fluid extraction has also been introduced to extract citronella essential oil (Silva et al. 2011). However, this method has drawbacks such as high investment costs and a new and unfamiliar method of operation (Mohamed and Mansoori 2002). Additionally, due to its low polarity, the extraction of polar analytes is difficult. This limitation may be overcome by adding small amounts of polar modifiers, such as methanol or ethanol, to the supercritical fluid. These measures enhance the solubility of solutes in supercritical fluid extraction, thus increasing the extraction efficiency (Xiao et al. 2007).
Due to the success of natural herbs and sales of environmentally friendly products with encouraging returns, many entrepreneurs and herbal companies are currently developing plantations of aromatic plants such as citronella grass (Nor Azah 2000). The commercialisation of citronella oil has led to the formation of small-scale citronella oil extraction facilities (Torres and Tio 2001). Ohmic-heated hydro-distillation has been proposed as an alternative method for citronella oil extraction because the proposed prototype size is suitable for small- or medium-scale extraction facilities. Ohmic-heated hydro-distillation has been reported as an environmentally friendly extraction or “green” method because it does not necessitate the use of any organic solvent for extraction and requires substantially less energy to operate (Gahavian et al. 2012).
The objectives of this study were to propose and verify the kinetic models and performance of three extraction methods, namely, ohmic-heated hydro-distillation, hydro-distillation, and steam distillation, in terms of the oil yield and the chemical, physical, and scanning electron microscopy properties of citronella.
EXPERIMENTAL
Citronella Grass Preparation
Citronella grass from Ceylon (Cymbopogon nardus) was obtained from the Malaysian Agricultural Research and Development Institute (MARDI), Kuala Linggi, Kuala Sungai Baru, Melaka. The citronella grass was cut approximately 15 cm from the plant base or ground level. Before extraction, 4 kg of citronella grass was crushed by a EUMA™ Three-Phase Asynchronous Motor Y90L-2 crusher. The crushed citronella grass was immediately put into the distiller unit.
Kinetics Study
For the first hour of extraction, the extracted oil was determined at 15-min intervals. During the following hour, the extracted oil was determined at 30-min intervals until it reached equilibrium. At the end of each interval, the extracted oil yield was estimated as follows,
Extracted oil yield (mL/kg) = V0/MS (1)
where V0 is the volume of citronella oil extracted from the sample (mL) and MS is the mass of the sample (kg).
Set-up of Ohmic-heated Hydro-distillation Unit
The ohmic-heated hydro-distillation system is shown in Fig. 1. The ohmic-heated hydro-distiller unit, which was 1.35 m long and had a capacity of 30 L, consisted of a central stainless steel 316 electrode (Fig. 2) that was 0.73 m long and 0.02 m in diameter in the middle of the distiller. An electrically insulated outer shell served as the outer electrode. The electrodes were connected to a three-phase alternating current step-down transformer 415/133/87-V power supply rated at 10 kVA with a maximum current of 60 A. Within the maximum current, two types of voltages could be used, i.e., 77 V and 50 V. The distillation unit was connected to a multi-tube condenser made from stainless steel 304. The extraction parameters used were a power input of 77 V up to the boiling point of water, followed by 50 V until the end of the extraction, a water-to-citronella ratio of 3:1, and a crushing frequency of once.
Fig. 1. The ohmic-heated hydro-distillation system: (1) ohmic-heated hydro distiller unit, (2) power supply, (3) multi-tube condenser unit, (4) temperature sensor, (5) clamp meter
Fig. 2. A central stainless steel 316 electrode
Hydro-distillation
Hydro-distillation was carried out using a similar distillation unit to the one shown above, except that the central electrode was replaced with a 3kW/3-phase heating element (Fig. 3). The extraction parameters were a water-to-citronella ratio of 3:1 and a crushing frequency of once.
Fig. 3. A 3kW/3 phase heating element
Steam Distillation
The extraction was performed using the same distillation unit as in Fig. 1 except that the central electrode was taken out from that unit and replaced with a perforated grid plate (Fig. 4(a)). The perforated grid plate was placed at the bottom of the distillation unit, and the citronella grass was placed on the grid. Saturated steam generated from the boiler was injected through the perforated grid plate, separating the steam inlet at the bottom of the distillation unit (Fig. 4(b)). The steam in the distillation unit was at atmospheric pressure, and the temperature was 100 °C. A single crushing motion was used.