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Coupling Microwave-Assisted Drying and Supercritical Carbon Dioxide

Extraction for Coconut Oil Processing

Article in Chemical Engineering and Science · February 2013

DOI: 10.12691/ces-1-1-3

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Chemical Engineering and Science, 2013, Vol. 1, No. 1, 12-16
Available online at http://pubs.sciepub.com/ces/1/1/3
© Science and Education Publishing
DOI:10.12691/ces-1-1-3

Coupling Microwave-Assisted Drying and Supercritical

Carbon Dioxide Extraction for Coconut Oil Processing
Armando T. Quitain1,*, Takashi Moriyoshi2, Motonobu Goto3
1
Graduate School of Science and Technology, Kumamoto University, Kumamoto, Japan
2
Research Center for Industrial Science and Technology (RIST Kagawa), Kagawa, Japan
3
Department of Chemical Engineering, Nagoya University, Nagoya, Japan
*Corresponding author: quitain@kumamoto-u.ac.jp

Received January 01, 2013; Revised February 05, 2013; Accepted February 28, 2013
Abstract Supercritical carbon dioxide extraction was applied to the processing of virgin coconut oil (VCNO),
which has been known to possess several functions such as antimicrobial properties as proven by many medical
doctors and clinical researchers. Prior to extraction, the sample was dried using microwave-assisted low-temperature
air drying method. Using these techniques, an oil recovery of 95% was obtained at 40°C and 20MPa at a processing
time of less than 20h. This is more efficient than the conventional cold-press method which has a normal oil
recovery of about 30 to 50 % at a longer processing time of 48 to 72h. The obtained oil has physical and chemical
properties that are almost identical to or better than the commercial VCNO, thus deemed to possess the same
antimicrobial and nutritional properties. The effects of extraction conditions were also investigated for optimization
analyses.

Keywords: supercritical carbon dioxide, extraction, natural product, microwave, virgin coconut oil
recovery of useful compounds from natural products
[7,8,9,10]. It has also proven its usefulness as a
1. Introduction replacement for organic solvents with its application in
large-scale extractions such as coffee decaffeination. Most
Virgin coconut oil (VCNO), which is currently being recently, several plants have been constructed worldwide
marketed as a nutritional supplement, is known to provide for the extraction of phytochemicals and nutraceuticals
health benefits like protection from viruses, fungi and from natural products such as ginseng [11]. In the
bacteria because of its high lauric acid content. Lauric acid presence of modifier such as ethanol (EtOH), supercritical
is a medium chain fatty acid, and in human or animal body, carbon dioxide could enhance extraction of polar
it naturally transforms into monolaurin, a major compounds like polyphenols [12], thus increasing the
component of mother's milk that enhances the immune value and in most cases, the therapeutic property of the
system of infants [1,2]. The VCNO’s unique and abundant extracts. Other technical advantages of supercritical
antimicrobial properties make it superior to any other oils carbon dioxide extraction include higher diffusion
[3]. One of the many clinical evidences of its therapeutic coefficient, lower viscosity and absence of surface tension,
power is the significant reduction in viral loads of an HIV- thus allowing rapid penetration into the pores of
positive patient, attributed to the inclusion of coconut in heterogeneous matrices, and selectivity during extraction
his diet [3,4,5]. may be manipulated. This technique does not leave
To date, extraction of VCNO is mostly done in a chemical residue in the products and reuse of carbon
community level using a cold-press method but the dioxide is also possible [13,14,15].
recovery is low at about 35 to 50%. As the demand for In the processing of virgin coconut oil, the use of
this superior oil increases, Dr. Fife, dubbed as “Dr. supercritical carbon dioxide has added benefits for easy
Coconut” due to his numerous studies on nutritional and process standardization, because of tunable operating
therapeutic properties of VCNO, has urged producers to parameters unlike the complex and tedious conventional
develop techniques for extraction of VCNO from cold-press method. Moreover, the quality of the products
community level to a standardized continuous production can also be highly guaranteed because it is a closed system.
[3]. However, the water content of the coconut may hinder the
One promising technique to obtain the oil at low extraction, and could lower the yield of oil, thus in this
temperature is by supercritical carbon dioxide extraction. regard a microwave-assisted low-temperature air-drying
This is the most widely used supercritical fluid, mainly method can be applied to dry the sample prior to
because it is cheap, relatively nontoxic, and has extraction.
convenient critical temperature of 31.1°C and critical This study investigated the application of supercritical
pressure of 7.4MPa [6]. Supercritical carbon dioxide carbon dioxide to the extraction of virgin coconut oil. To
extraction had been applied in our previous works on the increase extractability of the oil, the sample was pre-dried
 Chemical Engineering and Science 13

using microwave-assisted low-temperature air drying. The In ethanol-modified supercritical carbon dioxide
effects of extraction conditions were also investigated for experiments, after reaching a pressure of 8MPa, ethanol
optimization analyses. (Wako Chemicals, 99.5 %) was added gradually using a
JASCO Intelligent HPLC pump (PU-980) to reach the
desired concentration.
2. Experimental
2.4 High Performance Liquid
2.1 Coconut Sample Chromatography (HPLC) for Analysis of
The coconut sample was obtained from the Philippines Triglycerides
and was brought to Japan in unopened shell. The juice was
The chemical compositions of the oil samples were
removed from the freshly opened sample, and the meat analyzed using a JASCO Intelligent HPLC-RI apparatus.
was grated using a vegetable slicer. The water content of A mixture of acetonitrile, tetrahydrofuran and
about 50wt% of the grated coconut was then removed by
dichloromethane at 70, 20 and 10% (v/v), respectively
either microwave-assisted hot-air drying at 40°C or
served as the eluent at a flow rate of 1.0 ml/min. The
freeze-drying. The dried sample contains an oil fraction of
column temperature was set constant at 40°C throughout
about 65wt%, as determined by Soxhlet extraction with
the analysis. The injection volume was 10μl. Component
hexane for 5h. This agrees with the data reported for copra, separation was carried out in an Inertsil ODS-3V column
a solar-dried coconut meat [16]. This percentage of oil (250 x 4.6mm), and component detection was performed
was taken as the basis for the calculation of the oil
using an RI detector.
recovery in the succeeding supercritical carbon dioxide
extraction experiments.
2.5 Gas Chromatography-Flame Ionization
2.2 Microwave-Assisted Low-Temperature Detector (GC-FID) for Analysis of Fatty Acid
Air Drying Contents
Coconut samples were dried using a microwave- An improved rapid method developed by Ichihara et al.
assisted hot-air drying apparatus (Shikoku Instrumentation [17] was applied to determine the fatty acid contents of the
Co. Ltd., Japan). The apparatus operates at a frequency of oil. About 10mg of the sample was dissolved in 2ml
2.45GHz, similar to that of a domestic microwave oven, hexane (HPLC grade, Wako Chemicals), followed by the
with a power programmable from 0 to 1500W. Hot air at addition of 0.2ml of 2M methanolic KOH. The tube was
40°C was circulated, while microwave was irradiated to vortexed for 2min at room temperature. After mild
raise the temperature of the sample, while controlling it at centrifugation at 2000G for about 2min using Chibitan-R
40°C. In a typical drying experiment, about 1kg of centrifuge (Millipore, Japan), an aliquot portion of the
coconut sample was placed inside the microwave cavity, hexane layer was collected for GC-FID analysis.
then was dried until almost all the water content was Analysis was carried out using a Shimadzu GC-FID
removed, while measuring the changes in the weight of (GC-14B) analytical apparatus. The column was a
the sample every hour. Chrompack capillary column (CP Sil x88 Tailor Made
FAME, 0.25mm x 50m) from GL Sciences Co. (Japan).
The injector and the auxiliary temperatures were set at 220
2.3 Supercritical CO2 Extraction and 250°C, respectively. The column temperature was
Extraction experiments on coconut samples at pressures initially set at 100°C for 4min, and allowed to ramp up to
up to 20MPa were carried out using an experimental 210°C at a rate of 10°C/min, and then was maintained at
apparatus shown schematically in Figure 1. The typical 210°C for 5 min. The carrier gas (He, 99.99 %) pressure
operating temperature was set at 40°C and the pressure at was 0.2MPa. The injection volume was 0.2μl.
20MPa. In optimization studies, the temperature and
pressure were varied in the range of 28 to 40°C and 7 to
30MPa, respectively. Experiments at a pressure of 30MPa
were done in another apparatus almost similar to the one
in the figure except that carbon dioxide was introduced
from the bottom of the extractor, passing through the
sample in an upward direction.
In a typical run, about 70g of dried coconut meat
sample was placed in a 300-ml extractor (OM Labtech Co.,
Ltd, Japan). The extractor temperature was gradually set
to the desired level, while pumping carbon dioxide (purity
Figure 1. Schematic diagram of supercritical fluid extraction apparatus
of 99.5 %) into the extractor to reach a system pressure of
20MPa using a high-pressure pump (NS personal pump,
NP-KX-500J, Nihon Seimitsu Kagaku Co., Ltd., Japan). 2.6 Measurement of Absorbance Spectra by
The system was held for 2h at desired conditions, then UV-VIS Spectrophotometer
carbon dioxide was allowed to flow continuously through The physical property, especially with regards to the
the extractor for 5h at a rate of about 2L/min at room purity of the obtained oil, was determined and compared
temperature. The extracts were collected in a flask with the commercial virgin coconut oil by measuring the
immersed in an iced water bath at around 5°C. absorbance spectra using a UV-VIS recording
spectrophotometer (Shimadzu UV-2400PC).
14 Chemical Engineering and Science

3. Results and Discussion Supercritical carbon dioxide extraction was then

performed until most of the oil in the samples was
recovered. As shown in Figure 4, it took less than 20h to
3.1 Drying of Samples recover more than 95% of the oil. This is more
The comparison between the microwave-assisted and advantageous than the conventional cold-press method
conventional hot-air drying methods of coconut is shown which requires 48 to 72h of processing time to obtain an
in Figure 2. In the conventional hot air-drying method, it oil recovery of only about 30 to 50 %.
took about 10h to completely remove the moisture content,
which is about 50% of the weight of fresh coconut meat.
With microwave irradiation, the drying time reduced to
about half. In terms of efficiency, these two methods are
much better than the freeze-drying method which usually
requires about 3 days for the complete removal of the
moisture contents.

Figure 4. Time course of cumulative recovery of the oil at 40°C and

20MPa

3.3 Physical and Chemical Properties of the

Extracts Compared to Commercial Virgin
Figure 2. Comparison between conventional and microwave-assisted Coconut Oils
hot-air drying methods of coconut at 40°C
The composition of the obtained oil was analyzed using
HPLC and the chromatographs are shown in Figure 5 in
3.2 Preliminary Experiments on Supercritical comparison with those of the commercial virgin coconut
Carbon Dioxide Extraction oils and an ordinary coconut oil purchased from Nacalai
Preliminary experiments were carried out on various Tesque (Japan). The chromatograph showing the
dried coconut samples with different sizes and drying composition of the obtained oil resembles those of the
methods, and the results are shown in Figure 3. The commercial virgin coconut oils. The fatty acid contents of
recovery was significantly lower using coconut bits (B), the oil were then analyzed by GC-FID. The results in
which were in sizes of small cubes, as compared to the Table 1 show that the lauric acid content of the oil
grated (GT) or ground (GD) samples. The most likely obtained using supercritical carbon dioxide is a little bit
reason for this is that carbon dioxide could not easily higher compared to the commercial virgin coconut oils. In
penetrate and diffuse through the matrices of the coconut addition, the clarity of the extracts is almost identical to
bits. The highest recovery was obtained using the the commercial virgin coconut oils based on the measured
microwave-assisted air-dried samples, thus the absorbance spectra as shown in Figure 6.
microwave-assisted dried grated (GT) samples were used
in the succeeding experiments, unless otherwise specified.

Figure 5. HPLC-RI chromatograms showing chemical composition of

the extracted oil in comparison with the two commercial virgin coconut
oils and an ordinary coconut oil

The results indicated that the obtained oil has physical

Figure 3. Results of preliminary experiments on supercritical carbon and chemical properties that are almost identical to or
dioxide extraction of coconut oil at 40°C, 20MPa
 Chemical Engineering and Science 15

better than the commercial VCNO, thus deemed to Only a slight increase in the yield was observed with
possess the same antimicrobial and nutritional properties. the addition of 5mol% EtOH, as entrainer. It is not also
recommended to use an entrainer such as EtOH, because
3.4 Optimization Analyses the required post-treatment procedures to separate the
EtOH from the extracts would add up to the operating
3.4.1 Effect of Drying Methods on Extraction costs.
Extraction experiments were carried out on samples
dried using 3 different methods, i.e. hot-air, MW-assisted
hot-air and freeze-dry methods. As shown by the results in
Figure 7, no significant effect of the drying methods on
extraction yield was observed. However, the use of
microwave irradiation may have an effect on other
thermally labile and light-sensitive vitamins and minerals
present in the oil. In this regard, the contents of vitamin E
on each sample were measured using HPLC but the
amount was below the detection limit of the apparatus,
thus no valid conclusion could be drawn at present on the
effects of the drying methods on the composition of
vitamins and minerals present in the extracts.

Figure 7. Effect of drying methods on the recovery at 40°C and 20 MPa

Figure 8. Effect of pressure and addition of EtOH on the recovery of

coconut oil at 40°C
Figure 6. Absorbance spectra indicating the clarity of the extracts in
comparison with the commercial virgin coconut oil and an ordinary
coconut oil

Table 1. Fatty acid content of the oil in % relative mass

Fatty acids VCNO A VCNO B ScCO2 Ordinary
Capric Acid 7.13 7.81 7.97 7.47
Lauric Acid 53.20 53.89 55.96 53.10
Myrisric Acid 21.02 19.56 19.61 20.10
Palmitic Acid 9.70 8.91 8.05 9.56
Steatic Acid 2.87 2.41 2.26 2.91
Oleic Acid 5.29 6.25 4.68 6.87
Lonileic Acid 0.79 1.18 1.47 trace

3.4.2 Effect of Pressure and Addition of EtOH

At constant temperature of 40°C, an increase in
pressure from 20 to 30MPa decreased the oil recovery as
shown in Figure 8. This was likely due to a decrease in
solubility of the coconut oil in supercritical carbon dioxide Figure 9. Comparison of extraction at temperatures of 28 and 40°C at
at higher pressures. In reference to the data reported by 20MPa
King and Bott [18], at constant temperature, the solubility
3.4.3 Effect of Temperature
of soybean oil in supercritical carbon dioxide decreases
with increasing pressure. At a lower pressure of 10MPa, In tropical countries, virgin coconut oil is usually
the yield also decreased significantly. Moreover, the obtained by cold-press method at atmospheric temperature
recovery at a temperature of 30°C and a pressure of 7MPa range of 28 to 35°C. Supercritical carbon dioxide
was very low at 0.41%. extraction was also carried out at 28°C, below the critical
 16 Chemical Engineering and Science

temperature of CO2, at a pressure of 20MPa, and the Most of the experiments were carried out at the
results in comparison with that at 40°C are shown in Research Center for Industrial Science and Technology,
Figure 9. The initial rate of extraction was relatively Kagawa Industry Support Foundation (Takamatsu,
higher at subcritical temperature of 28°C compared to that Kagawa, Japan).
at 40°C, but as extraction time progressed beyond 15h, the
rate decreased. These results suggest that supercritical
condition of temperatures would be required for the CO 2 References
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