INFLUENCE OF THE PROCESS PARAMETERS ON SUPERCRITICAL CO2 EXTRACTION OF FENNEL ESSENTIAL OIL
ABSTRACT The aim of this study was to investigate the most convenient conditions of solvent flow rate in order to obtain the essential oil from fennel with supercritical CO2 and compare the corresponding yield with that of the oil obtained by hydrodistillation. The collected extracts were analyzed by GC-MS and the relative composition of the oils was determined.
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INFLUENCE OF THE PROCESS PARAMETERS
ON SUPERCRITICAL CO2 EXTRACTION
OF FENNEL ESSENTIAL OIL
Manuela Zorca, I. Găinar ? and Daniela Bala
abstract: The aim of this study was to investigate the most convenient conditions of solvent flow
rate in order to obtain the essential oil from fennel with supercritical CO2 and compare the
corresponding yield with that of the oil obtained by hydrodistillation. The collected extracts were
analyzed by GC-MS and the relative composition of the oils was determined.
Supercritical fluid extraction (SFE) is receiving great attention in the agrochemical field. It
can be used as an analytical method to prepare samples from complex natural products, but
it can also be applied as an industrial process to obtain new or improved-quality products
from vegetable matter. CO2 is the most widely used among the possible solvents in SFE
because it is cheap, simple to use and shows a great affinity to lipophilic compounds to be
extracted. Some attempts to use other solvents such as nitrous oxide have been performed;
cosolvent addition to CO2 has been studied too.
Essential oil production is one of the industrial processes that can be improved by the
adoption of SFE. In fact, the traditional techniques can produce thermal degradation of the
product (hydrodistillation) or its pollution by organic solvents (solvent extraction). SFE of
essential oils has been attempted by several authors, but the products obtained usually
shows a waxy consistency due to the simultaneous extraction of the oil, cuticular waxes and
other undesiderable compounds. It has been assessed that cuticular waxes can be eliminated
by fractional separation of the supercritical extracts by using two or more separators
operating in series at adequate process conditions. Fatty acids and their derivatives can be
completely eliminated in the extract by adopting adequate SFE process conditions .
At the University of Bucharest, we developed a laboratory scale SFE plant that allows the
fractional separation of supercritical extracts. This process arrangement is very effective in
obtaining high quality essential oils [2÷5]. In the present work, experiments have been
performed on fennel fruits (Foeniculum vulgare, fam. Apiaceae). The objective is to study
? Department of Physical Chemistry, Faculty of Chemistry, University of Bucharest,
4-12 Regina Elisabeta Blvd., 030018 Bucharest, ROMANIA
108 M. ZORCA ? I. GĂINAR ? D. BALA
the influence of CO2 flow rate on the composition of oils and on the yield of the
Tests on fennel fruits were performed on a laboratory unit based on an extraction vessel
equipped with two separators operated in series. A schematic representation and further
details on this apparatus have been given elsewhere . About 100 g of comminuted fennel
fruits were submitted to extraction in each run. Extractions (called SFE-1, SFE-2 and SFE-
3) were performed at three different CO2 flow rate: 1.0, 1.5 and 2.0 kg/h. Fractional
separation, exploited in two stages, was obtained setting the first separator at 90 bar and -
5°C and the second one at 18 bar and 10°C. These conditions allowed a very efficient
fractionation. In the first stage only cuticular waxes have been precipitated, while in the
second one a yellow liquid has been obtained. Chemical analysis of the extraction products
has been performed by GC-MS. Analytical procedures were described elsewhere . Yield
(η) of the produced essential oils has been evaluated. The plant material was also subjected
to hydrodistillation (HD) for 180 minutes according to the standard procedure .
Results and Discussion
The percentage composition of the fennel oil obtained under SFE conditions is given in the
Table 1. CO2 flow rate increased from 1.0 kg/h for SFE-1 to 2.0 kg/h for SFE-3 that
justifies the difference in composition between the extracts obtained under these conditions.
The major contribution comes from trans-anethole, which represents 61-64% of the SFE oil
The SFE extracts were also compared with the fennel oil isolated by hydrodistillation. The
results of a detailed analysis of the hydrodistilled oil (HD) are again given in Table 1. The
compounds isolated were practically the same as those extracted by the SFE process. The
hydrodistilled oil possessed the higher percentage of estragole, 6.01% against 4.20-4.96%
for SFE fennel oils.
Table 1. Percentage composition of fennel oil isolated by supercritical CO2 extraction (SFE) and
hydrodistillation (HD). The percentages are based on GC peak areas.
Compound Rta (min)
HD% SFE-1% SFE-2% SFE-3%
4.45 0.12 0.14 0.15 0.12
4.50 2.05 2.28 1.57 1.09
Camfene 4.81 0.27 0.31 0.39 0.24
5.10 0.09 0.11 – trb
Sabinene 5.29 0.15 0.09 0.10 0.13
5.30 0.14 0.13 0.14 0.11
5.57 0.61 0.45 0.39 0.28
5.83 0.48 0.26 0.32 0.25
INFLUENCE OF THE PROCESS PARAMETERS ON SUPERCRITICAL EXTRACTION 109
Compound Rta (min)
HD% SFE-1% SFE-2% SFE-3%
p-Cimene 6.24 0.93 0.42 0.25 0.23
Limonene 6.39 1.77 0.54 0.60 0.53
1.8-Cineole 6.42 1.18 0.52 0.11 0.10
6.65 0.10 0.07 0.05 –
6.85 0.05 – 0.07 tr
6.90 0.76 0.71 0.31 0.22
7.30 0.19 0.14 0.12 0.10
Linalool 7.64 0.22 0.32 0.36 0.13
Fenchone 8.23 20.29 23.29 24.05 25.38
8.47 0.13 0.09 0.14 0.06
Fenchol 8.64 0.05 tr 0.09 0.09
Camphor 8.75 0.38 0.58 0.41 0.17
Trans-Menthone 8.84 0.12 0.11 0.14 0.08
Isomenthone 9.02 tr 0.07 0.05 –
Trans-Menthol 9.16 – 0.09 0.10 0.12
4-Terpineol 9.21 0.27 0.14 0.18 0.09
Dihydrocarvone 9.46 0.33 0.17 0.15 0.16
Estragole 10.78 6.01 4.96 4.20 4.23
p-Anisaldehyde 10.84 0.96 0.40 0.46 0.41
Cis-Anethole 10.97 0.45 0.68 0.66 0.54
Trans-Anethole 11.11 59.09 61.18 62.77 64.09
Dihydrocarveol acetate 11.47 0.70 0.41 0.34 0.28
Hydrocarveol acetate 11.63 0.56 0.32 0.35 0.11
Eugenol 11.78 0.52 0.57 0.42 0.32
Methyleugenol 11.91 0.18 0.08 0.17 0.09
12.53 0.28 0.25 0.20 0.15
13.72 0.57 0.12 0.19 0.10
a Rt = retention time (min)
b tr = traces (<0.05%)
The characteristic fennel essential oil compounds are fenchone (23.29-25.38%), estragole
(4.20-4.96%) and trans-anethole (61.18-64.09%). Fenchone is the specific contributor to the
fennel flavour. The oil extracted under SFE-3 conditions had a higher content of fenchone
(25.38%) and trans-anethole (64.09%) compared with the SFE-1 and SFE-2 oils and a
lower content of estragole (4.23%) (see Fig. 1).
The oxygenated monoterpenes are considered to be the main constituents of the aroma of
many essential oils. In the fennel oil extracted under SFE-3 conditions, oxygenated
monoterpenes content amounted to 26.38% compared with 25.38% SFE-1 conditions. On
110 M. ZORCA ? I. GĂINAR ? D. BALA
the contrary, hydrocarbon monoterpenes were only 3.07% for SFE-3, 4.21% for SFE-2 and
5.23% for SFE-1 (see Fig. 2).
Fig. 1 The characteristic fennel essential oil compounds
Hydrocarbon monoterpenesOxygenated monoterpenes Sesquiterpenes
Fig. 2 Percentages by weight of terpenes obtained by supercritical fluid extraction (SFE)
and by hydrodistillation (HD).
Fig. 3 Fennel essential oil yield against extraction time, at different CO2 flow rate.
INFLUENCE OF THE PROCESS PARAMETERS ON SUPERCRITICAL EXTRACTION 111
Trans-anethole is the principal extracted component. At 2.0 kg/h CO2 flow rate the trans-
anethole content in the essential extracted oil is greater than 64%. The obtained products
show higher quality than those obtained by hydrodistillation (see Table 1). The changes of
the solvent flow rate have a relevant effect on the extraction yield and can serve to improve
the SFE technology. The extraction yield increases (2.88-3.91%) by increasing of CO2 flow
rate. The essential oil yields obtained by SFE were compared. In the case of fennel (see
Fig. 3), the maximum obtained yield was of about 3.91% (by weight of the charged
material) at SFE-3 conditions.
1. Reverchon, E. and Senatore, F. (1994) J. Agric. Food Chem. 42, 154-8.
2. Găinar, I., Vîlcu, R. and Mocan, M. (2002) Anal. Univ. Buc.-Chimie XI (vol. I), 63-7.
3. Găinar, I., Vîlcu, R. and Mocan, M. (2002) Revue Roumaine de Chimie 47(1-2), 29-32.
4. Vîlcu, R., Găinar, I. and Mocan, M. (2002) Anal. Univ. Buc.-Chimie XI (vol. II), 167-71.
5. Vîlcu, R., Mocan, M. and Găinar, I. (2003) Anal. Univ. Buc.-Chimie XII (vol. I- II), 297-302.
6. *** Farmacopeea Română, EdiŃia a X-a, Ed. Medicală, Bucureşti (1993).