Deoiling of Crude Lecithin Using SC-CO2 & Co-solvents

JFS: Food Engineering and Physical Properties
Deoiling of Crude Lecithin Using Supercritical
Carbon Dioxide in the Presence of Co-solvents
L. TEBERIKLER, S. KOSEOGLU, AND A. AKGERMAN
ABSTRACT: Deoiling of crude soybean lecithin using supercritical fluid mixtures of carbon dioxide and 2 different
co-solvents, ethanol and acetone, was studied at 62 °C and at pressures of 170 and 200 bars. Both ethanol and
acetone increased the solubility of oil considerably without any significant coextraction of phospholipids. It was
shown that deoiling could be achieved at lower pressures when a co-solvent is used leaving behind a valuable
product of high content phospholipids, whereas negligible oil extraction was observed with pure CO 2
at the same
conditions.
Keywords: crude soybean lecithin, deoiling, supercritical carbon dioxide, co-solvent, ethanol, acetone, phospholipids
Food Engineering and Physical Properties
Introduction
LECITHIN IS A BYPRODUCT OF THE EDIBLE OIL INDUSTRY AND
is obtained from the treatment of crude vegetable oil with
water or a weak acid. It refers to a complex mixture of phospholipids,
triglycerides, and some other substances, such as
glycolipids, free fatty acids, and carbohydrates.
A major phospholipid, phosphatidylcholine (PC), has
gained special attention during the last few decades due to
some health benefits it provides. It plays important roles in
cardiovascular and liver health and in reproduction and development.
Several studies suggested a possible therapeutic
use for PC in memory enhancement, liver protection, and
cholesterol reduction (Canty and Zeisel 1994; Krawczyk
1996). High purity phosphatidylcholine can be obtained by
fractionation of phospholipids, but before phospholipids can
be fractionated, crude lecithin has to go through a deoiling
process in which the neutral and polar lipids are separated.
Today, deoiling of lecithin is done by acetone extraction as
polar lipids, such as phospholipids and glycolipids, in contrast
to neutral lipids, are almost insoluble in acetone. An alternative
to acetone extraction is the treatment of lipid mixtures
with supercritical gases or supercritical gas mixtures
(Schneider 1989).
Previous studies have shown that supercritical carbon dioxide
is very effective in removing oil from different seed
matrices (Stahl and others 1980; Friedrich and List 1982;
Friderich and Pryde 1984; Christianson and others 1984; Fattori
and others 1988). Furthermore it was observed that
SCCO 2 does not dissolve phospholipids, and this can be used
to eliminate the degumming step in the oil refining process
(Friedrich and List 1982, 1985; Fattori and others 1987; List
and others 1993). Negligibly low solubility of phospholipids
has made it possible to use supercritical carbon dioxide for
deoiling of crude lecithin as well (Stahl and Quirin 1985; Eggers
and Wagner 1993).
The solubility of vegetable oil in supercritical carbon dioxide
increases with pressure. At 50 C solubility of soybean oil
was observed to increase from 0.1% at 200 bar to nearly
3.5% at 680 bar (Friedrich and Pryde 1984). In another study,
at 40 C and at a pressure of 660 to 700 bar, the extraction of
40 g of oil from ground soybean seeds required around 1.1
Nm 3 of carbon dioxide, whereas at 250 to 280 bar extraction
of 40 g of oil required more than 4 times this amount of carbon
dioxide (Stahl and others 1980). For deoiling of crude
soybean lecithin with pure CO 2 , pressures as high as 600 to
1000 bar are required (Eggers and Wagner 1993). In addition,
another drawback in using supercritical carbon dioxide for
deoiling of lecithin is the increasing viscosity of the lecithin
with the deoiling process, which prevents the complete removal
of the oil.
Various studies have shown that presence of an entrainer
(co-solvent) in the supercritical fluid enhances the oil solubility
at the same temperature and pressure, making it possible
to conduct the extraction at a lower pressure. Addition of
10% ethanol to SCCO 2 increased the solubility of palm oil
from 0.25% to 5% at 200 bar and 70 C (Brunner and Peter
1982). In a later study (Cocero and Calvo 1996) at 200 bar and
60 C with 10% ethanol in SCCO 2 , solubility of sunflower oil
seed was observed to be about 20 mg oil/g CO 2, while it was
negligibly small in neat CO 2 under the same conditions.
However, while it increases the oil solubility, ethanol present
as an entrainer in the SCCO 2 results in coextraction of phospholipids
(Temelli 1992; Cocero and Calvo 1996).
Propane was also studied as an entrainer in order to
maintain the lecithin in a liquid state in a countercurrent column
(Peter 1996). It was observed that using an extraction
fluid of 80 wt% propane and 20 wt% carbon dioxide decreased
the required operation pressure to 80 bar in the
temperature range of 40 to 55 C and made it possible to obtain
an oil-free product.
Although pure acetone has been the choice of solvent for
deoiling of crude lecithin, it has never been used as a co-solvent
in SCCO 2 for deoiling purposes. However, a process was
described by Stahl and Quirin (1985) in which crude lecithin
was dissolved in acetone with a mass ratio of 1 to 6, and the
acetone along with the oil dissolved was separated from the
lecithin with carbon dioxide extraction at 40 C and 160 bar,
but this process was not very different from the classical
deoiling process.
Currently, we are working on the extraction of phosphatidylcholine
from a crude lecithin obtained as a retentate of a
membrane oil refining process in order to produce high purity
phosphatidylcholine. Here, a part of that study is being
reported in which the objective is to carry out the deoiling of
850 JOURNAL OF FOOD SCIENCE—Vol. 66, No. 6, 2001 © 2001 Institute of Food Technologists

Deoiling of Crude Lecithin . . .
the crude lecithin (the membrane retentate) with supercritical
carbon dioxide at moderate pressures without significant
coextraction of phospholipids, especially phosphatidylcholine.
In order to achieve this objective, 2 different co-solvents,
ethanol and acetone, were used with supercritical carbon
dioxide and their performances were compared.
Materials and Methods
Materials
The crude soybean lecithin with oil content of 30% and
50% was obtained as a retentate of a membrane oil refining
process (Food Protein Research and Development Center,
Texas A&M Univ., College Station, Texas, U.S.A.). This is referred
to as “crude lecithin” in this manuscript. The sample
with 30% oil contained 20% phosphatidylcholine (PC), 13%
phosphatidylethalonamine (PE), and 10% phasphatidylinositol
(PI); the 1 with 50% oil contained 14% phosphatidylcholine
(PC), 10% phosphatidylethalonamine (PE), and 9% phosphatidylinositol.
Carbon dioxide used in the extractions was
obtained from Brazos Valley Welding Supply Inc. (Bryan, Texas,
U.S.A.). Ethanol (99.8%) and acetone (99.5%) were purchased
from Omni Solv-EM Industries (Gibbstown, N.J.,
U.S.A.) and VWR Scientific Products (West Chester, Pa.,
U.S.A.) respectively.
Experimental design
The experimental apparatus used for the removal of oil
from crude lecithin is shown in Figure 1. Two separate syringe
pumps (Isco Inc., Lincoln, Nebr., U.S.A.) were employed
for delivery of carbon dioxide and the co-solvent,
ethanol or acetone. The flow rates of CO 2 and the co-solvent
necessary to achieve the desired composition of the SC-CO 2 /
co-solvent mixture were calculated from a mass balance.
Density values of SC-CO 2 /ethanol and SC-CO 2 /acetone were
taken from Pohler and Kiran (1997a, 1997b). After bringing
the system to the desired temperature and pressurizing with
CO 2 to the desired pressure, CO 2 and the co-solvent were
mixed and passed through an equilibration coil. The flow
was passed through a bypass line until the steady state was
reached.
Outlet flow rate of co-solvent was determined by measuring
the volume collected in a sampling vial with respect to
time after expansion. The sampling vial contained activated
carbon, and it was cooled in an ice-bath to prevent the evaporation
of the co-solvent in order to close the mass balance.
CO 2 flow rate was measured with a flow meter. Once the
steady state was reached and the mass balance was confirmed,
the flow was switched to the extraction column. The
effluent from the extractor was bubbled through chloroform
in a sampling vial placed in the ice-bath after expansion via 2
backpressure regulators, in order to capture the extracted
material. Two backpressure regulators were used in series
for expansion in order to eliminate back pulsing in the extraction
column and to have a smooth, non-pulsing flow. Extracts
were dried under nitrogen and their amounts were determined
gravimetrically. Then the extracts were redissolved
in chloroform for further analysis of the individual phospholipid
fractions.
Extractions were conducted for 3 to 11 h on samples of 3
to 5 g of crude lecithin at pressures of 170 and 200 bar at a
temperature of 62 C. Co-solvent fractions of 5% and 10%
were used with the supercritical fluid flow rate of 1 and 2 ml/
min.
Acetone insolubles and phospholipid fractionation
Oil contents of the crude lecithin samples were determined
with the acetone insoluble matter, which was measured
according to AOCS Official Method Ja 4-46. Phospholipid
analyses were performed according to the high-pressure
liquid chromatographic (HPLC) analysis developed by
Hurst and Martin (1984). The HPLC flow rate was changed as
1 ml/min to provide a good separation of the peaks. There
was a 5-min isocratic equilibration time between each injection.
An injection loop of 5 L was used. HPLC column calibration
was performed using a standard mixture (obtained
from Sigma, St. Louis, Mo., U.S.A.), containing L--phosphatidylethanolamine
(PE), L--phosphatidylcholine (PC), L-
-phosphatidylinositol (PI), and L--lysophosphatidylcholine
(LPC). The standard mixture had 3.0 mg PC, 2.4 mg PE, 1.8
mg PI, and 0.6 mg LPC in 2 mL chloroform solution.
Results and Discussion
EXTRACTION OF OIL FROM GROUND SOYBEAN SEEDS WITH SUpercritical
carbon dioxide at 40 C and in the pressure
range of 200 to 700 bar was studied by Stahl and others
(1980), and the solubility behavior of soybean oil was reported.
Although some oil extraction was observed even at 200
Food Engineering and Physical Properties
Figure 1—Supercritical fluid extraction system: (1) Carbon
Dioxide Cylinder; (2) Co-solvent Reservoir; (3) Syringe Pump
for Carbon Dioxide; (4) Syringe Pump for Co-solvent; (5)
Equilibration Coil; (6) Heater; (7) Fixed-Bed Column; (8)
Backpressure Regulator; (9) Backpressure Regulator; (10)
Sampling Vial; (11) Flow meter
Figure 2—Lecithin deoiling with supercritical fluid mixtures
of carbon dioxide and ethanol. P = 200 bar, T = 62 C
Vol. 66, No. 6, 2001—JOURNAL OF FOOD SCIENCE 851

Deoiling of Crude Lecithin . . .
Food Engineering and Physical Properties
Table 1—Percentages of Phospholipids in the Crude Lecithin
with 40% oil and the Extracts
PI(%) PE(%) PC(%)
Crude lecithin (retentate) 10 13 20
Pure acetone extract 0.5 1.0 1.5
Pure ethanol extract 3.8 14.4 24.4
SCCO 2
/10% acetone extract 0.05 0 0
SCCO 2
/10% ethanol extract 0.04 0.12 1.75
SCCO 2
/5 % ethanol extract 0 0 0.41
bar by Stahl and others (1980), no extraction from the crude
lecithin was detected at 200 bar either at 40 C or at 70 C in
the current study. This might be due to the different nature
of oil sources used in the 2 studies. In the case of using crude
lecithin, a high mass transfer resistance would be expected
due to the high viscosity of the lecithin.
The preliminary tests on deoiling of crude lecithin with
pure CO 2 were encouraging at 900 bar and 90 C (Stahl and
Quirin 1985). In a later study, the best conditions for soybean
oil extraction from crude lecithin were observed to be at
high pressures between 600 and 1000 bar as well (Eggers and
Wagner 1993). Addition of ethanol as co-solvent with SCCO 2
was reported to increase the solubility of palm oil (Brunner
and Peter 1982), canola (Temelli 1992), and sunflower seed
oil (Cocero and Calvo 1996). Therefore, ethanol was chosen
as the first co-solvent and moderate pressures were used
(170 to 200 bar) to compare the effect of co-solvent addition
on deoiling of soybean lecithin. Soybean oil solubility appeared
to be directly proportional to ethanol content (Figure
2). Increasing the ethanol content from 5% to 10% increased
the oil removal from 23% to 54% in 140 min. Calvo and Cocero
(1996) observed a very similar effect of ethanol fraction.
The critical temperature of SCCO 2 /10 wt% ethanol mixture
was reported to be 60 C (Pohler and Kiran 1997b). Below
60 C, CO 2 and ethanol form 2 liquid phases. Extractions
in the current study were conducted at 62 C, a slightly higher
temperature than the critical temperature, to make sure
the extraction fluid was in 1 phase. Previous studies showed
that oil solubility decreases with temperature at low and
moderate pressures up to a crossover point (Temelli 1992;
Cocero and Calvo 1996). As the main interest of this research
was to perform the deoiling process at moderate pressures,
the minimum possible temperature was used, and the effect
of higher temperatures was not studied.
Figure 3 illustrates the effect of pressure on lecithin deoiling
with 10% ethanol. The total amount extracted at 170 bar
was slightly higher than the amount at 200 bar, although the
difference is probably within the experimental error limits.
Since the results were very similar at both pressures, 170 bar
was used as the operating pressure in the rest of the study.
Acetone was chosen as the second co-solvent because it is
still the choice solvent for commercial deoiling processes.
Gurdial and others (1993) studied critical properties of CO 2 /
acetone mixtures up to 8.4 wt% acetone content and Reaves
and others (1998) up to 9 wt% acetone content. Reaves and
others (1998) reported the critical temperature of SCCO 2 /9
wt% acetone as 59.2 C. Critical properties of mixtures having
acetone above 9 wt% have not been studied experimentally,
but Pohler and Kiran (1997a) predicted values in the entire
composition range. Here, the critical temperature of 90
wt%CO 2 /10 wt% acetone was reported as 75 C. Due to the
ambiguity in the literature, 10 wt% acetone was added in the
current study to CO 2 at 62 C, and 170 bar in a sapphire view
cell. A single phase was observed at these conditions; therefore
extraction with SCCO 2 /10 wt% acetone was also carried
out at 62 C and 170 bar for the purposes of comparison with
SCCO 2 /10 wt% ethanol extractions.
At 62 C and 170 bar, 10 wt% acetone and ethanol resulted
in similar extraction behavior (Figure 4). Phospholipids are
not soluble in CO 2 , but adding ethanol increased the polarity
of the solvent and caused small amounts of phospholipids to
be co-extracted. Table 1 summarizes the percentages of PI,
PE, and PC in the membrane retentate with 50% oil and in
the extracts obtained from this retentate. In addition to extractions
with SCCO 2 /10 wt% acetone, SCCO 2 /5 wt% ethanol,
and SCCO 2 /10 wt% ethanol, solvent extraction with pure
acetone and ethanol were also carried out. The phospholipid
composition of the extracts obtained by pure solvent extraction
is included in Table 1 as well. Acetone, when used either
as pure or as 10 wt% co-solvent in SCCO 2 did not cause any
appreciable extraction of phospholipids. On the other hand,
when extraction was done with pure ethanol, extracted material
had significant amounts of phospholipids, especially
PC, which was 24.4%. Using 10 wt% ethanol as a co-solvent
caused a slight co-extraction of phospholipids as well,
whereas with 5 wt% ethanol no phospholipid extraction was
observed. Therefore, it is clear that the slightly higher extrac-
Figure 3—Effect of pressure on oil extraction with SCCO 2
/
10% ethanol
852 JOURNAL OF FOOD SCIENCE—Vol. 66, No. 6, 2001
Figure 4—Deoiling of crude lecithin with different co-solvents.
P = 170 bar, T = 62 C

Deoiling of Crude Lecithin . . .
tion with 10 wt% ethanol than with 10 wt% acetone, which is
observed in Figure 4, was caused by the phospholipids extracted
along with oil.
Figure 5 illustrates oil removal from 2 different lecithin
samples with different oil contents as a function of time.
Both samples gave a high oil removal. When the sample with
30% oil content was used, 99% removal was obtained in 500
min, whereas the removal was 90% with the sample of 50%
oil content.
The final parameter studied was flow rate of the supercritical
fluid. Total amount of oil extracted with 10wt% acetone
at flow rates of 1.5 and 2 ml/min are shown in Figure 6.
Increasing the flow rate decreased the time of extraction.
This is an expected result as both the mass transfer rate due
to decreased mass transfer resistance and extraction fluid to
oil ratio increase with the increasing flow rate.
Conclusions
EFFECT OF USING ETHANOL AND ACETONE AS A CO-SOLVENT
in SCCO 2 on the deoiling of crude lecithin has been demonstrated.
Adding a co-solvent to SCCO 2 has made the deoiling
process possible at 170 bar, whereas no oil extraction was
observed when neat CO 2 was used at the same pressure.
Using 10wt% acetone or 5wt% ethanol in the SCF phase
did not cause any coextraction of phospholipids. Increasing
the ethanol fraction made the deoiling process faster, but it
also resulted in phospholipid coextraction. However, even
with 10 wt% ethanol, very small amounts of phospholipids
were extracted along with oil. It can be concluded that both
ethanol and acetone are suitable co-solvents in terms of increasing
the oil solubility without any considerable phospholipid
extraction. This allows the deoiling of crude lecithin at
lower pressures leaving behind a valuable product with a
high content phospholipids.
Figure 5—Effect of oil content on lecithin deoiling with
SCCO 2
/10% ethanol
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MS 20001580
Food Engineering and Physical Properties
Figure 6—Deoiling of crude lecithin with SCCO 2
/10% acetone
at different flow rates
Authors Teberikler and Akgerman are with the Chemical Engineering Dept.
and author Koseoglu is with the Food Protein Research and Development
Center at Texas A&M Univ., College Station, TX 77843. Direct inquiries to
Aydin Akgerman (E-mail: a-akgerman@tamu.edu).
Vol. 66, No. 6, 2001—JOURNAL OF FOOD SCIENCE 853