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

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