The Journal of Supercritical Fluids, 1995,8, 295-301
295
Supercritical Carbon Dioxide Extraction of Black
Pepper
Helena Sovov&,* Jaromir
Jez, Milena B6rtlov6, and Jitka St’astov6
Institute of Chemical Process Fundamentals, Academy of Sciences of the
Czech Republic, Rozvojova’ 135, Prague 16502, Czech Republic
Received January 17, 1995; accepted in revised form July 5, 1995
Oleoresin was extracted from ground black pepper with carbon dioxide at 28 MPa and 24 to 60 “C.
The yield and contents of piperine in the extract were determined as a function of extraction time and the
solvent amount. The concentration profile of piperine inside the fixed bed of pepper was also measured.
The total extract contained piperine and essential oil in the proper ratio to be used directly in food industry.
The experimental results showed a strong variation of extract composition during the extraction.
They were simulated using the extended Lack’s model with mass transfer coefficients in the solvent and
solid phase and with grinding efficiency as parameters. The parameters were determined individually for
each of the three extract components, representing essential oil, piper-me,and other nonpolar substances.
Keywords:
supercritical-fluid
extraction, black pepper, oleoresin, mass transfer, fractionation
INTRODUCTION
Food flavors and aroma are traditionally obtained
from spices in a rather complicated way. It involves separation of volatile essential oil with steam distillation
which is followed by extraction of oleoresin with liquid
solvent, separation of the solvent from the oleoresin using distillation, and mixing the oleoresin and essential oil
in the ratio occurring in the original spice. Extraction
with supercritical carbon dioxide enables us to obtain
complete and unchanged flavor and aroma in one step and
without any residues of organic solvents. As the extraction is carried out at a relatively low temperature and under inert atmosphere, the labile extract components are
preserved. The advantage of this procedure is demonstrated here on the extract from black pepper (Piper nigrum).
The dense carbon dioxide extraction from black pepper has been described in the literature several times.ib5 A
semicontinuous arrangement with the solvent flowing
through a fixed bed of ground pepper with constant rate
was used in all cases. Hubert and Vitzhum’** extracted
pepper at 350 atm and 60 “C with dry carbon dioxide for
three hours and then with wet CO2 at the same conditions
for another two hours. They obtained a yellowish semisolid mass with a crystalline fraction. The yield was 7 wt
%. There was 98% of piperine (the hot principle) transferred into the extract. Kasyanov et a1.3 extracted black
pepper, disintegrated into flakes of 0.14-0.18-mm thickness and a bulk density of 300 kg me3, with liquid carbon
0896-8446/95/0804-0295$7.50/O
dioxide below critical pressure. After three hours, they
obtained an oily liquid of yellow-brown color containing
yellow crystals. The yield was between 6.5 and 7.5 wt
%. Kurzhals at a1.4 extracted pepper at 52 “C and 78 bar
with a mixture of carbon dioxide and propane in molar ratio 58.8:41.2. After two hours there was 98% of piperine
transferred into the extract, and total yield was 18.7 wt %.
Beutler at a1.5 reported rate of pepper extraction to be dependent on the direction of solvent flow. Downflow of
carbon dioxide through the bed of extracted material was
more effective than the upflow; the initial loading increased from 2 mg g-l CO2 with the upflow to 3.4 mg g-*
CO2 with the downflow.
In this work, the change of mass transfer rate and
extract composition during the extraction are studied. The
process is described with a simplified mathematical model
of supercritical-fluid extraction from ground plant materials.6
MODEL
Mass Balance.
On the assumptions that a plug
flow of the solvent exists in the fixed bed of solid particles and that axial dispersion is negligible, the material
balances for an element of bed are given by
0 1995 PRA Press
296
SOVOV~et al.
The Journal of Supercritical Fluids, Vol. 8, No. 4, 1995
p,&+p
at s(l-E)-=,
Nab
’
If it is assumed that the solvent is solute-free at the entrance of the extractor and that all particles have the same
initial solute content x0, then the boundary conditions are
x(t=O,
h)=x,;
y(t=O,
h)=y,(h);
x=x,(1-rexp[-Z(h-hk)]}
(2)
for
rlZIY<Y’,,
y(t, h=O)=OP)
h>h,
x=1+exp[Y(41
-1exp(-Yh)
1
1
and the mass of solute extracted out of the fixed bed equals
l-r
E = Qjr(t,
h = 1)dt.
(4)
0
for
Rate of Interphase
Transfer.
As the plant
tissue is torn during the grinding, part of the solute is released. Concentration of this easily accessible solute in
the solid phase is rxc at the beginning of extraction. It is
extracted in the first period of extraction with a rate controlled by its diffusion in the solvent
J = k,ap, (yr - y) for x > (1 - r-)x,.
(5)
and for
r <Y<Y’,,
z-
for x5(1-r-)x,
E = Nx, w[ 1- exp( -Z)]
-!$p[Z(h
-1,]}
for
r/ZIY<Y’,
E=Nx,
1-ln
X
’
for Y < r / Z
(6)
with one solid-phase mass transfer coefficient k,.
Solution.
Equations 1 to 6 can be integrated
numerically to obtain the concentration profiles and the
mass of extract in dependence on time. However, an approximate analytical solution exists6 which can be applied
on conditions that (i) the accumulation term pf.c(&ldt) in
eq 2 can be neglected due to the low solubility yr, so that
the equation becomes
p.(l-E)-=J
5
Ndh
(7)
and with the mass of extract
The second period of extraction starts when the easily accessible solute has been removed. The rate of extraction
depends now on the diffusion of solute from the interior
of the plant tissue to the surface. Instead of taking into
account the complex nature of the vegetable matrix, we
apply a simplified formula
J=k,ap,(x-x+)
h 5 h,
(
l+[exp(Y)-l]exp
[ Y (;-
y)]o-‘)}I
y)
1
for
Y2Yy,.
63)
In these equations h, Y are dimensionless variables, hk is
the coordinate of the level inside the bed where the free solute has just been exhausted,
(24
h, =$ln(l+{exp[Y(Y-i)]-l}/r)
(ii) k, G kf, so that it holds in the second period y c<yr, x
- x+ 5 x, and eq 6 can be rearranged as follows:
J = k,ap,x( 1 - y / y,) for x 2 (1 - r)x,
(64
The set of eqs 1, 2a, 3-5, and 6a represents the extended
Lack’s model6 with the solid-phase concentration profile
x=x,[l-ZYexp(-Zh)]
for Y<rlZ
for
rlZSY<Y’k.
(9)
Yk is the dimensionless time when the free solute has
just been exhausted from the whole bed,
The Journal of Supercritical Fluids, Vol. 8, No. 4, 1995
(10)
Y’, =~++ln[l-r[l-exp(Y)]}
and Z, Y are quantities proportional
coefficients,
Extraction of Black Pepper 297
to the mass transfer
i
(__ -.--...._._._._.._._.__
- _____
z =
NkfaPf
Q(l - E)P, ’ ’ =
~fwo
Q(l - E)Y,
The solvent-phase mass transfer coefficient kf is assumed
to increase with interstitial solvent velocity according to
the relation7
k
f-
- ,,0.54
I
(11)
= Q0.54
which was proved in the range of v from 0.04 to 2.8 mm
I
j
!
@I
5
678
7_i
L
..--_._._--
__,.._.__i
Figure 1. Experimental apparatus for supercritical-fluid
extraction. 1, CO2 cylinder; 2, compressor; 3, pressure regulator; 4, surge tank; 5, extractor; 6, micrometer valve; 7,
separator; 8, wet flow meter.
s-1.
This model was used with good results to determine
the overall mass transfer coefficients kfa, k,a, and the
grinding efficiency r by matching the calculated and experimental extraction curves of grape oil.*
Multicomponent
Extraction.
If several solutes are extracted simultaneously, the overall mass of extract obtained during the time interval 9 - 9-1 equals
(13)
E(tj)-E(tj-l)=CIEi(tj)-Ei(tj-l)]
i
and the concentration of i-th component in j-th sample of
extract is
Wi,j
=[Ei(tj)-Ei(tjw~)]l[E(tj)sE(tj-,)]’
Cl41
If there are no interactions between the solutes, the model
of one-component extraction can be used to calculate the
amounts of extract E for each solute independently and to
substitute them for Ei in eqs 13 and 14.
EXPERIMENTAL
Materials.
Ground black pepper with mean particle size 0.05 mm was supplied by EKO Tanvald. It
contained 4.5 wt % piperine, 2.1 wt % essential oil and
11.5 wt % water. Average density of pepper determined
with pycnometer was 1339 kg m3, its bulk density after a
slight pressing was 636 kg rnM3. Density of pepper essential oil was 877 kg me3 at 20 “C.
The carbon dioxide was 99.5 to 99.7 wt % pure and
was supplied by Chemical Works Litvinov.
The amount of essential oil in pepper was determined using steam distillation. Concentration of piperine
in pepper was determined, after its quantitative extraction
with benzene, by UV spectrophotometry using a Unicam
SP1750. The maximum absorption peak of piperine in
benzene was at 342 nm. Piperine, limonene, a-pinene,
and Ppinene supplied by Fluka and declared as “purum”
were used as standards.
SCF extracts were analyzed by HPLC using a
Hewlett Packard 1090M chromatograph equipped with
diode array UV-VIS detector. The conditions were as follows: column 250-mm x 4-mm i.d.; Nucleosil C 18 5pm; mobile phase methanol; flow rate 0.6 mL mini.
Piperine content was determined at 340 nm, the other
components at 220 nm.
Equipment
and Procedure.
The supercritical-extraction apparatus is schematically represented in
Figure 1. It was operated in a single-pass mode of CO2
down through the bed of ground pepper, with extract recovery by depressurization to atmospheric pressure in micrometer valve. The bed of pepper was situated in the extractor between two layers of glass beads. The extractor
was a cylindrical stainless steel vessel immersed in thermostatic water bath. Two vessels were used alternatively:
150-mL extractor with 33-mm i.d., or 12-mL extractor
with 8-mm i.d. Extraction pressure was maintained
within 28 + 0.1 MPa. The capillary from the extractor to
the micrometer valve and the valve itself were wrapped
with heating tape and maintained at a temperature higher
than that in the extractor to prevent clogging. Extraction
yields were measured gravimetrically by collecting the
products precipitated at room temperature in glass U-tubes
used as the separator. The mass of carbon dioxide was determined by wet flow meter and by the pressure and temperature conditions measured at the end of assembly.
Extract samples were stored in the dark in a refrigerator to
prevent chemical reactions such as isomerization.
Conditions.
Solvent flow rates ranged from 0.8
to 1.9 g min-l, interstitial solvent velocity was in the
range from 0.06 to 1.5 mm 5-l. Pepper feed was between
6 and 61 g and the amount of CO;! consumed in one experiment was in the range from 180 to 540 g. Extraction
pressure was 28 MPa in all experiments, extraction temperatures were 24, 40, and 60 “C, total number of extraction experiments was 22.
298
Sovovi et al.
The Journal of Supercritical Fluids, Vol. 8, No. 4, 1995
110
100
6
90
00
70
2
E
60:
501
40:
30:
20:
10
8
Figure 2. Chromatozram of extract samnle obtained at 40 “C, detected at 220 nm. Conditions: pepper feed 31 g, solvent flow
fate 1.8 g mint, extract collected for 17 min from t = 10 min. Components: l-3, essential oil, 6, piperine, 4, 5, 7, and 8, unidentified substances.
One experiment at each temperature was stopped
when 30 to 60% of piperine had been extracted.
Depressurized bed of pepper was transferred gradually,
starting from the top, into six sampling vessels. Piperine
profile in the bed was estimated from the average piperine
concentrations in the individual samples.
RESULTS
Extracts
and
Rate
of
Extraction.
Appearance of extract samples taken during the extraction
was changing from a yellow liquid containing white crystals, over a pasty substance changing from yellow to orange and red and fading again, up to a light yellow powder. This suggests that the extraction of liquid essential
oil and carotenoids was practically complete.
A typical chromatogram of a pasty extract sample is
shown in Figure 2. The substances with longest retention times were identified by comparison with a chromatogram of pepper distillate (see Figure 3) as the main
components of essential oil. The oil is known to consist
mainly of monoterpenes as a-pinene, sabinene, ppinene,
and limonene,9 oxygenated monoterpenes as p-menthen-l01, 2,8-p-menthadien-l-01
and trans-pinocarveol,10 and
sesquiterpenes, as caryophyllene.3 Using limonene, CG
pinene, P-pinene, and piperine as standards, peak 2 was
identified as a mixture of monoterpenes, and peak 6 as
piperine. Substances corresponding to peaks 4, 5, 7, and
8 are non-volatile because they were not detected in the
essential oil. They are probably not polar since they
show high solubility in carbon dioxide. Most probably
these peaks represent lipids.
Starting here, only three (pseudo)components will
be distinguished in the extract: essential oil comprising
peaks l-3, piperine with peak 6, and lipids denoting the
other compounds. Figure 4 shows the changes of their
Figure 3. HPLC analysis of essential oil obtained from
black pepper by steam distillation.
0
0.2
1.3
2.1
3.7
8.3
Q/N
Figure 4. Changes of peak areas in HPLC chromatograms
of extract samples at the temperature 40 “C.
The Journal of Supercritical Fluids, Vol. 8, No. 4, 1995
Parameters
Component
of Extraction
T(“C)
Model
Extraction of Black Pepper 299
TABLE I
for 1, Essential
A,
r
Yr
Oil;
2, Piperine;
kfa* (mini)
3, Lipids
k,a (mini)
1
24
40
60
0.021
0.8
0.02
0.04
0.03
0.6
0.6
0.4
0.007
0.010
0.020
2
24
40
60
0.045
0.82
0.0013
0.0019
0.0033
0.9
0.8
0.6
0.003
0.004
0.008
3
24
40
60
0.013
0.017
0.019
0.5
0.003
0.005
0.004
0.2
0.2
0.16
0.004
0.006
0.012
* Parameter kp is related to the fixed interstitial solvent velocity v = 1 mm s-i
mutual relation in extract samples taken during the extraction. Peak areas detected by HPLC at 220 nm are plotted
against the mean extraction times multiplied by specific
solvent flow rate Q/N. Initial samples contain mainly the
essential oil, which is extracted fast. Percentage of piperine in the extract increases and piperine becomes the main
component in the extract sample at a distinct extraction
time. The higher the extraction temperature, the shorter
is this time.
Rate of extraction was increasing with the temperature. For example, in experiments carried out in the
smaller extractor, the specific amount of carbon dioxide
QtlN necessary to extract 5 wt % of organic compounds
from black pepper was 18 at 23 “C, 11 at 40 “C, and only
6 at 60 ‘C. The experiments were stopped after extraction
had slowed down below 0.5 mg g-i CO;?. As a result, the
yield obtained was 6.7 to 7.6 wt %, and the total extract
contained 28 to 31 wt % essential oil, 50 to 54 wt %
piperine, and 15 to 22 wt % other substances. For comparison, the standardized black pepper oleoresin contains
50 wt % piperine and 15 mL essential oil/100 g.
Comparison
with the Model.
There is an
interaction between the essential oil and lipids during the
extraction with carbon dioxide.” Besides, the solubility
of essential oil in carbon dioxide under extraction conditions is too high to permit neglecting the accumulation
term in eq 2. However, as most of the essential oil was
extracted in a short initial period and the further course of
extraction was not affected by its presence, we did not take
into account these complications and tried to fit the extended Lack’s mode1 on the experimental data, substituting
Ei, i = 1, 2, and 3 calculated from eq 8 into eqs 13 and 14.
Carbon dioxide density at 28 MPa was determined
with Altunin and Gadetskii’s equation:i2 pr = 968 kg mm3
at 24 “C, pf = 899 kg me3 at 40 “C, pf = 8 15 kg rnM3at 60
‘C. Density and void fraction of the solid phase, ps =
1340 kg m-3, E = 0.53, and the initial content of piperine
-0
0.2
0.4
0.6
0.8
i
h
Figure 5. Measured and calculated solid phase concentration profiles. Conditions: pepper feed 61 g, solvent flow
rate 1.8 g min.‘, extraction temperature 40 “C. Extraction
was stopped after 300 min. a) measured mean concentrations,
b) calculated profile.
and essential oil, x0’ = 0.021, xo2 = 0.045, were measured
independently.
The other model parameters listed in Table I were
determined by matching eq 13 to the experimental extraction curves, eq 14 to piperine concentration in extract
samples, and eq 7 to the experimental piperine concentration profiles in the bed. As these experimental data contain more information on piperine than on the pseudocomponents, parameters of piperine could be fitted better
than the others. The regression was performed at each extraction temperature separately, with sum of squares of
deviations of calculated points from experimental data as
the criterion. Solid-phase mass transfer coefficients k,a
and piperine solubility yr2 were found to be more temperature dependent than other parameters.
Accuracy of the piperine parameters was estimated
at 5% for r, 10% for yr and kfa, and 20% for k,a.
300
Sovovi et al.
ov
0
7
The Journal of Supercritical Fluids, Vol. 8, No. 4, 1995
30
10
CX,N20
Figure 6. Measured and calculated extraction curves.
Conditions: pepper feed 7 g, solvent flow rate 1.1 g min.‘,
extraction temperature 40 “C. (B) experimental data; (-)
model: a) piperine; b) piperine + essential oil; c) total extract.
80 ,
I
of the first section of the curve, r to the height of the edge
between the slow and fast extraction region, the solubility
yr to the horizontal shift of the steep section from the
origin, and kfa to the slope of this section. Slope of the
calculated extraction curve c in Figure 6 decreases step by
step, as the extraction curves of individual components
switch to the slow extraction period. Slight discrepancy
between the calculated extraction curve and experimental
points may be caused by hold-up of a small portion of extract inside the micrometer valve and by its irregular release in the course of extraction. In Figure 7, the calculated time dependence of piperine concentration in extract
samples shows unusual sharp-edge points corresponding
to the transitions between the fast and slow periods of extraction and suggests thus limits of application of the
simplified model.
CONCLUSION
Strong time fractionation takes place during the extraction of black pepper oleoresin with carbon dioxide at
temperatures ranging from 24 to 60 “C and at a pressure
of 28 MPa. It is explained by different solubilities and
mass transfer coefficients of extracted components - essential oil, piperine, and lipids. The rate of extraction
grows with the temperature because of the increasing solubility of piperine in carbon dioxide, and, in the second
extraction period, also due to the faster diffusion of all
components through the plant tissue.
ACKNOWLEDGMENT
The authors gratefully acknowledge the support of
the Grant Agency of the Czech Republic (Grant No.
5 10/93/2283).
0
2
4
6
8
U/N
Figure 7. Measured and calculated concentrations of
piperine in extract samples. Conditions: pepper feed 61 g,
solvent flow rate 1.7 g min-r, extraction temperature 24 “C.
(W) experimental data; (-)
model.
NOTATION
a
E
h
J
k
N
Q
Accuracy of these parameters for essential oil and lipids
was twice or three-times smaller. As mentioned above,
the parameters yr, kra for essential oil lack physical meaning due to the model inadequacy. The increase of the fitted initial concentration of the lipid pseudocomponent
with temperature could indicate that some components of
this mixture were practically insoluble in carbon dioxide
at lower temperatures.
Typical experimental data and corresponding model
curves are shown in Figures 5 to 7. In Figure 5, the easily accessible piperine is already exhausted from the first
quarter of the bed, where the slope of concentration profile
is relatively small. Fast increase of the slope denotes the
region of extraction from the surface of particles. In the
second half of the bed, the solvent is almost saturated and
the curve becomes flat. Parameter k,a relates to the slope
r
t
T
V
X
Y
Yr
Y
Z
specific interfacial area
mass of extract
dimensionless axial coordinate, 0 5 h 5 1
mass-transfer rate
mass-transfer coefficient
solid feed
mass flow rate of solvent
grinding efficiency, 0 5 r 5 1
time
temperature
interstitial solvent velocity
solid-phase concentration (g g-r)
solvent-phase concentration (g g-r)
solubility (g g-l)
parameter of the second period, defined by eq 11
parameter of the first period, defined by eq 11
GREEK
LETTERS
i
void fraction
wavelength
density
G
[=(Qy,/Nx,)t],
dimensionless time
SUPERSCRIPT
+
at interfacial boundary
The Journal of Supercritical Fluids, Vol. 8, No. 4, 1995
SUBSCRIPTS
f
i
j
k
S
0
1
2
3
solvent phase
i-th component
j-th sample
boundary between the first and second period
solid phase
initial conditions
essential oil
piperine
lipids
Extraction of Black Pepper 301
(4)
(5)
(6)
(7)
(8)
Kurzhals, H.-A.; Hubert, P. German Patent 2844781,
1980.
Beutler, H.-J.; Gaehrs, H. J.; Lenhard, U; Luerken, F.
Chem. Ing. Technol. 1980,60,
773.
SovovA H. Chem. Eng. Sci. 1994,49, 409.
Lee, A. K. K.; Bulley, N. R.; Fattori, M.; Meisen, A. J.
Am. Oil Chem. Sot. 1986,63, 921.
Sovova, H.; Kucera, J.; Jez, J. Chem. Eng. Sci. 1994,
49, 415.
(9)
Wrolstad, R. E.; Jennings, W. G. J. Food Sci. 1965,
30, 274.
REFERENCES
(1)
(2)
Vitzthum, 0.; Hubert, P. German Patent 2127611,
1973.
Hubert, P.; Vitzthum, 0. G. Angew. Chem. Int. Ed.
1978,
(3)
17,
710.
Kasyanov, G. I.; Pekhov, A. V.; Taran, A. A.
Naturalnye Pishchevye Aromatizatory CO,
Ekstrakty (Natural Food Aromas - CO, Extracts);
Pishchevaya Promyshlennostj: Moskva, 1978; pp 65,
88, 99.
(10) Jennings, W. G. J. Food Sci. 1971,36, 584.
(11) Sovova, H.; Komers, R.; Kucera, J.; Jez, J. Chem. Eng.
Sci. 1994, 49, 2499.
(12) Angus, S.; Armstrong, B.; de Reuck, K M.
International Thermodynamic Tables of the Fluid State
Carbon Dioxide; Pergamon Press: Oxford, 1976; p 38.