Solubility of Binary Solid Mixture -Carotene-Capsaicin in
Dense CO2
kerget and
eljko Knez*
Received for review December 11, 1996. Accepted February
27, 1997.
Abstract:
The equilibrium solubilities of binary solid mixture
-carotene-capsaicin in liquid and supercritical
CO2 were measured using a static-analytic method.
The solubilities of solid mixture components
in CO2 were determined at 25 and 40
C in the pressure
range from 100 to 300 bar. Measurements
were performed at two mass ratios of solid components
[w(carotene):w(capsaicin) 1:1 or
2:1,
respectively] and it was found that the mass ratio of both components
did not influence the
equilibrium solubility. The equilibrium data of the ternary system
-carotene-capsaicin-CO2 were
compared to the equilibrium solubility data of binary systems
-carotene-CO2 and
capsaicin-CO2.
It could be observed that the solubility of capsaicin was lower in
the presence of
-carotene. The
solubility of
-carotene in CO2 did not change in the
presence of capsaicin. As shown in the examples
in the paper, the data presented are important for designing the
separation process of coloring and
hot components from paprika.
Keywords: Dense carbon dioxide; solubility data; process parameters; paprika
The solubility data of solid mixtures in supercritical fluid (SCF) are rarely reported in literature. For most of the reported systems it was observed that the solubility of a particular solid component in the ternary system is considerably higher than that in the pure solid-SCF system at the same temperature and pressure (Lee et al., 1988). This was valid for the systems where the solutes were highly soluble in SCF. It was also reported for the system phenanthrene and 2,3-dimethylnaphthalene, the solubilities of which are low in the binary case, that the solubilities of the components decrease in the ternary case (Dobbs et al., 1987). However, the fundamental mechanism of the solubility changes that appear in solid mixtures has not yet been completely understood.
Capsaicin and -carotene are both components of
paprika (Capsicum annuum), one of the oldest
source
of natural colorants used in the food and cosmetic
industries.
-Carotene is one of several
carotenoids
found in paprika. Capsaicin is the most important
component among various capsaicinoids which causes
pungency of paprika and should therefore be removed
from coloring compounds (carotenoids). On the other
hand, capsaicin is used in stimulation medicine because
of its irritating effect on the receptors participating in
circulatory and respiratory reflexes. The extraction
process of paprika with organic solvents has shown
some disadvantages (solvents cannot be completely
removed, high temperatures of distillation can cause
extract denaturation, extracts contain byproducts as
fatty acids, capsaicin, etc.), which were minimized using
SCF as an extraction solvent. A process for the
production of paprika oleoresin with SC CO2 is relatively
well
described in literature (Coenen et al., 1982; Coenen and
Kriegel, 1983; Coenen and Hagen, 1983; Knez et al.,
1991; Knez and
kerget, 1994).
The solubility data for -carotene and capsaicin in
CO2 can be found in literature (Sakaki, 1992;
Cygnarowicz et al., 1990;
kerget et al., 1995; Knez and
Steiner, 1992); however, there were no data on the
behavior of the ternary system
-carotene-capsaicin-CO2.
In the present work the solubility of binary solid
mixture -carotene-capsaicin in CO2 was
determined.
The obtained data were compared to the solubility of
pure solid components in dense CO2 at the same
conditions (Knez and Steiner, 1992;
kerget et al.,
1995).
Apparatus. For the solubility measurements a
static-analytic method was used. The detailed description can
be
found in Knez and Steiner (1992) and kerget et al.
(1995).
Reagents. -Carotene with a minimum purity of 95%
was
obtained from Sigma Chemical (St. Louis, MO), Cat.
No.
C-9750. Capsaicin with a minimum purity of 98%
was
obtained from Sigma Chemical (St. Louis, MO), Cat.
No.
M-2028. Chloroform was 99% pure and was obtained
from
Kemika (Zagreb, CRO). CO2 was supplied by Linde
(Celje,
SLO) and was 99.97% pure.
Procedures. The 500 mL equilibrium cell was loaded
with
a sufficient amount of the -carotene-capsaicin mixture
with
appointed mass ratios (0.1 g of each component or 0.2 g of
-carotene and 0.1 g of capsaicin). The CO2 from the
supply
tank was cooled to a liquid state and compressed into the
equilibrium cell by a high-pressure pump. The
temperature
in the autoclave was regulated with a heating jacket
(accurate
to ±0.5
C). The component mixture-CO2
suspension was
mixed with a mechanical oscillating device under constant
operating conditions until equilibrium was reached. After
1
h of phase separation a sample of the mixture-CO2
solution
(approximately 1 mL) was taken through the sampling valve
into a trap with solvent (chloroform) where the components
were solubilized. The trap was immersed in a sub-zero
ethylene glycol-water bath. The amount of CO2
released was
measured with a rotameter. The pressure observed
while
taking the samples changed from 0.5 to 1 bar. The
temperature change was not detected. The volume of the
deadspace
between the cell and sampling valve was 1.1 ×
10-2 mL, when
compared with the volume of sample (approximately 1 mL)
was only 1.1%.
Since the quantity of the sample was sufficiently small compared to the volume of the equilibrium cell, further experiments could be done.
The concentration of solutes in the chloroform was determined by UV spectrophotometry. The absorbance was measured (accurate to ±0.001) at the absorption maximum of
460
nm for -carotene and 280 nm for capsaicin. It was found
that
capsaicin did not influence the absorbance of
-carotene at
460
nm. Low absorbance of
-carotene at 280 nm was
considered
in the determination of capsaicin concentration. The
HPLC
was used in order to check the purity of dissolved
-carotene
because it is labile against light and heat. The
chromatographic conditions were as follows: column, RP18 (ODS,
octadecylsilane-coated silica); mobile phase,
acetonitrile/dichloromethane/methanol (v/v/v 65/25/1); flow rate of mobile
phase,
2.5 mL min-1; wavelength, 450 nm. The
stability of capsaicin
was tested by TLC (plate, Silica gel 60 F 254; solvent,
diethyl
ether; reagent for detection, dichloroquinonechloroimide).
The
method is described by Wagner et al. (1983).
The solubility data of -carotene and capsaicin in the
ternary system
-carotene-capsaicin-CO2 at two
mass
ratios of solid components
w(carotene):w(capsaicin) =
1:1 and 2:1 are presented in Figures
1 and 2. It can
be
observed that the mass ratio of components has no
influence on the equilibrium solubilities. The
comparisons of binary and ternary solubility data for each
component show that the solubility of
-carotene does
not change in the presence of capsaicin. Oppositely,
the
solubility of capsaicin is lower in the presence of
-carotene. The solubility at 25
C is even
independent
of pressure.
For the binary system capsaicin-CO2 (Knez
and
Steiner, 1992) phase behavior where a slight inflection
of the 60 C solubility isotherm at approximately 260
bar could be observed (Figure 2). The melting point
of
capsaicin at ambient conditions is 65
C. In
present
work it was observed that in presence of CO2
the
melting point of capsaicin decreases with increasing
pressure to the temperature minimum of approximately
40
C at 100 bar.
For the 40 C solubility isotherm of capsaicin when
in mixture with
-carotene a similar trend as for the
60
C solubility isotherm of pure capsaicin can be
observed. From previously reported data about
the
presence of a second solid increasing the freezing point
depression significantly, regardless of whether its triple
point is higher or lower than that of the first solid
(Zhang et al., 1992), in the ternary system
-carotene-capsaicin-CO2 an even greater decrease of the
capsaicin
melting point can be proposed.
An attempt was made to correlate phase equilibrium
of the systems capsaicin-CO2 and
-carotene-CO2 with
the Peng-Robinson equation of state (McHugh and
Krukonis, 1986; Prausnitz et al., 1986; Van Ness and
Abbott, 1982). The required critical properties of
both
solid components (Table 1) were estimated with the
Lydersen group contribution method
(Lydersen, 1955;
Klincewicz and Reid, 1984; Somayajulu, 1989). The
interpolated sublimation pressure (Table 1) was estimated by the Riedel method (Van Ness and Abbott,
1982). Solid molar volume was obtained with the
regression of experimental data. The agreement of the
model with the data was bad, so no further correlation
of the binary solid mixture solubility data in CO2
was
carried out because the deviation would probably be
further enhanced. Peng Robinson equation of state is
obviously not an appropriate model for predicting equilibrium of the system capsaicin-CO2 (and also
-carotene-capsaicin-CO2). Beside the fact that all
physical
properties of solid components are predicted with models, the model used does not consider the solubilization
of CO2 in the capsaicin, which occurs due to
observed
melting point depression.
The extraction ratio K, defined
as
![]() |
Figure 3 Extraction ratios K of ![]() ![]() ![]() ![]() ![]() ![]() |
The dependency of extraction ratio on the pressure
confirms the results of paprika extraction experiments.
It was found (Knez et al., 1991; Knez and kerget,
1994)
that the best quality of paprika extract was obtained
when extraction was performed in two
steps:
The extraction data for three experiments at different conditions are summarized on Figure 4. With higher pressure or/and temperature the amount of extractable substances in the first step was increased due to lower selectivity of CO2. Similar data can be also found in literature (Coenen et al., 1982; Coenen and Kriegel, 1983; Coenen and Hagen, 1983).
From the obtained solubility data it can be concluded
that at lower pressures a higher separation of both
components can be achieved. This confirms the fact
that
the quality of paprika extract of coloring component is
better, when the aromatic components are extracted at
moderate pressure (90 bar) and moderate temperature
(40 C).
C1, -carotene; C2, capsaicin; Ci
(i = 1-4), constants;
CU, color units; K, extraction ratio; Mw,
molecular
weight (g/mol); Ps saturated vapor pressure
(Pa); Pc,
critical pressure (Pa); SCF, supercritical fluid;
Tb,
normal boiling point (K); Tc, critical
temperature (K);
Vc, critical volume (m3/kmol);
y, mole fraction; w, mass
ratio; zc, critical compressibility;
,
acentric factor.
*
To whom correspondence should be addressed (phone
+386 62 22 94 461; fax +386 62 22 50 13, +386 62 22
77 74; e-mail ZELJKO.KNEZUNI-MB.SI.
Abstract published in Advance ACS
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property |
|
estimated value |
method of estimation |
Capsaicin |
|||
molecular weight |
Mw (g/mol) |
305.42 |
|
normal boiling point |
Tb (K) |
853.7 |
Joback |
critical temperature |
Tc (K) |
1062.11 |
Lydersen |
critical pressure |
Pc (Pa) |
17.125 × 105 |
Lydersen |
critical volume |
Vc (m3/kmol) |
0.95 |
Lydersen |
critical compressibility |
zc |
0.1842 |
definition |
acentric factor |
|
1.1851 |
definition |
vapor pressure |
Ps (Pa) |
|
|
|
C1 |
154.4 |
Riedela |
|
C2 |
-25995.0 |
|
|
C3 |
-16.683 |
|
|
C4 |
0.47359 × 10-18 |
|
|
|||
molecular weight |
Mw (g/mol) |
536.88 |
|
normal boiling point |
Tb (K) |
1209.38 |
Joback |
critical temperature |
Tc (K) |
1485.57 |
Lydersen |
critical pressure |
Pc (Pa) |
7.993 × 105 |
Lydersen |
critical volume |
Vc (m3/kmol) |
1.846 |
Lydersen |
critical compressibility |
zc |
0.1195 |
definition |
acentric factor |
|
0.6927 |
definition |
vapor pressure |
Ps (Pa) |
|
|
|
C1 |
105.97 |
Riedela |
|
C2 |
-25171.0 |
|
|
C3 |
-10.393 |
|
|
C4 |
0.43787 × 10-18 |
|
a ln Ps (Pa) =
C1
+
+ C3
ln T +
C4T6.