Solubility of β-Carotene and Glyceryl Trioleate Mixture in Supercritical

Feb 21, 2014 - Faculty of Chemistry and Chemical Engineering, University of Maribor, Smetanova 17, SI-2000 Maribor, Slovenia. •S Supporting Informat...
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Solubility of β‑Carotene and Glyceryl Trioleate Mixture in Supercritical CO2 Darija Cör, Mojca Škerget, and Ž eljko Knez*

Faculty of Chemistry and Chemical Engineering, University of Maribor, Smetanova 17, SI-2000 Maribor, Slovenia S Supporting Information *

ABSTRACT: The phase behavior of the system β-carotene− glyceryl trioleate−CO2 has been investigated using a variablevolume high-pressure cell. The mass fraction of β-carotene in the initial mixture with glyceryl trioleate was 0.1. The gas rich phase was sampled in the pressure range from (25 to 60) MPa at temperatures of (313, 323, and 333) K. The solubilities in dense CO2 under the investigated conditions were in the range from (4.51·10−7 to 1.22·10−5) mol·mol−1 for β-carotene and from (0.38·10−3 to 1.91·10−3) mol·mol−1 for glyceryl trioleate. The results were compared with those found in the literature. The experimental data were correlated using a density based model proposed by Chrastil. Table 1. Studies of the Phase Equilibria for the β-Carotene− CO2 System

1. INTRODUCTION Carotenoids are natural pigments, and they include compounds such as antioxidants which are beneficial for health and decrease the risk of many diseases. They are present in plants and other organisms, that require light energy for photosynthesis and their role is to protect against oxidative damage that may arise during this process. They are yellow, orange and red plant pigments, soluble in fats. One of the most common carotenoid is β-carotene (C40H56) which has very strong red-orange color, is highly unsaturated, and contains 11 conjugated carbon− carbon double bonds.1 β-carotene is a hydrophobic antioxidant with no polar functional groups, soluble in lipids, with very high sensitivity to heat, light, and air.2 It is one of the most commonly used natural pigment in foods and one of the most important food additives.3 It is also one of the most efficient vitamin A precursors, and it helps protect humans against different types of cancer. Sustainable extraction of carotenoids nowadays is performed by supercritical extraction with carbon dioxide (SC−CO2), which is a nontoxic, nonflammable, chemically inert solvent and has easily attainable critical conditions (Tc/K = 304, pc/MPa = 7.38).4 Solubility or phase equilibrium data are very important for designing new processes where supercritical fluids are used as solvents.5 A number of studies have been published on the solubility of β-carotene in supercritical fluids.1,2,4−15,18,19 All studies listed in Table 1 deal with binary systems of β-carotene and SC−CO2, except for Sovova et al.4 and Araus et al.19 who also investigated the ternary system. From Table 1 it is evident that most experiments were carried out in a temperature range from (313 to 333) K and pressures up to 30 MPa. A high molar mass and specific shape of the β-carotene molecule probably indicate that its solubility in SC CO2 is lower in comparison with other fat soluble vitamins.6 Subra et al. carried out research on the © 2014 American Chemical Society

systema

a

p/MPa

T/K

B B T B B

9.0−28.0 6.0−35.0 12.0−28.0 10.0−30.0 20.0−32.0

310−340 313−333 313−333 298−313 313−353

B B B B B B B B B B and T

20.0−45.0 5.0−80.0 5.0−50.0 10.0−30.0 12.0−30.0 30.0 80.0−180.0 15.0−28.0 12.0−20.0 17.0−35.0

313−343 288−328 288−328 308−323 313−333 313−333 308−323 313−333 313−323 313−333

author(s) Subra et al. (1997)1 Hansen et al. (2001)2 Sovova et al. (2001)4 Škerget et al. (1995)5 Johannsen and Brunner (1997)6 Cygnarowicz et al. (1990)7 Jay et al. (1991)8 Jay and Steytler (1992)9 Sakaki (1992)10 Mendes et al. (1999)11 Cocero et al. (2000)12 Kraska et al. (2002)13 Huang et al. (2006)14 Saladana et al. (2006)15 Araus et al. (2011)19

B is binary; T is ternary.

solubility of β-carotene in SC CO2. The solubility was studied in a pressure range from (9 to 28) MPa and temperatures of (310, 320, 330, and 340) K. The obtained solubility values were in the range between (10−8 and 10−6) mol·mol−1, and the experimental data were correlated using the density-based equation proposed by Chrastil.1 Mendes et al. measured the solubility of β-carotene in CO2 at temperatures of (313, 323 and 333) K and pressures up to 30 MPa. The measured values Received: June 10, 2013 Accepted: February 11, 2014 Published: February 21, 2014 653

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were in the range from (2.0·10−9 to 6.27·10−6) mol·mol−1 and the highest solubility was obtained at 333 K and 27.4 MPa.11 Sovova et al. investigated the solubility of β-carotene in SC CO2 at pressures between (20 and 30) MPa and temperatures of (313, 323, and 333) K with vegetable oil as cosolvent.4 The solubility of β-carotene in SC CO2 with vegetable oil cosolvent was in the range from (2.28·10−7 to 7.47·10−7) mol·mol−1. Because of the poor solubility of carotenoids in pure SC−CO2 cosolvents such as triglycerides or/and alcohols can be used to increase the amount of dissolved compound.4 Araus et al. investigated the solubility of β-carotene−CO2 binary system and of the β-carotene−glyceryl trioleate−CO2 ternary system. The experiments were carried out at temperatures (313, 323, and 333) K and at pressures up to 35 MPa. The amount of βcarotene in vapor phase of the ternary system (β-carotene + glyceryl trioleate + CO2) was between (0.035·10−6 and 3.27· 10−6) mol·mol−1.19 Triglycerides are the main components in natural fats and oils and are also used as a raw material in many industries from petrochemical to pharmaceutical.16,17 One from the group of triglycerides is glyceryl trioleate. The phase equilibria of glyceryl trioleate in CO2, propane, pressurized methanol, and SF6 have already been investigated by other authors.20−28 Literature references on experimental data of the solubilities or phase equilibria of pure glyceryl trioleate, in binary and ternary systems in the presence of CO2 are presented in Table 2.

observed the phase behavior of methanol−glyceryl trioleate system at (6.0, 8.0, and 10.0) MPa in the temperature range from (353.2 to 463.2) K.24 Later a similar mixture of triglycerides−methanol and its phase behavior were investigated by Glišić.25 Garcia et al. performed high pressure equilibrium calculations for CO2−oleic acid−glyceryl trioleate system in the pressure range from (20 to 30) MPa and temperature range from (313 to 333) K. Equilibrium calculations were performed with ASPEN Plus software, and equilibrium data from Bharath et al. were used.26 Masuda et al. measured the solubility of glyceryl trioleate in supercritical carbon dioxide by a continuous flow system at various temperatures of (313, 323, 333, and 343) K and pressures of (15, 20, and 25) MPa. It was found out that solubility of glyceryl trioleate increases with pressure. Solubilities were in the range from (0.0107 to 0.286) mol·mol−1.27 Perko et al. determined experimentally the phase equilibrium of tristearin and glyceryl trioleate in CO2 and SF6. The experiments were carried out at temperatures (333, 343, and 363) K and over a pressure range from (1.6 to 45.1) MPa for CO2 and (1.6 to 31.0) MPa for SF6.28 Araus et al. have investigated a similar system as presented in our study, but at lower pressure conditions. The concentration of glyceryl trioleate in the ternary system (β-carotene−glyceryl trioleate−CO2) was in the range from (0.01 to 0.39) mmol· mol−1.19 Literature review indicated that the available phase equilibrium data for mixtures of triglycerides and β-carotene in SC CO2 are very limited, especially at elevated pressures. Because of the lack of solubility data at higher pressure we investigated the composition of the ternary β-carotene−glyceryl trioleate−CO2 system at pressures up to 65 MPa. The aim of the present research was also to investigate the phase behavior of the ternary mixture β-carotene−glyceryl trioleate−CO2 and to observe the effect of the added cosolvent glyceryl trioleate on the solubility of β-carotene in SC CO2. Therefore this study may represent a valuable contribution to the understanding of the phase behavior of that kind of systems. The mass fraction of β-carotene in the initial mixture with glyceryl trioleate was w = 0.1. The phase equilibrium of the ternary mixture β-carotene−glyceryl trioleate−CO2 was experimentally determined, and the experimental data were compared with those found in the literature. The experiments were performed in a pressure range from (25 to 60) MPa and temperatures of (313, 323, and 333) K.

Table 2. Studies of the Phase Equilibria for the Glyceryl Trioleate−CO2 System

a

systema

p/MPa

T/K

author(s)

B and T B B B B

17.0−35.0 10.0−52.0 5.4−24.1 15.0−25.0 1.9−50.7

313−333 333−353 313−333 313−343 333−363

Araus et al. (2011)19 Weber et al. (1999)20 Chen et al. (2000)21 Masuda et al. (2000)27 Perko et al. (2012)28

B is binary, and T is ternary.

Weber et al. measured the phase equilibrium of CO2−glyceryl trioleate binary mixture at (333 and 353) K and pressures up to 52 MPa. The solubility of glyceryl trioleate in CO2 was in the range from (8·10−5 to 1.2·10−3) mol·mol−1.20 Chen et al. determined experimentally the vapor−liquid equilibrium for the binary system CO2−glyceryl trioleate at (313 and 333) K and in the pressure range from (19.4 to 25.0) MPa. The measured values were between (0.1·10−3 and 0.6·10−3) mol·mol−1. They concluded that the solubility of glyceryl trioleate increases with increasing temperature at constant density.21 Bharath et al. investigated the vapor−liquid equilibria for the binary systems oleic acid−CO2 and glyceryl trioleate−CO2 with the aim of separating the fatty acids from triglycerides.22 Bottini et al. studied the phase behavior of the binary system glyceryl trioleate-propane in a temperature range from (340 to 400) K and pressures up to 16 MPa.23 Tang et al. measured and

2. EXPERIMENTAL SECTION 2.1. Materials. β-Carotene type β,β-carotene (catalog no. 7235-40-7, purity ≥ 0.97) and glyceryl trioleate (catalog no. 122-32-7, purity ≥ 0.99) were supplied by Sigma-Aldrich. Acetone (catalog no. 67-64-1, purity ≥ 0.99) was purchased from Carlo Erba. Carbon dioxide (purity 0.9995) was supplied by Messer MG (Ruše, Slovenia). Additional properties of the materials are presented in Table 3.

Table 3. Properties of the Materials compound

source

CAS No.

initial purity (mass fraction)

Mw/g·mol−1

purification method

β-carotene glyceryl trioleate acetone carbon dioxide

Sigma Aldrich Sigma Aldrich Carlo Erba Messer Company

7235-40-7 122-32-7 67-64-1

≥ 0.97 ≥ 0.99 ≥ 0.99 0.9995

536.87 885.43 58.08 44.01

none none none none

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2.3. Apparatus and Methods. High Pressure View Cell. The solubility was measured by using a high pressure, variablevolume cell (NWA GMBh, Lorrach, Germany) (Figure 1). The

Figure 2. Solubility y (mol·mol−1) of glyceryl trioleate in supercritical CO2 and comparison of present ternary (T) data with binary (B) literature data. ◆, 313 K, present work; ▲, 323 K, present work; ●, 333 K, present work; −, 333 K, B;20 ◇, 353 K, B;20 +, 313 K, B;21 X with a vertical line, 333 K, B;21 ○, 313 K, B;27 △, 323 K, B;27 □, 333 K, B.27

Figure 1. Scheme of the variable-volume high-pressure view cell used for phase equilibrium measurements: A, variable volume cell; B, sampling trap; C, graduated cylinder; V01−02, high pressure valves; PI, pressure indicator; TI, temperature indicator.

cell is made of stainless steel (AISI 316) with adjustable internal volume between (30 and 60) cm3 by means of a piston. The piston is connected to a hydraulic pressurization system and allows operating conditions up to 75 MPa and 473 K. The pressure was measured by electronic pressure gauge (WIKA to ± 0.1 %). The cell is provided with two sapphire windows for visual observation of the interior, a thermocouple for temperature monitoring (accurate ± 0.5 K), and two valves for loading and discharging the gas. The cell contains a bladeturbine stirrer to mix the phases and two 60 mm electric heaters inserted in the stainless steel coat of the cell.29 Phase Equilibrium Measurements. The view cell described above was used for determining the high-pressure phase equilibrium data of the ternary mixture β-carotene−glyceryl trioleate−CO2. The cell was loaded with approximately 5 mL of homogeneous β-carotene−glyceryl trioleate mixture with mass fraction of β-carotene w = 0.1. Afterward CO2 was introduced into the view cell using a high-pressure pump. The system was then heated up to the desired temperature. The content of the cell was mixed using the blade-turbine stirrer at 700 rpm for 1 h. After approximately 6 h in which the system was allowed to settle and reach equilibrium, the gas rich phase was sampled into a glass trap where the phase separation occurred at atmospheric pressure. The amount of sample in the trap was determined gravimetrically (accurate ± 0.0001). The volume of CO2 released during sampling was measured with disposal of water in a 100 mL graduated cylinder (to within ± 0.5 mL), and the amount of CO2 in the sample was calculated. The pressure change observed during sampling was between (0.05 and 0.5) MPa. No temperature change was detected. The sample obtained during sampling was further dissolved in a certain amount of acetone. The amount of β-carotene in each sample was then determined by UV spectrophotometry. The absorbance was measured using Varian, Cary 50 Probe UV−vis spectrophotometer (accurate to ± 0.0001) at a wavelength of 450 nm where β-carotene has the absorption maximum. The amount of glyceryl trioleate was determined as the difference between the total mass of the sample and the amount of β-carotene. At least three experiments were performed for each temperature, and the data presented in this study are the average values of these measurements (Figures 2 to 5).

Figure 3. Solubility y (mol·mol−1) of glyceryl trioleate in supercritical CO2 and comparison of present ternary (T) data with the ternary (T) literature data. ◆, 313 K, present work; ▲, 323 K, present work; ●, 333 K, present work; ◇, 313 K, T;19 △, 323 K, T;19 ○, 333 K, T.19

Figure 4. Solubility y (mol·mol−1) of β-carotene in supercritical CO2 and comparison present ternary (T) data with binary (B) literature data. ◆, 313 K, present work; ▲, 323 K, present work; ●, 333 K, present work; △, 313 K, B;2 +, 343 K, B;2 −, 310 K, B;1 X with a vertical line, 320 K, B;1 □, 330 K, B;1 ◇, 340 K, B;1 ○, 298 K, B;5 ■, 313 K, B.5

3. RESULTS AND DISCUSSION The experimental solubility data for β-carotene and glyceryl trioleate from the ternary β-carotene−glyceryl trioleate−CO2 655

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The solubility isotherms at (313, 323, and 333) K have a similar trend. At the same pressure a small difference in solubility values at (323 and 333) K were observed. From Figure 2 it can be seen that the solubility of glyceryl trioleate in a ternary mixture (β-carotene + glyceril trioleate + CO2) did not differ significantly from the literature data published by Chen et al. and Masuda et al., who investigated the binary system glyceryl trioleate−CO2.21,27 Chen et al. reported higher solubility of pure glyceryl trioleate in the gas rich phase at 313 K as compared to present work; however their experimental data were obtained with pure glyceryl trioleate in CO2 and at lower pressures.21 The solubility results of the present work at 333 K are higher than the ones determined by Webber et al. for the binary system of glyceryl trioleate−CO2.20 This difference in solubility results may be due to the presence of β-carotene in the mixture and to the longer time we allowed to establish the equilibrium compared with other works. From Figure 3 it can be observed that the trend of the solubility curves is most similar to the data obtained by Araus et al., who investigated the ternary system β-carotene−glyceryl trioleate−CO2 at temperatures of (313, 323, and 333) K and pressure up to 34 MPa. The concentration of glyceryl trioleate in the ternary was in range from (0.01 to 0.39) mmol·mol−1.19 From the isotherms in Figures 4 and 5 it can be observed that the solubility of β-carotene in SC CO2 increases with increasing pressure at constant temperature. The trends of the isotherms at (313, 323, and 333) K are similar. The highest solubility of β-carotene in CO2 was obtained at a temperature of 333 K and pressure around 60 MPa. Figures 4 and 5 also presents the comparison between the solubility of β-carotene in CO2 obtained in this work and other published solubility data.1,2,4,5,19 Most of the authors investigated the solubility of pure β-carotene in SC CO2 (Table 1). If we compare results from present work with the ones obtained by Škerget et al., who investigated the solubility of pure β-carotene in CO2, a similar trend of solubility curves can be seen, at 313 K in the pressure range from (25 to 30) MPa.5 At 25 MPa the difference in solubility is around 0.1 mol·mol−1, and it increases with pressure up to 2.7 mol·mol−1 at 30 MPa. The data of the system β-carotene−CO2 reported by Subra at al. at 340 K and pressures up to 25 MPa show a similar trend to our solubilities at 333 K and pressures up to 60 MPa.1 The solubility data obtained in this work at (313, 323, and 333) K are higher than those of most other studies.1,2,4,19 Similar, the solubility results of β-carotene in CO2 in the presence of vegetable oil, determined by Sovova et al. in the range from (25 to 30) MPa, are lower.4 With increasing temperature as well as pressure the difference between solubility results also increases. The trends of the isotherms reported by Araus et al., who measured the phase equilibrium in the ternary system βcarotene−glyceryl trioleate−2 at pressures up to 34 MPa, show the best fit with our solubility curves in Figure 5 at higher pressure. The concentration of glyceryl trioleate in the ternary (β-carotene−glyceryl trioleate−CO2) was in range from (0.01 to 0.39) mmol·mol−1.19 Araus et al. concluded that the comparison between the β-carotene solubility data in pure CO2 and in CO2 modified with glyceryl trioleate indicate a positive effect of glyceryl trioleate on the amount of β-carotene dissolved in the gas.19 This also applies to present study case where all solubilities are above other data reported at the same conditions. It is difficult to define a reason for the disparities among the data. The discrepancies between values can be the consequence

Figure 5. Solubility y (mol·mol−1) of β-carotene in supercritical CO2 and comparison present ternary (T) data with ternary (T) literature data. ◆, 313 K, present work; ▲, 323 K, present work; ●, 333 K, present work; ○, 313 K, T;19 △, 323 K, T;19 ◇, 333 K, T;19 ■, 313 K, T;4 +, 323 K, T;4 □, 333 K, T.4

system are presented in Table 4. The initial mass fraction of βcarotene in the mixture with glyceryl trioleate was w = 0.1. The Table 4. Experimental Data on Mole Fraction Solubilities (y) of β-Carotene (1) and Glyceryl Trioleate (2) in SC CO2 at Different Temperatures (T) and Pressures (P)a in the Gas Phase gas phase T/K

P/MPa

y1·106

y2·103

313 313 313 313 313 323 323 323 323 323 333 333 333 333 333

25.2 30.3 41.5 52.2 60.8 24.9 28.1 40.2 50.0 60.8 25.2 31.1 40.1 49.2 60.1

0.452 0.761 1.194 3.078 5.026 0.926 2.101 3.696 6.641 11.042 0.620 2.310 5.865 8.229 12.160

0.422 0.527 0.778 1.129 1.369 0.470 0.529 1.015 1.443 1.699 0.521 0.637 1.070 1.514 1.905

a Standard uncertainties u for the mole fraction solubilities in gas phase (y): u(y1) = 0.017·10−6, u(y2) = 0.011·10−3, u(T) = 0.5 K and u(P) = 0.05; the condensed state of the solutes is liquid.

data are also presented in Figures 2 to 5 separately for each component as a function of pressure. A comparison of experimental equilibrium data with the available literature data was also performed and is displayed in Figures 2 to 5.1,2,4,5,19−21,27 The obtained experimental data in the ternary (T) mixture were compared with literature binary (B) data, and the results are presented in Figures 2 and 4. Also a comparison of experimental data in the ternary (T) mixture with ternary system data from the literature was performed in Figures 3 and 5. From Figures 2 and 3, it can be seen that the solubility of glyceryl trioleate in the gas rich phase increases with increasing pressure at constant temperature. The highest solubility was measured at a pressure of 60 MPa and a temperature of 333 K. 656

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Table 5. Ternary System β-Carotene + Glyceryl Trioleate + CO2: Solubility Constants of Chrastil Model for β-Carotene and Glyceryl Trioleate in SC CO2

of the presence of impurities that may affect the measurements. Another factor may be the difficulty of measuring such low solubilities. During the experiments degradation and oxidation of β-carotene can also occur. Tuma et al. investigated the degradation and thermal modification of β-carotene isomers in CO2. They concluded that the thermal degradation was dominant at 350 K. This temperature was above our research.30 To avoid this, we tried to minimize the exposure of the samples to heat, air, and light. At highest conditions of temperature and pressure applied in solubility experiments, the absorbance of β-carotene was measured before and after the experiment. The initial solution was prepared, and after that the specific amount of sample was weighted and diluted with acetone. Then the absorbance was determined. The test was done also for the sample which was exposed to CO2 at 60 °C and pressure range between (25 to 60) MPa for 14 days. The same amount as the first time was weighed and diluted, and afterwards the absorbance was determined. It was found out that there was no significant difference in absorption maximum and absorbance between the samples before and after experiment. Therefore, it can be concluded that there was no thermal degradation of β-carotene during experiments, even more because the solution of βcarotene and glyceryl trioleate was changed frequently. The longer time allowed for establishing equilibrium and different experimental procedures may be also responsible for the difference between the data reported by different authors. The different mass ratios of β-carotene and glyceryl trioleate can be also responsible for disparities among the data. The experimental data were further correlated with the equation proposed by Chrastil:31 ln c = k ln ρ + a /T + b

glyceryl trioleate β-carotene

k

a

b

7.61 15.73

−3463.65 −11826.90

−38.02 −73.43

Figure 6. Ternary system β-carotene + glyceryl trioleate + CO2: solubility c (g·m−3) of glyceryl trioleate as a function of CO2 density ρ (kg·m−3). ◆, 313 K, present work; ▲, 323 K, present work; ●, 333 K, present work; , Chrastil model.

(1)

Parameters a and b are defined as:

a=−

ΔH R

⎛ [1000M ]k ⎞ B ⎟⎟ + q b = −ln⎜⎜ ⎝ [MA + kMB] ⎠

(2)

(3) Figure 7. Ternary system β-carotene + glyceryl trioleate + CO2: solubility c (g·m−3) of β-carotene as a function of CO2 density ρ (kg· m−3). ◆, 313 K, present work; ▲, 323 K, present work; ●, 333 K, present work; , Chrastil model.

where c is the solubility of the solute in the supercritical fluid (g·m−3), ρ is the gas density (kg·m−3), k is the number of gas molecules which associate with one molecule of solute to form solvato-complexes, ΔH (heat of solvation + heat of vaporization) is the total process enthalpy, q is a constant, and MA and MB are molecular weights of the solute and gas, respectively.31 The solubilities c (g·m−3) of glyceryl trioleate and β-carotene as a function of density ρ (kg·m−3) and comparison of present ternary (T) data with the ternary (B) literature data are shown in the Supporting Information. Parameter k was obtained from the slope of the plot ln(c) = f(ln(ρ)) at constant temperature. The logarithm of concentration varies linearly with the reciprocal temperature at constant gas density and the slope of the line gives parameter a. The value of b was determined such as to minimize the sum of the deviation of experimental data from the values calculated by eq 1.10 The determined k, a, and b values are presented in Table 5. The comparison between experimental and calculated phase equilibrium data for the glyceryl trioleate−CO2 and of βcarotene−CO2 systems are presented in Figures 6 and 7. The calculated isotherms are parallel in both cases and show good

fitting with the experimental results. In case of β-carotene the absolute relative deviations (% AARD) between calculated and experimental data at (313, 323, and 333) K are 24.7%, 6.5%, and 15.5%, respectively. For glyceryl trioleate the obtained % AARD at (313, 323, and 333) K are 1.4%, 2.5%, and 3.7%, respectively.

4. CONCLUSIONS In this study, the phase behavior of the ternary mixture βcarotene−glyceryl trioleate−CO2 with an initial mass fraction of w = 0.1 has been investigated at three different temperatures in the pressure range from (25 to 60) MPa. The aim of the work was to determine the solubility of the β-carotene−glyceryl trioleate mixture in SC CO2 at higher pressures than available in the literature. The purpose was also to correlate the experimental data using the density based model proposed by Chrastil. The high-pressure variable-volume cell was used for 657

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the experiments, and the gas rich phase was sampled and analyzed. For all three isotherms, the solubility of β-carotene in the gas rich phase increases as system pressure increases as well as of glyceryl trioleate. The results show that glyceryl trioleate has a positive impact on the solubility of β-carotene in supercritical CO2. In comparison with the literature data for binary systems, the solubility of β-carotene in the ternary mixture increased, while the solubility of glyceryl trioleate remained nearly unchanged. The highest solubility in dense gas phase both for β-carotene and glyceryl trioleate were obtained in this work at a pressure around 60 MPa and a temperature of 333 K. The logarithm of solubility varies linearly with the logarithm of density for both β-carotene−CO2 and glyceryl trioleate−CO2 systems, and the linear correlations showed a good fitting to the values obtained by applying the Chrastil model.

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ASSOCIATED CONTENT

S Supporting Information *

Experimental results of the solubility of β-carotene and glyceryl trioleate in SC CO2 presented in Supporting Figures 1 to 4 as ln c−ln ρ at constant temperature. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Fax: +386 2 2516750; e-mail: [email protected]. Notes

The authors declare no competing financial interest.

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REFERENCES

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dx.doi.org/10.1021/je400553y | J. Chem. Eng. Data 2014, 59, 653−658