LiquidâLiquid Equilibrium Data for the System Lard + Oleic Acid +

Article pubs.acs.org/jced

Liquid−Liquid Equilibrium Data for the System Lard + Oleic Acid + Ethanol + Water at 318.2 K: Cholesterol Distribution Coefficients Maira G. Granero, Christianne E. C. Rodrigues, and Cintia B. Gonçalves* Department of Food Engineering (ZEA-FZEA), University of São Paulo (USP), P.O. Box 23, 13635-900 Pirassununga, São Paulo, Brazil ABSTRACT: This research reports liquid−liquid equilibrium data for the system lard (swine fat), cis-9-octadecenoic acid (oleic acid), ethanol, and water at 318.2 K, as well as their correlation with the nonrandom two-liquid (NRTL) and universal quasichemical activity coefficient (UNIQUAC) thermodynamic equations, which have provided global deviations of 0.41 % and 0.53 %, respectively. Additional equilibrium experiments were also performed to obtain cholesterol partition (or distribution) coefficients to verify the availability of the use of ethanol plus water to reduce the cholesterol content in lard. The partition experiments were performed with concentrations of free fatty acids (commercial oleic acid) that varied from (0 to 20) mass % and of water in the solvent that varied from (0 to 18) mass %. The percentage of free fatty acids initially present in lard had a slight effect on the distribution of cholesterol between the phases. Furthermore, the distribution coefficients decreased by adding water in the ethanol; specifically, it resulted in a diminution of the capability of the solvent to remove the cholesterol.

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INTRODUCTION Oils and fats are essential nutrients for humans because they play important functions as energy sources, carriers of fatsoluble vitamins and essential fatty acids, main flavor sources of foods, hormone production, and the development of cell membranes.1 Industrially, oils and fats have played significant roles in the growth of several areas of chemical, pharmaceutical, cosmetic, and, most importantly, food products. The consumption of animal fats in diets was frequent in ancient civilizations. Lard (swine fat), for instance, was the more often used product for domestic frying in addition to raw matter in the mass production of breads and cakes. In the food manufacturing, this kind of fat is an essential ingredient, mainly in embedded products.2 Nevertheless, studies on nutrition have revealed the deleterious effects of some fats, such as saturated fat, mainly those found in animal products.3−5 Besides having an elevated concentration of cholesterol, animal fat, when overeaten, can raise the levels of bad cholesterol, LDL-c, and reduce the levels of good cholesterol, HDL-c, thus increasing the likelihood of heart disease.6 For these motives, in many industrial formulations, lard was substituted for fats from vegetable fonts, which are obtained by hydrogenation process. Even though they are free of cholesterol, the hydrogenated vegetable fats have worse effects than fats from animal sources because trans fatty acids are produced during the hydrogenation process.7 The harmful effects of trans fatty acids necessitate research into processes that allow a decrease of the cholesterol level in fat, which varies between 61.0 mg/100 g and 123.1 mg/100 g.8−10 Several studies on the reduction of cholesterol in foods have been conducted, such as extraction with supercritical carbon dioxide,11 molecular distillation,12 and extraction with aqueous alkaline solution.13 An alternative method that could be used for this intent is © 2012 American Chemical Society

the liquid−liquid extraction (LLE), wherein cholesterol is taken out with an alcoholic solvent that exhibits an affinity toward cholesterol. The literature contains several reports regarding the use of liquid− liquid extraction to remove free fatty acids and other minor components present in vegetable oils,14−35 but no work has been reported on this subject using animal fats. Through the determination of liquid−liquid equilibrium data, this work studied the viability of the use of liquid−liquid extraction to reduce the concentration of cholesterol in lard. Because lard also has an elevated level of free fatty acids, this parameter was also studied. This manuscript references the liquid−liquid equilibrium for the system lard + oleic acid + ethanol + water + cholesterol at 318.2 K. The experimental data set was used to obtain the parameters of the nonrandom two-liquid (NRTL) and universal quasichemical (UNIQUAC) equations.

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MATERIALS Lard (swine fat) obtained from the slaughterhouse of the Faculty of Animal Science and Food Engineering−University of São Paulo (FZEA−USP, Pirassununga, State of São Paulo/Brazil) was the source of triacylglycerols. Commercial cis-9-octadecenoic acid (oleic acid, CAS No. 112-80-1) from Synth (Brazil) was the source of fatty acids. Swine fat from a commercial brand (Sadia, Brazil) was utilized as the font of triacylglycerols for the experiments that involved cholesterol partition coefficients. All fatty reagents, lards, and the commercial oleic acid were analyzed by gas chromatography of the fatty acid methyl esters to establish the fatty acid composition in Received: January 5, 2012 Accepted: April 18, 2012 Published: April 26, 2012 1728

dx.doi.org/10.1021/je300189x | J. Chem. Eng. Data 2012, 57, 1728−1736

Journal of Chemical & Engineering Data

Article

Table 1. Fatty Acid Composition of the Fatty Compounds Mb

lard (FZEA)

symbol

fatty acid

Cx:ya

g·mol−1

mole fraction

C La M Pt P Po Ma Mo S O L Ln A Ga Aa

decanoic dodecanoic tetradecanoic pentadecanoic hexadecanoic cis-hexadec-9-enoic heptadecanoic cis-heptadec-9-enoic octadecanoic cis-octadec-9-enoic cis,cis-octadeca-9,12-dienoic all-cis-octadeca-9,12,15-trienoic icosanoic cis-icos-9-enoic all-cis-eicosa-5,8,11,14-tetraenoic

C10:0 C12:0 C14:0 C15:0 C16:0 C16:1 C17:0 C17:1 C18:0 C18:1 C18:2 C18:3 C20:0 C20:1 C20:4

172.27 200.32 228.38 242.40 256.43 254.42 270.45 268.43 284.49 282.47 280.45 278.43 312.54 310.52 304.47

0.0006 0.0011 0.0135 0.0008 0.2240 0.0157 0.0037 0.0012 0.1160 0.2843 0.2994 0.0214 0.0033 0.0063 0.0086

a

lard (Sadia)

mass fraction

mole fraction

mass fraction

0.0004 0.0008 0.0112 0.0007 0.2087 0.0145 0.0036 0.0012 0.1199 0.2918 0.3051 0.0217 0.0037 0.0072 0.0095

0.0013 0.0011 0.0163 0.0006 0.2614 0.0264 0.0033 0.0027 0.1280 0.4018 0.1385 0.0053 0.0018 0.0067 0.0048

0.0008 0.0008 0.0136 0.0005 0.2447 0.0245 0.0032 0.0026 0.1329 0.4142 0.1418 0.0054 0.0021 0.0076 0.0053

lard (literature)c

oleic acid

mole fraction

mass fraction

mole fraction

mass fraction

0.0179

0.0150

0.0566

0.0469

0.2875 0.0322 0.0050

0.2700 0.0300 0.0050

0.0724 0.0473

0.0673 0.0436

0.1296 0.4205 0.1022 0.0049

0.1350 0.4350 0.1050 0.0050

0.0215 0.5968 0.1918 0.0137

0.0221 0.6112 0.1950 0.0139

Cx:y; x: number of carbons, y: number of double bonds. bM: molar mass. cSource: Jenkins.46

accordance with the official AOCS method Ce1-62(97).36 Samples were transformed in fatty acid methyl esters in accordance with the AOCS official method Ce2-66(97).36 A capillary gas chromatograph (Shimadzu 2010 AF, Japan) with a flame ionization detector was utilized. The chromatographic experimental setting was as follows: Crossbond-PEG 0.25 μm, 30 m × 0.25 mm i.d. (RTx-Wax, Restek, Bellefonte, PA, USA) capillary column; helium carrier gas at a rate of 0.74 mL·min−1; injection temperature of 523.2 K; column temperature of (433.2 to 518) K (rate of 3 K·min−1); detection temperature of 553 K; and injection volume of 1.0 μL. External standards (Supelco, Bellefonte, PA, USA) were used to identify the fatty acid methyl esters. Quantification was established by internal normalization. The probable triacylglycerol composition of the lard was found from its fatty acid profile, using the statistical methodology recommended by Antoniosi Filho et al.37 A 99.5 % pure anhydrous ethanol (CAS No. 64-17-5), purchased from Merck (Germany), and deionized water (Millipore, Milli-Q, Bedford, MA, USA, CAS No. 7732-18-5) was used throughout the investigation. A cholesterol standard (CAS No. 57-88-5) with a purity greater than 95 % was obtained from Sigma-Aldrich (Saint Louis, MO, USA).

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clear, with a distinct interface, and the compositions of both phases were measured. The free fatty acid content was obtained by titration, according to the official International Union of Pure and Applied Chemistry (IUPAC) method 2201,38 using an automatic buret (Metrohm, model Dosimat 775, Herisan, Switzerland). The solvent content (ethanol + water) was found by evaporation in a vacuum oven (inside absolute pressure = 126 mmHg) (Tecnal, model TE-395, Piracicaba, SP, Brazil) at 313.2 K until steady masses were achieved. The water content was obtained by Karl Fischer titrations in accordance with AOCS official method Ca 23-55,36 using a KF Titrino (Metrohm, model 787 KF Titrino, Herisan, Switzerland). The triacylglycerol (lard) concentration was calculated by the difference. This procedure was used in our prior works.16−24,29,31,34 All measures were carried out in triplicate, and the standard deviations ranged at the following intervals: (0.08·10−2 to 0.35) mass % for fatty acids, (0.08·10−1 to 0.74) mass % for ethanol, (0.01·10−2 to 0.13) mass % for water, and (0.09·10−1 to 0.67) mass % for lard. The obtained results were validated by mass balance calculations following the method created by Marcilla et al.39 and used in Rodrigues et al.21 Another intent of this research was the calculation of interaction NRTL and UNIQUAC parameters involving cholesterol (a minor compound present in lard) and the major compounds of the fatty system. For this purpose, additional tests were carried out to obtain cholesterol distribution coefficients using commercial lard (Sadia) as the source of triacylglycerols. To prepare the systems, commercial lard that contained known masses of oleic acid (varying from (0 to 20) mass %) was mixed with ethanolic solutions that contained from (0 to 18) mass % of water, at (318.2 ± 0.1) K. All compounds were weighed on an analytical balance (Adam, model PW 254, Milton Keynes, UK), accurate to 0.0001 g, and inserted in polypropylene tubes (15 mL, Corning Inc., USA), which were strongly agitated for 30 min and placed in a thermostatic bath at (318.2 ± 0.1) K (Tecnal, model TE-2005, Piracicaba, SP, Brazil), accurate to 0.1 K, for 24 h. Following the equilibrium achievement, aliquots of the two phases were collected, being the concentrations of cholesterol measured by spectroscopy, in accordance with the method illustrated by Saldanha et al.,40 which was modified to samples of this research. A complete explanation of the methodology can be found in Gonçalves and

EXPERIMENTAL PROCEDURE

The liquid−liquid equilibrium experiments were performed using equilibrium cells made of glass, following the same method reported in Gonçalves et al.16 Fatty systems were prepared by mixing known amounts of commercial oleic acid to lard (FZEA). Following the same procedure adopted in our previous work,18 the fatty systems were mixed with each alcoholic solvent (anhydrous ethanol and ethanol containing 6.11 ± 0.03 and 11.92 ± 0.02 water content in mass %), in a mass ratio of 1:1 of oil to solvent at 318.2 ± 0.1 K. These data were required to obtain the NRTL and the UNIQUAC parameters. The system temperature was controlled with a thermostatic bath (Tecnal, model TE-2005, Piracicaba, SP, Brazil), accurate to 0.1 K. Each component was weighed using an analytical balance (Adam, model PW 254, Milton Keynes, UK), accurate to 0.0001 g. The system was strongly agitated with a magnetic agitator (IKA, model Lab disk, Staufen, Germany) for 30 min and left stationary for at least 24 h. After this procedure, the two phases got 1729



Article

Table 3. Mean Molar Masses M, and Parameters ri′ and qi′

Table 2. Probable Triacylglycerol Composition of Lard M

c

groupa

main TAGb

g·mol−1

C46:0 C48:0 C50:0 C52:0 C48:1 C50:1 C52:1 C54:1 C48:2 C50:2 C52:2 C54:2 C56:2 C50:3 C52:3 C54:3 C56:3 C50:4 C52:4 C54:4 C56:4 C52:5 C54:5 C54:6 C54:7

PPM PPP PPS SSP MOP PPO POS SSO MLP PPL OOP OOS SGaO MOL POL OOO OOGa LLM LLP OOL OLGa LLPo LLO LLL LLLn

779.28 807.33 835.39 863.44 805.32 833.37 861.42 889.48 803.30 831.35 859.41 887.46 915.51 829.34 857.39 885.44 913.50 827.32 855.38 883.43 911.48 853.36 881.41 879.40 877.38

lard (FZEA) mole fraction

mass fraction

0.0142 0.0191 0.0101 0.0084 0.0512 0.0491 0.0147 0.0069 0.0610 0.1113 0.0471

0.0133 0.0185 0.0101 0.0079 0.0494 0.0490 0.0151 0.0064 0.0587 0.1109 0.0484

0.0180 0.1332 0.0916 0.0049 0.0051 0.0817 0.1152 0.0046 0.0143 0.0915 0.0403 0.0065

0.0173 0.1322 0.0939 0.0052 0.0049 0.0809 0.1179 0.0049 0.0141 0.0934 0.0410 0.0066

compound

M/g·mol−1

ri′

qi′

lard (FZEA) lard (Sadia) commercial oleic acid ethanol water cholesterol

863.43 860.27 275.80 46.07 18.02 386.65

0.044162 0.043940 0.046436 0.055905 0.051069 0.044950

0.035827 0.035671 0.037817 0.056177 0.077713 0.033560

lard (Sadia) mole fraction

mass fraction

0.0039 0.0220 0.0281 0.0137 0.0173 0.0983 0.0885 0.0236 0.0061 0.0582 0.1730 0.0782 0.0034 0.0140 0.1102 0.1156 0.0048

0.0035 0.0206 0.0273 0.0138 0.0162 0.0953 0.0886 0.0244 0.0057 0.0562 0.1729 0.0806 0.0036 0.0135 0.1098 0.1190 0.0051

0.0289 0.0800

0.0287 0.0822

the mean molar mass of the pseudo-components, C is the quantity of compounds in the pseudo-components, and G is the total quantity of groups. Rk and Qk are the van der Waals values presented in Magnussen et al.42 r′i =

1 M̅ i

C

G

∑ xj ∑ νk(j)R k j

k

1 M̅ i

C

G

∑ xj ∑ νk(j)Q k j

k

(1)

Parameter evaluation was achieved by minimization of the objective function, OF(w) (see eq 2), according to the method described by Stragevitch and d'Avila:43 D

OF(w) =

N K−1

∑∑ ∑ m

0.0275 0.0047

q′i =

n

i

2 ⎡⎛ OP,exptl OP,calcd ⎞ − winm ⎢⎜ winm ⎟⎟ ⎢⎜⎝ OP σ winm ⎠ ⎣

⎛ w AP,exptl − w AP,calcd ⎞2 ⎤ inm ⎟⎟ ⎥ + ⎜⎜ inm AP σ ⎠ ⎥⎦ ⎝ winm

0.0282 0.0048

a

x:y; x: number of carbons (excluding glycerol carbons); y: number of double bonds. bGroups with a total triacylglycerol (TAG) mole fraction lower than 0.0050 were excluded. cMolar mass.

(2)

In eq 2, D is the quantity of groups of data m, N is the quantity of tie lines n, K is the quantity of compounds or pseudocomponents i in the group of data m, and w is the mass fraction. The superscripts OP and AP refer to the oil and alcoholic phases, correspondingly; exptl and calcd represent experimental and calculated values. The parameters σwOP and σwAP are the standard inm inm deviations of the mass fractions in both phases. In the present work, the liquid−liquid equilibrium data were utilized to determine the NRTL and UNIQUAC interaction parameters involving lard (1), commercial oleic acid (2), ethanol (3), and water (4). For the pair ethanol (3)−water (4), the interaction parameters published by Gonçalves and Meirelles18 were used. The deviations between experimental and calculated concentrations (Δw) were evaluated by eq 3:

Granero.41 The analysis of cholesterol in each phase was performed in triplicate, and the uncertainties of partition coefficients (calculated by error propagation) varied from (0.04 to 3.42) %.

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MODELING APPROACH The liquid−liquid equilibrium data for the system lard + oleic acid + ethanol + water were utilized to fit the NRTL and UNIQUAC parameters, at 318.2 K. Both equations were initially created in mole fraction, but due to the great variation in the molar masses of the compounds, mass fractions were utilized as the unity of concentration in this experiment.15 The NRTL and UNIQUAC models in mass fraction was reported by Gonçalves et al.16 The adjustment of the parameters was made by considering the system lard + oleic acid + ethanol as a pseudo-ternary system. Furthermore, the systems that contained lard + oleic acid + ethanol + water were considered as pseudo-quaternary systems. For the adjustment procedure, lard was considered as a triacylglycerol with the mean molar mass of the fat. A similar approach was applied to the commercial oleic acid under the assumption that different compounds in every fatty group perform similarly in the liquid−liquid system. Namely, a pseudo-component with the equivalent average physical−chemical properties can satisfactorily substitute such compounds. This suggestion has been successfully used in our previous works.16−24 The volume and the area values, ri′ and qi′, essential for the UNIQUAC equation were obtained using eq 1, in which xj is the mole fraction of the compound contained in every pseudocomponent i, v(j) k is the quantity of groups k in molecule j, Mi is

Δw = 100 N

×

K

∑n ∑i [(wiOP,exptl )2 + (wiAP,exptl )2 ] − wiOP,calcd − wiAP,calcd ,n ,n ,n ,n 2NK (3)

Liquid−liquid flash calculations were performed using the estimated NRTL and UNIQUAC parameters to predict the liquid−liquid equilibrium for the system lard (commercial brand Sadia) + oleic acid + ethanol at 318.2 K. The UNIQUAC and NRTL parameters involving the cholesterol and the major pseudo−components (lard, oleic acid, ethanol, and water) were also calculated. It was considered that cholesterol (5) is a compound infinitely diluted (∞) in the system. In this situation, the distribution coefficient of the component or pseudo-component (i), obtained in accordance with eq 4, could be represented by the distribution coefficient at infinite dilution, k∞ i . Such an approach was also used by Rodrigues et al.21 in their study about tocopherol distribution coefficient. As described in 1730



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Table 4. Liquid−Liquid Equilibrium Data (in Mass Fraction, w) for the System Lard (1) + Oleic Acid (2) + Ethanol (3) at (318.2 ± 0.1) K global composition

alcoholic phase

oil phase

lard brand

w1

w2

w3

w1

w2

w3

w1

w2

w3

FZEA

0.4885 0.4818 0.4799 0.4780 0.4596 0.4559 0.4385 0.4375 0.5172 0.4808 0.4895 0.4615 0.4543 0.4490 0.4313

0.0000 0.0108 0.0141 0.0215 0.0314 0.0400 0.0487 0.0591 0.0000 0.0108 0.0184 0.0330 0.0439 0.0508 0.0600

0.5115 0.5074 0.5060 0.5005 0.5090 0.5041 0.5128 0.5034 0.4828 0.5084 0.4921 0.5055 0.5018 0.5002 0.5087

0.0765 0.0944 0.0947 0.1020 0.1219 0.1277 0.1537 0.1794 0.0841 0.0927 0.0961 0.1161 0.1314 0.1540 0.1759

0.0000 0.0130 0.0165 0.0258 0.0367 0.0465 0.0548 0.0662 0.0000 0.0131 0.0226 0.0381 0.0506 0.0578 0.0683

0.9235 0.8926 0.8888 0.8722 0.8414 0.8258 0.7915 0.7544 0.9159 0.8942 0.8813 0.8458 0.8180 0.7882 0.7558

0.8091 0.7805 0.7719 0.7517 0.7406 0.7132 0.6655 0.6262 0.8034 0.7826 0.7623 0.7300 0.7005 0.6645 0.6270

0.0000 0.0099 0.0128 0.0201 0.0286 0.0373 0.0450 0.0562 0.0000 0.0097 0.0169 0.0299 0.0408 0.0475 0.0567

0.1909 0.2096 0.2153 0.2282 0.2308 0.2495 0.2895 0.3176 0.1966 0.2077 0.2208 0.2401 0.2587 0.2880 0.3163

Sadia

Table 5. Liquid−Liquid Equilibrium Data (in Mass Fraction, w) for the System Lard (1) + Oleic Acid (2) + Ethanol (3) + Water (4) at (318.2 ± 0.1) K global composition w4S

a

0.0611

0.1192

a

alcoholic phase

oil phase

w1

w2

w3

w4

w1

w2

w3

w4

w1

w2

w3

w4

0.4975 0.4893 0.4773 0.4700 0.4450 0.4348 0.4243 0.4118 0.4019 0.3773 0.4959 0.4818 0.4577 0.4441 0.4047 0.3223 0.3049

0.0000 0.0105 0.0216 0.0310 0.0408 0.0606 0.0715 0.0839 0.1021 0.1215 0.0000 0.0219 0.0407 0.0602 0.1026 0.1739 0.2025

0.4718 0.4696 0.4705 0.4685 0.4828 0.4738 0.4734 0.4735 0.4657 0.4706 0.4440 0.4371 0.4418 0.4366 0.4340 0.4437 0.4339

0.0307 0.0306 0.0306 0.0305 0.0314 0.0308 0.0308 0.0308 0.0303 0.0306 0.0601 0.0592 0.0598 0.0591 0.0587 0.0601 0.0587

0.0168 0.0163 0.0218 0.0221 0.0261 0.0356 0.0393 0.0442 0.0572 0.0759 0.0043 0.0035 0.0075 0.0106 0.0202 0.0455 0.0704

0.0000 0.0110 0.0227 0.0334 0.0444 0.0645 0.0752 0.0897 0.1076 0.1299 0.0000 0.0205 0.0378 0.0559 0.0962 0.1710 0.1997

0.9127 0.9099 0.8939 0.8812 0.8647 0.8360 0.8255 0.8118 0.7770 0.7425 0.8619 0.8432 0.8276 0.8032 0.7605 0.6846 0.6316

0.0705 0.0628 0.0616 0.0633 0.0648 0.0639 0.0600 0.0543 0.0582 0.0517 0.1338 0.1328 0.1271 0.1303 0.1231 0.0989 0.0983

0.8961 0.8820 0.8653 0.8525 0.8273 0.7888 0.7702 0.7478 0.7081 0.6671 0.9289 0.8942 0.8645 0.8289 0.7593 0.6260 0.5639

0.0000 0.0098 0.0193 0.0297 0.0395 0.0582 0.0686 0.0805 0.0992 0.1169 0.0000 0.0238 0.0441 0.0658 0.1099 0.1779 0.2067

0.0998 0.1035 0.1106 0.1117 0.1269 0.1463 0.1543 0.1638 0.1844 0.2054 0.0601 0.0692 0.0782 0.0917 0.1143 0.1737 0.2063

0.0041 0.0047 0.0048 0.0061 0.0063 0.0067 0.0069 0.0079 0.0083 0.0106 0.0110 0.0128 0.0132 0.0136 0.0165 0.0224 0.0231

w4S = water mass fraction in the ethanolic solvent.

Rodrigues et al.,21 using the isoactivity criterion, this distribution coefficient for the minor component (in our study, cholesterol), k∞ 5 , can be calculated using eq 5: ki = wiAP/wiOP

(4)

̂ )∞ k5∞ = (γ5̂AP)∞ /(γ5OP

(5)

prediction of phase compositions using the global experimental composition of the systems. The infinite dilution activity coefficient (γ∞ i ) can be calculated by considering the cholesterol mass fraction tend toward zero, whereas the concentrations of the other compounds of the system are kept constant. The determination of the NRTL and UNIQUAC interaction parameters involving the cholesterol and the other compounds (lard, oleic acid, ethanol, and water) was performed in accordance with the method described by Rodrigues et al.,21 in which the distribution coefficient objective function, eq 7, is minimized according to the methodology suggested by Pessôa Filho.44

The mass fraction-scale activity coefficient, γ̂i, can be associated with the UNIQUAC and NRTL activity coefficient, γi, according to eq 6: K

γi ̂ = γi /Mi(∑ wj /Mj) j=1

N

(6)

OF(k5) =

For γ∞ 5 calculations, the phase equilibrium was established by the interaction parameters involving the main components of the pseudo-quaternary system (lard, oleic acid, ethanol, and water). Such parameters were utilized to execute flash calculations for the

∑n = 1 (k5exptl − k5calcd)2 N

⎛ p2 ⎞ + Q ∑ ⎜⎜ l ⎟⎟ L⎠ l=1 ⎝ L

(7)

In eq 7, n is the tie line indicator, N is the total quantity of tie lines, k5 is the cholesterol distribution coefficient, and exptl and 1731



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Table 6. NRTL and UNIQUAC Interaction Parameters between Lard (1) + Oleic Acid (2) + Ethanol (3) + Water (4) + Cholesterol (5) at (318.2 ± 0.1) K thermodynamic model UNIQUAC

pair ij

Aij/K

Aji/K

αij

Aij/K

Aji/K

12 13 14 15 23 24 25 34 35 45

−101.17 137.66 −1178.8 −4560.9 −398.34 12621.0 −192.66 −67.100 −4263.0 155.77

−124.71 1417.4 3871.1 1916.1 250.17 11474.0 −269.01 −255.04 −54.308 −2329.4

0.56254 0.56996 0.14789 0.69898 0.57000 0.10000 0.62304 0.47000 0.71465 0.11241

279.41 232.04 1035.7 −393.94 33.314 191.04 910.56 332.23 −596.93 −1126.2

−225.49 −48.028 −145.34 −246.46 −81.115 −2.6601 −266.32 −330.34 −139.85 1282.3

Table 7. Mean Deviations in Phase Compositions Δw/% system lard (FZEA) + oleic acid + ethanol lard (FZEA) + oleic acid + 6.11 mass % aqueous ethanol lard (FZEA) + oleic acid + 11.92 mass % aqueous ethanol global deviation of the correlation lard (Sadia) + oleic acid + ethanol (prediction)

NRTL UNIQUAC 0.57 0.24

0.58 0.31

0.39

0.62

0.41 5.87

0.53 4.46

RESULTS

Table 1 presents an association between the fatty acid composition of the two brands of lard (FZEA and Sadia) and the characteristic composition obtained from the literature. The fatty acid composition of the commercial oleic acid is also shown in Table 1. As one can see in Table 1, the fatty acid composition of the lard from FZEA is slightly different from that published as well as that found in the commercial brand (Sadia). This difference occurs mainly in relation to the concentrations of oleic and linoleic fatty acids. Oleic acid is the main fatty acid in the characteristic composition of lard found in the literature and in the commercial brand, whereas the second linoleic acid is present in higher concentrations in lard produced in FZEA. This difference can be explained by the fact that pigs reared in FZEA are used in animal nutrition studies and therefore have a different diet, which may result in the variation found in the fatty acid composition. Nevertheless, because the acidity of lard is usually expressed in mass % of oleic acid, we decided to obtain the liquid−liquid equilibrium data using oleic acid as the main fatty acid in lard from FZEA. The probable triacylglycerol compositions of the lard samples calculated from the fatty acid compositions are presented in Table 2. In Table 2, the principal triacylglycerol corresponds to the compound of highest concentration in the isomer set with x carbons and y double bonds. Thus, some fatty acids that appear in Table 1, such as the trans acids and those with odd numbers of carbons, are not explicitly stated in Table 2. For instance, the triacylglycerol PPoS is part of the 50:1 group, in which PPO is the main triacylglycerol. Furthermore, triacylglycerol groups whose total composition was less than 0.3 mass % were ignored. The calculation of the molar masses (M) of the fats were performed from the compositions (in mole fraction) given in Table 2. The calculated molar mass values for all components in addition to the volume and area parameters are shown in Table 3. In Table 3, despite the difference in the fatty acid composition of the fats, especially regarding the levels of oleic and linoleic acids, the molar masses obtained are similar. Tables 4 and 5 present the global composition of the mixtures and the correspondent tie-lines for the pseudo-ternary model systems composed of lard (FZEA and Sadia) + oleic acid + ethanol and the pseudo-quaternary systems composed of lard (FZEA) + oleic acid + ethanol + water, respectively. Mass balance calculations provided deviations not higher than 0.5 %, which indicate that the experimental data presented an excellent quality. Figure 1 shows the experimental points and calculated tielines for the system lard, oleic acid, ethanol, and water (6.11 mass %). The equilibrium diagram was schemed in triangular coordinates, assuming ethanol + water as a single solvent. Figure 1 shows that UNIQUAC and NRTL equations provided a good description of the phase compositions. The interaction parameters of the NRTL and UNIQUAC equations are presented in Table 6. The deviations involving the experimental and the calculated concentrations were calculated by eq 3 and are presented in Table 7. Figure 2 represents the equilibrium parameters (distribution coefficients of lard, k1, and oleic acid, k2, and the selectivity, S2/1) as a function of the acidity at the global composition (w2OC). Mathematically, the equilibrium parameters can be obtained by eqs 4 and 8:

Figure 1. Equilibrium diagram for the system lard (1) + oleic acid (2) + 6.11% aqueous solvent [ethanol (3) + water (4)] at 318.2 K. ○, experimental; modeling: - - -, NRTL; ···, UNIQUAC.

NRTL

Article

calcd denote experimental and calculated values, correspondingly. The extra expression is a penalty function recommended by Kang and Sandler45 to prevent the interaction parameters have very large absolute values: Q is an insignificant value that does not modify the function, l, L, and pl refer to the UNIQUAC or NRTL parameter indicator, the total number of parameters, and the UNIQUAC or NRTL parameter, respectively. The values of r′ and q′ for the cholesterol molecule were also obtained by eq 1 using a mole fraction of cholesterol equal to 1.

S2/1 = 1732

k2 k1

(8) dx.doi.org/10.1021/je300189x | J. Chem. Eng. Data 2012, 57, 1728−1736


Article

Figure 2. Distribution coefficients of lard (k1) and oleic acid (k2), and selectivities (S2/1) for systems of lard (1) + oleic acid (2) + ethanol (3) + water (4) at 318.2 K. Experimental: □, anhydrous ethanol; ○, 6.11 % of water in ethanol; △, 11.92 % of water in ethanol; modeling: - - -, NRTL; ···, UNIQUAC.

the fatty compounds in the alcoholic solvent. These results indicate that aqueous ethanol exhibits an inferior capability for the removal of fatty acids. In contrast, this fact is favorable from the perspective of reducing the loss of neutral (or purified) fat during the process. Figure 2a also shows that the higher the free fatty acid level in the global composition, the higher the values of k1, and the higher the fat content in the alcoholic phase. This behavior occurs because fatty acids increase the mutual solubility between the fat and the alcoholic solvent. Figure 2b indicates that the higher the water percentage in the solvent, the higher the selectivity value. Because selectivity is a parameter that indicates the ability of the solvent to extract fatty acids without solubilization of great quantities of neutral fat, these results indicate that, although the aqueous solvents extract less fatty acids, they provide a reduction in the loss of neutral fat throughout the liquid−liquid extraction process. Figure 2b also presents the result of the increase of the free acidity in the global composition (wOC 2 ) on the selectivity values. The solvent selectivities decrease with the increase of wOC 2 ; however, in general, the selectivity is much greater for solvents with higher water content. Such behavior has been observed and discussed in previous works of our research group for various vegetable oils, including corn,16 rice bran,17 palm,18 and cottonseed.21 Figure 2 also shows a comparison between experimental k1, k2, and S2/1 values and those obtained by the thermodynamic equations. As one can see, both models produce very similar results for the calculation of the equilibrium parameters. The parameters for the NRTL and UNIQUAC equations were used for the calculation of liquid−liquid equilibrium for the system lard (Sadia), oleic acid, and ethanol at 318.2 K. Flash calculations for the prediction of phase concentrations were carried out considering the global composition of the systems. The deviations between the experimental and predicted concentrations were obtained via eq 3 and are presented in Table 7. Figure 3 presents the experimental points and the estimated tie-lines for the system lard (Sadia) + oleic acid + ethanol. Even with the dissimilarity involving the fatty acids compositions of

Figure 3. Equilibrium diagram for the system lard (Sadia) (1) + oleic acid (2) + ethanol (3) at 318.2 K. ■, experimental; prediction: - - -, NRTL; ···, UNIQUAC.

The error bars indicated in Figure 2 were calculated by error propagation, using eqs 4 and 8, as well as the standard deviations of the phase's compositions. As can be observed in Figure 2, the error bars are very small for the majority of experimental data. In fact, the higher values were obtained for selectivities, especially for low levels of free fatty acids in the lard and 11.92 mass % of water in the solvent. In these conditions, low concentrations of neutral lard in the alcoholic phase (wAP 1 ) were obtained, and consequently, a relatively high standard deviation of wAP 1 occurred. This fact influenced the uncertainties of the lard distribution coefficient and the experimental solvent selectivity, once they are calculated by error propagation. As one can see in Figure 2a, the fatty compound distribution coefficients (k1 and k2) show a decrease when water is added to ethanol. This is because the presence of water increases the polarity of the solvent and therefore decreases the solubility of 1733



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Table 8. Experimental and Calculated Cholesterol Distribution Coefficients (k5) for the System Lard (1) + Oleic Acid (2) + Ethanol (3) + Water (4) + Cholesterol (5) at (318.2 ± 0.1) K global composition (in mass fractions, w) w1

w2

w3

w4

exptl

calcd (NRTL)

calcd (UNIQUAC)

0.0008 0.0316 0.0607 0.0647 0.1097 0.1538 0.1874 w2Lb

0.4973 0.4988 0.4976 0.4963 0.4990 0.4987 0.4985 w1

0.0012 0.0012 0.0012 0.0012 0.0012 0.0012 0.0012 w2

0.5011 0.4842 0.4708 0.4700 0.4450 0.4232 0.4065 w3

0.0004 0.0158 0.0304 0.0325 0.0548 0.0769 0.0938 w4

1.052 0.710 0.451 0.445 0.341 0.271 0.226 exptl

1.071 0.669 0.479 0.460 0.328 0.265 0.235 calcd (NRTL)

1.036 0.682 0.499 0.481 0.339 0.265 0.230 calcd (UNIQUAC)

0.0523 0.1024 0.1525 0.2018

0.4736 0.4486 0.4239 0.3991

0.0262 0.0512 0.0763 0.1009

0.4699 0.4698 0.4695 0.4697

0.0304 0.0304 0.0304 0.0304

0.560 0.575 0.593 0.612 exptl

additional experiments

a

k5

w4Sa

w1

w2

w3

w4

0.4749 0.4729 0.4521 0.4567 0.4751

0.0261 0.0255 0.0467 0.0421 0.0261

0.4985 0.4708 0.4688 0.4498 0.4393

0.0005 0.0308 0.0324 0.0514 0.0595

1.136 0.577 0.576 0.401 0.378

0.576 0.593 0.599 0.607 calcd (NRTL)

0.550 0.584 0.605 0.615 calcd (UNIQUAC)

1.121 0.570 0.570 0.405 0.351

1.157 0.544 0.557 0.409 0.353

w4S = water mass fraction in the ethanolic solvent. bw2L = oleic acid mass fraction in the lard.

Figure 4. Cholesterol distribution coefficients (k5). Experimental: ○, as a function of the free oleic acid concentration in the lard (w2L); □, as a function of the water concentration in the solvent (w4S); modeling: - - -, NRTL; ···, UNIQUAC.

different water contents (w4S). The first seven data of Table 8 were used to evaluate the influence of water content in the solvent on the cholesterol partition coefficients (at constant free acidity in the lard). The following four data allowed to evaluate the influence of the free fatty acid content in the lard on the cholesterol partition coefficients (at constant water content in the solvent). To increase the database for the modeling procedure, five extra experiments were prepared varying the free acidity in the lard and the water content in the solvent at random. As one can see, the cholesterol distribution coefficients present a slight increase with the increase of the free oleic acid concentration in the lard. However, such values are powerfully affected when water is added to the ethanol. Explicitly, the larger

the two lard samples, the parameters obtained to the studied systems permit a good estimation of the phase equilibrium for systems that contain swine fat. Figure 3 also shows that the thermodynamic models miscalculate (over or underestimate) some solvent concentrations of the alcoholic phase, which justifies the higher deviation obtained in this case. With the intention of finding interaction parameters involving cholesterol and the major pseudo-components, some additional experiments were executed for determining cholesterol distribution coefficients. Table 8 shows the global composition of the systems and the experimental and calculated cholesterol distribution coefficients obtained for systems that contained lard with different free oleic acid concentrations (w2L) and ethanol with 1734



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(5) Bhupathiraju, S. N.; Tuckerm, K. L. Coronary heart disease prevention: Nutrients, foods, and dietary patterns. Clin. Chim. Acta 2011, 412, 1493−1514. (6) Stewart, J. W.; Kaplan, M. L.; Beitz, D. C. Microbiological Pork with a high content of polyunsaturated fatty acids lowers LDL cholesterol in women. Am. J. Clin. Nutr. 2001, 74, 179−187. (7) Eller, F. J.; List, G. R.; Teel, J. A.; Steidley, K. R.; Adlof, R. O. Preparation of Spread Oils Meeting U.S. Food and Drug Administration Labeling Requirements for Trans Fatty Acids via Pressure-Controlled Hydrogenation. J. Agric. Food Chem. 2005, 53, 5982−5984. (8) Heshmati, A.; Khodadadi, I. Reduction of cholesterol in beef suet using lecithin. J. Food Compos. Anal. 2009, 22, 684−688. (9) Ludke, M. C. M. M.; Lopez, J. Fatty acids concentration and level of cholesterol in diets for humans and present in swine carcasse (in Portuguese). Cienc. Rural 1999, 29, 181−187. (10) Yen, G. C.; Chen, C. J. Effects of fractionation and the refining process of lard on cholesterol removal by β-cyclodextrin. J. Food Sci. 2000, 65, 622−624. (11) Froning, G. W.; Fieman, F.; Wehling, R. L.; Cuppett, S. L.; Niemann, L. Supercritical carbon-dioxide extraction of lipids and cholesterol from dehydrated chicken meat. Poultry Sci. 1994, 73, 571− 575. (12) Lanzani, A.; Bondioli, P.; Mariani, C.; Folegatti, L.; Venturini, S.; Fedeli, E.; Barreteau, P. A New Short-Path Distillation System Applied to the Reduction of Cholesterol in Butter and Lard. J. Am. Chem. Soc. 1994, 71, 609−614. (13) Gu, Y. F.; Chen, Y.; Hammond, E. G. Use of Cyclic Anhydrides to Remove Cholesterol and Other Hydroxy Compounds from Fats and Oils. J. Am. Chem. Soc. 1994, 71, 1205−1209. (14) Shah, K. J.; Venkatesan, T. K. Aqueous Isopropyl Alcohol for Extraction of Free Fatty Acids from Oils. J. Am. Chem. Soc. 1989, 66, 783−787. (15) Batista, E.; Monnerat, S.; Kato, K.; Stragevich, L.; Meirelles, A. J. A. Liquid-Liquid Equilibrium for Systems of Canola oil, Oleic acid, and Short Chain Alcohols. J. Chem. Eng. Data 1999, 44, 1360−1364. (16) Gonçalves, C. B.; Batista, E.; Meirelles, A. J. A. Liquid-Liquid Equilibrium Data for the System Corn Oil + Oleic Acid + Ethanol + Water at 298.15 K. J. Chem. Eng. Data 2002, 47, 416−420. (17) Rodrigues, C. E. C.; Antoniassi, R.; Meirelles, A. J. A. Equilibrium Data for the System Rice Bran Oil + Fatty Acids + Ethanol + Water at 298.2 K. J. Chem. Eng. Data 2003, 48, 367−373. (18) Gonçalves, C. B.; Meirelles, A. J. A. Liquid−liquid equilibrium data for the system palm oil + fatty acids + ethanol + water at 318.2 K. Fluid Phase Equilib. 2004, 221, 139−150. (19) Rodrigues, C. E. C.; Pessôa Filho, P. A.; Meirelles, A. J. A. Phase equilibrium for the system rice bran oil + fatty acids + ethanol+ water + c-oryzanol + tocols. Fluid Phase Equilib. 2004, 216, 271−283. (20) Rodrigues, C. E. C.; Silva, F. A.; Marsaioli, A., Jr.; Meirelles, A. J. A. Deacidification of Brazil nut and macadamia nut oils by solvent extraction: liquid−liquid equilibrium data at 298.2 K. J. Chem. Eng. Data 2005, 50, 517−523. (21) Rodrigues, C. E. C.; Reipert, E. C. D.; Souza, A. F.; Pessôa Filho, P. A.; Meirelles, A. J. A. Equilibrium data for systems composed by cottonseed oil + commercial linoleic acid + ethanol + water + tocopherols at 298.2 K. Fluid Phase Equilib. 2005, 238, 193−203. (22) Rodrigues, C. E. C.; Filipini, A.; Meirelles, A. J. A. Phase Equilibrium for Systems Composed by High Unsatured Vegetable Oils + Linoleic Acid + Ethanol + Water at 298.2 K. J. Chem. Eng. Data 2006, 51, 15−21. (23) Rodrigues, C. E. C.; Onoyama, M. M.; Meirelles, A. J. A. Optimization of the rice bran oil deacidification process by liquid− liquid extraction. J. Food Eng. 2006, 73, 370−378. (24) Gonçalves, C. B.; Filho, P. A. P.; Meirelles, A. J. A. Partition of nutraceutical compounds in deacidification of palm oil by solvent extraction. J. Food Eng. 2007, 81, 21−26. (25) Mohsen-Nia, M.; Mahdi, D. Liquid-liquid equilibrium for systems of (corn oil plus oleic acid plus methanol or ethanol) at (303.15 and 313.15) K. J. Chem. Eng. Data 2007, 52, 910−914.

the water content, the lower the solvent capability for removing the cholesterol. In Figure 4a, the cholesterol distribution coefficient, k5, is presented as a function of the free oleic acid content in the fat (w2L). Figure 4b shows k5 as a function of the water concentration in the ethanol (w4S). The error bars indicated in Figure 4 were calculated by error propagation, using eq 4 and the standard deviations of the cholesterol concentrations in the phases in equilibrium. As can be seen, the error bars are very small, since the uncertainties of the cholesterol partition coefficients were not higher than 3.42 %. It is important to note that the error bars appear larger in Figure 4a due to the scale used to plot it. In addition, Figure 4 indicates that the UNIQUAC and NRTL equations offer an excellent description of the cholesterol distribution coefficients; the second one, however, gives better results. The mean deviations involving the experimental and calculated cholesterol distribution coefficient, k5, was obtained using eq 9 and presented values of 0.022 and 0.018 for the UNIQUAC and the NRTL equations, respectively. The interaction parameters involving cholesterol and the major components of the systems are shown in Table 6. ⎛ ∑N (k exptl − k calcd)2 ⎞1/2 5, n 5, n ⎟ Δk5 = ⎜⎜ n = 1 ⎟ N ⎝ ⎠

(9)

■

CONCLUSION Liquid−liquid equilibrium data for the system lard + oleic acid + ethanol + water were obtained at 318.2 K. As already observed in our previous works, the oleic acid distribution coefficients decrease as well as the selectivities increase when water is added to the ethanol. The NRTL and UNIQUAC equations also provided a good calculation of the liquid−liquid equilibrium, with mean deviations of 0.62 % or less concerning the experimental data. Furthermore, this work also showed that it is feasible to reduce the cholesterol content of lard by liquid−liquid extraction using ethanol (with or without the addition of water) as a solvent.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel: +55-19-3565-4353. Fax: + 5519-3565-4284. Funding

The authors wish to acknowledge FAPESP (Fundaçaõ de Amparo à Pesquisa do Estado de São Paulo 06/00646-6, 06/ 06206-6, and 05/53095-2) for financial support. Notes

The authors declare no competing financial interest.

■

REFERENCES

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LiquidâLiquid Equilibrium Data for the System Lard + Oleic Acid +

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