Equilibrium Data of Aqueous Two-Phase Systems Composed of Poly

Jun 11, 2012 - Phone: 55-31-38991618. ... Equilibrium data were determined for aqueous two-phase systems composed of poly(ethylene glycol) (PEG), ...
0 downloads 0 Views 985KB Size
Download PDF
Article pubs.acs.org/jced

Equilibrium Data of Aqueous Two-Phase Systems Composed of Poly(ethylene glycol) and Maltodextrin Fabíola Lopes Caetano Machado,† Jane Sélia dos Reis Coimbra,*,† Abraham Damian Giraldo Zuniga,‡ Angélica Ribeiro da Costa,§ and Joaõ Paulo Martins∥ †

Department of Food Technology, Federal University of Viçosa, P. H. Rolfs Av., s/n, 36570-000, Viçosa, MG, Brazil Food Engineering, Federal University of Tocantins, NS 15 Av., ALCNO 14, 77123-360, Palmas, TO, Brazil § State University of Southwest Bahia, Primavera Square, 40, 45700-000, Itapetinga, BA, Brazil ∥ Federal Institute of South of Minas Gerais, Dr. João Beraldo, 242, 37550-000, Pouso Alegre, MG, Brazil ‡

ABSTRACT: Equilibrium data were determined for aqueous two-phase systems composed of poly(ethylene glycol) (PEG), maltodextrin (MD), and water. The systems were prepared by varying the PEG molar mass (4000 g·mol−1, 6000 g·mol−1, and 8000 g·mol−1) and the dextrose equivalent (DE) of the MD (10.5 and 15). The temperatures tested were 298.2 K, 308.2 K, and 318.2 K. For the systems studied it was observed that the molar mass of the PEG did not sensitively affect the equilibrium curve position, and as the DE of MD increased, the concentration of polymers used to form the phases decreased. In some systems temperature minimally influenced the displacement of the equilibrium curve.

■

INTRODUCTION Technologies for the fabrication of food and pharmaceutical products involve a wide variety of microorganisms whose useful activity allows either direct or indirect participation in numerous alimentary processes. In the production of these microorganisms, as in basically all biotechnological operations, a crucial step is the separation and purification of the product due to the elevated operational cost of this process. When the research material is made up of living cells, various additional cautions are taken during the recovery process due to their sensibility to external factors such as pressure, temperature, and pH. The common methods for cell separation are filtration and centrifugation, but their application on the industrial scale is limited and may reduce the number of live cells. In the extraction of biocompounds by liquid−liquid extraction, organic solvents are being increasingly substituted by aqueous solvents. This is because many organic solvents are toxic to microorganisms or denature proteins which limit their used in biotechnological processes.1,2 Aqueous two-phase systems (ATPS) provide an adequate alternative for the separation of biomolecules. ATPS's are composed of polymers/salts or polymers/polymer dissolved in water which, under determined conditions, forms two immiscible or partly immiscible phases. The ATPS's are © 2012 American Chemical Society

appropriate for separation and purification of biological substances since they present a mild environment during processing due to the high water content and low interfacial tension between phases. Purification is the result of a differential partition of the molecule of interest and impurities between the two liquid phases. ATPS's have been utilized in the determination of hydrophobic properties of cell membranes and extractive bioconversion of biocompounds, as well as the separation and purification of metals, proteins, enzymes, hormones, organelles, and cells.1,3 Acquisition of equilibrium data and the properties of ATPS are necessary for the design of extraction processes and for the development of models that can predict biomolecules partitioning between phases. However some ATPS's containing polymers and salts may occasionally cause damage to biomolecules due to elevated salt contents used in system composition, creating the problem of residue removal. The most common system to overcome this problem is that composed of two polymers, generally PEG + dextran, although this system is very costly to be used in large-scale processes. This obstacle may be solved by utilizing alternative Received: February 25, 2012 Accepted: May 30, 2012 Published: June 11, 2012 1984

dx.doi.org/10.1021/je3002442 | J. Chem. Eng. Data 2012, 57, 1984−1990

Journal of Chemical & Engineering Data

Article

Analysis of Phase Compositions. For the construction of the phase diagrams, concentrations of MD and water were quantified. The PEG content was calculated using a mass balance. MD Quantification. MD was quantified according to the method of Dubois et al.12 Analytical curves were constructed using MD concentrations of 10 μg, 20 μg, 30 μg, 40 μg, 60 μg, and 80 μg in 2 mL of solution. The sample absorbance was read with a spectrophotometer (Varian, Cary 50, Palto Alto, CA, USA) at 488 nm. The samples were diluted using deionized water prior to colorimetric quantification to fit the polymer concentrations in the analytical curve range. In all cases the samples were analyzed in triplicate. The expanded uncertainty of the MD data performed within this work, with a level of confidence of 95 %, was estimated to be 1·10−6 g. Water Content Quantification. The water concentration was determined using beach sand treated with sulfuric acid and sodium hydroxide to a neutral pH and also dried in an oven (Fanem, 315, Sao Paulo, Brazil) according to the AOAC13 and Silva et al.11 The beach sand was treated with sulfuric acid (w = 0.95 %, Vetec, Rio de Janeiro, Brazil) at a 1:1 ratio. The material was then washed with deionized water until reaching pH 7. After this process sodium hydroxide (w = 0.32, Vetec, Rio de Janeiro, Brazil) was added to the sand at a 1:1 ratio. The material was washed with deionized water until reaching pH 7 and then dried in an oven at 378.2 K overnight. Subsequently the sand was maintained at 773.2 K for 24 h in a muffle furnace. It was then cooled to the ambient temperature (293.2 K) in a desiccator and stored in closed recipients. Aliquots of the sample phases were added to the previously weighed sand (analytical balance Denver M-310, USA) in a Petri dish. The material was maintained for 4 h in an oven at 348.2 K, followed by 1 h in a desiccator. This procedure was repeated until obtaining a constant weight. In all cases the samples were analyzed in triplicate. The expanded uncertainty of the water data performed within this work, with a level of confidence of 95 %, was estimated to be 2·10−5 g. PEG Content Quantification. The PEG content was obtained by a mass balance (wPEG = 1 − wMD − wH2O; where wPEG is the PEG mass fraction, wMD is the MD mass fraction, and wH2O is the water mass fraction). In all cases the samples were analyzed in triplicate. The uncertainty of the PEG data was estimated to be 3·10−2 g. Experimental Data Fitting. The data obtained for the equilibrium curves were fitted using the sigmoidal equation proposed by Tubio et al.14 a wPEG = y0 + W −x 1 + exp − MDb 0 (1)

polymers. Therefore, the possibility of using low-cost starch derived polymers, such as maltodextrin (MD), to substitute dextran is quite attractive.4,5 MD is a linear-chain polymer of glucose, with broad applicability in industry as a cheap, almost tasteless, noncrystallizing carrier for many food ingredients and pharmaceuticals. It is usually obtained from starch, either by enzymatic or by combined enzymatic-heat treatment.6 MDs are commercialized with different values of dextrose equivalent (DE), which is the degree of starch hydrolysis. Equilibrium data and some physical properties for systems composed of PEG + MD, at 298.2 K, are reported in literature.4,7,8 However, it should be emphasized that the majority of equilibrium data for polymer/polymer ATPS's uses the PEG + dextran system.1,9,10 Therefore, our objective was to obtain equilibrium data for PEG + MD + water systems at different temperatures so that they can be employed in the design and scaling up of liquid−liquid extraction equipment for the separation of biomolecules. The diagrams studied in this work were composed by PEG 4000 + MD-DE 15 + water (at 308.2 K), PEG 6000 + MD-DE 15 + water (at 298.2 K and 308.2 K), PEG 8000 + MD-DE 15 + water (at 298.2 K and 308.2 K), PEG 4000 + MD-DE 10.5 + water (at 308.2 K and 318.2 K), PEG 6000 + MD-DE 10.5 + water (at 308.2 K and 318.2 K), and PEG 8000 + MD-DE 10.5 + water (at 308.2 K and 318.2 K).

■

MATERIALS AND METHODS Materials. PEG with different molar masses of 4000 g·mol−1, 6000 g·mol−1, and 8000 g·mol−1 used in this work was purchased from Merck (Darmstadt, Germany). MD with an average DE of 15 was supplied by Fluka (Newport News, VA, USA, purity 0.99), and MD with an average DE of 10.5 was a gift from Refinações de Milho Brasil (RMB, Sao Paulo, Brazil, purity 0.99, 2800 g·mol−1 with a polydispersity index of 2.85 previously determined by size exclusion chromatography). Deionized water (Milli-Q, Millipore, Billerica, MA, USA) was utilized in all experiments (R ≥ 18.2 MΩ·cm−1). All other reagents were of analytical grade with a minimum purity of 0.99. Equilibrium Data. Stock solutions containing MD (wMD = 0.5) and PEG (wPEG = 0.5) were prepared by the addition of Milli Q water to a known quantity of the polymer. The diagrams for biphasic systems PEG 4000 + MD-DE 15 (308.2 K), PEG 6000 + MD-DE 15 and PEG 8000 + MD-DE 15 (298.2 K and 308.2 K), and PEG 4000 + MD-DE 10.5, PEG 6000 + MD-DE 10.5, and PEG 8000 + MD-DE 10.5 (308.2 K and 318.2 K) were determined in a mixing cell constructed according to Silva et al.11 Mixtures consisting of known masses of PEG and MD stock solutions were prepared by weighing aliquots on an analytical balance (Denver, M-310, Bohemia, NY, USA). The mixing cell utilized was constructed of borosilicate glass and sealed with a Teflon cork which has two openings, one for a thermometer and the other to feed the system. The flask had a water-filled jacket for temperature control with a capacity of 50 mL. The system was agitated using a magnetic stirrer for 1 h, and it was then maintained at rest in a thermostatic bath with an accuracy of ± 0.1 K (Tecnal, TE-184, Brazil) for 12 h which was the time necessary to reach equilibrium. After this treatment, the two phases became clear and transparent, and the interface was well-defined. Samples of the two phases were analyzed.

(

)

where y0, x0, a, and b are fit parameters. Volume Phase Ratio. The volume phase ratio was calculated as the ratio between the volume in the upper phase rich in PEG and the volume in the lower phase rich in MD. This ratio was obtained by determining the volumes of the phases when varying the concentration of the polymer, molar mass of the PEG, and DE of the MD. The phases were removed from the mixing cells with the aid of Pasteur pipettes. These phases collected were then weighed and the volumes calculated from the density. Tie Line Slope (TLS) Calculation. The influence of temperature, PEG molar mass, and DE of MD on equilibrium data of the PEG + MD ATPS was determined based on either 1985

dx.doi.org/10.1021/je3002442 | J. Chem. Eng. Data 2012, 57, 1984−1990

Journal of Chemical & Engineering Data

Article

Table 1. Phase Composition for PEG/MD-DE 15 Systems total system

top phase

bottom phase

100wMD

100wPEG

100wH2O

100wMD

100wPEG

100wH2O

100wMD

100wPEG

100wH2O

20.00 20.00 20.00 22.00 20.00 20.00 20.00 20.00 35.00 20.00 20.00 35.00 19.85 19.97 30.00

8.50 10.00 12.00 8.00 10.00 12.00 8.50 10.00 8.00 10.00 12.00 8.00 9.93 12.03 10.00

71.50 70.00 68.00 70.00 70.00 68.00 71.50 70.00 57.00 70.00 68.00 57.00 70.22 68.00 60.00

15.75 13.47 11.79 13.80 13.47 11.79 15.75 13.94 12.75 14.25 12.07 12.86 13.70 14.31 14.23

9.73 12.52 15.68 10.70 12.52 15.68 9.73 12.36 22.92 20.75 15.52 12.17 12.74 14.91 19.39

74.52 74.01 72.53 75.50 74.01 72.53 74.52 73.70 64.33 65.00 72.41 74.97 73.56 70.78 66.38

38.18 42.00 44.50 42.50 45.50 48.32 38.18 41.00 47.63 38.89 44.83 49.36 40.19 42.66 47.87

0.00 0.00 0.11 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

61.82 58.00 55.39 57.50 54.50 51.68 61.82 59.00 52.37 61.11 55.17 50.64 59.81 57.34 52.13

PEG 4000/308.2 K

PEG 6000/298.2 K

PEG 6000/308.2 K

PEG 8000/298.2 K

PEG 8000/308.2 K

an increase or decrease of the phase separation region and variation in tie line slope (TLS). An increase or decrease in the TLS indicates changes in polymer concentration. The TLS can be calculated as follows:10 TLS =

TP BP C PEG − C PEG

CTP PEG

TP BP CMD − CMD

(2)

CTP MD

where and are the mass fractions of PEG and MD in BP the top phase rich in PEG, and CBP PEG and CMD are the polymer mass fractions in the bottom phase rich in MD. Physical Properties of the Phases. The density of the phases was determined by the pycnometer method (25 mL), and the viscosity was measured using a sphere rheoviscometer (KD 2.1, Tecnal, Sao Paulo, Brazil) at 298.2 K. In all cases the samples were analyzed in triplicate. The uncertainties of density and viscosity values for the saline and polymeric phases were of 0.02 % for density and 0.07 % for viscosity.

■

Figure 1. Phase diagram of the PEG 8000 + MD-DE 15 + water system: ■, 298.2 K; ▲, 308.2 K.

RESULTS AND DISCUSSION Several equilibrium diagrams were built for the PEG + MD system containing different polymer molar masses. Temperatures of 298.2 K and 308.2 K were used for MD-DE 15 and 308.2 K and 318.2 K for MD-DE 10.5. Tie lines were determined for each polymer combination. Equation 1 was assumed to be suitable to fit the equilibrium data as the R2 values were greater than 0.97. PEG + MD-DE 15 Systems. The experimental compositions for all PEG + MD-DE 15 systems are given in Table 1 where all results are expressed as PEG mass fraction (wPEG), MD mass fraction (wMD), and water mass fraction (wH2O). In some systems, values near zero were obtained for the content of PEG in the MD rich phase. It is therefore likely that all PEG was excluded from the MD rich phase in these ATPS's. A similar behavior for some PEG + MD systems were observed by Silva and Meirelles.8 The phase separation process is not very well-understood, and more studies are necessary to reveal the mechanism involved in the split phase when two polymers chemically distinct and water or polymer, salt (organic or inorganic), and water are mixing in certain ranges of composition and temperature. Influence of Temperature. Figure 1 shows the equilibrium data of the system composed of PEG 8000 g·mol−1 + MD-DE

15 at 298.2 K and 308.2 K. An increase in temperature minimally displaces the region of phase separation, indicating a small modification in both heat capacity (ΔCp) and enthalpy (ΔH) associated with the phase segregation process. In the range of values tested, the displacement of equilibrium curve (I to I′) was most noticeable in the region corresponding to high values of PEG and low values of MD. The difference of the values obtained for the composition of phases at 298.2 K and 308.2 K was on average 17 % and 11 % for PEG and MD, respectively. In this case, at lower temperatures the ATPS can be formed in lower polymer concentration which reduces costs associated to acquisition of reagents and favors separation of biocompounds close to ambient temperatures. Influence of the PEG Molar Mass. Figure 2 shows the equilibrium curves obtained for systems composed of PEG with molar mass of (4000, 6000, and 8000) g·mol−1 and MD with DE 15. In the region containing no experimental data points, extrapolation was performed by adjusting a sigmoidal equation proposed by Tubio et al.14 In Figure 2 the equilibrium curves are closer in the extreme right of the region where the critical point is likely located, but in the extreme left the curves are more separated. 1986

dx.doi.org/10.1021/je3002442 | J. Chem. Eng. Data 2012, 57, 1984−1990

Journal of Chemical & Engineering Data

Article

Figure 3. Phase diagram of the PEG 6000 + MD-DE 10.5 + water system: ■, 308.2 K; ▲, 318.2 K. Figure 2. Phase diagram of the PEG + MD-DE 15 + water system at 308.2 K: ▼, PEG 4000; ■, PEG 6000; ▲, PEG 8000.

concentrations of MD and PEG with reduced molar mass present the same behavior as PEG + salt systems. In Figure 4, the diagram for the PEG 8000 + MD-DE 10.5 system at 308.2 K and 318.2 K can be observed. The effect of temperature was not significant, and it was only possible to observe an increase in the TLS. The difference between this behavior and that presented by PEG 8000 + MD-DE 15 (Figure 1) indicates the influence of the type of MD used, which does not have the same value of DE, as well as of the system temperatures, which were different due to gelification of MD-DE 10.5 at 298.2 K. Also, little difference in the phase separation area was observed by Zaslavsky10 when comparing equilibrium data for the systems PEG 6000 + dextran 70,

PEG + MD-DE 10.5 Systems. The experimental compositions for all PEG + MD-DE 10.5 systems are given in Table 2. All results are expressed as mass fractions. Influence of Temperature. Figure 3 represents the diagram for an ATPS composed of PEG 6000 + MD-DE 10.5. The temperature rise induces inverse behavior to that verified for the PEG 8000 + MD-DE 15 system. Such behavior is in accordance with Albertsson1 for ATPS's formed of PEG 1500 + dextran in the temperature range of 0 K to 293.15 K. A similar behavior was also observed for the PEG + potassium phosphate systems11 as well for ATPS Ucon 50-HB5100 + sodium citrate.14 Probably ATPS's composed of PEG + MD with lower Table 2. Phase Composition for PEG/MD-DE 10.5 Systems total system

PEG 4000/308.2 K

PEG 4000/318.2 K

PEG 6000/308.2 K

PEG 6000/318.2 K

PEG 8000/308.2 K

PEG 8000/318.2 K

top phase

bottom phase

100wMD

100wPEG

100wH2O

100wMD

100wPEG

100wH2O

100wMD

100wPEG

100wH2O

22.00 20.00 20.00 30.00 22.00 20.00 20.00 30.00 22.00 24.96 26.83 20.00 20.00 29.75 30.00 22.00 25.00 26.83 20.00 22.00 26.90 30.00

8.00 10.00 12.00 10.00 8.00 10.00 12.00 10.00 8.00 10.00 11.67 8.00 10.00 7.50 10.00 8.00 10.00 11.67 10.00 12.00 11.67 12.50

70.00 70.00 68.00 60.00 70.00 70.00 68.00 60.00 70.00 64.04 51.50 72.00 70.00 62.75 60.00 70.00 65.00 51.50 70.00 66.00 61.43 57.50

14.06 11.56 10.17 9.35 13.33 12.18 10.37 10.01 12.76 11.72 10.18 11.00 9.99 11.00 9.72 11.30 9.20 8.59 10.45 10.65 9.18 7.73

10.07 13.39 16.09 21.38 11.35 12.92 16.57 21.99 11.22 15.84 20.32 12.03 14.74 18.00 21.77 13.70 17.99 22.12 14.36 18.35 22.32 28.22

75.87 75.05 73.74 69.27 75.32 74.90 73.06 68.00 76.02 72.44 69.50 76.97 75.27 71.00 68.51 75.00 72.81 69.29 75.19 71.00 68.50 64.05

37.36 44.49 46.74 49.80 39.09 41,51 44.42 49.80 38.78 44.96 50.27 36.91 41.87 44.95 49.59 39.93 43.56 47.22 40.00 43.40 47.12 49.92

0.64 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

62.00 55.51 53.26 50.20 60.91 58.49 55.58 50.20 61.22 55.04 49.73 63.09 58.13 55.05 50.41 60.07 56.44 52.78 60.00 56.60 52.88 50.08

1987

dx.doi.org/10.1021/je3002442 | J. Chem. Eng. Data 2012, 57, 1984−1990

Journal of Chemical & Engineering Data

Article

Influence of the MD-DE. The importance of DE resides in the type of application of the MD. For example, in the encapsulation process of soluble solids in a spray dryer, utilization of MD with greater values of DE is most suitable since it is less viscous.15 Figure 6 shows the phase diagrams for the PEG 8000 + MD system with the two distinct DE values. It is observed that the

Figure 4. Phase diagram of the PEG 8000 + MD-DE 10.5 + water system: ■, 308.2 K; ▲, 318.2 K.

polyvinylalcohol + dextran 70, and polyvinylpyrrolidone + dextran 70, at 311.2 K and 323.2 K. Influence of the PEG Molar Mass. Figure 5 shows the equilibrium curves obtained for systems composed of PEG with

Figure 6. Phase diagram of the PEG 8000 + MD ATPS at 308.2 K: ▲, MD-DE 15; ■, MD-DE 10.5.

equilibrium curve is elevated with the increase in the DE value, with a consequent reduction of the phase separation region. Therefore, it can be stated that the greater the DE value, greater is the quantity of polymer necessary to form two phases since the molar mass of MD is lower. Changes in the TLS were also verified. For low DE values, the tie lines are parallel, making the curve more symmetric, whereas for high DE values these lines have a more accentuated slope. The molar mass of the MD is greater for lower DE values. This behavior is in accordance with Albertsson1 for PEG + dextran systems. Published literature has reported some equilibrium data for ATPS's composed of PEG + MD. Szlag et al.4 obtained equilibrium data for PEG 8000 + MD systems with a molar mass of 1800 g·mol−1, DE equal to 10, at 298.2 K. In the present study it was used MD with DE of 10.5, at 308.2 K and 318.2 K. Thus, as can be observed in Figure 7, the data showed the same tendency but with a small difference in behavior at the region near the critical point. Volume Phase Ratio. The influence of system composition, the molar mass of PEG, and the DE of MD on the volume phase ratio was evaluated for the systems presented in Tables 3 to 5. It was observed that the volume phase ratio approaches 1 when the MD concentration increases (Table 3). For systems with low concentrations of PEG there was no phase separation, indicating the existence of a minimal PEG concentration for phase formation. A volume phase ratio near 1 is important for the operation of continuous processing equipment. If this value is far from 1, a large quantity of one phase compared to the volume of the other phase must be used, which may prejudice the process if the cost of the phase used in greater quantity is high. Contrarily, in a batch process, a volume phase ratio distant from 1 is satisfactory if the desired compound is collected in the phase in lower quantities, which guarantees its separation and preconcentration.

Figure 5. Phase diagram of the PEG + MD-DE 10.5 + water system at 308.2 K: ▲, PEG 4000; ■, PEG 6000; ▼, PEG 8000.

molar mass of 4000 g·mol−1, 6000 g·mol−1, and 8000 g·mol−1 and MD with DE 10.5. Equilibrium curves constructed with the sigmoidal equation fitted to experimental data show that the molar mass of PEG has a minimal influence on the region of separation when compared to PEG 4000 g·mol−1 or PEG 6000 g·mol−1 with 8000 g·mol−1. In the region containing no experimental data points, extrapolation was performed by adjusting the sigmoidal equation proposed by Tubio et al.14 In Figure 5 a small increase in the phase separation region can be observed for PEG 4000 and is represented by an ellipse. The same effect was reported by Zaslavsky10 for equilibrium data of PEG + dextran ATPS; the author concluded that increase in molar mass of both polymers caused an increase in the phase separation region. Similar behavior was verified by Silva et al.11 for PEG + phosphate systems when using PEG with a lower molar mass. 1988

dx.doi.org/10.1021/je3002442 | J. Chem. Eng. Data 2012, 57, 1984−1990

Journal of Chemical & Engineering Data

Article

Figure 7. Observed equilibrium data versus literature data: ▲, PEG 8000 + MD-DE10 at 298.2 K (Szlag et al.4); ■, PEG 8000 + MD-DE 10.5 at 308.2 K.

Figure 8. Phase diagram for the PEG 6000 + MD-DE 10.5 system at 318.2 K.

Table 3. Effect of the Concentration of Polymers PEG 4000 g·mol−1 and MD-DE 15 on Volume Phase Ratio at 298.2 K 100wMD

100wPEG

vol. phase ratio

20 10 14 10 12 10 12 10 7 6.2 5 5 8

7 5 8 10 15 15 20 20 20 17.3 15 20 35

20 20 6 6 4 4 3.3 3.8 3 no phase formation no phase formation no phase formation 0.5

concentrations are represented in mass fraction %. The volume phase ratio was calculated using the density of the phases. Table 4 presents the volume phase ratios for the systems A, B, and C of Figure 8 calculated by applying the lever rule in the tie lines. An increase in the concentration of one polymer causes an elevation in the volume of the polymer-rich phase. The effect of PEG molar mass, DE of the MD, and temperature on the average volume phase ratio is summarized in Table 5. The Tukey16 test was used to evaluate the results, and it was observed that all average values differed significantly at a probability of 5 %. In accordance with Table 5, an increase in molar mass of the PEG tends to reduce the volumetric ratio between the phases, by increasing the volume of the bottom phase rich in MD. The difference in the volume phase ratio between the system with MD-DE 15 and MD-DE 10.5 is more pronounced than between systems with MD of the same DE. The volume of the lower phase of the system containing MD-DE 10.5 is shown to be greater than the volume of the lower phase for systems containing MD-DE 15, reducing the phase ratio. When the value of DE increases, the number of long-chain polysaccharides present decreases. Therefore, the system whose bottom phase is rich in MD and contains the greatest number of long chains will have a lower volume phase ratio. In relation to temperature, an increase in temperature reduced the volume of the lower phase, increasing the solubility and the phase ratio of the systems. Physical Properties of the Phases. The viscosity of the bottom phase rich in MD is much greater than that of the top phase rich in PEG. The values of viscosity of the top phase varied from 6.32 mPa·s to 12.12 mPa·s, and the values of the bottom phase ranged from 82.93 mPa·s to 100.61 mPa·s. A large difference in viscosity is beneficial since the phase separation times decrease. The phase rich in MD has a greater density than that rich in PEG. It was also observed that PEG solutions with greater molar masses present greater densities. The density of the top phase ranged from 994.4 kg·m−3 to 1015.7 kg·m−3 and of the bottom phase from 1076.6 kg·m−3 to 1113.4 kg·m−3.

Table 4. Effect at the Global Point Concentration of the PEG 6000 g·mol−1 + MD-DE 10.5 System on the Phase Ratio at 318.2 K system

100wPEG

100wMD‑DE 10.5

vol. phase ratio

A B C

8 8 13

20 30 20

1.94 0.71 2.40

Table 5. Effect of PEG Molar Mass, MD-DE, and Temperature on the Volume Phase Ratio of the System PEG (w = 0.10) + MD (w = 0.20) PEG 4000

PEG 6000

PEG 8000

MD-DE

298.2 K

308.2 K

298.2 K

308.2 K

298.2 K

308.2 K

15.0 10.5

3.66

3.82 2.16

2.63

3.31 2.05

2.56

2.75 1.94

The effect of PEG and MD concentration on the volume phase ratio can be studied in a phase diagram by evaluating the tie line length (TLL). Global point A in Figure 8 represents the system containing 20 % mass fraction MD-DE 10.5 and 8 % mass fraction PEG. Its mass phase ratio can be calculated by the lever rule, dividing the length of line AE by line AD as the 1989

dx.doi.org/10.1021/je3002442 | J. Chem. Eng. Data 2012, 57, 1984−1990

Journal of Chemical & Engineering Data

■

Article

(13) AOAC International. Official Methods of Analysis, 16th ed.; AOAC International: Gaithersburg, MD, 1997; Vol. 2, pp 1−43. (14) Tubio, G.; Nerli, B. B.; Pico, G. A.; Venâncio, A.; Teixeira, J. Liquid−Liquid Equilibrium of the Ucon 50-HB5100/Sodium Citrate Aqueous Two-Phase Systems. Sep Purif. Technol. 2009, 65, 3−8. (15) Kenyon, M. M. Modified Starch, Maltodextrin, and Corn Syrup Solids as Wall Materials for Food Encapsulation. In Encapsulation and Controlled Release of Food Ingredients; Risch, S. J., Reineccius, G. A., Eds.; ACS Symposium Series 590; American Chemical Society: Washington, DC, 1995; pp 42−50. (16) Tukey, J. W. The problem of multiple comparisons. In The Collected Works of John W. Tukey VIII. Multiple Comparisons: 1948− 1983; Chapman and Hall: New York, 1953; pp 1−300.

CONCLUSIONS The temperature has a small influence on the phase separation. The molar mass of PEG does not affect the biphasic area. The increase of temperature and molar mass of the PEG elevated the TLS, causing a decrease in concentration of MD in the lower phase. The increase in DE of MD affected the equilibrium diagrams, thus decreasing the minimal concentration necessary for the formation of phases.

■

AUTHOR INFORMATION

Corresponding Author

*Fax: 55-31-38992208. Phone: 55-31-38991618. E-mail: [email protected]. Funding

The authors wish to acknowledge the National Council of Technological and Scientific Development (CNPq), the Foundation to Research Support of the Minas Gerais State (FAPEMIG) for their financial support, and the Foundation to Research Support of the Bahia State (FAPESB). Notes

The authors declare no competing financial interest.

■

REFERENCES

(1) Albertsson, P. A. Partition of Cell Particles and Macromolecules, 3rd ed.; John Wiley: Sweden, 1960. (2) Coimbra, J. S. R.; Teixeira, J. A. C. Engineering Aspects of Milk and Dairy Products, 1st ed.; CRC Press Taylor & Francis Group: New York, 2010. (3) Kepka, C.; Rhodin, J.; Lemmens, R.; Tjerneld, F.; Gustavsson, P. E. Extraction of Plasmid DNA from Escherichia Coli Cell Lysate in a Thermoseparating Aqueous Two-Phase System. J. Chromatogr., A 2004, 1024, 95−104. (4) Szlag, D. C.; Giuliano, K. A.; Snyder, S. M. A Low-Cost Aqueous Two-Phase System for Affinity Extraction. In Downstream Processing and Bioseparation; Hamel, J. F. P., Hunter, J. B., Sikdar, S. K., Eds.; ACS Symposium Series 419; American Chemical Society: Washington, DC, 1990; pp 71−86. (5) Silva, L. H. M.; Meirelles, A. J. A. Bovine Serum Albumin, AlfaLactoalbumin and Beta-Lactoglobulin Partitioning in Polyethylene Glycol/Maltodextrin Aqueous-Two-Phase Systems. Carbohydr. Polym. 2000, 42, 279−282. (6) Carareto, N. N. D.; Monteiro Filho, E. S.; Pessôa Filho, P. A.; Meirelles, A. J. A. Water Activity of Aqueous Solutions of Ethylene Oxide-Propylene Oxide Block Copolymers and Maltodextrins. Braz. J. Chem. Eng. 2010, 27, 173−181. (7) Giraldo-Zuniga, A. D.; Coimbra, J. S. R.; Arquete, D. A.; Minim, L. A.; da Silva, L. H. M.; Maffia, M. C. Interfacial Tension and Viscosity for Poly(ethylene glycol) + Maltodextrin Aqueous TwoPhase Systems. J. Chem. Eng. Data 2006, 51, 1144−1147. (8) Silva, L. H. M.; Meirelles, A. J. A. Phase Equilibrium in Polyethylene Glycol/Maltodextrin Aqueous Two-Phase Systems. Carbohydr. Polym. 2000, 42, 273−278. (9) Zijlstra, G. M.; Gooijer, C. D.; Van Der Pol, L. A.; Tramper, J. Desing of Aqueous Two-Phase Systems Supporting Animal Cell Growth: a First Step Toward Extractive Bioconversions. Enzyme Microb. Technol. 1996, 19, 2−8. (10) Zaslavsky, B. Y. Aqueous Two-Phase Partitioning - Physical Chemistry and Bioanalytical Applications; Marcel Dekker, Inc: New York, 1995. (11) Silva, L. H. M.; Coimbra, J. S. R.; Meirelles, A. J. A. Equilibrium Phase behavior of Poly(ethylene glycol) + Potassium Phosphate + Water Two- Phase Systems at Various pH and Temperatures. J. Chem. Eng. Data 1997, 42, 398−401. (12) Dubois, M.; Gilles, K. A.; Hamilton, J. K.; Rebers, P. A.; Smith, F. Colorimetric Method for Determination of Sugars and Related Substances. Anal. Chem. 1956, 28, 350−356. 1990

dx.doi.org/10.1021/je3002442 | J. Chem. Eng. Data 2012, 57, 1984−1990