Recovery of Isoflavones from the Soy Whey Wastewater Using Two

Article pubs.acs.org/IECR

Recovery of Isoflavones from the Soy Whey Wastewater Using TwoStage Batch Foam Fractionation Wei Liu, Zhao Liang Wu,* Yan Ji Wang,* Yan Li Zhao, Wei Chao Liu, and Yang Yu School of Chemical Engineering and Technology, Hebei University of Technology, No. 8 Guangrong Road, Dingzi Gu, Hongqiao District, Tianjin 300130, People’s Republic of China ABSTRACT: The feasibility of recovering bioactive substances without surface activity from their aqueous solutions was studied using biosurfactants as collectors. For recovering the isoflavones from the soy whey wastewater, a two-stage batch foam fractionation was developed using the soy proteins as collectors. The results showed that when the conditions of the first stage were temperature of 60 °C, pH of 5.0, volumetric air flow rate 80 of mL/min, and loading liquid volume of 400 mL, a high isoflavones enrichment ratio of 4.05 was obtained and the residual solution could be used as the feeding solution of the second stage. When the conditions of the second stage were temperature of 25 °C, pH of 5.0, and volumetric air flow rate of 150 mL/ min, the soy proteins concentration in the residual solution could decrease to 622 mg/L. By reusing the foamate of the second stage as the feeding solution of the first stage, the total isoflavones recovery percentage reached 87.72%.

1. INTRODUCTION Nutrient intake is an important part of a healthy diet and is associated with a number of positive health outcomes. Isoflavones, a group of important phytonutrients, are phenolic secondary metabolites found mostly in legumes.1 Many animal and human clinical studies as well as epidemiological studies have been carried out to prove the associations of isoflavones with the health benefits of soy-based food consumption, such as prevention of hormone-dependent cancers, treatment of cardiovascular diseases, and relief of menopausal symptoms, etc.2 Isoflavones are known as phytoestrogen because they are structurally similar to estrogen and hence can exert various pharmacological actions, such as anticancer, antihypertensive, antioxidative, and antiallergic activities.3 Thus, isoflavones have aroused increasing interest in using them as nutritional and functional additives in the food processing industry.4 The basic chemical structure of isoflavones is presented in Figure 1.

it is significant to develop a more cost-effective technique for recovering the isoflavones from the soy whey wastewater. Foam fractionation is an adsorptive separation technique, and it utilizes the differences in the adsorption properties of substances on the bubble surface to realize concentration and purification.7 It is generally acknowledged that foam fractionation has many advantages, such as low energy consumption, simple operation process, and environmental compatibility. Therefore, foam fractionation has been studied in the field of environmental engineering for treating the wastewater containing hazardous substances.8,9 This technique is mainly used in enrichment or removal of surfactants from aqueous solutions. Moreover, some nonsurfactants can also be separated using a surfactant as collector.10 In order to recover the isoflavones from the soy whey wastewater using foam fractionation, a suitable surfactant is required because the isoflavones are nonsurfactants. Foam fractionation has aroused increasing interest as a promising biotechnology for recovering the bioactive substances with surface activity from the downstream processing of bioproducts, such as proteins, enzymes, and fermentation products.11 However, how to effectively recover the bioactive substances without surface activity from the feed solutions or the wastewaters has been a serious problem to be urgently solved, especially for the small molecules. Li et al.12 had investigated the technology of foam fractionation for recovering streptomycin sulfate using sodium dodecyl sulfate (SDS) as collector. However, SDS is a chemical surfactant, and it will undoubtedly cause secondary pollution and affect the applications of the bioactive substances if it is not removed during the process of foam fractionation. Thus, biosurfactants have been proposed as alternatives to chemical surfactants.

Figure 1. Basic chemical structure of isoflavones.

However, isoflavones are massively lost in the discharged soy whey wastewater during the process of soy-based food processing. It will be of great commercial value to recover the isoflavones from the soy whey wastewater. Currently, several techniques have been reported for separating the isoflavones from their aqueous solutions, involving precipitation, resin adsorption, and membrane separation.5,6 But it is difficult for these techniques to achieve industrialization because of their high cost and complex operation. Therefore, © XXXX American Chemical Society

Received: May 7, 2013 Revised: August 12, 2013 Accepted: August 26, 2013

A

dx.doi.org/10.1021/ie401442t | Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Industrial & Engineering Chemistry Research

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for dissolving genistein, which was used as authentic standard isoflavones. Acetonitrile and acetic acid (purchased from Fisher Scientific, Pittsburgh, PA) were used as the mobile phase for high performance liquid chromatography (HPLC) analysis. All the reagents above were analytical grade. 2.2. Equipment and Instruments. Figure 2 presents the schematic diagram of the experimental setup. The column was

Biosurfactants had been used as foam stabilizers for concentrating the bioactive substances with weak surface activity.13 So far, there are not any references on the recovery of bioactive substances without surface activity using biosurfactants as collectors. Biosurfactants are a kind of amphiphilic compounds produced by biosynthesis with pronounced surface and emulsifying activities. Compared with chemical surfactants, biosurfactants have the advantages of good biodegrability, low toxicity, and ecological acceptability.14 Biosurfactants have a variety of potential industrial applications because of these outstanding characteristics, especially in the food industry. Consequently, it is worthwhile to use biosurfactants as collectors for recovering the bioactive substances without surface activity from their aqueous solutions using foam fractionation. Apparently, isoflavones can be not effectively adsorbed on the bubble surface because of their high hydrophilicity. However, it has been pointed out that protein and polyphenol can form a complex using hydrogen bonding and ionic or hydrophobic interactions.15 The complex can adsorb on the bubble surface during the process of foam fractionation. In addition, the soy whey wastewater contains a large quantity of soy proteins which are typical biosurfactants.16 Therefore, it is feasible for using foam fractionation to recover the isoflavones from the soy whey wastewater based on the interactions with the soy proteins. Enrichment ratio and recovery percentage are generally used to indicate foam fractionation performance.17 The former is more important to recover the desired substances from their aqueous solutions. In this study, the discharged soy whey wastewater during the process of soy protein isolate (SPI) production was used as an actual research system, in which the concentration of isoflavones was 400 mg/L. Fourier transform infrared spectroscopy (FTIR) was applied to determine the existence of the protein−isoflavone complexes in the soy whey wastewater. The experiments were carried out in a foam fractionation column with the inclined angle of 50°.16 The effects of temperature, pH, volumetric airflow rate, and liquid loading volume on the enrichment ratio and the recovery percentage of the isoflavones were investigated, respectively. Furthermore, a two-stage batch foam fractionation technology was developed. The first stage was aimed at achieving a high isoflavones enrichment ratio, and the second stage was aimed at decreasing the soy proteins concentration as low as possible. It was expected that the two-stage technology could highly concentrate the desired substances in the foamate of the first stage and decrease the concentration of collectors in the residual solution of the second stage. The purpose of all the efforts was to lay a foundation for the industrialization of recovering the isoflavones from the soy whey wastewater using foam fractionation and thereby provide some new ideas for recovering bioactive substances without surface activity from their aqueous solutions using biosurfactants as collectors.

Figure 2. Schematic diagram of the experimental setup.

constructed of a polymethyl methacrylate tube with an inner diameter of 44 mm. Its length was 1200 mm, which was divided into a vertical part of 800 mm and a tilted part of 400 mm. The two parts were joined using an elbow of 50°. A porous polyethylene membrane with pore diameter of 250 μm was mounted at the bottom of the column to serve as gas distributor. The column was tightly wound using a silicone tube to control the temperature inside it. A foam collector was attached to the top of the column, where the foam was collected and collapsed. The resulting liquid, called the foamate, comprised a concentrated solution of the surface active substances. An air compressor was used to bubble the air into the column using a rotameter for controlling air flow rate. An air moistening bottle was placed between the rotameter and the column, and the temperature of the water in the bottle was the same as that in the column. 2.3. Determination of Foaming Ability and Foam Stability. The foaming ability and the foam stability were determined using the Ross-miles method. The soy whey wastewater of 200 mL was taken in a scaled pipet with an orifice of internal diameter 2.9 mm and length 10 mm. The wastewater in the pipet was allowed to fall from a height of 900 mm on to 50 mL of the wastewater present in a cylindrical vessel of internal diameter 50 mm surrounded by a water jacket. All measurements were performed at different setting temperatures. The foam height in the receiver was measured immediately after the last drop of the solution fell from the foam pipet.18 Therefore, the foaming ability and foam stability could be described by foam height (mm) and half collapse time (time1/2, s) of the foam phase. 2.4. Determination of the Protein−Isoflavone Complexes. In this work, FTIR was used for determining the existence of the protein−isoflavone complexes in the soy whey wastewater. The soy whey wastewater of 25 mL was filtered using a 0.45 μm membrane filter to remove undissolved materials. The filtrate was freeze-dried (Eyela Fdu-1200, Tokyo Rikakikai Co. Ltd., Tokyo, Japan), and the resultant powder was collected as the sample of the soy whey wastewater. The FTIR spectra of the soy proteins and the soy whey wastewater were collected between 4000 and 400 cm−1 on a Vector-22 infrared spectrophotometer (Bruker, Germany) with 256 scans at a resolution of 4 cm−1 using the KBr method. In addition, the

2. MATERIALS AND METHODS 2.1. Materials and Reagents. The soy whey wastewater was provided by Yu Xin Soy Protein Industry Co. Ltd., Shandong, China, and its properties were COD of 10000 mg/L, BOD of 8000 mg/L, TN of 1500 mg/L, soy proteins of 4000 mg/L, isoflavones of 400 mg/L, and pH of 4.3. The soy proteins and genistein were purchased from Sigma Chemical Co. (St. Louis., MO, USA). Ethanol (obtained from Fengchuan Chemical Reagent Factory Co. Ltd., Tianjin, China) was used B



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data were recorded and processed using Opus software (Bruker, Germany). 2.5. Determination of the Isoflavones Concentration. The soy whey wastewater of 5 mL was filtered using a 0.45 μm membrane filter to remove undissolved materials. The filtrate was freeze-dried, and the resultant powder was extracted with 10 mL of 80% ethanol using ultrasonic concussion for 20 min and centrifuged (4500 rpm, 10 min). The resultant supernatant was filtrated using a 0.45 μm membrane filter, and it was used for determining the isoflavones concentration in the soy whey wastewater using HPLC. The soy whey wastewater was analyzed under the conditions of a diode array detector (Agilent Technologies, Inc., USA), a Symmetry C18 (250 mm × 4.6 mm, 5 μm, Shimadzu, Japan), column temperature of 40 °C, mobile phase 0.1% acetic acid and acetonitrile (70:30, v/v), detection wavelength of 260 nm, flow rate of 1.0 mL/min, and injection volume of 20 μL. 2.6. Determination of the Soy Proteins Concentration. The soy proteins concentration in the wastewater was determined by Coomassie Brilliant Blue protein assay.19 The standard curve was worked out using BSA as reference protein at the maximum absorption wavelength 595 nm. The linearfitting equation was A = 6.475C + 0.0562, r2 = 0.9994, and the range of C was from 0.01 g/L to 0.1 g/L, where A and C were the absorption value at λ = 595 nm and the soy proteins concentration, respectively. 2.7. Performance Parameters of Foam Fractionation. The performance parameters of foam fractionation include the enrichment ratio (E) and the recovery percentage (R), and they are determined as follows. E=

R=

C0V0 − CwVw C0Vf

(1)

C0V0 − CwVw × 100% C0V0

(2)

Figure 3. FTIR spectra of (1) the soy proteins and (2) the soy whey wastewater.

isoflavones. Presumably the main interaction was esterification because the stretching vibration of CO was more intense than that of C−O in the ester group, thus the stretching vibrations of CO were strengthened and the amino groups of the soy proteins were released. The above results of FTIR analysis indicated that the protein−isoflavone complexes existed in the soy whey wastewater. 3.2. Determination of the Optimal Processing Conditions for the First Stage Foam Fractionation. Generally, it is acknowledged that the enrichment ratio and the recovery percentage perform an opposite trend in foam fractionation.20,21 Thus, it is impossible for achieving simultaneously both high enrichment ratio and high recovery percentage by using only one stage foam fractionation. Then a two-stage batch foam fractionation technology was designed in the present work. The first stage foam fractionation was aimed at obtaining a high isoflavones enrichment ratio in the resulting foamate. In this stage, the effects of temperature, pH, volumetric air flow rate, and loading liquid volume on the enrichment ratio and the recovery percentage of the isoflavones were investigated for optimizing the processing conditions. 3.2.1. Effects of Temperature on E and R. Temperature is an important parameter affecting the performance of foam fractionation, especially when solution viscosity is high. So the effects of temperature were first investigated under the conditions of liquid loading volume of 400 mL, volumetric air flow rate of 80 mL/min, and pH of 5.0. Temperature ranged from 25 to 70 °C. The results are presented in Figure 4. As shown in Figure 4, the isoflavones enrichment ratio increased from 1.79 to 4.36, while the recovery percentage decreased from 76.74% to 21.32% with increasing temperature from 25 to 70 °C. In order to explain this trend, the effects of temperature on viscosity and foam properties of the soy whey wastewater were studied. Viscosity is an important indicator of fluidity, and it can be measured using an Ubbelohde viscometer. From Table 1, with the increase of temperature, the viscosity of the soy whey wastewater decreased. When temperature was low, a high viscosity led to an enormous attraction force between the molecules in the liquid and thus resulted in a poor fluidity. The entrained liquid in the foam phase was difficult to flow back into the bulk liquid phase in the column, resulting in a slow foam drainage velocity. So the liquid holdup was high and the enrichment ratio was low. With increasing temperature, the

where Co and Cw are the isoflavones concentrations in the feeding solution and the residual solution (mg/L), respectively. Vo, Vf, and Vw are the volumes (L) of the feeding solution, the foamate, and the residual solution, respectively.

3. RESULTS AND DISCUSSION 3.1. FTIR Analysis for the Protein−Isoflavone Complexes. FTIR was used for determining the existence of the protein−isoflavone complexes in the soy whey wastewater. The FTIR spectra of the soy proteins and the soy whey wastewater are presented in Figure 3. The FTIR spectrum of the soy proteins showed the prominent absorption bands at ∼3425.23 cm−1 (for O−H stretching vibrations), ∼1621.60 cm−1 (for CO stretching vibrations), ∼1222.21 cm−1 (for C−N stretching vibrations), and ∼1200−1000 cm−1 (for C−O stretching vibrations). The FTIR spectrum of the soy whey wastewater consisted of prominent absorption bands of the hydroxyl group (∼3411.84 cm−1), the amino group (∼3306.53 cm−1 and ∼1539.90 cm−1), the aromatic nucleus (∼3100.59 cm−1), the conjugated carbonyl group (∼1653.44 cm−1), the phenolic hydroxyl group (∼1236.52 cm−1), and the carbon− oxygen single bond (∼1075.67 cm−1). The stretching vibrations of the aromatic nucleus, the conjugated carbonyl group, and the phenolic hydroxyl group mainly came from the isoflavones. The FTIR spectrum of the soy whey wastewater suggested that complexation was generated between the soy proteins and the C



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Figure 4. Effects of temperature on E and R. The experimental conditions are liquid loading volume of 400 mL, volumetric air flow rate of 80 mL/min, and pH of 5.0.

Figure 5. Effects of pH on E and R. The experimental conditions are temperature of 60 °C, liquid loading volume of 400 mL, and volumetric air flow rate of 80 mL/min.

Table 1. Effects of Temperature on the Viscosity and Foam Properties of the Soy Whey Wastewater

the isoflavones and the soy proteins. Therefore, the effects of pH on the enrichment of the isoflavones are closely associated with the soy proteins. In general, the surface excess of a protein is the highest and the intermolecular repulsion is the smallest at its isoelectric point because the net charge of the protein molecule is zero. Thus, the maximal enrichment ratio of a protein should occur at its isoelectric point.24 However, the soy proteins are a group of proteins of which isoelectric points are in the range of pH 4.5−5.7.25 Therefore, it is necessary to consider the change of surface tension under the range of pH 4.0−7.0. The surface tension of a protein is minimal at its isoelectric point.26 As shown in Figure 6, the surface tension

temp (°C)

viscosity (mPa·s)

25 30 40 50 60 70

1.20 ± 0.02 1.06 ± 0.01 0.847 ± 0.01 0.712 ± 0.01 0.623 ± 0.02 0.489 ± 0.01

time1/2 (s) 256 206 125 80 53 17

± ± ± ± ± ±

0.2 0.2 0.2 0.2 0.2 0.2

foam height (mm) 138 145 154 173 195 211

± ± ± ± ± ±

2 2 2 2 2 2

intense molecular thermal motion supplied energy to overcome the attraction force between the molecules, so viscosity decreased. The decrease of viscosity in the interstitial liquid between the bubbles accelerated foam drainage and, thus, contributed to improving the enrichment ratio.22 The foam properties of the soy whey wastewater were characterized by the foaming ability and the foam stability. From Table 1, with the increase of temperature, the foaming ability increased and the foam stability decreased. Moreover, the proteins are a kind of temperature sensitive biological macromolecules. In order to recover the isoflavones from the soy whey wastewater, foam fractionation should be operated under the appropriate temperature. According to the above results, the foam stability substantially decreased with increasing temperature and it was difficult to do the experiments when temperature increased over 60 °C. Considering the above factors, 60 °C was selected as the optimal temperature for recovering the isoflavones from the soy whey wastewater. 3.2.2. Effects of pH on E and R. pH affects the performance of foam fractionation due to its effects on the net charge, the interfacial tension, and the surface rigidity, especially for a protein.23 Therefore, the effects of pH were studied under the conditions of temperature of 60 °C, loading liquid volume of 400 mL, and volumetric air flow rate of 80 mL/min. pH ranged from 3.0 to 8.0. The results are presented in Figure 5. From Figure 5, with the increase of pH from 3.0 to 8.0, the isoflavones enrichment ratio increased from 3.78 to 4.05 and then decreased to 3.19 while the recovery percentage decreased from 51.53% to 40.50% and then increased to 60.17%. The maximum isoflavones enrichment ratio of 4.05 was obtained at pH 5.0. Although the isoflavones have no surface activity, they can adsorb on the gas−liquid interface via complexation between

Figure 6. Effect of pH on surface tension. The experimental conditions are temperature of 60 °C and volume of 50 mL.

first decreased and then increased with the increase of pH from 4.0 to 7.0. The minimal surface tension appeared at pH 5.0. In addition, isoflavones existed as neutral molecules under the weak acidic conditions, and hence, the protein−isoflavone complexes were stable.27 As a result, pH 5.0 was selected as the optimal value for recovering the isoflavones from the soy whey wastewater. 3.2.3. Effects of Volumetric Air Flow Rate on E and R. Volumetric air flow rate can significantly affect both interfacial adsorption and foam drainage.28 Thus, the effects of volumetric air flow rate were investigated under the conditions of temperature of 60 °C, loading liquid volume of 400 mL, and pH of 5.0, respectively. Volumetric air flow rate ranged from 50 mL/min to 220 mL/min. The results are presented in Figure 7. D



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From Figure 8, the isoflavones enrichment ratio decreased from 4.05 to 3.10 while the recovery percentage increased from 40.50% to 60.91% with increasing loading liquid volume from 400 to 800 mL. With increasing loading liquid volume, the time for foam drainage became short, thus resulting in a high liquid holdup and a low enrichment ratio. On the contrary, the height of the foam phase increased with the decrease of loading liquid volume, so the bubble residence time in the foam phase increased, resulting in improving bubble coalescence and foam drainage. Therefore, the isoflavones enrichment ratio was improved. However, it was difficult to obtain the foamate when loading liquid volume was less than 400 mL because the foam became unstable. Thus, 400 mL was selected as the optimal loading liquid volume for recovering the isoflavones from the soy whey wastewater. On the basis of the above results, a high isoflavones enrichment ratio of 4.05 was obtained under the optimal processing conditions of temperature of 60 °C, pH of 5.0, volumetric air flow rate of 80 mL/min, and loading liquid volume of 400 mL. In addition, the isoflavones concentration in the residual solution decreased from 400 mg/L to 264 mg/L and the soy proteins concentration decreased from 4000 mg/L to 2330 mg/L, respectively. Furthermore, some internal components with enhancing foam drainage and reflux could also be used in the single column for further improving the enrichment ratio of isoflavones.30,31 3.3. Determination of the Optimal Processing Conditions for the Second Stage Foam Fractionation. In the first stage foam fractionation, a high isoflavones enrichment ratio was obtained under the optimal processing conditions. However, the concentrations of the isoflavones and the soy proteins were still high in the residual solution of the first stage. In this study, the soy proteins were used as collectors for recovering the isoflavones from the soy whey wastewater. The concentration of collector in the residual solution should be decreased as low as possible during the process of foam fractionation. So a second stage foam fractionation was designed for further decreasing the soy proteins concentration by using the residual solution of the first stage as the feeding solution. For simplifying the processing conditions of the two-stage batch foam fractionation technology, only the volumetric air flow rate of the second stage was optimized with loading liquid volume, temperature, and pH fixed at 360 mL, 25 °C, and 5.0, respectively. Volumetric air flow rate ranged from 80 mL/min to 220 mL/min. The results are presented in Figure 9.

Figure 7. Effects of volumetric air flow rate on E and R. The experimental conditions are temperature of 60 °C, pH of 5.0, and liquid loading volume of 400 mL.

From Figure 7, the isoflavones recovery percentage increased from 22.16% to 75.03% while the enrichment ratio decreased from 5.54 to 1.17 with the increase of volumetric air flow rate. When volumetric air flow rate was low, slowly rising bubbles contributed to improving interfacial adsorption in the liquid phase and thus achieved a high excess surface concentration of the protein−isoflavone complexes. Furthermore, it was wellknown that the direction of foam drainage was opposite to that of the rising bubbles in the foam phase. A lower volumetric air flow rate had a higher residence time of the rising bubbles in the foam phase, resulting in improving foam drainage. So the liquid holdup was lower and the enrichment ratio was higher.29 However, the isoflavones recovery percentage was significantly decreased. By considering both the enrichment ratio and the recovery percentage, the optimal volumetric air flow rate was 80 mL/min for the first stage foam fractionation. 3.2.4. Effects of Loading Liquid Volume on E and R. If the height of the foam fractionation column is fixed, loading liquid volume mainly affects the residence times of the bubbles in the bulk liquid phase and the foam phase, respectively. The effects of loading liquid volume on the performance of foam fractionation were investigated with temperature, pH, and volumetric air flow rate fixed at 60 °C, 5.0, and 80 mL/min, respectively. On the basis of the column’s height, loading liquid volume ranged from 400 to 800 mL. The results are presented in Figure 8.

Figure 8. Effects of loading liquid volume on E and R. The experimental conditions are temperature of 60 °C, pH of 5.0 and volumetric air flow rate of 80 mL/min.

Figure 9. Schematic diagram of the two-stage batch foam fractionation technology. E



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Figure 10. Effects of volumetric air flow rate on E, R, and Cp. The experimental conditions are temperature of 25 °C, pH of 5.0, and liquid loading volume of 360 mL.

as high as 87.72%. Meanwhile, the soy proteins concentration could decrease from 4000 mg/L to 622 mg/L. Therefore, it was significantly effective for the two-stage batch foam fractionation to recover the isoflavones from the soy whey wastewater using the soy proteins as collectors. Additionally, the foamate of the first stage could be used as raw material for purifying the isoflavones. It was unnecessary for the soy proteins to be removed because they were also a kind of food resource with high nutritional value and were widely used as supplements and dietary ingredients in the food industry.32

As shown in Figure 9, the soy proteins concentration in the residual solution first decreased from 1676 mg/L to 622 mg/L and then tended to be constant with increasing volumetric air flow rate from 80 mL/min to 220 mL/min. Accordingly, the isoflavones enrichment ratio decreased from 1.93 to 1.16 while the recovery percentage increased from 63.26% to 90.15%. When volumetric air flow rate was 150 mL/min, the isoflavones enrichment ratio of 1.53 was obtained with a high recovery percentage of 79.33%, and the soy proteins concentration in the residual solution was decreased to a minimum. Meanwhile, the soy proteins concentration in the foamate of the second stage was 3917 mg/L and the isoflavones concentration was 404 mg/ L, which approached to those in the soy whey wastewater, and thus, the foamate could be used as the feeding solution for the first stage foam fractionation. Therefore, 150 mL/min was selected as the optimal volumetric air flow rate for decreasing the soy proteins concentration in the residual solution of the second stage. On the basis of the above studies, the optimal processing conditions of the two-stage batch foam fractionation were determined. In the first stage, foam fractionation was performed under the conditions of temperature of 60 °C, pH of 5.0, volumetric air flow rate of 80 mL/min, and loading liquid volume of 400 mL. A high isoflavones enrichment ratio of 4.05 was obtained. In the second stage, the residual solution of the first stage was used as the feeding solution of the second stage and the experiments were performed under the conditions of temperature of 25 °C, pH of 5.0, volumetric air flow rate of 150 mL/min, and loading liquid volume of 360 mL. Then the soy proteins concentration was decreased to 622 mg/L. In addition, the foamate of the second stage could be used as the feeding solution and added into the first stage foam fractionation because the concentrations of the isoflavones and the soy proteins were both close to those in the initial soy whey wastewater. Therefore, the schematic diagram of the two-stage batch foam fractionation technology is presented in Figure 10. With reusing the foamate of the second stage as the feeding solution of the first stage, the two-stage batch foam fractionation for recovering the isoflavones from the soy whey wastewater had a high isoflavones enrichment ratio of 4.05 and the total isoflavones recovery percentage could reach

4. CONCLUSIONS In this study, foam fractionation was used for recovering the isoflavones from the soy whey wastewater. The experimental results showed that the isoflavones could be effectively concentrated and recovered using the soy proteins as collectors. In addition, a two-stage batch foam fractionation was developed for achieving a high isoflavones enrichment ratio in the foamate of the first stage and a low soy proteins concentration in the residual solution of the second stage, simultaneously. In the first stage, a high isoflavones enrichment ratio of 4.05 was obtained under the optimal processing conditions of temperature of 60 °C, pH of 5.0, volumetric air flow rate of 80 mL/min, and loading liquid volume of 400 mL. The second stage was carried out under the conditions of temperature of 25 °C, pH of 5.0, and volumetric air flow rate of 150 mL/min using the residual solution of the first stage as the feeding solution. Then, the soy proteins concentration in the residual solution of the second stage was decreased to 622 mg/L. By the two-stage batch foam fractionation, the enrichment ratio and the recovery percentage of the isoflavones could reach as high as 4.05 and 87.72%, respectively. It was demonstrated that the two-stage batch foam fractionation could effective recover the isoflavones from the soy whey wastewater using the soy proteins as collectors. In conclusion, biosurfactants are useful in the enrichment of nonsurfactants from aqueous solutions based on their interactions, and the method can be referenced for the recovery of other bioactive substances without surface activity from the feed solutions or wastewater using biosurfactants as collectors. F



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(16) Jiang, C. S.; Wu, Z. L.; Li, R.; Liu, Q. Technology of protein separation from whey wastewater by two-stage foam separation. Biochem. Eng. J. 2011, 55, 43−48. (17) Qian, S.; Wu, Z.; Zheng, H.; Geng, Y. Study on riboflavin recovery from wastewater by a batch foam separation process. Sep. Sci. Technol. 2009, 44, 1−14. (18) Ross, J.; Miles, G. D. An apparatus for comparison of foaming properties of soaps and detergents. Oil Soap 1941, 18, 99−102. (19) Liau, C. Y.; Lin, C. S. A modified coomassie brilliant blue G 250 staining method for the detection of Chitinase activity and molecular weight after polyacrylamide gel electrophoresis. J. Biosci. Bioeng. 2008, 106, 111−113. (20) Merz, J.; Zorn, H.; Burghoff, B.; Schembecker, G. Purification of a fungal cutinase by adsorptive bubble separation: a statistical approach. Colloids Surf., A 2011, 382, 81−87. (21) Shea, A. P.; Crofchek, C. L.; Payne, F. A.; Xiong, Y. L. Foam fractionation of α-lactalbumin and β-lactoglobulin from a whey solution. Asia-Pac. J. Chem. Eng. 2009, 4, 191−203. (22) Qu, Y. H.; Zeng, G. M.; Huang, J. H.; Xu, K.; Fang, Y. Y.; Li, M. Recovery of surfactant SDS and Cd2+ from permeate in MEUF using a continuous foam fractionators. J. Hazard. Mater. 2008, 155, 32−38. (23) Clarkson, J. R.; Cui, Z. F.; Darton, R. C. Effect of solution conditions on protein damage in foam. Biochem. Eng. J. 2000, 4, 107− 114. (24) Burapatana, V.; Booth, E. A.; Prokop, A.; Tanner, R. D. Effect of Buffer and pH on detergent-assisted foam fractionation of cellulase. Ind. Eng. Chem. Res. 2005, 44, 4968−4972. (25) Rawel, H. M.; Czajka, R.; Rohn, S.; Kroll, J. Interactions of different phenolic acids and flavonoids with soy proteins. Int. J. Biol. Macromol. 2002, 30, 137−150. (26) Maruyama, H.; Seki, H.; Suzuki, A.; Inoue, N. Batch foam separation of a solution protein. Water Res. 2007, 41, 710−718. (27) Piskula, M. K.; Yamakoshi, J.; Iwai, Y. Daidzein and genistein but nor their glucosides are absorbed from rat stomach. FEBS Lett. 1999, 447, 287−291. (28) Crofcheck, C.; Gillette, K. Evaluation of foam fractionation column scale-up for recovering bovine serum albumin. Trans. Am. Soc. Agric. Eng. 2003, 46, 1759−1764. (29) Tharapiwattananon, N.; Scamehorn, J. F.; Osuwan, S.; Harwell, J. H.; Haller, K. J. Surfactant recovery from water using foam fractionation. Sep. Sci. Technol. 1996, 31, 1233−1258. (30) Li, R.; Wu, Z.; Wang, L.; Yang, Q.; Zhu, H. Enhancing foam drainage by spiral internal components of different thread pitches and inclined angles and their applications to enrichment of SDS. Sep. Purif. Technol. 2012, 98, 109−117. (31) Martin, P. J.; Dutton, H. M.; Winterburn, J. B.; Baker, S.; Russell, A. B. Foam fractionation with reflux. Chem. Eng. Sci. 2010, 65, 3825−3835. (32) Cassini, A. S.; Marczak, L. D. F.; Noreña, C. P. Z. Water adsorption isotherms of texturized soy protein. J. Food Eng. 2006, 77, 194−199.

AUTHOR INFORMATION

Corresponding Authors

*Tel.: +86 222656 4304. Fax: +86 222656 4304. E-mail address: [email protected]. Address: School of Chemical Engineering and Technology, Hebei University of Technology, No. 8 Guangrong Road, Dingzi Gu, Hongqiao District, Tianjin 300130, People’s Republic of China. *Tel.: +86 222656 4294. Fax: +86 222656 4294. E-mail address: [email protected]. Address: School of Chemical Engineering and Technology, Hebei University of Technology, Key Lab of Green Chemical Technology & High Efficient Energy Saving, No. 8 Guangrong Road, Dingzi Gu, Hongqiao District, Tianjin 300130, People’s Republic of China. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the Natural Science Foundation of China (21236001) and the Natural Science Foundation of Hebei, China (B2011202056).

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REFERENCES

(1) Zuo, Y. B.; Zeng, A. W.; Yuan, X. G.; Yu, K. T. Extraction of soybean isoflavones from soybean meal with aqueous methanol modified supercritical carbon dioxide. J. Food Eng. 2008, 89, 384−389. (2) Sirtori, C. R. Risks and benefits of soy phytoestrogens in cardiovascular diseases, cancer, climacteric symptoms and osteoporosis. Drug Saf. 2001, 24, 665−682. (3) Nara, K.; Nihei, K. I.; Ogasawara, Y.; Koga, H.; Kato, Y. Novel isoflavone diglycoside in groundnut (Apios americana Medik). Food Chem. 2011, 124, 703−710. (4) Genovese, M. I.; Barbosa, A. C. L.; Pinto, M. D. S.; Lajolo, F. M. Commercial soy protein ingredients as isoflavone sources for functional foods. Plant Food. Hum. Nutr. 2007, 62, 53−58. (5) Li, H.; Liu, J.; Li, D.; Wang, H. Study on separation and purification of genistein in the soybean residue using macroporous resin adsorption. Ind. Eng. Chem. Res. 2012, 51, 44−49. (6) Xu, L.; Lamb, K.; Layton, L.; Kumar, A. A membrane-based process for recovering isoflavones from a waste stream of soy processing. Food Res. Int. 2004, 37, 867−874. (7) Brunner, C. A.; Stephan, D. G. Foam fractionation. Ind. Eng. Chem. 1965, 57, 40−48. (8) Lu, K.; Zhang, X. L.; Zhao, Y. L.; Wu, Z. L. Removal of color form textile dyeing wastewater by foam separation. J. Hazard. Mater. 2010, 182, 928−932. (9) Huang, S. D.; Wilson, D. J. Foam separation of mercury (II) and cadmium (II) from aqueous systems. Sep. Sci. Technol. 1975, 11, 215− 222. (10) Boonyasuwat, S.; Chavadej, S.; Malakul, P.; Scamehorn, J. F. Anionic and cationic surfactant recovery from water using a multistage foam fractionation. Chem. Eng. J. 2003, 93, 241−252. (11) Burghoff, B. Foam fractionation applications. J. Biotechnol. 2012, 161, 126−137. (12) Li, J.; Wu, Z. L.; Li, R. Technology of streptomycin sulfate separation by two-stage foam separation. Biotechnol. Prog. 2012, 28, 733−739. (13) Chai, J.; Loha, V.; Prokop, A.; Tanner, R. D. Effect of bubble velocity and pH step changes on the foam fractionation of sporamin. J. Agric. Food Chem. 1998, 46, 2868−2872. (14) Banat, I. M. Biosurfactants production and possible uses in microbial enhanced oil recovery and oil pollution remediation: a review. Bioresour. Technol. 1995, 51, 1−12. (15) Siebert, K. J. Effects of protein-polyphenol interactions on beverage haze, stabilization, and analysis. J. Agric. Food Chem. 1999, 47, 353−362. G


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