Rhamnolipid assisted recovery of lycopene from the tomato-based processing wastewater using foam fractionation

Accepted Manuscript Rhamnolipid assisted recovery of lycopene from the tomato-based processing wastewater using foam fractionation Wei Liu, Zhaoliang Wu, Yanji Wang, Rui Li, Linlin Ding, Di Huang PII: DOI: Reference:

S0260-8774(15)00191-0 http://dx.doi.org/10.1016/j.jfoodeng.2015.04.024 JFOE 8149

To appear in:

Journal of Food Engineering

Received Date: Revised Date: Accepted Date:

20 January 2015 6 April 2015 26 April 2015

Please cite this article as: Liu, W., Wu, Z., Wang, Y., Li, R., Ding, L., Huang, D., Rhamnolipid assisted recovery of lycopene from the tomato-based processing wastewater using foam fractionation, Journal of Food Engineering (2015), doi: http://dx.doi.org/10.1016/j.jfoodeng.2015.04.024

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Rhamnolipid assisted recovery of lycopene from the tomato-based processing wastewater using foam fractionation Wei Liu, Zhaoliang Wu*, Yanji Wang, Rui Li, Linlin Ding, Di Huang School of Chemical Engineering and Technology, Hebei University of Technology, No.8 Guangrong Road, Dingzi Gu, Hongqiao District, Tianjin, 300130, China

ABSTRACT The feasibility of foam fractionation for recovering lycopene from the tomato-based processing wastewater was investigated by using tomato proteins as the collectors. Rhamnolipid would be used as the foam stabilizer to improve the interfacial adsorption of protein-lycopene complex. Under the optimal conditions of rhamnolipid concentration 1.5 g/L, temperature 50 ºC, pH 7.0, volumetric gas flow rate 150 mL/min and loading liquid volume 500 mL, the enrichment ratio and the recovery percentage of lycopene were 4.42 and 83.43%, respectively. Meanwhile, the recovery percentage of rhamnolipid reached 94.52% in the foamate. Moreover, rhamnolipid in the supernatant of the foamate could be reused to recover lycopene from tomato-based processing wastewater for three times with a constant recovery percentage of lycopene. This work has provided a new insight into the recovery of a non-surface-active material from its aqueous solution and is expected to facilitate the research on the resourceful treatment of food wastewaters. Keywords: lycopene, rhamnolipid, foam fractionation, co-adsorption Running title: Recovery of lycopene from wastewater using foam fractionation

1. Introduction

*

Corresponding author. Tel.: +86 222656 4304; Fax: +86 222656 4304. E-mail address: [email protected] (Zhaoliang Wu) * Corresponding author. Tel.: +86 222656 4294; Fax: +86 222656 4294. E-mail address: [email protected] (Yanji Wang) 1

Tomato (Solanum lycopersicum L.) is an important horticultural crop in most parts of the world (Leyva et al., 2015). Tomato-based products such as tomato juice, ketchup, tomato paste, tomato soup, pizza sauce and spaghetti sauce are popular in the human daily diet (Lenucci et al., 2006). On the basis of epidemiological studies, the regular consumption of fresh tomato or tomato-based products has been inversely correlated to the development of widespread human diseases (Omoni and Aluko, 2005; Giovannucci et al., 1995; Rao and Agarwal, 1998). The health benefits of tomato or tomato-based products are often related to the carotenoid (Krinsky, 1989). Lycopene (Fig. 1) is a biologically occurring carotenoid and it is the pigment principally responsible for the characteristic deep-red color of ripe tomato and tomato-based products (Huang et al., 2008). At cellular level, lycopene is present in thylakoid membrane as a protein-lycopene complex due to its lipophilic nature (Shi and Maguer, 2000). In recent years, lycopene has attracted an increasing attention for its biological and physicochemical properties, especially its effects as a natural antioxidant. Although lycopene has not provitamin A activity, its physical quenching rate constant with singlet oxygen is almost twice as high as that of β-carotene (Agarwal and Rao, 2000). These advantages make its presence in the diet of considerable interest. The tomato-based processing industry produces large amounts of wastewater from the steps of elution, crush and cleaning (Iaquinta et al., 2009). At present, the biochemical technology has been used to treat the wastewater based on its good biodegradability. It has been reported that lycopene is massively lost in the tomato-based processing wastewater (Liu et al., 2008). Therefore, it will be of great commercial value to explore a cost-effective technology to recover lycopene from the tomato-based processing wastewater. Lycopene is generally separated from skins and seeds of tomato by organic solvent extraction, enzyme reaction extraction or

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supercritical liquid extraction (Papaioannou et al., 2008; Choudhari and Ananthanarayan, 2007; Shi et al., 2009). Obviously, these methods are not practical to recover lycopene from the tomato-based processing wastewater because of a huge discharge volume but a low lycopene concentration. Foam fractionation, an adsorptive technology, utilizes bubbles as media to achieve the separation of desired materials based on the differences in adsorption properties of materials on the gas-liquid interface (Li et al., 2014). This technology has been widely used for separating a trace surfactant owing to its outstanding advantages, such as high efficiency, low consumption and environmental compatibility (Aksay and Mazza, 2007, Wang et al., 2013). Furthermore, foam fractionation can also be used to concentrate a non-surface-active material from its aqueous solution through the interaction with a surfactant. In this case, the surfactant is called as the collector (Boonyasuwat et al., 2003). In principle, lycopene can be adsorbed on the gas-liquid interface by using tomato proteins as the collectors because the proteins are typical surface-active materials, so as to achieve enrichment. The surface properties of different surface-active materials are very different. It is difficult for some materials with weak surface activity to form a stable foam at a low concentration. This obstacle can be overcome by adding a small amount of the material with a strong surface activity to its solution for achieving co-adsorption (Grieves and Kyle, 1982). In adsorption, the interfacial behavior of protein/surfactant mixtures resembles the co-adsorption of synthetic polymer/surfactant mixtures (Green et al., 2000). For a mixture such as poly(ethylene oxide) (PEO) and dodecyltrimethylammonium bromide (CTAB), the amount of adsorbed CTAB progressively increases with its bulk concentration. With the increase of the CTAB surface excess, the PEO surface excess decreases and before the critical micellar

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concentration (CMC) of CTAB is reached, PEO is completely removed from the bubble surface (Cooke et al., 1998). Therefore, it is significant to choose a compatible surfactant for co-adsorbing protein-lycopene complex and thus to effectively recover lycopene from the tomato-based processing wastewater. The novelty of this work was to recover a non-surface-active material with bioactivity by foam fractionation using two biosurfactants, in which one biosurfactant was used as the collecor and another one played a role of foam stabilizer. Generally, foam fractionation was performed for recovering a non-surface-active material from its aqueous solution using a surfactant, which could simultaneously perform the dual roles of collector and frother (Lu et al., 2010, Zhang et al., 2014). However, in this work, tomato proteins exhibited a good affinity with lycopene but their foamability was weak. Thus, rhamnolipid, one of glycolipid-type biosurfactants, was produced by Pseudomonas aeruginosa and utilized for co-adsorbing protein-lycopene complex from the tomato-based processing wastewater (Benincasa et al., 2002). For recovering lycopene, nitrogen gas was used as carrier gas. The effects of rhamnolipid concentration, temperature, pH, volumetric gas flow rate and loading liquid volume on the separation efficiency of lycopene were investigated, respectively. Furthermore, the reusability of rhamnolipid was also discussed for reducing the engineering cost. This work would be expected to provide a new insight into resourceful treatment of food wastewaters. 2. Materials and Methods 2.1 Materials and reagents Tomato was obtained from the local market. The chemical reagents of sodium carbonate, acetonitrile, 2-bromoacetophenone, triethylamine, phosphoric acid, ethanol, acetone, methanol and isopropanol were purchased from Fengchuan Chemical

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Reagent Factory Co. Ltd., Tianjin, China. Coomassie Brilliant Blue G-250 was supplied by Dingguo Biotechnology Co. Ltd., Beijing, China. Bovine serum albumin was got from Lianxing Biotechnology Co. Ltd., Tianjin, China. Rhamnolipid (90%, w/v) was purchased from Zijin Biotechnology Co. Ltd., Zhejiang, China. The standards of lycopene and β-carotene were purchased from Sigma Chemical Co., St. Louis, MO, USA. Deionized water was delivered using a Millipore Milli-Q system from Barnstead International, Dubuque, IA, USA. 2.2 Foam fractionation Fig. 2 presents the schematic diagram of the experimental setup. The foam fractionation column was constructed of a polymethyl methacrylate tube with an inner diameter of 44 mm and its length was 1000 mm. A porous polyethylene membrane with a pore diameter of 250 μm was mounted at the bottom of the column to serve as a gas distributor. In each experiment, nitrogen gas was sparged through the gas distributor to form numerous bubbles in the bulk liquid phase, resulting in a stable foam phase. With the foam rising, the interstitial liquid would be returned the bulk liquid phase owing to foam drainage. An U-shaped end was attached to the top of the column and enabled the foam to be flowed into a container, where the foam was collected and collapsed. The solution after breaking foam was called as the foamate, in which the surface-active material was greatly enriched. The performance of foam fractionation was evaluated by the enrichment ratio (E) and the recovery percentage (R) and they are expressed as follows. E=

R=

Cf

(1)

C0

C f ×Vf C0 × V0

× 100%

(2)

where C0 and Cf are the concentrations of lycopene in the feeding solution and the 5

foamate (g/L), respectively; V0 and Vf are the volumes (L) of the feeding solution and foamate, respectively. 2.3 Preparation of the tomato-based processing wastewater A simulated tomato-based processing wastewater was used as a research system because the preservation of an actual wastewater was difficult and lycopene was easily oxidized and degraded under natural conditions (Topal et al., 2006). The preparation procedure were described as follows: 500 g of tomato were squeezed by a juicer and then diluted with 200 mL of distilled water containing 10 mM sodium carbonate, which could be used to neutralize the organic acid released from the broken cells. Through full stirring using a stirrer, the supernatant was separated by centrifugation at 5000 rpm for 15 min at 30 ºC. Then, the supernatant was collected and used as the feeding solution, in which the concentrations of tomato proteins and lycopene were 0.84 g/L and 0.06 g/L, respectively. 2.4 Measurement of foam stability Foam stability was measured using a DFA 100 foam analyzer (KRÜSS, Germany) (Oetjen et al., 2014). Firstly, 50 mL of the sample solution were loaded into a transparent glass column of 40 mm in inner diameter. Then, a foam was generated by bubbling nitrogen gas through a gas distributor of 16-40 μm in pore diameter into the column at a volumetric gas flow rate of 0.3 L/min for 15 s. Time1/2 for foam decay was recorded by the foam analyzer to evaluate foam stability. 2.5 Measurement of the rhamnolipid concentration The concentration of rhamnolipid was measured using a modification method (Schenk et al., 1995). 20 mL of the test solution were freeze-dried using a lyophilizer (Eyela Fdu-1,200, Tokyo Rikakikai Co. Ltd., Tokyo, Japan) and the powder was dissolved in 1 mL of acetonitrile containing 2-bromoacetophenone and triethylamine

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in the molar ratio of approximately 1:4:2 (acetonitrile/2-bromoacetophenone/ triethylamine). The reactions were carried out at 80 ºC for 1 h. The solutions were filtered using a 0.22 μm membrane filter for HPLC analysis. The samples were analyzed by an Agilent 1100 HPLC system with a Zorbax Eclipse ADB-C18 (250×4.6 mm2, 5 μm, Agilent Technologies, Inc., USA) for determining the derivatized rhamnolipid phenacyl esters under the following HPLC conditions. The column temperature was maintained at 30 ºC with a mobile phase consisting of solvent A: acetonitrile, and solvent B: 3.3 mM phosphoric acid. The following gradient for solvent A was applied as follows: 50 % (v/v) for 3 min; from 50 % to 100 % for 19 min; 100 % for 5 min; from 100 % to 50 % for 3 min; 50 % for 10 min. The samples were measured by an ultraviolet detector at the maximal absorption wavelength of 244 nm. The flow rate was 1.0 ml/min and the injection volume was 20 μL. 2.6 Measurement of the concentration of tomato proteins The concentration of tomato proteins was measured by Coomassie Brilliant Blue Protein assay (Liau and Lin, 2008). 1 mL of the test protein solution was mixed into 5 mL of the prepared Coomassie Brillant Blue solution (200 mg of Coomassie Brilliant Blue G-250 were dissolved in 100 mL of 95 % ethanol and then 200 mL of 85 % phosphoric acid were added. The resulting solution was diluted to a final volume of 2 L.). The Coomassie Brilliant Blue formed a blue complex with the proteins. After 5 min of incubation, the absorbance was measured at 595 nm by using the UV-752N spectrophotometer, against a standard solution of bovine serum albumin (0.1-1 g/L) in 0.15 M sodium chloride. 2.7 Measurement of the concentration of lycopene 20 mL of the test solution were freeze-dried using a lyophilizer and the powder was put into a small boiling tube (14 cm ×14mm) containing 1 mL of acetone. Through

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full mixing, the tube was placed in an ultrasonic concussion (53 KHz) for 30 min in a cooling bath to be controlled at 0 ºC. The whole process was performed at the condition of dark. The supernatants were filtered using a 0.22 μm membrane filter for HPLC analysis. The samples were analyzed by the same HPLC equipment described as the above. The column temperature was maintained at 30 ºC with a mobile phase of methanol and acetonitrile (50:50, v/v). The maximal absorption wavelength and the flow rate were set as 472 nm and 1.0 ml/min, respectively. The injection volume was 20 μL. 2.8 Reusability of rhamnolipid After foam fractionation, the foamate was adjusted to pH 4.8 and then placed in dark for 3 h (Kramer and Kwee, 1977). The precipitate was separated from the supernatant, in which the concentration of proteins in the supernatant decreased as low as 0.08 g/L and that of rhamnolipid was nearly unchanged. Then, the supernatant could be mixed with the feeding solution for achieving the reusability of rhamnolipid. 3. Results and Discussion 3.1 Effect of rhamnolipid concentration When a surfactant is introduced into a solution containing surface-active materials, the interface adsorption layer properties and bulk aggregation behaviors will be significantly

changed.

Dickinsion

(1998)

has

presented

two

mechanisms

(solubilization and displacement) on the interfacial adsorption of a protein-surfactant mixed system. The effect of rhamnolipid concentration on the recovery of lycopene was investigated under the conditions of loading liquid volume 500 mL, volumetric gas flow rate 150 mL/min, pH 7.0 and temperature 50 ºC. Rhamnolipid concentration ranged from 0.3 g/L to 2.5 g/L. The results are presented in Fig. 3. As shown in Fig. 3, with the increase of rhamnolipid concentration from 0.3 g/L to

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2.5 g/L, the enrichment ratio of lycopene drastically decreased from 5.19 to 2.02, while the recovery percentage increased from 58.79% to 83.43% and then decreased from 83.43% to 65.71%. The decrease of the lycopene recovery percentage might be attributed to the displacement effect resulted from the increase of rhamnolipid concentration. Green et al. (2000) had investigated the adsorption of lysozyme and pentaethylene glycol monododecyl ether (C12E5) on the gas-liquid interface. Their result indicated that the displacement effect was a gradual process, in which competitive adsorption played an important role. The parallel neutron measurements showed that, at a low C12E5 concentration, the surface layer was predominantly occupied by lysozyme. With increasing C12E5 concentration, the surface layer consisted of both lycozyme and C12E5. Eventually, the adsorbed lysozyme was completely replaced by C12E5 as the concentration of C12E5 was further increased. Therefore, the recovery percentage of lycopene presented a downward trend with the increase of rhamnolipid concentration from 1.5 g/L to 2.5 g/L. The schematic representation of the displacement effect between rhamnolipid and protein-lycopene complex can be depicted as Fig. 4. Furthermore, the time1/2 of the feeding solution was also gradually prolonged with increasing rhamnolipid concentration (Fig. 3). An increase in foam stability resulted in increasing the recovery percentage but wet foam could be undesirably produced, resulting in decreasing the enrichment ratio (Rujirawanich et al., 2011). Based on above analysis, 1.5 g/L was chosen as the optimal rhamnolipid concentration for the following experiments. 3.2 Effect of temperature During a foam fractionation operation, it is necessary that both the enrichment ratios and the recovery percentages of desired materials are as high as possible. Increasing temperature is an effective method to achieve the effective separation by

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promoting interfacial adsorption and enhancing foam drainage (Liu, et al., 2013). The effect of temperature on the recovery of lycopene was investigated under the conditions of rhamnolipid concentration 1.5 g/L, loading liquid volume 500 mL, volumetric gas flow rate 150 mL/min, and pH 7.0. Temperature ranged from 30 ºC to 60 ºC. The results are presented in Fig. 5. As shown in Fig. 5, the enrichment ratio of lycopene first increased from 3.16 to 4.42 and then dramatically decreased from 4.42 to 2.31, while the recovery percentage continuously decreased from 90.12% to 59.96% with increasing temperature from 30 ºC to 60 ºC. The increase of temperature can intensify molecular thermal motion and thus contribute to promote interfacial adsorption, resulting in a high surface excess concentration of surface-active materials (Kumpabooth, et al., 1999). Moreover, it is well known that temperature can significantly affect the liquid fluidity. When temperature was low, a high viscosity leaded to an enormous attraction force between the molecules in the liquid and thus resulted in a poor fluidity. With increasing temperature, the intense molecular thermal motion supplied energy to overcome the attraction force between the molecules and thus viscosity decreased. The decrease of the viscosity in the interstitial liquid between bubbles could accelerate foam drainage and thus the foam phase became drier. The viscosities of the feeding solution at different temperatures were measured using an Ubbelohde viscometer and the data are plotted in Fig. 5. The viscosity of the feeding solution was difficult to be accurately measured when temperature exceeded 50 ºC because of the occurrence of aggregation. This phenomenon could be explained from the two following aspects. On the one hand, a high temperature could cause the self-association of protein molecules (Sorgentini et al., 1995). On the other hand, hydrophobic interaction would be strengthened with the increase of temperature, resulting in the hydrophobic

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association between proteins and other macromolecules (Frank and Evans, 1945). The aggregates could not be adequately adsorbed on the gas-liquid interface or transported by the rising foam and thus the recovery percentage decreased. Therefore, a high temperature was not conducive to achieving a high recovery percentage of lycopene. Furthermore, a high temperature might induce the isomerization of lycopene from all-trans isomers to cis isomers (Shi and Maguer, 2000). Considering the above factors, 50 ºC was chosen as the optimal operating temperature for recovering lycopene from the tomato-based processing wastewater. 3.3 Effect of pH pH is an important parameter which can influence the performance of foam fractionation by affecting foam properties, such as bubble size, interfacial tension and rigidity (Mukhopadhyay et al., 2010; Ekici et al., 2005). Moreover, the physicochemical properties of bioactive materials are strongly dependent on the pH of the initial feeding solution. The effect of pH on the recovery of lycopene was investigated under the conditions of rhamnolipid concentration 1.5 g/L, loading liquid volume 500 mL, volumetric gas flow rate 150 mL/min and temperature 50 ºC. pH ranged from 3.0 to 9.0. The results are presented in Fig. 6. As shown in Fig. 6, with the increase of pH from 3.0 to 9.0, the recovery percentage of lycopene first increased from 52.76% to 83.43% and then decreased from 83.43% to 70.43%, while the enrichment ratio continuously increased from 2.01 to 4.82. Both the recovery percentage of lycopene and the time1/2 of the feeding solution were maximal at pH 7.0. The surface activity of rhamnolipid was reported to be the highest between pH 7.0 and 7.5 (Zhang and Miller, 1992). Lycopene has not surface activity, but it can adsorb on the gas-liquid interface by forming the protein-lycopene complex with tomato proteins. Some experiments demonstrated that

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the maximal surface excess concentration of a protein occurred at its isoelectric point (pI) (Montero et al., 1993; Maruyama et al., 2007). However, the maximal recovery percentage of lycopene did not appear at tomato protein pI 4.8 (Kramer and Kwee, 1977).This results indicated that the surface activity of rhamnolipid could directly determine the foam stability, thereby affecting the recovery percentage of lycopene. Additionally, the configuration of lycopene was unstable under strong acidic conditions and easily isomerized from all-trans isomer to cis isomer (Nelis and Leenheer, 1991). Therefore, pH 7.0 was chosen as the optimal pH for recovering lycopene from the tomato-based processing wastewater. 3.4 Effect of volumetric gas flow rate The important role of volumetric gas flow rate on the performance of foam fractionation has been confirmed in many researches (Liu et al., 2013; Boonyasuwat et al., 2005). Volumetric gas flow rate can affect the liquid holdup of the rising foam by controlling its residence time in the foam phase. The effect of volumetric gas flow rate on the recovery of lycopene was investigated under the conditions of rhamnolipid concentration 1.5 g/L, loading liquid volume 500 mL, pH 7.0 and temperature 50 ºC. Volumetric gas flow rate ranged from 100 mL/min to 300 mL/min. The results are presented in Fig. 7. As shown in Fig. 7, the enrichment ratio of lycopene decreased from 6.37 to 1.33, while the recovery percentage increased from 63.20% to 92.17% with increasing volumetric gas flow rate from 100 mL/min to 300 mL/min. In foam fractionation, a volume of bulk liquid will be entrained into the foam phase by the introduced bubbles. Then, gravity and capillary forces cause a backflow of the entrained liquid, which makes the foam to become dryer while rising. Thus, the concentration of surface active material between lamellae and Plateau borders increases (Lu et al., 2005).

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When volumetric gas flow rate was low, slowly rising bubbles contributed to prolong their residence time in foam phase, thus foam drainage was enhanced, resulting in a low liquid holdup and a high enrichment ratio. In contrast, a high liquid holdup and a low enrichment ratio were found as a high volumetric gas flow rate due to the reverse effects. However, the recovery percentage was low at a low volumetric gas flow rate. By considering both enrichment ratio and recovery percentage, 150 mL/min was chosen as the optimal volumetric gas flow rate for recovering lycopene from the tomato-based processing wastewater. 3.5 Effect of loading liquid volume When the column height is fixed, loading liquid volume may affect the residence times of bubbles in the liquid phase and the rising foam in the foam phase, respectively. The effect of loading liquid volume on the recovery of lycopene was investigated under the conditions of rhamnolipid concentration 1.5 g/L, pH 7.0, volumetric gas flow rate 150 mL/min and temperature 50 ºC. The loading liquid volume ranged from 300 mL to 800 mL. The results are presented in Fig. 8. As shown in Fig. 8, the enrichment ratio of lycopene decreased from 7.94 to 1.36, while the recovery percentage increased from 56.44% to 88.44% with increasing loading liquid volume from 300 mL to 800 mL. The increase of loading liquid volume prolonged the residence time of bubbles in the liquid phase and facilitated the adsorption of a surface active material on the gas-liquid interface. Meanwhile, the residence time of the rising foam in the foam phase was shortened and thus the foam at the top of the column possessed a high liquid holdup. Thus, the recovery percentage of surface active material was high but the enrichment ratio was low. Although a higher enrichment ratio could be obtained at a lower loading liquid volume, coalescence and disproportionation of the bubbles inside the dry foam might result in

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a lower recovery percentage (Burghoff, 2012). In order to effectively recover lycopene from tomato extract, 500 mL were chosen as the optimal loading liquid volume of the experimental column. Under the optimal operating conditions of initial rhamnolipid concentration 1.5 g/L, pH 7.0, volumetric gas flow rate 150 mL/min, loading liquid volume 500 mL and temperature 50 ºC, the enrichment ratio and the recovery percentage of lycopene could reach 4.42 and 83.43%, respectively. As shown in Fig. 9, the foamate exhibited a reddish color in comparison with the color of the feeding solution. The HPLC chromatogram of the foamate manifested that both lycopene and β-carotene were concentrated by using foam fractionation. Meanwhile, the recovery percentage of rhamnolipid reached 94.52% in the foamate. 3.6 Reusability of rhamnolipid The reusability of a surfactant has a great significance for its applications in industrial downstream processing. The results of rhamnolipid reusability are summarized in Fig. 10. As shown in Fig. 10, the enrichment ratio of lycopene decreased while the recovery percentage increased with increasing the reusing time of the supernatant from one to seven. This result was because the amount of rhamnolipid in the foamate gradually decreased with increasing the reusing time of the supernatant, thereby the concentration of rhamnolipid in the feeding solution also decreased. The low concentration of rhamnolipid decreased the time1/2 of the foam and thus the unstable foam promoted foam drainage, resulting in a high enrichment ratio and a low recovery percentage of lycopene. The result of reusability indicated that the rhamnolipid in the supernatant could be reused to recover lycopene from the tomato-based processing wastewater for three times with a constant recovery percentage of lycopene.

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Subsequently, a small quantity of rhamnolipid was added to the feeding solution for maintaining the optimal rhamnolipid concentration of 1.5 g/L, and thereby the continuous operation of foam fractionation for recovering lycopene from the tomato-based processing wastewater using the co-adsorption effect of rhamnolipid was realized. 4. Conclusions In this work, the recovery of lycopene from the tomato-based processing wastewater using foam fractionation based on the co-adsorption effect between rhamnolipid and protein-lycopene complex was studied. Under the optimal operating conditions of rhamnolipid concentration 1.5 g/L, temperature 50 ºC, pH 7.0, volumetric gas flow rate 150 mL/min and loading liquid volume 500 mL, the enrichment ratio and the recovery percentage of lycopene could reach 4.42 and 83.43%, respectively. By adjusting pH and then precipitating tomato proteins, the supernatant of the foamate could be reused to recover lycopene from the tomato-based processing wastewater for 3 times with a constant recovery percentage of lycopene. It was demonstrated that foam fractionation was an effective method for recovery of lycopene from the tomato-based processing wastewater and the method could be referenced for separating a bioactive material without surface activity existed in its aqueous solution in the form of complex with a biosurfactant with poor surface activity by using another biosurfactant as the foam stabilizer. ACKNOWLEDGMENTS This work was financially supported by the Natural Science Foundation of China (No. 21346008) and the Natural Science Foundation of China (No. 21236001). References Agarwal, S., & Rao, A.V. (2000). Tomato lycopene and its role in human health and

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chronic diseases. Canadian Medical Association Journal, 163 (6), 739-744. Aksay, S., & Mazza, G. (2007). Optimization of protein recovery by foam separation using response surface methodology. Journal of Food Engineering, 79(2), 598-606. Benincasa, M., Contiero, J., Manresa, M.A., & Moraes, I.O. (2002). Rhamnolipid production by Pseudomonas aeruginosa LBI growing on soapstock as the sole carbon source. Journal of Food Engineering, 54(4), 283-288. Boonyasuwat, S., Chavadej, S., Malakul, P., & Scamehorn, J.F. (2003). Anionic and cationic surfactant recovery from water using a multistage foam fractionator. Chemical Engineering Journal, 93(3), 241-252. Boonyasuwat, S., Chavadej, S., Malakul, P., & Scamehorn, J.F. (2005). Surfactant recovery from water using a multistage foam fractionator: Part I effects of air flow rate, foam height, feed flow rate and number of stages. Separation Science and Technology, 40(9), 1835-1853. Burghoff, B. (2012). Foam fractionation applications. Journal of Biotechnology, 161(2), 126-137. Choudhari, S.M., & Ananthanarayan, L. (2007). Enzyme aided extraction of lycopene from tomato tissues. Food Chemistry, 102(1), 77-81. Cooke, D.J., Blondel, J.A.K., Lu, J., Thomas, R.K., Wang, Y., Han, B., Yan, H., & Penfold, J. (1998). Interaction between poly(ethylene oxide) and monovalent dodecyl sulfates studied by neutron reflection. Langmuir, 14(8), 1990-1995. Dickinson, E. (1998). Proteins at interfaces and in emulsions stability, rheology and interactions. Journal of the Chemical Society, Faraday Transactions, 94, 1657-1669. Ekici, P., Backleh-Sohrt, M., & Parlar, H. (2005). High efficiency enrichment of total

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Figure Captions Fig. 1. Structure of lycopene (all-trans isomer) Fig. 2. Schematic diagram of the experimental setup Fig. 3. Effects of rhamnolipid concentration on E and R of lycopene and time1/2 of the feeding solution Fig. 4. Schematic representation of the structural changes to the protein-lycopene complex/rhamnolipid system at the gas-liquid interface with increasing bulk rhamnolipid concentration Fig. 5. Effects of temperature on E and R of lycopene and viscosity of the feeding solution Fig. 6. Effects of pH on E and R of lycopene and time1/2 of the feeding solution Fig. 7. Effects of volumetric gas flow rate on E and R of lycopene Fig. 8. Effects of loading liquid volume on E and R of lycopene Fig. 9 The photo of the tomato-based processing wastewater before and after foam fractionation and the HPLC chromatogram of the foamate (1. the residual solution, 2. the feeding solution, 3. the foamate) Fig. 10. Effects of the reusing time of rhamnolipid on E and R of lycopene and time1/2 of the feeding solution

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1

3 2

5 4

9

7 6

8

11 10

13 12

15 14

14'

12'

10'

8'

6'

4'

15'

13' 11'

9'

7'

5'

Fig. 1. Structure of lycopene (all-trans isomer)

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2' 3'

1'

Fig. 2. Schematic diagram of the experimental setup

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Fig. 3. Effects of rhamnolipid concentration on E and R of lycopene and time1/2 of the feeding solution

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Fig. 4. Schematic representation of the structural changes to the protein-lycopene complex/rhamnolipid system at the gas-liquid interface with increasing bulk rhamnolipid concentration

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Fig. 5. Effects of temperature on E and R of lycopene and viscosity of the feeding solution

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Fig. 6. Effects of pH on E and R of lycopene and time1/2 of the feeding solution

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Fig. 7. Effects of volumetric gas flow rate on E and R of lycopene

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Fig. 8. Effects of loading liquid volume on E and R of lycopene

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Fig. 9 The photo of the tomato-based processing wastewater before and after foam fractionation and the HPLC chromatogram of the foamate (1. the residual solution, 2. the feeding solution, 3. the foamate)

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Fig. 10. Effects of the reusing time of rhamnolipid on E and R of lycopene and time1/2 of the feeding solution

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Highlights 1. The recovery of lycopene from the tomato-based processing wastewater was studied. 2. Rhamnolipid was used as the foam stabilizer for achieving co-adsorption effect. 3. Lycopene were greatly enriched through foam fractionation by adding rhamnolipid. 4. Rhamnolipid in the supernatant of the foamate could be reused to recover lycopene.

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