In the Laboratory
Foam Fractionation of Lycopene: An Undergraduate Chemistry Experiment Yan Wang, Mingjie Zhang,* and Yongliang Hu Department of Chemistry, School of Science, Tianjin University, Tianjin 300072, P. R. China *
[email protected] Lycopene is an acyclic carotene with 11 conjugated double bonds that occur in various geometrical isomers. It is most readily found in ripe tomatoes, watermelon, pink grapefruit, guava, and papaya (1). Lycopene has been used as natural food colorant for many years, and recently it has attracted considerable attention as a pharmaceutical component (2, 3). These studies indicate that lycopene plays a role in cancer prevention and cardiovascular health. Lycopene is insoluble in water so conventionally its extraction requires the use of organic solvents (4, 5). Supercritical carbon dioxide extraction (6), which is comparatively complex, has also been used to extracted lycopene. In previous work, we developed a method for the extraction of lycopene using a surfactant emulsion (7). The method is viable and environmentally friendly, but it requires the use of high temperatures. In this article a novel method for the extraction of lycopene by foam fractionation is described. Compared with our previous method, the foam fractionation has two advantages: milder operating conditions and simpler experimental setup. Foam fractionation is a process for separating and concentrating chemicals that utilizes differences in their surface activities. It involves the production of a stable foam by forcing gas into the liquid, which causes formation of bubbles in the solution. Hydrophobic materials are attached by adsorption to the bubbles, which then rise to the surface of the liquid. At the liquid surface, the bubbles often create a foam phase. This foam then travels up a column and finally collapses into a concentrated liquid product (8, 9). Experimental Procedure An aqueous solution of surfactant CPS, a copolymer of nbutyl acrylate, styrene, and acrylic acid, was prepared by the instructor according to the literature (7). This preparation should be done by a teacher before class. The acrylic acid and styrene are toxic and will cause contact burns and severe irritation if they come in contact with exposed skin or the respiratory system. All polymerization steps should be carried out in a hood and gloves should be worn at all times. Tomato paste (5.0 g), aqueous CPS (1.5 g), and 70 mL of water were added to a 100 mL three-neck round-bottom flask equipped with a 60 cm fractionating column and a dispersion tube connected to an air pump (1.2 L/min). The fractionating column was then connected to a Y-adaptor, a vacuum adaptor, and a receiving flask. The setup is shown Figure 1. The mixture was stirred for 20 min, and then air was introduced from the air pump to produce a stable foam that flowed into the receiving flask through the fractionating column. The flow of air was continued until no more bubbles flowed into the receiving 510
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Figure 1. Foam fractionation setup.
flask, which took about 1 h. The pink product was acidified to a pH of 1 with phosphoric acid (85%). The precipitate of crude lycopene was collected by centrifugation. The filtrate can be reused by simply adding sodium hydroxide to the solution until the pH is 9. UV-Vis Spectra Analysis Lycopene (1.0 mg) obtained from the foam fractionation was dissolved in 10 mL of acetone, and the UV spectrum was recorded. A typical spectrum is shown in Figure 2. The absorption peaks at 445, 471, and 502 nm are characteristic absorption peaks for lycopene. The spectrum matches previously reported spectra of lycopene extracted from tomatoes (10-12). Thus foam fractionation is a viable method for the extraction of lycopene from tomato paste. Hazards CPS may irritate the eyes and skin. Phosphoric acid is corrosive and causes severe irritation and burns to any area of contact. Sodium hydroxide is caustic and may cause irritation of the eyes and skin. Acetone is flammable, is harmful if swallowed or inhaled, and causes irritation to skin, eyes, and respiratory tract.
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Vol. 87 No. 5 May 2010 pubs.acs.org/jchemeduc r 2010 American Chemical Society and Division of Chemical Education, Inc. 10.1021/ed8001682 Published on Web 03/10/2010
In the Laboratory
the isolation of natural products and principles of extraction. This experiment is suitable for an undergraduate laboratory course. All the materials for the experiment are easily obtainable, and the results are reproducible. The experiment has many advantages: mild operating conditions, simple experimental setup, safe solvents and auxiliaries, and a reusable reagent. Literature Cited
Figure 2. Spectrum of lycopene in acetone. According to the literature ( J. Agric. Food Chem. 2005, 53, 8997-9004), the UV/vis spectra assumed to correspond to 13-cis- and 9-cis-lycopene had a peak around 320 and 360 nm.
Summary This experiment was designed as a laboratory project for undergraduate chemistry majors. In our experience the students have enjoyed the experiment, and it has been a great success. The aqueous solution of surfactant was prepared by the instructor before class and used by the students directly. The tomato paste was purchased from a local grocery store and used as is. When 60 students performed the experiment, all the students obtained the desired product. It took students about three hours to do this experiment. This is the first report of foam fractionation being used to extract lycopene from tomato paste. It has been shown to be a viable and environmentally friendly experiment, which includes
r 2010 American Chemical Society and Division of Chemical Education, Inc.
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1. Rao, A. V.; Agarwal, S. Nutr. Res. ( N.Y.) 1999, 19, 305–323. 2. Cadoni, E.; De Giorgi, M. R.; Medda, E.; Poma, G. Dyes Pigm. 2000, 44, 27–32. 3. Choudhari, S. M.; Ananthanarayan, L. Food Chem. 2007, 102, 77–81. 4. Gerster, H. J. Am. Coll. Nutr 1997, 16, 109–126. 5. Mortensen, A.; Skibsted, L. H. J. Agric. Food Chem. 1997, 45, 2970–2977. 6. Choudhari, S. M.; Singhal, R. S. J. Food Eng. 2008, 89, 349–354. 7. Zhu, J.; Zhang, M. J.; Liu, Q. W. J. Chem. Educ. 2008, 85, 256–257. 8. Aksay, S.; Mazza, G. J. Food Eng. 2007, 79, 598–606. 9. Linkea, D.; Zorna, H.; Gerken, B.; Parlarb, H.; Berger, R. G. Enzyme Microb. Technol. 2007, 40, 273–277. 10. Tan, B.; Soderstrom, D. N. J. Chem. Educ. 1989, 66, 259–260. 11. Montesano, D.; Fallarino, F.; Cossignani, L.; Bosi, A.; Simonetti, M. S.; Puccetti, P.; Damiani, P. Eur. Food Res. Technol. 2008, 226, 327–335. 12. Qiu, W. F.; Jiang, H. H.; Wang, H. F.; Gao, Y. L. Food Chem. 2006, 97, 516–523.
Supporting Information Available Detailed student procedures and instructors' notes. This material is available via the Internet at http://pubs.acs.org.
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