Foam And Adsorption Properties Of Bovine Serum Albumin And Lysozyme In Foam Fractionation

In recent years, foam fractionation has attracted more people’s attention and got a rapid development in biochemical engineering because of its advantages of low energy consumption, non-pollution and operation at room temperature and atmospheric pressure.There have been not only many references of lab-scale researches but also a few commercial reports on concentrating biosurfactants using foam fractionation. To promote the application of foam fractionation in biochemical engineering, it is very important to study the selective separation of biosurfactants and make them purified with each other.The study of the foam properties and the thermodynamic adsorption properties of biosurfactants on the bubble surface from their multi-component solutions is the key for the purification of them.Foaming ability and foam stability were characterized by initial foam height and half-time of foam, respectively. The relational expression between the initial foam height of the solution with two biosurfactants and their concentration bellow the critical micelle concentration(CMC) was determined by using the extended Szyszkowski equation and Rosen’s empirical model. The relational expression between the half-time of foam of the solution with two biosurfactants and their concentration bellow the CMC was established on the basis of the rules that the gravitational potential energy and the surface energy all decreased with the bubble breakup in the foam phase. An aqueous solution with bovine serum albumin(BSA) and lysozyme(LZM) was used as the simulation system to verify the accuracy of these relational expressions. The results showed that the two relational expressions could be used to accurately predict the foam properties of the solution with BSA and LZM. The effect of BSA on the foam properties of the solution was more significant than that of LZM.Redlich-Peterson equation was used to determine the adsorption isotherms of BSA and LZM on the bubble surface from the binary solution and the corresponding distributioncoefficients and the separation factor were determined on the basis of their adsorption isotherms. The results showed that Redlich-Peterson equation could be effectively used to describe the equilibrium adsorption of BSA and LZM on the bubble surface from the binary solution. The surface excess of BSA on the bubble surface was more than that of LZM and the effect of the BSA concentration on the surface excesses of BSA and LZM was more significant than that of the LZM concentration. According to the adsorption isotherms, it could be indicated that the BSA concentration had significant effects on the distribution coefficient of LZM, but the LZM concentration had almost no effects on the distribution coefficient of BSA. The separation factor of BSA to LZM was a constant, 5.89, and was irrelative to the BSA and LZM concentrations. The adsorption of BSA and LZM on the bubble surface was heterogeneous because of their different molecular sizes and charges.During the adsorption process, BSA was easily absorbed on the bubble surface owing to its zero net charge. Then, the electrostatic repulsion between LZM molecules hindered the absorption of them on the bubble surface.