Study On The Separation And Purification Of Antimicrobial Lipopeptide By Magnetic Microspheres

Surfactin is widely recognized as the most powerful biosurfactant with properties of inhibitory effect of bacteria, significant emulsion and foamy effect. Because the Surfactin molecular has smaller weight, higher thermal stability, better water-solubility, non-immunogenic, non-toxic side effects on people and no damage on the natural flavor of the food, it meets the requirements of additive for functional food and green food. Surfactin can be used widely in functional food. In the condition of advocating the supremacy of human health now, biosurfactant will become a widely used food additive in the future. Some chemists has tried to carry out chemical synthesis of surfactant with special activities with disadvantages of multi-step synthesis and high cost. The efficient way to obtain it is by fermentation. The common separation way of Surfactin is acid precipitation. This method is simple, high yields, but low purity. Therefore we need to find a more convenient separation method. The principle of magnetic separation is very simple, which is that the surface of magetic particles was modified with ion exchange, affinity group or a hydrophobic ligand. Then they can be mixed with the liquid sample, the magnetic particles can be quickly separated with the role of the external magnetic field after combining with the purpose product. Compared with conventional separation methods, magnetic separation technology has the advantages of simple operation and purification steps. All that can be done in a container without expensive device, and be automated more easily.The effects of different reaction conditions on the properties of Fe3O4 magnetic nanoparticles were tested, which were prepared by co-precipitation method, and the preparation conditions were also optimized. The optimum preparation conditions of magnetic nanoparticles are as follows:Fe+/Fe+ molar ratio of 0.75, pHll of the reaction solution, reaction temperature of 50℃, crystallization temperature of 50℃, and crystallization time of 2.Oh. Under the optimum conditions, the mean size of Fe3O4 magnetic nanoparticles was about 12nm. The particles also have the properties of high purity granular, better crystalline. The saturation magnetization of Fe3O4 magnetic nanoparticles was 62emu/g.Their magnetic microspheres of compositive P-cyclodextrin were prepared by inverse suspension and cross linking method. They were analyzed by transmission electron microscope and infrared spectrometer. It showd that β-cyclodextrin had been wrapped in Fe3O4 magnetic nanoparticles with a better shape of β-cyclodextrin composite microspheres.In the end, magnetic adsorption properties of β-cyclodextrin composite micro spheres on Surfactin were studied. The adsorption of β-cyclodextrin composite microspheres on Surfactin reached equilibrium after 4h. With the surfactant concentration of 2.5g/L, the adsorption temperature of 10℃ and the solution of pH7, the adsorption effect of surfactant on the magnetic microspheres was the best. The adsorption isotherms of magnetic microspheres on surfactant can be used with the Langmuir isotherm adsorption equation. Elution experiments showed that when the magnetic microspheres reached adsorption equilibrium,58% of surfactant can be resolved by absolute ethanol and the surfactant purity reached 87.6%.