Separation And Purification Of L-tryptophan In E.coli Fermentation Broth

L-tryptophan is one of the eight essential amino acids indispensable in human and animal survival activities.Since the 20th century,biological sciences have continuously developed and medical technology has been continuously improved.The market demand for L-tryptophan in the fields of medicine,animal feed and food addition has also increased,and its future development prospects are broad.Taking the fermentation broth of L-tryptophan as the research object,the fermentation broth is separated and purified by solid-liquid separation,decolorization,nanofiltration membrane filtration,and crystallization.Based on the microbial fermentation method,This study analyzes the composition and content of L-tryptophan fermentation broth,optimizes the extraction process of L-tryptophan fermentation broth,and uses ceramic membrane filtration to significantly improve the removal rate of bacterial and protein during the solid-liquid separation of L-tryptophan fermentation broth.And through studying the performance of different types of activated carbon,this paper determines the best decolorization conditions,the optimal type of nanofiltration membrane as well as the ideal reaction conditions,and the control of the concentration and crystallization process conditions are finally determined to improve the yield of L-tryptophan separation and purification rate.Based on the above purpose,the main research results of this paper are as follows:1.Analytical method for rapid determination of L-tryptophan in fermentation broth.Through the HPLC method,the various components and their contents in the fermentation broth were analyzed and detected.As a result,the water content in the L-tryptophan fermentation broth was 68.72%,and the solid content was 31.28%,of which L-tryptophan accounted for 1.32%,phenylalanine 0.22%,inorganic salts 3.94%,sugar 0.22%,other substances 25.04%.2.Research on the solid-liquid separation process and decolorization process of fermentation brothChoose 1%Na2SO3 as antioxidant,adjust pH4.0,prevent L-tryptophan in fermentation broth from decomposing,The L-tryptophan and water in the fermentation broth and other macromolecular substances are preliminarily passed through a ceramic membrane for separation,protein removal rate was 78%,bacterial removal rate was 99%,and L-tryptophan yield was 97%.And then ecolorize the separated liquid.The best conditions for the decolorization process are:at a temperature of 60℃,use the powdered activated carbon at 1%as the decolorizing agent,add it to the separated fermentation broth,decolorize for 30 min,through suction filter to remove activated carbon after decolorization is finished.Finally,the measured light transmittance of the fermentation broth can reach 78%,and the yield of L-tryptophan is 95%.3.Research on the filtration of nanofiltration membrane and crystallization technology in the process of separation and purification of fermentation brothThe decolorized fermentation supernatant was filtered using a nanofiltration membrane with a membrane model of NF 800,under a pressure of 1.2 MPa,and a temperature of 40℃.The recovery rate of L-tryptophan was up to 95%,and the light transmittance was 83%.After concentration and cooling crystallization,the final product of L-tryptophan is obtained by centrifugation.Under the technical condition above,the total recovery rate of L-tryptophan in the fermentation broth reached 61%.