Process Optimization Of L-Tryptophan Production By Fermentation

L-tryptophan is one of the eight essential amino acids and has been widely used in pharmaceutical, food and forage industry. Compared with international levels, L-tryptophan fermentation in our country exhibited lower production, conversion ratio and extraction ratio as well as slower detection. In this report, the calibration model for L-tryptophan concentration monitoring was developed by the near infrared spectroscopy (NIRS), the strategy of fed-batch fermentation was used for improving the L-tryptophan production, in addition, the process of L-tryptophan purification was optimized based on the property of fermentation broth. The main contents and results are as follows:The traditional method for L-tryptophan concentration detecting is time consuming. The calibration model was established based on the near infrared spectroscopy and the method of partial least square. In order to examine the stability and accuracy of the model, we compared the predicted value with the accurate value of L-tryptophan concentration, and the average relative error was5.16%. It laid a strong basis for the detection of L-tryptophan production on line and offline.Concentration of16amino acids except L-tryptophan was test during the process of fermentation. We noticed that the consumption rate of L-glutamate acid at the early stage of fermentation was the fastest. According to this phenomenon, an extra amount L-glutamate acid was added into the fermentation medium. The biomass and L-tryptophan production was increased by2.63%and2.05%, respectively.The metabolic pathway of L-tryptophan indicated that L-glutamine is an amino donor of L-tryptophan. L-glutamine was added during the metaphase of fermentation. The biomass and L-tryptophan production was increased by6.37%and6.16%, respectively.Glucose feeding strategy is a key strategy in L-tryptophan fermentation by recombinant Escherichia coli. Based on the characteristic of L-tryptophan metabolism, a novel glucose feeding strategy based on the glucose-stat feeding strategy and DO-stat feeding strategy was implemented, and its effect on the metabolic flux of L-tryptophan was tested. Under the optimized conditions, the metabolic flux of Embden-Meyerhof-Parnas pathway and the tricarboxylic acid cycle was reduced, but the metabolic flux of phosphopentose pathway was elevated. Above all, the biomass and L-tryptophan production increased by5.93%and7.02%, respectively.Based on the property of fermentation broth, the L-tryptophan purification proces was improved by optimizing the micro-filtration technology, ultra-filtration technology and the acticarbon-adsorption technology. Under the optimized condition, the ratio of protein and pigment removal as well as the recovery of L-tryptophan reached98.52%,94.46%and82.07%, respectively. This study laid a basis for optimization of L-tryptophan fermentation process and purification technology of L-tryptophan.