Directed Breeding And Ferment Optimization Of L-lactic Acid Producing Strain Bacillus Coagulans

Bacillus coagulans was widely used in industrial L-lactic acid production, its high optical purity, fermentation conversion rate, less energy consumption, and can achieve L-lactic acid by directly use corn meal saccharification liquid. However,during fermentation process,because the existence of the disaccharide,trisaccharide and tetrasaccharide oligosaccharide generated from saccharification liquid,Bacillus coagulans has low utilization rate of these sugars,the high residual sugars greatly affect the lactic acid extraction and purification. These were critical for affecting the lactic acid market applications. This study will focus on the rapid consumption of residual sugar by Bacillus coagulans, Based on the selective mutation breeding program and fermentation optimization, improve the residual total sugar consumption ability of Bacillus coagulans, so as to shorten the fermentation time and reduce production costs.By UV and LiCl, and photosensitive reagent were treated with 8-MOP producing strains, with maltulose as carbon source, was selected by using calcium carbonate bromocresol purple plate selective culture medium, a strain maltulose consumption mutant UM-27 faster, then use the method of continuous culture, by controlling the dilution rate and time increased maltulose concentration, domestication of the mutant strain UM-27, the screening of the strains with high residual sugar consumption ability. Then, the effect of medium conditions on L-lactic acid fermentation were optimized in shake flask. Firstly, the Plackett-Burman software was used for screening the major factors on L-lactic acid production in the original medium contain corn steep liquor, potassium dihydrogen phosphate, peptone, ammonium sulfate, magnesium sulfate, manganese sulfate, sodium nitrate and calcium carbonate. The statistic results showed that corn steep liquor, calcium carbonate and potassium dihydrogen phosphate were the key factors. Secondly, central composite response surface experimental design and statistical analysis were applied to optimize the concentration of these three factors. Experiment and analysis result identified the optimal medium composition. The obtained medium condition was used for further investigatinon.Further, in 5 L fermentor using strain UM-27A fermentation experiment, the effect of ventilation fermentation, key factors than speed, pH and temperature were optimized research. The results show that, the ventilation ratio 0.03, rotate speed is 200 rpm, the pH value is 5.3, and the two stage of the prophase temperature,45℃ and 50℃ late control mode, the optimal fermentation control process, cycle glucose consumption stage (26 h) compared with the original strain (42 h) shortened 19 h. At the same time,the residual total sugar concentration dropped below 0.4% need only 45-50 h, which was shorter than the control (96 h), significantly improved the lactic acid production efficiency and product quality.The studies on mutant strains screening and key fermentation conditions controlling optimization,laid the foundation for further amplification and optimization on industrial fermentation processes.