Screening And Fermentation Condition Optimization Of L-Lactic Acid Fermentation By Lactic Acid Bacteria With Rape Cake Hydrolyzate As Nitrogen Source

Bacteria fermentation has advantages such as high academic conversion, low ventilation consumption and easy separation. Due to feedback inhibition and substrate inhibition, it is important to screen L-lactid acid high-producing bacteria with high acid-tolerance and high sugar-tolerance. Compound nourishment condition is necessary to bacteria's growth and fermentation, so Rape Cake Hydrolyzate as Nitrogen Source has great importance on decreasing the cost of lactic acid production. Medium optimization by Genetic Neural Networks can supply references to related research.(1)Lactobacillus casei CICC6002 as the parent strain was treated by UV. After preliminary screening and secondary screening, mutant U-2 got the output which was 6.87% higher than the parent strain. And then, mutant U-2 was treated by DES-ultrasonic and screening, mutants D-8,D-17 and D-20 got the output increase of 8.70%,13.04% and 10.14% respectively.(2)After the oriented selection by acid MRS medium and high-sugar MRS slab for enhancing acclimatization of acid- tolerance and sugar- tolerance, finally a high-yielding strain named NT-7 was selected, which could grow in the environment of 40 g/L lactic acid and 200 g/L glucose. After 72-hour fermentation, the mutant gave a L-lactic acid output of 88 g/L, 41.94% higher than the parent strain. After eight-generation, the output of lactic acid had been proved stable.(3)In order to reduce the manufacturing cost of lactic acid and increase the compound usage of rape cake, rape cake hydrolyzate was used to replace beef extract etc. as nitrogen source. The model of BP Neural Networks was set up on the basis of uniform experiment along with the results of single-factor experiments. Neural Networks was optimized by Genetic Algorithms. The obtained optimal medium ingredients were (g.L^-1): glucose 110.43, rape cake hydrolyzate(dry weight)87.75, corn liquid21.18, (NH₄)₂HC₆H₅O₇2.85. In the optimal medium, the output was 94g/L , which was 9.30% higher than the output in the original medium.(4)The optimum fermentation conditions of NT-7 was investigated by single-factor experiments: incubation 10%,medium capacity 25ml /250ml, still cultivation at 37°C. The result of 4 L bio-reactor identified the output of shaking flask's fermentation .