Breeding And Fermentation Conditions Optimization Of Associated Bacteria In 2-keto-L-Gulonic Acid Fermentation

Adding glucose in the process of fermentation could extend the exponential phase of associated bacteria and result a second major growth period, by which the yields of 2-keto-L-gulonic Acid could be increased. The result of experiment showed that conversion was increased by adding some amount of glucose. The optimum adding time was at 20 h-28 h in the process of fermentation, and the optimum concentration of glucose was 0.008%, the inoculation was 15%. Among the different treats, the best one was the treat that adding glucose at 20 h of fermentation, whose conversion was increased by 4.70%.Three strains of Bacillus thuringiensis isolated from samples of soils and pesticide products were obtained by a short-cycle and high conversion screening model, after insect rejuvenation and several times of screening, an improved strain was obtained and named as strain B15-14. The results of shaking fermentation showed that, compared with strains 25-b applied in current vitamin c industry production, the new strains B15-14 shorten the fermentation cycle by 8 h and increased conversion by 10.21%. Its genetic stability was also observed.In order to exploit the fermentation potential of new strains B15-14, the research on effects of some single factors on fermentation was conducted. The results showed that optimum concentration of L-sorbose was 7%, the optimum ventilation was 20-30 ml (250 ml flask), the optimum temperature was 29-33℃,31℃for the best, initial pH ranged from 6.0 to 7.5 and the optimum pH was 7.0.The optimum multi-factor fermentation conditions of strains B15-14 was inspected by the method of uniform design. The results showed that the optimum fermentation medium concentration of ingredients as follows:corn pulp was 3.02%, KH2PO4 was 0.25%, MgSO4 was 0.03%, urea was 0.43%. Under the optimum fermentation conditions, the conversion was 85.28%.