Breeding Of The High Temperature Resistant High Production Lactobacillus Rhamnosus And Study Of The New Lactic Acid Fermentation Technology

L-lactic acid is an important organic acid which is widely used in pharmaceutical, food and chemical fields; as the main raw material of synthesizing the new biodegradable - polylactic acid (PLA), L-lactic acid has a broad application prospects. Currently, there are many issues during the lactic acid fermentation such as low yield and long period of fermentation, and the high energy consumption and other issues, resulting in high production costs of L-lactic acid, which hindered its development. To solve the above problems, the study focused on the high-temperature resistant and high-yield breeding, fermentation process control analysis and the new lactate fermnetation designing, in order to improve the L-lactic acid fermentation and to reduce production costs.(1) A strain Lactobacillus rhamnosus HG09 producing high optical purity L-lactic acid was used as the original strain. Mutations by ultraviolet combined with chemostat screening methods to improve the efficiency of positive mutant screening; Finally, a high-temperature resistant and high-yield lactic acid bacteria was obtained, when it was fermented at 50℃for 48h, lactate production reached 84.6±1.8 g/L, 92.7% higher than the original strain, and the volumetric productivity reached 1.76±0.04 g/(L·h). After a single factor optimization, it was found that under the conditions of 42℃, 150 g/L of initial sugar, 8% inoculum, pH 5.8, the final lactic acid production and the volumetric productivity reached 136±1.2 g/L and 3.6±0.03 g/(L·h), respectively, 80% higher than the original strain.(2) According to the reported immobilization methods, the fermentation of immobilized lactic acid bacteria were studied, the high strength, good mass transfer colloidal particles were obtained after 7% PVA and 1.5% sodium alginate mixture reaction with saturated boric acid, 2% calcium chloride mixture. The fermentation yield and productivity of the immobilized lactic acid bacteria were similar with that of the free bacterial fermentation , and it can be reused for a long time. Continuous fermentation of immobilized lactic acid bacteria was also studied, by mathematical modeling, using Matlab curve fitting method, and the important parameters in the fermentation process were obtained; According to the parameters and the mathematical model, we analyzed the impact of the lactate and glucose on lactic acid fermentation process, and obtained an optimized control conditions.(3)We combined expanded bed adsorption with the fermentation of organic acids to resolve the end-product inhibition in the lactic acid fermentation process; through this process combined with fed fermentation, lactic acid production reached the 200±2.3 g/L, the conversion rate reached 91.8±1.1%, the volumetric productivity reached 4.4±0.05 g/(L·h), which was 109.6% higher than the batch fermentation, and 57.1% higher than the fed-batch fermentation. Moreover, the problem of pollution in the traditional fermentation method was solved. In addition , the product yield can reach 85% ~ 99%, which was significantly increased compared with the conventional calcium method fermentation.