| The paper focused on selections and breeding of the lactic acid bacteria producing L-lactic acid with homolactic fermentation from the nature. Firstly, this lactic acid bacteria was modified by N+ implantation and through the cultivation of the mutant under sugar and lactic acid with high concentration, the correspondent sugar and acid-resistant strain was screened and determined, and then the fermentation characteristics and cultivation conditions of the selected strain was studied. Finally, the product separation through the anion-exchange resin was investigated. The detailed contents were as followed:1. Through the screening in the nature, 20 strains producing L-lactic acid were obtained. And a homolactic fermentation strain LBO, which had a higher yield of L-lactic acid about 22g/L, was determined by the second screening and the experiment of fermentation characteristics. The strain LBO was induced by the N+ implantationof low energy and the best inducement dose was found to be 1.2 × 10 ions/s under the best implantation energy 50 Kev. And a mutant strain LB1 was obtained accordingly by the screening. The L-lactic acid yield of strain LB1 was 43 g/L and the yield of original strain LBO was 22 g/L.2.A strain LB1-1D which tolerated high concentration of lactic acid and sugar was obtained by taming and cultivating in the circumstance with high concentration of sugar and lactic acid. The strain's critical growth concentration of lactic acid and sugar were 24 g/L and 150 g/L respectively. The yield could reach 54g/L if CaCO3 was added and 26g/L if not. Besides, the strain was determined to be Lactobacillus agilis LB1-1D by the study of LB1-1D colonial, cell morphology, physiochemical characteristics and fermentation speciality etc..3. The optimization of fermentation media about the strain Lactobacillus agilis LB1-1D was researched. Different sorts of carbon and nitrogen resources, growth factor, metal ions of inorganic salt were studied in the single factor experiment. Three ingredient (rice saccharifing liquid, corn syrup, tomato juice) ratio of media was optimized through Response Surface Analysis (Central Composite Design). The function relationship between main factors and response value (L-lactic acid yield) was established, and the regression equation was obtained. The regression equation was:y==-0.03x12-0.13x22-0.02x32+0.05x1x2+0.07x1x3+0.06x2x3+5.73x1-2.68x2-8.1x3-142.03. Through analyzing the regression equation, the optimal concentrations of the factors were obtained: rice saccharifying liquid 113.23g/L, com syrup 13.9mL/L, tomato juice 11.8mL/L. And the optimal media was as followed: The rice saccharifing liquid 111.23 g/L, corn syrup 11.8mL/L, tomato juice 13.9mL/L, sodium acetate 0.5g, MgS04 · 7H2O 0.2g, MnSO4· 4H2O 0.01 g, FeSO4· 7H2O 0.01g, NaCl 0.0 1g, water 1000 mL.4. The cultivation conditions of the strain Lactobacillus agilis LB1-1D was studied and the optimal conditions were as followed: the inoculation size 10%, the fermentation temperature 37℃, the neutralizer NH4OH. Different fermentationmodels dealing with oxygen control were investigated in detail. The result showed the yield was higher in the model of quasi-anaerobic cultivation after aerated cultivation than that of stationary cultivation or aeration cultivation, and the best time for making the quasi-anaerobic cultivation was after 14 hours aerated cultivation, the yield and the usage percentage of sugar was 103 g/L and 92% respectively.5. L-lactic acid separation with ion exchange resin was studied, and the most suitable ion exchange resin D185 was selected, and its exchange capacity and the desorption ratio was 75g/L and 87% respectively. Glucose and amino nitrogen were not absorbed by the resin and the most suitable reproductive alkali was NH3 H2O. The process of the absorption-desorption condition of the D185 was studied and the results showed that when pH was 9 or so and the absorption velocity was 4mL/min, the yield of L-lactic acid was much better and reached 73%. During the desorp...
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