| ?-PGA, synthesized by microorganism, is a kind of polypeptide polymer formed by glutamic acid monomer through amide linkage. With many superior features such as biodegradable, biocompatible,non-toxic, soluble in water, chelating with metalions, etc. It is widely used in food, environmental protection, agriculture, medicine and other fields. This paper focuses on mutation breeding of ?- PGA producing strain, fermentation process scale-up and preparation of super absorbent polymer. The main research content is as follows:(1)ARTP was used to mutate the Bacillus subtilis ZF-5 and the mutagenesis conditions were as follows: treatment distance 2 mm, the optimum treatment time 300 s, sample volume 10 ?L, aeration rate10 SLM. With non-lipopeptide production, high ?-PGA yield and neutral red qualitative detection of molecular size as the screening criteria, mutant XA-3 was isolated from the mutant library. During the batch fermentation process in flask and 5L tank, only a little foam was produced, the product viscosity was higher, and non-lipopeptides was synthesized. The yield of ?-PGA at 18 h was 26.3 g/L in 5 L tank. Under the same conditions, the broth viscosity of XA-3 attained 185 Pa·s at the end of stable phase, increased by20% relative to that of the orginal strain.(2)Based on fermentation research of Bacillus subtilis XA-3 in 5 L fermentor, the scale-up experiment was conducted in 30 L fermentor. The results showed that XA-3 strain had the relatively rapid cell growth rate in 5 L tank.At 12 h, the process was stable phase, the glucose consumption rate was 49 g/L, OD600 reached the 20.5, amino nitrogen consumption rate was 1.1 g/L, ?-PGA yield reached the 18.1 g/L. With rapid accumulation during the steady and decline period, the highest yield attained 24.4 g/L. In 30 L, the cell growth rate was relatively slow, the stable phase was after 22 h. Then, the glucose consumption rate was 50 g/L, OD600 reached the 19.5, amino nitrogen consumption rate was 0.96 g/L, ?-PGA yield reached35.6 g/L. After the accumulating of ?-PGA in stable period, the highest yield reached 48.2 g/ L, increasing by 97% than that in 5 L tank. Through the feed-batch fermentation, the effects of glucose on ?-PGA producing were studied, The optimum experimental results were as follow. The suitable initial concentrations of glucose were 100 g/L, with adding amount of 100 g/L, and final concentrations were 200g/L. The optimum feeding time of glucose was about 22 h at end-log phase. The optimum yield of ?-PGA was up to 64.16 g/L at 58 h, increased by 33.1% than that of batch fermentation process.(3)The super absorbent polymer was prepared through the reaction between purified ?-PGA and ethylene glycol diglycidyl ether or its polymer. With single factor experiment, effects of ?-PGA concentration, cross-linking agent concentration, temperature, pH and reaction time on water absorption were researched. Based on water absorption and yield, polyethylene glycol diglycidyl ether 205 was chosen as crosslinking agent. Through the five factors three levels orthogonal experiment, the optimal conditions were temperature 40?, pH 5, ?-PGA 160 g/L, crosslinking agent concentration 20% of ?-PGA, of reaction time 46 h. The highest water absorption could reach 1431.91 g/g.(4)The puried ?-PGA absorbent polymer were analyzed by infrared spectroscopy and scanning electron microscope. The morphology was latticed stereochemical structure. |
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