| ?-poly-L-lysine??-PL?,an homopolymer formed by the dehydration and condensation of lysine monomer,is mainly obtained by liquid aerobic fermentation.?-PL is mainly used in food preservation.A lot of research work about ?-PL fermentation technology has been carried out in this laboratory,which used glycerol as carbon source and obtained a high level of fermentation.But compared to glycerol as a carbon source,fermentation using glucose as carbon source has the advantages of better ?-PL antibacterial effect and higher tank volume at the end of fermentation.Therefore this paper used glucose as carbon source and uesd S.albulus M-Z18 as the research object.To determine the best ?-PL fermentation technology,this study optimized the feeding modes of carbon source and nitrogen source and fermentation technology,and amplified the best ?-PL fermentation technology to 50 L and 10 m3 fermentor.At last the coupled process of ?-PL fermentation with resin in situ product removal was studied.The main investigation results as follows:?1?The optimal feeding conditions of carbon source and nitrogen source in fed-batch fermentation process were established.First,the optimum initial glucose concentration was determined to be 90 g·L-1.By comparing the effects of different glucose feeding modes on fed-batch fermentation,the pulse feeding of 10-30 g·L-1 was the best glucose feeding mode in the 5 L stirred fermentor.On this basis,we investigated the effect of different feeding glucose concentrations on the fermentation.The results showed that the feeding glucose concentration could be controlled in the rang of 700-900 g·L-1 and the total volume of the fermentation broth could be increased with appropriate reduction.By comparing the effects of different concentrations of ammonia nitrogen on fed-batch fermentation,the concentration in the range of 0.1-0.5 g·L-1 was more favorable for fermentation.On this basis,the effects of ammonium sulfate pulse feeding and variable speed feeding on the fermentation were investigated.Finally,we found that the 0.5 g·L-1 ammonia nitrogen pulse feeding was the best way of ammonium sulfate feeding.?2?The optimal fermentation technology with glucose as carbon source was established.By comparing two-stage pH control and pH shock fed-batch fermentation,we found pH shock fermentation was more suitable for production.By investigating the effects of recovery pH,pH shock time,the minimum shock pH and dissolved oxygen level in the middle and later stage of fermentation on fed-batch fermentation,the optimum conditions were recovery pH 3.85,the pH shock time 9 h,the minimum shock pH 3.0 and 20% dissolved oxygen.Under this conditions,the yield of fed-batch fermentation in 5 L fermentor reached 47.13 g·L-1 and it increased by 27.3% compared with that before optimization.In 50 L and 10 m3 fermentor,the yield of fed-batch fermentation reached 27.50 and 23.60 g·L-1 respectively.?3?The phenomenon of product inhibition in batch fermentation was studied and the coupled process of ?-PL fermentation with resin in situ product removal was investigated.By adding different concentrations of exogenous ?-PL to explore product inhibition phenomenon,the results showed that in the batch fermentation when the adding concentration of ?-PL was more than 10 g·L-1,the synthesis of ?-PL would be affected in different degree,the higher the adding concentration,the less ?-PL synthesis.When 40 g·L-1 ?-PL was added,the synthesis of ?-PL was decreased by 35.7% compared with the control.Therefore product inhibition existed in the fermentation of S.albulus M-Z18.By comparing the ?-PL adsorption capacity and desorption rate of different resins in the fermentation medium of pH 4.0,the Amberlite IRC-50 resin was chosen as the adsorbent.After 4 days shake flask fermentation,the yield was greatly improved by adding different volume of resin and the yield was increased by 30.0% with 1mL resin.When 500 mL Amberlite IRC-50 resin was added into 5 L fermentor,the yield reached 34.50 g·L-1 and it increased by 29.9% compared with that without resin. |
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