Screening Of Pullulan Strains By UV Metagenesis And Optimization Of The Fermentation Conditions

Pullulan is a major Polysaccharide produced by strains of Aureobasidium Pullulans. It has the potential multi-utilization. In this paper, Pullulan fermentation strain was selected, both the media and fermentation process was optimized. The main research contents and results are as follows:(1) UV mutagenesis was used to obtain a mutant strain of Aureobasidium Pullulans which could produce high yield of Pullulan and low secretion of black pigment, one high pullulan-producing strain was achieved, which was 31% higher than the initial strain.(2) The proper seed medium conditions of shake-flask were as follows:sucrose 100.0g/L, peptone 5.0 g/L, K2HPO4 2.0 g/L, MgSO4 0.4 g/L, NaCl 2.0 g/L, pH 7.0. And the proper seed age and inoculum were 36 h and 2%(v/v). On this condition, the biomass is 14.7 g/L.(3) Through the response surface method, this paper obtained the proper fermentation conditions of shake-flask were as follows:sucrose 150.00 g/L, peptone 6.34 g/L, K2HPO4 7.91 g/L, NaCl 3.00 g/L, MgSO4 0.46 g/L, FeSO4 0.05 g/L, initial pH 6.5. The yield of pullulan is 73.12 g/L, which was 18.68% higher than the origin media.(4) Based on the above optimum condition, batch fermentation process of pullulan in 30L bioreactor was investigated. The result showed that 400r/min agitation and 1.0 vvm aeration were good for pullulan synthesis. The yield of pullulan is 81.28 g/L.(5) On the basis of the experimental data of batch fermentation in the 30 L bioreactor, the modeling of the kinetics of pullulan fermentation process was studied. Mathematic models of cell growth, product generation and substrate depletion in batch fermentation were proposed according to the Gompterz equation and the Logistic equation.The above models could fit the profiles of cell growth, production formation and substrate depletion well. It might be helpful to understand and guide further optimization of pullulan fermentation in the future.