Mutation And Screen Of Aureobasidium Pullulans And Fermentation Technology

Pullulan is major polysaccharide produced by strains of Aureobasidium pullulans. Because of its non-toxic, edible, low calorie, plasticity, good film forming quality and its film very low permeability to nitrogen and oxigen, it is widely used in food preservation, packaging bags, additives, pharmaceuticals, pesticides, sewage treatment and many other fields. It owns great development prospects and value.In this paper, Aureobasidium pullulans was studied on cell morphology, physical and chemical mutation, mutant strain screening and optimization of culture medium developed to fermentor cultivation. Results showed its application potential.1.Aureobasidium pullulans cells growth and morphology diversity in different culture conditions were observed and studied through microscopic and photomicrographic observation.2.The strain sensitivity to 60Coγ-ray irradiation, UV irradiation and nitrate mutation was studied. Mortality curves obtained through the three kinds of mutation respectively,Three special strains with good characteristics were screened out through mutation step by step. There were strain 27# with pigment-free production of pullulan, high polysaccharide production strain 3# and strain 3#-1 which had the character of self-flocculate and sediment with pigment in later fermentation.3.Mediums with glucose and ammonium sulfate as the basic carbon and nitrogen source for above three mutants had been optimized respectively by flask-shaking culture, with orthogonal experiments. Experiments developed to use sugar and bean cake as carbon and nitrogen source through gradually orthogonal optimization. The results showed that strain 3# reached maximum pullulan production of 42.33g/L, and sugar conversion rate was 52.9%.4.Strian3# and 3#-1 were fermented in 10 liters fermentor respectively for extension experiment. And parameters of fermentation process such as pH, dissolved oxygen, carbon source consumption and biomass growth rate were all studied and comprehended. The highest polysaccharide yield of strian3# reached 29.7g/L, only by fermenting for 72 hours, while the glucose conversion rate reached 55%.5.Results of study on strains27# and 3#-1 were showed as follows.27# maintained cell morphology of yeast-like cells for a long time and produced very litter pigment into the fermentation broth, but the polysaccharide production relatively lower. Strain 3#-1 cell was self-flocculate and sediment with pigment in the later fermentation stage, this made the cells and pigment easily separated from the fermentation liquid, which was beneficial to the follow-up extract of polysaccharide. The production of polysaccharide by 3#-1 in bio-reactor was little lower than that by 3#, but it is different from strain 3#, after 5d's fermentation the pullulan accumulation still continuous. The characteristics of this mutant strain are still need to do more deep improvement and optimization. 6.In the medium optimization process, it had found that oxygen shock had a great effect on cell growth and polysaccharide production, oxygen shock may help strain cells keeping a certain morphology form, and leading to increase production of polysaccharide. Oxygen shock occurred accidentally in the culture process, the information about it was still very superficial, and there were not enough tests to explain its mechanism. In the future expansion experiments, it should have a further observation and study on this phenomenon carefully.