Preliminary Study About Pullulan Fermentation By Aureobasidium Pullulans

Pullulan is a linear homopolysaccharide which is comprised of glucose units, it has been produced by Aureobasidium pullulans, and it is also a kind of Microbiology exopolysaccharide with a high using value. It has unique linkage pattern inside the molecule and gives it unique distinctive physical properties. For instance, adhesive ability, the capacity to form fibers, the capacity to form biodegradable film, and so on. Thus, it was used widely in food industry, medical industry, industry and so on. Pullulan can be used as making food wrap film, food additives, capsules, blood plasma substitutes, heavy metal removal, environmental pollution control agents, emulsifiers, adhesive, gelling agents and so on. As what says on the document, Aureobasidium pullulans ferments and formed exopolysaccharide, during the fermentation, it is easy to from the melanin which is hard to erase, giving the following process some problem,during the fermentation, the growth and metabolism of the thallium can infects the amylase production. So, the research of pullulan should concentrate on produce the strain which do not produce melanin and optimize fermentation conditions. So that it can make progress in theory foundation of large-scale industry production.Preserved in the laboratory have a mutagenic by the University of Pennsylvania state dealt with melanin production mold strains of Aureobasidium pullulans known sugar yield of 32.9 g/L. In this study, this strain was the original strain, to be more productive strains of UV mutagenesis breeding and bred high-yielding strains of the fermentation broth and the optimization of fermentation conditions. The results showed that:（1）In the growth period of Aureobasidium pullulans, observed by microscopy, Aureobasidium pullulans cells have a variety of forms of cell morphologies with the extension of time, only similar to the yeast-like cells to produce pullulan, and the expansion of the number of cells and extracellular polysaccharide yield a positive correlation. And then by repeated fermentation cultivation found that the expansion of cells in the fermentation of the seventh cell reached the maximum production rate.（2）Under the condition of irradiating by the Ultraviolet lamp of 30W in 30cm distance, the mutant strain can be breeding out. In the original medium for the fermentation medium, the exopolysaccharide yield of up to 46.96 g / L, which is 1.43 times the original strain can, therefore, this mutant as a follow-up fermentation optimization experiments starting strain.（3）A preliminary fermentation study about mutant strain UV^-1, including shake flask fermentation and 5 L fermentation tank. At first, optimization of fermentation into the fermentation medium optimization. Three factors having significant effect have been selected through the single factor experiment: Sucrose as carbon source and its content are 50 g/L、55 g/L、60 g/L. Yeast extract as nitrogen source its content are 3 g/L、5 g/L、7 g/L. Choosing Magnesium ion as metal ion. On the basis, using response surface central composite design to optimize the level of significant factors. The results showed that: the carbon sources, concentration, nitrogen sources, nitrogen sources （yeast extract, yeast extract） content and metal ions on pollutant production rate has a significant effect （P <0.05 ）, the interaction of carbon and nitrogen sources are relatively obvious, carbon and metal ions and nitrogen sources and metal ions interaction was not significant. The optimized process parameters: sucrose was 56.63 g / L yeast extract was （yeast extract concentration） 3.74 g / L, the metal ions with Mg2+, the yield of 61.2985 g/L.Similarly optimization of fermentation conditions on flask, and ultimately determines the optimal parameters are: 1% inoculums, fermentation temperature was 28℃, the liquid volume of 100mL, pH 5.5, at this time polysaccharide production was 61.092 g/L.（4）Based on the preliminary exploration about the fermentation conditions in 5L fermentator, obtaining the best process parameters: According to the 1% inoculation activation of 24h activation strain, Fermentation temperature is 28℃, the volume of liquid is 3 L, Air flow is 2 L/min, dissolve of oxygen do not lower 40%, speed of revolution is 200r/min, pH is 5.0 in the whole fermentation process. 7 days later, the final polysaccharide production was 67.63 g/L, it is 1.103 times to shake flask fermentation yield.