Optimization Of Pullulan Fermentation Process By Response Surface Optimization

Pullulan is an extracellular microbial polysaccharide produced by strain of Aureobasidium pullulans. It is a natural water-soluble neutral glucan. Pullulan has excellent physical and chemical nature of colorless,tasteless,non-toxic,excellent film forming properties,water solubility,adhesion easy biodegradation and so on. Therefore it can be widely used in food, medicine, daily chemicals, building materials, paper, printing, electronics, tobacco and other industries. It is a new multi-functional biological product with great economic value. It can be easily degradation and have not an impact on the environment. Pullulan has been widely used in many fields, but it is very expensive and no large-scale production in China.Therefore, low-cost and high-yield strains of pullulan was obtained for industrial production firstly. The point is of making production costs reduced by corn syrup instead of yeast extract production. The fermentation conditions were optimized by Response Surface Optimization to increase pullulan production.In this study, Aureobasidium pullulans was used as the original strain.First of all, components of production medium by the single factor test. The single factor was molasses and sugar, corn syrup and yeast extract powder, NH4NO3 and (NH4) 2SO4, K2HPO4, and KH2PO4, NaCl, and MgSO4·7H2O. The results showed that the highest pullulan yield of single-factor conditions are as follows:sugar 1 lOg/L, corn steep liquor 4 g/L, NH4NO3 0.4 g/L, K2HPO4 2g/L, NaCl 1.5 g/L and MgSO4·7H2O 0.15 g/L. Then fermentation medium was studied for carbohydrate production by Plackeet-Burman. we can see the quality was infullenced significantly by NH4NO3 and K2HPO4. After, the maximum was determined by teepest ascent method.As the starting point of this experiment in this region is on top with application of corn syrup instead of yeast extract as nitrogen source, pullulan production, lower production costs. It was designed by application of SSAS software.response for NH4NO3, K2HPO4, and corn syrup three media components, and response surface analysis to determine the optimal medium ratio, the result is corn syrup 0.702g/L, NH4NO3 0.072 g/L, K2HPO40.138 g/L. At this point the highest pullulan yield was 23.22g/L. The confirmatory test, polysaccharide production was 23.58g/L to the predicted value. It can be seen, pullulan production and pullulan medium were improved.The different initial pH, fermentation temperature, fermentation time, inoculum size, medium volume, speed, and seed age were used in this single-factor test based on this optimized medium. The results showed that the highest pullulan yield of single-factor conditions were:initial pH 6.5, flask size 1000ml (loaded 50ml broth), inoculum 3%, seed age 72h, fermentation time and 6d, rotation speed 190r/min, the fermentation temperature of 29℃. In this experiment the polysaccharides yield was significant on the initial pH and fermentation time on the polysaccharides yield. The highest point was determined by the steepest ascent method. Finally, the optimal ratio of fermentation conditions was obtained.It was pH5.713 fermentation time 7.673d (184h)and pullulan production 25.30g/L. Confirmatory test, polysaccharide production was 25.59g/ L, close to the predicted value. Therefore, pullulan fermentation conditions were improved by response surface method.