Production of Biopolymer Levan by Bacillus subtilis using Non-Ionic Surfactants

Levan, an exoploysaccharide, was produced by Bacillus subtilis and its yield was characterized as a function of saccharose concentration (10%) and fermentation time (96h).Under these conditions , after 60 h in saccharose medium, levan production reached 33.5 g/L .The results show that an increase in fermentation time caused a decrease in the levan production. The effect of nonionic surfactants on levan production was studied by the addition of 0.5 g/l surfactants to shake flask culture. The nonionic surfactants Tween 80, Tween 40 and Triton X-100 improved levan production and the maximum yield (48.8 g/l) was obtained with Tween -80 compared with that of the control fermentation. Central composite design (CCD) was used to determine the maximum levan production at optimum values for three process parameters (Tween 80 concentration, pH, and temperature) each at levels in a laboratory fermentor. The maximum levan yield (59.00g/l) was obtained with Tween 80 and at pH 7.0 and temperature 37°C. The results predicted by the design were found in good agreement (Y = 62.139) with the experimental results(Y=59.00) indicating the applicability of proposed model. The multiple regression analysis and ANOVA showed the individual and cumulative effect of pH and temperature and surfactant concentration on levan production indicating that the production increased with the increase of pH up to 7.0 , temperature 37°C and surfactant concentration (Tween 80) 0.875g/l. The effects of each variables represented by 3D surface plot, contour plot and optimized plot were helpful in predicting results by performing a limited set of experiments.