Application of fractional factorial design to levan production by Zymomonas mobilis

Levan is a non-toxic, biologically active, extra cellular polysaccharide composed solely by fructose units. Optimization of levan production by Zymomonas mobilis strain ZAG-12 employing a 2(4-1) 1 fractional factorial design was performed to analyze the influence of the temperature (20, 25 e 30 degrees C) agitation (50, 75 e 100 rpm), and the initial concentrations of both sucrose (150, 200 e 250 g. L-1) and yeast extract ( 2.0, 3.5 e 5.0g. L-1) on final levan concentration. Aerobic fermentation was performed batchwise in 500mL Pyrex flasks for 72 hours. Biomass, ethanol, levan and sucrose were determined at beginning and also at end of the fermentations. The experiments showed that the final levan concentration depended on initial sucrose concentration, temperature and agitation velocity and that the initial concentration of yeast extract did not influence levan production. However, when the production of ethanol and biomass were considered, it became evident that yeast extract was a significant variable. The best conditions for levan production occurred at 100 rpm agitation, 20 degrees C and 250g. L-1 of initial sucrose resulting in 14.67g. L-1 of levan.