6533b824fe1ef96bd1280993

RESEARCH PRODUCT

Cultivation ofZymomonas mobilis 113 S at Different Mixing Regimes and their Influence on the Levan Formation

subject

description

The Zymomonas mobilis I 13 S strain was cultivated in a bioreactor with a working volume of 1.4 I at different stirring regimes in a 15% initial sucrose medium The levan obtained in the fermentation process was analyzed by gel filtration. Because the sucrose/biomass ratio in the fermentation broth decreased to below 300 g/g, the insufficient concentration of sucrose might have decreased the concentration of levan. Besides the growth characteristics of the population, the mixing intensity and flow structure were also found to influence the molecular mass of levan. At 600 rpm, the microorganisms produced levan with a molecular mass lower than at 300 rpm. The stirring of a fermentation broth with levan without cells at 300 rpm and 900 rpm showed changes in the molecular mass approximately at 20 kD and 5 kD. The size of eddies in the fermenter was supposed to determine the size of a levan molecule. Because the size of the eddy may be compared with that of a levan molecule, it explains the decline in the molecular mass of levan.