Effects of carbon/nitrogen ratio, dissolved oxygen and impeller type on gellan gum production in Sphingomonas paucimobilis

Abstract

Among exopolysaccharides, gellan gum is used widely as a gelling agent and food additive, and its commercial market is rapidly increasing. To optimize the fermentation production of gellan gum in Sphingomonas paucimobilis ZJU3108, carbon/nitrogen (C/N) ratio, dissolved oxygen (DO) and impeller type were studied. The C/N ratio, rather than the absolute concentration of carbon or nitrogen source, was found to be the major factor affecting cell growth. A C/N ratio above 20.7 had no significant effect on gellan gum production. Although the final yield of gellan gum increased with C/N ratio increase, the glucose to gellan gum conversion rate decreased. This was due to the high viscosity, which caused oxygen limitation from 16 h to 40 h in the inhomogeneous broth. Due to low stationary phase oxygen demand, the effect of DO on biomass and gellan gum production was reduced. A simple DO control strategy was developed to maintain 30% DO for the first 32 h cultivation, followed by anaerobic conditions for the remaining 8 h. Comparison of different impellers suggested that an anchor impeller with impeller diameter of 11.0 cm (D* = 11.0 cm) was suitable for high yields of high molecular weight gellan gum. These studies simplify production of gellan gum by fermentation and improve its yield.