Exopolysaccharide production by Rhizobium radiobacter using constant impeller tip speed methodology

Exopolysaccharides (EPSs) have many potential uses in several fields. However, the cost of production of many exopolysaccharides is disadvantageous and the labour requirement is costly. Apart from the use of exopolysaccharides as a food additive, they also have increasingly important applications in sectors such as medicine and cosmetics.

This study aimed to scale up exopolysaccaride production by Rhizobium radiobacter from 500 mL Erlenmeyer to 2000 mL in a stirred tank bioreactor using constant impeller tip speed methodology. Rhizobium radiobacter, obtained from the American Type Culture Collection (ATCC) in a total of 19358 strains, was used to produce exopolysaccarides. The cells were grown in 30 °C with a pH value of 5.5 for 96 h at 238 rpm in the bioreactor and at 180 rpm in Erlenmeyer. The 3.5-dinitrosalicylic acid (DNS) assay and phenol-sulphuric acid method were used to determine the reducing sugar and total sugar levels, respectively.

The biomass produced in the bioreactor was found to be 5.48±0.02 g/L, which was 13% better than that produced in the flask. On the other hand, an exopolysaccharide yield of 12.38±0.01 g/g was obtained in the bioreactor, and an increase of 7% was recorded when compared with Erlenmeyer production.

For EPS production, cost-effective conditions were determined according to this process in order to both increase product efficiency and reduce production costs. In addition, in order to increase product quantity and efficiency, processes with shorter production times can be designed and appropriate environmental conditions can be provided.