Rheological and morphological characterization of the culture broth during exopolysaccharide production by Enterobacter sp.

Enterobacter sp. was grown on glycerol byproduct from the biodiesel industry for the production of a value-added exopolysaccharide (EPS). The culture broth was characterized in terms of its morphological and rheological properties throughout the cultivation run. Microscopic observations revealed the formation of cell aggregates surrounded by the EPS at the beginning of the cultivation run, while, at the end, aggregates were reduced and an EPS matrix with the cells embedded in it was observed. The apparent viscosity of the culture broth increased over time, which was attributed to the increase of the EPS concentration in the first period of the cultivation run. However, in the final stage, the creation of new polymer interactions within the complex culture broth was likely the reason for the viscosity increase observed, since there was not a significant variation of the EPS concentration, average molecular weight or chemical composition. The broth presented a Newtonian behavior at the beginning of the run, changing to pseudoplastic as the EPS concentration increased, and revealed to follow the Cox–Merz rule.