EFFECT OF MIXING AND MASS-TRANSFER CONDITIONS ON GELLAN PRODUCTION BYAUROMONAS-ELODEA

The effect of fermenter hydrodynamics on gellan fermentation kinetics and theological properties of the culture broth were studied using var ious mixing and mass transfer conditions. Different impeller systems, such as a helical ribbon (HR250), Rushton turbines (RT600) and a pitch ed-blade turbine combined with an in-flow turbine (CT600) were tested along with extra oxygen supply (HR2500x) or reduced nitrogen amount in the culture medium (HR250N). The highest gellan productions (around 1 3 g/l of native gellan) were observed when oxygen transfer capacity wa s good (i.e. HR2500x, HR250N, CT800 and RT600). The volumetric power i nput was found to be a good tool to evaluate the gellan synthesis prog ress especially with the helical ribbon impeller where no stagnant zon e formation occurred. Macromixing conditions affected the theological properties of the final broth. For instance, the highly heterogeneous conditions (with RT600) led to a more sheat-thinning broth with a lowe r yield stress value than the most homogeneous conditions (with HR2500 x). Good correlations between yield stress value and gellan concentrat ion were established with respect to the fermentation pattern.