Influence of fermentation hydrodynamics on gellan gum physico-chemical characteristics

The physico-chemical characteristics of gellan gum polymers produced using various impeller systems and different aeration conditions were studied. The degree of esterification, average molecular weight (M(w)), intrinsic viscosity ([eta]), and molecular weight distribution of the highly clarified polymers were found to be greatly dependent upon the fermenter hydrodynamics. For example, the highly homogeneous conditions of fermentation obtained with a helical ribbon impeller led to a gellan exhibiting a molecular weight twice as high as that prepared from the most heterogeneous fermentations obtained with Rushton turbines, The composition of the polymer itself is also affected since the degree of esterification of gellan can vary with the fermentation conditions. Finally, a Mark-Houwink relation (i.e. [eta] = KM(w)(a)) has been tentatively established for the deesterified gellan polymer.