The rheological properties of the fermentation broth during pullulan produc
tion from synthetic medium by Aureobasidium pullulans P56 in a stirred tank
fermenter were investigated. The mycelial forms and the production of extr
acellular polysaccharide were responsible for the non-newtonian flow behavi
our of the fermentation broth. The rheological behaviour can be characteriz
ed by a power law type of equation. The relationship shear rate/sheat stres
s and shear rate/apparent viscosity showed a non-newtonian behaviour of the
fermentation broth. The power law index was found to be a sensitive factor
for the indication of the pseudoplastic behaviour of the broth.