Pullulan fermentations by Aureobasidium pullulans with various initial ammonium ion concentrations were evaluated in a 2-L bioreactor The results demonstrated that A pullulans produced highest pullulan (23 1 g/L) when the initial ammonium sulfate was 7 at 5 g/L The purity of produced pullulan was 94 6% Seven gram per liter of ammonium sulfate produced more biomass due to the higher level of nitrogen source but the pullulan degrading enzyme activity was detected after the depletion of sucrose which reduced pullulan concentration From the results of fed-batch fermentation addition of 10 g/L of sucrose suppressed A pullulans from producing pullulan-degrading enzyme Additionally the modified-Gompertz equation demonstrated its generality to fit all pullulan production biomass production and sucrose consumption curves at three ammonium sulfate levels After incorporating the degrading factor a re-modified-Gompertz equation was obtained that can adequately describe the decrease of pullulan at the late fermentation stage (C) 2010 Elsevier Ltd All rights reserved