Production of xylanase by Aspergillus awamori on synthetic medium in stirred tank and airlift tower loop reactors: The influence of stirrer speed and phosphate concentration

The interrelations between various process parameters were evaluated for the cultivation of Aspergillus awamori on synthetic medium in stirred tank and airlift tower loop reactors. The influence of the stirrer speed on the fungal morphology and on the xylanase production were investigated in the stirred tank reactor. With increasing stirrer speed the pellet size decreased. The highest xylanase activity was obtained at intermediate stirrer speed. The influence of the initial phosphate concentration on the morphology and enzyme activity was investigated in the airlift tower loop reactor. At low phosphate concentration loose pellets with 6 mm in diameter, at intermediate phosphate concentration dense pellets with 4 mm in diameter and at high phosphate concentration hollow pellets with 7 mm in diameter were observed. The fast decrease of the cell mass concentration in large pellets was caused by cell lysis. The highest xylanase activities were obtained with low phosphate concentration. The xylanase formation was repressed by the presence of glucose. The spore concentration influences the morphology as well. The composition of the fungal cell mass depends on the cultivation time and the morphology. High carbon recoveries were obtained for the cultivations in the stirred tank and airlift tower loop reactors with different fungal morphologies.