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 f or the cultivation of Aspergillus awamori on synthetic medium in stirr ed tank and airlift tower loop reactors. The influence of the stirrer speed on the fungal morphology and on the xylanase production were inv estigated in the stirred tank reactor. With increasing stirrer speed t he pellet size decreased. The highest xylanase activity was obtained a t intermediate stirrer speed. The influence of the initial phosphate c oncentration 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 concentrati on hollow pellets with 7 mm in diameter were observed. The fast decrea se of the cell mass concentration in large pellets was caused by cell lysis. The highest xylanase activities were obtained with low phosphat e 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 ti me and the morphology. High carbon recoveries were obtained for the cu ltivations in the stirred tank and airlift tower loop reactors with di fferent fungal morphologies. (C) 1997 Elsevier Science B.V.