Production of xylanase by Aspergillus awamori on complex medium in stirred tank and airlift tower loop reactors

Abstract

Aspergillus awamori was cultivated on complex medium containing wheat bran as sole carbon source in the precultures as well as in the main cultures in stirred tank and airlift tower loop reactors. The decomposition of the wheat bran particles by α-amylase and xylanase produced by the fungus was investigated by monitoring the enzyme activities, the CO 2 production rate, the concentrations of reducing sugars, glucose, xylose, phosphate and ammonium as well as by applying transmission electron microscopy. By applying synthetic medium in the preculture, the time lag was longer, the growth faster, the xylanase activity higher in the main culture, than by using wheat bran in the preculture. With increasing the stirrer speed the intimate contact between the pellets and the wheat bran was reduced, which caused a decrease of the growth and the xylanase production. By applying ground wheat bran, filamentous mycelium was formed, the growth and the substrate uptake rates increased, but the xylanase production decreased due to the less intimate contact between the fungus and the wheat bran. In the airlift tower loop reactor filamentous mycelium was formed due to the low specific power input. In spite of the high medium viscosity, high xylanase productivity was obtained. With ground wheat bran the particles were completely covered by filamentous mycelium, medium viscosity strongly increased and as consequence the growth and xylanase production decreased.