Submerged production of pectolytic enzymes by Aspergillus niger: effect of different aeration/agitation regimes

Abstract

The production of a pectolytic enzyme complex in a 10-l strirred tank bioreactor was studied using the Aspergillus niger mutant A 138. A time course of the fermentation showed that the enzyme synthesis is not associated with growth. Maximal activity was reached after 95 h and from that time on it remained constant. Redox potential and pH values proved to be valuable indicators of the initiation and end of enzyme synthesis. The specific morphology of the fungus, growing in distinct pellets with long peripheral hyphae, resulted in a very dense and viscous broth. It represented a special problem for heat and mass transfer. An attempt was made to overcome this problem by different agitation and aeration regimes. These parameters did not change the morphology but had a marked influence on enzyme synthesis. When, at the time of maximal growth rate, aeration was increased from 0.5 vvm to 1.2 vvm, and agitation from 300 rpm to 500 rpm, the depectinizing activity was doubled in comparison with the results obtained when 0.5 vvm and 300 rpm were used throughout fermentation. When more intensive agitation was employed from the beginning of the process, the depectinizing activity was lowered from 60 to 45 units/ml, together with the viscosity and polygalacturonase activity. However, at the same time, the pectin esterase and pectinlyase yields increased. The required fermentation time was reduced from 95 to 65 h.