Effect of stirring and pump on membrane processing of Aspergillus carbonarius culture broth for polygalacturonase

Stirring effect in a stirred membrane cell and the type of pumping action in a cross-flow filtration system were assessed from the viewpoint of recovery of polygalacturonase (PG) from Aspergillus carbonarius culture broth. PG and protein loss increased with stirring speed (shear stress) as well as processing time under simulated conditions of a stirred membrane cell. When the stirring conditions did not exceed the critical speed of 400 rpm, corresponding to a shear stress of 2.1 Pa, higher recoveries of PG (88%) and protein (96%) were obtained. Processing culture broth using a gear pump increased PG and protein loss with processing time and resulted in 71% PG and 54% protein loss after 3 h of pumping, while the loss of PG and protein was negligible when a peristaltic pump was used. The results revealed that processing shear sensitive enzymes like PG required determination of critical shear stress and selection of suitable pump to prevent losses in the membrane process.