The technique of ultrafiltration can be applied for the recovery of biocatalysts in discontinuous as well as continuous reaction processes. The operation of ultrafiltration membrane reactors requires establishment of a certain shear rate along the membrane surface in order to prevent pronounced concn. polarization or even a gel layer of the enzyme to occur. Such a recirculating flow exposes the enzyme to shear forces and may be responsible for enhanced catalyst deactivation. The enzyme b-galactosidase [9031-11-2] from Aspergillus niger has been examd. with respect to its stability towards hydrodynamic stress. Drastic differences in the rate of enzyme denaturation were found by applying a variety of pumps. The observations may be explained by cavitational phenomena. Membrane reactor operation showed that there exists an optimum of shearing due to the adverse effects of concn. polarization and shear denaturation on the overall loss of catalytic activity. [on SciFinder (R)]