A cyclic batch enzyme membrane reactor (CBEMR) incorporating an 8000-Da polyethersulphone membrane was intended for enhancing the enzyme use in the production of a whey protein hydrolysate. The operation of the CBEMR comprises three consecutive stages: (i) proteolysis, (ii) ultrafiltration and (iii) enzyme recycle and re-use. A mechanistic mathematical model comprising zero-order kinetics for the hydrolysis and second-order deactivation for the enzyme was proposed and validated through experiments. Two alternative operation modes were proposed for the CBEMR: isothermal versus non-isothermal operation. The performance of both modes was assessed in terms of enzyme consumption and number of enzyme uses versus the productivity required. Furthermore, the optimisation of both modes was carried out, comparing their optimal operation as enzyme consumption. First, the optimal number of enzyme uses is a function of the productivity required for the CBEMR. The best isothermal operation of the CBEMR yields an optimal number of enzyme uses equal to 4 at 59.7 degrees C for productivity values below 0.59 h(-1). That means a maximal saving of enzyme of 18% against a traditional discontinuous batch reactor. Secondly, the non-isothermal optimal operation allows us to improve the yield in comparison to the isothermal operation. As a matter of fact, some additional saving can be achieved (up to 11%). (C) 2009 Elsevier Ltd. All rights reserved.