A torus reactor was used to perform hydrolysis of casein with a protease immobilized on beads. Chitosan beads with two different sizes were tested as immobilization matrices. The mechanical resistance of beads in the torus reactor was tested for different times and rotation speeds. Chitosan beads were considered to be suitable as an immobilizing support. The more stable hydrolysis rates in successive assays were obtained with the protease grafted onto the largest chitosan beads. The kinetics parameters of free and immobilized enzymes were determined and compared in batch stirred tanks and torus reactors. Immobilization decreased the enzyme activity to only 5% of the free enzyme activity. No significant differences for apparent kinetic constant (K-m) were observed between immobilized and free enzyme. The apparent reaction rate constant (V-max) was 25 times less with immobilized enzyme in the torus reactor than with free enzyme in the batch reactor. (C) 2004 Elsevier Ltd. All rights reserved.