Response surface methodology (RSM) and centre composite design (CCD) were used to optimize immobilization of beta-galactosidase (BGAL) from Pisum sativum onto two matrices: Sephadex G-75 and chitosan beads. The immobilization efficiency of 75.66% and 75.19% were achieved with Sephadex G-75 and chitosan, respectively. There was broad divergence in physico-chemical properties of Sephadex-PsBGAL and chitosan-PsBGAL Chitosan-PsBGAL was better suited for industrial application based on its broad pH and temperature optima, higher temperature stability, reusability etc. Sephadex-PsBGAL and chitosan-PsBGAL showed much variation in their catalytic properties with respect to soluble enzyme. About 50% loss in activity of Sephadex-PsBGAL and chitosan-PsBGAL were observed after 12 and 46 days at 4 degrees C, respectively. Chitosan-PsBGAL showed higher rate of lactose hydrolysis present in milk and whey at room temperature and 4 degrees C than Sephadex-PsBGAL. In both cases, lactose of milk whey was hydrolyzed at higher rate than that of milk. (C) 2008 Elsevier Ltd. All rights reserved.