Response surface methodology was used for process optimization to covalently immobilize xylanase on the surface of glutaraldehyde-alginate beads. The process, optimized with respect to minimum 'enzyme load', had an efficiency of >91%. An increase in K(m) (from 0.9 to 1.49%), V(max) (from 7092 to 8000 lU/ml). optimum pH (from 5 to 5.5) and temperature (from 40 to 45 degrees C) was recorded after immobilization. An improvement in thermostability of immobilized xylanase, judged by increased half-lives and D-values, was also observed. Thermodynamically, the better stability of immobilized xylanase could be attributed to the increase in enthalpy (Delta H) and free energy (Delta G) change after covalent attachment. The enzyme could be reused 5 times while retaining >85% of its original activity. The method of immobilization can overcome the problem of reduced permeability of xylan, a high molecular weight substrate, to its enzyme which is conventionally entrapped within the alginate beads. (C) 2011 Elsevier Ltd. All rights reserved.