An extracellular xylanase was purified from Aspergillus niger DFR-5 up to absolute homogeneity using (NH4)(2)SO4 fractionation (30-65%), size exclusion (Sephadex G-100) and ion-exchange (DEAE-cellulose) chromatography. The preparation yielded a single peak in RP-HPLS confirming its purity. Molecular mass of xylanase as revealed by gel filtration and SDS-PAGE was similar to 32 kDa confirming its monomeric nature. Various kinetic parameters of xylanase towards thermo-inactivat on were calculated. Delta H degrees, Delta S degrees and Delta G of thermal denaturation suggested that enzyme undergoes significant processes of aggregation instead of unfolding during denaturation. A central composite rotatable design was used to study the interactive effects of temperature, pH and time on xylanase stability which revealed the existence of significant interactions between them. A regression equation was developed to deduce the residual activity of xylanase under any conditions of experimental parameters within the domain. The findings will be useful while applying the enzyme in different juice clarification where pH varies considerably. (c) 2010 Elsevier Ltd. All rights reserved.