Activities, stabilities, and reaction kinetics of three free and chitosan–clay composite immobilized enzymes

Abstract

Thermal and pH stabilities of free and immobilized α-amylase, β-amylase, and glucoamylase were compared, in which immobilization support was prepared by equal weights of chitosan and activated clay and were cross-linked with glutaraldehyde. It was shown that the relative activities of immobilized enzymes are higher than free enzymes over broader pH and temperature ranges. α-Amylase and glucoamylase immobilized on composite bead maintained 81% of their original activities after 50 times of repeated use. Thermal deactivation energies of free and immobilized enzymes were obtained according to the Arrhenius’ equation. The Michaelis constant ( K m) and the maximum rate of starch hydrolysis reaction ( V max) were also calculated according to the Lineweaver–Burk plot. It was found that the K m and V max values with immobilized enzymes were larger than those with free enzymes, except for the V max value with glucoamylase.