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

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 (Km) and the maximum rate of starch hydrolysis reaction (Vmax) were also calculated according to the Lineweaver-Burk plot. It was found that the Km and Vmax values with immobilized enzymes were larger than those with free enzymes, except for the Vmax value with glucoamylase.