Stability and reactivity of acid phosphatase immobilized on composite beads of chitosan and ZrO₂ powders

Equal weights of chitosan and ZrO₂ powders were mixed in acetic acid solution to prepare the composite beads. They were then cross-linked with glutaraldehyde and stored with and without freeze-drying before use. The physicochemical properties of acid phosphatase immobilized on four types of the supports (wet/dried pure chitosan beads, wet/dried chitosan-ZrO₂ composite beads) were compared. Various parameters including glutaraldehyde concentration, cross-linking time, enzyme concentration, temperature, and pH on enzyme activity were studied. It was shown that the activity yield of enzyme immobilized on the dried chitosan-ZrO₂ beads was the highest, and the relative activity remained above 83.2% within pH 2.9-5.8. Regardless of wet or dried beads, the Michaelis constant K_M and maximum rate of reaction V_max of acid phosphatase immobilized on chitosan-ZrO₂ composite beads were 1.8 times larger than those on pure chitosan beads. Of the four immobilized enzymes, the use of wet chitosan-ZrO₂ bead as the support showed the lowest thermal deactivation energy (78 kJ mol^-1).