Porous chitosan beads of superior mechanical properties for the covalent immobilization of enzymes

Abstract

Porous chitosan beads of superior mechanical properties were produced via a two stepped treatment process. First, the chitosan ionotropic gelation solution was supplemented with Na2CO3, which acted as a porogen. Afterwards, the beads were chemically cross-linked with glutaraldehyde. This treatment also caused the produced porous chitosan beads to acquire higher observed activities of immobilized β-d-galactosidase (β-gal). The observed activities of the β-gal immobilized onto the 0.2M and the 0.35M Na2CO3 treated beads were 1.63 and 1.91 fold respectively, higher than the activity offered by the control beads. Nevertheless, both the control beads and the 0.2M Na2CO3 beads caused the optimum pH range of β-gal to shift from 4.6–5.1 to ∼2.7–5. The enzyme’s optimum temperature shifted from 55 to 60°C after its immobilization onto the control chitosan beads whereas the β-gal immobilized onto the 0.2M Na2CO3 chitosan beads exhibited a temperature optimum of 55–60°C. The reusability study revealed the superiority of the 0.2M Na2CO3 treated beads which retained 59.1% of their initial activity during the 13th enzymatic cycle. On the other hand, the control chitosan beads were fragmented and lost their activity after only four enzymatic cycles.