Sodium bicarbonate‐gelled chitosan beads as mechanically stable carriers for the covalent immobilization of enzymes

The poor mechanical stability of chitosan has long impeded its industrial utilization as an immobilization carrier. In this study, the mechanical properties of chitosan beads were greatly improved through utilizing the slow rate of the sodium bicarbonate‐induced chitosan gelation and combining it with the chemical cross‐linking action of glutaraldehyde (GA). The GA‐treated sodium bicarbonate‐gelled chitosan beads exhibited much better mechanical properties and up to 2.45‐fold higher observed activity of the immobilized enzyme (β‐D‐galactosidase (β‐gal)) when compared to the GA‐treated sodium tripolyphosphate (TPP)‐gelled chitosan beads. The differences between the sodium bicarbonate‐gelled and the TPP‐gelled chitosan beads were proven visually and also via scanning electron microscopy, elemental analysis, and differential scanning calorimetry. Moreover, the optimum pH, the optimum temperature, the apparent K_m, and the apparent V_max of the β‐gals immobilized onto the two aforementioned types of chitosan beads were determined and compared. A reusability study was also performed. This study proved the superiority of the sodium bicarbonate‐gelled chitosan beads as they retained 72.22 ± 4.57% of their initial observed activity during the 13^th reusability cycle whereas the TPP‐gelled beads lost their activity during the first four reusability cycles, owing to their fragmentation. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:347–361, 2018