Textural and Structural Characterizations of Mesoporous Chitosan Beads for Immobilization of Alpha-Amylase: Diffusivity and Sustainability of Biocatalyst

Abstract

In the present study, textural and structural characterizations of chitosan bead for immobilization of alpha amylase were studied in detail by N₂ adsorption–desorption, Microspore Analysis (MP), Barrett–Joyner–Halenda (BJH) plots and Field Emission Scanning Electron Microscope (FESEM) observations. Pore structure observation revealed chemical activation of chitosan bead by glutaraldehyde can change both the isotherm type of adsorption and pores shape. In consistence with textural analysis, the high value of pore volume distribution with range of mesopores region indicated the porosity of activated chitosan bead was uniformly increased. Intra-particle diffusion model indicated that 97.6% of amylase was adsorbed inside the mesopores of activated chitosan bead owing to increase in k_id(rate constant) and reduce of boundary layer effect on diffusion process. In addition, the stability experiments (pH, storage and thermal stability), enzyme leakage, Ca²⁺ and salt concentration effects were evaluated for immobilized amylase and compared with its free form. Ca²⁺ concentration of 1 mM shows an excellent impact on relative activity of amylase in its free and immobilized form. NaCl experiments indicated that 84% of amylase was covalently immobilized on activated chitosan beads. Further, the Michaelis–Menten kinetic coefficients, K_m (~0.4mg/ml) and, V_max(~227 U/mg Enzyme), point out strong affinity and high activity of immobilized enzyme