Comparative study in kinetics and thermodynamic characteristics of immobilized caseinase on novel support from basalt by physical adsorption and covalent binding

Aspergillus niger WA 2017 caseinase was immobilized on a novel support prepared from raw material (basalt) by physical adsorption (PA) and covalent binding (CB). A physicochemical characterization of the more appropriate (glass-ceramic with particle size >= 1.0 mm) was performed by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). One-factor-at-a-time (OFAT) experiments and the response surface methodology (RSM) were used to optimize the immobilization conditions for the maximum immobilization yield (IY %) and to understand the importance and interaction of the affected factors. Under optimized conditions the IY was increased by 2.4 and 1.6-fold, respectively for PA and CB caseinase. Compared to PA caseinase, CB caseinase showed the higher activation energy (Ea), half life time (t(1/2)), decimal reduction time (D-value), activation energy for denaturation (Ed) and Michaelis constant (Km). The thermodynamic parameters for irreversible inactivation indicated that enthalpy (Delta H degrees), Gibbs free energy (Delta G degrees) and entropy (Delta S degrees) were higher for CB caseinase than that for PA caseinase within 50-70 degrees C. Caseinase supported on GC particles by PA and CB retained 21.3 and 57.5%, respectively of its initial activity after 7 consecutive cycles.