Production, immobilization and thermodynamic studies of free and immobilized Aspergillus awamori amylase

Abstract

Enzyme cost, stability and its thermodynamic characteristics are the main criteria for industrial use. In this study, Aspergillus awamori amylase was constitutively produced using various agro-industrial wastes. Olive oil cake gave the highest activity (230U/g). The amylase was partially purified to 2.81-fold purification. Immobilization was achieved using different carriers by covalent binding. The novel carrier Ca+2 alginate (Alg) starch (St)/polyethyleneimine (PEI)/glutaraldehyde (GA), showed the highest operational stability and was selected for further studies. The optimum temperature for the free and immobilized form was 50°C and 55–60°C, respectively. The immobilization process had a major role in improving enzyme thermal stability. In comparison to free enzyme, the immobilized form showed the highest optimum temperature, activation energy (Ea) and deactivation rate constants (kd). Also, t1/2, D-values (decimal reduction time), change in enthalpy (ΔH° kJmol−1), and Gibbs free energy (ΔG°) increased and was higher than the native enzyme within 50–80°C. The magnitude of negative value of entropy (ΔS° kJmol−1) for immobilized enzyme was negative for the free and immobilized enzymes revealing that native form of enzyme was in more ordered state. Km and Vmax values were slightly affected by the temperature variations 40–70°C.