The Stability Improvement of Aspergillus fumigatus α-Amylase by Immobilization onto Chitin-Bentonite Hybrid

Enzyme immobilization is a powerful method to improve the stability, reuse, and enzymatic properties of enzymes. The immobilization of the α-amylase enzyme from Aspergillus fumigatus on a chitin-bentonite (CB) hybrid has been studied to improve its stability. Therefore, this study aims to obtain the higher stability of α-amylase enzyme to reduce industrial costs. The procedures were performed as follows: production, isolation, partial purification, immobilization, and characterization of the free and immobilized enzymes. The CB hybrid was synthesized by bentonite, chitin, and glutaraldehyde as a cross-linker. The free enzyme was immobilized onto CB hybrid using 0.1 M phosphate buffer pH 7.5. The free and immobilized enzymes were characterized by optimum temperature, Michaelis constant (K(M)), maximum velocity (V(max)), thermal inactivation rate constant (k(i)), half-life (t(1/2)), and transformation of free energy because of denaturation (ΔG(i)). The free enzyme has optimum temperature of 55°C, K(M) = 3.04 mg mL(−1) substrate, V(max)=10.90 μmolemL(−1)min(−1), k(i) = 0.0171 min(−1), t(1/2) = 40.53 min, and ΔG(i) = 104.47 kJ mole(−1). Meanwhile, the immobilized enzyme has optimum temperature of 60°C, K(M) = 11.57 mg mL(−1) substrate, V(max)=3.37 μmolemL(−1)min(−1), k(i) = 0.0045 min(−1), t(1/2) = 154.00 min, and ΔG(i) = 108.17 kJ mole(−1). After sixth cycle of reuse, the residual activity of the immobilized enzyme was 38%. The improvement in the stability of α-amylase immobilized on the CB hybrid based on the increase in half-life was four times of the free enzyme.