Immobilization of Aspergillus fumigatus α-Amylase via Adsorption onto Bentonite/Chitosan for Stability Enhancement

Abstract

Stability enhancement attempted in this study demonstrated that significant improvement in the stability of the α-amylase isolated from Aspergillus fumigatus was achieved by immobilizing the enzyme on a bentonite/chitosan hybrid matrix using the adsorption method. Centrifugation was used to isolate the α-amylase, which was then refined using (NH4)2SO4 salt precipitation and dialysis. The purity of the α-amylase improved 19.40 times when compared to that of the crude extract. The optimal temperature for free α-amylase is 50˚C, while the optimum temperature for α-amylase/bentonite/chitosan is 60˚C. The KM value of α-amylase/bentonite/chitosan was 1.69 ± 0.08 mg mL-1 substrate and the Vmax value was 52.32 ± 3.29 µmol mL-1 min-1, whereas for free α-amylase, the KM value of 2.56 ± 0.09 mg mL-1 substrate and the Vmax value of 3.78 ± 0.09 µmol mL-1 min-1 were obtained. The ΔGi value of free α-amylase is 102.68 ± 0.30 kJ mol-1 and the t½ is 21.23 ± 0.23 min, whereas the ΔGi value of α-amylase/bentonite/chitosan is 104.43 ± 0.00 kJ mol-1 and the t½ is 94.29 ± 0.91 min. The higher values of ΔGi and t½ demonstrated that α-amylase/bentonite/chitosan has better stability than that of free α-amylase. Another important finding is that α-amylase/bentonite/chitosan was able to retain their activity as high as 47.61 ± 0.53% after six recycles, indicating that the enzyme has the potential to be used in industry.