Immobilization of Aspergillus terreus URM4658 inulinase in calcium alginate beads, evaluation of their biochemical characteristics and kinetic/thermodynamic parameters, and application on inulin hydrolysis.

Abstract

The present study aimed to immobilize an inulinase obtained from Aspergillus terreus URM4658 by entrapment in calcium alginate beads. The immobilization process yielded a satisfactory yield (92.72%) using 1.25% sodium alginate and 0.35 M CaCl₂ with a curing time of 90 min. The immobilized enzyme exhibited optimum pH and temperature at 7.0 and 60 °C, respectively, showing an increased affinity for the substrate after the immobilization process, as evidenced by the decrease in K_m compared to its free form. Moreover, the immobilized inulinase demonstrated good thermostability at 50 and 60 °C, as observed from the t_1/2 (649.83-420.84 min) and D-values (2158.67-1398.00 min), respectively. The immobilized biocatalyst also exhibited good reusability, maintaining 92.73% of residual activity after 10 reaction cycles and no loss of activity after 30 days of storage. A continuous inulin hydrolysis operation in a packed bed reactor was performed using the immobilized inulinase, and a maximum release of total reducing sugars and nystose of 3.27 and 0.82 g L^-1, respectively, was observed. The results indicate that an immobilized biocatalyst is a promising alternative for bioprocess involving inulin-rich feedstocks.