Immobilization of inulinase from Aspergillus niger NCIM 945 on chitosan and its application in continuous inulin hydrolysis

Crude inulinase from Aspergillus niger (A. niger) NCIM 945 was immobilized on chitosan beads using a two-step covalent immobilization approach. Immobilization conditions were optimized to achieve 86% immobilization efficiency with 83 inulinase activity units/g of wet support. At lower pH values (pH 2.5 and 3) the relative activity of the immobilized enzyme was higher than the free enzyme. Also, thermal stability increased considerably at 50 and 60 °C after immobilization on chitosan beads. The Km values of free and immobilized inulinase were 0.25 and 0.21 mM, respectively and Vmax values were close to 0.2 μM/min/mL. In a continuous packed bed column 5% w/v inulin was completely hydrolyzed at optimized conditions of flow rate (0.1 mL/min) and incubation temperature (60 °C). This resulted in volumetric productivity of 68 g/L/h. This simple and efficient covalent immobilization approach has a potential for continuous inulin hydrolysis.