Improved stability of Aspergillus niger inulinase (ANI) by covalent immobilization using glutaraldehyde on carboxylated multiwalled carbon nanotubes (c-MWCNTs)

In this study, ANI was immobilized on c-MWCNTs via the crosslinker reagent glutaraldehyde via a covalent bonding method with 100% binding yield and 82.6% activity yield. While immobilization did not change the optimum pH range (5.5–6.5) or optimum temperature range (55–65°C) of the enzyme, it improved the pH and thermal stability of the enzyme. The V _max values obtained for the free and immobilized enzymes were 671.1 µmol/mg/min and 568.2 µmol/mg/min, respectively, and the K _m values were 662.3 g/L and 699.3 g/L, respectively. The initial activity of the immobilized enzyme was maintained under optimum activity conditions for 20 consecutive uses and for 30 days under optimum storage conditions. Using immobilized ANI, FOS syrup was obtained at a concentration of 546.9 g/L from 600 g/L inulin solution with a 91.15% conversion ratio. Consequently, the immobilized ANI enzyme obtained in this study can be used for the production of FOS from inulin in industry.