The effect of particle size of carboxylated carbon nano tubes on immobilization efficiency of Aspergillus niger inulinase enzyme

This thesis study is aimed to investigate the effect of particule dimension of carboxylated multi-walled carbon nanotubes (c-MWCNT) on the immobilization of Aspergillus niger inulinase (ANI) enzyme. ANI was immobilized on different c-MWCNTs by adsorption method. By optimizing the immobilization conditions, 100% binding yield and 89.35% activity yield were obtained with c-MWCNT that has 48-78 nm diameter. Free ANI (SANI) and immobilized ANI (IANI) were characterized by determining the optimum pH, optimum temperature, pH stability, thermal stability and Michaelis-Menten Constants (Km and Vmax). While the optimum pH range expanded from (5.5-6.5) to (3.5-7.5), the optimum temperature range was expanded from (55-65 oC) to (50-75 oC). The pH and thermal stabilities of ANI were increased after immobilization. It was observed that IANI more stable than SANI at all pH range and all temperature range, tested. Immobilization reduced the enzyme's maximum velocity (Vmax) and affinity for inulin as a substrate. Vmax values for SANI and IANI were calculated as 671.1 μmol/mg.min and 602.4 μmol/mg.min, respectively, while Km values were calculated as 662.3 g/L and 689.7 g/L, respectively. When the Km increased, affinity of enzymes for the substrate is decreased. The immobilized enzyme saved its initial activity under optimum activity conditions for 20 consecutive batch uses. The immobilized enzyme maintained its initial activity for 30 days under storage conditions (stored within a 0.1 M sodium phosphate buffer solution which its pH 6.0 at +4 °C in the refrigerator.) until next use. As a result, it can be said that the immobilized enzyme obtained in this study can be used for industrial applications.