Utilization of rice hull ash as a support material for immobilization of Candida cylindracea lipase

Rice hull ash was heated in a muffle furnace at 700 degrees C for 2 h and metallic oxides were leached with 10% sulfuric acid. The acid-activated ash was then examined for immobilization of Candida cylindracea lipase. Immobilization was carried out by direct addition of the enzyme solution to the activated ash suspended in hexane. The immobilized lipase retained 30% of its hydrolytic activity, but thermal stability was greatly increased. Half-lives of the immobilized enzyme at 50, 60, and 70 degrees C were 45, 17, and 4 min, respectively. Optimal pH of the immobilized enzyme was 7.2. The apparent K-m and V-max for olive oil were 41 mM and 99.5 mu mol/h-mg solid, respectively.