Immobilization studies and biochemical properties of free and immobilized Rhizopus oryzae lipase onto CaCO3: A comparative study

Lipase from Rhizopus oryzae (ROL) was immobilized by physical adsorption onto CaCO3. The immobilization yield was more than 95% during 30 min and corresponds to the loading of 2570 IU/g support. The optimum temperature for both free and immobilized lipase activities was 37 °C. After 24 h of incubation at 50 °C, the immobilized ROL maintained 67% of its initial activity, while the free enzyme was completely inactivated. Therefore, the immobilization seems to improve highly the lipase thermal stability. Besides, the immobilized lipase showed a higher stability than free lipase when stored at 4 °C. The kinetics of the olive oil hydrolysis by the immobilized lipase showed that the hydrolysis rate reached the maximum within 15 min of incubation with the substrate. The hydrolytic activity of the immobilized lipase on olive oil used as substrate was higher than that of the free lipase form, as shown by a higher amount of released free oleic acid. We studied the ethyl oleate ester (biofuel) synthesis by immobilized and free ROL. The conversion yield of this ester was also found to be higher with the immobilized lipase than with the free lipase form (83% versus 6%). Furthermore, electron microscopy allowed us to observe that the morphology of the surface of CaCO3 after the adsorption of ROL showed a large contact area of multipoint attachment with the enzyme.