Immobilization of Rhizopus oryzae lipase on silica aerogels by adsorption: Comparison with the free enzyme

Rhizopus oryzae lipase (ROL) was immobilized by physical adsorption onto silica aerogels. The functional properties of immobilized lipase were determined and compared to the soluble lipase ones. The optimum temperature for both free and immobilized lipase activities was 37 °C. We found that the immobilization of R. oryzae lipase onto silica aerogels increased remarkably its stability at high temperatures and within a wade pH range. Besides the immobilized enzyme exhibited a high tolerance to apolar solvent and retained its fully activity in suspension after 4 months of storage at 4 °C. This immobilized biocatalyst is applied in n-butyl oleate synthesis by esterification of oleic acid with n-butanol, using hexane as an organic solvent. The best conversion yield of the ester butyl oleate was obtained with the immobilized lipase (80% versus 35% with the free lipase). This catalytic esterification has been carried on the presence of hexane at 37 °C with oleic acid to butanol molar ratio of 1:1 and 450 IU of immobilized lipase. Furthermore, the reuse of the lipase immobilized by adsorption allowed us to observe that its can achieved 12 successive cycles, without a significant loss of its catalytic activity. Such results revealed good potential for recycling under non-aqueous system.