INTERESTERIFICATION OF PALM MIDFRACTION AND STEARIC-ACID WITH RHIZOPUS-ARRHIZUS LIPASE IMMOBILIZED ON POLYPROPYLENE

Lipase from Rhizopus arrhizus was immobilized by physical adsorption o n hydrophobic microporous polypropylene supports with a specific activ ity of 0.15 U/mg-support. The immobilized enzyme catalyst was employed for the interesterification of palm midfraction and stearic acid in t he presence of n-hexane and low water content. The effects of reaction parameters which include water content, enzyme loading, temperature, the molar ratio of stearic acid to palm midfraction and substrate conc entration were examined. Immobilized lipase retains nearly the same si gma value as that of fresh immobilized lipase after 68 days of storage at 4 degrees C. The half-life of the immobilized lipase with 0.2%w/v water content is ca.7 days.