ESTERIFICATION AND INTERESTERIFICATION ACTIVITIES OF LIPASES FROM RHIZOPUS-NIVEUS AND MUCOR-MIEHEI IN 3 DIFFERENT TYPES OF ORGANIC MEDIA - A COMPARATIVE-STUDY

The esterification of oleic acid by ethanol using lipases from Rhizopu s niveus and Mucor miehei as catalysts was evaluated in microaqueous, biphasic (n-hexane-water) and surfactant-enriched biphasic systems con taining different amounts of water. The results showed that for R. niv eus lipase-catalyzed esterification in a microaqueous system, a water content corresponding to a water activity of 0.75 is optimal from a ki netic point of view. In biphasic systems, the influence of the water c ontent on the thermodynamics of the reaction and the effect of the int erfacial area between phases on the velocity of the biocatalysis were demonstrated. In addition, the water content was shown to influence th e velocity of the reaction in the surfactant-enriched biphasic system. It was also demonstrated that, from a kinetic point of view, both lip ases are by far more efficient in biphasic systems. From a thermodynam ic point of view, biphasic systems allow interesting esterification ra tes to be obtained whereas they were shown to be less suitable than th e microaqueous system to carry on interesterification reactions. (C) 1 998 Elsevier Science Inc.