Surfactant interference on lipase catalysed reactions in microemulsions

The hydrolysis of palm oil with lipase as a catalyst was carried out in two different microemulsion systems. One system was based on a nonionic surfactant, pentaethylene glycol monododecyl ether (C12EO5) and the other system was based on an anionic surfactant, sodium bis(2-ethylhexyl)sulphosuccinate (AOT). The yield of free fatty acid produced by the reaction was found to be much lower in the C12EO5 system compared to the AOT system. Radiochromatography showed that the low yield was due to enzymatic esterification on the nonionic surfactant. Kinetic measurements showed that the reaction rate is about ten times faster in the AOT based microemulsion than in the nonionic system. Differences in the microemulsion structure and interfacial tensions in the two systems were found to be of no significant importance for explaining this difference. Kinetic data of mixed surfactant microemulsions indicated that the observed difference in the reaction rates of the AOT and the C12EO5 microemulsion systems was a consequence of the C12EO5 surfactant competing with the substrate for the active site of the enzyme. The reason why C12EO5 surfactant inhibited the reaction, and AOT surfactant did not, was found to be related to differences in the structures of the hydrophobic part of the surfactant.