Abstract: The kinetics of safflower oil hydrolysis catalyzed by a lipase from Aspergillus niger was investigated in a solvent-free medium and an AOT/isooctane/phosphate buffer microemulsion medium. The activation energy of the reaction was calculated from the Arrhenius plot to be 32.205 and 7.391 kJ/mol in the solvent-free medium and the microemulsion medium, respectively. The denaturation of the lipase in microemulsion was faster than that in the solvent-free medium. The apparent Michaelis constant Km was 0.135 mol/L in the solvent-free medium and 0.101 mol/L in the microemulsion medium. The experiment indicated that the inhibition of alcohol towards the lipase was reversible and competitive in both the solvent-free medium and the microemulsion medium. In addition, the inhibition by substrate appeared in these two systems when the substrate concentration exceeded 0.819 mol/L. The micelle catalysis theory and ester bond hydrolysis mechanism were used to explain the difference of lipase-catalyzed oil hydrolysis in the solvent-free medium and the microemulsion medium.

Key words: solvent-free medium, microemulsion medium, lipase, safflower oil, hydrolysis, kinetics