Esterification by Rhizopus delemar lipase in organic solvent using sugar ester reverse micelles

The esterification of oleic acid with octyl alcohol catalyzed by Rhizopus delemar lipase was investigated in reverse micellar system of sugar ester DK-F-110. High initial reaction rate was obtained by preparing the micellar organic phase with extremely low water content. The maximum rate was obtained at a W-0 (= [H2O]/[amphiphile]) of 2.5. The highest reaction rate occurred at pH 6. With decreasing DK-F-110 concentration, the initial reaction rate was slightly decreased. The optimal temperature for lipase activity was around 313 K (40 degreesC). Apparent activation energy of the esterification in the system was 43.7 kJ/mol. The lipase showed 40% of its esterification activity after 28 h incubation in the DK-F-110 micellar organic phase. The reaction kinetics in this system were recognized as ping-pong bi-bi mechanism. From a Michaelis-Menten analysis, apparent kinetic parameters were determined. The turnover number of the DK-F-110 system was larger than that of the sodium bis(2-ethylhexyl)sulfosuccinate (AOT) system. (C) 2001 Elsevier Science B.V. All rights reserved.