RESUMO
This study compares two solvents for enzymatic reactions: supercritical carbon dioxide (SCCO(2)) and organic solvent (n-hexane). The model reaction that was chosen was the esterification of oleic acid by ethanol catalyzed by an immobilized lipase from Mucor miehei (Lypozyme). The stability of the enzyme appeared to be quite good and similar in both media but was affected by the water content. Partition of water between solvents and immobilized enzyme has been calculated from experimental adsorption isotherms. The water content of the solid phase has a dramatic influence on the activity of the enzyme and its optimum value for activity was about 10% (w/w) in both media. A kinetic study enabled a Ping-Pong Bi-Bi reaction mechanism with inhibition by ethanol to be suggested. Despite some differences in kinetic constants, activity was in the same range in both media. Hypotheses for explaining the kinetic constant variations have been proposed and particular attention has been paid to the pH effects.
RESUMO
The kinetic of the esterification of oleic acid by ethanol catalyzed by immobilized lipase of Mucor miehei in n-hexane as a solvent has been completely studied. The kinetics of the reaction are suggested to agree with a Ping-Pong Bi Bi mechanism in which only inhibition by excess of ethanol has been identified. Values of all apparent kinetic parameters were computed. No evidence of any significant external diffusional limitation which could account for these values has been detected. Optimization of water content through distribution ratio of water between solvent and support was examined.
