Esterification and Transesterification Catalysed by Cutinase in Reverse Micelles of Ctab For the Synthesis of Short Chain Esters

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Abstract
Reverse micelles formed using the cationic surfactant, hexadecyltrimethylammoniumbromide (CTAB) were applied as a reaction medium for esterification and transesterification (alcoholysis) reactions catalysed by a recombinant lipolytic enzyme, cutinase. Reactions were initially studied with either the alcohol substrate (acyl acceptor) or chloroform as cosurfactant. Chloroform was inhibitory to the enzyme. The enzyme demonstrated specificity towards short chain substrates and these were used to study some relevant parameters affecting specific activity. Optimum values for Wo, buffer concentration, pH, CTAB concentration and temperature were identified. Optimum value for Wo was the same for the two reactions whereas the effects of buffer concentration, pH, CTAB concentration and temperature were different. An optimum level of alcohol was identified, this was the same for both reaction types but the value was dependent on the alcohol. Fatty acids showed inhibitory effects at comparatively low concentrations compared to ester which showed no inhibitory effects at much higher concentrations. Reducing the enzyme concentration resulted in an increase of specific activity. Cutinase showed good stability in CTAB reverse micelles with hexanol as cosurfactant, (half life > 100 days), whereas in the presence of chloroform a rapid loss of much of the activity was observed in the first few hours.