Lipase-catalyzed synthesis of isoamyl butyrate: Optimization by response surface methodology

Immobilized lipase from Mucor miehei (Lipozyme IM-20) was employed in the esterification of butyric acid and isoamyl alcohol to synthesize isoamyl butyrate in n-hexane. Response surface methodology based on five-level, five-variable central composite rotatable design was used to evaluate the effects of important variables-enzyme/substrate (E/S) ratio (5-25 g/mol), acid concentration (0.2-1.0 M), alcohol concentration (0.25-1.25 M), incubation period (12-60 h), and temperature (30-50 degrees C)-on esterification yield of isoamyl butyrate. In the range of parameters studied, the extent of esterification decreased with temperature, lower E/S ratios, and incubation periods. Excess acid and alcohol concentrations (i.e., acid/alcohol > 1.4 or alcohol/acid > 1.4) were found to decrease yield probably owing to inhibition of the enzyme by acid or alcohol, the former being more severe. The optimal conditions achieved are as follows: E/S ratio, 17 g/mol; acid concentration, 1.0 M; incubation period, 60 h; alcohol concentration, 1.25 M; and temperature, 30 degrees C. With these conditions, the predicted value was 1.0 M ester, and the actual experimental value was 0.98 M. Paper no. J9224 in JAOCS 76, 1483-1488 (December 1999).