Lipase catalyzed synthesis of flavor esters in non-aqueous media: Optimization of the yield of pentyl 2-methylpropanoate by statistical analysis

In this study, the synthesis of pentyl 2-methylpropanoate employing a commercial lipase from Candida rugosa was investigated, the emphasis being placed on analyzing the effects of various process conditions on the yield of ester. The response surface methodology (RSM) and five-level-five-factor cen- tral composite rotatable design (CCRD) were used to evaluate the effects of variables, namely the initial water content, 0.0-2.0 % (w/v), the reaction tem- perature, 35-75 °C, the enzyme concentration, 1.0-5.0 g dm -3 , the acid/alcohol mole ratio, 1:2-5:2, and the reaction time, 4-48 h, on the yield (%) of ester. The production of pentyl 2-methylpropanoate was optimized and an ester yield response equation was obtained, enabling the prediction of ester yields from known values of the five main factors. It seems that the enzyme concentration, reaction time and acid/alcohol mole ratio predominantly determine the conver- sion process, while the amount of added water amount had no significant in- fluence on the ester yield. Conversion of around 92 % of the substrate to ester could be realized using a concentration of lipase as low as 4.0 g dm -3 and in a relatively short time (26 h) at 35 °C, when a high substrate mole ratio of 2.5 was used.