Short chain flavour ester synthesis by a new esterase from Bacillus licheniformis

The newly characterized esterase from Bacillus licheniformis was used for ethyl ester synthesis in n-heptane by direct esterification with fatty acids of different chain lengths. The highest reaction rates and yields were obtained with caproic (C6) and caprylic (C8) acids reflecting the enzyme specificity for mid-chain length fatty acids. The rate of ethyl caproate formation increased linearly with the enzyme concentration in the range 0–40 mg/ml. The enzyme displayed maximum activity with 0.1% (v/v) addition of water. The initial reaction rate was maximal at 67°C but the highest yield (95%) was obtained at 45°C. Kinetic parameters were determined for caproic acid: KM of 38.4 mM and VM of 8.3 μmol/min/ml (at 0.25 M ethanol), and for ethanol KM of 12.3 mM and VM of 1.3 μmol/min/ml (at 0.25 M caproic acid). The highest activities and yields were observed for solvents having log P≥3.2. The enzyme was used three times without activity loss.