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

The newly characterized esterase from Bacillus licheniformis was used for e thyl ester synthesis in n-heptane by direct esterification with fatty acids of different chain lengths. The highest reaction rates and yields were obt ained with caproic (C6) and caprylic (C8) acids reflecting the enzyme speci ficity for mid-chain length fatty acids. The rate of ethyl caproate formati on 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 degrees C but the highest yield (95%) was obtained at 45 degrees C. Kinetic parameters were determined for caproic acid: K-M of 38.4 mM and V-M of 8.3 mu mol/min/ml (at 0.25 M ethan ol), and for ethanol K-M of 12.3 mM and V-M of 1.3 mu mol/min/ml (at 0.25 M caproic acid). The highest activities and yields were observed for solvent s having log P greater than or equal to 3.2. The enzyme was used three time s without activity loss. (C) 2000 Elsevier Science B.V. All rights reserved .