Enzymatic Mechanism and Energetics in the Optimized Biosynthesis of the Flavor and Fragrance Ester Geranyl Acetate

N. S. Yaakub, M. S. Mohamad Annuar, N. N. A. Razak and K. Khalid

Abstract
Geranyl acetate, a significant natural fragrance compound, is typically available only in minute quantities from plant sources. This study focuses on the biosynthesis of this compound through enzymatic esterification of geraniol with acetic acid, utilizing the environmentally benign and generally safe solvent, acetone. The optimization process initially involved key synthesis variables, including acetic acid and geraniol concentrations, temperature, and enzyme loading. Subsequently, a thermodynamic investigation of the biosynthesis was conducted alongside kinetic elucidation, providing insights into the mechanism of the lipase-mediated esterification, which was revealed to follow a Ping-Pong Bi-Bi mechanism with no apparent inhibition by either substrate. The reaction is endothermic, with calculated changes in enthalpy (ΔH), and entropy, (ΔS) at 66 kJ mol–1 and 217 J mol–1 K–1, respectively. The activation energy, Ea, was determined to be 28 kJ mol−1. Esterification was non-spontaneous below 30 °C but shifted to spontaneous at higher temperatures. These findings hold significance for the development of biocatalytic processes.

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Keywords
geranyl acetate, esterification, Candida antarctica, kinetics, thermodynamic