Simultaneous geraniol and citronellol transesterification using Pseudomonas fluorescens lipase for the production of fragrance, flavour and pharmaceutical esters: a kinetic study

Abstract

Terpene esters are one of the most important and versatile compounds for the flavour, fragrance and pharmaceutical industries and are currently produced commercially using petrochemical-based starting materials and chemical catalysis routes. There is a current need in the industry to develop alternatives to the current production process due to an increased demand for natural products, environmental safety and sustainability. This paper for the first time demonstrates a kinetic study for the simultaneous transesterification of geraniol and citronellol using Pseudomonas Fluorescens lipase to produce geranyl and citronellyl esters. The study initially screened the influence of the molar ratio of alcohol to vinyl acetate for individual alcohol transesterification, revealing that increasing the molar ratio led to higher ester yields. The optimised conditions were determined as follows: a molar ratio of 1:4, temperature of 40 °C, agitation speed of 250 RPM, and an enzyme loading of 10 wt.% of alcohol. After 24 hours, the conversion rates reached 95% and 87% for geraniol and citronellol, respectively. These conditions were then applied to the simultaneous transesterification of citronellol and geraniol, with the best experimental condition being a molar ratio of 1:8. The kinetic study demonstrated that the simultaneous transesterification followed a ternary complex mechanism with vinyl acetate inhibition, which was consistent with the experimental data. A preliminary experiment involving the transesterification of rose oil resulted in a conversion rate of 32% for citronellol and 50% for geraniol after 30 hours of reaction time. Overall, this study showcases the potential of enzyme catalysts to selectively produce terpene esters from heterogeneous terpene alcohol mixtures and can be extended to terpene alcohols present in natural essential oils.