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

Abstract

This study aims to develop, for the very first time, a kinetic model for the simultaneous transesterification of geraniol and citronellol using Pseudomonas fluorescens lipase to produce their respective esters. This allows us to test the feasibility of the bioprocess and comprehend the enzyme behaviour, fine-tune process efficiency, and predict process performance. Geranyl and citronellyl esters are key ingredients in fragrance and flavour formulations in the food sector, as well as bioactive compounds for pest and insect repellents in the agricultural sector. Unlocking a greener and sustainable production of these terpene esters directly from plant-derived essential oil is crucial to meet the 2050 net zero targets to produce bio-based chemicals. The simultaneous transesterification of geraniol and citronellol in a batch reactor successfully achieved conversions of 66 % for citronellol and 94 % for geraniol within 5 h. Key optimum conditions were 1:8 molar ratio (geraniol:vinyl acetate), an enzyme loading of 10 wt % of geraniol, temperature of 40 °C, and a stirring speed of 250 RPM. The results indicated that simultaneous transesterification followed a ternary complex mechanism with competitive inhibition by alcohol. Initial testing of rose geranium oil under optimised conditions yielded 32 % citronellol and 50 % geraniol conversion after 30 h. Overall, this study shows promise as a green pathway utilising enzyme catalysis to selectively produce esters from diverse terpene mixtures and can be extended to terpene alcohols derived from flower essential oils.