Bioproduction of Geranyl Esters by Integrating Microbial Biosynthesis and Enzymatic Conversion

Geranyl esters (GEs) are valuable monoterpene esters derived from the esterification of geraniol and various carboxylic acids with a range of unique aromas and properties, making them valuable in perfumery, pharmaceutical, and cosmetic applications. Lipase-mediated esterification is considered to be a sustainable process but is challenged by the lack of a compatible catalytic method in conjunction with a customized microbial biosynthesis of geraniol. In this study, we developed an integrated process to convert glycerol and various carboxylates into GEs. The process includes microbial biosynthesis of geraniol using metabolically engineered Escherichia coli and enzymatic conversion of geraniol into GEs in a fermentation medium-organic biphasic system using an immobilized lipase. The enzymatic step for esterifying the target carboxylates with geraniol achieved >90% conversion under the optimized condition. Coupled with the geraniol from microbial fermentation, 0.59 g/L geranyl butyrate and 1.04 g/L geranyl hexanoate were produced subsequently, demonstrating the feasibility of converting renewable source into monoterpene esters through this integrated process, which bypassed feeding extra geraniol in the conventional lipase-mediated GE synthesis.