Deep eutectic solvents for enzymatic esterification of racemic menthol

Enzymatic esterification is an effective route that can contibute for the separation of racemic (rac) mixtures, and is thus of great importance for the pharmaceutical, food and cosmetic industries. All the processes involved in this methodology should be environmentally friendly, biocompatible, fast and cost effective. The use of deep eutectic solvents (DES) can comply with all these metrics. In this work, we report on the use of DES in the enzymatic esterification of menthol, one of the largest traded flavours and aromas worldwide. Solid rac-menthol was mixed with solid lauric acid at different molar ratios, yielding a DES liquid at room temperature or slightly above. Rac-menthol and lauric acid were the DES components and also the esterification reaction substrates. The DES reacted promptly when Candida rugosa lipase was added, and the conversions of rac-menthol reached up to 44% after 3 hours of reaction. Enzyme activity was dependent on the molar ratio of the substrates, as well as on the water activi...