Ultrasound irradiation accelerates the lipase-catalyzed synthesis of methyl caffeate in an ionic liquid

Abstract

Methyl caffeate is a natural ingredient with several biological activities, but its preparation is generally limited to chemical synthesis. To set up a simple, high-yield and low-cost synthesis process for obtaining methyl caffeate, a novel synthesis method using the lipase-catalyzed esterification of methanol and caffeic acid in an ionic liquid under ultrasound irradiation was established. A maximum yield of 99.79% was obtained using ultrasound irradiation with an ultrasound frequency of 25kHz and ultrasound power of 150W under the following optimal conditions: Novozym 435 as a biocatalyst, [Bmim][Tf2N] as the reaction medium, lipase concentration of 60g/L, reaction temperature of 75°C, and reaction time of 9h. Using the optimal conditions under ultrasound irradiation, the reaction time was reduced 0.75-fold, and the apparent kinetic parameter (Vm/Km) was increased 2-fold. The lipase could be reused 11 times without significant loss of activity. The results suggest that ultrasound irradiation can accelerate lipase-catalyzed synthesis of methyl caffeate in an ionic liquid.