Continuous synthesis of cinnamate ester using membrane reactor in a solvent-free system

Cinnamic acid is a phenolic compound with the potential to act as a natural antioxidant. Cinnamic acid esterification can be performed by adding a long-chain alcohol to one of its hydroxyl groups to improve its antioxidant activity. In this study, cinnamic esters were synthesized in an enzymatic membrane reactor (EMR) and were carried out continuously. This study aimed to determine the optimum conditions for the synthesis of cinnamic esters using various types of alcohols (e.g., butanol, hexanol, and octanol) as alkyl group donors and the impact of the esterification on the antioxidant activity. The continuous synthesis of cinnamic esters with TL IM lipozyme as the biocatalyst had the highest conversion (20.91%) with 1-butanol as the alkyl donor, in a synthesis strategy of a 12-h batch followed by continuous operation with a residence time of 9 h. The resulting ester increased the antioxidant activities by 2.18 and 3.85-fold, respectively based on the DPPH and FRAP assays.