Ester Synthesis in Aqueous Media by Lipase: Alcoholysis, Esterification and Substrate Hydrophobicity

Abstract

Lipases are versatile biocatalysts commonly used for flavor ester synthesis in media with low-water activity. This research studied the mechanism of ester synthesis by lipase Palatase in coconut cream and phosphate buffer with alcohols and fatty acids. When ethanol was added as the alcohol substrate, hydrolysis of triglycerides dominated over synthesis of esters. When fusel alcohols (fusel oil) were used as the alcohol substrate, ester synthesis dominated over lipid hydrolysis. However, there was no visible pattern of fatty acid production and then reutilization in relation to ester synthesis in either case. Higher consumption of octanoic acid was obtained than that of butyric acid in both coconut cream and buffer systems spiked with the same alcohol. This indicated the preferential utilization of more hydrophobic substrates for esterification by lipase in aqueous media. These results suggest that the lipase Palatase-catalyzed ester synthesis in aqueous media was mainly hydrophobicity-dependent esterification. Practical Applications Esters are important flavor compounds that are applied in food products. The effects of substrate hydrophobicity and reaction environment on the catalytic behavior of a lipase during ester synthesis in an aqueous system of coconut cream and fusel oil were investigated. Useful information was obtained on the in situ generation of esters in food materials. This study has implications for lipase-catalyzed synthesis of flavor esters in other aqueous food matrices.