Regioselective synthesis of sucrose monoester by lipase-catalyzed reaction in water activity-controlled system

Abstract

Sucrose fatty acid esters are potentially important as surfactants in food, detergent, cosmetic and pharmaceutical industry and also used as fine chemicals. In the present work, we have investigated its esterification reaction in solvent-free heterogeneous reaction system using lipase. The formation of sucrose monocaprate from sucrose and capric acid catalyzed by lipase was chosen as a model reaction. Simple esterification reaction was performed by mixing lipase, sucrose, and capric acid without synthesizing any substrate derivatives and without using solvent, for the first time. The products were extracted and subjected to TLC and GC. The success of this reaction in solvent-free system is due greatly to the control of optimal water activity during esterification reaction. A suitable pair of solid salt hydrate was used and it was added directly in reaction mixture. The salt hydrate pair can take up or release water as required to keep constant conditions during the reaction and thereby acts as buffers of water activity. Several salt hydrate pairs were investigated and it was determined that pair of barium hydroxide-$8H_2O/1H_2O$ acted to control the optimal water level in the reaction mixture and its water activity was 0.44. Reaction yield was increased significantly with salt hydrate pair. It was 25.3 % in optimum condition. Regioselectivity of lipase on sucrose in this reaction system was examined. It was found that sucrose-6-monocaprate was formed highly selectively.