Lipase-Catalyzed Synthesis Of Sugar Fatty Acid Esters

Lipase (EC3.1.1.3) primarily responsible for the hydrolysis of acylglycerides, is widely used in organic synthesis as they can accept a wide range of substitutes and are quite stable in nonaqueous organic solvents. A variety of lipases have been successfully used to catalyse the reaction between sugar and fatty acids but the high prices of lipase prevent them from industrial use. A lipase that is relatively cheap is applied in this work to produce sugar esters.First immobilized lipase Candida sp. is slected for its high esterification activity. And the effects of temperature, PH value, water activity and organic solvents on the enzyme activity are measured. Results show that it get highest esterification activity at 50℃in hexane, a pH value of 8.0, very low initial water activity and hydrophobic can help it keep higher activity.A solid phase method is applied with immobilized lipase Candida sp. as biocatalyst and small amount of acetone as adjuvant to complete the reaction between glucose and stearic acid. Analysts confirmed the product and show that monoester is regioselectively produced as is reported in literatures. Parameters affecting convertion are examined and a maximum convertion of 40.4% is gained in the reaction of 1mmol glucose and 1mmol stearic acid after 48h in the condition of: 35℃, initial water activity 0.75, 0.4g enzyme, 2ml acetone and 0.8g molecular sieve as water absorbant. Acids with medium to long carbon chains are favored in the reaction and only the acylation of monosaccharides is successfully achieved.Compared with the results catalyzed by other lipase such as CAL-B and MML, the initial reaction rate in the experiment is compareable, showing the ability of Candida sp. to facilitate the reaction while the productivity is relatively low maybe as a result of poor organic resistant and bad mass transfor caused by the enzyme carrier.A mathematical expression corresponsible to a simplified ping-pong mechanism is employed to exzamine the kinetics of the reaction and it fit well to the experimental data. Results indicate the acylation of the enzyme is the rate-limiting step of the reaction and a very rapid deactivation is predicted by the kinetic model.