A COMPARISON BETWEEN LIPASE-CATALYZED ESTERIFICATION OF OLEIC-ACID WITH GLYCEROL IN MONOLAYER AND MICROEMULSION SYSTEMS

Lipase-catalyzed synthesis-esterification of oleic acid with glycerol - was carried out in L2 microemulsions and in monolayers. The microemu lsions were based on isooctane as a nonpolar component and various wat er-glycerol mixtures as polar component. The substrate, oleic acid/sod ium oleate, constituted the microemulsion surfactant. The lipase resid es mainly in the water pools. Monolayers of oleic acid/sodium oleate w ere formed on subsolutions of glycerol and water, and the enzyme solut ion was injected under the compressed monolayers. Thus, the arrangemen t of the reactants at the oil-water interface of the microemulsion can be regarded as analogous to that at the air-water interface of the mo nolayer. The microemulsion structure was characterized by self diffusi on nuclear magnetic resonance. It was found that the higher the glycer ol-to-water ratio, the lower are the water D-values. The reactions in microemulsions generally gave a low degree of oleic acid conversion. T he yield increased with increasing glycerol-to-water ratio. Monoglycer ides were the main product, and no triglyceride could be detected. The monolayer experiments gave a somewhat higher degree of conversion, wi th tri- and diglycerides being the major reaction products. The reason why triglycerides are formed in monolayer experiments but not in micr oemulsions is believed to be due to an unfavorable partitioning of the diglyceride in the microemulsion systems. Once formed, the diglycerid e will partition into the hydrocarbon domain and became inaccessible f or reaction with the enzyme-O-acyl intermediate at the oil-water inter face. In addition, the interfaces in the two systems are different. Th e monolayer interface is static, whereas the microemulsion interface i s highly dynamic, and this difference may also influence the product p attern.