Lipase Catalyzed Processes and Reactions in Microemulsions
Lipase catalyzed reactions in microemulsions have been investigated recently along two different lines of research. Such systems are believed to be biomimetic, i.e. they mimic lipase catalyzed in vivo processes. Futhermore, they are preparatively useful for lipid transformations.
Both fields are reviewed here. In the studies on biometic reactions special emphasis has been put on the role of the amphiphillic substances, both of natural and synthetic origin, used in the systems. These investigations are helpful. e.g. in clarifying the role of bile salts in in vivo lipolysis.
In the field of lipid transformations the majority of work has been done on transesterification and hydrolysis of triglycerides. Transesterification is a useful way to synthesize novel or uncommon triglycerides. A preparatively interesting example is the manufacture of cocoa butter from palm oil and stearic acid. Regioselective hydrolysis is an efficient way to produce 2-monoglycerides in high yields. Glycerolysis is a way to produce a mixture of 1- and 2-monoglycerides. Enzymatic synthesis of triglycerides from glycerol and fatty acids has so far not been successful.
Finally, the structure of protein-containing micelles is discussed. It is shown that the structure of the palisade layer between oil and water domains is decisive of the reaction process. In general, nonionic surfactants are unsuitable since the polyethylene glycol chains, which stretch out into the water domains, prevent the enzyme from reaching the interface. In AOT based microemulsions the reactions run smoothly since the lipase has good access to the interfacial region and, thus, to the hydrophobic triglyceride substrate.
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