Abstract
Lipases are quite useful for synthesizing structured lipids (SLs) which are triacylglycerols (TGs) having particular fatty acid (FA) residues at specific positions. In regard to the number of FA species and their distribution in the glycerol molecule, TGs may be classified as; AAA-, ABA-, AAB-, and ABC-types. AAA-type TGs can be synthesized from FA and glycerol either chemically or enzymatically. Even with a stoichiometric mixture of substrates, nearly complete synthesis is possible. The syntheses of other types of TGs require positionally specific reactions, for which regio-specifc lipases are useful. ABA-type SLs are synthesized by either 1) 1, 3-position-specific lipase-catalyzed acyl exchange of TG with FA or with FA ethylester (FAEt); or 2) 1, 3-position specific lipase-catalyzed acy-lation of glycerol with FA, giving symmetric 1, 3-diacyl-sn-glycerol. Subsequent to chemical acylation at the sn-2 position; or 3) 1, 3-position-specific lipase-catalyzed deacylation of TG gives 2-monoacylglycerol, which then undergoes reacylation at 1 and 3 positions with FA or FA ethylester. AAB-type SL is obtained by lipase-catalyzed mono-substitution at the 1 or 3 position of AAA-type TG with FA or FAEt, thus avoiding formation of any di-substituted by-product. Stereopreference to sn-1 position over sn-3 position of a certain lipase makes possible the syntheses of chiral AAB-and ABC-type TGs.
