Enzymatic synthesis of structured lipids

Lipases are powerful tools for the syntheses of structured lipids (SLs) which are triacylglycerols (TGs) having particular fatty acid (FA) residues at specific positions. With respect to the number of FA species and their distribution in glycerol molecule, TGs are classified into several types; AAA, ABA, AAB, and ABC types. Among them, AAA-type TGs can be synthesized from FA and glycerol either chemically or enzymatically. Even at stoichiometric mixture of the substrates, almost complete reaction is possible. Syntheses of the other types of TGs require positionally specific reactions, for which the use of regiospecifc lipases are effective. ABA-type SLs are synthesized by (1) sn-1,3-position-specific lipase-catalyzed interesterification of two different TGs, (2) sn-1,3-position-specific lipase-catalyzed acyl exchange of TG with FA or with FA ethylester (FAEt), (3) sn-1,3-position-specific lipase-catalyzed acylation of glycerol with FA giving symmetric 1,3-diacyl-sn-glycerol, followed by chemical acylation at sn-2 position. ABB-type SL is prepared by lipase-catalyzed monosubstitution at either sn-1 or -3 position of TG with FA or with FAEt, avoiding formation of disubstituted by-product. Stereopreference to sn-1 position over sn-3 position of a certain kind of lipase enables the syntheses of chiral ABB- and ABC-type TGs.