Enzymatic synthesis of high-purity structured lipids with caprylic acid at1,3-positions and polyunsaturated fatty acid at 2-position

We attempted to synthesize high-purity structured triacylglycerols (TAG) wi th caprylic acid (CA) at the 1,3-positions and a polyunsaturated fatty acid (PUFA) at the 2-position by a two-step enzymatic method. The first step wa s synthesis of TAC of PU FA (TriP), and the second step was acidolysis of T riP with CA. Candida antarctica lipase was effective for the first reaction . When a reaction medium of PUFA/glycerol (3:1, mol/mol) and 5% immobilized Candida lipase was mixed for 24 h at 40 degreesC and 15 mm Hg, syntheses o f TAC of gamma -linolenic, arachidonic, eicosapentaenoic, and docosahexaeno ic acids reached 89, 89, 88, and 83%, respectively. In these reactions, the lipase could be used for at least 10 cycles without significant loss of ac tivity. In the second step, the resulting trieicosapentaenoin was acidolyze d at 30 degreesC for 48 h with 15 mol parts CA using 7% of immobilized Rhiz opus delemar lipase. The CA content in the acylglycerol fraction reached 40 mol%. To increase the content further, the acylglycerols were extracted fr om the reaction mixture with n-hexane and were allowed to react again with CA under conditions similar to those of the first acidolysis. After three s uccessive acidolysis reactions, the CA con tent reached 66 mol%. The conten t of dicapryloyl-eicosapentaenoyl-glycerol reached 86 wt% of acylglycerols, and the ratio of 1,3-dicapryloyl-2-eicosapentaenoyl-glycerol to 1(3),2-dic apryloyl-3(1)-eicosapentaenoyl-glycerol was 98:2 (w/w). In this reaction, t he lipase could be used for at least 20 cycles without significant loss of activity. Repeated acidolysis of the other TriP with CA under similar condi tions synthesized 1,3-dicapryloyl-2 -gamma -linolenoyl-glycerol, 1,3-dicapr yloyl-2-arachi-donoyl-glycerol, and 1,3-dicapryloyl-2-docosahexaenoyl-glyce rol in yields of 58, 87, and 19 wt%, respectively.