Two-step enzymatic synthesis of docosahexaenoic acid-rich symmetrically structured triacylglycerols via 2-monoacylglycerols |
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Authors: | Roxana Irimescu Kiyomi Furihata Kazuhiko Hata Yugo Iwasaki Tsuneo Yamane |
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Affiliation: | (1) Central Research Laboratory, Nippon Suisan Kaisha, Ltd., 192-0906 Hachioji-shi, Tokyo, Japan;(2) Laboratory of Molecular Biotechnology, Graduate School of Bio- and Agro-Sciences, Nagoya University, 464-8601 Nagoya, Japan |
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Abstract: | Symmetrically structured triacylglycerols (TG) rich in docosahexaenoic acid (DHA) with caprylic acid (CA) at the outer positions
were synthesized enzymatically form bonito oil in a two-step process: (i) ethanolysis of bonito oil TG to 2-monoacylglycerols
(2-MG) and fatty acid ethyl esters, and (ii) reesterification of 2-MG with ethyl caprylate. Ethanolysis catalyzed by immobilized
Candida antarctica lipase (Novozym 435) yielded 92.5% 2-MG with 43.5% DHA content in 2 h. The 2-MG formed were reesterified with ethyl caprylate
by immobilized Rhizomucor miehei lipase (Lipozyme IM) to give structured TG with 44.9% DHA content based on fatty acid composition with caprylic acid (CA)
excluded] in 1 h. The final structured lipids comprised 85.3% TG with two CA residues and one original fatty acid residue,
13% TG with one CA residue and two original fatty acid residues, and 1.7% tricaprylolglycerol (weight percent). The amount
of TG with two CA residues and one C22 residue (22∶6=DHA, 22∶5, and 22∶4) was 51 wt%. The 1,3-dicapryloyl-2-docosahexaenoylglycerol to 1,2(2,3)-dicapryloyl-3 (1)-docosahexaenoylglycerol
ratio (based on high-performance liquid chromatography peak area percentages) was greater than 50∶1. The recovery of TG as
structured lipids after silica gel column purification was approximately 71%. Ethyl esters and 2-MG formed at 2 h of ethanolysis
could be used to determine the positional distribution of fatty acids in the intial TG owing to the high 1,3-regiospecificity
of Novozym 435 and the reduced acyl migration in the system. |
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Keywords: | Esterification ethanolysis fish oil immobilized Candida antarctica lipase immobilized Rhizomucor miehei lipase lipase regiospecificity regioselective analysis of triacylglcerols symmetrically structured triacylglycerols |
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