Enzymatic synthesis of structured lipids from single cell oil of high docosahexaenoic acid content

The lipase-catalyzed acidolysis of a single-cell oil (SCO) containing docos ahexaenoic acid (DHA) and docosapentaenoic acid (DPA) with caprylic acid (C A) was investigated. The targeted products were structured lipids containin g CA residues at the sn-1 and -3 positions and a DHA or DPA residue at the sn-2 position of glycerol. Rhizomucor miehei lipase (RML) and Pseudomanas s p. KWI-56 lipase (PSL) were used as the biocatalysts, When PSL was used > 6 0 mol% of total SCO fatty acids (FA) were exchanged with CA, with DHA and D PA as well as the other saturated FA being exchanged. The content of the tr iacylglycerols (TG) containing two CA and one DHA or DPA (number of carbon atoms = 41, i.e., C-41) residue was high (36%), and the isomer with the des ired configuration (unsaturated FA residue at the sn-2 position) represente d 77-78% of C-41. In the case of RML, CA content reached only 23 mol% in th e TG. A large amount of DHA and DPA residues remained unexchanged with RML, so that the resulting oil was rich in TC species containing two or three D HA or DPA residues (46%). TG C-41 amounted to 22%, almost all of which had the desired configuration. This result suggested that the difference in the degree of acidolysis by the two enzymes was due to their different selecti vity toward DHA and DPA, as well as the difference in their positional spec ificities.