PC, 44 % LPC and 17 % GPC present in the product mixture, based on moles of
phospholipids, according to the^31 P-NMR studies.
Additional results are exhibited in Figures 4 and 5, which demonstrate the power
of the^31 P-NMR technique in this field. Figure 4 shows the extent of hydrolysis as
well as changes of PC and LPC during the progress of the reaction. From these
results, it is evident that major changes in composition occurred already during
the first 3 h of the reaction in terms of extent of hydrolysis and PC and LPC incor-
poration. More detailed insight into the progress of the reaction is provided in Figure
5. At the beginning of the reaction 1-LPC was the predominant hydrolysis product.
After 3 h, 27 % 1-LPC, 9 % 2-LPC, 10 %sn-glycerol-3-phosphatidylcholine (GPC)
and 55 % PC were present (molar basis). After 6 h, 1-LPC and 2-LPC had leveled out
at 16 % content, but after 48 h an equilibrium was reached with 2-LPC now dom-
inating in the hydrolysis product mixture at 36 % content, with only 6 % 1-LPC,
15 % GPC and 45 % PC present in the reaction mixture.
Based on these findings, the mechanism displayed in Scheme 7 was proposed for
the lipase-catalyzed acidolysis of PC with free fatty acids. The proposed mechanism
explains how PC of higher than 50 % EPA content can be formed with both thesn-1
andsn-2 positions involved, as well as the participation of all the intermediates
implied by the^31 P-NMR spectroscopy analysis. According to that mechanism,
the lipase utilizes water to bring about hydrolysis at thesn-1 position of the starting
PC to produce 1-LPC. That intermediate can undergo either re-esterification to form
EPA-enriched PC or a much slower acyl migration to form 2-LPC. The lipase can
easily hydrolyze that intermediate to form GPC. Esterification at thesn-1 position of
GPC with EPA by the aid of the lipase, followed by acyl migration to form EPA-
enriched 2-LPC and finally lipase-catalyzed esterification with EPA, leads to the
formation of the highly EPA-enriched PC. Thus, the postulated mechanism can
be used to rationalize the reaction system behavior: EPA-enriched PC and (presum-
182 10 Enrichment of Lipids with EPA and DHA by Lipase
Figure 5. Composition of various PL intermediates during the progress of the acidolysis reaction with
70 % lipase dosage.