Preparation of phospholipids highly enriched with n‐3 polyunsaturated fatty acids by lipase

The immobilized 1,3‐regiospecific Rhizomucor miehei lipase (Lipozyme™) was employed to catalyze the transesterification reaction (acidolysis) of 1,2‐diacyl‐sn‐glycero‐3‐phosphatidylcholine with n‐3 polyunsaturated fatty acids under nonaqueous solvent‐free conditions. With a concentrate of 55% eicosapentaenoic acid (EPA) and 30% docosahexaenoic acid (DHA) and pure phosphatidylcholine from egg yolk, phospholipids of 32% EPA and 16% DHA content were obtained, presumably as a mixture of phosphatidylcholine and lysophosphatidylcholine. 31P nuclear magnetic resonance (NMR) analysis turned out to be a valuable technique to study the details of the reactions involved. It revealed that when 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphatidylcholine was transesterified with 98% pure EPA, a substantial amount of hydrolysis side reaction took place (39%), leading to a product mixture of 39% phosphatidylcholine, 44% lysophosphatidylcholine, and 17% sn‐glycerol‐3‐phosphatidylcholine. The lysophosphatidylcholine constituent comprised 70% EPA, whereas the phosphatidylcholine component contained 58% EPA. The 31P NMR technique provided valid information about the mechanism of the reaction. It became evident that a high dosage of lipase containing 5% water afforded optimal conditions for the optimal extent of EPA incorporation into the phospholipids, under which the extent of hydrolysis side reaction remained relatively high.