Front Matter

integrity and functions at the lower temperatures, by adding to the membrane fluidity

and mobility as a result of their higher unsaturation. Among the PL, phosphatidyl-

choline (PC) and phosphatidylethanolamine (PE) are by far the most abundant in fish

flesh, especially the former, which commonly comprises 50–60 % of the total PL

content.

PL of vegetable and plant origin are highly enriched with n-6 fatty acids and

commonly used as health supplements. Purified PL of fish origin highly enriched

with n-3 PUFA, on the other hand, are not available on the market at all. They

are by no means readily obtainable, since tedious extraction procedures from fish

are required (Haraldsson et al. 1993a). We therefore decided to attempt the prepara-

tion of such PL highly enriched with EPA and DHA from the more readily available

plant or animal lecithins (Haraldsson and Thorarensen, 1995; 1999).

Attempts to prepare PL enriched with n-3 PUFA by various esterification reactions

involving lipases (Totani and Hara, 1991; Mutua and Akoh, 1993) and phospholi-

pases (Na et al., 1990; Mutua and Akoh, 1993; Ha ̈rro ̈d and Elfman, 1995) have

usually resulted in low yields as a result of predominant hydrolysis side reac-

tions, and the incorporation of the n-3 PUFA did not reach any elevated levels. Ta-

kahashi and co-workers (Hosokawa et al.,1995a) have succeeded in enhancing the

incorporation of EPA into soy PC while at the same time suppressing the hydrolysis

side reaction in a lipase-catalyzed acidolysis with Lipozyme. This was accomplished

by using propylene glycol as a water-mimic in hexane as a solvent, the claimed PC

recovery being 80 %. Thus, a far lower water content was required for the catalyst to

perform. The authors assumed that the EPA incorporation took place explicitly at the

sn-1 position and that 80 % of the theoretical incorporation level was reached, which

corresponds to about 35 % EPA content in the resulting PC. These authors have also

reported on the preparation of structured PC highly enriched with EPA and DHA at

thesn-2 position (Hosokawa et al., 1995b). This was accomplished by a direct es-

terification of 2-lysophosphatidylcholine (2-LPC) from soya with EPA and DHA

using porcine phospholipase A 2 in glycerol as a solvent with formamide as a

water-mimic. The molar yields were apparently far lower or close to 40 %.

In our own contribution to this field preliminary studies were conducted on pure

diacyl-sn-glycero-3-phosphatidylcholine from egg yolk in lipase-catalyzed interes-

terification reactions with concentrates comprising 55 % EPA and 30 % DHA as free

acids (acidolysis) and ethyl esters (interesterification), according to Scheme 6 (sim-

plified, only shown for EPA). Reaction conditions almost identical to those pre-

viously described for cod liver oil TG and shark liver oil EL were applied. As could

be anticipated for lipase, the rate of the reactions involving the PC possessing the

zwitterionic head groups, was much lower when compared to their native TG. Ac-

cordingly, much higher quantities of lipase were required, up to 5- to 10-fold that

used previously, which again resulted in high extent of hydrolysis side reaction.

Lipozyme was far more efficient than theCandida antarcticalipase and became

the lipase of choice for further studies.

The interesterification reaction was found to proceed at a comparable rate to the

acidolysis reaction, and similar incorporation levels of EPA and DHAwere obtained.

As before, EPAwas a considerably better substrate than DHA. It was decided to look

further into the acidolysis reaction, since the water-associated hydrolysis side reac-

tions were largely suppressed by the excessive amounts of free fatty acids present in

180 10 Enrichment of Lipids with EPA and DHA by Lipase