Front Matter

an important role during the process. Based on the above results a proposed pathway

for the rather complicated reactions is illustrated in Scheme 4.

Interesterification reaction involving tributyrin and pure EPA and DHA as ethyl

esters under identical conditions offered similar products (Haraldsson et al., 1993c;

1995). This reaction is also illustrated in Scheme 3. Similar treatment of glycerol

with concentrated ethyl esters of EPA and DHA was observed to be inferior to

the above-mentioned processes in terms of extent of conversion (Haraldsson et

al., 1992). Finally, it is evident that the immobilizedCandida antarcticalipase is

superior to other lipases in terms of the direct esterification reaction between gly-

cerol and free fatty acids, as can be witnessed by several literature reports (Haralds-

son et al., 1992; Li and Ward, 1993a; He and Shahidi, 1997).

It was also demonstrated that this methodology can be used to provide TG of a

composition identical to any composition of the starting free acids (Haraldsson et al.,

1992). A similar procedure (which is on the point of industrialization in Norway) is

designed to produce pure TG that are highly enriched with EPA and DHA. TG of

higher than 90 % purity were obtained when a mixture of MG, DG and TG obtained

by hydrolysis of tuna oil with theCandida rugosalipase and thus enriched with DHA

was treated with Lipozyme and free fatty acids (McNeill et al., 1996; Moore and

McNeill, 1996). It is most probable that this procedure has already been scaled-

up and industrialized in Europe for providing DHA concentrates as TG for infant

formula.

10.4 Ether lipids highly enriched with EPA and DHA

Nonpolar glyceryl ether lipids of the 1-O-alkyl-2,3-diacyl-sn-glycerol type are major

constituents in the liver oils of various species of elasmobranch fish such as dogfish

and shark (Kayama and Mankura, 1998; Sargent, 1989). They have been claimed to

display various beneficial effects on human health (Mangold and Paltauf, 1983). The

1-O-alkyl-sn-glycerols are highly valuable compounds, bearing a strong resem-

blance to the well-known platelet activating factors, and can be prepared from

the unsaponifiable fraction of dogfish and shark liver oil. There are three main fatty

alcohol constituents present in the 1-O-alkyl moiety of the glyceryl ethers, C16 : 0,

C18 : 0and C18:1, the last being the most abundant. They correspond to chimyl, batyl

and selachyl alcohols, respectively, named after their sources in the liver oils of

chimeras, sharks and rays of the Chimaeroidei, Batoidei and Selachoidei fa-

milies. Their structure is illustrated in Figure 3. Very recently, we have demonstrated

that lipase can be used to resolve kinetically racemic mixtures of these alcohols

(Haraldsson et al., 1999).

In order possibly to combine the claimed beneficial effects of EL and fish oil, EL

were treated with EPA and DHA by the lipase catalysis procedures already described

(Haraldsson and Thorarensen, 1994). The EL were isolated in a pure state, as was

established by high-field NMR, from shark liver oil concentrates using preparative

HPLC. EPA and DHA made up only 0.4 and 2.5 % of the initial fatty acid composi-

tion of the EL acyl counterparts, respectively. Pure 1-O-alkyl-sn-glycerols were ob-

tained from the EL by sodium methoxide-catalyzed methanolysis.

178 10 Enrichment of Lipids with EPA and DHA by Lipase