cerols. In addition, the lipase may be expected to act directly at the mid-position of
the acylglycerols, despite its regioselectivity, presumably much more slowly. It is
assumed that the more protic conditions associated with the acidolysis reaction
may enhance the acyl-migration processes in that case, although the excessive
amounts of free acids present will slow the hydrolysis reactions and at the same
time retard incorporation into the mid-position.
10.3.2 Homogeneous triacylglycerols of EPA and DHA
Using the methodology described above, the EPA and DHA fatty acid composition of
the TG product was determined by a weighted average of the initial fatty acid com-
position of the cod liver oil TG and the composition of the n-3 concentrates. Thus, in
order to obtain elevated levels of EPA and DHA into an ordinary fish oil such as cod
liver oil, excessive amounts of concentrates were needed. To avoid that limitation
and to obtain TG of composition identical to the concentrates being used, a modified
procedure based on a direct esterification of free fatty acids with glycerol was devel-
oped (Haraldsson et al., 1993c; 1995). This also opened the possibility of synthesiz-
ing TG homogeneous with either EPA or DHA, i.e. 100 % EPA or DHA. This was
considered our synthetic challenge and primary goal – the crown on the TG issue in
terms of EPA and DHA enrichment.
A different lipase, this time an immobilized nonregiospecific yeast lipase from
Candida antarctica[also available commercially from Novo Nordisk in Denmark
(SP 382); has now been replaced by Novozyme], was highly efficient in generating
TG of both 100 % EPA and 100 % DHA content. This was accomplished by a direct
esterification of glycerol with stoichiometric amount of pure EPA and DHA, without
any solvent, by stirring at 65 8 C under vacuum, with a 10 % dosage of the immo-
bilized lipase, as based on the weight of substrates. The co-produced water was
10.3 Enrichment of triacylglycerols with EPA and DHA 175
Scheme 2. A simplified proposed pathway for the transesterification reactions of triacylglycerols with
free acids or monoester.