of a solvent using Lipozyme (Haraldsson and Kristinsson, 1998) (Scheme 9). By a
similar methodology they were able to purify EPA free of DHA to above the 90 %
purity levels from a free fatty acid concentrate of EPA in high recoveries. These
examples demonstrate that enrichment levels well beyond the urea crystallization
method can be obtained highly efficiently by lipase. The fact that an immobilized
lipase can be reused 20 to 40 times or more, with little or no deterioration of the
lipase, suggests that the application of lipase in the field of fish oils is a highly
feasible choice from the industrial point of view.
10.7 Structured lipids containing EPA and DHA
Lipases have also found important application in producing structurally labeled TG
(Gunstone, 1998) with the n-3 PUFA located either at the mid-position or the end-
positions. This is based on using 1,3-regiospecific lipases for transesterification or
hydrolysis of TG with the fatty acids in thesn-2 position remaining almost intact in
the acylglycerol products. That usually is dependent upon the reaction time and the
slower acyl-migration processes must be avoided or kept to a minimum. From a
nutritional point of view, structured lipids containing n-3 PUFA at the mid-position
with medium-chain fatty acid (MCFA) at the end-position have recently received
most attention.
Shimada and co-workers reported on the production of structured lipids containing
DHA in thesn-2 position by exchanging fatty acids at the 1- and 3-positions of tuna
oil for caprylic acid using an immobilized 1,3-regiospecificRhizopus delemarlipase
(Shimada et al., 1996). Yamane’s group reported on the lipase-catalyzed acidolysis of
single-cell oil containing DHA and docosapentaenoic acid (DPA) with caprylic acid
(Iwasaki et al., 1999). They were aiming at structured lipids containing caprylic acid
at thesn-1 andsn-3 positions and DHA or DPA at thesn-2 positions of the product.
Similarly, Xu and co-workers treated fish oils with caprylic acid using Lipozyme as a
biocatalyst in a solvent-free system in a pilot-scale production (Xu et al., 1998).
Schmid and co-workers have approached the synthesis of structured TG contain-
ing EPA and DHA in the mid-position differently by proposing a two-step strategy
(Schmid et al., 1998). Their strategy is based on the generation of 2-MG highly
enriched with n-3 PUFA. They were produced in high yield and excellent purity
from fish oil TG, which were subjected to an acidolysis reaction in an organic sol-
vent, catalyzed by 1,3-regiospecific lipases. Subsequent esterification of the 2-MG
with fatty acids is supposed to result in structured TG highly enriched with n-3 PUFA
located in thesn-2 position. This approach is illustrated in Scheme 10.
10.7 Structured lipids containing EPA and DHA 185
Scheme 9. Direct esterification of fish oil free acids with ethanol by lipase.