Front Matter

PUFAs. In addition, the activities on PUFA glycerides was in the order of mono->

di->triglycerides, and tri-PUFAwas scarcely hydrolyzed. These specificities of the

lipase resulted in the accumulation of PUFA-rich glycerides (mainly triglycerides) in

the reaction mixture (Shimada et al., 1995c).

We also investigated which fatty acids were enriched in glycerides by selective

hydrolysis. As shown in Figure 1, selective hydrolysis of PUFA-containing oil re-

leased the constituent fatty acids from glycerol backbone according to the fatty acid

specificity of lipase. In the reaction, stearic acid was not enriched in the glyceride

fraction. However, hydrolysis of cocoa fat substitute (SOS fat; 1,3-stearoyl-2-oleoyl-

glycerol; purity, 69 %) withCandidalipase efficiently enriched stearic acid in gly-

cerides (Shimada et al., 1995b). SOS fat contains stearic and oleic acids as main

components and palmitic and linoleic acids as minor ones. Because stearic acid

was the poorest substrate of the lipase, the fatty acid was enriched in the glycerides.

The GLA content was not raised more than 46 wt% in the selective hydrolysis of

borage oil withCandidalipase, even though the hydrolysis extent increased (Figure

3). However, the GLA content was raised by repeating the hydrolysis after the re-

moval of FFAs from the reaction mixture (Table 2). We also performed the hydrolysis

of triglycerides containing 22 %, 35 %, and 45 % GLA. The release rate of total fatty

acids became slow with increasing GLA content in the substrate, but the release rate

of GLA did not depend on the GLA content. These results showed that the increase of

the GLA content in glycerides was disturbed by FFAs accumulated in the reaction

mixture, and by the structure of the triglyceride (Shimada et al., 1998b). The con-

tinuous removal of FFAs from the reaction mixture should improve the efficiency of

the PUFA enrichment.

8.3 Production of highly absorbable structured lipid

containing PUFA and medium-chain fatty acid

8.3.1 Structured lipid

In general, natural oils and fats contain saturated or mono-unsaturated fatty acids at

the 1,3-positions and highly unsaturated fatty acids at the 2-position. However, the

distribution of fatty acids along the glycerol backbone is not specified, and natural

oils and fats are not always the best for humans with respect to their structure and

physical properties. Thus, modification by chemical and/or biochemical procedures

has been attempted to improve their quality. These modified lipids are structured

lipids in a wide sense. Meanwhile, structured lipids in a narrow sense are triglycer-

ides having particular fatty acids at specific positions of glycerol. Structured lipids in

a wide sense include single cell oil produced by microorganisms and PUFA-rich oil,

as described earlier. Functional lipids composed only of specific fatty acids are also

structured lipids in a wide sense. Several low-calorie oils of this group have been

commercialized; e.g., triglycerides with behenic acid and medium-chain fatty acids

(Caprenin), triglycerides with short-chain fatty acids and stearic acid (Salatrim), and

triglycerides with medium- and long-chain fatty acids. Structured lipids in a narrow

134 8 Production of Functional Lipids Containing Polyunsaturated Fatty Acids with Lipase