Front Matter

when it is used as an ingredient of various kinds of food, the processing procedures

will be easier; and (iii) it can be used as a more effective starting material for the

purification of PUFA. PUFA-rich oil has been traditionally produced by winteriza-

tion. However, the maximum DHA content is 30 % at most according to the method

in the industrial production of DHA-rich oil from tuna oil. Meanwhile, application of

lipase can enrich PUFA more efficiently. In general, lipases act on PUFAvery weakly

(Shimada et al., 1995a,b; 1998a), and PUFA can be enriched in the glyceride fraction

by hydrolysis of PUFA-containing oil with the enzymes. This reaction, termed se-

lective hydrolysis, is applicable to enrichment of the other PUFAs, AA and GLA.

DHA- and GLA-rich oils produced by the method are commercialized as health

foods.

8.2.1 Production of DHA-rich oil from tuna oil

Lipases fromCandida rugosa(Tanaka et al., 1992; Shimada et al., 1994),Geotri-

chum candidum(Shimada et al., 1994), andPenicillium abeanum(Sugihara et al.,

1996) have highly hydrolyzing ability, but act on DHA very weakly. Thus, these

lipases are suitable for the production of DHA-rich oil from tuna oil. In particu-

lar,Candidalipase (Lipase-OF; Meito Sangyo, Aichi, Japan) is available indust-

rially, and is useful for the production of DHA-rich oil. We investigated several

factors affecting the reaction, and determined the following reaction conditions:

a mixture of tuna oil, 50 % water, and 200 units (U) g–1reaction mixture was in-

cubated at 35 8 C with stirring (Shimada et al., 1994). One unit of lipase is the amount

that liberates 1lmol of fatty acid per minute from olive oil. Figure 1 shows a typical

time course of the selective hydrolysis under these conditions. Hydrolysis proceeded

rapidly until 4 h, and gradually thereafter. The contents of palmitic, palmitoleic, and

oleic acids in glycerides decreased rapidly, and the stearic acid content decreased

after a 1–h lag. The EPA content decreased gradually after an increase within

the first hour. The content of DHA increased with increasing hydrolysis extent,

and reached 48 wt% after 24 h. The time course showed that the lipase activity

on the constituent fatty acids was in the order: palmitoleic, oleic acids>palmitic

acid>stearic acid>EPA>DHA. In addition, the glyceride fraction after the 24-h

hydrolysis contained 88 wt% triglycerides, 10 wt% diglycerides, and 2 wt% mono-

glycerides.

When tuna oil was hydrolyzed withCandidalipase in a mixture containing 50 %

water, the DHA content in glycerides depended only on the hydrolysis extent. Tuna

oil was hydrolyzed at 35 8 C for 24 h with various amounts of the lipase, and the

correlation between the hydrolysis extent and the DHA content in glycerides is

shown in Figure 2. The DHA content was raised from 23 to 45 wt% in a 78 % yield

at 60 % hydrolysis, and to 50 wt% at 70 % hydrolysis in a 70 % yield. Using the

selective hydrolysis, 45–50 wt% DHA oil has been commercialized as a health

food in Japan since 1994.

8.2 Production of PUFA-rich oils by selective hydrolysis 129