Front Matter

sense have superior properties compared to natural oils and fats. For example, a

triglyceride with stearic or behenic acid at 1,3-positions and oleic acid at 2-position

(SOS or BOB) is used as cocoa butter equivalent, and triglyceride with oleic acid at

1,3-positions and palmitic acid at 2-position triglyceride (OPO) is used in an infant

formula. Because triglycerides with medium-chain fatty acids at 1,3-positions and

long-chain fatty acids at 2-position (MLM-type) are hydrolyzed to 2-monoglyceride

and fatty acids faster than natural oils and fats with long-chain fatty acids (LLL-

type), MLM-type structured lipids are absorbed extensively into the intestinal mu-

cosa (Ikeda et al., 1991; Christensen et al., 1995). Therefore, MLM-type structured

lipids containing functional fatty acids are expected as nutrition for patients with

maldigestion and malabsorption of lipids, and as high-value added health foods.

We attempted to produce MLM-type structured lipids containing PUFAs and essen-

tial fatty acids by acidolysis of natural oils with caprylic acid (8 : 0, CA) using im-

mobilizedRhizopus delemarlipase in an organic solvent-free system, and to purify

the structured lipids from the reaction mixture by molecular distillation.

8.3.2 Preparation of immobilized lipase

Acidolysis of natural oils with CA must be performed in a system without water in

order to repress simultaneous hydrolysis. When a soluble lipase is used in the system,

the enzyme will not disperse well because of aggregation. This problem can be

solved by use of immobilized lipase. In this study, we selected a 1,3-positional spe-

cificR. delemarlipase (Ta-Lipase; Tanabe Seiyaku, Osaka, Japan) which is used as a

flavor enzyme for the production of bread, and attempted to immobilize the lipase on

a ceramic carrier (SM-10; NGK Insulator, Aichi, Japan) (Shimada et al., 1996a).

After the ceramic carrier (50 g) was suspended in 200mL of 10 %Rhizopuslipase

solution, 600 mL cold acetone (– 80 8 C) was added gradually with stirring gently, and

the precipitate dried under reduced pressure. Approximately 90 % of lipase was

immobilized on the carrier, but the lipase scarcely showed acidolysis activity in

a reaction mixture without water. A reaction mixture containing 2 % water effi-

ciently activated the lipase. Thus, the first reaction was performed at 30 8 C for

48 h in a mixture of tuna oil/CA (1 : 1, w/w), 4 % immobilized lipase, and 2 % water

with shaking at 130 oscillations/min (Table 3). As a result, 31 mol% CA was incor-

porated into glycerides, though 18 % partial glycerides were also generated by si-

multaneous hydrolysis. To repress the hydrolysis, the subsequent reactions were

conducted by transferring the immobilized lipase to a fresh oil/CA substrate mixture

without addition of water. The CA amount in glycerides was slightly increased in the

second reaction, and the generation of partial glycerides was reduced to below 1 % in

the third reaction. Therefore, immobilized lipase that had been treated twice (first

with adding water; second without adding water) was employed for the production of

a MLM-type structured lipid containing DHA.

8.3 Production of highly absorbable structured lipid 135