Front Matter

reaction, the reaction was performed batchwise at 30 8 C in a mixture of 13.5 mL

borage oil/CA (1 : 2, w/w) and 0.5 g immobilized lipase with shaking. The reaction

was repeated by transferring the lipase to a fresh substrate mixture every 2 days; the

daily amount of substrate converted to structured lipid by 1 g of the enzyme was the

same as that of the flow reaction. As shown in Figure 7, the efficiency of the flow

reaction completely agreed with that of the batch reaction. From the industrial view-

point, the flow reaction with fixed-bed reactor has the following advantages. (i) The

carrier of immobilized enzyme is not destroyed even if the lipase is continuously

used for more than 100 days. (ii) The procedure of continuous flow reaction is easier

than that of batch reaction. (iii) The period of contact of substrates with the lipase is

shorter: flow reaction (retention time), 1.3 h; batch reaction, 48 h. The shorter reac-

tion time is advantageous to the processing of an oil containing unstable PUFAs.

The reaction mixture contains triglycerides and FFAs, the molecular weights of

which are different. Thus, taking advantage of the differences in their boiling points,

an attempt was made to purify triglycerides by film distillation (Shimada et al.,

1999b). The reaction mixture that eluted from the above column after 30–50

days was collected, and 1 kg of the mixture was used for the distillation. The dis-

tillation was performed by measuring the acid value of the residue as a guide. When

the distillation was performed at 130 8 C and 0.2 mmHg, 644 g was obtained as the

first distillate, the acid value being 369. Because the acid value of the residue was 54,

the distillation temperature was increased to 170 8 C. As a result, 52 g was separated

as the second distillate (acid value 202), but the acid value of the residue was still 26.

Further distillation at 195 8 C brought the third residue to 2.6 with 24.8 % of recovery.

The third residue contained 98.7 % triglycerides, 0.5 % diglycerides, and 0.8 %

FFAs. This result showed that film distillation removed FFAs very effectively

from the reaction mixture.

8.4 Production of a structured lipid containing AA and

palmitic acid

Human milk contains 20–25 % of palmitic acid, and about 70 % of the fatty acid is

esterified to the 2-position of triglycerides (Breckenridge et al., 1969; Martin et al.,

1993). Pancreatic lipase hydrolyzes dietary oils and fats to FFAs and 2-monoglycer-

ides, and the absorption efficiency of free palmitic acid is relatively low compared

with that of free unsaturated fatty acids (Jensen et al., 1986). This result supports that

fat absorption is higher in infants fed fats with PA at 2-position of triglycerides than

1,3-position (Innis et al., 1994). It has been hypothesized from these facts that the

high absorption efficiency of human milk fat is the result of specific positioning of

PA at the 2-position of the triglyceride moiety (Fomon et al., 1970; Innis et al., 1994).

Thus, we attempted to synthesize 1,3-arachidonoyl-2-palmitoyl-glycerol (designated

APA) in high purity as a material for absorption studies (Shimada et al., 2000). Tri-

palmitin (palmitic acid, 90 %; stearic acid, 8 %) and AA (91 %) was used as a start-

ing material. ImmobilizedRhizopuslipase was used after the pretreatment in a sub-

strate mixture containing 2 % water as described above. The acidolysis of tripalmitin

with AAwas conducted as follows: a mixture of 10 g AA/tripalmitin (1 : 5, w/w) and

8.4 Production of a structured lipid containing AA and palmitic acid 141