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Food Lipids: Chemistry, Nutrition, and Biotechnology

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Figure 4 Pathway for eicosanoid biosynthesis.<br />

disturbances, dermatitis, <strong>and</strong> growth retardation (29). Therefore, n-3 PUFAs such as<br />

DHA must be included in their diet <strong>and</strong> in SL design.<br />

Structured lipids containing n-3 PUFAs <strong>and</strong> MCFAs have been synthesized<br />

chemically by hydrolysis <strong>and</strong> r<strong>and</strong>om esterification of fish oil <strong>and</strong> MCTs. They have<br />

been shown to inhibit tumor growth <strong>and</strong> to improve nitrogen balance in Yoshida<br />

sarcoma-bearing rats (30). We have successfully used lipases as biocatalysts to synthesize<br />

position-specific SLs containing n-3 PUFAs with ability to improve immune<br />

function <strong>and</strong> reduce serum cholesterol concentrations (31,32). EPA is important in<br />

preventing heart attacks primarily because of its antithrombotic effect (33). It was<br />

also shown to increase bleeding time <strong>and</strong> to lower serum cholesterol concentrations<br />

(33). Studies with nonhuman primates <strong>and</strong> human newborns suggest that DHA is<br />

essential for the normal functioning of the retina <strong>and</strong> brain, particularly in premature<br />

infants (34). Other studies have shown that n-3 fatty acids can decrease the number<br />

<strong>and</strong> size of tumors <strong>and</strong> increase the time elapsed before the appearance of tumors<br />

(35).<br />

The n-3 fatty acids are essential in growth <strong>and</strong> development throughout the life<br />

cycle of humans <strong>and</strong> therefore should be included in the diet. <strong>Nutrition</strong>al experts<br />

consider a level of 2–5% of n-3 fatty acids optimum in enhancing immune function<br />

in SL as shown in Table 1. Polyunsaturated fatty acids of the n-3 series are antagonists<br />

of the arachidonic acid (20:4n-6) cascade (Fig. 5). The mode of action of fish<br />

oil n-3 PUFAs on functions mediated by n-6 PUFAs is summarized in Table 2 (36).<br />

The n-3 PUFAs inhibit tissue eicosanoid biosynthesis by preventing the action of<br />

�-6 desaturase <strong>and</strong> cyclooxygenase/lipoxygenase enzymes responsible for the conversion<br />

of 18:2n-6 to 20: 4n-6 <strong>and</strong> 20:4n-6 to eicosanoids, respectively. The amount<br />

of 18:2n-6 determines the 20:4n-6 content of tissue phospholipid pools <strong>and</strong> affects<br />

eicosanoid production. Eicosanoids are divided into prostanoids (prostagl<strong>and</strong>ins,<br />

prostacyclins, <strong>and</strong> thromboxanes), which are synthesized via cyclooxygenase, <strong>and</strong><br />

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

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