09.12.2012 Views

Food Lipids: Chemistry, Nutrition, and Biotechnology

Food Lipids: Chemistry, Nutrition, and Biotechnology

Food Lipids: Chemistry, Nutrition, and Biotechnology

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

are nearly completely hydrolyzed <strong>and</strong> absorbed faster, mainly as free fatty acids <strong>and</strong><br />

rarely as 2-MAGs. These MCFAs are then transported as FFAs bound to serum<br />

albumin in portal venous blood.<br />

Figure 14 shows a proposed modified pathway for MCT, LCT, <strong>and</strong> SL metabolism.<br />

The proposed metabolic routes for SL based on current evidence are indicated<br />

in italics. The metabolism of an SL is determined by the nature <strong>and</strong> position of the<br />

constituent fatty acids on the glycerol moiety. This may account for the differences<br />

in the pathway of absorption: lymphatics versus portal.<br />

Evidence for lymphatic absorption of MCFAs <strong>and</strong> storage in adipose tissue is<br />

accumulating (103–107). Jensen et al. (107) observed the presence of more C10:0<br />

than C8:0 fatty acids in the lymph of canine model fed an SL containing MCTs <strong>and</strong><br />

fish oil versus its physical mixture, despite an overall ratio of C10:0 to C8:0 of 0.3<br />

in their diets. Analysis of the SL molecular species revealed that MCFAs in lymph<br />

were present as mixed TAGs, suggesting that the MCFAs at the 2-position may<br />

account for the improved absorption. The 2-MAGs apparently were reesterified with<br />

endogenous or circulating LCFAs <strong>and</strong> subsequently absorbed through the lymphatic<br />

system. Also, feeding of high levels of MCTs can lead to lymphatic absorption <strong>and</strong><br />

presence of MCFAs in the chylomicrons.<br />

Enhanced absorption of 18:2n-6 was observed in cystic fibrosis patients fed SL<br />

containing LCFAs <strong>and</strong> MCFAs (89,108). Rapid hydrolysis <strong>and</strong> absorption of an SL<br />

containing MCFAs at the sn-1 <strong>and</strong> sn-3 positions <strong>and</strong> an LCFA at the sn-2 position<br />

have been reported (89,109,110). To improve the absorption of any fatty acid, its<br />

esterification to the 2-position of the glycerol moiety is suggested. Mok et al. (111)<br />

reported that the metabolism of an SL differs greatly from that of a similar physical<br />

mixture. The purported benefit of fish oil n-3 PUFAs can be attributed to their absorption<br />

as 2-MAGs. This factor is important in the construction of novel or designer<br />

SL molecules for food, therapeutic, <strong>and</strong> nutritional use.<br />

Figure 14 Proposed modified metabolic pathways for medium chain <strong>and</strong> long chain triacylglycerols<br />

<strong>and</strong> structured lipids.<br />

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

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!