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

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

very enriched in medium chain length fatty acids, especially during seed development/maturation.<br />

2. Involvement of Kennedy Pathway<br />

The GPAT activities in C. lanceolata, C. procumbrens, <strong>and</strong> C. wrightii are characterized<br />

by selectivity toward 10:0–14:0-CoA > 18:X/16:0-CoA substrates (188,189).<br />

Perhaps the most critical step in these species is the LPAAT reaction. For 12:0/<br />

14:0 LPA species, acyl-CoA of fewer than 16 carbons are utilized as substrates for<br />

the second esterification step, resulting in PA products with medium chain fatty acyl<br />

residues at both sn-1 <strong>and</strong> sn-2 sites, <strong>and</strong> this pattern also occurs for palm endosperm<br />

LPAAT (166). When 18:1�9-LPA is available for reaction, LPAAT exhibits a strict<br />

preference for another 18:1�9-CoA to become esterified to form di-18:1�9-PA in<br />

Cuphea spp. (188,189), or in the case of palm kernel LPAAT, either 12:0- or<br />

18:1�9-CoA is used to yield di-18:1�9-PA <strong>and</strong> 12:0,18:1�9-PA (172). In coconut endosperm,<br />

10:0/12:0/14:0-CoA is preferred for reactions with both 12:0/18:1�9-LPA species (190,191). In palm endosperm, 18:1�9-LPA is preferred to 12:0-LPA (172),<br />

whereas in coconut endosperm the reverse is the case (190).<br />

The result of LPAAT <strong>and</strong> subsequent PTP action in Cuphea spp. is a bimodal<br />

distribution of di-18:1�9-acylglycerol <strong>and</strong> di-10:0/12:0/14:0-acylglycerol (188).<br />

DAGAT is selective for the latter diacylglycerol species <strong>and</strong> specifically utilizes<br />

another 10:0/12:0/14:0-CoA for the final step in assembling triaclyglycerol (181,188).<br />

The di-18:1�9-acylglycerol is almost exclusively used for exchange (CPT) to the PC<br />

pool for incorporation into functional lipids. Thus, the combined selectivities of the<br />

GPAT, LPAAT, <strong>and</strong> DAGAT strictly segregate fatty acids into storage <strong>and</strong> functional<br />

glycerolipids (188,192). The CPT enzyme is not believed to play a major role<br />

in excluding various diacylglycerol species from the PC pool (181). Rather, the lack<br />

of di-10:0/12:0/14:0-PC in the PC pool may be accounted for in the comparatively<br />

high DAGAT activity toward di-10:0/12:0/14:0-acylglycerol (<strong>and</strong> rapid channeling<br />

into triacylglycerol), or the existence of two discrete metabolic pools of diacylglycerol:<br />

one for PC exchange <strong>and</strong> the other for triacylglycerol assembly (181).<br />

E. Oils Enriched in Unusual Fatty Acids<br />

1. General Aspects<br />

Very long chain fatty acids (VLCFAs), oxygenated fatty acids [such as ricinoleic<br />

acid (18:1�9,12-OH), <strong>and</strong> vernolic acid (18:1�9,12/13-epoxy)], <strong>and</strong> those with unusual doublebond<br />

positions (�5, �6, �11) are treated as a group. An underst<strong>and</strong>ing of how these<br />

unusual fatty acids are channeled in the host plants is useful in building a comprehensive<br />

view of triacylglycerol assembly in all plants <strong>and</strong> provides insight into genetic<br />

traits that may be worthwhile to exploit in plant oils used for foods.<br />

VLCFAs include those of 20–24 acyl carbons. The most notable are erucic<br />

(22:1�13) <strong>and</strong> gondoic (20:1�11) acids in rapeseed, <strong>and</strong> the same fatty acids plus<br />

20:1�5, 22:2�5,13 in meadowfoam, where the �5 double bond arises from �5DES<br />

action after ACE-mediated elongation from the 16:0/18:1�9 parent fatty acid (193).<br />

Other species relevant to this grouping include mustard (Sinapis alba <strong>and</strong> Brassica<br />

spp.), Crambe spp., groundnuts (source of 20:0, 22:0, <strong>and</strong> 24:0), honesty (Lunaria<br />

annua, source of nervonic acid, 24:1�15), borage, black currant <strong>and</strong> evening primrose<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!