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Food Lipids: Chemistry, Nutrition, and Biotechnology

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Figure 26 Glyceroglycolipid structures <strong>and</strong> nomenclature.<br />

I. Fat-Soluble Vitamins<br />

1. Vitamin A<br />

Vitamin A exists in the diet in many forms (Fig. 28). The most bioactive form is the<br />

all-trans retinol, <strong>and</strong> cis forms are created via light-induced isomerization (Table 8).<br />

The 13-cis isomer is the most biopotent of the mono- <strong>and</strong> di-cis isomers. The �<strong>and</strong><br />

�-carotenes have biopotencies of about 8.7% <strong>and</strong> 16.7% of the all-trans retinol<br />

activity, respectively. The daily value (DV) for vitamin A is 1000 retinol equivalents<br />

(RE), which represents 1000 �g of all-trans retinol or 6000 �g of�-carotene. Vitamin<br />

A can be toxic when taken in levels exceeding the %DV. Some reports suggest<br />

that levels of 15,000 RE per day can be toxic [38].<br />

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

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