Carotenoids are red, yellow, and orange pigments that absorb light in the 400- to 500-nm region of the visible spectrum (Isler, 1971). They are synthesized by photosynthetic microorganisms and plants, but not by animals. Particularly rich sources are yellow-orange fruits and dark green, leafy vegetables. About 700 naturally occurring carotenoids have been identified, of which about 50 can serve as precursors for vitamin A (Olsen, 1992). All are primarily symmetrical, C-40, polyisoprenoid structures with an extensive conjugated double-bond system (Fig. 1). The conjugated backbone of isoprene units is usually inverted at the center of the molecule, imparting the symmetry. Changes in the geometrical configuration about the double bonds result in many cis and trans isomers.
|Title of host publication||Fat-Soluble Vitamins|
|Editors||Peter J. Quinn, Valerian E. Kagan|
|Place of Publication||London|
|Number of pages||27|
|Publication status||Published - 1998|