21] Relation of cis-trans isomers of carotenoids to developmental processes

Abstract

This chapter describes the methods that permit the quantitation of cis-canthaxanthins—in addition to the all-trans-canthaxanthin and their metabolic precursors—in different stages of the Artemia life cycle to relate their occurrence, fate, and tissue distribution to developmental processes. Natural carotenoids mainly occur in their most stable stereochemical configuration—that is, the all-trans form. If cis isomers are present in biological materials, such as fruits and vegetables, they have often been formed artifactually from the all-trans form, mainly because of processing. However, the genuine presence of cis-carotenoids has been documented in a number of organisms, including higher plants, photosynthetic bacteria, algae, and the brine shrimp Artemia. The cis-canthaxanthins demonstrated in the latter organism were found to display a more characteristic biological fate than their all-trans counterpart. For a long time all-trans-canthaxanthin and its metabolic precursors, echinenone and β-carotene, have been considered the major carotenoids in Artemia. The application of nonaqueous reversed-phase chromatography in conjunction with photodiode array detection to encysted embryos of this organism led to the discovery of genuine cis-canthaxanthin.