Metabolism of canthaxanthin, a red diketocarotenoid, by chickens

Canthaxanthin, (4,4'-diketo-beta,beta-carotene), a red carotenoid used to extend the dominant wavelength of the yellow pigments in the skin and egg yolk of chickens, was fed (70 micrograms/g diet) to chicks depleted of normal tissue oxycarotenoids. High performance liquid chromatography analysis of tissues from such chicks revealed that a portion of canthaxanthin was reduced to 4-hydroxyechinenone (4-hydroxy-4'-keto-beta,beta-carotene) that in turn was reduced in part to isozeaxanthin (4,4'-dihydroxy-beta,beta-carotene). The alcohols thus formed were acylated in part to 4-hydroxyechinenone monoester and isozeaxanthin monoester and diester. Individual metabolites were identified by retention times, ratios A470/A430, and stopped-flow spectral analyses, which were identical in each case to authentic standards. Ratios of canthaxanthin to metabolites varied with the tissue, but in general metabolites were concentrated in the integument.