IDOXANTHIN, A MAJOR CAROTENOID IN THE FLESH OF ARCTIC CHARR (SALVELINUS-ALPINUS) FED DIETS CONTAINING ASTAXANTHIN

Three year-classes (1 +, 2 + and 3 +) of Arctic charr were fed diets c ontaining 63 or 114 mg astaxanthin kg(-1) for 3 months. Effects of fis h size and dietary inclusion level of astaxanthin on carotenoid compos ition of the flesh were examined. Idoxanthin (3,3',4'-trihydroxy-beta, beta-carotene-4-one), a metabolite of astaxanthin, was identified by U V-visible spectroscopy, mass spectrometry (MS), and co-chromatography with an authentic standard on thin-layer and high-performance liquid-c hromatography (TLC and HPLC). Idoxanthin comprised 60-76% of the total carotenoids in the flesh of the Arctic charr after 3 months. The othe r major carotenoid was astaxanthin. The ratio between the 3',4'-cis an d 3',4'-trans glycolic isomers of idoxanthin was close to 1:1. The pro portion of idoxanthin (% of total carotenoid) was size-dependent, and the smallest fish contained the highest percentage of idoxanthin. Ther e was no effect of astaxanthin level on carotenoid composition. The re sults indicate that a high proportion of astaxanthin metabolites in Ar ctic charr is part of its natural development. (C) 1997 Elsevier Scien ce B.V.