Accumulation of astaxanthin all-E, 9Z and 13Z geometrical isomers and 3 and 3 ' RS optical isomers in rainbow trout (Oncorhynchus mykiss) is selective

Concentrations of all-E-, 9Z- and 13Z- geometrical and (3R,3'R), (3R,3'S) a nd (3S,3'S) optical isomers of astaxanthin were determined in rainbow trout liver, gut tissues, kidney, skin and blood plasma to evaluate their body d istribution. Two cold-pelleted diets containing predominantly all-E-astaxan thin (36.9 mg/kg astaxanthin, 97% all-E-, 0.4% 9Z-, 1.5% 13Z-astaxanthin, a nd 1.1% other isomers, respectively) or a mixture of all-E- and Z-astaxanth ins (35.4 mg/kg astaxanthin, 64% all-E-, 18.7% 9Z-, 12.3% 13Z-astaxanthin, and 2.0% other isomers, respectively), were fed to duplicate groups of trou t for 69 d. Individual E/Z isomers were identified by VIS- and H-1-NMR-spec trometry, and quantified by high-performance liquid chromatography. Signifi cantly higher total carotenoid concentration was observed in plasma of trou t fed diets with all-E-astaxanthin (P < 0.05). The relative E/Z-isomer conc entrations of plasma, skin and kidney were not significantly different amon g groups, whereas all-E-astaxanthin was higher in intestinal tissues and 13 Z-astaxanthin was lower in liver of trout fed all-E-astaxanthin (P < 0.05). The relative amount of hepatic 13Z-astaxanthin (39-49% of total astaxanthi n) was higher than in all other samples (P < 0.05). Synthetic, optically in active astaxanthin was used in all experiments, and the determined dietary ratio between the 3R,3'R:3R,3'S (meso):3S,3'S optical isomers was 25.3:49.6 :25.1. The distribution of RIS-astaxanthin isomers in feces, blood, liver a nd fillet was similar to that in the diets. The ratio between (3S,3'S)- and (3R,3'R)-astaxanthin in the skin and posterior kidney was ca. 2:1 and 3:1, respectively, regardless of dietary E/Z-astaxanthin composition. The resul ts show that geometrical and optical isomers of astaxanthin are distributed selectively in different tissues of rainbow trout.