Bioavailability of all-E-astaxanthin and Z-isomers of astaxanthin in rainbow trout (Oncorhynchus mykiss)

Two cold-pelleted diets containing either 36.9 or 35.4 mg kg(-1) of predominantly all-E-astaxanthin (97% of total astaxanthin) or a mixture of all-E-and Z-astaxanthin (64 and 36%, respectively), were fed to duplicate groups of rainbow trout (Oncorhynchus mykiss) in freshwater (initial weight 0.4 kg) for 69 days. Average final weight was ca. 1.0 kg for both groups and the specific growth rate was 1.2-1.3% d(-1). The all-E-and Z-isomer mixture of astaxanthin was produced from Carophyll Pink(R) by an iodine-catalyzed isomerization. Flesh astaxanthin concentrations increased from 1.7 mg kg(-1) in the initial sample to 6-7 mg kg(-1) after 31 days. After 69 days, flesh carotenoid concentration of the trout fed all-E-astaxanthin tended to be higher than in trout fed the astaxanthin stereoisomer mixture (10.0 and 8.6 mg kg(-1), respectively). At the end of the experiment, the trout fed all-E-astaxanthin had significantly redder (through the color tristimuli analysis CIE [1976], a* tristimuli value) flesh than rainbow trout fed a mixture of all-E-and Z-astaxanthin. Apparent digestibility coefficients (ADC) of total astaxanthin were significantly higher in trout fed all-E-astaxanthin (79%) compared to trout fed the stereoisomer mixture (64%). No significant differences in the ADC of all-E-astaxanthin was observed between the two treatments, indicating a competitive mechanism of uptake of the different stereoisomers. ADC of all-E-astaxanthin was higher than that of 9Z- and 13Z-astaxanthin, and the ADC of 13Z-astaxanthin was significantly higher than that for 9Z-astaxanthin. This indicates that the Z-astaxanthin isomers are not utilized to the same extent as all-E-astaxanthin for flesh pigmentation. No significant differences were observed in total astaxanthin retention in the flesh. However, the retention of all-E-astaxanthin was higher in trout fed the stereoisomer mixture of astaxanthin than in the group fed all-E-astaxanthin. The better utilization of digestible carotenoids in the trout fed a mixture of all-E- and Z-astaxanthin isomers did not fully compensate for the low digestibility of astaxanthin in this group. No differences in astaxanthin stereoisomer composition in the flesh were observed between treatments. This indicates a selectivity in metabolism of the different stereoisomers of astaxanthin, either during absorption, transport or deposition. or their combinations and suggests that substantial isomerization of astaxanthin Z-isomers occurs in the liver. The retention of dietary astaxanthin in the flesh was as high as 24-32%. No significant differences in ADC were observed for dry matter, protein, fat or energy, while ADC for ash was significantly higher for the group fed the diet containing all-E-astaxanthin. The tendency for higher retention of digestible total astaxanthin In the flesh of trout fed a stereoisomer mixture of astaxanthin suggests that the stereoisomer composition of the dietary astaxanthin may influence the absorption capacity and bioavailability of total astaxanthin, probably by increasing intestinal micellar load of total astaxanthin. (C) 1997 Elsevier Science B.V.