Utilization of (3S ,3′S )-astaxanthin acyl esters in pigmentation of rainbow trout (Oncorhynchus mykiss )

The deposition of natural, optically active, astaxanthin fatty acid esters in rainbow trout (Oncorhynchus mykiss) was studied. Mono-esterified and di-esterified (3S,3′S) astaxanthin were purified from the green microalga Haematococcus pluvialis and incorporated into extruded diets and compared with diets containing synthetic racemic astaxanthin (Carophyll Pink) and a total carotenoid extract from the alga. All sources of astaxanthin achieved >4 mg kg−1 in the white muscle after 6 weeks feeding. No significant difference (P > 0.05) between the deposition of astaxanthin or total carotenoid for the different diets was observed. Other xanthophylls, namely lutein, zeaxanthin and idoxanthin were found in the white muscle of rainbow trout fed all diets and together accounted for 10–14% of total carotenoid. Astaxanthin was deposited in the white muscle in the stereochemical form administered in the diet, i.e. racemic astaxanthin for Carophyll Pink and ˜100% (3S,3′S)-astaxanthin for the algal sources. In contrast, epimerization of (3S,3′S) astaxanthin from the alga was observed for the astaxanthin esters deposited in the skin of rainbow trout, with a ratio close to 1.0:2.0:1.0 (3S,3′S:3R,3′S:3R,3′R).