| Summary: | The study investigated egg quality aspects such as astaxanthin concentration, <i>E</i>/<i>Z</i>-isomer ratio, and yolk color in laying hens fed with astaxanthin-containing diets. Dried <i>Paracoccus carotinifaciens</i> cell powder (Panaferd-AX) and fine cell powder (Panaferd-P) were used as sources of astaxanthin, with average particle diameters of approximately 100 μm and 10 μm, respectively. <i>Paracoccus carotinifaciens</i> contains valuable rare carotenoids such as adonirubin and adonixanthin, and thus the concentrations of these carotenoids in egg yolk were also evaluated. The <i>E</i>/<i>Z</i>-isomer ratios of the egg yolk carotenoids were determined by normal-phase high-performance liquid chromatography (HPLC) with an improved solvent system. Feeding diets containing <i>P. carotinifaciens</i> resulted in increased concentrations of astaxanthin, adonirubin, and adonixanthin in egg yolk, as well as a marked increase in the yolk color fan score; values associated with the Panaferd-P-containing diet were higher than those associated with the Panaferd-AX-containing diet. For example, the astaxanthin concentration in egg yolks of hens fed with the Panaferd-AX- and Panaferd-P-containing diets for 21 days were 1.21 μg/g and 1.85 μg/g, respectively. This indicates that the pulverization treatment of the <i>P. carotinifaciens</i> powder increased the efficiency of carotenoid accumulation in the egg yolk. Moreover, more than 95% of astaxanthin in <i>P. carotinifaciens</i> was present as the all-<i>E</i>-isomer. However, approximately 25% of astaxanthin in egg yolk was present as the <i>Z</i>-isomers. In recent years, astaxanthin <i>Z</i>-isomers have attracted substantial attention as they exhibit a greater bioavailability and bioactivity than the all-<i>E</i>-isomer. These data are important not only for understanding egg yolk pigmentation but also for improving the nutritional value of hens’ egg yolk through the addition of <i>P. carotinifaciens</i> to their diet.
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