Evaluation and improvement of storage stability of astaxanthin isomers in oils and fats.

Astaxanthin Z-isomers potentially have greater bioavailability and biological activity than (all-E)-astaxanthin. However, the stability of the Z-isomers is lower than the all-E-isomer, which is a serious problem affecting its practical use. In this study, we investigated the impacts of different suspension media (oils and fats) and additives on astaxanthin isomer stability and identified suitable ones for astaxanthin stabilization. The evaluations showed that several vegetable oils and antioxidants significantly improved astaxanthin isomer stability, e.g., when soybean and sunflower oils were used as the suspension medium, astaxanthin isomers were hardly degraded; however the total Z-isomer ratio decreased from ~80% to ~50% during 6-week storage at 30 °C. Moreover, it was revealed that (9Z)-astaxanthin showed higher stability than the 13Z- and 15Z-isomers. Hence, to maintain astaxanthin concentration and the Z-isomer ratio over long periods, it is important to use suitable suspension mediums and antioxidants, and select a Z-isomerization method that increases (9Z)-astaxanthin ratio.

Astaxanthin Z-isomer-rich diets enhance egg yolk pigmentation in laying hens compared to that in all-E-isomer-rich diets.

The effects of feeding diets containing astaxanthin with different Z-isomer ratios to laying hens on egg qualities, such as astaxanthin concentration in egg yolk and yolk color, were investigated. As the astaxanthin source, a natural microorganism Paracoccus carotinifaciens was used. Astaxanthin with different Z-isomer ratios was prepared by thermal treatment with different conditions and then added to the basal diet at a final astaxanthin concentration of 8 mg/kg. We found that, as the Z-isomer ratios of astaxanthin in the diet increased, the astaxanthin concentration in egg yolk and the yolk color fan score also increased significantly. Importantly, feeding a 50.6% Z-isomer ratio diet increased astaxanthin concentration in egg yolk by approximately fivefold and the color fan score by approximately 2 compared to that in hens fed an all-E-isomer-rich diet. Moreover, we showed that feeding Z-isomer-rich astaxanthin to laying hens increased plasma astaxanthin concentration by more than five times in comparison to that in hens fed an all-E-isomer-rich diet. These results indicate that Z-isomers of astaxanthin have higher bioavailability than that of the all-E-isomer and thus they exhibit greater egg yolk-accumulation efficiency.