The purpose of the present study was to clarify the differences in the bioavailability and tissue accumulation efficiency between (all-E)-and (Z)-astaxanthin. Astaxanthin with a high proportion of the Z-isomer (especially rich in the 9Z-and 13Zisomers) was prepared from (all-E)-astaxanthin by thermal treatment and solid−liquid separation. The all-E-isomer-or Z-isomer-rich diet was fed to male rats for 2 weeks. After the feeding period, blood and tissue samples were collected, and their astaxanthin levels were evaluated. The Z-isomer-rich astaxanthin diet resulted in higher levels of astaxanthin in blood and many tissues (in particular, skin, lung, prostate, and eye) compared to the all-E-isomer-rich diet. Moreover, the Z-isomer-rich diet enhanced the level of the 13Zisomer in blood and tissues rather than that of the 9Z-isomer. These results strongly supported that astaxanthin Z-isomers have greater bioavailability and tissue accumulation efficiency than the all-E-isomer. Moreover, (13Z)-astaxanthin would have higher bioavailability and tissue accumulation than the other isomers.
Recent studies have shown that Z-isomers of carotenoids
exhibit greater bioavailability and tissue accumulation efficiency
than the natural isomer, the all-E-isomers. Here,
we attempted to carry out the Z-isomerization of Paracoccus carotinifaciens-derived carotenoids (astaxanthin,
adonirubin, and adonixanthin) by subcritical water processing. An
aqueous solution dispersed with P. carotinifaciens was treated in a pressure-resistant vessel in the range of 140–240
°C and 4–16 MPa. The processing pressure in the above
range did not affect carotenoid isomerization; however, depending
on the heating temperature, the total Z-isomer ratio
markedly increased, and carotenoid degradation was also accelerated.
Moreover, to promote the Z-isomerization efficiency,
the effect of adding an entrainer, ethanol, was investigated. The
results showed that the addition of ethanol markedly promoted the Z-isomerization efficiency. Finally, we achieved over 50%
of the total Z-isomer ratio of P. carotinifaciens-derived carotenoids while inhibiting their degradation by 30 min
subcritical water processing.
The effects of high-temperature supercritical CO 2 (SC-CO 2 ) extraction on Z-isomerization and recovery of carotenoids (astaxanthin, adonirubin, and adonixanthin) from Paracoccus carotinifaciens are investigated. The high-temperature extraction, especially at >100 °C, not only increases the total Z-isomer ratio of carotenoids in the resulting extracts but also improves carotenoid recovery. For example, when the SC-CO 2 extraction is performed at 60 °C and 30 MPa with an entrainer (ethanol), the total Z-isomer ratio and the recovery of astaxanthin are 11.1% and 28.4%, respectively, whereas at 120 °C, the values increase to 54.2 and 56.4%, respectively. The significant improvement in the extraction efficiency of carotenoids at high temperatures can be attributed to the increase in the ratio of carotenoid Z-isomers with high solubility in SC-CO 2 . Moreover, the effects of extraction pressure and entrainer content on Z-isomerization and recovery of carotenoids are also investigated. The results show that higher pressure and ethanol content resulted in lower Z-isomer ratios and higher recoveries of carotenoids. As the Z-isomers of carotenoids have greater bioavailability and potentially exhibit superior biological activities than the all-E-isomers, high value-added carotenoids, and higher yield can be simultaneously achieved with high-temperature extraction. Practical applications: As carotenoid extraction is usually performed using toxic organic solvents, residual solvents are a serious concern. In addition, naturally occurring carotenoids (mainly the all-E-isomers) have low bioavailability. These are important issues that need to be overcome for the industrial use of carotenoids. The Z-isomer-rich carotenoids obtained by SC-CO 2 extraction under high-temperature conditions have great potential to solve these issues simultaneously.
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