Extraction of Fucoxanthin Isomers from the Edible Brown Seaweed Undaria pinnatifida Using Supercritical CO2: Effects of Extraction Conditions on Isomerization and Recovery of Fucoxanthin

Fucoxanthin, a characteristic carotenoid found in brown seaweeds, has been reported to exert beneficial biological activities, including antiobesity and anticancer activities Moreover, the Z-isomers of this compound potentially have greater bioavailability and biological activities than the naturally predominant all-E-isomer. Therefore, the consumption of Z-isomer-rich fucoxanthin through daily meals and dietary supplements may have beneficial effects. In this study, we aimed to investigate the effects of different extraction conditions on the Z-isomer ratio and recovery of fucoxanthin obtained from Undaria pinnatifida using supercritical CO2 (SC-CO2), particularly focusing on the high-temperature conditions that enhance thermal Z-isomerization. High-temperature SC-CO2 extraction at ≥ 120°C was found to enhance the thermal isomerization of fucoxanthin. For example, when the extraction was performed at 40, 80, 120, and 160°C and 30 MPa for 30 min with a co-solvent (ethanol), the total Z-isomer ratios were 11.7, 11.5, 18.7, and 26.5%, respectively. Furthermore, the high-temperature extraction significantly improved fucoxanthin recovery under high-pressure (≥ 30 MPa) conditions in the presence of the co-solvent. For example, when fucoxanthin was extracted at 40, 80, 120, and 160°C under the same conditions as above, the recoveries were 17.5, 20.6, 30.7, and 29.5%, respectively. Hence, the high-temperature SC-CO2 extraction of fucoxanthin from U. pinnatifida would not only enhance health benefits of fucoxanthin via the Z-isomerization but also improve the productivity. Moreover, the use of non-toxic CO2 and a low-toxicity organic solvent (ethanol) ensures that the final fucoxanthin product is safe for consumption. The Z-isomer-rich fucoxanthin obtained using this method is accordingly considered to have potential for use as a dietary supplement.