A comprehensive review of recent advances and future perspectives on astaxanthin geometrical isomers: Biological...

Astaxanthin, a xanthophyll carotenoid, exists in multiple geometric isomer forms owing to its conjugated polyene chains. In general, the all-E-isomer is predominant in nature; however, the Z-isomers are gaining increasing attention owing to their superior bioavailability and enhanced biological activity. In addition, Z-isomerization of the all-E-isomer induces significant changes in the physicochemical properties (e.g., solubility and crystallinity), leading to improved processing efficiency. Therefore, this review summarizes recent advances in isomerization techniques, including thermal treatment, light and microwave irradiation, and catalytic methods, for the efficient production of the Z-isomers. It also outlines analytical methods for identifying isomers for structural characterization. Furthermore, the physicochemical differences between the isomers, including solubility, crystallinity, and stability, are summarized in the context of processing and formulation. Finally, future prospects and potential applications of the Z-isomer-rich astaxanthin in the food, cosmetic, and feed industries are discussed, along with current limitations.