Thermal isomerization of astaxanthin esters in the green alga Haematococcus lacustris without any chemicals

Abstract

Recent evidence indicates that carotenoid Z-isomers have higher oral bioavailability and biological activity than the all-E-isomers. Therefore, many researchers have investigated the development of efficient carotenoid isomerization techniques, primarily thermal treatment. However, most of them studied the free form of carotenoids. In this study, the thermal isomerization characteristics of astaxanthin esters derived from the food-grade Haematococcus alga were investigated. For practical applications, edible oils were used as the medium in the isomerization process, and organic solvents or other chemicals were not used. Furthermore, a continuous heated flow isomerization system was installed. The optimal heating conditions increased the total Z-isomer ratio of astaxanthin esters to approximately 60% while inhibiting astaxanthin decomposition. The resulting Z-isomer-rich astaxanthin esters displayed excellent storage stability. The stability was shown to be potentially higher than that of the free form. This superior stability of the Z-structure of ester forms was demonstrated by density-functional theory. The observations of this study would contribute to the practical applications of Z-isomer-rich astaxanthin materials.