Rapid and Continuous Astaxanthin Isomerization in Subcritical Ethanol

Abstract

Recent studies have shown that Z-isomers of astaxanthin have greater bioavailability and biological activity than the all-E-isomer. Hence, it is important to develop efficient and practical Z-isomerization methods. This study attempted to establish a continuous-flow isomerization system for (all-E)-astaxanthin in subcritical ethanol. Specifically, the effects of temperature, pressure, time, and addition of antioxidants and a natural catalyst, allyl isothiocyanate, on the Z-isomerization and degradation were investigated. Continuous high-temperature processing (>140 °C) efficiently promoted astaxanthin Z-isomerization within a few minutes, but simultaneously accelerated its degradation. We found that the thermal degradation could be inhibited by adding specific antioxidants, especially ascorbic acid. Finally, using the continuous-flow system with ascorbic acid, 60.3% of total Z-isomer ratio of astaxanthin was achieved while inhibiting the degradation at 200 °C and 10 MPa in just 30 s. This efficient and environmentally friendly isomerization technology is an effective means for the production of Z-isomer-rich astaxanthin materials.

Supercritical CO2 Extraction of Carotenoids (Astaxanthin, Adonirubin, and Adonixanthin) from Paracoccus carotinifaciens: Improved Z‐Isomer Ratio and Recovery of Carotenoids via High‐Temperature Extraction

“…The rate of formation of (mono-Z)astaxanthin decreased in the order of 13Z-> 9Z-> 15Z-isomers. This trend is similar to our recent studies on the thermal isomerization of (all-E)-astaxanthin in organic solvents, [29,30] which can be explained in terms of the differences in the potential and activation energies of the mono-Z-isomers, that is, their relative potential energies decrease in the order of 15Z-> 13Z-> 9Zisomers, and the magnitude of the activation energy of isomerization from the all-E-isomer to individual mono-Z-isomer decreases in the order of 9Z-> 13Z-> 15Z-isomers. [31,32] The reason for the small amount of the 15Z-isomer despite its low activation energy is thought to be its high potential energy, which makes the 15Z-isomer thermodynamically unstable.…”

“…In fact, we have recently demonstrated that astaxanthin is degraded in a short time by heating above 140 °C. [30] On the other hand, many studies have demonstrated that the extraction efficiency of lipid-soluble components, such as triacylglycerols, decreases at temperatures above 80 °C. [33][34][35][36] However, for astaxanthin, adonirubin, and adonixanthin, the recovery rates showed an increasing trend up to 120 °C.…”

“…This might be due to an increase in the extraction solvent polarity, that is, the solvent polarity increment resulted in a decrease in the solubility of astaxanthin and adonixanthin. [25,38] Furthermore, an increase in ethanol content may have accelerated the thermal degradation of those carotenoids, resulting in a reduction of their recoveries (note that astaxanthin is rapidly degraded under subcritical ethanol conditions [30] ). From the above, a low ethanol flow rate is preferable from the viewpoint of the total Z-isomer ratio of carotenoids, while a high ethanol flow rate is preferable from the viewpoint of carotenoid recovery.…”

Oral Supplementation with Z-Isomer-Rich Astaxanthin Inhibits Ultraviolet Light-Induced Skin Damage in Guinea Pigs

“…The predominant astaxanthin Z -isomers in Z-AST-D were the 9 Z - and 13 Z -isomers, representing 18.5% and 38.4%, respectively, of the total astaxanthin content. Moreover, the 15 Z -isomer and three unidentified Z -isomers (possibly the di- Z -isomers [ 19 , 20 , 21 , 22 ]) were also present. The absorption spectra of astaxanthin isomers are shown in Figure 1 b.…”

“… ( a ) Normal-phase HPLC chromatograms of an (all- E )-astaxanthin-rich diet (E-AST-D; total Z -isomer ratio = 3.2%) and a ( Z )-astaxanthin-rich diet (Z-AST-D; total Z -isomer ratio = 84.4%) and ( b ) absorption spectra of peaks a–c and (all- E )-, (9 Z )-, (13 Z )-, and (15 Z )-astaxanthin. Peaks a–c were tentatively identified as astaxanthin Z -isomers [ 19 , 20 , 21 , 22 ]. …”