High-efficiency lycopene isomerization with subcritical ethyl acetate in a continuous-flow reactor

Astaxanthin Isomers: A Comprehensive Review of Isomerization Methods and Analytic Techniques

The presence of multiple conjugated double bonds and chiral carbon atoms endows astaxanthin with geometric and optical isomers, and these isomers widely exist in biological sources, food processing, and in vivo absorption. However, there remains no systematic summary of astaxanthin isomers regarding isomerization methods and analytic techniques. To address this need, this Review focuses on a comprehensive analysis of Z-isomerization methods of astaxanthin, including solvent system, catalyst, and heat treatment. Comparatively, high-efficiency and health-friendly methods are more conducive to put into practical use, such as food-grade solvents and food-component catalysts. In addition, we outline the recent advances in analysis techniques of astaxanthin isomers, as well as the structural characteristics reflected by various methods (e.g., HPLC, NMR, FTIR, and RS). Furthermore, we summarized the related research on the safety evaluation of astaxanthin isomers. Finally, future trends and barriers in Z-transformation and analysis of astaxanthin isomers are also discussed.

High-temperature Supercritical CO2 Extraction of Lycopene from Tomato Powder for Enhancing Z-Isomerization and Recovery of Lycopene

This study aimed to investigate the effect of extraction conditions (temperature, pressure, and entrainer content) on the total Z-isomer ratio and recovery of lycopene in the extracts obtained after supercritical CO₂ (SC-CO₂) extraction of lycopene from tomato powder, with a particular focus on high-temperature conditions (≥ 80°C). The results showed that high-temperature SC-CO₂ extraction promoted the thermal isomerization of lycopene in a temperature-dependent manner up to 120℃. For example, when lycopene extraction was carried out at 80, 100, 120, and 140°C and a pressure of 30 MPa with an entrainer, ethanol, for 180 min, the total Z-isomer ratios obtained were 25.0, 57.2, 67.2, and 67.0%, respectively. The entrainer content also affected the Z-isomer ratio of lycopene, but the pressure had little effect. Interestingly, when SC-CO₂ extraction was performed under high-temperature conditions (≥ 100°C), the extraction efficiency of lycopene was dramatically improved, e.g., when lycopene was extracted at 80, 100, 120, and 140°C under the same other conditions as above, the recovery rates of lycopene were 4.6, 28.5, 79.9, 84.8%, respectively. In general, SC-CO₂ extraction of fat-soluble components is performed at temperatures in the range of 40-80°C because the SC-CO₂ density decreases with increasing temperature, and thus, their solubility (extraction efficiency) decreases. However, our results showed that the lycopene recovery increased in a temperature-dependent manner, which might be due to the solubility enhancement associated with thermal Z-isomerization of lycopene (i.e., lycopene Z-isomers have greater solubility than the naturally occurring all-E-isomer). The high-temperature SC-CO₂ extraction of lycopene from tomato materials not only enhances the Z-isomer ratio of lycopene in the resulting extracts but also improves lycopene recovery. This new finding will greatly contribute to the value addition and cost reduction of natural lycopene sources obtained by SC-CO₂ extraction.

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.

Application of E/Z-Isomerization Technology for Enhancing Processing Efficiency, Health-Promoting Effects, and Usability of Carotenoids: A Review and Future Perspectives

Carotenoids are naturally occurring pigments whose presence in the diet is beneficial to human health. Moreover, they have a wide range of applications in the food, cosmetic, and animal feed industries. As carotenoids contain multiple conjugated double bonds in the molecule, a large number of geometric (E/Z, trans/cis) isomers are theoretically possible. In general, (all-E)-carotenoids are the most predominant geometric isomer in nature, and they have high crystallinity and low solubility in various mediums, resulting in their low processing efficiency and bioavailability. Technological developments for improving the processing efficiency and bioavailability of carotenoids utilizing the Z-isomerization have recently been gaining traction. Namely, Z-isomerization of carotenoids induces a significant change in their physicochemical properties (e.g., solubility and crystallinity), leading to improved processing efficiency and bioavailability as well as several biological activities. For the practical use of isomerization technology for carotenoids, the development of efficient isomerization methods and an acute understanding of the changes in biological activity are required. This review highlights the recent advancements in various conventional and unconventional methods for carotenoid isomerization, such as thermal treatment, light irradiation, microwave irradiation, and catalytic treatment, as well as environment-friendly isomerization methods. Current progress in the improvement of processing efficiency and biological activity utilizing isomerization technology and an application development of carotenoid Z-isomers for the feed industry are also described. In addition, future research challenges in the context of carotenoid isomerization have been elaborated upon.