An optimized isomerization method was developed by heating all-E-astaxanthin in ethyl acetate (70 °C) with I-TiO₂ catalyst, yielding 22.7% and 16.9% of 9Z- and 13Z-astaxanthin, respectively, in 2 h, with 92–95% purity after semipreparative HPLC purification. 13Z-Astaxanthin had higher antioxidant activity than all-E- and 9Z-astaxanthins in oxygen radical absorbing capacity assay for lipophilic compounds, photochemiluminescence, and cellular antioxidant activity (CAA) assays, and 9Z-astaxanthin was higher in DPPH radical-scavenging activity assay and lower in CAA assay. All isomers were relatively stable between pH 2.0 and 11.6, except 13Z- and 9Z-astaxanthins at pH 2.0, suggesting they may be converted after passing the gastric phase in vivo. Metal ions did not significantly (p < 0.05) affect the stability. Results of the current study provides a means for further study into the mechanisms related to in vivo transformation and bioavailability of Z-astaxanthins, and their application in the development of functional foods and nutraceutical products.

中文翻译：

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快速高效地将全E-虾青素转化为9 Z-和13 Z-异构体并评估其稳定性和抗氧化活性

通过在I-TiO ₂催化剂中在乙酸乙酯中（70°C）加热全E-虾黄素，开发了一种优化的异构化方法，在2小时内分别得到22.7％和16.9％的9 Z-和13 Z-虾黄素。半制备型HPLC纯化后，其纯度为92–95％。在亲脂性化合物的氧自由基吸收能力测定，光化学发光和细胞抗氧化剂活性（CAA）测定中，13 Z-虾青素具有比全E-和9 Z-虾青素更高的抗氧化活性，而9 ZDPPH自由基清除活性测定法中的-astaxanthin较高，而CAA测定法中的-astaxanthin较低。所有异构体在pH 2.0和11.6之间相对稳定，但pH 2.0时13 Z-和9 Z-虾青素除外，这表明它们在体内通过胃相后可能会被转化。金属离子没有显着影响（p <0.05）。本研究的结果为进一步研究与Z-虾青素的体内转化和生物利用度有关的机制及其在功能性食品和营养产品开发中的应用提供了一种手段。