The degradation and isomerization of all-trans-zeaxanthin in a model system during illumination, in the absence or presence of iodine, were investigated. A high-performance liquid chromatography method was developed using the C-30 column to separate all-trans-zeaxanthin and its cis-isomers. Three mono-cis-isomers and four di-cis-isomers were assigned by high-performance liquid chromatography-photo diode array detection-atmospheric pressure chemical ionization-mass spectrometry (HPLC-DAD-APCI-MS), namely, 15/15’-cis-, 13/13’-cis-, 9/9’-cis-13,15-di-cis-, 9,15-di-cis-, 9,13-di-cis-, and 9,9’-di-cis-zeaxanthin. 13/13’-cis- and 9, 13-di-cis-zeaxanthin were the major cis-isomers of zeaxanthin formed during illumination. Di-cis-zeaxanthin was favored during illumination in the presence of iodine. The degradation of total amount of all-trans-zeaxanthin during illumination was found to fit a first-order model. The degradation rate of iodine-catalyzed photoisomerization of all-trans-zeaxanthin was faster than that of non-iodine-catalyzed photoisomerization. Isomerization and degradation of all-trans-zeaxanthin and its cis-isomers during illumination proceeded simultaneously.
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Zhang et al. (2015) studied this question.
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