It has been postulated that chemical or enzymatic catabolism of carotenoids could produce apo‑carotenoids which have biological activity. Our objective was to generate and chemically characterize a series of apo‑luteinoids (i.e. products resulting from the catabolism of lutein) which could putatively be found in vivo. Lutein was oxidized using potassium permanganate to produce a series of apo‑luteinals/luteinone of subsequently shorter chain lengths, from apo‑8'‑luteinal to apo‑11‑luteinal. Sodium borohydride reduced this mixture into the corresponding alcohols (i.e. apo‑luteinols). Similarly, Tollens' reagent was employed to oxidize the aldehyde series into carboxylic acids (i.e. apo‑luteinoic acids). Mixtures of products were separated via HPLC and characterized in-line using photodiode array (PDA) and tandem mass spectrometry (MS-MS). A global HPLC-PDA-MS/MS method was developed to separate the products, and application of the methods to the symmetric xanthophyll zeaxanthin further confirmed the ε- and β-ring species. These methods can be employed for the study of lutein oxidation products in plants, foods and biological samples.
Keywords: Apo‑luteinals/luteinone; Apo‑luteinoic acids; Apo‑luteinols; Liquid chromatography-mass spectrometry; Lutein; Oxidation; Zeaxanthin.
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