Production, separation, and characterization of apo-luteinoids by LC-MS/MS.

It has been postulated that chemical or enzymatic catabolism of carotenoids could produce apo­carotenoids which have biological activity. Our objective was to generate and chemically characterize a series of apo­luteinoids (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 apo­luteinals/luteinone of subsequently shorter chain lengths, from apo­8'­luteinal to apo­11­luteinal. Sodium borohydride reduced this mixture into the corresponding alcohols (i.e. apo­luteinols). Similarly, Tollens' reagent was employed to oxidize the aldehyde series into carboxylic acids (i.e. apo­luteinoic 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 ß-ring species. These methods can be employed for the study of lutein oxidation products in plants, foods and biological samples.