Considerable progress in carotenoids research has been made to understand the carotenoid metabolism in animals including human. Epidemiological and clinical studies have correlated with dietary intake of carotenoids on reduction of vitamin A deficiency, age-related macular degeneration, cancer and cardiovascular diseases. Recent findings demonstrate the existence of carotenoid metabolites in vivo and their efficacy have made greater insight on prospecting carotenoid metabolites. Owing to their biological activity, exploration of analytical methods for the characterization of carotenoid metabolites is considered to be important before addressing the stability and bioactivity. Although few studies are available on carotenoid metabolites, their structural characterization in biological samples require a substantial refining of analytical protocols like isolation, purification, prerequisite of equipment parameters and robustness in hyphenated techniques.Recently, researchers have focused on biotransformation of carotenoids and made an attempt to screen their metabolites by high-throughput analytical strategies. However, till date there is no detailed analytical techniques available to fingerprint carotenoid metabolites, due to interference with complex biological matrices. This review highlights the carotenoid metabolism, possible bioconversion and available bio-analytical techniques to characterize metabolites in vivo. Further, advancement in sensitivity, mode of ionization and fragmentation patterns of metabolites were also discussed. The identification of carotenoid metabolites in system specific will have further insight in the emerging field of nutritional metabolomics.

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This study reports on the results of repeated gavages and dietary feeding of lutein dispersed either in phospholipids or fatty acid micelles or vegetable oils and the effects on lutein bioavailability and antioxidant enzymes in rats. For the gavage study, rats (n = 5/group) were intubated with lutein solubilized either in oleic acid (OLA, 18:1n-9) or linoleic acid (LNA, 18:2n-6) or phosphatidylcholine (PC) or lysophosphatidylcholine (LPC) or no phospholipid (NoPL) micelles for 10 days. For the dietary study, rats (n = 5/group) were fed a diet containing fenugreek leaf (lutein source), either with olive (OO) or sunflower (SFO) or groundnut (GNO, control) oil or L: -alpha-lecithin (PL) for 4 weeks. The gavage study showed that the plasma, liver and eye lutein levels in OLA and LPC groups were higher by 23.9, 20.8 and 25.5% and 16.1, 28.5 and 14.0% than LNA and PC groups, respectively. The dietary study showed the plasma (35.0 and 43.5%) and eye (18.5 and 37.0%) lutein levels in OO were higher than SFO and GNO groups. The plasma and eye lutein levels in the PL group were higher by 20 and 31.3% than in the control. It is evident that OO and PL modulate lutein absorption, which in turn modulates antioxidant enzymes and fatty acids in plasma and tissues compared to SFO. Hence, selection of the fat source may be vital to enhancing the lutein bioavailability.

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