Carotenoid esters analysis and occurrence: What do we know so far?

Carotenoids possessing hydroxyl groups can be found in nature both as free xanthophylls and as carotenoid esters, i.e. acylated with fatty acids. A single carotenoid can be acylated with different fatty acids, resulting in a high number of possible structures of carotenoid esters. The analysis of carotenoid esters can be challenging; although extraction techniques are essentially the same as those used for free carotenoids, depending on the sample composition, interfering compounds such as triacylglycerides are also present in the extract in significant amounts to cause high background noise and ionization suppression in mass spectrometric analysis. Besides analysis of UV-visible spectrum features, identification of carotenoid esters must include tandem mass spectrometry (MSn) because no changes in the carotenoid molecule chromophore occur due to acylation with fatty acids. Although carotenoid esters are widespread found in foods, especially in fruits, and their bioavailability is equivalent or even higher than that of the free carotenoid, occurrence of xanthophyll esters is very limited in human plasma and tissues. Challenges and further investigations needed on the topics above are given in this review.