Esterification of xanthophylls and its effect on chemical behavior and bioavailability of carotenoids in the human

Although the biologic actions of carotenoids in human health and their potential use in the prevention of vitamin A deficiency are clear, knowledge is still lacking on routes modulating their absorption and metabolism. One issue concerning both absorption and a key chemical activity of carotenoids (antioxidant capacity) has scarcely been considered: xanthophylls included in our diet are commonly esterified with fatty acids. In this review, the current knowledge of the role of esterification in antioxidant capacity and absorption of carotenoid esters is examined. Although esterification does not change the chromophore properties of the carotenoid molecule, it does modify the immediate molecular environment; thus, chemical activities may be altered depending on the kind of fatty acid bound to the xanthophyll. In particular, the saturated or unsaturated nature of fatty acids is linked with the efficiency of antioxidant action. Moreover, as no carotenoid esters have been detected in plasma and peripheral tissues, they must be hydrolyzed, involving a specific step before absorption. To date, there have been few studies that examined the effect of carotenoid esterification, but this subject is receiving increasing attention. The enzymes involved in the hydrolysis of carotenoid esters are not known, and the suitability of esters as substrate for common lipolytic enzymes is under investigation.