Structures, Nomenclature and General Chemistry of Carotenoids and Their Esters
Carotenoids are widespread isoprenoids that intervene in actions ranging from the collection of light and photoprotection to the regulation of gene expression and communication within or between species, to mention only some examples. They are, therefore, much more than natural pigments, as they are versatile compounds that are eliciting increasing interest in different disciplines, such as plant science, agriculture, food science and technology, nutrition and health, among others. Although carotenoids in humans are found almost exclusively free, in foods they can be associated with other molecules, like sugars, proteins or fatty acids. Such associations can result in substantial changes in their properties. Indeed, food xanthophylls are commonly found in the form of esters, above all in many fruits. This modification markedly influences properties such as solubility and susceptibility to oxidation, which in turn can have impacts on relevant aspects that explain their levels in foods and humans, such as their biosynthesis, deposition, stability and bioavailability, among others. The study of the esterification of carotenoids is undoubtedly gaining popularity. In this chapter, nomenclature and structural aspects related to isoprenoids, carotenoids, fatty acids and, finally, carotenoid esters are presented, with references to some physical–chemical properties and their importance at different levels.