Functions of Carotenoid Metabolites and Breakdown Products

Abstract

It is not only intact carotenoids but also fragments of carotenoid molecules that have important natural functions and actions. The electron-rich polyene chain of the carotenoids is very susceptible to oxidative breakdown, which may be enzymic or non-enzymic. Central cleavage gives C₂₀ compounds, retinoids, as described in Chapter 16. Cleavage at other positions gives smaller fragments, notably C₁₀, C₁₃ and C₁₅ compounds that retain the carotenoid end group. The formation of these is described in Chapter 17 and in Volume 3, Chapter 4. Oxidative breakdown can also take place during storage, processing and curing of plant material, and the products contribute to the desired aroma/flavour properties of, for example, tea, wine and tobacco. The importance of vitamin A (C₂₀) in animals is well known. Vitamin A deficiency is still a major concern in many parts of the world. It can lead to blindness and serious ill-health or death, especially in young children. Volatile smaller carotenoid fragments (‘norisoprenoids’) are widespread scent/flavour compounds in plants.