Chemistry and Biotechnology of Carotenoids

Carotenoids are one of the most widespread groups of pigments in nature and more than 600 of these have been identified.
Beside provitamin A activity, carotenoids are important as antioxidants and protective agents against various diseases.
They are isoprenoids with a long polyene chain containing 3 to 15 conjugated double bonds, which determines their
absorption spectrum. Cyclization at one or both ends occurs in hydrocarbon carotene, while xanthophylls are formed by
the introduction of oxygen. In addition, modifications involving chain elongation, isomerization, or degradation are also
found. The composition of carotenoids in food may vary depending upon production practices, post-harvest handling,
processing, and storage. In higher plants they are synthesized in the plastid. Both mevalonate dependent and independent
pathway for the formation of isopentenyl diphosphate are known. Isopentenyl diphosphate undergoes a series of addition
and condensation reactions to form phytoene, which gets converted to lycopene. Cyclization of lycopene either leads to the
formation of β-carotene and its derivative xanthophylls, β-cryptoxanthin, zeaxanthin, antheraxanthin, and violaxanthin or
α-carotene and lutein. Even though most of the carotenoid biosynthetic genes have been cloned and identified, some aspects
of carotenoid formation and manipulation in higher plants especially remain poorly understood. In order to enhance the
carotenoid content of crop plants to a level that will be required for the prevention of diseases, there is a need for research
in both the basic and the applied aspects.