**2.1 Classification of carotenoids**

Carotenoids can broadly be classified into two subgroups according to their chemical structure—(1) carotenes (hydrocarbon carotenoids), which are made up of carbon and hydrogen. Examples of carotenes include α-carotene, β-carotene, β, ψ-carotene (γ-carotene), and lycopene; (2) oxycarotenoids or xanthophylls (oxygenated carotenoids), which are derivatives of the hydrocarbons (carotenes) and are constituted by carbon, hydrogen, and oxygen atom in the form of hydroxy, epoxy, or oxy groups. Examples of xanthophylls include β-cryptoxanthin, lutein, zeaxanthin, astaxanthin, fucoxanthin, and peridinin [13, 14, 16–18]. Moreover, carotenoids are divided into primary or secondary. Primary carotenoids are compounds required by plants in photosynthesis (β-carotene, violaxanthin, and neoxanthin), whereas secondary carotenoids are localized in non-photosynthetic organs of plants, such as fruits and flowers (α-carotene, β-cryptoxanthin, zeaxanthin, antheraxanthin, capsanthin, and capsorubin) [14].
