Carotenoids are
secondary metabolite responsible for colored pigments in
plants and microbes (Li et al., 2022). They are a class of C40 tetraterpenoids consisting of eight
isoprenoid units, and can be classified into
carotenes and
xanthophylls on the basis of their functional groups (Saini et al., 2015).
Carotenes can be linear (phytoene, phytofluene, and ζ-
carotene ) or branched (β-
carotene and α-
carotene ).
Xanthophylls comprise β,β-
xanthophylls (β-
cryptoxanthin ,
zeaxanthin , violaxanthins, and neoxanthin) and β,ε-
xanthophylls (α-
cryptoxanthin , α-
carotene , and
lutein ). Citrus
fruits are complex sources of
carotenoids , which are the principal pigments responsible for the typical
orange color of most types (Chen, 2020). The difference in total
carotenoid content and the diversity of
carotenoid isomer proportion also accounts for other
colors of citrus
fruits , such as yellow, red, and pink (Chen, 2020).