Chemistry Reference
In-Depth Information
11
Carotenoids
Carotenoids are also terpenoids, belonging to a very large family of organic pig-
mented compounds. They are tetraterpenoids: terpenoids of eight isoprene units (dis-
cussed in Chapter 4), possessing 40 carbons within the molecular skeleton, as shown
in Figure 11.1.
Carotenoids are of importance to both the plant and the host microorganism.
Carotenoids are typically found in photosynthetic plants or fungi, algae, and animal
products. They are also found in eggs, animal tissues, fruits, and many vegetables.
Carotenoids are involved in the photosynthetic process and offer protection against
photodamage. They provide the yellow, orange, and red colors to their respective
fruits and vegetables. Carotenoids are one of the two key pigments that contribute to
the skin yellowness of humans. They are also recognized as valuable nutritional
compounds to the human body. They are essential for enhancing the immune sys-
tem, possess photoprotection ability, and may support reproductive health.
β-Carotene in the body is a form of provitamin A and acts as an antioxidant
considered beneficial in preventing human diseases. The carotene is cleaved by the
enzyme β- carotene-15,15′-dioxygenase to form retinol (Figure 11.2).
The more than 600 known carotenoids can be divided into two categories:
xanthophylls and carotenes. Xanthophylls are those derivatives containing oxygen
atoms, whereas carotenes only contain carbon and hydrogen. In this chapter, four
carotenoids are described in detail: β-carotene (provitamin A), lutein, zeaxanthin
(for eye health), and lycopene (for cardio health).
HISTORICAL NOTE
The earliest studies on carotenoids date to the early 19th century. Although at
the time many carotenoids were discovered and named, their structures were
not known. As an example, in 1831, carotene was discovered and isolated by
the scientist Wackenroder as a by-product of the search for a medical agent—
an anthelminthic (ridding the body of parasitic worms). In 1837, Berzelius
named the yellow pigments obtained from autumn leaves as xanthophylls.
By the 1860s, lutein was isolated, followed 10  years later by the identifica-
tion of carotene in animal tissues. The first separation and purification of
carotenes and xanthophylls via chromatography was achieved around 1910 by
Willstatter and Mieg, who first established the empirical formula of C 40 H 56
for β-carotene, and C 40 H 56 O 2 for xanthophylls. However, it required 20 more
years before Karrer elucidated the chemical structures of carotenoids and
demonstrated the transformation of carotenoids into vitamin A in the body.
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