Produce Color and Appearance 193
Numerous carotenoid preparations derived from both natural sources (annatto, saf-
fron, tomato, and paprika) and synthetic compounds (beta-carotene, canthaxanthin,
astaxanthin, beta-apo-8-carotenal, and beta-apo-8-carotenoic acid ethyl ester) are
available commercially as food colorants. Animals do not have the ability to syn-
thesize carotenoids and depend on ingestion of these compounds from feed. Subse-
quent transformation of carotenoids in animals may lead to the formation of char-
acteristic body pigments.
7.2.1 CHEMICAL DEFINITION AND STRUCTURE
According to the tentative rules of the International Union of Pure and Applied
Chemistry (IUPAC) Commission on Nomenclature of Organic Chemistry,
carotenoids are a class of hydrocarbons (carotenes) and their oxygenated derivatives
(xanthophylls) consisting of eight isoprenoid units. These units are joint in such a
manner that the arrangement is reversed at the center of the molecule, such that the
two central methyl groups are in a 1,6 positional relationship and the remaining non-
terminal methyl groups are in a 1,5 positional relationship (IUPAC, 1971).This definition was affirmed in the rules for the nomenclature of carotenoids pub-
lished in 1975 (IUPAC, 1975). These 13 rules include the definition of the class of
compounds, stem name “carotene,” specific names and end group designations,
numbering of carotenoid hydrocarbons, definitions of norcarotenoids and secocaro-
tenoids, changes in hydrogenation level, oxygenated derivatives, numbering of oxy-
genated derivatives, retro nomenclature, Apo nomenclature, higher carotenoids, ste-
reochemistry, and trivial names.
Numerous definitions of carotenoids found in literature are derived from the
classic definition published by Karrer and Tucker (1950). Traditional names of
carotenoids are frequently used to avoid the relative complexity of IUPAC’s system-
atic nomenclature. It is desirable that in scientific publications traditional names be
accompanied by systematic names. The structure of lycopene, shown on Figure 7.2,
is commonly used to formally derive structures of other carotenoids. Numbering of
carbons in the lycopene formula is used for all carotenoids. Almost all of over 600
naturally occurring carotenoids may be shown as compounds deduced from lycopene
by one or more of the following: hydrogenation, dehydrogenation, cyclization, and
oxidation. They are soluble in lipids and not soluble in water, with the exception of
some that have strong polar groups such as norbixin with two carboxylic groups in
its molecule.
FIGURE 7.2Lycopene.
4(^35)
2
1
17
6
7
8
9
10
11
12
13
14
15
19 20
16
18
15'
14'
13'
12'
11'
10'
9'
19'
8'
7'
6'
5'
18' 4'
3'
17'
2'
16' 1'
20'