Food Chemistry

240 3 Lipids

Bixin (XVIII) (3.138)

Bixin is the main pigment of annato extract.
Annato originates from the West Indies and
the pigment is isolated from the seed pulp of
the tropical bushBixa orellana. Bixin is the
monomethyl ester of norbixin, a dicarboxylic
acid homologous to crocetin.

β-apo-8′-carotenal*(XIX) (3.139)

Carotenoids are, as a rule, present in plants as
a complex mixture. For example, the orange has
more than 50 well characterized compounds, of
which only those that exceed 5% of the total
carotenoids are presented in Table 3.57.
Hydroxy-carotinoids are often present as esters of
fatty acids; e. g., orange juice contains 3-hydroxy-
β-carotene (cryptoxanthin) esterified with lauric,
myristic and palmitic acid. The quantitative
analysis of this ester fraction is used as proof of an
adulteration of orange juice with mandarin juice.

Table 3.57.Major carotenoid components in orange
juice

Carotenoid As percent of
total carotenoids

Phytoene (I) 13
ξ-Carotene (III) 5. 4
Cryptoxanthin 5. 3
(3-Hydroxy-β-carotene)
Antheraxanthin 5. 8
(5,6-Epoxyzeaxanthin)
Mutatoxanthin (XVI) 6. 2
Violaxanthin (XIII) 7. 4
Luteoxanthin (XIV) 17. 0
Auroxanthin (XV) 12. 0

cThe prefix “apo” indicates a compound derived from

a carotenoid by removing part of its structure.

3.8.4.2 PhysicalProperties

Carotenoids are very soluble in apolar solvents,

including edible fats and oils, but they are

not soluble in water. Hence, they are denoted

“lipochromes”. Carotenoids are readily extracted

from plant sources with petroleum ether, ether or

benzene. Ethanol and acetone are also suitable

solvents.

The color of carotenoids is the result of the

presence of a conjugated double bond system in

the molecules. The electron excitation spectra of

such systems are of interest for elucidation of

their structure and for qualitative and quantitative

analyses.

Carotenoids show three distinct maxima in the

visible spectrum, with wavelength positions

dependent on the number of conjugated double

Table 3.58.Absorption wavelength maxima for some

carotenoids

Compound Conjugated Wavelength, nm

double bonds (petroleum ether)

A. Effect of the number of conjugated double bonds

Phytoene (I) 3 275 285 296

Phytofluene (II) 5 331 348 367

ξ-Carotene (III) 7 378 400 425

Neurosporene 9 416 440 470

Lycopene (IV) 11 446 472 505

B. Effect of the ring structure

γ-Carotene (V) 11 431 462 495

β-Carotene (VII) 11 425 a 451 483

aMaximum absorption wavelength is not unequivocal

(cf. Fig. 3.47).