Antioxidant Properties of Singlet Oxygen Suppressors - Natural Antioxidants and Biocides from Wild Medicinal Plants - page 78

coupling process) (Schmidt, 2004). The tri-
plet energy of b-carotene (88 kJ/mol) is just
slightly smaller than that of 1 O 2 (96 kJ/mol),
which allows it to suppress 1 O 2 (Foote and
Denny, 1968; Ogilby and Foote, 1982).
Over 600 different carotenoids have been
identified up to now. Several synthetic path-
ways lead to different molecules with conju-
gated polyene systems. Phytoene is synthesized
from the union of two C 20 geranylgeranyl pyro-
phosphatate units and from that lycopene is
obtained by enzymatic hydrogen elimination
(Fig. 6.14). b-Carotene, the cyclic derivative of

lycopene, is a precursor of vitamin A and is
an orange substance found in carrots, man-
goes, apricots and sweet potatoes. b-Carotene
OH derivatives (such as lutein; Fig. 6.14) are
responsible for the yellow colour in the leaves
in the autumn (Biesalski, 2007). b-Carotene is
used in the food industry and in the industry
of food supplements. Bixin results from lyco-
pene oxidation and it is the main carotenoid
found in the seed coat of urucum fruits ( Bixa
orellana L. ; Fig. 6.15), which is cultivated in
tropical countries of South and Central
America, Africa and Asia.

Phytoene

Lycopene

COOCH 3

HOOC

Bixin

R

R = H, β -Carotene

R

R = OH, Zeaxanthin

O

R

R = H, Canthaxanthin
R = OH, Astraxanthin

R

O

OH

Lutein

HO

Fig. 6.14. Chemical structures of phytoene, lycopene, b -carotene and some other dietary carotenoids.