Lycopene
(see chemical structure), a carotenoid in the same
family as beta-carotene, is what
gives tomatoes, pink grapefruit, apricots, red oranges, watermelon, rosehips,
and guava their red color. Lycopene is not merely a pigment. It is a powerful antioxidant that has
been shown to neutralize free radicals, especially
those derived from oxygen, thereby conferring protection against prostate
cancer, breast cancer, atherosclerosis, and associated coronary artery disease.
It reduces LDL (low-density lipoprotein) oxidation and helps reduce cholesterol
levels in the blood. In addition, preliminary research suggests lycopene may
reduce the risk of macular degenerative disease, serum lipid oxidation, and
cancers of the lung, bladder, cervix, and skin. The chemical properties of
lycopene responsible for these protective actions are well-documented.
Lycopene is
a phytochemical,
synthesized by plants and microorganisms but not by animals. It is an acyclic
isomer of beta-carotene. This highly unsaturated hydrocarbon contains 11
conjugated and 2 unconjugated double bonds, making it longer than any other
carotenoid. As a polyene, it undergoes cis-trans isomerization induced by
light, thermal energy, and chemical reactions. Lycopene obtained from plants
tends to exist in an all-trans configuration, the most thermodynamically stable
form. Humans cannot produce lycopene and must ingest fruits, absorb the
lycopene, and process it for use in the body. In human plasma, lycopene is
present as an isomeric mixture, with 50% as cis isomers.
Although
best known as an antioxidant, both oxidative and non-oxidative mechanisms are
involved in lycopene's bioprotective activity. The nutraceutical activities
of carotenoids such as beta-carotene are related to their ability to form
vitamin A within the body. Since lycopene lacks a beta-ionone ring structure,
it cannot form vitamin A and its biological effects in humans have been
attributed to mechanisms other than vitamin A. Lycopene's configuration enables
it to inactivate free radicals. Because free radicals are electrochemically
imbalanced molecules, they are highly aggressive, ready to react with cell
components and cause permanent damage. Oxygen-derived free radicals are the
most reactive species. These toxic chemicals are formed naturally as
by-products during oxidative cellular metabolism. As an antioxidant, lycopene
has a singlet-oxygen-quenching ability twice as high as that of beta-carotene
(vitamin A relative) and ten times higher than that of alpha-tocopherol
(vitamin E relative). One non-oxidative activity is regulation of gap-junction
communication between cells. Lycopene participates in a host of chemical
reactions hypothesized to prevent carcinogenesis and atherogenesis by
protecting critical cellular biomolecules, including lipids, proteins, and DNA.
Lycopene is
the most predominant carotenoid in human plasma, present naturally in greater
amounts than beta-carotene and other dietary carotenoids. This perhaps
indicates its greater biological significance in the human defense system. Its
level is affected by several biological and lifestyle factors. Because of its
lipophilic nature, lycopene concentrates in low-density and very-low-density
lipoprotein fractions of the serum. Lycopene is also found to concentrate in
the adrenal, liver, testes, and prostate. However, unlike other carotenoids,
lycopene levels in serum or tissues do not correlate well with overall intake
of fruits and vegetables.
Research
shows that lycopene can be absorbed more efficiently by the body after it has
been processed into juice, sauce, paste, or ketchup. In fresh fruit, lycopene
is enclosed in the fruit tissue. Therefore, only a portion of the lycopene that
is present in fresh fruit is absorbed. Processing fruit makes the lycopene more
bioavailable by increasing the surface area available for digestion. More
significantly, the chemical form of lycopene is altered by the temperature
changes involved in processing to make it more easily absorbed by the body.
Also, because lycopene is fat-soluble (as are vitamins, A, D, E, and
beta-carotene), absorption into tissues is improved when oil is added to the
diet. Although lycopene is available in supplement form, it is likely there is
a synergistic effect when it is obtained from the whole fruit instead, where
other components of the fruit enhance lycopene's effectiveness.
Source: http://chemistry.about.com/cs/biochemistry/a/aa050401a.htm
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