Everything about Lycopene totally explained
| Section2 =
| Section3 =
}}
Lycopene is a bright red
carotenoid pigment and
phytochemical found in
tomatoes and other red fruits. Its name is derived from the tomato's species classification,
Solanum lycopersicum. In plants, algae, and other photosynthetic organisms, lycopene is an important intermediate in the biosynthesis of many carotenoids, including
beta carotene, which are responsible for pigmentation, photosynthesis, and photo-protection. Structurally, it's a
tetraterpene assembled from eight
isoprene units, composed entirely of carbon and hydrogen, and is insoluble in water. Lycopene's eleven conjugated double bonds give it its deep red color and are responsible for its
antioxidant activity. Due to its strong color and non-toxicity, lycopene is a useful
food coloring.
Lycopene isn't an essential nutrient for humans, but it's commonly found in the diet, mainly from dishes prepared with tomato sauce. When absorbed from the stomach, lycopene is transported in the blood by various
lipoproteins and accumulates in the liver, adrenal glands, and testes. Of all the carotenoids, lycopene is one of the most potent
antioxidants; particularly able to quench
singlet oxygen and peroxyl radicals, both of which are thought to be responsible for damaging
DNA in a process which can lead to the
initiation of cancer. Because researchers have found an inverse correlation between consumption of tomatoes and cancer risk, lycopene is being investigated as a potential agent for the prevention of some types of cancers, particularly
prostate cancer.
Structure and physical properties
Lycopene is a symmetrical
tetraterpene assembled from 8
isoprene units. It is a member of the carotenoid family of compounds, and because it consists entirely of carbon and hydrogen, is also a
carotene. Isolation procedures for lycopene were first reported in 1910, and the structure of the molecule was determined by 1931. In its natural, all-
trans form, the molecule is long and straight, constrained by its system of eleven conjugated double bonds. Each double bond in this extended
π electron system reduces the energy required for electrons to transition to higher
energy states, allowing the molecule to absorb visible light of progressively longer wavelengths. Lycopene absorbs all but the longest wavelengths of visible light, so it appears red.
Plants and photosynthetic bacteria naturally produce all-
trans lycopene, but a total of 72 geometric isomers of the molecule are possible. When exposed to light or heat, lycopene can undergo
isomerization to any of a number of these
cis-isomers, which have a bent rather than linear shape. Different isomeres were shown to have different stabilities due to their molecular energy (highest stability: 5-cis ≥ all-trans ≥ 9-cis ≥ 13-cis > 15-cis > 7-cis > 11-cis: lowest). In the human bloodstream, various
cis-isomers constitute more than 60% of the total lycopene concentration, but the biological effects of individual isomers have not been investigated.
Lycopene is insoluble in water, and can be dissolved only in organic solvents and oils. Because of its non-polarity, lycopene in food preparations will stain any sufficiently
porous material, including most plastics. While a tomato stain can be fairly easily removed from fabric (provided the stain is fresh), lycopene
diffuses into plastic, making it impossible to remove with hot water or detergent. If lycopene is
oxidized (for example, by reacting with bleaches or acids), the double bonds between the carbon atoms will be broken; cleaving the molecule, breaking the conjugated double bond system, and eliminating the
chromophore.
Role in photosynthesis
Carotenoids like lycopene are important pigments found in photosynthetic pigment-protein complexes in plants, photosynthetic bacteria, fungi, and algae. They are responsible for the bright colors of fruits and vegetables, perform various functions in photosynthesis, and protect photosynthetic organisms from excessive light damage. Lycopene is a key intermediate in the biosynthesis of many important carotenoids, such as
beta-carotene, and
xanthophylls.
Biosynthesis
The biosynthesis of lycopene in eukaryotic plants and in prokaryotic cyanobacteria is similar, as are the enzymes involved. Synthesis begins with
mevalonic acid, which is converted into
dimethylallyl pyrophosphate. This is then condensed with three molecules of
isopentenyl pyrophosphate (an isomer of dimethylallyl pyrophosphate), to give the twenty carbon
geranylgeranyl pyrophosphate. Two molecules of this product are then condensed in a tail-to-tail configuration to give the forty carbon
phytoene, the first committed step in carotenoid biosynthesis. Through several desaturation steps, phytoene is converted into lycopene. The two terminal isoprene groups of lycopene can be cyclized to produce beta carotene, which can then be transformed into a wide variety of xanthophylls.
Dietary sources
Fruits and
vegetables that are high in lycopene include tomatoes,
watermelon, pink
grapefruit, pink
guava,
papaya, red bell pepper,
gac, and
rosehip. Tomatoes and tomato based sauces, juices, and ketchup account for more than 85% of the dietary intake of lycopene. The lycopene content of tomatoes depends on species and increases as the fruit ripens.
Unlike other fruits and vegetables, where nutritional content such as
vitamin C is diminished upon cooking,
processing of tomatoes increases the concentration of
bioavailable lycopene. Lycopene in tomato paste is four times more bioavailable than in fresh tomatoes. This is because lycopene is insoluble in water and is tightly bound to vegetable fiber. Thus processed tomato products such as pasteurized tomato juice, soup, sauce, and ketchup contain the highest concentrations of bioavailable lycopene. Cooking and crushing tomatoes (as in the
canning process) and serving in oil-rich dishes (such as
spaghetti sauce or
pizza) greatly increases assimilation from the digestive tract into the bloodstream. Lycopene is fat-soluble, so the oil is said to help absorption.
Lycopene may be obtained from vegetables and fruits such as the tomato, but another source of lycopene is the fungus
Blakeslea trispora.
Pharmacokinetics
| Distribution of lycopene |
| Tissue |
nmol/g wet weight |
| Liver |
1.28–5.72 |
| Kidney |
0.15–0.62 |
| Adrenal |
1.9–21.6 |
| Testes |
4.34–21.4 |
| Ovary |
0.25–0.28 |
| Adipose |
0.2–1.3 |
| Lung |
0.22–0.57 |
| Colon |
0.31 |
| Breast |
0.78 |
| Skin |
0.42 |
After ingestion, lycopene is incorporated into lipid
micelles in the small intestine. These micelles are formed from dietary fats and bile acids, and help to solubilize the hydrophobic lycopene and allow it to permeate the intestinal mucosal cells by a passive transport mechanism. Little is known about the liver metabolism of lycopene, but like other carotenoids, lycopene is incorporated into
chylomicrons and released into the lymphatic system. In blood plasma, lycopene is eventually distributed into the
very low and
low density lipoprotein fractions. Lycopene is mainly distributed to fatty tissues and organs such as the adrenal glands, liver, and testes.
Adverse effects
Lycopene is non-toxic and is commonly found in the diet, but cases of excessive carotenoid intake have been reported. In a middle aged woman who had prolonged and excessive consumption of tomato juice, her skin and liver were colored orange-yellow and had elevated levels of lycopene in her blood. After three weeks on a lycopene-free diet her skin color returned to normal.
Antioxidant properties and potential health benefits
Lycopene may be the most powerful carotenoid quencher of
singlet oxygen, being 100 times more efficient in test tube studies of singlet-oxygen quenching action than
vitamin E, which in turn has 125 times the quenching action of
glutathione (water soluble). Singlet oxygen produced during exposure to
ultraviolet light is a primary cause of
skin aging.
Given its antioxidant properties, substantial scientific and clinical research has been devoted to a possible correlation between lycopene consumption and general health. Early research suggested some amelioration of
cardiovascular disease,
cancer,
diabetes,
osteoporosis, and even male
infertility.
After extensive review reported in November 2005, the
United States Food and Drug Administration has cast significant doubt on the potential for lowering disease risk, showing no link between lycopene and prevention of prostate cancer. The FDA review permitted a highly limited qualified claim to be used for tomatoes and tomato products which contain lycopene, as a guide that wouldn't mislead consumers, namely:
Very limited and preliminary scientific research suggests that eating one-half to one cup of tomatoes and/or tomato sauce a week may reduce the risk of prostate cancer. FDA concludes that there's little scientific evidence supporting this claim.
The related carotenoid antioxidant, beta-carotene, has been shown to increase the number of prostate cancer cases in a subset of patients, although this area of research remains controversial and ongoing.
Notes and references
==
Further Information
Get more info on 'Lycopene'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://lycopene.totallyexplained.com">Lycopene Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
