Lycopene
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Lycopene is an organic compound classified as a tetraterpene and a carotene.<ref name=KO>Template:Cite book</ref> Lycopene (from the Neo-Latin Lycopersicon, the name of a former tomato genus) is a bright red carotenoid hydrocarbon found in tomatoes and other red fruits and vegetables.
Occurrence
[edit]Aside from tomatoes or tomato products like ketchup, it is found in watermelons, grapefruits, red guavas, and baked beans.<ref name=lpi/> It has no vitamin A activity.<ref name="lpi">Template:Cite web</ref>
In plants, algae, and other photosynthetic organisms, lycopene is an intermediate in the biosynthesis of many carotenoids, including beta-carotene, which is responsible for yellow, orange, or red pigmentation, photosynthesis, and photoprotection.<ref name=lpi/>
Like all carotenoids, lycopene is a tetraterpene.<ref name=lpi/> It is soluble in fat, but insoluble in water.<ref name=lpi/> Eleven conjugated double bonds give lycopene its deep red color.<ref name=lpi/>
Owing to the strong color, lycopene is used as a food coloring (registered as E160d) and is approved for use in the US,<ref>Template:Cite web</ref> Australia and New Zealand (registered as 160d),<ref>Australia New Zealand Food Standards CodeTemplate:Cite web</ref> and the European Union (E160d).<ref>Template:Cite web</ref>
Structure and physical properties
[edit]Lycopene is a symmetrical tetraterpene because it consists entirely of carbon and hydrogen and is derived from eight isoprene subunits.<ref name=lpi/> 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 somewhat flat, constrained by its system of 11 conjugated double bonds. The extended conjugation is responsible for its deep red color.<ref name=lpi/>
Plants and photosynthetic bacteria produce all-trans lycopene.<ref name=lpi/> When exposed to light or heat, lycopene can undergo isomerization to any of a number of cis-isomers, which have a less linear shape. Isomers distinct stabilities, with highest stability: 5-cis ≥ all-trans ≥ 9-cis ≥ 13-cis > 15-cis > 7-cis > 11-cis: lowest.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> In human blood, various cis-isomers constitute more than 60% of the total lycopene concentration, but the biological effects of individual isomers have not been investigated.<ref>Template:Cite journal</ref>
Carotenoids like lycopene are found in photosynthetic pigment-protein complexes in plants, photosynthetic bacteria, fungi, and algae.<ref name=lpi/> They are responsible for the bright orange–red 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 carotenoids, such as beta-carotene, and xanthophylls.<ref>Template:Cite web</ref>
Dispersed lycopene molecules can be encapsulated into carbon nanotubes enhancing their optical properties.<ref>Template:Cite journal</ref> Efficient energy transfer occurs between the encapsulated dye and nanotube—light is absorbed by the dye and without significant loss is transferred to the nanotube. Encapsulation increases chemical and thermal stability of lycopene molecules; it also allows their isolation and individual characterization.<ref> Template:Cite journal</ref>
Biosynthesis
[edit]The unconditioned biosynthesis of lycopene in eukaryotic plants and in prokaryotic cyanobacteria is similar, as are the enzymes involved.<ref name=lpi/> 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 20-carbon geranylgeranyl pyrophosphate. Two molecules of this product are then condensed in a tail-to-tail configuration to give the 40-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.<ref name=lpi/>
Staining and removal
[edit]Lycopene is the pigment in tomato sauces that turns plastic cookware orange. It is insoluble in plain water, but it can be dissolved in organic solvents and oils. Because of its non-polarity, lycopene in food preparations will stain any sufficiently porous material, including most plastics. To remove this staining, the plastics may be soaked in a solution containing a small amount of chlorine bleach.<ref>Template:Cite news</ref> The bleach oxidizes the lycopene, thus rendering it colourless.
Diet
[edit]Consumption by humans
[edit]Absorption of lycopene requires that it be combined with bile salts and fat to form micelles.<ref name=lpi/> Intestinal absorption of lycopene is enhanced by the presence of fat and by cooking.<ref name=lpi/> Lycopene dietary supplements (in oil) may be more efficiently absorbed than lycopene from food.<ref name=lpi/>
Lycopene is not an essential nutrient for humans, but is commonly found in the diet mainly from dishes prepared from tomatoes.<ref name=lpi/> The median and 99th percentile of dietary lycopene intake have been estimated to be 5.2 and 123 mg/d, respectively.<ref name="pmid16046742"/>
Sources
[edit]| Source | mg wet weight |
|---|---|
| Gac aril | 2~6 per gram<ref>Template:Cite journal</ref><ref>Template:Cite web</ref> |
| Raw tomato | 4.6 per cup |
| Tomato juice | 22 per cup |
| Tomato paste | 75 per cup |
| Tomato ketchup | 2.5 per tablespoon |
| Watermelon | 13 per wedge |
| Pink grapefruit | 2 per half grapefruit |
Fruits and vegetables that are high in lycopene include autumn olive, gac, tomatoes, watermelon, pink grapefruit, pink guava, papaya, seabuckthorn, wolfberry (goji, a berry relative of tomato), and rosehip.<ref name=lpi/> Ketchup is a common dietary source of lycopene.<ref name=lpi/> Although gac (Momordica cochinchinensis Spreng) has the highest content of lycopene of any known fruit or vegetable (multiple times more than tomatoes),<ref name="tran">Template:Cite journal</ref><ref name="Ishida2004">Template:Cite journal</ref> tomatoes and tomato-based sauces, juices, and ketchup account for more than 85% of the dietary intake of lycopene for most people.<ref name=lpi/> The lycopene content of tomatoes depends on variety and increases as the fruit ripens.<ref>Template:Cite journal</ref>
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.<ref name=lpi/><ref>Template:Cite journal</ref> Lycopene in tomato paste is up to four times more bioavailable than in fresh tomatoes.<ref>Template:Cite journal</ref> Processed tomato products such as pasteurized tomato juice, soup, sauce, and ketchup contain a higher concentration of bioavailable lycopene compared to raw tomatoes.<ref name=lpi/><ref>Template:Cite book</ref>
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. Gac has high lycopene content derived mainly from its seed coats.<ref>Template:Cite journal</ref> Cara Cara navel oranges, and other citrus fruit, such as pink grapefruits, also contain lycopene.<ref name=lpi/><ref>Template:Cite journal</ref> Some foods that do not appear red also contain lycopene, e.g., baked beans.<ref name=lpi/> When lycopene is used as a food additive (E160d), it is usually obtained from tomatoes.<ref name=lpi/><ref>Template:Cite journal</ref>
Adverse effects
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Lycopene is non-toxic and commonly found in the diet, mainly from tomato products.<ref name=lpi/> There are cases of intolerance or allergic reaction to dietary lycopene, which may cause diarrhea, nausea, stomach pain or cramps, gas, and loss of appetite.<ref name="mayo">Template:Cite web</ref> Lycopene may increase the risk of bleeding when taken with anticoagulant drugs.<ref name=mayo/> Because lycopene may cause low blood pressure, interactions with drugs that affect blood pressure may occur. Lycopene may affect the immune system, the nervous system, sensitivity to sunlight, or drugs used for stomach ailments.<ref name=mayo/>
Lycopenemia is an orange discoloration of the skin that is observed with high intakes of lycopene.<ref name="pmid16046742">Template:Cite journal</ref> The discoloration is expected to fade after discontinuing excessive lycopene intake.<ref name="pmid16046742"/>
Research and potential health effects
[edit]A 2020 review of randomized controlled trials found conflicting evidence for lycopene having an effect on cardiovascular risk factors,<ref>Template:Cite journal</ref> whereas a 2017 review concluded that tomato products and lycopene supplementation reduced blood lipids and blood pressure.<ref name="ChengKoutsidis2017">Template:Cite journal</ref>
A 2015 review found that dietary lycopene was associated with reduced risk of prostate cancer,<ref name="Chen">Template:Cite journal</ref> whereas a 2021 meta-analysis found that dietary lycopene did not affect prostate cancer risk.<ref>Template:Cite journal</ref> Other reviews concluded that research has been insufficient to establish whether lycopene consumption affects human health.<ref>Template:Cite journal</ref>
Regulatory status in Europe and the United States
[edit]In a review of literature on lycopene and its potential benefit in the diet, the European Food Safety Authority concluded there was insufficient evidence for lycopene having antioxidant effects in humans, particularly in skin, heart function, or vision protection from ultraviolet light.<ref name="efsa">Template:Cite journal</ref>
Although lycopene from tomatoes has been tested in humans for cardiovascular diseases and prostate cancer, no effect on any disease was found.<ref name="ReferenceA">Template:Cite web</ref> The US Food and Drug Administration, in rejecting manufacturers' requests in 2005 to allow "qualified labeling" for lycopene and the reduction of various cancer risks, provided a conclusion that remains in effect Template:Asof: Template:Blockquote
In a review of research through 2024, the US National Cancer Institute concluded that the FDA has not approved the use of lycopene as effective for treating any medical condition, including various types of cancer.<ref name="nci">Template:Cite web</ref>
See also
[edit]References
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