Lycopene is an organic compound classified as a tetraterpene and a carotene. Lycopene (from the Neo-Latin Lycopersicum, the tomato species) is a bright red carotenoid hydrocarbon found in tomatoes and other red fruits and vegetables.
Aside from tomatoes, it is found in red carrots, watermelons, grapefruits, and papayas. It is not present in strawberries or cherries. It has no vitamin A activity.
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. Like all carotenoids, lycopene is a tetraterpene. It is insoluble in water. Eleven conjugated double bonds give lycopene its deep red color. Owing to the strong color, lycopene is useful as a food coloring (registered as E160d) and is approved for use in the US, Australia and New Zealand (registered as 160d) and the European Union.
Lycopene is a symmetrical tetraterpene because it consists entirely of carbon and hydrogen and is derived from eight isoprene subunits. 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.
Plants and photosynthetic bacteria produce all-trans lycopene. 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. 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.
Carotenoids like lycopene are found in photosynthetic pigment-protein complexes in plants, photosynthetic bacteria, fungi, and algae.