CAROTENE

APPLICATIONS

Carotene is used as a substance to colour products such as juice, cakes, desserts, butter and margarine. 
Carotene is approved for use as a food additive in the EU (listed as additive E160a) Australia and New Zealand (listed as 160a) and the US.
β –carotene can be used in a wide range of food and beverages including cider, malt beverages, water-based flavored drinks, margarines, cheeses, cake fillings, custards, yogurts, processed nuts, precooked pastas and noodles.

DESCRIPTION

Carotene is any of several orange or red crystalline hydrocarbon pigments (such as C40H56) that occur in the chromoplasts of plants and in the fatty tissues of plant-eating animals and are convertible to vitamin A. 
Carotene is a fat-soluble precursor of vitamin A that exists in green and yellow vegetables. 
A small portion of carotene is absorbed from the intestines and contributes to the yellow serum color. 
The carotenes include β-Carotene, α-carotene and γ-carotene. 

The term carotene (also carotin, from the Latin carota, "carrot") is used for many related unsaturated hydrocarbon substances having the formula C40Hx, which are synthesized by plants but in general cannot be made by animals (with the exception of some aphids and spider mites which acquired the synthesizing genes from fungi). Carotenes are photosynthetic pigments important for photosynthesis. 
Carotenes contain no oxygen atoms. 
They absorb ultraviolet, violet, and blue light and scatter orange or red light, and (in low concentrations) yellow light.

Carotenes are responsible for the orange colour of the carrot, after which this class of chemicals is named, and for the colours of many other fruits, vegetables and fungi (for example, sweet potatoes, chanterelle and orange cantaloupe melon). 
Carotenes are also responsible for the orange (but not all of the yellow) colours in dry foliage. 

They also (in lower concentrations) impart the yellow coloration to milk-fat and butter. 
Omnivorous animal species which are relatively poor converters of coloured dietary carotenoids to colourless retinoids have yellowed-coloured body fat, as a result of the carotenoid retention from the vegetable portion of their diet. 
The typical yellow-coloured fat of humans and chickens is a result of fat storage of carotenes from their diets.

Carotenes contribute to photosynthesis by transmitting the light energy they absorb to chlorophyll. 
They also protect plant tissues by helping to absorb the energy from singlet oxygen, an excited form of the oxygen molecule O2 which is formed during photosynthesis.

β-Carotene is composed of two retinyl groups, and is broken down in the mucosa of the human small intestine by β-carotene 15,15'-monooxygenase to retinal, a form of vitamin A. 
β-Carotene can be stored in the liver and body fat and converted to retinal as needed, thus making it a form of vitamin A for humans and some other mammals. 
The carotenes α-carotene and γ-carotene, due to their single retinyl group (β-ionone ring), also have some vitamin A activity (though less than β-carotene), as does the xanthophyll carotenoid β-cryptoxanthin. 
All other carotenoids, including lycopene, have no beta-ring and thus no vitamin A activity (although they may have antioxidant activity and thus biological activity in other ways).

Animal species differ greatly in their ability to convert retinyl (beta-ionone) containing carotenoids to retinals. 
Carnivores in general are poor converters of dietary ionone-containing carotenoids. 
Pure carnivores such as ferrets lack β-carotene 15,15'-monooxygenase and cannot convert any carotenoids to retinals at all (resulting in carotenes not being a form of vitamin A for this species); while cats can convert a trace of β-carotene to retinol, although the amount is totally insufficient for meeting their daily retinol needs.

Carotene, any of several organic compounds widely distributed as pigments in plants and animals and converted in the livers of many animals into vitamin A. 
These pigments are unsaturated hydrocarbons (having many double bonds), belonging to the isoprenoid series. 
Several isomeric forms (same formula but different molecular structures) are subsumed under the name.

In plants, carotenes impart yellow, orange, or red colours to flowers (dandelion, marigold), fruits (pumpkin, apricot), and roots (carrot, sweet potato). 
In animals they are visible in fats (butter), egg yolks, feathers (canary), and shells (lobster).

The term carotene refers to a class of related organic compounds with the formula C40H56. 
Carotenes exist in several isomers that have the same formula but different molecular structures. 
These yellow-orange pigments are synthesized by plants and photosynthetic bacteria, while animals must obtain them as a nutrient from the diet.

Along with chlorophyll and other pigments found in specialized chloroplasts, carotenes absorb energy from sunlight to be used in photosynthesis, a process in which solar energy is converted into potential chemical energy in the form of glucose. 
The carotene molecules transmit the absorbed light energy to chlorophyll to be funneled into the reactions of photosynthesis.

Carotene is also the precursor to vitamin A in animals. 
Although several carotenes are capable of producing vitamin A, the most active form is the isomer beta-carotene. 
Vitamin A plays an important role in vision.

In all living organisms, carotenes function as antioxidants, which work by making themselves available for energetically favorable oxidation (donation of electrons). As such, they can be useful for curbing the excesses of damaging free radicals, which contain an unpaired electron and thus are highly reactive. 
Free radicals oxidize the molecules that make up cell membranes and other vital tissues, altering their function. 
Antioxidants like the carotenes react readily with these free radicals before they can react with other compounds in the organism.

Carotenes contribute a yellow or orange pigmentation to fruits such as apricots, root vegetables like carrots and sweet potatoes, and flowers such as dandelions and marigolds. 
The leafy greens broccoli and spinach are also good dietary sources, though the presence of carotene is visually masked by the green of chlorophyll molecules. Carotenes also give color to milk fat and egg yolks, and contribute to the ornamental hue of lobster shells.

Carotenes (and their parent group, the carotenoids) are examples of ubiquitous compounds called isoprenoids, which may be thought of as the “sensual molecules” that contribute diverse colors and fragrances to the natural world. 
They attest to nature’s ability to use simple building blocks to create an array of compounds. 
The carotenes and other isoprenoids also demonstrate the functional role of beauty in the perpetuation of life.

MOLECULAR STRUCTURE

Chemically, carotenes are polyunsaturated hydrocarbons containing 40 carbon atoms per molecule, variable numbers of hydrogen atoms, and no other elements. 
Some carotenes are terminated by hydrocarbon rings, on one or both ends of the molecule. 
All are coloured to the human eye, due to extensive systems of conjugated double bonds. 
Structurally carotenes are tetraterpenes, meaning that they are synthesized biochemically from four 10-carbon terpene units, which in turn are formed from eight 5-carbon isoprene units.

Carotenes are found in plants in two primary forms designated by characters from the Greek alphabet: alpha-carotene (α-carotene) and beta-carotene (β-carotene). Gamma-, delta-, epsilon-, and zeta-carotene (γ, δ, ε, and ζ-carotene) also exist. 
Since they are hydrocarbons, and therefore contain no oxygen, carotenes are fat-soluble and insoluble in water (in contrast with other carotenoids, the xanthophylls, which contain oxygen and thus are less chemically hydrophobic).

CHEMICAL STRUCTURE AND PROPERTIES

Chemically, carotene is a terpene, one of a large class of hydrocarbons derived biosynthetically from units of isoprene, which has the molecular formula C5H8. Carotenes are synthesized from eight units of isoprene, which may be considered one of nature's preferred building blocks.

Carotene naturally occurs in a variety of isomeric forms, which are designated by characters from the Greek alphabet. 
Although alpha-carotene (α-carotene) and beta-carotene (β-carotene) are the two primary forms of carotene, gamma, delta, and epsilon (γ, δ and ε-carotene) configurations also exist.

The two primary isomers of carotene, α-carotene and β-carotene, differ in the position of double bonds in the cyclic group at the end of the molecule.
Carotenes absorb light because they contain extended networks of alternating single and double bonds (i.e., they are polyenes). 
These double carbon-carbon bonds interact in a process known as conjugation, which results in an overall lower energy state. 

Normally, carbon-carbon double bonds that are not conjugated or only partially conjugated absorb light in the ultraviolet region of a spectrum; however, the absorption energy state of polyenes with numerous conjugated double bonds can be lowered such that they enter the visible region of the spectrum, resulting in compounds that are colored yellow and orange.

HISTORY

The discovery of carotene from carrot juice is credited to Heinrich Wilhelm Ferdinand Wackenroder, a finding made during a search for antihelminthics, which he published in 1831. He obtained it in small ruby-red flakes soluble in ether, which when dissolved in fats gave 'a beautiful yellow colour'. 
William Christopher Zeise recognised its hydrocarbon nature in 1847, but his analyses gave him a composition of C5H8. 
It was Léon-Albert Arnaud in 1886 who confirmed its hydrocarbon nature and gave the formula C26H38, which is close to the theoretical composition of C40H56. 
Adolf Lieben in studies, also published in 1886, of the colouring matter in corpora lutea, first came across carotenoids in animal tissue, but did not recognise the nature of the pigment. 
Johann Ludwig Wilhelm Thudichum, in 1868–1869, after stereoscopic spectral examination, applied the term 'luteine'(lutein) to this class of yellow crystallizable substances found in animals and plants. 
Richard Martin Willstätter, who gained the Nobel Prize in Chemistry in 1915, mainly for his work on chlorophyll, assigned the composition of C40H56, distinguishing it from the similar but oxygenated xanthophyll, C40H56O2. 
With Heinrich Escher, in 1910, lycopene was isolated from tomatoes and shown to be an isomer of carotene. Later work by Escher also differentiated the 'luteal' pigments in egg yolk from that of the carotenes in cow corpus luteum.

PRODUCTION

Most of the world's synthetic supply of carotene comes from a manufacturing complex located in Freeport, Texas and owned by DSM. 
Together these suppliers account for about 85% of the β-carotene on the market. 
In Spain natural β-carotene is produced from fungus Blakeslea trispora, as does DSM but at much lower amount when compared to its synthetic β-carotene operation. 

In Australia, organic β-carotene is produced from dried marine algae Dunaliella salina grown in harvesting ponds situated in Karratha, Western Australia. 
Australia is also producing β-carotene from microalgae grown in two sites in Australia that are the world's largest algae farms. 
In Portugal, the industrial biotechnology company is producing natural all-trans-β-carotene from a non-genetically-modified bacteria of the genus Sphingomonas isolated from soil.

Carotenes are also found in palm oil, corn, and in the milk of dairy cows, causing cow's milk to be light yellow, depending on the feed of the cattle, and the amount of fat in the milk (high-fat milks, such as those produced by Guernsey cows, tend to be yellower because their fat content causes them to contain more carotene).
Carotenes are also found in some species of termites, where they apparently have been picked up from the diet of the insects.

In plants and photosynthetic bacteria, carotenes are synthesized from isopentenyl pyrophosphate, the basic 5-carbon building block. 
Their 40-carbon skeletons are built by the successive addition of five-carbon units to form a 20-carbon intermediate, which is then joined tail-to-tail with a second 20-carbon molecule. 
Phytoene, a 40-carbon molecule, condenses to yield lycopene. 
Cyclization of both ends of lycopene produces the characteristic ring structure of beta-carotene.

FUNCTIONS IN LIVING ORGANISMS 

-Carotenes are light-harvesting pigments in photosynthesis

Carotenoids are present in plants and photosynthetic bacteria. 
They absorb light at other wavelengths than those absorbed by the two types of chlorophyll pigments (called chlorophyll a and b), thus extending the range of light that can be absorbed from sunlight and used for photosynthesis. 
Carotenes and other light-absorbing pigments present in the antennas of chloroplasts funnel the energy of absorbed light to the two chlorophyll molecules at the reaction center, where high-energy molecules such as ATP and NADPH are ultimately generated.

-Beta-carotene is a precursor to vitamin A in animals

Beta-carotene can be stored in the liver and converted to vitamin A as needed, thus making it a provitamin (i.e., a precursor to the vitamin). 
Vitamin A (also known as retinol) is a fat-soluble alcohol that plays a crucial role in vision; it is converted to a component of the light-sensitive pigment rodopsin present in the retina of the eye.

-Carotenes serve as antioxidants

Along with vitamins C and E, and a group of related compounds called coenzyme Q, carotones also act as antioxidants in a variety of organisms. 
They shelter prokaryotes from the deleterious effects of light, and protect vital cell functions in plants against the destructive effects of ultraviolet light, acting in a sense like the plant’s sunscreen.

-The color of carotene plays a role in reproduction

A wide range of carotenoids and other colorful compounds abound in the plant kingdom. 
The benefits for the plant in expending resources to produce these compounds are visible in their role in attracting insects for pollination and luring animals for seed distribution.

Carotenoids are also common in animals, which cannot synthesize these molecules and must obtain them through the diet; in animals, they often function as ornamental features. 
For example, the red coloring of lobsters’ shells is created by carotene pigments. 
It has been proposed that carotenoids are used in ornamental traits because, given their physiological and chemical properties, they can be taken as honest indicators of individual health; hence, they are useful signposts when selecting potential mates.

SOURCES

-Dietary sources

Beta-carotene is the most common isomer and can be found in a variety of plants, including certain flowers (e.g., dandelions and marigolds), fruits (e.g., pumpkin, apricot, and cantaloupe), root vegetables (e.g. carrots and sweet potatoes), and leafy greens (e.g., broccoli and spinach). 
β-carotene is also responsible for the coloration of yellow-orange bell peppers.

Pigmentation caused by carotenes is also manifested in certain animals and animal products, such as egg yolks, the shells of lobsters, and the yellow-colored milk of Guernsey cows, noted for its high beta-carotene content.

-Carotene supplements

Beta-carotene was isolated from carrots early in the twentieth century, and first synthesized by scientists around 1950. 
Today, most of the world's synthetic supply of carotene comes from a manufacturing complex located in Freeport, Texas and owned by DSM. 

SYNONYMS

xanthophyll 
provitamin A
carotin
beta-carotene (related)
carotenoid (related) 
sitosterol (related) 
betacarotene (related)
lycopene (related)