Betaxanthins
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Betalains are a class of red and yellow tyrosine-derived pigments found in plants of the order Caryophyllales, where they replace
anthocyanin Anthocyanins (), also called anthocyans, are water-soluble vacuolar pigments that, depending on their pH, may appear red, purple, blue, or black. In 1835, the German pharmacist Ludwig Clamor Marquart gave the name Anthokyan to a chemical compo ...
pigments. Betalains also occur in some higher order fungi. They are most often noticeable in the petals of flowers, but may color the fruits, leaves, stems, and roots of plants that contain them. They include pigments such as those found in beets.


Description

The name "betalain" comes from the Latin name of the common beet (''Beta vulgaris''), from which betalains were first extracted. The deep red color of beets, bougainvillea,
amaranth ''Amaranthus'' is a cosmopolitan genus of annual or short-lived perennial plants collectively known as amaranths. Some amaranth species are cultivated as leaf vegetables, pseudocereals, and ornamental plants. Catkin-like cymes of densely pack ...
, and many
cacti A cactus (, or less commonly, cactus) is a member of the plant family Cactaceae, a family comprising about 127 genera with some 1750 known species of the order Caryophyllales. The word ''cactus'' derives, through Latin, from the Ancient Greek ...
results from the presence of betalain pigments. The particular shades of red to purple are distinctive and unlike that of anthocyanin pigments found in most plants. There are two categories of betalains: * Betacyanins include the reddish to violet betalain pigments. Among the betacyanins present in plants include betanin, isobetanin, probetanin, and neobetanin. * Betaxanthins are those betalain pigments which appear yellow to orange. Among the betaxanthins present in plants include vulgaxanthin, miraxanthin, portulaxanthin, and indicaxanthin. The physiological function of betalains in plants is uncertain, but there is some evidence that they may have fungicidal properties. Additionally, betalains have been found in fluorescent flowers, though their role in these plants is also uncertain. Gelber und roter Mangold.JPG, Swiss chard, showing one plant expressing yellow betaxanthins and another expressing red betacyanins. Cactus in Bloom 01.jpg, Flowers of the cactus '' Mammillaria sp.'' contain betalains. Amaranthus caudatus0.jpg, Inflorescences of '' Amaranthus caudatus'' (love-lies-bleeding) contain large quantities of betacyanins.


Chemistry

Betalains were first isolated and its chemical structure discovered in 1960 at the University of Zurich by Dr. Tom Mabry. It was once thought that betalains were related to anthocyanins, the reddish pigments found in most plants. Both betalains and anthocyanins are water-soluble pigments found in the vacuoles of plant cells. However, betalains are structurally and chemically unlike anthocyanins and the two have never been found in the same plant together. For example, betalains contain nitrogen whereas anthocyanins do not. It is now known that betalains are aromatic indole derivatives synthesized from tyrosine. They are not related chemically to the anthocyanins and are not even
flavonoid Flavonoids (or bioflavonoids; from the Latin word ''flavus'', meaning yellow, their color in nature) are a class of polyphenolic secondary metabolites found in plants, and thus commonly consumed in the diets of humans. Chemically, flavonoids ...
s. Each betalain is a glycoside, and consists of a sugar and a colored portion. Their synthesis is promoted by light. The most heavily studied betalain is betanin, also called beetroot red after the fact that it may be extracted from red beet roots. Betanin is a
glucoside A glucoside is a glycoside that is derived from glucose. Glucosides are common in plants, but rare in animals. Glucose is produced when a glucoside is hydrolysed by purely chemical means, or decomposed by fermentation or enzymes. The name was o ...
, and hydrolyzes into the sugar glucose and betanidin. It is used as a food coloring agent, and the color is sensitive to pH. Other betalains known to occur in beets are isobetanin, probetanin, and neobetanin. The color and antioxidant capacity of betanin and indicaxanthin (betaxanthin derived of -proline) are affected by dielectric microwave heating. Addition of TFE (
2,2,2-trifluoroethanol 2,2,2-Trifluoroethanol is the organic compound with the formula CF3CH2OH. Also known as TFE or trifluoroethyl alcohol, this colourless, water-miscible liquid has a smell reminiscent of ethanol. Due to the electronegativity of the trifluoromethy ...
) is reported to improve the hydrolytic stability of some betalains in aqueous solution. Furthermore, a betanin- europium(III) complex has been used to detect calcium dipicolinate in bacterial spores, including ''
Bacillus anthracis ''Bacillus anthracis'' is a gram-positive and rod-shaped bacterium that causes anthrax, a deadly disease to livestock and, occasionally, to humans. It is the only permanent ( obligate) pathogen within the genus ''Bacillus''. Its infection is a ...
'' and ''
B. cereus ''Bacillus cereus'' is a Gram-positive rod-shaped bacterium commonly found in soil, food, and marine sponges. The specific name, ''cereus'', meaning "waxy" in Latin, refers to the appearance of colonies grown on blood agar. Some strains are ha ...
''. Other important betacyanins are amaranthine and isoamaranthine, isolated from species of '' Amaranthus''.


Semisynthetic derivatives

Betanin extracted from the red beet was used as starting material for the
semisynthesis Semisynthesis, or partial chemical synthesis, is a type of chemical synthesis that uses chemical compounds isolated from natural sources (such as microbial cell cultures or plant material) as the starting materials to produce novel compounds with ...
of an artificial coumarinic betalaine. The betanin was hydrolyzed to betalamic acid, and this was coupled to 7-amino-4-methylcoumarin. The resulting betalain was applied as a fluorescent probe for the live-cell imaging of ''Plasmodium''-infected erythrocytes.


Taxonomic significance

Betalain pigments occur only in the Caryophyllales and some
Basidiomycota Basidiomycota () is one of two large divisions that, together with the Ascomycota, constitute the subkingdom Dikarya (often referred to as the "higher fungi") within the kingdom Fungi. Members are known as basidiomycetes. More specifically, Basi ...
(mushrooms), for instance Hygrophoraceae (
waxcaps ''Hygrocybe'' is a genus of agarics (gilled fungi) in the family Hygrophoraceae. Called waxcaps in English (sometimes waxy caps in North America), basidiocarps (fruit bodies) are often brightly coloured and have dry to waxy caps, white spores, an ...
). Where they occur in plants, they sometimes coexist with anthoxanthins (yellow to orange
flavonoid Flavonoids (or bioflavonoids; from the Latin word ''flavus'', meaning yellow, their color in nature) are a class of polyphenolic secondary metabolites found in plants, and thus commonly consumed in the diets of humans. Chemically, flavonoids ...
s), but never occur in plant species with anthocyanins. Among the flowering plant
order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...
Caryophyllales, most members produce betalains and lack anthocyanins. Of all the families in the Caryophyllales, only the Caryophyllaceae (carnation family) and Molluginaceae produce anthocyanins instead of betalains. The limited distribution of betalains among plants is a synapomorphy for the Caryophyllales, though their production has been lost in two families.


Economic uses

Betanin is commercially used as a natural food dye. It can cause
beeturia Beeturia is the passing of red or pink urine after eating beetroots or foods colored with beetroot extract or beetroot pigments. The color is caused by the excretion of betalain (betacyanin) pigments such as betanin. The coloring is highly varia ...
(red urine) and red feces in some people who are unable to break it down. The interest of the food industry in betalains has grown since they were identified by '' in vitro'' methods as
antioxidant Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals. This can lead to polymerization and other chain reactions. They are frequently added to industrial products, such as fuels and lubricant ...
s, which may protect against oxidation of low-density lipoproteins.


See also

* Biological pigment


References


External links

*
Betalain synthesis diagram
{{Phytochemicals Natural dyes Food antioxidants