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Betalains are a class of red and yellow
tyrosine -Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group. The word "tyrosine" is from the G ...
-derived
pigments A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compoun ...
found in plants of the order
Caryophyllales Caryophyllales ( ) is a diverse and heterogeneous order of flowering plants that includes the cacti, carnations, amaranths, ice plants, beets, and many carnivorous plants. Many members are succulent, having fleshy stems or leaves. The betalai ...
, where they replace anthocyanin 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 The beetroot is the taproot portion of a beet plant, usually known in North America as beets while the vegetable is referred to as beetroot in British English, and also known as the table beet, garden beet, red beet, dinner beet or golden beet ...
.


Description

The name "betalain" comes from the
Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
name of the common beet (''Beta vulgaris''), from which betalains were first extracted. The deep red color of beets,
bougainvillea ''Bougainvillea'' ( , ) is a genus of thorny ornamental vines, bushes, and trees belonging to the four o' clock family, Nyctaginaceae. It is native to eastern South America, found from Brazil, west to Peru, and south to southern Argentina. ...
, amaranth, and many cacti 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 Betanin, or Beetroot Red, is a red glycosidic food dye obtained from beets; its aglycone, obtained by hydrolyzing away the glucose molecule, is betanidin. As a food additive, its E number is E162. The color of betanin depends on pH; between fo ...
, isobetanin, probetanin, and neobetanin. * Betaxanthins are those betalain pigments which appear yellow to orange. Among the betaxanthins present in plants include
vulgaxanthin Vulgaxanthins are a group of betaxanthins, or the predominant yellow plant pigments found in red beets, among other plants like ''Mirabilis jalapa'' and swiss chard. They are antioxidant pigments, types I, II, III, IV, and V. Like all betaxanth ...
,
miraxanthin Betalains are a class of red and yellow tyrosine-derived Biological pigment, pigments found in plants of the order Caryophyllales, where they replace anthocyanin pigments. Betalains also occur in some higher order fungi. They are most often notice ...
, portulaxanthin, and
indicaxanthin Indicaxanthin is a type of betaxanthin, a plant pigment present in beets, in ''Mirabilis jalapa'' flowers, in cacti such as prickly pears (''Opuntia sp.'') or the red dragonfruit ('' Hylocereus costaricensis''). It is a powerful antioxidant. Med ...
. 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 Chard or Swiss chard (; ''Beta vulgaris'' subsp. ''vulgaris'', Cicla Group and Flavescens Group) is a green leafy vegetable. In the cultivars of the Flavescens Group, the leaf stalks are large and often prepared separately from the leaf blade; ...
, showing one plant expressing yellow betaxanthins and another expressing red betacyanins. Cactus in Bloom 01.jpg, Flowers of the
cactus 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 Gree ...
''
Mammillaria ''Mammillaria'' is one of the largest genera in the cactus family (Cactaceae), with currently 200 known species and varieties recognized. Most of the mammillaria are native to Mexico, but some come from the southwest United States, the Caribbea ...
sp.'' contain betalains. Amaranthus caudatus0.jpg, Inflorescences of ''
Amaranthus caudatus ''Amaranthus caudatus'' (also known as ''Amaranthus edulis'' and ''Amaranthus mantegazzianus'') is a species of annual flowering plant. It goes by common names such as love-lies-bleeding, pendant amaranth, tassel flower, velvet flower, foxtail a ...
'' (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
vacuole A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic m ...
s 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 Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
whereas anthocyanins do not. It is now known that betalains are
aromatic In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...
indole Indole is an aromatic heterocyclic organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other c ...
derivatives synthesized from
tyrosine -Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group. The word "tyrosine" is from the G ...
. They are not related chemically to the anthocyanins and are not even flavonoids. Each betalain is a
glycoside In chemistry, a glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycoside ...
, and consists of a sugar and a colored portion. Their synthesis is promoted by light. The most heavily studied betalain is
betanin Betanin, or Beetroot Red, is a red glycosidic food dye obtained from beets; its aglycone, obtained by hydrolyzing away the glucose molecule, is betanidin. As a food additive, its E number is E162. The color of betanin depends on pH; between fo ...
, also called beetroot red after the fact that it may be extracted from red beet roots. Betanin is a glucoside, and hydrolyzes into the sugar
glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...
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) 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 An endospore is a dormant, tough, and non-reproductive structure produced by some bacteria in the phylum Bacillota. The name "endospore" is suggestive of a spore or seed-like form (''endo'' means 'within'), but it is not a true spore (i.e., ...
, including '' Bacillus anthracis'' and '' B. cereus''. Other important betacyanins are amaranthine and isoamaranthine, isolated from species of ''
Amaranthus ''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 pac ...
''.


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
coumarin Coumarin () or 2''H''-chromen-2-one is an aromatic organic chemical compound with formula . Its molecule can be described as a benzene molecule with two adjacent hydrogen atoms replaced by a lactone-like chain , forming a second six-membered h ...
ic 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 (mushrooms), for instance Hygrophoraceae ( waxcaps). Where they occur in plants, they sometimes coexist with
anthoxanthin Anthoxanthins (flavones and flavonols)Isolation of a UDP-glucose: Flavonoid 5-O-glucosyltransferase gene and expression analysis of anthocyanin biosynthetic genes in herbaceous peony (Paeonia lactiflora Pall.). Da Qiu Zhao, Chen Xia Han, Jin Tao ...
s (yellow to orange flavonoids), but never occur in plant species with anthocyanins. Among the flowering plant order Caryophyllales, most members produce betalains and lack anthocyanins. Of all the
families Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideal ...
in the Caryophyllales, only the
Caryophyllaceae Caryophyllaceae, commonly called the pink family or carnation family, is a family of flowering plants. It is included in the dicotyledon order Caryophyllales in the APG III system, alongside 33 other families, including Amaranthaceae, Cactacea ...
(carnation family) and
Molluginaceae The Molluginaceae are a family of flowering plants recognized by several taxonomists. It was previously included in the larger family Aizoaceae. The APG III system of 2009 made no change in the status of the family as compared to the APG II syst ...
produce anthocyanins instead of betalains. The limited distribution of betalains among plants is a
synapomorphy In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to hav ...
for the Caryophyllales, though their production has been lost in two families.


Economic uses

Betanin is commercially used as a natural
food dye Food coloring, or color additive, is any dye, pigment, or substance that imparts color when it is added to food or drink. They come in many forms consisting of liquids, powders, gels, and pastes. Food coloring is used in both commercial food ...
. It can cause beeturia (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 ''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called " test-tube experiments", these studies in biology ...
'' methods as antioxidants, which may protect against oxidation of
low-density lipoprotein Low-density lipoprotein (LDL) is one of the five major groups of lipoprotein that transport all fat molecules around the body in extracellular water. These groups, from least dense to most dense, are chylomicrons (aka ULDL by the overall dens ...
s.


See also

*
Biological pigment Biological pigments, also known simply as pigments or biochromes, are substances produced by living organisms that have a color resulting from selective color absorption. Biological pigments include plant pigments and flower pigments. Many biol ...


References


External links

*
Betalain synthesis diagram
{{Phytochemicals Natural dyes Food antioxidants