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 Gr ...
-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
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
''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
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 betaxanthin ...
,
miraxanthin,
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.
Medi ...
.
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
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 ...
'' 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
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 mo ...
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 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 Gr ...
. 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
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 glycosides. ...
, 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
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, using ...
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''.
Other important betacyanins are
amaranthine and
isoamaranthine, isolated from species of ''
Amaranthus''.
Semisynthetic derivatives
![Betalamic acid](https://upload.wikimedia.org/wikipedia/commons/b/b5/Betalamic_acid.svg)
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
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. Ideall ...
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 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
''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 an ...
'' 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 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 densit ...
s.
See also
*
Biological pigment
References
External links
*
Betalain synthesis diagram
{{Phytochemicals
Natural dyes
Food antioxidants