Betalains are a class of red and yellow tyrosine-derived pigments found in plants of the order Caryophyllales, where they replace anthocyanin pigments. Betalains also occur in some higher order fungi. [1] 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 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, and many cacti results from the presence of betalain pigments. [2] 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: [3]
The physiological function of betalains in plants is uncertain, but there is some evidence that they may have fungicidal properties. [4] Additionally, betalains have been found in fluorescent flowers, though their role in these plants is also uncertain. [5]
Betalains (betacyanins) were first isolated and its chemical structure discovered in 1960 at the University of Zurich by Dr. Tom Mabry. [6] 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. [7] [8] For example, betalains contain nitrogen whereas anthocyanins do not. [2]
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 flavonoids. [9] Each betalain is a glycoside, and consists of a sugar and a colored portion. Their synthesis is promoted by light. [3]
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, and hydrolyzes into the sugar glucose and betanidin. [2] 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 l-proline) are affected by dielectric microwave heating. [10] Addition of TFE (2,2,2-trifluoroethanol) is reported to improve the hydrolytic stability of some betalains in aqueous solution. [11] Furthermore, a betanin-europium(III) complex has been used to detect calcium dipicolinate in bacterial spores, including Bacillus anthracis and B. cereus . [12]
Other important betacyanins are amaranthine and isoamaranthine, isolated from species of Amaranthus .
In the first step of the biosynthetic pathway, L-tyrosine is converted to L-3,4-dihydroxyphenylalanine (l-DOPA) by 3-hydroxylation by a cytochrome P450 enzyme. For dopa, the biosynthesis branches: a) on the one hand, its oxidation occurs by a CYP enzyme to cyclo-dopa; [13] (b) on the other hand, the aromatic ring of dopa is activated by a dopa-4,5-dioxygenase [14] opened to seco-dopa, from which betalamic acid is formed by spantane recyclization. This then reacts spontaneously with cyclo-dopa to form betanidine on the one hand, or on the other hand after its prior glucosylation by a cyclo-dopa glucosyltransferase [15] to red-purple betanin, the simplest betacyan. In addition, betalamic acid reacts spontaneously with various amino acids or amines to form yellow-orange colored betaxanthins (see figure). The diversity of betacyans results from different glucosylation of betanidine and its subsequent acylation with aliphatic and aromatic carboxylic acids.
Betanin extracted from the red beet [16] was used as starting material for the semisynthesis 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. [17]
Betalain pigments occur only in the Caryophyllales and some Basidiomycota (mushrooms), [18] for instance Hygrophoraceae (waxcaps). [19] Where they occur in plants, they sometimes coexist with anthoxanthins (yellow to orange flavonoids), but never occur in plant species with anthocyanins. [20]
Among the flowering plant order 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. [18] The limited distribution of betalains among plants is a synapomorphy for the Caryophyllales, though their production has been lost in two families.
Betanin is commercially used as a natural food dye. 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 methods as antioxidants, [21] which may protect against oxidation of low-density lipoproteins. [22]
Beta vulgaris (beet) is a species of flowering plant in the subfamily Betoideae of the family Amaranthaceae. Economically, it is the most important crop of the large order Caryophyllales. It has several cultivar groups: the sugar beet, of greatest importance to produce table sugar; the root vegetable known as the beetroot or garden beet; the leaf vegetable known as chard or spinach beet or silverbeet; and mangelwurzel, which is a fodder crop. Three subspecies are typically recognised. All cultivars, despite their quite different morphologies, fall into the subspecies Beta vulgaris subsp. vulgaris. The wild ancestor of the cultivated beets is the sea beet.
Flavonoids are a class of polyphenolic secondary metabolites found in plants, and thus commonly consumed in the diets of humans.
Polyphenols are a large family of naturally occurring phenols. They are abundant in plants and structurally diverse. Polyphenols include phenolic acids, flavonoids, tannic acid, and ellagitannin, some of which have been used historically as dyes and for tanning garments.
The beetroot or beet is the taproot portion of a Beta vulgaris subsp. vulgaris plant in the Conditiva Group. The plant is a root vegetable also known as the table beet, garden beet, dinner beet, or else categorized by color: red beet or golden beet. It is also a leaf vegetable called beet greens. Beetroot can be eaten raw, roasted, steamed, or boiled. Beetroot can also be canned, either whole or cut up, and often are pickled, spiced, or served in a sweet-and-sour sauce.
Plant physiology is a subdiscipline of botany concerned with the functioning, or physiology, of plants.
l-DOPA, also known as l-3,4-dihydroxyphenylalanine and used medically as levodopa, is made and used as part of the normal biology of some plants and animals, including humans. Humans, as well as a portion of the other animals that utilize l-DOPA, make it via biosynthesis from the amino acid l-tyrosine.
Delphinidin is an anthocyanidin, a primary plant pigment, and also an antioxidant. Delphinidin gives blue hues to flowers in the genera Viola and Delphinium. It also gives the blue-red color of the grape variety Cabernet Sauvignon, and can be found in cranberries and Concord grapes as well as pomegranates, and bilberries.
Caffeic acid is an organic compound with the formula (HO)2C6H3CH=CHCO2H. It is a polyphenol. It is a yellow solid. Structurally, it is classified as a hydroxycinnamic acid. The molecule consists of both phenolic and acrylic functional groups. It is found in all plants as an intermediate in the biosynthesis of lignin, one of the principal components of biomass and its residues. It is chemically unrelated to caffeine; the related name is due to its presence in coffee.
Betanin, or beetroot red, is a red glycosidic food dye obtained from beets; its aglycone, obtained by hydrolyzing the glucose molecule, is betanidin. As a food additive, its E number is E162. As a food additive, betanin has no safety concerns.
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 biological structures, such as skin, eyes, feathers, fur and hair contain pigments such as melanin in specialized cells called chromatophores. In some species, pigments accrue over very long periods during an individual's lifespan.
Gomphrena globosa, commonly known as globe amaranth, is an edible plant from the family Amaranthaceae. The round-shaped flower inflorescences are a visually dominant feature and cultivars have been propagated to exhibit shades of magenta, purple, red, orange, white, pink, and lilac. Within the flowerheads, the true flowers are small and inconspicuous.
Beeturia is the passing of red or pink urine after eating beetroots or foods colored with beetroot extract or beetroot betalain pigments. The color is caused by the excretion of the betalain pigments, such as betanin.
Indicaxanthin is a type of betaxanthin, a plant pigment present in beets, in Mirabilis jalapa flowers, in cacti such as prickly pears or the red dragonfruit. It is a powerful antioxidant.
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 betalain pigments are unique in plants of this order and occur in all its core families with the exception of Caryophyllaceae and Molluginaceae. Noncore families, such as Nepenthaceae, instead produce anthocyanins.
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 named a chemical compound that gives flowers a blue color, Anthokyan, in his treatise "Die Farben der Blüthen". Food plants rich in anthocyanins include the blueberry, raspberry, black rice, and black soybean, among many others that are red, blue, purple, or black. Some of the colors of autumn leaves are derived from anthocyanins.
Phenolic compounds—natural phenol and polyphenols—occur naturally in wine. These include a large group of several hundred chemical compounds that affect the taste, color and mouthfeel of wine. These compounds include phenolic acids, stilbenoids, flavonols, dihydroflavonols, anthocyanins, flavanol monomers (catechins) and flavanol polymers (proanthocyanidins). This large group of natural phenols can be broadly separated into two categories, flavonoids and non-flavonoids. Flavonoids include the anthocyanins and tannins which contribute to the color and mouthfeel of the wine. The non-flavonoids include the stilbenoids such as resveratrol and phenolic acids such as benzoic, caffeic and cinnamic acids.
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 betaxanthins, they cannot be hydrolyzed by acid to aglycone without degradation. Water activity also affects stability of this antioxidant. It has been studied as a natural nutritional additive but instability remains a problem.
In biochemistry, naturally occurring phenols are natural products containing at least one phenol functional group. Phenolic compounds are produced by plants and microorganisms. Organisms sometimes synthesize phenolic compounds in response to ecological pressures such as pathogen and insect attack, UV radiation and wounding. As they are present in food consumed in human diets and in plants used in traditional medicine of several cultures, their role in human health and disease is a subject of research. Some phenols are germicidal and are used in formulating disinfectants.
Aureusidin synthase is an enzyme with systematic name 2',4,4',6'-tetrahydroxychalcone 4'-O-beta-D-glucoside:oxygen oxidoreductase.
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