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]
L-Tyrosine or tyrosine 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 Greek tyrós, meaning cheese, as it was first discovered in 1846 by German chemist Justus von Liebig in the protein casein from cheese. It is called tyrosyl when referred to as a functional group or side chain. While tyrosine is generally classified as a hydrophobic amino acid, it is more hydrophilic than phenylalanine. It is encoded by the codons UAC and UAU in messenger RNA.
A catecholamine is a monoamine neurotransmitter, an organic compound that has a catechol and a side-chain amine.
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.
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.
Plant physiology is a subdiscipline of botany concerned with the functioning, or physiology, of plants.
l-DOPA, also known as levodopa and l-3,4-dihydroxyphenylalanine, 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. l-DOPA is the precursor to the neurotransmitters dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline), which are collectively known as catecholamines. Furthermore, l-DOPA itself mediates neurotrophic factor release by the brain and CNS. In some plant families, l-DOPA is the central precursor of a biosynthetic pathway that produces a class of pigments called betalains. l-DOPA can be manufactured and in its pure form is sold as a psychoactive drug with the INN levodopa; trade names include Sinemet, Pharmacopa, Atamet, and Stalevo. As a drug, it is used in the clinical treatment of Parkinson's disease and dopamine-responsive dystonia.
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.
Cyanidin is a natural organic compound. It is a particular type of anthocyanidin. It is a pigment found in many red berries including grapes, bilberry, blackberry, blueberry, cherry, chokeberry, cranberry, elderberry, hawthorn, loganberry, açai berry and raspberry. It can also be found in other fruits such as apples and plums, and in red cabbage and red onion. It has a characteristic reddish-purple color, though this can change with pH; solutions of the compound are red at pH < 3, violet at pH 7-8, and blue at pH > 11. In certain fruits, the highest concentrations of cyanidin are found in the seeds and skin. Cyanidin has been found to be a potent sirtuin 6 (SIRT6) activator.
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.
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 pigments. The color is caused by the excretion of betalain (betacyanin) pigments such as betanin. The coloring is highly variable between individuals and between different occasions, and can vary in intensity from invisible to strong. The pigment is sensitive to oxidative degradation under strongly acidic conditions. Therefore, the urine coloring depends on stomach acidity and dwell time as well as the presence of protecting substances such as oxalic acid. Beeturia is often associated with red or pink feces.
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.
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 compound that gives flowers a blue color for the first time 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.
The phenolic content in wine refers to the phenolic compounds—natural phenol and polyphenols—in wine, which 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.
The color of wine is one of the most easily recognizable characteristics of wines. Color is also an element in wine tasting since heavy wines generally have a deeper color. The accessory traditionally used to judge the wine color was the tastevin, a shallow cup allowing one to see the color of the liquid in the dim light of a cellar. The color is an element in the classification of wines.
Myrtillin is an anthocyanin. It is the 3-glucoside of delphinidin. It can be found in all green plants, most abundantly in black beans, blackcurrant, blueberry, huckleberry, bilberry leaves and in various myrtles, roselle plants, and Centella asiatica plant. It is also present in yeast and oatmeal. The sumac fruit's pericarp owes its dark red colour to anthocyanin pigments, of which chrysanthemin, myrtillin and delphinidin have yet been identified.
Blue flower colour was always associated with something unusual and desired. Blue roses especially were assumed to be a dream that cannot be realised. Blue colour in flower petals is caused by anthocyanins, which are members of flavonoid class metabolites. We can diversify three main classes of anthocyanin pigments: cyaniding type responsible for red coloration, pelargonidin type responsible for orange colour and delphinidin type responsible for violet/blue flower and fruits coloration. The main difference in the structure of listed anthocyanins type is the number of hydroxyl groups in the B-ring of the anthocyanin. Nevertheless, in the monomeric state anthocyanins never show blue colour in the weak acidic and neutral pH. The mechanism of blue colour formation are very complicated in most cases, presence of delphinidin type pigments is not sufficient, great role play also the pH and the formation of complexes of anthocyanins with flavones and metal ions.
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