Superposition of spectra of chlorophyll a and b with oenin (malvidin 3O glucoside), a typical anthocyanin, in an acidic solution. While chlorophylls absorb in the blue and yellow/red parts of the visible spectrum, oenin absorbs mainly in the green part of the spectrum, where chlorophylls do not absorb at all.
In flowers, bright-reds and -purples are adaptive for attracting pollinators. In fruits, the colorful skins also attract the attention of animals, which may eat the fruits and disperse the seeds. In photosynthetic tissues (such as leaves and sometimes stems), anthocyanins have been shown to act as a "sunscreen", protecting cells from high-light damage by absorbing blue-green and ultraviolet light, thereby protecting the tissues from photoinhibition, or high-light stress. This has been shown to occur in red juvenile leaves, autumn leaves, and broad-leaf evergreen leaves that turn red during the winter. The red coloration of leaves has been proposed to possibly camouflage leaves from herbivores blind to red wavelengths, or signal unpalatability, since anthocyanin synthesis often coincides with synthesis of unpalatable phenolic compounds.
In addition to their role as light-attenuators, anthocyanins also act as powerful antioxidants. However, it is not clear whether anthocyanins can significantly contribute to scavenging of free radicals produced through metabolic processes in leaves, since they are located in the vacuole and, thus, spatially separated from metabolic reactive oxygen species. Some studies have shown hydrogen peroxide produced in other organelles can be neutralized by vacuolar anthocyanin.
The absorbance pattern responsible for the red color of anthocyanins may be complementary to that of green chlorophyll in photosynthetically active tissues such as young Quercus coccifera leaves. It may protect the leaves from attacks by plant eaters that may be attracted by green color.
Red cabbage (anthocyanin dye) extract at low pH (left) to high pH (right)
Anthocyanins can be used as pH indicators because their color changes with pH; they are pink in acidic solutions (pH < 7), purple in neutral solutions (pH ~ 7), greenish-yellow in alkaline solutions (pH > 7), and colourless in very alkaline solutions, where the pigment is completely reduced.
Anthocyanins are found in the cell vacuole, mostly in flowers and fruits but also in leaves, stems, and roots. In these parts, they are found predominantly in outer cell layers such as the epidermis and peripheral mesophyll cells.
The highest recorded amount appears to be specifically in the seed coat of black soybean (Glycine max L. Merr.) containing some 2,000 mg per 100 g and in skins and pulp of black chokeberry (Aronia melanocarpa L.) (table). However, the Amazonian palmberry, açaí, having about 320 mg per 100 g of which cyanidin-3-glucoside is the most prevalent individual anthocyanin (approximately 10 mg per 100 g), is also a high-content source for which only a small fraction of total anthocyanins has been determined to date. Due to critical differences in sample origin, preparation and extraction methods determining anthocyanin content, the values presented in the adjoining table are not directly comparable.
Nature, traditional agriculture, and plant breeding have produced various uncommon crops containing anthocyanins, including blue- or red-flesh potatoes and purple or red broccoli, cabbage, cauliflower, carrots, and corn. Tomatoes have been bred conventionally for high anthocyanin content by crossing wild relatives with the common tomato to transfer a gene called the anthocyanin fruit tomato (aft) gene into a larger and more palatable fruit.
Anthocyanins are present in about 10% of tree species in temperate regions, although in certain areas such as New England, up to 70% of tree species may produce the pigment.
Many science textbooks incompletely state that autumn coloration (including red) is the result of breakdown of green chlorophyll, which unmasks the already-present orange, yellow, and red pigments (carotenoids, xanthophylls, and anthocyanins, respectively). While this is indeed the case for the carotenoids and xanthophylls (orange and yellow pigments), anthocyanins are not synthesized until the plant has begun breaking down the chlorophyll.
The anthocyanins, anthocyanidins with sugar group(s), are mostly 3-glucosides of the anthocyanidins. The anthocyanins are subdivided into the sugar-free anthocyanidinaglycones and the anthocyanin glycosides. As of 2003, more than 400 anthocyanins had been reported while more recent literature (early 2006), puts the number at more than 550 different anthocyanins. The difference in chemical structure that occurs in response to changes in pH is the reason why anthocyanins are often used as pH indicators, as they change from red in acids to blue in bases.
Anthocyanins are thought to be subject to physiochemical degradation in vivo and in vitro. Structure, pH, temperature, light, oxygen, metal ions, intramolecular association, and intermolecular association with other compounds (copigments, sugars, proteins, degradation products, etc.) are generally known to affect the color and stability of anthocyanins. B-ring hydroxylation status and pH have been shown to mediate the degradation of anthocyanins to their phenolic acid and aldehyde constituents. Indeed, significant portions of ingested anthocyanins are likely to degrade to phenolic acids and aldehyde in vivo, following consumption. This characteristic confounds scientific isolation of specific anthocyanin mechanisms in vivo.
Leucoanthocyanidins were once believed to be the immediate precursors of the next enzyme, a dioxygenase referred to as anthocyanidin synthase or leucoanthocyanidin dioxygenase. Flavan-3-ols, the products of leucoanthocyanidin reductase (LAR), have been recently shown to be their true substrates.
The resulting unstable anthocyanidins are further coupled to sugar molecules by enzymes such as UDP-3-O-glucosyltransferase to yield the final relatively stable anthocyanins.
More than five enzymes are thus required to synthesize these pigments, each working in concert. Even a minor disruption in any of the mechanism of these enzymes by either genetic or environmental factors would halt anthocyanin production. While the biological burden of producing anthocyanins is relatively high, plants benefit significantly from environmental adaptation, disease tolerance, and pest tolerance provided by anthocyanins.
In anthocyanin biosynthetic pathway, L-phenylalanine is converted to naringenin by phenylalanine ammonialyase (PAL), cinnamate 4-hydroxylase (C4H), 4-coumarate CoA ligase (4CL), chalcone synthase (CHS) and chalcone isomerase (CHI). And then, the next pathway is catalyzed the formation of complex aglycone and anthocyanin composition by flavanone 3-hydroxylase (F3H), flavonoid 3'-hydroxylase (F3'H), dihydroflavonol 4-reductase (DFR), anthocyanidin synthase (ANS), UDP-glucoside: flavonoid glucosyltransferase (UFGT) and methyl transferase (MT). Among those, UFGT is divided into UF3GT and UF5GT, which are responsible for the glucosylation of anthocyanin to produce stable molecules.
The phenolic metabolic pathways and enzymes can be studied by mean of transgenesis of genes. The Arabidopsis regulatory gene in the production of anthocyanin pigment 1 (AtPAP1) can be expressed in other plant species.
Although anthocyanins are powerful antioxidants in vitro, this antioxidant property is unlikely to be conserved after the plant is consumed. As interpreted by the Linus Pauling Institute and European Food Safety Authority, dietary anthocyanins and other flavonoids have little or no direct antioxidant food value following digestion. Unlike controlled test-tube conditions, the fate of anthocyanins in vivo shows they are poorly conserved (less than 5%), with most of what is absorbed existing as chemically modified metabolites that are rapidly excreted.
The increase in antioxidant capacity of blood seen after the consumption of anthocyanin-rich foods may not be caused directly by the anthocyanins, but instead may result from increased uric acid levels derived from metabolism of flavonoids.
Dye-sensitized solar cells
Anthocyanins have been used in organic solar cells because of their ability to convert light energy into electrical energy. The many benefits to using dye-sensitized solar cells instead of traditional pn junction silicon cells include lower purity requirements and abundance of component materials, such as titania, as well as the fact they can be produced on flexible substrates, making them amenable to roll-to-roll printing processes.
Research on health benefits
Richly concentrated as pigments in berries, anthocyanins were the topics of research presented at a 2007 symposium on health benefits that may result from berry consumption.
According to a 2009 study: "A growing body of evidence suggests anthocyanins and anthocyanidins may possess analgesic properties in addition to neuroprotective and anti-inﬂammatory activities".
In vitro, anthocyanins possess MAO inhibitory activity for both MAO-A and MAO-B; MAO function is connected to neurodegenerative diseases, depression, and anxiety. The relevance to humans of anthocyanins and MAO activity requires further research, however.
Anthocyanins also fluoresce; combined with their antioxidant properties, this can be a powerful tool for plant cell research, allowing live cell imaging for extended periods of time without a requirement for other fluorophores.
According to the American Cancer Society, researchers are investigating the positive effects phytochemicals such as anthocyanin may have in the human diet, by researching the possible effect of specific compounds. However, there have been no strong studies in humans showing that any phytochemical supplement can prevent or treat cancer.
Use as visual markers to mark genetically modified materials
Anthocyanin production can be engineered into genetically modified materials to enable their visual identification.
^The importance of being red when young: anthocyanins and the protection of young leaves of Quercus coccifera from insect herbivory and excess light. Panagiota Karageorgou and Yiannis Manetas, Tree Physiol, 2006, 26 (5), pages 613-621, doi:10.1093/treephys/26.5.613
^ abWu X, Gu L, Prior RL, McKay S (December 2004). "Characterization of anthocyanins and proanthocyanidins in some cultivars of Ribes, Aronia, and Sambucus and their antioxidant capacity". Journal of Agricultural and Food Chemistry52 (26): 7846–56. doi:10.1021/jf0486850. PMID15612766.
^Siriwoharn T, Wrolstad RE, Finn CE, Pereira CB (December 2004). "Influence of cultivar, maturity, and sampling on blackberry (Rubus L. Hybrids) anthocyanins, polyphenolics, and antioxidant properties". Journal of Agricultural and Food Chemistry52 (26): 8021–30. doi:10.1021/jf048619y. PMID15612791.
^Wada L, Ou B (June 2002). "Antioxidant activity and phenolic content of Oregon caneberries". Journal of Agricultural and Food Chemistry50 (12): 3495–500. doi:10.1021/jf011405l. PMID12033817.
^Hosseinian FS, Beta T (December 2007). "Saskatoon and wild blueberries have higher anthocyanin contents than other Manitoba berries". Journal of Agricultural and Food Chemistry55 (26): 10832–8. doi:10.1021/jf072529m. PMID18052240.
^Lieberman S (2007). "The antioxidant power of purple corn: a research review". Alternative & Complementary Therapies13 (2): 107–110. doi:10.1089/act.2007.13210.
^Selecting new peach and plum genotypes rich in phenolic compounds and enhanced functional properties. Bolivar A. Cevallos-Casals, David Byrne, William R. Okie and Luis Cisneros-Zevallos, Food Chemistry, 2006, 96, pages 273–328, doi:10.1016/j.foodchem.2005.02.03
^Choung MG et al. (December 2001). "Isolation and determination of anthocyanins in seed coats of black soybean (Glycine max (L.) Merr.)". J. Agric. Food Chem.49 (12): 5848–51. doi:10.1021/jf010550w. PMID11743773.
^Schauss AG et al. (November 2006). "Phytochemical and nutrient composition of the freeze-dried amazonian palm berry, Euterpe oleraceae mart. (acai)". Journal of Agricultural and Food Chemistry54 (22): 8598–603. doi:10.1021/jf060976g. PMID17061839.
^Del Pozo-Insfran D, Brenes CH, Talcott ST (March 2004). "Phytochemical composition and pigment stability of Açai (Euterpe oleracea Mart.)". Journal of Agricultural and Food Chemistry52 (6): 1539–45. doi:10.1021/jf035189n. PMID15030208.
^Krenn L et al. (November 2007). "Anthocyanin- and proanthocyanidin-rich extracts of berries in food supplements--analysis with problems". Pharmazie62 (11): 803–12. PMID18065095.
^Siriwoharn T, Wrolstad RE, Finn CE, Pereira CB (December 2004). "Influence of cultivar, maturity, and sampling on blackberry (Rubus L. Hybrids) anthocyanins, polyphenolics, and antioxidant properties". J Agric Food Chem52 (26): 8021–30. doi:10.1021/jf048619y. PMID15612791.
^Jones CM, Mes P, Myers JR (2003). "Characterization and inheritance of the Anthocyanin fruit (Aft) tomato". The Journal of Heredity94 (6): 449–56. doi:10.1093/jhered/esg093. PMID14691311.
^Butelli E et al. (November 2008). "Enrichment of tomato fruit with health-promoting anthocyanins by expression of select transcription factors". Nature Biotechnology26 (11): 1301–8. doi:10.1038/nbt.1506. PMID18953354.
^ abAgati G et al. (March 2005). "Nondestructive evaluation of anthocyanins in olive (Olea europaea) fruits by in situ chlorophyll fluorescence spectroscopy". Journal of Agricultural and Food Chemistry53 (5): 1354–1363. doi:10.1021/jf048381d. PMID15740006.
^ abcArchetti, Marco; Döring, Thomas F.; Hagen, Snorre B.; Hughes, Nicole M.; Leather, Simon R.; Lee, David W.; Lev-Yadun, Simcha; Manetas, Yiannis; Ougham, Helen J. (2011). "Unravelling the evolution of autumn colours: an interdisciplinary approach". Trends in Ecology & Evolution24 (3): 166–73. doi:10.1016/j.tree.2008.10.006. PMID19178979.
^Davies, Kevin M. (2004). Plant pigments and their manipulation. Wiley-Blackwell. p. 6. ISBN1-4051-1737-0.
^Andersen, Øyvind M.; Jordheim, Monica (2008), "Anthocyanins- food applications", 5th Pigments in Food congress- for quality and health, University of Helsinki, ISBN978-952-10-4846-3
^Gary Woodward, Paul Kroon, Aedin Cassidy and Colin Kay. (2009). Anthocyanin Stability and Recovery: Implications for the Analysis of Clinical and Experimental Samples. J. Agric. Food Chem., 2009, 57 (12), pp 5271–5278
^Nakajima J, Tanaka Y, Yamazaki M, Saito K (July 2001). "Reaction mechanism from leucoanthocyanidin to anthocyanidin 3-glucoside, a key reaction for coloring in anthocyanin biosynthesis". The Journal of Biological Chemistry276 (28): 25797–803. doi:10.1074/jbc.M100744200. PMID11316805.
^Kovinich N, Saleem A, Arnason JT, Miki B (2010). "Functional characterization of a UDP-glucose:flavonoid 3-O-glucosyltransferase from the seed coat of black soybean (Glycine max (L.) Merr.)". Phytochemistry71 (11–12): 1253–63. doi:10.1016/j.phytochem.2010.05.009. PMID20621794.
^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 Ge and Jun Tao, Electronic Journal of Biotechnology, 15 November 2012, Volume 15, Number 6, doi:10.2225/vol15-issue6-fulltext-7
^Two glycosyltransferases involved in anthocyanin modiﬁcation delineated by transcriptome independent component analysis in Arabidopsis thaliana. Keiko Yonekura-Sakakibara, Atsushi Fukushima, Ryo Nakabayashi1, Kousuke Hanada, Fumio Matsuda, Satoko Sugawara, Eri Inoue, Takashi Kuromori, Takuya Ito, Kazuo Shinozaki, Bunyapa Wangwattana and Mami Yamazaki, nt Journal, 2012, volume 69, pages 154–167, doi:10.1111/j.1365-313X.2011.04779.x
^Xiang Li et al. (2010). "Purple canola: Arabidopsis PAP1 increases antioxidants and phenolics in Brassica napus leaves". J. Agric. Food Chem.58 (3): 1639–1645. doi:10.1021/jf903527y. PMID20073469.
^Seeram, Navindra P. (2008). "Berry Fruits: Compositional Elements, Biochemical Activities, and the Impact of Their Intake on Human Health, Performance, and Disease". Journal of Agricultural and Food Chemistry56 (3): 627–9. doi:10.1021/jf071988k. PMID18211023.
^Korte, Gabriele; Dreiseitel, Andrea; Schreier, Peter; Oehme, Anett; Locher, Sanja; Hajak, Goeran; Sand, Philipp G. (2009). "An Examination of Anthocyanins' and Anthocyanidins' Affinity for Cannabinoid Receptors". Journal of Medicinal Food12 (6): 1407–10. doi:10.1089/jmf.2008.0243. PMID20041802.
^Wiltshire EJ, Collings DA (October 2009). "New dynamics in an old friend: dynamic tubular vacuoles radiate through the cortical cytoplasm of red onion epidermal cells". Plant & Cell Physiology50 (10): 1826–39. doi:10.1093/pcp/pcp124. PMID19762337.