Phlobaphene is the red pigment present in the pericarp of certain maize varieties
Phlobaphenes (or phlobaphens, CAS No.:71663-19-9) are reddish, alcohol-soluble and water-insoluble phenolic substances. They can be extracted from plants, or be the result from treatment of tannin extracts withmineral acids[1] (tanner's red).[2] The namephlobaphen come from theGreek roots φλoιὀς (phloios) meaningbark and βαφή (baphe) meaningdye.[3][4]
No biological activities have currently been reported for phlobaphenes.[5] Phlobaphenes fromhawthorn fruits (Fructus Crataegi) may have a specific action on thecoronary circulation[citation needed]. They are converted intohumins in soils.[6]
Natural phlobaphenes are the commonbark,pericarp,cobglume andseed coat (testa)pigments. They have not been found in flowers, unless the brown and black pigments in the involucrum of certain compositae are found to be of the phlobaphene type.[7]
In bark, phlobaphenes accumulate in thephellem layer of cork cambium, part of thesuberin mixture.[8]
Manycinchona barks contain a particular tannin,cinchotannic acid, which by oxidation rapidly yields a dark-coloured phlobaphene[9] calledred cinchonic,[10]cinchono-fulvic acid orcinchona red.[11]
They are common inredwoods barks likeSequoia sempervirens[12] or in oak barks where the chief constituent,quercitannic acid, a molecule also present inquercitron, is an unstable substance, having a tendency to give off water to form anhydrides (phlobaphenes), one of which is calledoak-red (C28H22O11).
Cuscuta europaea L., the European dodder, is reported to contain 30,000 ppm in the root.[13]
The common tormentil (Potentilla erecta)
Phlobaphenes can be extracted from the root of thecommon tormentil (Potentilla erecta) astormentil red.
Kola nut
Phlobaphens can be found in thekola nut (where they are calledkola red),[14]chocolate liquor (calledcocoa red)[15] or in the red skins or testa of the peanut.[16] They are also reported in the fruits of the genusCrataegus (Fructus Crataegi)or can be extracted fromhop flowers.[17]
Copious flow of kino from a wound near the base of the trunk of aCorymbia calophylla (marri)
The chief constituent ofkino iskinotannic acid, of which it contains 70 to 80 per cent. It also contains kino red, a phlobaphene produced from kinotannic acid by oxidation.[18]
Phlobaphenes are not present in the model plantArabidopsis thaliana but can be studied as the pigment responsible for the red color in some monocot cereals, includingwheat,[19]maize[20] orsorghum.[21]
In maize, phlobaphenes are synthesized in the flavonoids synthetic pathway[22] from polymerisation offlavan-4-ols[23] by the expression of maize pericarp color1 (p1) gene[24] which encodes an R2R3myb-liketranscriptional activator[25] of the A1 gene encoding for thedihydroflavonol 4-reductase (reducingdihydroflavonols into flavan-4-ols)[26] while another gene (Suppressor of Pericarp Pigmentation 1 or SPP1) acts as asuppressor.[27] The p1 gene encodes an Myb-homologous transcriptional activator of genes required for biosynthesis of red phlobaphene pigments, while the P1-wr allele specifies colorless kernelpericarp and redcobs, and unstable factor for orange1 (Ufo1) modifies P1-wr expression to confer pigmentation in kernel pericarp, as well as vegetative tissues, which normally do not accumulate significant amounts of phlobaphene pigments.[24] The maize P gene encodes a Myb homolog that recognizes the sequence CCT/AACC, in sharp contrast with the C/TAACGG bound by vertebrate Myb proteins.[28]
It is a dark-colored resin-like substance made of water-insoluble, alcohol-soluble polymers.[31]
Phlobaphens can be formed under action of acids or heating ofcondensed tannins or of the fraction of tannins calledphlobatannins. Water containing soda can be used for the conversion ofhop tannins into phlobaphens.[32] When heated withhydrochloric acid, tannins incocoa solids yield a glucose and a phlobaphene.[33]
Ordinary or warm soluble quebracho (also known as insoluble quebracho) is the natural extract obtained directly from thequebracho wood. This type of extract is rich in condensed tannins of natural high molecular weight (phlobaphenes), which are not easily soluble. Its use is therefore limited to small additions during sole leather tannage carried out in hot liquors (temperature above 35 °C) to improve the yield and the water-proofness of the leather. The cold soluble extracts are obtained by subjecting the ordinary extract to asulfiting process which transforms the phlobaphenes into completely soluble tannins. The cold soluble quebracho extracts are the most universally known and used types. The main properties of these extracts are: a very rapid penetration, a high tannin content and a relatively low percentage of non-tannins. The rather low acid and medium salt content characterise them as mild tanning extracts (low astringency).
Phlobaphenes formation (tannins condensation and precipitation) can be minimized in using strong nucleophiles, such asphloroglucinol,m-phenylenediamine andurea, during pine tannins extraction.[34]
The use of synthetic tanninneradol D can help solubilize phlobaphene in tanning solutions.[35]
^Buchanan, M. A.; Lewis, H. F.; Kurth, E. F. (1944). "Chemical Nature of Redwood Tannin and Phlobaphene".Industrial & Engineering Chemistry.36 (10):907–910.doi:10.1021/ie50418a008.
^Hager's Handbuch der Pharmazeutischen Praxis, List, P.H. and Horhammer, L., Vols. 2–6, Springer-Verlag, Berlin, 1969–1979
^Stansbury, Mack F.; Field, Elsie T.; Guthrie, John D. (1950). "The tannin and related pigments in the red skins (Testa) of peanut kernels".Journal of the American Oil Chemists' Society.27 (8): 317.doi:10.1007/BF02649320.S2CID95107923.
^abBraess, CH; Cocciolone, SM; Bushman, S; Sangar, V; McMullen, MD; Peterson, T (1976). "Is Igls worth a journey? Report on the 19th International Congress on General Medicine of the SIMG in Igls/Innsbruck, September 22–27, 1975".Zeitschrift für Allgemeinmedizin.52 (8):432–433.PMID1266355.
^Lee E.A; Harper V (2002). "Suppressor of Pericarp Pigmentation 1 (SPP1), a novel gene involved in phlobaphene accumulation in maize (Zea mays L.) pericarps".Maydica.47 (1):51–58.INIST13772300.
^Grotewold, Erich; Drummond, Bruce J.; Bowen, Ben; Peterson, Thomas (1994). "The myb-homologous P gene controls phlobaphene pigmentation in maize floral organs by directly activating a flavonoid biosynthetic gene subset".Cell.76 (3):543–553.doi:10.1016/0092-8674(94)90117-1.PMID8313474.S2CID42197232.
^Boddu, Jayanand; Svabek, Catherine; Ibraheem, Farag; Jones, A. Daniel; Chopra, Surinder (2005). "Characterization of a deletion allele of a sorghum Myb gene yellow seed1 showing loss of 3-deoxyflavonoids".Plant Science.169 (3): 542.doi:10.1016/j.plantsci.2005.05.007.INIST16983977.
^Boddu, Jayanand; Jiang, Cizhong; Sangar, Vineet; Olson, Terry; Peterson, Thomas; Chopra, Surinder (2006). "Comparative Structural and Functional Characterization of Sorghum and Maize Duplications Containing Orthologous Myb Transcription Regulators of 3-Deoxyflavonoid Biosynthesis".Plant Molecular Biology.60 (2):185–199.doi:10.1007/s11103-005-3568-1.PMID16429259.S2CID23841582.
^Sealy-Fisher, V. J.; Pizzi, A. (1992). "Increased pine tannins extraction and wood adhesives development by phlobaphenes minimization".Holz Als Roh- und Werkstoff.50 (5): 212.doi:10.1007/BF02663290.S2CID6585979.
