Editing Rhubarb (section)

==Phytochemistry and potential toxicity==
The roots and stems contain [[natural anthraquinone|anthraquinones]], such as [[emodin]] and [[Rhein (molecule)|rhein]].<ref name="mehta" /> [[Emodin]] "represents a [[Genotoxicity|genotoxic]] risk for humans" while [[Rhein (molecule)|rhein]] is "a compound devoid of genotoxic capabilities".<ref>{{Cite journal |last1=EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS) |last2=Younes |first2=Maged |last3=Aggett |first3=Peter |last4=Aguilar |first4=Fernando |last5=Crebelli |first5=Riccardo |last6=Filipič |first6=Metka |last7=Frutos |first7=Maria Jose |last8=Galtier |first8=Pierre |last9=Gott |first9=David |last10=Gundert-Remy |first10=Ursula |last11=Kuhnle |first11=Gunter Georg |last12=Lambré |first12=Claude |last13=Leblanc |first13=Jean-Charles |last14=Lillegaard |first14=Inger Therese |last15=Moldeus |first15=Peter |date=January 2018 |title=Safety of hydroxyanthracene derivatives for use in food |journal=EFSA Journal |volume=16 |issue=1 |pages=e05090 |doi=10.2903/j.efsa.2018.5090 |pmc=7009633 |pmid=32625659}}</ref> The anthraquinones have been separated from powdered rhubarb root for purposes in [[traditional medicine]],<ref name="Barceloux2012"/> although long-term consumption of [[natural anthraquinone|anthraquinones]] has been associated with [[acute kidney failure]].<ref name="drugs">{{cite web |title=Rhubarb |url=https://www.drugs.com/npp/rhubarb.html |publisher=Drugs.com |access-date=26 January 2020 |date=13 May 2019}}</ref>

The rhizomes contain [[stilbenoid]] compounds (including [[rhaponticin]]), and the [[flavanol]] [[glucoside]]s (+)-[[catechin-5-O-glucoside|catechin-5-''O''-glucoside]] and (−)-[[catechin-7-O-glucoside|catechin-7-''O''-glucoside]].<ref name=Nonaka>{{cite journal|title=Flavanol glucosides from rhubarb and ''Rhaphiolepis umbellata''|journal=Phytochemistry|volume=22|issue=7|pages=1659–1661|doi=10.1016/0031-9422(83)80105-8|year=1983|last1=Nonaka|first1=Gen-Ichiro|last2=Ezaki|first2=Emiko|last3=Hayashi|first3=Katsuya|last4=Nishioka|first4=Itsuo|bibcode=1983PChem..22.1659N }}</ref>

===Oxalic acid===

Rhubarb leaves contain [[poison]]ous substances, including [[oxalic acid]], a [[nephrotoxin]].<ref name=drugs/> The long term consumption of oxalic acid leads to kidney stone formation in humans. Humans have been poisoned after ingesting the leaves, a particular problem during [[World War I]] when the leaves were mistakenly recommended as a food source in Britain.<ref>{{cite journal | last1 = Robb | first1 = H. F. | year = 1919 | title = Death from rhubarb leaves due to oxalic acid poisoning | journal = J. Am. Med. Assoc. | volume = 73 | issue = 8| pages = 627–628 | doi=10.1001/jama.1919.02610340059028}}</ref><ref>Cooper, M. R., Johnson, A. W. (1984). ''Poisonous plants in Britain and their effects on animals and man''. Her Majesty's Stationery Office, London, England. {{ISBN|978-0-11-242529-8}}</ref><ref>{{Cite web|title=Rheum x hybridum: The Poison Garden website |url=http://www.thepoisongarden.co.uk/atoz/rheum_x_hybridum.htm|access-date=2023-02-23|archive-url=https://web.archive.org/web/20200223042439/http://www.thepoisongarden.co.uk/atoz/rheum_x_hybridum.htm |archive-date=23 February 2020 }}</ref> The toxic rhubarb leaves have been used in flavouring extracts, after the oxalic acid is removed by treatment with precipitated chalk (i.e., [[calcium carbonate]]).

The {{LD50}} (median lethal dose) for pure oxalic acid in rats is about 375&nbsp;mg/kg [[body weight]],<ref>{{cite web|title=Rhubarb poisoning on rhubarbinfo.com|url=http://www.rhubarbinfo.com/rhubarb-poison.html|archive-url=https://web.archive.org/web/19991012022418/http://rhubarbinfo.com/rhubarb-poison.html|url-status=usurped|archive-date=12 October 1999}}</ref> or about 25 grams for a {{convert|65|kg|lb|adj=on}} human. Other sources give a much higher oral [[Lowest published lethal dose|LD<sub>Lo</sub>]] (lowest published lethal dose) of 600&nbsp;mg/kg.<ref>{{cite web | author = Safety Officer in Physical Chemistry | title = Safety (MSDS) data for oxalic acid dihydrate | publisher = Oxford University | date = 13 August 2005 | url = http://msds.chem.ox.ac.uk/OX/oxalic_acid_dihydrate.html | access-date = 30 December 2009}}</ref> While the oxalic acid content of rhubarb leaves can vary, a typical value is about 0.5%,<ref>{{cite journal|vauthors=Pucher GW, Wakeman AJ, Vickery HB |title=The Organic Acids of Rhubarb (Rheum Hybridum) |url=http://www.jbc.org/cgi/content/citation/126/1/43 |journal=Journal of Biological Chemistry|volume=126 |issue=1 |pages=43–54 |year= 1938|doi=10.1016/S0021-9258(18)73892-1 |doi-access=free }}</ref> meaning a 65&nbsp;kg adult would need to eat 4 to 8&nbsp;kg (9 to 18&nbsp;lbs) to obtain a lethal dose, depending on which lethal dose is assumed.  Cooking the leaves with [[Sodium bicarbonate|baking soda]] can make them more poisonous by producing soluble [[oxalate]]s.<ref>Everist, Selwyn L. (1974), ''Poisonous Plants of Australia''.  Angus and Robertson, Melbourne. p. 583. {{ISBN|978-0-207-12773-1}}</ref> The leaves are believed to also contain an additional, unidentified toxin,<ref>{{cite encyclopedia|url=https://www.nlm.nih.gov/medlineplus/ency/article/002876.htm|title=Rhubarb leaves poisoning|encyclopedia=Medline Plus Medical Encyclopedia}}</ref> which might be an anthraquinone [[glycoside]] (also known as [[senna glycoside]]s).<ref>{{cite web|url=http://www.cbif.gc.ca/pls/pp/ppack.info?p_psn=171&p_type=all&p_sci=sci|title=Canadian Poisonous Plants Information System|publisher=Cbif.gc.ca|date=1 September 2009|access-date=5 March 2010|archive-url=https://web.archive.org/web/20090122112906/http://www.cbif.gc.ca/pls/pp/ppack.info?p_psn=171&p_type=all&p_sci=sci|archive-date=22 January 2009}}</ref>

In the [[petiole (botany)|petioles]] (leaf stalks), the proportion of oxalic acid is about 10% of the total 2–2.5% acidity, which derives mainly from [[malic acid]].<ref name=b1/> Serious cases of rhubarb poisoning are not well documented.<ref name="Barceloux2009">{{cite journal |last1=Barceloux |first1=DG |title=Rhubarb and oxalosis (Rheum species). |journal=Disease-a-Month  |date=June 2009 |volume=55 |issue=6 |pages=403–11 |doi=10.1016/j.disamonth.2009.03.011 |pmid=19446684|url=https://kundoc.com/pdf-rhubarb-and-oxalosis-rheum-species-.html}}</ref> Both fatal and non-fatal cases of rhubarb poisoning may be caused not by oxalates, but rather by toxic [[anthraquinone]] glycosides.<ref name=drugs/><ref name="Barceloux2009" /><ref name=savage1999>{{cite journal |last1=Noonan |first1=SC |last2=Savage |first2=GP |title=Oxalate content of foods and its effect on humans. |journal=Asia Pacific Journal of Clinical Nutrition |date=March 1999 |volume=8 |issue=1 |pages=64–74 |pmid=24393738 |url=http://apjcn.nhri.org.tw/server/APJCN/8/1/64.pdf|doi=10.1046/j.1440-6047.1999.00038.x }}</ref>