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[[File:Agarplate redbloodcells edit.jpg|thumb|A [[blood agar]] plate used to culture bacteria and diagnose infection]]
'''Agar''' ({{IPAc-en|ˈ|eɪ|ɡ|ɑːr}} or {{IPAc-en|ˈ|ɑː|g|ər}}), or '''agar-agar''', is a [[gelling agent|jelly-like substance]] consisting of [[polysaccharides]] obtained from the cell walls of some species of [[red algae]], primarily from "ogonori" (''[[Gracilaria]]'') and "tengusa" ([[Gelidiaceae]]).<ref>{{cite web|last1=Shimamura |first1=Natsu |title=Agar |url=http://www.tokyofoundation.org/en/topics/japanese-traditional-foods/vol.-4-agar |website=The Tokyo Foundation |access-date=19 December 2016 |date=August 4, 2010}}</ref><ref>{{cite book|title=Oxford Dictionary of English |edition=2nd |year=2005 |title-link=Oxford Dictionary of English}}</ref> As found in nature, agar is a mixture of two components, the linear
Agar has been used as an ingredient in [[dessert]]s throughout Asia and also as a solid [[substrate (biology)|substrate]] to contain [[Growth medium|culture media]] for [[microbiology|microbiological]] work. Agar can be used as a [[laxative]]; an [[appetite suppressant]]; a [[vegan]] substitute for [[gelatin]]; a thickener for [[soup]]s; in [[Fruit preserves#Jelly|fruit preserves]], ice cream, and other desserts; as a clarifying agent in [[brewing]]; and for [[sizing]]
== Etymology ==
The word ''agar'' comes from '''agar-agar''', the [[Malay language|Malay]] name for red algae (''[[Gigartina]]'', ''[[Eucheuma]]'',<ref>{{cite book |last1=Chapman |first1=V. J. |last2=Chapman |first2=D.J. |title=Seaweeds and their Uses |date=1980 |publisher=Springer Netherlands |location=Dordrecht |isbn=978-94-009-5808-1 |page=148 |edition=third}}</ref> ''[[Gracilaria]]'') from which the jelly is produced.<ref>{{cite book |last= Balfour |first=Edward. |title= The cyclopædia of India and of eastern and southern Asia: commercial, industrial and scientific, products of the mineral, vegetable, and animal kingdoms, useful arts and manufactures |url= https://archive.org/details/in.ernet.dli.2015.283118 |publisher= B. Quaritch |year= 1885 |page=[https://archive.org/details/in.ernet.dli.2015.283118/page/n76 71] }}</ref><ref name="Wilkinson">{{Cite encyclopedia|url=https://nla.gov.au/nla.obj-60272771/view?partId=nla.obj-435838799#page/n18/|title=agar |dictionary=A Malay-English dictionary (romanised) |last=Wilkinson |first=Richard James |publisher=Salavopoulos & Kinderlis |location=Mytilene, Greece |date=1932 |volume=I |page=9 |via=[[Trove|TROVE]], [[National Library of Australia]]}}</ref> It is also known as '''Kanten''' ({{lang-ja|寒天}}) (from the phrase '''''kan'''-zarashi [[Tokoroten|tokoro'''ten''']]'' ({{lang|ja|寒曬心太}}) or
== History ==
{{See also|Edible seaweed|Seaweed farming}}
[[File:Ogo.jpg|thumb|upright|[[Ogonori]], the most common red algae used to make agar]]
Macroalgae have been used widely as food by coastal cultures, especially in [[Southeast Asia]].<ref>{{cite book|url=https://books.google.com/books?id=5umXDDmqxwIC&q=agar+gelling+southeast+asia+dessert&pg=PA31|title=Encyclopedia of Modern Coral Reefs: Structure, Form and Process|publisher=Springer Science & Business Media|isbn=9789048126385|page=31|language=en|last1=Hopley|first1=David|year=2010}}</ref><ref name="Zaneveld"/> In the [[Philippines]], ''[[Gracilaria]]'', known as ''[[gulaman
[[Carrageenan]], derived from gusô (''[[Eucheuma]]'' spp.), which also congeals into a gel-like texture is also used similarly among the [[Visayan peoples]] and have been recorded in the even earlier ''Diccionario De La Lengua Bisaya, Hiligueina y Haraia de la isla de Panay y Sugbu y para las demas islas'' (c.1637) of the [[Augustinians|Augustinian]] missionary [[:es:Alonso de Méntrida|Alonso de Méntrida]] {{In lang|es}}. In the book, Méntrida describes gusô as being cooked until it melts, and then allowed to congeal into a sour dish.<ref>{{cite book |last1=de Mentrida |first1=Alonso |title=Diccionario De La Lengua Bisaya, Hiligueina Y Haraya de la isla de Panay |date=1841 |publisher=En La Imprenta De D. Manuel Y De D. Felis Dayot |page=380}}</ref>
Jelly seaweeds were also favoured and foraged by [[Malays (ethnic group)|Malay]] communities living on the coasts of the [[Riau Archipelago]] and [[Singapore]] in Southeast Asia for centuries.<ref>{{Cite magazine|url=https://biblioasia.nlb.gov.sg/vol-17/issue-3/oct-dec-2021/|title=The Role of Foraging in Malay Cuisine|author=Khir Johari|date=Oct–Dec 2021|magazine=BiblioAsia|volume=17|issue=3|pages=20–23|publisher=[[National Library Board]], Singapore}}</ref>▼
▲In [[Ambon Island]] in the [[Maluku Islands]] of [[Indonesia]], agar is extracted from ''Graciliaria'' and eaten as a type of pickle or a sauce.<ref name="Zaneveld"/> Jelly seaweeds were also favoured and foraged by [[Malays (ethnic group)|Malay]] communities living on the coasts of the [[Riau Archipelago]] and [[Singapore]] in Southeast Asia for centuries. 19th century records indicate that dried ''Graciliaria'' were one of the bulk exports of [[British Malaya]] to China. Poultices made from agar were also used for swollen knee joints and sores in [[Johore]] and Singapore.<ref name="Zaneveld">{{cite journal |last1=Zaneveld |first1=Jacques S. |title=The Utilization of Marine Algae in Tropical South and East Asia |journal=Economic Botany |date=1959 |volume=13 |issue=2 |pages=89–131 |url=https://www.jstor.org/stable/4288011}}</ref><ref>{{Cite magazine|url=https://biblioasia.nlb.gov.sg/vol-17/issue-3/oct-dec-2021/|title=The Role of Foraging in Malay Cuisine|author=Khir Johari|date=Oct–Dec 2021|magazine=BiblioAsia|volume=17|issue=3|pages=20–23|publisher=[[National Library Board]], Singapore}}</ref>
The application of agar as a food additive in Japan is alleged to have been discovered in 1658 by Mino Tarōzaemon ({{lang|ja|{{linktext|美濃}} {{linktext|太郎}}{{linktext|左|衞|門}}}}), an innkeeper in current [[Fushimi-ku, Kyoto]] who, according to legend, was said to have discarded surplus seaweed soup ([[Tokoroten]]) and noticed that it gelled later after a winter night's freezing.<ref name="DifcoMan">{{cite book|url=http://www.bd.com/ds/technicalCenter/misc/difcobblmanual_2nded_lowres.pdf|title=Difco & BBL Manual|publisher=Becton Dickinson and Company|editor1=Mary Jo Zimbro |editor2=David A. Power |editor3=Sharon M. Miller |editor4=George E. Wilson |editor5=Julie A. Johnson|edition=2nd|page=6|access-date=2013-07-17|archive-url=https://web.archive.org/web/20120606174455/http://www.bd.com/ds/technicalCenter/misc/difcobblmanual_2nded_lowres.pdf|archive-date=2012-06-06|url-status=dead}}</ref>
Agar was first subjected to chemical analysis in 1859 by the French chemist [[Anselme Payen]], who had obtained agar from the marine algae ''Gelidium corneum''.<ref>Payen, Anselme (1859) [http://gallica.bnf.fr/ark:/12148/bpt6k3006f/f523.image.langEN "Sur la gélose et le nids de salangane"] (On agar and swiftlet nests), ''Comptes rendus''
Beginning in the late 19th century, agar began to be used as a solid medium for growing various microbes. Agar was first described for use in microbiology in 1882 by the German microbiologist [[Walther Hesse]], an assistant working in [[Robert Koch|Robert Koch's]] laboratory, on the suggestion of his wife [[Fanny Hesse]].<ref>Robert Koch (10 April 1882) [http://babel.hathitrust.org/cgi/pt?id=mdp.39015020075001;view=1up;seq=235 "Die Aetiologie der Tuberculose"] (The etiology of tuberculosis), ''Berliner Klinische Wochenschrift'' (Berlin Clinical Weekly), '''19''' : 221–230. From p. 225: ''"Die Tuberkelbacillen lassen sich auch noch auf anderen Nährsubstraten kultiviren, wenn letztere ähnliche Eigenschaften wie das erstarrte Blutserum besitzen. So wachsen sie beispielsweise auf einer mit Agar-Agar bereiteten, bei Blutwärme hart bleibenden Gallerte, welche einen Zusatz von Fleischinfus und Pepton erhalten hat."'' (The tubercule bacilli can also be cultivated on other media, if the latter have properties similar to those of congealed blood serum. Thus they grow, for example, on a gelatinous mass which was prepared with agar-agar, which remains solid at blood temperature, and which has received a supplement of meat broth and peptone.)</ref><ref name="ln">{{cite magazine|url=http://www.labnews.co.uk/features/history-of-the-agar-plate/|title=History of the Agar Plate|date=November 1, 2005|magazine=Laboratory News|author=Smith, A.|access-date=November 3, 2012|archive-url=https://web.archive.org/web/20121014060019/http://www.labnews.co.uk/features/history-of-the-agar-plate/|archive-date=October 14, 2012|url-status=dead}}</ref> Agar quickly supplanted gelatin as the base of microbiological media, due to its higher melting temperature, allowing microbes to be grown at higher temperatures without the media liquefying.<ref name="hesse">{{cite journal|year=1992|title=Walther and Angelina Hesse–Early Contributors to Bacteriology|url=http://www.asm.org/ccLibraryFiles/FILENAME/0000000227/580892p425.pdf|journal=ASM News|volume=58|issue=8|pages=425–428|author=Hesse, W.|translator=Gröschel, D.H.M.|access-date=22 January 2017|archive-url=https://web.archive.org/web/20170630173511/https://www.asm.org/ccLibraryFiles/FILENAME/0000000227/580892p425.pdf|archive-date=30 June 2017|url-status=dead|df=dmy-all}}</ref>
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== Chemical composition ==
[[File:Agarose polymere.svg|right|thumb|The structure of an [[agarose]] polymer
Agar consists of a mixture of two [[polysaccharide]]s: agarose and agaropectin, with agarose making up about 70% of the mixture, while agaropectin makes about 30% of it.<ref name=FAO3/> Agarose is a linear polymer, made up of repeating units of [[Agarose#Structure|agarobiose]], a disaccharide made up of [[D-galactose]] and 3,6-anhydro-L-galactopyranose.<ref name=FAO1/> Agaropectin is a heterogeneous mixture of smaller molecules that occur in lesser amounts, and is made up of alternating units of D-galactose and L-galactose heavily modified with acidic side-groups, such as [[sulfate]], [[glucuronate]], and [[pyruvate]].<ref>{{cite web |access-date=2023-03-21 |url=https://water.lsbu.ac.uk/water/agar.html |title=Agar |archive-url=https://web.archive.org/web/20220926200632/https://water.lsbu.ac.uk/water/agar.html |archive-date=2022-09-26 |website=London South Bank University}}</ref><ref name=FAO3>{{cite book|chapter-url=http://www.fao.org/docrep/field/003/AB730E/AB730E03.htm |title=Training manual on Gracilaria culture and seaweed processing in China |chapter=III: Properties, Manufacture, and Application of Seaweed Polysaccharides – Agar, Carageenan, and Algin |publisher=Food and Agriculture Organization, United Nations|date=August 1990 |access-date=2011-04-27}}</ref><ref name=FAO1>{{cite book|chapter-url=http://www.fao.org/docrep/x5822e/x5822e03.htm |title=Production and Utilization of Products from Commercial Seaweeds|chapter=Chapter 1 – Production, Properties and Uses of Agar |author1=Rafael Armisen |author2=Fernando Galatas |publisher=Food and Agriculture Organization, United Nations |date=1987 |editor=McHugh DJ |isbn=92-5-102612-2}}</ref>
== Physical properties ==
Agar exhibits a phenomenon known as [[hysteresis#Liquid–solid-phase transitions|hysteresis]]
==Uses==
=== Culinary ===
[[File:Sago Gulaman.jpg|thumb|''[[Sago]] at [[gulaman]]'' in [[Filipino cuisine]] is made from agar (''[[gulaman]]''), pearl [[sago]], and sugar syrup flavored with [[Pandanus amaryllifolius|pandan]].|210x210px]]
Agar-agar is a natural vegetable [[gelatin]] counterpart.<ref name=":0">{{Cite book |last=Wings of Success |title=The Advantages of Being a Vegetarian: Selected Tips |pages=9–10}}</ref><ref>{{Cite book |last=Livlaid |first=Nele |title=Plant-Based Made Easy: The Complete Practical Guide to Transitioning to Healthy Whole Food Diet |publisher=Nutriplanet (Swing & Step OU) |year=2018 |isbn=9789949882465}}</ref> It is white and semi-[[translucent]] when sold in packages as washed and dried strips or in powdered form.<ref name=":0" /><ref name=":1">{{Cite book |last=Stobart |first=Tom |title=Cook's Encyclopaedia |publisher=Grub Street Publishing |year=2016 |isbn=9781910690833}}</ref> It can be used to make jellies,<ref>{{Cite book |
Agar-agar is approximately 80% [[dietary fiber]], so it can serve as an intestinal regulator.<ref>{{Cite journal |last=Marden |first=Orison Swett |date=1921 |title=Constipation is a Crime |journal=The New Success: Marden's Magazine |publisher=Lowrey-Marden |volume=5 |pages=113}}</ref> Its bulking quality has been behind [[fad diet]]s in Asia, for example the ''kanten'' (the Japanese word for agar-agar<ref name="oxford" />) diet. Once ingested, ''kanten'' triples in size and absorbs water. This results in the consumers feeling fuller.
==== Asian culinary ====
One use of agar in [[Japanese cuisine]]
==== Other culinary ====
[[File:00114jfCuisine of Bulacan Food Cakes Delicaciesfvf 30.jpg|thumb|''[[Crema de mangga]]'', a traditional [[Filipino cuisine|Filipino]] fruitcake, is made with an agar layer on top to keep the fruit components in place.]]
It can be used as addition to or as a replacement for [[pectin]] in jams and marmalades, as a substitute to gelatin for its superior gelling properties, and as a strengthening ingredient in souffles and custards. Another use of agar-agar is in a [[Russian cuisine|Russian]] dish ''ptich'ye moloko'' ([[bird's milk]]), a rich jellified custard (or soft [[meringue]]) used as a cake filling or chocolate-glazed as individual sweets.
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=== Microbiology ===
==== Agar plate ====
[[Image:Agar Plate.jpg|right|thumb|
{{Main|Agar plate}}
An agar plate or [[Petri dish]] is used to provide a [[growth medium]] using a mix of agar and other nutrients in which microorganisms, including [[bacteria]] and [[fungi]], can be cultured and observed under the microscope. Agar is indigestible for many organisms so that microbial growth does not affect the gel used and it remains stable. Agar is typically sold commercially as a powder that can be mixed with water and prepared similarly to gelatin before use as a growth medium. Nutrients are typically added to meet the nutritional needs of the [[microbe]]s organism, the formulations of which may be "undefined" where the precise composition is unknown, or "defined" where the exact chemical composition is known.
Different algae produce various types of agar. Each agar has unique properties that suit different purposes. Because of the agarose component, the agar solidifies. When heated, agarose has the potential to melt and then solidify. Because of this property, they are referred to as "physical gels
There are a variety of different types of agar that support the growth of different microorganisms. A nutrient agar may be permissive, allowing for the cultivation of any non-fastidious microorganisms; a commonly-used nutrient agar for bacteria is the Luria Bertani (LB) agar which contains [[lysogeny broth]], a nutrient-rich medium used for bacterial growth.<ref>{{Cite journal |date=2009-03-01 |title=LB agar |url=http://cshprotocols.cshlp.org/content/2009/3/pdb.rec11683 |journal=Cold Spring Harbor Protocols |language=en |volume=2009 |issue=3 |pages=pdb.rec11683 |doi=10.1101/pdb.rec11683 |issn=1940-3402}}</ref> Additionally, 2216 Marine Broth (MB) agar, with high salt content, is optimized for growing heterotrophic marine bacteria like those of the Vibrio genus, while Terrific Broth (TB) agar is used to non-selectively culture high yields of the bacterium ''E. coli''. More generally, enriched media is an agar variety that is infused with the necessary nutrients required by fastidious organisms to grow. Despite the large diversity of agar mediums, yeast extract is a common ingredient across all varieties as it is a macronutrient that provides a nitrogen source for all bacterial cell types.
[[File:Lactose fementing (LF), and non-lactose fermenting (NLF) colonies on MacConkey agar.jpg|thumb]] Other fastidious organisms may require the addition of different biological fluids such as horse or sheep blood, serum, egg yolk, and so on.<ref>{{Citation |last1=Clark |first1=David P. |title=Chapter 7 [[File:Microorganisms-11-01566-g008.webp|thumb]]
==== Motility assays ====
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A common identification assay involves culturing a sample of the organism deep within a block of nutrient agar. Cells will attempt to grow within the gel structure. Motile species will be able to migrate, albeit slowly, throughout the gel, and infiltration rates can then be visualized, whereas non-motile species will show growth only along the now-empty path introduced by the invasive initial sample deposition.
Another setup commonly used for measuring [[chemotaxis]] and chemokinesis utilizes the under-agarose cell migration assay, whereby a layer of agarose gel is placed between a cell population and a chemoattractant. As a concentration gradient develops from the diffusion of the chemoattractant into the gel, various cell populations requiring different stimulation levels to migrate can then be visualized over time using microphotography as they tunnel upward through the gel against gravity along the gradient.
=== Plant biology ===
[[Image:Physcomitrella growing on agar plates.jpg|thumb|''[[Physcomitrella patens]]'' plants growing [[axenic]]ally [[in vitro]] on [[agar plate]]s.
Research grade agar is used extensively in [[plant]] biology as it is optionally supplemented with a nutrient and/or vitamin mixture that allows for seedling germination in Petri dishes under sterile conditions (given that the seeds are sterilized as well). Nutrient and/or vitamin supplementation for ''[[Arabidopsis thaliana]]'' is standard across most experimental conditions. [[Murashige and Skoog medium|Murashige & Skoog]] (MS) nutrient mix and Gamborg's B5 vitamin mix in general are used. A 1.0% agar/0.44% MS+vitamin dH<sub>2</sub>O solution is suitable for growth media between normal growth temps.
When using agar, within any growth medium, it is important to know that the solidification of the agar is pH-dependent. The optimal range for solidification is between 5.4 and 5.7.<ref>{{cite book|last1=Kim|first1=Se-Kwon|title=Handbook of marine macroalgae : biotechnology and applied phycology|date=2011|publisher=John Wiley & Sons Inc.|location=Hoboken, NJ|isbn=9780470979181|edition=1st imp.}}</ref> Usually, the application of potassium hydroxide is needed to increase the pH to this range. A general guideline is about 600
This medium nicely lends itself to the application of specific concentrations of phytohormones etc. to induce specific growth patterns in that one can easily prepare a solution containing the desired amount of hormone, add it to the known volume of GM, and autoclave to both sterilize and evaporate off any solvent that may have been used to dissolve the often-polar hormones. This hormone/GM solution can be spread across the surface of Petri dishes sown with germinated and/or etiolated seedlings.
Experiments with the [[moss]] ''[[Physcomitrella patens]]'', however, have shown that choice of the gelling agent – agar or [[Gellan gum|Gelrite]] – does influence [[phytohormone]] sensitivity of the
{{cite journal|title=Gelrite and agar differently influence cytokinin-sensitivity of a moss |journal=Journal of Plant Physiology |volume=146 |issue=3 |pages=369–371|author1 = Birgit Hadeler|author2 = Sirkka Scholz|author3=Ralf Reski |author-link3=Ralf Reski |doi=10.1016/s0176-1617(11)82071-7|year=1995 }}</ref>
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