View source for Alginic acid

{{Short description|Polysaccharide found in brown algae}}
{{Chembox
| Verifiedfields = changed
| verifiedrevid = 477314688
| ImageFile = Alginsäure.svg
| ImageSize = 250px
| IUPACName =
| OtherNames = Alginic acid; E400; [<small>D</small>-ManA(β1→4)<small>L</small>-GulA(α1→4)]<sub>n</sub>
|Section1={{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 9005-32-7
| EINECS = 232-680-1
| UNII_Ref = {{fdacite|changed|FDA}}
| UNII = 8C3Z4148WZ
| PubChem =
| SMILES =
| ChemSpiderID_Ref = {{chemspidercite|changed|chemspider}}
| ChemSpiderID = None
 }}
|Section2={{Chembox Properties
| Formula = (C<sub>6</sub>H<sub>8</sub>O<sub>6</sub>)<sub>n</sub>
| MolarMass = 10,000 – 600,000
| Appearance = White to yellow, fibrous powder
| Density = 1.601{{nbsp}}g/cm<sup>3</sup>
| MeltingPt =
| BoilingPt =
| Solubility =
| pKa = 1.5–3.5
 }}
|Section6={{Chembox Pharmacology
| ATCCode_prefix = A02
| ATCCode_suffix = BX13
}}
|Section7={{Chembox Hazards
| MainHazards =
| FlashPt =
| AutoignitionPt =
 }}
}}
[[File:Giantkelp2 300.jpg|thumb|''[[Macrocystis pyrifera]]'', the largest species of giant [[kelp]]]]
'''Alginic acid''', also called '''algin''', is a naturally occurring, edible [[polysaccharide]] found in [[brown algae]].  It is [[hydrophilic]] and forms a viscous [[natural gum|gum]] when hydrated. With metals such as sodium and calcium, its salts are known as '''alginates'''. Its colour ranges from white to yellowish-brown. It is sold in [[wikt:filamentous|filamentous]], granular, or powdered forms. 

It is a significant component of the [[biofilms]] produced by the bacterium ''[[Pseudomonas aeruginosa]]'', a major pathogen found in the lungs of some people who have [[cystic fibrosis]].<ref name="davies">{{cite journal | last=Davies | first=JC | title=Pseudomonas aeruginosa in cystic fibrosis: pathogenesis and persistence. | journal=Paediatric Respiratory Reviews | volume=3 | issue=2 | year=2002 | issn=1526-0542 | pmid=12297059 | pages=128–34| doi=10.1016/S1526-0550(02)00003-3 }}</ref> The biofilm and ''P. aeruginosa'' have a high resistance to [[antibiotics]],<ref name="boyd">{{cite journal | last1=Boyd | first1=A | last2=Chakrabarty | first2=AM | title=Pseudomonas aeruginosa biofilms: role of the alginate exopolysaccharide. | journal=Journal of Industrial Microbiology | volume=15 | issue=3 | year=1995 | issn=0169-4146 | pmid=8519473 | pages=162–8| doi=10.1007/BF01569821 | s2cid=42880806 | doi-access=free }}</ref> but susceptible to inhibition by [[macrophages]].<ref name="Leid">{{cite journal | last1=Leid | first1=JG | last2=Willson | first2=CJ | last3=Shirtliff | first3=ME | last4=Hassett | first4=DJ | last5=Parsek | first5=MR | last6=Jeffers | first6=AK | title=The exopolysaccharide alginate protects Pseudomonas aeruginosa biofilm bacteria from IFN-gamma-mediated macrophage killing. | journal=Journal of Immunology | volume=175 | issue=11 | date=1 November 2005 | issn=0022-1767 | pmid=16301659 | pages=7512–8|url=http://www.jimmunol.org/content/175/11/7512.full.pdf| doi=10.4049/jimmunol.175.11.7512 | s2cid=1011606 | doi-access=free }}</ref>

==Structure==
Alginic acid is a linear [[copolymer]] with [[homopolymer]]ic blocks of (1→4)-linked β-D-[[Mannuronic acid|mannuronate]] (M) and α-L-[[Guluronic acid|guluronate]] (G) residues, respectively, [[covalently]] linked together in different sequences or blocks. The [[monomer]]s may appear in homopolymeric blocks of consecutive [[G-residues]] (G-blocks), consecutive [[M-residues]] (M-blocks) or alternating M and G-residues (MG-blocks). α-L-guluronate is the C-5 [[epimer]] of β-D-mannuronate.

==Forms==
Alginates are refined from brown [[seaweeds]]. Throughout the world, many of the [[Phaeophyceae]] class brown seaweeds are harvested to be processed and converted into sodium alginate. Sodium alginate is used in many industries including food, animal food, fertilisers, textile printing, and pharmaceuticals. Dental impression material uses alginate as its means of gelling. Food grade alginate is an approved ingredient in processed and manufactured foods.<ref>{{cite web|title=Alginates|url=https://www.ams.usda.gov/sites/default/files/media/Alginates%20TR%202015.pdf|publisher=Agricultural Marketing Service, US Department of Agriculture|access-date=1 March 2018|date=5 February 2015}}</ref>

Brown seaweeds range in size from the giant [[kelp]] ''[[Macrocystis pyrifera]]''  which can be 20–40 meters long, to thick, leather-like seaweeds from 2–4 m long, to smaller species 30–60&nbsp;cm long.  Most brown seaweed used for alginates are gathered from the wild, with the exception of ''[[Laminaria japonica]]'', which is cultivated in China for food and its surplus material is diverted to the alginate industry in China.

Alginates from different species of brown seaweed vary in their chemical structure resulting in different physical properties of alginates. Some species yield an alginate that gives a strong [[gel]], another a weaker gel, some may produce a cream or white alginate, while others are difficult to gel and are best used for technical applications where color does not matter.<ref>FAO fisheries technical paper 441, Tevita Bainiloga Jnr, School of Chemistry, University College, University of New South Wales and Australian Defence Force Academy Canberra Australia</ref>

Commercial grade alginate are extracted from giant [[kelp]] ''[[Macrocystis pyrifera]]'', ''[[Ascophyllum nodosum]]'', and types of ''[[Laminaria]]''. Alginates are also produced by two [[bacteria]]l [[genera]] ''[[Pseudomonas]]'' and ''[[Azotobacter]]'', which played a major role in the unravelling of its [[biosynthesis]] [[Metabolic pathway|pathway]]. Bacterial alginates are useful for the production of micro- or nanostructures suitable for medical applications.<ref name=2Remminghorst>{{cite book |author=Remminghorst and Rehm|year=2009|chapter=Microbial Production of Alginate: Biosynthesis and Applications|title=Microbial Production of Biopolymers and Polymer Precursors|publisher=Caister Academic Press|isbn = 978-1-904455-36-3}}</ref>

Sodium alginate (NaC<sub>6</sub>H<sub>7</sub>O<sub>6</sub>) is the [[sodium salts|sodium salt]] of alginic acid. Sodium alginate is a gum.

Potassium alginate (KC<sub>6</sub>H<sub>7</sub>O<sub>6</sub>) is the potassium [[salt (chemistry)|salt]] of alginic acid.

[[Calcium alginate]] (CaC<sub>12</sub>H<sub>14</sub>O<sub>12</sub>), is made from sodium alginate from which the sodium ion has been removed and replaced with calcium ([[ion exchange]]).

==Production==
The manufacturing process used to extract sodium alginates from brown seaweed fall into two categories: 1) calcium alginate method and, 2) alginic acid method.

Chemically the process is simple, but difficulties arise from the physical separations required between the slimy residues from viscous solutions and the separation of gelatinous precipitates that hold large amounts of liquid within their structure, so they resist [[filtration]] and [[centrifugation]].<ref>FAO Fisheries Technical Paper, 2003</ref>

==Uses==

Alginate absorbs water quickly, which makes it useful as an additive in [[dehydrated]] products such as [[diet aid|slimming aids]], and in the manufacture of paper and textiles. 

Alginate is also used for [[waterproofing]] and [[fireproofing]] fabrics, in the food industry as a [[thickening]] agent for drinks, ice cream, cosmetics, as a [[gelling agent]] for jellies, known by the [[E number#E400–E499|code E401]] and sausage casing.<ref>{{Cite web |title=What is Sodium Alginate (E401) in food? Properties, Uses, Safety |author= |work=FOODADDITIVES |date=14 May 2020 |url= https://foodadditives.net/thickeners/sodium-alginate/}}</ref><ref>{{Cite book |title=Bioactive Seaweeds for Food Applications |first1=Yimin|last1=Qin |date=17 July 2018 |url=https://www.sciencedirect.com/topics/food-science/sausage-casing|doi=10.1016/C2016-0-04566-7|isbn=9780128133125 |archive-url=https://web.archive.org/web/20231109163125/https://www.sciencedirect.com/topics/food-science/sausage-casing |archive-date=2023-11-09 }}</ref> Sodium alginate is mixed with [[soybean]] protein to make [[meat analogue]].<ref>{{Cite book |last1=Arasaki |first1=Seibin |title=Low Calorie, High Nutrition Vegetables from the Sea |last2=Arasaki |first2=Teruko |publisher=Japan Publications, Inc. |date=January 1983 |isbn=0-87040-475-X |edition=1st |location=Tokyo, Japan |pages=35}}</ref>

Alginate is used as an ingredient in various [[pharmaceutical]] preparations, such as [[Gaviscon]], in which it combines with [[bicarbonate]] to inhibit [[Gastroesophageal reflux disease|gastroesophageal reflux]]. 

Sodium alginate is used as an [[Impression (dental)|impression]]-making material in [[dentistry]], [[prosthetic]]s, [[lifecasting]], and for creating positives for small-scale [[casting]].

Sodium alginate is used in [[reactive dye printing]] and as a thickener for [[reactive dye]]s in [[textile printing|textile screen-printing]].{{citation needed|date=October 2015}} Alginates do not react with these dyes and wash out easily, unlike [[starch]]-based thickeners. It also serves as a material for [[micro-encapsulation]].<ref>{{Cite journal|title = Microencapsulation and storage stability of polyphenols from Vitis vinifera grape wastes|journal = Food Chemistry|date = 2016-01-01|pages = 614–621|volume = 190|doi = 10.1016/j.foodchem.2015.05.117|pmid = 26213018|first1 = Oier|last1 = Aizpurua-Olaizola|first2 = Patricia|last2 = Navarro|first3 = Asier|last3 = Vallejo|first4 = Maitane|last4 = Olivares|first5 = Nestor|last5 = Etxebarria|first6 = Aresatz|last6 = Usobiaga| url=https://figshare.com/articles/journal_contribution/5028350 }}</ref>

Calcium alginate is used in different types of medical products, including skin [[wound dressing]]s to promote healing,<ref>{{cite journal|journal=Wound Repair Regen|year=2002|volume=10|issue=5|pages=271–85|title=Calcium: a potential central regulator in wound healing in the skin|author=Lansdown AB|pmid=12406163|doi=10.1046/j.1524-475x.2002.10502.x|s2cid=10092676}}</ref><ref>{{Cite journal|last1=Stubbe|first1=Birgit|last2=Mignon|first2=Arn|last3=Declercq|first3=Heidi|last4=Vlierberghe|first4=Sandra Van|last5=Dubruel|first5=Peter|date=2019|title=Development of Gelatin-Alginate Hydrogels for Burn Wound Treatment|journal=Macromolecular Bioscience|language=en|volume=19|issue=8|pages=1900123|doi=10.1002/mabi.201900123|pmid=31237746|s2cid=195355185|issn=1616-5195}}</ref> and may be removed with less pain than conventional dressings.{{citation needed|date=October 2015}}

==Alginate hydrogels==

Alginate may be used in a [[hydrogel]] consisting of [[microparticle]]s or bulk gels combined with [[nerve growth factor]] in [[bioengineering]] research to stimulate [[brain tissue]] for possible [[Regeneration (biology)|regeneration]].<ref>{{Cite journal|title = Nanofibrous gelatin scaffolds integrated with NGF-loaded alginate microspheres for brain tissue engineering|journal = J. Tissue Eng. Regen. Med.|volume = 12|issue = 2|pages = e707–e719|date = 2016|doi = 10.1002/term.2353|pmid = 27863118|first1 = M.|last1 = Büyüköz|first2 = E.|last2 = Erdal|first3 = S.A.|last3 = Altinkaya|s2cid = 206528926|hdl = 11147/6844|hdl-access = free}}</ref> In research on bone reconstruction, alginate [[composite material|composites]] have favorable properties encouraging regeneration, such as improved [[porosity]], [[cell proliferation]], and [[Strength of materials|mechanical strength]], among other characteristics.<ref>{{cite journal|pmid=25020082|year=2015|last1=Venkatesan|first1=J|title=Alginate composites for bone tissue engineering: A review|journal=International Journal of Biological Macromolecules|volume=72|pages=269–81|last2=Bhatnagar|first2=I|last3=Manivasagan|first3=P|last4=Kang|first4=K. H.|last5=Kim|first5=S. K.|doi=10.1016/j.ijbiomac.2014.07.008}}</ref>

Alginate hydrogel is a common biomaterial for bio-fabrication of scaffolds and tissue regeneration.<ref>{{Cite journal|last1=Rastogi|first1=Prasansha|last2=Kandasubramanian|first2=Balasubramanian|date=2019-09-10|title=Review of alginate-based hydrogel bioprinting for application in tissue engineering|url=https://doi.org/10.1088/1758-5090/ab331e|journal=Biofabrication|language=en|volume=11|issue=4|pages=042001|doi=10.1088/1758-5090/ab331e|pmid=31315105|bibcode=2019BioFa..11d2001R|s2cid=197543168|issn=1758-5090}}</ref>
By the covalent attachment of thiol groups to alginate high in situ gelling and mucoadhesive properties can be introduced. The thiolated polymer ([[thiomer]]) forms disulfide bonds within its polymeric network and with cysteine-rich subdomains of the mucus layer.<ref>{{cite journal |last1=Leichner |first1=C |last2=Jelkmann |first2=M |last3=Bernkop-Schnürch |first3=A |title=Thiolated polymers: Bioinspired polymers utilizing one of the most important bridging structures in nature |journal=Adv Drug Deliv Rev |date=2019 |volume=151-152 |pages=191–221 |doi=10.1016/j.addr.2019.04.007 |pmid=31028759|s2cid=135464452 }}</ref> Thiolated alginates are thus used as in situ gelling hydrogels<ref>{{cite journal |last1=Xu |first1=G |last2=Cheng |first2=L |last3=Zhang |first3=Q | last4=Sun|first4=Y | last5=Chen |first5=C |last6=Xu |first6=H |last7=Chai |first7=Y | last8=Lang|first8=M |title= In situ thiolated alginate hydrogel: Instant formation and its application in hemostasis|journal= J Biomater Appl |date=2016 |volume=31 |issue=5 |pages=721–729 |doi=10.1177/0885328216661557|pmid= 27485953|s2cid=4267830 }}</ref>and as mucoadhesive drug delivery systems.<ref>{{cite journal |last1=Kassem |first1=AA |last2=Issa |first2=DA |last3=Kotry |first3=GS | last4=Farid |first4=RM |title= Thiolated alginate-based multiple layer mucoadhesive films of metformin for intra-pocket local delivery: in vitro characterization and clinical assessment |journal= Drug Dev. Ind. Pharm. |date=2017 |volume=43 |issue=1 |pages=120–131 |doi=10.1080/03639045.2016.1224895 |pmid=27589817 |s2cid=25076932 }}</ref>

==See also==
* [[Hyaluronic acid]]: a polysaccharide in animals.
* [[Agar]]

==References==
{{Reflist}}

==External links==
* [http://www.cybercolloids.net/library/alghistory/history-alginate-chemistry-seaweeds Alginate seaweed sources] {{Webarchive|url=https://web.archive.org/web/20130917233613/http://www.cybercolloids.net/library/alghistory/history-alginate-chemistry-seaweeds |date=2013-09-17 }}
* [http://www.cybercolloids.net/library/alginate/introduction-alginate-production Alginate properties] {{Webarchive|url=https://web.archive.org/web/20130917065320/http://www.cybercolloids.net/library/alginate/introduction-alginate-production |date=2013-09-17 }}

{{Drugs for peptic ulcer and GORD}}
{{Authority control}}

{{DEFAULTSORT:Alginic Acid}}
[[Category:Polysaccharides]]
[[Category:Natural gums]]
[[Category:Edible thickening agents]]
[[Category:Copolymers]]
[[Category:Dental materials]]
[[Category:Excipients]]
[[Category:Algal food ingredients]]
[[Category:Brown algae]]
[[Category:Food stabilizers]]
[[Category:E-number additives]]