Alginic acid

Alginic acid, also called algin, is a naturally occurring, edible polysaccharide found in brown algae. It is hydrophilic and forms a viscous 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 filamentous, granular, or powdered forms.

Alginic acid
Names
Other names
Alginic acid; E400; [D-ManA(β1→4)L-GulA(α1→4)]n
Identifiers
ChemSpider
  • None
ECHA InfoCard 100.029.697
EC Number
  • 232-680-1
E number E400 (thickeners, ...)
UNII
Properties
(C6H8O6)n
Molar mass 10,000 – 600,000
Appearance White to yellow, fibrous powder
Density 1.601 g/cm3
Acidity (pKa) 1.5–3.5
Pharmacology
A02BX13 (WHO)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references
Macrocystis pyrifera, the largest species of giant kelp

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.[1] The biofilm and P. aeruginosa have a high resistance to antibiotics,[2] but susceptible to inhibition by macrophages.[3]

Structure

Alginic acid is a linear copolymer with homopolymeric blocks of (1→4)-linked β-D-mannuronate (M) and α-L-guluronate (G) residues, respectively, covalently linked together in different sequences or blocks. The monomers 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.[4]

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 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.[5]

Commercial grade alginate are extracted from giant kelp Macrocystis pyrifera, Ascophyllum nodosum, and types of Laminaria. Alginates are also produced by two bacterial genera Pseudomonas and Azotobacter, which played a major role in the unravelling of its biosynthesis pathway. Bacterial alginates are useful for the production of micro- or nanostructures suitable for medical applications.[6]

Sodium alginate (NaC6H7O6) is the sodium salt of alginic acid. Sodium alginate is a gum.

Potassium alginate (KC6H7O6) is the potassium salt of alginic acid.

Calcium alginate (CaC12H14O12), 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.[7]

Uses

Alginate absorbs water quickly, which makes it useful as an additive in dehydrated products such as 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, and as a gelling agent for jellies, known by the code E401.[8] Sodium alginate is mixed with soybean protein to make meat analogue.[9]

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

Sodium alginate is used as an impression-making material in dentistry, prosthetics, lifecasting, and for creating positives for small-scale casting.

Sodium alginate is used in reactive dye printing and as a thickener for reactive dyes in textile screen-printing. Alginates do not react with these dyes and wash out easily, unlike starch-based thickeners. It also serves as a material for micro-encapsulation.[10]

Calcium alginate is used in different types of medical products, including skin wound dressings to promote healing,[11][12] and may be removed with less pain than conventional dressings.

Alginate hydrogels

Alginate may be used in a hydrogel consisting of microparticles or bulk gels combined with nerve growth factor in bioengineering research to stimulate brain tissue for possible regeneration.[13] In research on bone reconstruction, alginate composites have favorable properties encouraging regeneration, such as improved porosity, cell proliferation, and mechanical strength, among other characteristics.[14]

Alginate hydrogel is a common biomaterial for bio-fabrication of scaffolds and tissue regeneration.[15] 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.[16] Thiolated alginates are thus used as in situ gelling hydrogels[17]and as mucoadhesive drug delivery systems.[18]

See also

References
  1. Davies, JC (2002). "Pseudomonas aeruginosa in cystic fibrosis: pathogenesis and persistence". Paediatric Respiratory Reviews. 3 (2): 128–34. doi:10.1016/S1526-0550(02)00003-3. ISSN 1526-0542. PMID 12297059.
  2. Boyd, A; Chakrabarty, AM (1995). "Pseudomonas aeruginosa biofilms: role of the alginate exopolysaccharide". Journal of Industrial Microbiology. 15 (3): 162–8. doi:10.1007/BF01569821. ISSN 0169-4146. PMID 8519473. S2CID 42880806.
  3. Leid, JG; Willson, CJ; Shirtliff, ME; Hassett, DJ; Parsek, MR; Jeffers, AK (1 November 2005). "The exopolysaccharide alginate protects Pseudomonas aeruginosa biofilm bacteria from IFN-gamma-mediated macrophage killing" (PDF). Journal of Immunology. 175 (11): 7512–8. doi:10.4049/jimmunol.175.11.7512. ISSN 0022-1767. PMID 16301659. S2CID 1011606.
  4. "Alginates" (PDF). Agricultural Marketing Service, US Department of Agriculture. 5 February 2015. Retrieved 1 March 2018.
  5. 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
  6. Remminghorst and Rehm (2009). "Microbial Production of Alginate: Biosynthesis and Applications". Microbial Production of Biopolymers and Polymer Precursors. Caister Academic Press. ISBN 978-1-904455-36-3.
  7. FAO Fisheries Technical Paper, 2003
  8. "What is Sodium Alginate (E401) in food? Properties, Uses, Safety". FOODADDITIVES. 14 May 2020.
  9. Arasaki, Seibin; Arasaki, Teruko (January 1983). Low Calorie, High Nutrition Vegetables from the Sea (1st ed.). Tokyo, Japan: Japan Publications, Inc. p. 35. ISBN 0-87040-475-X.
  10. Aizpurua-Olaizola, Oier; Navarro, Patricia; Vallejo, Asier; Olivares, Maitane; Etxebarria, Nestor; Usobiaga, Aresatz (2016-01-01). "Microencapsulation and storage stability of polyphenols from Vitis vinifera grape wastes". Food Chemistry. 190: 614–621. doi:10.1016/j.foodchem.2015.05.117. PMID 26213018.
  11. Lansdown AB (2002). "Calcium: a potential central regulator in wound healing in the skin". Wound Repair Regen. 10 (5): 271–85. doi:10.1046/j.1524-475x.2002.10502.x. PMID 12406163. S2CID 10092676.
  12. Stubbe, Birgit; Mignon, Arn; Declercq, Heidi; Vlierberghe, Sandra Van; Dubruel, Peter (2019). "Development of Gelatin-Alginate Hydrogels for Burn Wound Treatment". Macromolecular Bioscience. 19 (8): 1900123. doi:10.1002/mabi.201900123. ISSN 1616-5195. PMID 31237746. S2CID 195355185.
  13. Büyüköz, M.; Erdal, E.; Altinkaya, S.A. (2016). "Nanofibrous gelatin scaffolds integrated with NGF-loaded alginate microspheres for brain tissue engineering". J. Tissue Eng. Regen. Med. 12 (2): e707–e719. doi:10.1002/term.2353. hdl:11147/6844. PMID 27863118. S2CID 206528926.
  14. Venkatesan, J; Bhatnagar, I; Manivasagan, P; Kang, K. H.; Kim, S. K. (2015). "Alginate composites for bone tissue engineering: A review". International Journal of Biological Macromolecules. 72: 269–81. doi:10.1016/j.ijbiomac.2014.07.008. PMID 25020082.
  15. Rastogi, Prasansha; Kandasubramanian, Balasubramanian (2019-09-10). "Review of alginate-based hydrogel bioprinting for application in tissue engineering". Biofabrication. 11 (4): 042001. Bibcode:2019BioFa..11d2001R. doi:10.1088/1758-5090/ab331e. ISSN 1758-5090. PMID 31315105. S2CID 197543168.
  16. Leichner, C; Jelkmann, M; Bernkop-Schnürch, A (2019). "Thiolated polymers: Bioinspired polymers utilizing one of the most important bridging structures in nature". Adv Drug Deliv Rev. 151–152: 191–221. doi:10.1016/j.addr.2019.04.007. PMID 31028759. S2CID 135464452.
  17. Xu, G; Cheng, L; Zhang, Q; Sun, Y; Chen, C; Xu, H; Chai, Y; Lang, M (2016). "In situ thiolated alginate hydrogel: Instant formation and its application in hemostasis". J Biomater Appl. 31 (5): 721–729. doi:10.1177/0885328216661557. PMID 27485953. S2CID 4267830.
  18. Kassem, AA; Issa, DA; Kotry, GS; Farid, RM (2017). "Thiolated alginate-based multiple layer mucoadhesive films of metformin for intra-pocket local delivery: in vitro characterization and clinical assessment". Drug Dev. Ind. Pharm. 43 (1): 120–131. doi:10.1080/03639045.2016.1224895. PMID 27589817. S2CID 25076932.
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