Alginic acid, also called algin, is a naturally occurring, edible
polysaccharide found in
brown algae
Brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Northern Hemisphere. Brown algae are the major seaweeds of the temperate and p ...
. It is
hydrophilic
A hydrophile is a molecule or other molecular entity that is attracted to water molecules and tends to be dissolved by water.Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon'' Oxford: Clarendon Press.
In contrast, hydrophobes are no ...
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
The word filament, which is descended from Latin ''filum'' meaning " thread", is used in English for a variety of thread-like structures, including:
Astronomy
* Galaxy filament, the largest known cosmic structures in the universe
* Solar filamen ...
, granular, or powdered forms.
It is a significant component of the
biofilms
A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular po ...
produced by the bacterium ''
Pseudomonas aeruginosa'', a major pathogen found in the lungs of some people who have
cystic fibrosis.
The biofilm and ''P. aeruginosa'' have a high resistance to
antibiotics
An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention ...
,
but susceptible to inhibition by
macrophages.
Structure
Alginic acid is a linear
copolymer
In polymer chemistry, a copolymer is a polymer derived from more than one species of monomer. The polymerization of monomers into copolymers is called copolymerization. Copolymers obtained from the copolymerization of two monomer species are some ...
with
homopolymeric blocks of (1→4)-linked β-D-
mannuronate (M) and α-L-
guluronate (G) residues, respectively,
covalently
A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms ...
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
In stereochemistry, an epimer is one of a pair of diastereomers. The two epimers have opposite configuration at only one stereogenic center out of at least two. All other stereogenic centers in the molecules are the same in each. Epimerization is ...
of β-D-mannuronate.
Forms
Alginates are refined from brown
seaweeds
Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of ''Rhodophyta'' (red), '' Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...
. 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.
Brown seaweeds range in size from the giant
kelp
Kelps are large brown algae seaweeds that make up the order Laminariales. There are about 30 different genera. Despite its appearance, kelp is not a plant - it is a heterokont, a completely unrelated group of organisms.
Kelp grows in "underwat ...
''
Macrocystis pyrifera
''Macrocystis pyrifera'', commonly known as giant kelp or bladder kelp, is a species of kelp (large brown algae), and one of four species in the genus '' Macrocystis''. Despite its appearance, it is not a plant; it is a heterokont. Giant kelp i ...
'' 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
''Saccharina japonica'' is a marine species of the Phaeophyceae (brown algae) class, a type of kelp or seaweed, which is extensively cultivated on ropes between the seas of China, Japan and Korea. It has the common name sweet kelp. It is widely ...
'', 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.
Commercial grade alginate are extracted from giant
kelp
Kelps are large brown algae seaweeds that make up the order Laminariales. There are about 30 different genera. Despite its appearance, kelp is not a plant - it is a heterokont, a completely unrelated group of organisms.
Kelp grows in "underwat ...
''
Macrocystis pyrifera
''Macrocystis pyrifera'', commonly known as giant kelp or bladder kelp, is a species of kelp (large brown algae), and one of four species in the genus '' Macrocystis''. Despite its appearance, it is not a plant; it is a heterokont. Giant kelp i ...
'', ''
Ascophyllum nodosum
''Ascophyllum nodosum'' is a large, common cold water seaweed or brown alga (Phaeophyceae) in the family Fucaceae, being the only species in the genus ''Ascophyllum''. It is a seaweed that only grows in the northern Atlantic Ocean, also known in ...
'', and types of ''
Laminaria
''Laminaria'' is a genus of brown seaweed in the order Laminariales (kelp), comprising 31 species native to the north Atlantic and northern Pacific Oceans. This economically important genus is characterized by long, leathery laminae and relati ...
''. Alginates are also produced by two
bacterial
genera ''
Pseudomonas
''Pseudomonas'' is a genus of Gram-negative, Gammaproteobacteria, belonging to the family Pseudomonadaceae and containing 191 described species. The members of the genus demonstrate a great deal of metabolic diversity and consequently are able to ...
'' and ''
Azotobacter
''Azotobacter'' is a genus of usually Motility, motile, oval or spherical bacteria that form thick-walled cysts (and also has hard crust) and may produce large quantities of capsular Mucus, slime. They are aerobic, free-living soil Microorganism ...
'', which played a major role in the unravelling of its
biosynthesis
Biosynthesis is a multi-step, enzyme- catalyzed process where substrates are converted into more complex products in living organisms. In biosynthesis, simple compounds are modified, converted into other compounds, or joined to form macromolecule ...
pathway. Bacterial alginates are useful for the production of micro- or nanostructures suitable for medical applications.
Sodium alginate (NaC
6H
7O
6) is the
sodium salt
Sodium salts are salts composed of a sodium cation and the conjugate base anion of some inorganic or organic acids. They can be formed by the neutralization of such acids with sodium hydroxide.
Categorization
Sodium salts can be categorized in ...
of alginic acid. Sodium alginate is a gum.
Potassium alginate (KC
6H
7O
6) is the potassium
salt of alginic acid.
Calcium alginate
Calcium alginate is a water-insoluble, gelatinous, cream-coloured substance that can be created through the addition of aqueous calcium chloride to aqueous sodium alginate. Calcium alginate is also used for entrapment of enzymes and forming artif ...
(CaC
12H
14O
12), is made from sodium alginate from which the sodium ion has been removed and replaced with calcium (
ion exchange
Ion exchange is a reversible interchange of one kind of ion present in an insoluble solid with another of like charge present in a solution surrounding the solid with the reaction being used especially for softening or making water demineralised, ...
).
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
Filtration is a physical separation process that separates solid matter and fluid from a mixture using a ''filter medium'' that has a complex structure through which only the fluid can pass. Solid particles that cannot pass through the filter m ...
and
centrifugation
Centrifugation is a mechanical process which involves the use of the centrifugal force to separate particles from a solution according to their size, shape, density, medium viscosity and rotor speed. The denser components of the mixture migrate ...
.
Uses
Alginate absorbs water quickly, which makes it useful as an additive in
dehydrated
In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...
products such as
slimming aids, and in the manufacture of paper and textiles. It is also used for
waterproofing and
fireproofing fabrics, in the food industry as a
thickening
A thickening agent or thickener is a substance which can increase the viscosity of a liquid without substantially changing its other properties. Edible thickeners are commonly used to thicken sauces, soups, and puddings without altering their ta ...
agent for drinks, ice cream, cosmetics, and as a
gelling agent for jellies, known by the
code E401. Sodium alginate is mixed with
soybean flour to make
meat analogue.
Alginate is used as an ingredient in various
pharmaceutical preparations, such as
Gaviscon, in which it combines with
bicarbonate
In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula .
Bicarbonate serves a crucial biochemic ...
to inhibit
gastroesophageal reflux. Sodium alginate is used as an
impression-making material in
dentistry,
prosthetic
In medicine, a prosthesis (plural: prostheses; from grc, πρόσθεσις, prósthesis, addition, application, attachment), or a prosthetic implant, is an artificial device that replaces a missing body part, which may be lost through trau ...
s,
lifecasting
Lifecasting is the process of creating a three-dimensional copy of a living human body, through the use of molding and casting techniques.casting
Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a ''casting'', which is ejected ...
.
Sodium alginate is used in
reactive dye printing and as a thickener for
reactive dye
In a reactive dye, a chromophore (an atom or group whose presence is responsible for the colour of a compound) contains a substituent that reacts with the substrate. Reactive dyes have good fastness properties owing to the covalent bonding that oc ...
s 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.
Calcium alginate is used in different types of medical products, including skin
wound dressing
A dressing is a sterile pad or compress applied to a wound to promote healing and protect the wound from further harm. A dressing is designed to be in direct contact with the wound, as distinguished from a bandage, which is most often used to hold ...
s to promote healing, and may be removed with less pain than conventional dressings.
Alginate hydrogels
Alginate may be used in a
hydrogel
A hydrogel is a crosslinked hydrophilic polymer that does not dissolve in water. They are highly absorbent yet maintain well defined structures. These properties underpin several applications, especially in the biomedical area. Many hydrogels ar ...
consisting of
microparticles or bulk gels combined with
nerve growth factor
Nerve growth factor (NGF) is a neurotrophic factor and neuropeptide primarily involved in the regulation of growth, maintenance, proliferation, and survival of certain target neurons. It is perhaps the prototypical growth factor, in that it was on ...
in
bioengineering
Biological engineering or
bioengineering is the application of principles of biology and the tools of engineering to create usable, tangible, economically-viable products. Biological engineering employs knowledge and expertise from a number o ...
research to stimulate
brain tissue
The human brain is the central organ of the human nervous system, and with the spinal cord makes up the central nervous system. The brain consists of the cerebrum, the brainstem and the cerebellum. It controls most of the activities of the ...
for possible
regeneration. In research on bone reconstruction, alginate
composites have favorable properties encouraging regeneration, such as improved
porosity,
cell proliferation
Cell proliferation is the process by which ''a cell grows and divides to produce two daughter cells''. Cell proliferation leads to an exponential increase in cell number and is therefore a rapid mechanism of tissue growth. Cell proliferation re ...
, and
mechanical strength
The field of strength of materials, also called mechanics of materials, typically refers to various methods of calculating the stresses and strains in structural members, such as beams, columns, and shafts. The methods employed to predict the re ...
, among other characteristics.
Alginate hydrogel is a common biomaterial for bio-fabrication of scaffolds and tissue regeneration.
See also
*
Hyaluronic acid
Hyaluronic acid (; abbreviated HA; conjugate base hyaluronate), also called hyaluronan, is an anionic, nonsulfated glycosaminoglycan distributed widely throughout connective, epithelial, and neural tissues. It is unique among glycosaminoglyca ...
: a polysaccharide in animals.
*
Agar
Agar ( or ), or agar-agar, is a jelly-like substance consisting of polysaccharides obtained from the cell walls of some species of red algae, primarily from ogonori (''Gracilaria'') and "tengusa" (''Gelidiaceae''). As found in nature, agar i ...
References
External links
Alginate seaweed sourcesAlginate properties
{{DEFAULTSORT:Alginic Acid
Polysaccharides
Natural gums
Edible thickening agents
Copolymers
Dental materials
Excipients
Algal food ingredients
Brown algae
Food stabilizers
E-number additives