Chemical Properties
white to pale yellow-beige powder
Usage
corrosive moisture sensitive
Definition
A polysaccharide composed of β,d-mannuronic acid residues linked so that the carboxyl group of each unit is free, while the aldehyde group is shielded by a glycosidic linkage. It is a linear polymer of the mannuronic acid in the pyranose ring form.
Definition
A yellow-white organic solid
that is found in brown algae. It is a complex
polysaccharide and produces, in even
very dilute solutions, a viscous liquid. Alginic
acid has various uses, especially in the
food industry as a stabilizer and texture
agent.
Production Methods
Alginic acid is a hydrophilic colloid carbohydrate that occurs
naturally in the cell walls and intercellular spaces of various species
of brown seaweed (Phaeophyceae). The seaweed occurs widely
throughout the world and is harvested, crushed, and treated with
dilute alkali to extract the alginic acid.
Pharmaceutical Applications
Alginic acid is used in a variety of oral and topical pharmaceutical
formulations. In tablet and capsule formulations, alginic acid is used
as both a binder and disintegrating agent at concentrations of 1–5%
w/w. Alginic acid is widely used as a thickening and suspending
agent in a variety of pastes, creams, and gels; and as a stabilizing
agent for oil-in-water emulsions.
Alginic acid has been used to improve the stability of
levosimendan.
Therapeutically, alginic acid has been used as an antacid.In
combination with an H2-receptor antagonist, it has also been
utilized for the management of gastroesophageal reflux.
Safety
Alginic acid is widely used in food products and topical and oral
pharmaceutical formulations. It is generally regarded as a nontoxic
and nonirritant material, although excessive oral consumption may
be harmful. Inhalation of alginate dust may be an irritant and has
been associated with industrially related asthma in workers
involved in alginate production. However, it appears that the cases
of asthma were linked to exposure to unprocessed seaweed dust
rather than pure alginate dust. An acceptable daily intake of
alginic acid and its ammonium, calcium, potassium, and sodium
salts was not set by the WHO because the quantities used, and the
background levels in food, did not represent a hazard to health.
LD50 (rat, IP): 1.6 g/kg
storage
Alginic acid hydrolyzes slowly at warm temperatures producing a
material with a lower molecular weight and lower dispersion
viscosity.
Alginic acid dispersions are susceptible to microbial spoilage on
storage, which may result in some depolymerization and hence a
decrease in viscosity. Dispersions should therefore be preserved with
an antimicrobial preservative such as benzoic acid; potassium
sorbate; sodium benzoate; sorbic acid; or paraben. Concentrations
of 0.1–0.2% are usually used.
Alginic acid dispersions may be sterilized by autoclaving or
filtration through a 0.22 μm filter. Autoclaving may result in a
decrease in viscosity which can vary depending upon the nature of
any other substances present.
Alginic acid should be stored in a well-closed container in a cool,
dry place.
Purification Methods
To 5g of acid in 550mL water containing 2.8g KHCO3 are added 0.3mL of acetic acid and 5g potassium acetate. EtOH is added to make the solution to 25% (v/v) in EtOH, and any insoluble material is discarded. Further addition of EtOH, to 37% (v/v), precipitated alginic acid. Collect the acid and dry it in vacuo. [Pal & Schubert J Am Chem Soc 84 4384 1962.]
Incompatibilities
Incompatible with strong oxidizing agents; alginic acid forms
insoluble salts in the presence of alkaline earth metals and group III
metals with the exception of magnesium.
Regulatory Status
GRAS listed. Accepted in Europe for use as a food additive.
Included in the FDA Inactive Ingredients Database (ophthalmic
preparations, oral capsules, and tablets). Included in the Canadian
List of Acceptable Non-medicinal Ingredients. Included in nonparenteral
medicines licensed in the UK.
