Name: Potassium Alginate
CAS No: Potassium alginate [9005-36-1]
USP-NF: Potassium Alginate
Alginic acid, potassium salt; E402; Improved Kelmar; potassium polymannuronate.
Potassium alginate [9005-36-1]
(C6H7O6K)n Potassium alginate is the potassium salt of alginic acid, a polyuronide made up of a sequence of two hexuronic acid residues, namely D-mannuronic acid and L-guluronic acid. The two sugars form blocks of up to 20 units along the chain, with the proportion of the blocks dependent on the species of seaweed and also the part of the seaweed used. The number and length of the blocks is important in determining the physical properties of the alginate produced; the number and sequence of the mannuronate and guluronate residues varies in the naturally occurring alginate. The USP32–NF27 describes potassium alginate as consisting chiefly of the potassium salt of alginic acid, a linear glycuronoglycan consisting of b-1,4 linked D-mannuronic acid and L-guluronic acid units in the pyranose form.
See Section 4.
Potassium alginate is widely used in foods as a stabilizer, thickener, and emulsifier; however, its use as a pharmaceutical excipient is currently limited to experimental hydrogel systems. The viscosity, adhesiveness, elasticity, stiffness, and cohesiveness of potassium alginate hydrogels have been determined and compared with values from a range of other hydrogel-forming materials.(1) The effect of calcium ions on the rheological properties of procyanidin hydrogels containing potassium alginate and intended for oral administration has also been investigated.(2)
Potassium alginate occurs as a white to yellowish, fibrous or granular powder; it is almost odorless and tasteless.
See Table I.
Particle size distribution Average particle size 150 mm (Improved Kelmar). Solubility Potassium alginate is soluble in water, dissolving to form a viscous hydrophilic colloidal solution. It is insoluble in ethanol (95%) and in hydroalcoholic solutions in which the alcohol content is greater than 30% by weight; also insoluble in chloroform, ether, and acids having a pH lower than about 3. When preparing solutions of potassium alginate it is important to ensure proper dispersion of the particles, as poor dispersion will lead to the formation of large lumps of unhydrated powder and significantly extended hydration times. Viscosity (dynamic) 400 mPa s (for a 1% dispersion of Improved Kelmar). Vicosities of 4.32 103 mPa s (2.5% dispersion) and 31.1 103 mPa s (4% dispersion) have been reported.(1) Potassium alginate hydrates readily in hot or cold water; in solution, the acid groups of the alginate become ionized and a viscous solution is obtained. The viscosity is proportional to the concentration and molecular weight of the material used. As the temperature rises, a reversible decrease in viscosity occurs. The addition of calcium ions to potassium alginate solutions results in crosslinking and in the formation of gels; where the crosslinks formed are strong and numerous, the gel becomes thermally irreversible.
In the solid state, potassium alginate is a stable material that is not prone to microbial spoilage. Over time, a slow reduction in the degree of polymerization can occur, which may be reflected in a reduction in the viscosity of solutions. As both temperature and moisture can impair the performance of potassium alginate, storage below 258C is recommended. Potassium alginate solutions are stable at pH 4–10; long-term storage outside this range can result in depolymerization of the polymer through hydrolysis. Gelation or precipitation of the alginate can occur at pH values less than 4. Liquid or semisolid alginate formulations should be preserved: suitable preservatives are sodium benzoate, potassium sorbate, or parabens. Potassium alginate should be stored under cool, dry conditions in a well-closed container.
Incompatible with strong oxidizers.
Alginate obtained from brown seaweed is subjected to demineralization, extraction, and precipitation of alginic acid. Following neutralization, the potassium alginate obtained is dried and milled.
Potassium alginate is widely used in food products. It is currently used as an excipient only in experimental pharmaceutical formulations
Observe normal precautions appropriate to the circumstances and quantity of material handled. When heated to decomposition, potassium alginate emits acrid smoke and irritating fumes. Potassium alginate may be irritant to the skin, eyes and lungs. Gloves, eye protection, suitable protective clothing, and respiratory equipment should be worn.
GRAS listed. Accepted for use in foods in the USA and Europe
Alginic acid; ammonium alginate; calcium alginate; propylene glycol alginate; sodium alginate
A specification for potassium alginate is contained in the Food Chemicals Codex (FCC).(3)