what is sodium alginate

what is sodium alginate


Sodium alginate, a natural polysaccharide, has the necessary stability, solubility, viscosity and safety of pharmaceutical excipients. Alginate extract in phaeophyceae was first studied in 1881 by the British chemist E.C.Stanford. He found that the alginate extract has several interesting properties such as the ability to concentrate solution, form gel and form film. Based on this, he submitted several applications for industrial production but large-scale industrial production of alginate was carried out 50 years later. The commercial production began in 1927 and now the worldwide production capacity is about 30,000 tons every year, of which 30% is used in the food industry while the rest in other industries such as the pharmaceutical industry and dentistry.


Molecular Formula: (C6H7NaO6)x

Molecular Weight: 216.12303

Application: the food industry, and the industries such as the pharmaceutical industry and dentistry

CAS Number: 9005-38-3

Boiling point:495.2°C at 760 mmHg [1]

Vapor Pressure: 6.95E-12mmHg at25°C

Solubility: slightly soluble in water


Sodium alginate is a natural polysaccharide carbohydrate extracted from laminaria japonica and widely used as thickening, emulsifying, stabilizing, binding and sizing agents, in those fields including food, medicine, textile, dyeing & printing, papermaking and household chemicals. Since 1980s, its application in the food industry has already got new extension. It is not only a kind of safe food additive but also base material of bionic food or dietary food. Since it in fact is a kind of natural cellulose, it helps to slow down the absorption of fat, carbohydrate and cholate. It also has the function of reducing serum cholesterol so that it plays a role in preventing such modern diseases as hypertension, diabetes and obesity. Moreover, it can restrain the accumulation of poisonous metals like strontium, cadmium and plumbum in the intestinal tract. Due to these vital functions, sodium alginate receives more and more attention at home and abroad. The Japanese call food rich in sodium alginate longevity food and the Americans call it a fantastic food additive.


Physical Properties


1. Shape

Sodium alginate is powder in white or faint yellow and nearly odorless.


  2. Solubility

Sodium alginate is soluble in water but insoluble in such organic solvents as alcohol, ether and chloroform. It becomes thick liquid when soluble in water and the pH value of 1% solution is 6-8. When the pH value is 6-9, the viscosity is stable but the viscosity will decrease when heated to80 ℃.


 3. Toxicity

Sodium alginate is non-toxic, LD50>5000mg/kg.


4. Gel Property

Chelating agents can exert an influence on the properties of sodium alginate solution. Chelating agents feature strong complexation to divalent ions so that sodium alginate can be stabilized in the system.


5. PH Value

Sodium alginate is slightly soluble in water but insoluble in most organic solvents. It is soluble in the alkaline solution and enables the solution to be viscous. The sodium alginate powder will get wet in the presence of water and the hydration makes its surface viscous. After that the particles will rapidly glue together to form crumps, which can be totally hydrated and dissolved at a very slow pace. However, if there exist other chemical compounds which will compete hydration with it, then sodium alginate will be difficult to dissolve in water. Furthermore, glucose, starch and protein in water will decrease the hydration rate of sodium alginate, and then it is necessary to prolong the mixing time. The pH value of sodium alginate in 1% distilled water solution is about 7.2.

6. Stability


Sodium alginate possesses hygroscopicity and its content of moisture in the balanced state depends on relative humidity. Dry sodium alginate, if stored in a tightly closed container and in temperature25℃or below, is very stable. The sodium alginate solution is also stable in pH 5-9. DP (degree of polymerization) and the molecular weight are directly related to the viscosity of its solution. In storage, the decrease of viscosity can be used to estimate DP and sodium alginate with high DP is not as stable as that with low DP.


7. Thickening Property


As the thickening agent of beverages and dairy products, sodium alginate has unique advantages in thickening effect. With favorable fluidity, it enables the drinks to possess a smooth taste and also prevents the viscosity-decreasing phenomenon during the sterilizing process. When it is used as the thickening agent, if it is necessary, products with relatively high molecular weight should be used and calcium can be added by an appropriate amount, which can greatly increase the viscosity of sodium alginate.


As the stabilizing agent of cold drinks like ice cream, sodium alginate is a high grade stabilizing agent because it enables such cold drinks as ice cream to produce a smooth appearance and a soft taste. Since calcium alginate can form a thermal irreversible gel, it is not likely to become rough (the growth of ice crystals) in the processes of transportation and storage and the metaboly phenomenon of ice cream caused by temperature fluctuation will not happen. Meanwhile, ice cream of this kind is fee from extraneous odor when eaten because not only the expansion rate but the melting point have been increased, which in turn makes the quality and benefits of the products remarkably improved. Such products possess a soft, smooth and favorable taste. The added content of sodium alginate is small, usually 1-3% and the added content overseas is about 5-10%.


As the stabilizing agent of dairy products and beverages, sodium alginate enables frozen milk to have a favorable taste, no sticky and stiff feelings, viscosity when stirred.

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On April 3rd, 2013, posted in: Products and Techniques, Sodium Alginate by Tags:

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