SODIUM ALGINATE

Prepared at the 41st JECFA (1993), published in FNP 52 Add 2 (1993) superseding specifications prepared at the 39th JECFA (1992), published in FNP 54 Add 1 (1992)

SYNONYMS

INS No. 401

DEFINITION

Sodium alginate is the sodium salt of alginic acid.

C.A.S. number

9005-38-3

Chemical formula

(C₆ H₇ NaO₆)_n

Structural formula

Structural formula from Phillips, Wedlock and Williams: Gums and Stabilizers for the Food Industry 5 (1990) by permission of Oxford University Press.

Formula weight

Structural unit : 198.11 (theoretical), 222 (actual average)

Macromolecule : 32,000 - 250,000 (typical average)

Assay

Yields, on the dried basis, not less than 18.0% and not more than 21.0% of carbon dioxide (CO₂), equivalent to not less than 90.8% and not more than 106.0% of sodium alginate (C₆H₇ NaO₆)_n.

DESCRIPTION

Occurs as white to yellowish brown filamentous, grainy, granular or powdered forms

FUNCTIONAL USES

Stabilizer, thickener

CHARACTERISTICS

IDENTIFICATION

Solubility

Dissolves slowly in water, forming a viscous solution; insoluble in ethanol and ether

Precipitate formation with calcium chloride

To a 0.5% solution of the sample in sodium hydroxide TS add one-fifth of its volume of a 2.5% solution of calcium chloride. A voluminous, gelatinous precipitate is formed. This test distinguishes ammonium alginate from gum arabic, sodium carboxymethyl cellulose, carrageenan, gelatin, gum ghatti, karaya gum, carob bean gum, methyl cellulose and tragacanth gum.

Precipitate formation with ammonium sulfate

To a 0.5% solution of the sample in sodium hydroxide TS add one-half of its volume of a saturated solution of ammonium sulfate. No precipitate is formed. This test distinguishes ammonium alginate from agar, sodium carboxymethyl cellulose, carrageenan, de-esterified pectin, gelatin, carob bean gum, methyl cellulose and starch.

Colour reaction

Passes test

Dissolve as completely as possible 0.01 g of the sample by shaking with 0.15 ml of 0.1 N sodium hydroxide and add 1 ml of acid ferric sulfate TS. Within 5 min, a cherry-red colour develops that finally becomes deep purple.

Test for sodium

Passes test

PURITY

Loss on drying

Not more than 15% (105^o, 4 h)

Water-insoluble matter

Not more than 1% on the dried basis

See description under TESTS

Total ash

Not less than 18% and not more than 27% on the dried basis

Proceed as directed in the Total Ash test under Alginic Acid

Arsenic

Not more than 3 mg/kg (Method II)

Lead

Not more than 10 mg/kg

Prepare a sample solution as directed for organic compounds in the Limit Test, using 10 µg of lead ion (Pb) in the control

Heavy metals

Not more than 40 mg/kg

Test 0.5 g of the sample as directed in the Limit Test (Method II)

METHOD OF ASSAY

Proceed as directed under Carbon Dioxide Determination by Decarboxylation. Each ml of 0.25 N sodium hydroxide consumed is equivalent to 5.5 mg of carbon dioxide (CO₂) or 27.75 mg of sodium alginate (equivalent weight 222).