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Prepared at the 41st JECFA (1993), published in FNP 52 Add 2 (1993) superseding specifications prepared at the 39th JECFA (1992), published in FNP 52 Add 1 (1992) |
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SYNONYMS |
INS No. 400 |
DEFINITION |
Alginic acid is a naturally occurring hydrophilic colloidal polysaccharide obtained from the various species of brown seaweed (Phaeophyceae). It is a linear copolymer consisting mainly of residues of ß-1,4-linked D-mannuronic acid and alpha-1,4- linked L-glucuronic acid. These monomers are often arranged in homopolymeric blocks separated by regions approximating an alternating sequence of the two acid monomers. |
C.A.S. number |
9005-32-7 |
Chemical formula |
(C6H8O6)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.
The number and sequence of the Mannuronate and Glucuronate residues shown above vary in the naturally occurring alginate. The associated water molecules are not shown. |
Formula weight |
Structural unit: 176.13 (theoretical); 200 (actual average) Macromolecule : 32,000 - 250,000 |
Assay |
Yields, on the dried basis not less than 20.0% and not more than 23.0% of carbon dioxide (CO2), equivalent to not less than 91.0% and not more than 104.5% of alginic acid (C6H8O6)n . |
DESCRIPTION |
White to yellowish brown filamentous, grainy, granular or powdered forms |
FUNCTIONAL USES |
Stabilizer and thickener |
CHARACTERISTICS | |
IDENTIFICATION | |
Solubility |
Insoluble in water and organic solvents; dissolves slowly in solutions of sodium carbonate, sodium hydroxide and trisodium phosphate |
pH |
2.0-3.5 (0.3 in 10 suspension) |
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 alginic acid 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 alginic acid 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. |
PURITY | |
Loss on drying |
Not more than 15% (105o, 4h) |
Total ash |
Not more than 4% on the dried basis |
Sodium hydroxide insoluble matter |
Not more than 1% on the dried basis Weigh accurately about 1 g of the sample and dissolve in 100 ml of sodium hydroxide TS, centrifuge and decant. Wash the residue five times with water by mixing, centrifuging and decanting. Transfer the residue by means of water to a tared fine glass filter, dry for 1 h at 105o, cool and weigh. Calculate as percentage of the dry weight. |
Arsenic |
Not more than 3 mg/kg (Method II) |
Lead |
Not more than 10 mg/kg Prepare a sample 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 25 mg of alginic acid (equivalent weight 200). |