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Propylene glycol alginate

Prepared at the 49th JECFA (1997)
superseding specifications prepared at the 44th JECFA (1995),
published in FNP 52 Addendum 3 (1995)


1,2-propane-diol ester of alginic acid; hydroxypropyl alginate; propane 1,2-diol alginate; INS No. 405.


Propylene glycol alginate is an ester of alginic acid in which some of the carboxyl groups are esterified with propylene glycol, some neutralized with an appropriate alkali and some remain free.

C.A.S. number


Chemical formula

(C9H14O7)n (esterified)

Formula weight

Structural unit: 234.21 (theoretical)
Macromolecule: 10,000 - 600,000 (typical average)


Yields, on the dried basis, not less than 16% and not more than 20% of carbon dioxide (CO2).


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


Stabilizer, thickener, emulsifier




Soluble in water giving a viscous, colloidal solution; soluble in up to 60% aqueous ethanol depending upon degree of esterification.

Precipitate formation with sulphuric acid

To 10 ml of a 1% solution of the sample add 1 ml of sodium hydroxide TS. Heat in a boiling water bath for about 5 min, cool and add 1 ml of dilute sulphuric acid TS. A gelatinous precipitate is formed.

Precipitate formation with lead acetate

To 5 ml of a 1% solution of the sample add 1 ml of lead acetate TS. A gelatinous precipitate is formed


Loss on drying

Not more than 20% (105°, 4h)

Water-insoluble matter

Not more than 2% on the dried basis
See description under TESTS

Total propylene glycol

Not less than 15% and not more than 45%.
See description under TESTS.

Free propylene glycol

Not more than 15% See description under TESTS


Not more than 3 mg/kg (Method II)


Not more than 5 mg/kg Prepare a sample solution as directed for organic compounds in the Limit Test, using 5 m g of lead ion (Pb) in the control

Microbiological criteria

Total plate count: Not more than 5,000 colonies per gram.

Initially prepare a 10-1 dilution by adding a 50 g sample to 450 ml of Butterfield's phosphate buffered dilution water and homogenizing in a high speed blender.

Yeasts and moulds: Not more than 500 colonies per gram

Coliforms: Negative by test

Salmonella: Negative by test



Water-insoluble matter

Disperse 2 g of the sample, weighed to the nearest 0.1 mg, in 800 ml of water in a 2,000-ml flask. Neutralize to pH 7 with sodium hydroxide TS and then add 3 ml in excess. Add 40 ml of hydrogen peroxide solution containing 30% by weight H2O2, cover the flask and boil for 1 h with frequent stirring. Filter while hot through a tared Gooch crucible provided with a glass fibre filter (2.4 cm, No 934 AH, Reeve Angel & Co, Clifton, N.Y., USA, or equivalent). If slow filtration is caused by high viscosity of the sample solution, boil until the viscosity is reduced enough to permit filtration. Wash the crucible thoroughly with hot water, dry the crucible and its contents at 105° for 1 h, cool and weigh. Calculate as percentage of the dry weight.

Total popylene glycol

Sample solution:

Weigh, to the nearest 0.1 mg, 1 g of the sample previously dried and dissolve in 100 ml distilled water in a 400-ml beaker. After dissolution add 50 ml of 0.1 N sodium hydroxide and stir for 30 min. At the end of this period neutralize with 0.1 N hydrochloric acid and precipitate the gum with 25 ml of a 5% calcium chloride solution. Filter the mixture using fast filter paper collecting the filtrate in a 250-ml volumetric flask. Wash the precipitate with several small portions of distilled water combining the washings with the filtrate and dilute to the mark with distilled water.

Periodic acid, 0.029 M:

Add 5.500 g of periodic acid and 200 ml of distilled water to a 1-litre volumetric flask. Dilute to the mark with glacial acetic acid.


Pipette a 25-ml aliquot of the sample solution and 25 ml of the 0.029 M periodic acid into a 250-ml conical flask, swirl and let stand for 30 min. At the end of this period add approximately 2 g of potassium iodide and titrate with 0.1 N sodium thiosulfate using 1% starch solution as an indicator.

Perform a blank determination using 50 ml of distilled water and 25 ml of 0.029 M periodic acid. Calculate the percentage of propylene glycol by the formula:


A = ml 0.1 N sodium thiosulfate used for blank
B = ml 0.1 N sodium thiosulfate used for sample
W = weight of the sample (in grams)

Free propylene glycol

Determine the percentage of free propylene glycol in the sample by extracting 2 g of sample for 2 hours under reflux, using 80 ml of propan-2-ol. Allow the solution to cool to room temperature, then determine the quantity of free propylene glycol using titration with 0.029 M periodic acid as described under the procedure for Total propylene glycol.


Proceed as directed under Carbon Dioxide Determination by Decarboxylation in the General Methods. Each ml of 0.25 N Sodium hydroxide consumed is equivalent to 5.5 mg of carbon dioxide (CO2).

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