GELLAN GUM

Prepared at the 37th JECFA (1990), published in FNP 52 (1992)

SYNONYMS

INS No. 418

DEFINITION

Gellan Gum is a high-molecular-weight polysacchride gum produced by a pure culture fermentation of a carbohydrate by Pseudomonas elodea, purified by recovery with isopropyl alcohol, dried, and milled. It comprises principally a high-molecular-weight polysaccharide composed of a tetrasaccharide repeating unit of one rhamnose, one glucuronic acid, and two glucoses, and substituted with about 0-5% acyl (glyceryl and acetyl) groups as the O-glycosidically linked esters. The glucuronic acid is neutralized to a mixed potassium, sodium, calcium, and magnesium salt.

C.A.S. number

71010-52-1

Assay

Yields, on the dried basis, not less than 3.3% and not more than 6.8% of carbon dioxide (CO₂)

DESCRIPTION

Off-white powder

FUNCTIONAL USES

Thickening agent, gelling agent, stabilizer

CHARACTERISTICS

IDENTIFICATION

Solubility

Soluble in water, forming a viscous solution; insoluble in ethanol

Gel test with calcium ion

Add 1.0 g of the sample to 99 ml of water, and stir for about 2 h, using a motorized stirrer having a propeller-type stirring blade. Draw a small amount of this solution into a wide bore pipet and transfer into a 10% solution of calcium chloride. A tough worm-like gel will be formed immediately.

Gel test with sodium ion

Add 1.0 g of the sample to 99 ml of water, and stir for about 2 h, using a motorized stirrer having a propeller-type stirring blade. Add 0.50 g of sodium chloride, heat to 80° with stirring, and hold at 80° for 1 min. Allow the solution to cool to room temperature. A firm gel is formed.

PURITY

Loss on drying

Not more than 15% (105°, 2½ h)

Ash (total)

4% - 12% (105°, 4 h)

Nitrogen

Not more than 3%

Isopropyl alcohol

Not more than 750 mg/kg

See description under TESTS

Microbiological criteria

Total plate count: Not more than 10,000 colonies per gram

E. coli: Negative by test

Salmonella: Negative by test

Yeasts and moulds: Not more than 400 colonies per gram

See description under TESTS

Arsenic

Not more than 3 mg/kg (Method II)

Lead

Not more than 5 mg/kg

Heavy metals

Not more than 30 mg/kg

Test 0.5 g of the sample as directed in Method II under the Heavy metals Limit Test using a platinum crucible for the ignition and 15 ug of lead ion (Pb) in the control (Solution A).

TESTS

PURITY TESTS

Isopropyl alcohol

Isopropyl alcohol (IPA) Standard Solution:

Transfer 500.0 mg of chromatographic quality isopropyl alcohol into a 50-ml volumetric flask, dilute to volume with water, and mix. Pipet 10 ml of this solution into a 100-ml volumetric flask, dilute to volume with water, and mix.

Tertiary butyl alcohol (TBA) Standard Solution:

Transfer 500.0 mg of chromatographic quality tert-butyl alcohol into a 50-ml volumetric flask, dilute to volume with water, and mix. Pipet 10 ml of this solution into a 100-ml volumetric flask, dilute to volume with water, and mix.

Mixed Standard Solution:

Pipet 4 ml each of the IPA standard solution and of the TBA standard solution into a 125-ml graduated Erlenmeyer flask, dilute to about 100 ml with water, and mix. This solution contains approximately 40 µg each of isopropyl alcohol and of tert-butyl alcohol per ml.

Sample preparation:

Disperse 1 ml of a suitable antifoam emulsion, such as Dow-Corning G-10 or equivalent, in 200 ml of water contained in a 1000-ml round-bottom distilling flask. Add about 5 g of the sample, accurately weighed, and shake the flask for 1 h, on a wrist-action mechanical shaker. Connect the flask to a fractionating column and distil about 100 ml; adjust the heat so that foam does not enter the column. Add 4.0 ml of TBA Standard Solution to the distillate to obtain the Sample Preparation.

Procedure:

Inject about 5 µl of the Mixed Standard Solution into a suitable gas chromatograph equipped with a flame-ionization detector and a 1.8-m x 2.3-mm stainless steel column packed with 80/100-mesh Porapak QS or equivalent. The carrier is helium flowing at 80 ml per min. The injection port temperature is 200°, the column temperature 165°, and the detector temperature 200°. The retention time of isopropyl alcohol is about 2 min, and that of tert-butyl alcohol about 3 min.

Determine the areas of the IPA and TBA peaks, and calculate the response factor, f, by the formula A_IPA/A_TBA, in which A_IPA is the area of the isopropyl alcohol peak, and A_TBA is the area of the tert-butyl alcohol peak.

Similarly, inject about 5 µl of the Sample Preparation, and determine the peak areas, recording the area of the isopropyl alcohol peak as a_IPA, and that of the tert-butyl alcohol peak as a_TBA. Calculate the isopropyl alcohol content, in mg/kg, in the sample taken by the formula:

(a_IPA x 4000)(f x a_TBA x W)

in which W is the weight of the sample taken, in g.

METHOD OF ASSAY

Processed as directed under Carbon Dioxide Determination by Decarboxylation, using about 1.2 g of the sample weighed accurately.