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GUAR GUM

Prepared at the 44th JECFA (1995), published in FNP 52 Add 3 (1995) superseding specifications prepared at the 17th JECFA (1973), published in FNP 4 (1978)


SYNONYMS

Gum cyamopsis, guar flour; INS No. 412

DEFINITION

Primarily the ground endosperm of the seeds from Cyamopsis tetragonolobus (L) Taub., (Fam. Leguminosae) consisting mainly of polysaccharides of high molecular weight (200,000-300,000), composed of galactomannans; mannose: galactose ratio is about 2:1.

C.A.S. number

9000-30-0

DESCRIPTION

White to yellowish-white, nearly odourless, free-flowing powder

FUNCTIONAL USES

Thickener, stabilizer

CHARACTERISTICS

IDENTIFICATION

Solubility

Soluble in water

Gel formation

Add small amounts of sodium borate TS to a solution of the sample. A gel is formed.

Viscosity

Transfer 2 g of the sample into a 400-ml beaker and moisten thoroughly with about 4 ml of isopropanol. Add, with vigorous stirring, 200 ml of water and continue the stirring until the gum is completely and uniformly dispersed. An opalescent, viscous solution is formed. Transfer 100 ml of this solution into another 400-ml beaker, heat the mixture in a boiling water bath for about 10 min and cool to room temperature. There is no substantial increase in viscosity (differentiating guar gum from carob bean gum).

Test for galactose and mannose

Passes test

See description under TESTS

Microscopic examination

Place some ground sample in an aqueous solution containing 0.5% iodine and 1% potassium iodide on a glass slide and examine under microscope. Guar gum shows close groups of round to pear formed cells, their contents being yellow to brown. (Carob bean gum contains long stretched tubiform cells, separated or slightly interspaced. Their brown contents are much less regularly formed than in guar gum).

PURITY

Loss on drying

Not more than 15.0% (105o, 5 h)

Borate

Not detectable

Dissolve 1 g of the sample in 100 ml of water. The solution should remain fluid and not form a gel on standing. Mix 10 ml of dilute hydrochloric acid with the solution, and apply one drop of the resulting mixture to turmeric paper. A brownish red colour, which upon drying becomes intensified and changes to greenish black when moistened with ammonia TS, should not be formed.

Total ash

Not more than 1.5%

Acid insoluble matter

Not more than 7.0%

Protein

Not more than 10.0%

Proceed as directed under Nitrogen Determination (Kjeldahl Method). The percent of nitrogen in the sample multiplied by 6.25 gives the percent of protein in the sample

Starch

Not detectable by the following test:

To a 1 in 10 solution of the sample add a few drops of iodine TS. No blue colour should be produced

Arsenic

Not more than 3 mg/kg (Method II)

Lead

Not more than 5 mg/kg

Prepare a sample solution as directed for organic compounds in the Limit Test, using 5 µg of lead ion (Pb) in the control

Heavy metals

Not more than 20 mg/kg

Test 1 g of the sample as directed in the Limit Test (Method II)

TESTS

IDENTIFICATION TESTS

Test for galactose and mannose

Boil a mixture of 100 mg of the sample and 20 ml of 10% sulfuric acid for 3 hr. Allow to cool and add excess barium carbonate mixing with a magnetic stirrer until the solution is of pH 7, and filter. Evaporate the filtrate in a rotary evaporator at 30-50o in vacuum until a crystallized (or syrupy) residue is obtained. Dissolve in 10 ml of 40% methanol. This is the hydrolysate. Place 1 to 10 µl spots of hydrolysate on the starting line of two chromatoplates of silica gel and spots containing 1 to 10 µg of galactose and mannose expected to be present in the hydrolysate. Use two solvent systems, one for each plate: A. a mixture of formic acid, methyl ethyl ketone, tertiary butanol and water (15:30:40:15 by vol.) and B. a mixture of isopropanol, pyridine, acetic acid and water (40:40:5:20 by vol.) to develop the plates. After development, spray with a solution of 1.23 g anisidine and 1.66 g phthalic acid in 100 ml ethanol and heat the plates at 100o for 10 min. A greenish yellow colour is produced with hexoses, a red colour with pentoses and a brown colour with uronic acids. Compare sample with those for the solution of galactose and mannose.


Source: Joint FAO/WHO Expert Committee on Food Additives (JECFA)


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