CAROB BEAN GUM

Prepared at the 44th JECFA (1995), published in FNP 52 Add 3 (1995) superseding specifications prepared at the 35th JECFA (1989), published in FNP 49 (1989)

SYNONYMS

Locust bean gum, algaroba, carob gum, INS No. 410

DEFINITION

Primarily the ground endosperm of the seeds from Ceratonia siliqua (L.) Taub. (Fam. Leguminosae) mainly consisting of high molecular weight (approximately 310,000) polysaccharides composed of galactomannans; the mannose: galactose ratio is about 1:2; may be purified by washing with ethanol or isopropanol.

C.A.S. number

9000-40-2

DESCRIPTION

White to yellowish white, nearly odourless powder

FUNCTIONAL USES

Thickener, stabilizer

CHARACTERISTICS

IDENTIFICATION

Solubility

Soluble in hot water, insoluble in ethanol

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, slightly 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 an appreciable increase in viscosity (differentiating carob bean gum from guar 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. Carob bean gum contains long stretched tubiform cells, separated or slightly interspaced. Their brown contents are much less regularly formed than in Guar gum. (Guar gum shows close groups of round to pear shaped cells. Their contents are yellow to brown).

PURITY

Loss on drying

Not more than 14.0% (105^o, 5 h)

Total ash

Not more than 1.2% (800º, 3-4 h)

Acid-insoluble

matter

Not more than 4.0%

Test 1.5 g of sample, accurately weighed

Protein

Not more than 7.0%

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

Starch

Not detectable by the following method: To a 1 in 10 solution of the sample add a few drops of iodine TS. No blue colour is produced.

Ethanol and isopropanol

Not more than 1%, singly or in combination

See description under TESTS

Arsenic

Not more than 3 mg/kg (Method II)

Lead

Not more than 5 mg/kg

Use 5 Tg 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

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^o-50^o 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 Tg 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 100^o 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.

PURITY TESTS

Ethanol and isopropanol

Principle

The alcohols are converted to the corresponding nitrite esters and determined by Headspace Gas Chromatography.

Sample preparation

Dissolve 100 mg of sample in 10 ml of water using sodium chloride as a dispersing agent if necessary.

Internal standard solution

Prepare an aqueous solution containing 50 mg/l of n-propanol.

Standard alcohol solution

Prepare an aqueous solution containing 50 mg/l each of ethanol and isopropanol.

Procedure

Weigh 200 mg of urea into a 25-ml "dark vial" (Reacti-flasks, Pierce, Rockford, IL, USA, or equivalent). Purge with nitrogen for 5 min. and then add 1 ml of saturated oxalic acid solution, close with a rubber stopper and swirl. Add 1 ml of sample solution, 1 ml of internal standard solution and simultaneously start a stop watch (T=0). Swirl the vial and recap with an open screw cap fitted with a silicone rubber septum. Swirl until T=30 sec. At T=45 sec inject through the septum 0.5 ml of an aqueous solution of sodium nitrite (250 g/l). Swirl until T=70 and at T=150 sec withdraw through the septum 1 ml of the headspace using a pressure lock syringe (Precision Sampling Corp., Baton Rouge, Louisiana, USA, or equivalent.

Gas chromatography

Insert syringe needle in the injection port; precompress the sample, then open the syringe and inject the sample.

Use the following conditions

Column

- material: glass

- lenhth: 90 cm

- inner diameter: 4 mm

- packing: first 15 cm packed with chrompack (or equivalent) and the remainder with Porapak R 120-150 mesh (or equivalent)

Carrier gas: nitrogen

Flow rate: 80 ml/min

Detector: flame ionization

Temperatures

- inj. Port: 250º

- column: 150º isothermal

Calculation

Quantify the ethanol and isopropanol present in the sample by comparing the peak areas with the corresponding peaks obtained by chromatographing the headspace produced by substituting in the procedure 1 ml of Standard alcohol solution for 1 ml of Sample solution.