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CURDLAN

 

New specification prepared at the 53rd JECFA (1999) and published in FNP 52 Add 7 (1999).

SYNONYMS

Beta-1,3-glucan

DEFINITION

Curdlan is a high molecular weight polymer of glucose, b -1,3-glucan, produced by pure culture fermentation from a non-pathogenic and non-toxicogenic strain of bacterium Agrobacterium biobar 1 (identified as Alcaligenes faecalis var. myxogenes at the time of discovery) or Agrobacterium radiobactor. Curdlan consists of b -(1,3)-linked glucose residues and has the unusual property of forming an elastic gel upon heating its aqueous suspension.

C.A.S. number

54724-00-4

Chemical formula

(C6H10O5)n

Structural formula

 

Assay

Not less than 80% (calculated as anhydrous glucose)

DESCRIPTION

Odourless or almost odourless, white to nearly white powder

FUNCTIONAL USES

Firming agent, gelling agent, stabilizer, thickener

CHARACTERISTICS

 

IDENTIFICATION

 

Solubility (FNP 5)

Insoluble in water and ethanol

Solubility in alkali

Passes test
Suspend 0.2 g of the sample in 5 ml of water, add 1 ml of 3 N sodium hydroxide, and shake. The sample dissolves.

Gel formation

Heat 2% aqueous suspension of the sample in a boiling water bath for 10 min and cool. A firm gel forms.

Precipitate formation with cupric tartrate

Passes test
See description under TESTS

PURITY

 

Gel strength

Not less than 600 g/cm (2% aqueous suspension)
See description under TESTS

pH (FNP 5)

6.0 - 7.5 (1% aqueous suspension)

Loss on drying (FNP 5)

Not more than 10% (60 for 5 h, in vacuum)

Sulfated ash (FNP 5)

Not more than 6%
Test 1 g of the sample (Method I)

Nitrogen (FNP 5)

Not more than 0.3%
Test 1 g of the sample (Method II)

Lead (FNP 5)

Not more than 0.5 mg/kg
Prepare a sample solution as directed for organic compounds in the Limit Test and determine by atomic absorption spectroscopy (FNP 5)

Microbiological criteria (FNP 5)

Total plate count: Not more than 1,000 cfu/g
E. coli: Negative in 1 g

TESTS

IDENTIFICATION TESTS

 

Precipitate formation

with cupric tartrate

Add 5 ml of sulfuric acid TS to 10 ml of a 2% aqueous suspension of the sample, heat in a boiling water bath for 30 min and cool. Neutralize the mixture with barium carbonate and centrifuge it at 900 g for 10 min. Add 1 ml of the supernatant to 5 ml of hot alkaline cupric tartrate TS. A copious red precipitate of cuprous oxide is formed.

Gel strength

Place 200 mg of the sample into the tube of a Potter homogenizer, add 10 ml of water and homogenize at about 3,500 rpm for 5 min. Transfer the suspension into a 16 mm 150 mm test tube, deaerate in vacuum for 3 min and heat in a boiling water bath for 10 min to form a gel. Cool in running water, let stand for 30 min, then remove the gel from the test tube. Cut the gel accurately at distances of 20 mm and 30 mm from the bottom to obtain a piece 10 mm long. Determine gel strength with a Rheo Meter Model CR-200D (Sun Scientific Co., Ltd., Japan; Load cell: 1,000 g) or an equivalent instrument, under the following conditions:

 

Measurement mode: 4
Velocity of moving plate: 250 mm/min
Plunger: cylindrical type, 0.5 cm diameter

 

Read the breaking point of gel (A). Calculate gel strength using the following formula.

 

Gel strength (g/cm) = 1,000A/p r

Where
r = the radius of the plunger (cm)

METHOD OF ASSAY

Transfer about 100 mg of the sample, accurately weighed, into a 100-ml volumetric flask and dissolve in about 90 ml of 0.1 N sodium hydroxide. Add 0.1 N sodium hydroxide to volume and mix well. Transfer 5 ml of the solution into a 100-ml volumetric flask, add water to volume and mix well. To 1 ml of the solution add 1 ml of a 5 in 100 solution of reagent grade phenol and 5 ml of sulfuric acid TS, shake vigorously and cool in ice-cold water. Prepare blank and a reference standard solution in the same manner using 0.1 ml of water and 100 mg of reagent grade glucose, respectively. Determine the absorbances of the sample solution and the reference standard solution in 1-cm cells at 490 nm with a suitable spectrophotometer, using the blank solution as the blank.

Calculate the content (%) of curdlan in the sample using the following formula:

 

Curdlan content (%) = (A/AR) (0.9 WR/W) 100

Where

A = the absorbance of the sample solution

AR = the absorbance of the reference standard solution

0.9 = the molecular weight of anhydrous glucose divided by the molecular weight of glucose

W = the weight of the sample (mg)

WR = the weight of the glucose standard used as reference (mg)

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