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CARRAGEENAN

Prepared at the 29th JECFA (1985), published in FNP 34 (1986) and in FNP 52 (1992)


SYNONYMS

INS No. 407

Products of commerce are sold under different names such as: Irish moss gelose, Carrageenan (from Chondrus and Gigartina spp.), Eucheuman (from Eucheuma spp.), Iridophycan (from Iridaea spp.), Hypnean (from Hypnea spp.), Furcellaran or Danish agar (from Furcellaria fastigiata)

DEFINITION

Carrageenan is a generic term for chemically similar hydrocolloids obtained by aqueous extraction from certain members of the class Rhodophyceae (red seaweeds). Specific national legislation may limit the sources for manufacture of carrageenan. The purity and identity criteria in this monograph apply to the chemical substance(s) which are generically carrageenan hydrocolloids according to the Description.

The principal commercial sources of carrageenans are the following families of the class Rhodophyceae:

Furcellariacaea such as Furcellaria

Gigartinaceae such as Chondrus, Gigartina, Iridaea

Hypnaeceae such as Hypnea

Phyllophoraceae such as Phyllophora, Gynmogongrus, Ahnfeltia

Solieriaceae such as Eucheuma, Anatheca, Meristotheca.

C.A.S. number

9000-07-1

DESCRIPTION

Carrageenan is a hydrocolloid consisting mainly of the ammonium, calcium, magnesium, potassium and sodium sulfate esters of galactose and 3,6-anhydrogalactose copolymers. These hexoses are alternately linked alpha-1,3 and ß-1,4 in the polymer. The relative proportion of cations existing in carrageenan may be changed during processing to the extent that one may become predominant.

The prevalent copolymers in food-grade carrageenan hydrocolloid are designated as kappa-, iota-, and lambda-carrageenan. Kappa-carrageenan (C.A.S. number, 11114-20-8) is mostly the alternating polymer of D-galactose-4-sulfate and 3,6-anhydro-D-galactose; iota- carrageenan is similar, except that the 3,6-anhydrogalactose is sulfated at carbon 2. Between kappa- carrageenan and iota-carrageenan there is a continuum of intermediate compositions differing in degree of sulfation at carbon 2. In lambda-carrageenan (C.A.S. number 9062-07-1), the alternating monomeric units are mostly D-galactose-2- sulfate (1,3-linked) and D-galactose-2,6-disulfate (1,4-linked).

Carrageenan hydrocolloids are obtained by extraction from seaweeds into water or aqueous dilute alkali. The hydrocolloid may be recovered by alcohol precipitation, by drum drying or by precipitation in aqueous potassium chloride and freezing. The alcohols used during recovery and purification are restricted to methanol, ethanol and isopropanol. Articles of commerce may be diluted with sugars for standardization purposes, mixed with salts to obtain specific gelling or thickening characteristics or may contain emulsifiers carried over from drum drying processes. Carrageenan is a yellowish or tan to white, coarse to fine powder that is practically odourless.

FUNCTIONAL USES

Thickener, gelling agent, stabilizer

CHARACTERISTICS

IDENTIFICATION

Solubility

Insoluble in ethanol; soluble in water at a temperature of about 80o, forming a viscous, clear or slightly opalescent solution that flows readily; disperses in water more readily if first moistened with alcohol, glycerin, or a saturated solution of sucrose in water

Infrared absorption

Passes test

See description under TESTS

Identification of hydrocolloid and predominant type of copolymer

Passes tests

See description under TESTS

Test for sulfate groups

To a solution of 100 mg of sample in 20 ml of water add 3 ml of N barium chloride and 5 ml of 2 N hydrochloric acid and filter if there is precipitate. Boil the filtrate for 5 min. A white, crystalline precipitate is formed.

Test for galactose and anhydrogalactose

Proceed as directed under Gum ConstituentsIdentification using the following as reference standards: galactose, rhamnose, galacturonic acid, 3,6-anhydrogalactose, mannose, arabinose and xylose. Galactose and 3,6-anhydrogalactose should be present.

PURITY

Loss on drying

Not more than 12% (105o to constant weight)

Viscosity of a 1.5% solution

Not less than 5 centipoises at 75o

See description under TESTS

Sulfate

Not less than 15% and not more than 40% (as SO4) on the basis of dry hydrocolloid content of commercial product. The dry hydrocolloid content of commercial products is defined as the sample minus percent loss on drying and percent of added substances (i.e., sugars, salts or emulsifiers).

See description under TESTS

Total ash

Not less than 15% and not more than 40% on dry weight basis.

Weigh 2 g of the sample to the nearest 0.1 mg and transfer into a previously ignited, tared silica or platinum crucible. Heat the sample with a suitable infra-red heat lamp, increasing the intensity gradually, until it is completely charred and then continue for an additional 30 min. Transfer the crucible and charred sample into a muffle furnace and ignite at about 550º for 1 h, then cool in a desiccator and weigh. Repeat the ignition in the muffle furnace until a constant weight is attained. If a carbon- free ash is not obtained after the first ignition, moisten the charred spot with a 1-in-10 solution of ammonium nitrate and dry under an infra-red heat lamp before igniting again. Calculate the percentage of total ash from the dry-weight of the sample. Retain ash for the Acid-insoluble ash test.

Acid-insoluble ash

Not more than 1%

Boil the ash obtained as directed under Total ash, above, with 25 ml of dilute hydrochloric acid TS for 5 min, collect the insoluble matter on a tared crucible or ashless filter, wash with hot water, ignite and weigh. Calculate the percentage of acid-insoluble ash from the weight of sample taken for the Total ash test.

Acid insoluble matter

Not more than 2%

Residual solvents

Not more than 0.1% of ethanol, isopropanol or methanol, singly or in combination

See description under TESTS

Arsenic

Not more than 3 mg/kg (Method II)

Lead

Not more than 10 mg/kg

Heavy metals

Not more than 40 mg/kg

Test 0.5 g of the sample as directed in the Limit Test (Method II)

TESTS

IDENTIFICATION TESTS

Infrared absorption

Obtain infrared absorption spectra on the gelling and non-gelling fractions of the sample by the following procedure: Disperse 2 g of the sample in 200 ml of 2.5% potassium chloride solution, and stir for 1 h. Let stand overnight, stir again for 1 h, and transfer into a centrifuge tube. (If the transfer cannot be made because the dispersion is too viscous, dilute with up to 200 ml of the potassium chloride solution.) Centrifuge for 15 min at approximately 1000 g.

Remove the clear supernatant, resuspend the residue in 200 ml of 2.5% potassium chloride solution, and centrifuge again. Coagulate the combined supernatants by adding 2 volumes of 85% ethanol or isopropanol (NOTE: Retain the sediment for use as directed below). Recover the coagulum, and wash it with 250 ml of the alcohol. Press the excess liquid from the coagulum, and dry it at 60o for 2 h. The product obtained is the non-gelling fraction (lambda-carrageenan).

Disperse the sediment (retainted above) in 250 ml of cold water, heat at 900 for 10 min, and cool to 60o. Coagulate the mixture, and then recover, wash, and dry the coagulum as described above. The product obtained is the gelling fraction (kappa- and iota-carrageenan).

Prepare a 0.2% aqueous solution of each fraction, cast films 0.0005 cm thick (when dry) on a suitable nonsticking surface such as Teflon, and obtain the infra-red absorption spectrum of each film. (Alternatively, the spectra may be obtained on potassium bromide pellets if care is taken to avoid moisture).

Carrageenan has strong, broad absorption bands, typical of all polysaccharides, in the 1000 to 1100 cm-1 region. Absorption maxima are 1065 and 1020 cm-1 for gelling and non-gelling types, respectively. Other characteristic absorption bands and their intensities relative to the absorbance at 1050 cm-1 are as follows:

Absorbance Relative to 1050 cm-1

Wave

Number Molecular

(cm-1) Assignment Kappa Iota Lambda

1220-1260 ester sulfate 0.2-1.2 1.2-1.6 1.4-2.0

928-933 3,6-anhydrogalactose 0.2-0.6 0.2-0.4 0 - 0.2

840-850 galactose-4-sulfate 0.1-0.5 0.2-0.4 -

825-830 galactose-2-sulfate - - 0.2-0.4

810-820 galactose-6-sulfate - - 0.1-0.3

800-805 3,6-anhydrogalactose

-2-sulfate 0-0.2 0.2-0.4 -

Identification of hydrocolloid and predominant type of copolymer

Add 4 g of sample to 200 ml of water, and heat the mixture in a water bath at 80o, with constant stirring, until dissolved. Replace any water lost byevaporation, and allow the solution to cool to room temperature. It becomes viscous and may form a gel.

To 50 ml of the solution or gel add 200 mg of potassium chloride, then reheat, mix well, and cool. A short-textured ("brittle") gel indicates a carrageenan of a predominantly kappa type, a compliant ("elastic") gel indicates a predominantly iota type. If the solution does not gel, the carrageenan is of a predominatly lambda type.

PURITY TESTS

Viscosity of a 1.5% solution

Transfer 7.5 g of the sample into a tared, 600-ml tall-form (Berzelius) beaker, and disperse with agitation for 10 to 20 min in 450 ml of deionized water. Add sufficient water to bring the final weight to 500 g, and heat in water bath, with continuous agitation, until a temperature of 80o is reached (20 - 30 min). Add water to adjust for loss by evaporation, cool to 76-77o, and heat in a constant temperature bath at 75o. Pre-heat the bob and guard of a Brookfield LVF or LVT viscometer to approximately 75º in water, then dry the bob and guard, and attach them to the viscometer, which should be equipped with a No. 1 spindle (19 mm in diameter, approxiamtely 65 mm in length) and capable of rotating at 30 rpm. Adjust the height of the bob in the sample solution, start the viscometer rotating at 30 rpm and, after six complete revolutions of the viscometer, take the viscometer reading on the 0-100 scale.

If the viscosity is very low, increased precision may be obtained by using the Brookfield UL (ultra low) adapter or equivalent. (Note. Samples of some types of carrageenan may be too viscous to read when a No. 1 spindle is used. Such samples obviously pass the specification, but if a viscosity reading is desired for other reasons, use a No. 2 spindle and take the reading on the 0-100 scale or on the 0-500 scale.)

Record the results in centipoises, obtained by multiplying the reading on the scale by the factor given by the Brookfield manufacturer.

Sulfate

Weigh 1 g of sample to the nearest 0.1 mg in a 100-ml long-neck bottom round flask. Add 50 ml 0.2N hydrochloric acid. Fit a cooler consisting preferably of 5 round bulbs and heat to boiling under reflux for 1 h. Add 25 ml 10% (by volume) hydrogen peroxide solution and continue boiling under reflux per 5 h when the solution becomes completely clear. Transfer the solution to a 600-ml beaker. Bring to boil and stir in dropwise 10 ml of a 10% solution of barium chloride. Let stand for 2 h on a boiling water bath. Filter the precipitate through ash-free filter paper meant for slow filtration (blue ribbon) and wash it with boiling distilled water until the filtrate is free from chloride. Dry the filter paper in a drying oven, gently combust the filter and ash at 1,000o in a tared silica crucible. Let cool when the ash is white. Weigh and calculate percentage sulfate from the weight in mg (P) of the barium sulfate obtained as P x 0.04116.

Residual solvents

Standard Alcohol Solution:
Transfer 500.0 mg each of chromatographic quality methanol, ethanol and isopropanol 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.

TBA Standard Solution:
Transfer 500.0 mg of chromatographic quality tertiary-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 Standard Alcohol 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 of each alcohol and of tertiary-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 24/40 round-bottom distilling flask. Add about 5 g of the sample, accurately weighed, and shake for 1 h on a wrist-action mechanical shaker. Connect the flask to a fractionating column, and distil about 100 ml, adjusting 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 3.2-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 200o, the column temperature is 165o, and the detector temperature is 200o. The retention time of isopropanol is about 2 min, and that of tertiary-butyl alcohol about 3 min.

Determine the areas of the methanol, ethanol, isopropanol and TBA peaks, and calculate each response factor, f, by the formula A /ATBA, in which A is the area of each alcohol peak.

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

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


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


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