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Carrageenan

Carrageenan.

Carrageenan [9000-07-1].

? Carrageenan is the hydrocolloid obtained by extraction with water or aqueous alkali, from some members of the class Rhodophyceae (red seaweeds). Carrageenan consists chiefly of potassium, sodium, calcium, magnesium, and ammonium sulfate esters of galactose and 3,6-anhydrogalactose copolymers. These hexoses are alternately linked -1,3 and -1,4 in the polymer. The prevalent copolymers in the hydrocolloid are designated kappa-, iota-, and lambda-carrageenan. Kappa-carrageenan 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, the alternating monomeric units are mostly D-galactose-2-sulfate (1,3-linked) and D-galactose-2,6-disulfate (1,4-linked). The ester sulfate content for Carrageenan ranges from 18 percent to 40 percent. In addition, it contains inorganic salts that originate from the seaweed and from the process of recovery from the extract.

Carrageenan is recovered by alcohol precipitation, by drum drying, or by freezing. The alcohols used during recovery and purification are restricted to methanol, alcohol, and isopropyl alcohol. Carrageenan that is recovered by drum-roll drying may contain mono- and di-glycerides or up to 5 percent of polysorbate 80 used as roll-stripping agents.

Packaging and storage— Preserve in tight containers, preferably in a cool place. Solubility in water— Not more than 30 mL of water is required to dissolve 1 g at a temperature of 80.

Identification—

A: A solution (1 in 50) prepared by heating a uniform dispersion in a hot water bath to 80 (Solution A) becomes more viscous upon cooling and may form a gel.

B: To 10 mL of Solution A, while still hot, add 4 drops of potassium chloride solution (1 in 10), mix, 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 predominantly lambda type.

C: Dilute a portion of Solution A with about 4 parts of water, and add 2 to 3 drops of methylene blue TS: a blue, stringy precipitate is formed (also positive for furcellaran, a

usp31nf26s2_Carrageenan

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