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Properties, Production and Uses of Carrageenan

Carrageenans are commercially important hydrophilic colloids (water-soluble gums) which occur as matrix material in numerous species of red seaweeds (Rhodophyta) wherein they serve a structural function analogous to that of cellulose in land plants. Chemically they are highly sulfated galactans. Due to their half-eater sulfate moieties they are strongly anionic polymers.

Carrageenan is a collective term for polysaccharides prepared by alkaline extraction (and modification) from red seaweed (Rhodophycae), mostly of genus Chondrus, Eucheuma, Gigartina and Iridaea. Different seaweeds produce different carrageenans.

Carrageenans are sulfated polymers made up of galactose units. Several fractions have been determined, but a common backbone can be defined. Carrageenan consists of a main chain of D-galactose residues linked alternately α - (1 → 3) and β - (1 → 4).

The differences between the fractions are due to the number and to the position of the sulfate groups and to the possible presence of a 3.6 anhydro-bridge on the galactose linked through the 1 - and 4 -positions.
Carrageenan consists of alternating 3-linked-b-D-galactopyranose
and 4-linked-a-D-galactopyranose units

Carrageenans are linear polymers of about 25,000 galactose derivatives with regular but imprecise structures, dependent on the source and extraction conditions. Idealized structures are given below and k-carrageenan, for example, has been found to contain a small proportion of the dimer associated with i-carrageenan.
Carrageenan extraction Procedure

Uses of Carrageenan
There are some general uses of carrageenan :
  1. Gelling Agent (Hot water, milk)
  2. dairy desserts (milk-gels, flans, custards) 
  3. chocolate milks 
  4. ices, ice creams and related products 
  5. meat preserves 
  6. petfoods 
  7. air-fresheners 
  8. enzyme 
  9. in vitro meristem culture 

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