Alginates
Molecular structure
Alginates are salts of alginic acid - alginic acid is a polyuronide made up of a sequence of two hexuronic acid residues:
- (beta) - D - mannuronic acid unit and
- (alpha) - L - guluronic acid
Three types of blocks exist:
- Homogeneous mannuronic acid (M-M-M-M )
- Homogeneous guluronic acid (G-G-G-G)
- Alternating acids (M-G-M-G)
The two sugars are not distributed at random along the chain, but sometimes form blocks of up to twenty units. The proportion of these blocks depends on the species of seaweed and whether the stipe ("stalk") or blade ("leaf") of the seaweed is used. The number and length of the blocks is very important as these factors determine the physical properties of alginates.
