Alginates Flashcards
Alginic acid is a linear copolymer (unbranched) composed of
- D-manuronic acid (M)
- L-guluronic acid (G)
Alginic acid and calcium alginate are
water-insoluble
All the alginate salts are insoluble to
fats & oils and organic solvents
Alginate must be dispersed
d before dissolution can take place
prepare a uniform aqueous solution of ALGIN before it is utilized
as a thickening agent
Poor dispersion in water will occur if
sodium alginate is added too rapidly,
Alginates form gels
with a number of
divalent cations. E.g. Ca2+ (non-toxiic)
Gelation involved binding of Ca2+
in poly-L-guluronate segments (G) (with
chain length of > 20 residues
The amount of G blocks & the average G-block length
significantly affect gel formation & gel strength.
High G content and long
G blocks give alginates
high calcium reactivity
and the strongest gel forming potential
- A cavity that acts as a binding site for calcium ions between two diaxially linked G residues is formed
produces a 3D structure (‘egg-box’), in which the calcium interacts with the carboxyls and with the electronegative oxygen atoms of the hydroxyl group (OH).
Gelation involves
chain dimerization and later aggregation of the dimer
After gelation, the water molecules are
physically entrapped
by the alginate matrix/network but retain their ability to migrate
The alginate gel is considered a semi-solid
material,
d the junction zones at which
the alginate polymers are bound represent
the solid state
