Thermoreversible gelling agents

Gelatin
Gel formed on cooling. Molecules undergo a coil-helix transition followed by
aggregation of helices.
Agar
Gel formed on cooling. Molecules undergo a coil-helix transition followed by
aggregation of helices.
Kappa Carrageenan
Gel formed on cooling in the presence of salts notably potassium salts. Molecules
undergo a coil-helix transition followed by aggregation of helices. Potassium ions bind specifically to the helices. Salts present reduce electrostatic repulsion between chains promoting aggregation.
Iota Carrageenan
Gel formed on cooling in the presence of salts. Molecules undergo a coil-helix transition followed by aggregation of helices. Salts present reduce electrostatic repulsion between chains promoting aggregation.
Low methoxyl (LM) pectin
Gels formed in the presence of divalent cations, notably calcium at low pH (3±4.5).
Molecules crosslinked by the cations. The low pH reduces intermolecular electrostatic repulsions.
Gellan gum
Gels formed on cooling in the presence of salts. Molecules undergo a coil-helix transition followed by aggregation of helices. Salts reduce electrostatic repulsions between chains and promote aggregation. Multivalent ions can act by crosslinking chains. Low acyl gellan gels are thermoreversible at low salt concentrations but non-thermoreversible at higher salt contents (b 100mM) particularly in the presence of divalent cations.
Methyl cellulose and hydroxypropylmethyl cellulose
Gels formed on heating. Molecules associate on heating due to hydrophobic interaction of
methyl groups.
Xanthan gum and locust bean gum or konjac mannan
Gels formed on cooling mixtures. Xanthan and polymannan chains associate following the xanthan coil-helix transition. For locust bean gum the galactose deficient regions are involved in the association.

source: hydrocolloids