Alginates
Functionality
Structuring using alginates
In solution alginates can be used as thickening or gelling agents. These properties depend on the presence or absence of calcium ions.
- Thickening
When a soluble alginate is dissolved, the acid groups are entirely ionized and a viscous solution is obtained. With high viscosity and shear-thinning properties, its rheology is typical of solutions of flexible coil macromolecules. These two properties are proportional to the concentration and the molecular weight. As the temperature rises, the viscosity decreases. This is reversible.
- Calcium-induced gelation of alginates
The guluronic segments of alginate chains can adopt the form of a buckled ribbon. In the presence of calcium ions, segments that are homogeneous can associate to form aggregates similar to an "eggbox". Within these junction zones the chains are in a regular pleated structure, which is stabilized by calcium ions, each neutralizing a negative charge on two different chains. As a result, alginates richer in these blocks form stronger gels. When the calcium-induced crosslinks are strong and numerous, an alginate gel will be thermally irreversible.
- Properties:
- Cold soluble (in a calcium free medium)
- Gel only in the presence of calcium or acid
- Strong, cohesive
- Thermo-resistant.