Hydrocolloids

Alginates

Alginates are natural polysaccharides extracted from brown seaweed. They are highly versatile ingredients as they are both cold-soluble and cold-setting and in the gel form are also heat stable.

Cargill can supply grades of alginic acid and alginates that meet the specifications of Ph.Eur. and USP/NF, when tested accordingly.

Brand names

• SATIALGINE™ - thickening alginates
• ALGOGEL™ - gelling alginates
• CECALGUM™ - specific self-gelling composition

Applications

Alginates can be used in creams, lotions and masks in both skin care and body care. Under micro-spheres, alginates form beads creating an effective delivering system and also can act as a haemostatic in aftershaves.

Functionalities

Alginates are used as thickening or gelling agents in solution. These properties depend on the presence or absence of calcium ions.

Viscosity control agent - as a thickening agent, alginates offer a broad range of flow properties for aqueous-based systems
Film-former
Cold-gelling agent - alginates are the ideal alternative to protect sensitive active ingredients
Stabilizing

Chemistry

Alginates are salts of alginic acid, which is a polyuronide made up of a sequence of two hexuronic acids: beta-D mannuronic acid and alpha-L guluronic acid.

The distribution of these 2 sugars determines the physical and rheological properties of alginates. The type of salt determines its water solubility: sodium and potassium alginates are soluble in water whereas alginic acid and calcium alginate have very low water solubility.

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.

Divalent ions-induced gelation of alginates
The guluronic segments of alginate chains can adopt the form of a buckled ribbon. In the presence of divalent ions such as calcium, segments that are homogeneous can associate to form aggregates similar to an "egg-box". 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 cross-links are strong and numerous, an alginate gel will be thermally irreversible.