Alginic acid (E400) is a polysaccharide, a viscous rubber-like substance extracted from the brown algae (Phaeophyceae) of Japanese kelp (Laminaria japonica Aresch). The content of alginic acid in kelp ranges from 15 to 30%.
Alginic acid is insoluble in water and in most organic solvents. 1 part of alginic acid adsorbs 300 parts by weight of water, which causes its use as a thickener.
Alginic acid is a polymer chain consisting of two monomers-residues of polyuronic acids (D-mannuronic and L-guluronic) in different proportions, varying depending on the specific type of algae. Alginates in the human body are not digested and are excreted through the intestines.
Alginic acid and alginates are widely used in medicine (as an antacid) and as food additives (thickeners). Alginic acid removes heavy metals (lead, mercury, etc.) and radionuclides from the body. Many of the healing properties of seaweed are explained by alginic acid.