Alginate is a polysaccharide, like starch and cellulose. It is composed of several building units (typically 100–3000) linked together in a flexible chain. Long molecules constructed from identical or nearly identical building units are called polymers, while the building units themselves are called monomers. Polymers of natural origin are commonly called biopolymers.
Alginate is built upon the basis of two sugars, which are both uronates, the salts of mannuronic and guluronic acid. When producing alginates, uronic acid is converted into the salt-forms mannuronate (M) and guluronate (G). See Figure 4.
The G- and M- units are joined together in one of three blocks: GG... , MM... , and MG.... These are illustrated in Figure 5. The proportion, distribution, and length of these blocks determine the chemical and physical properties of the alginate molecules.
The chemical composition of alginate varies according to seaweed species and even within different parts of the same plant. As with all products produced from natural resource, alginate properties are subject to seasonal variations. By selecting raw materials with varying but known properties, FMC BioPolymer is able to manufacture alginates with consistent properties in a wide range of grades.