Alginate

Alginate is an anionic polysaccharide derived from brown seaweed and some bacteria. It is a linear copolymer of two uronic acids, β-D-mannuronic acid (M) and α-L-guluronic acid (G), arranged in blocks of M, G, and MG. In salt form, sodium alginate is water-soluble, while acidification yields alginic acid, which is insoluble. The composition and molecular weight vary with source, giving a range of physical properties.

Gelation occurs when alginate interacts with divalent cations such as calcium. G-blocks preferentially bind calcium ions to form junction zones, often described by the egg-box model, producing hydrogels with tunable strength and permeability. The rheology of alginate solutions is viscous and typically shear-thinning, and the viscosity is influenced by the M/G ratio and molecular weight as well as temperature and ion concentration.

Production and purification involve extracting alginate from brown seaweed under alkaline conditions to solubilize it, followed by purification and precipitation. The dominant commercial salt is sodium alginate, with alginic acid and calcium alginate produced for specific uses.

Applications are broad. In the food industry, alginates serve as thickeners, stabilizers, and gelling agents (often listed as E400) in dairy, fruit products, sauces, and beverages. In medicine and biotechnology, they are used for wound dressings, dental impression materials, and cell encapsulation or immobilization, as well as for controlled-release formulations. Other uses include textile printing, paper sizing, and cosmetics.

Safety and regulation: alginates are generally recognized as safe for many food applications and are subject to purity standards to limit contaminants. They are valued for biocompatibility and a wide range of commercial applications.