Introduction to Alginates

Alginate molecules were first described by the British chemist E.C.C. Stanford in 1881. They are the most abundant polysaccharides in brown algae, accounting for 40% of dry matter. They are widely found in various types of brown algae, such as species of macrocystis, durvillaea, laminaria, sargassum, lessonia, ecklonia, turbinaria and ascophyllum. Structurally, alginates are a complete family of linear copolymers containing blocks of (1,4)-linked β-D-mannuronate (M) and α-L-guluronate (G) residues. The blocks are composed of consecutive G residues (GGGGGG), consecutive M residues (MMMMMM), and alternating M and G residues (GMGMGM). Alginate molecules provide plants with the flexibility and strength that are essential properties for adapting to growing conditions in the sea. Because of their ability to form hydrogels, alginate molecules have been widely used as stabilizers, thickeners, gelling agents and emulsifiers since their discovery in 1881.

Properties

The properties of alginates are mainly described as follows.

• Viscosity

The viscosity of alginate solution is pH responsive. As the pH decreases, the viscosity of the alginate solution increases and reaches a maximum around pH=3-3.5 as the carboxylate groups in the alginate backbone become protonated and form hydrogen bonds. In addition, the viscosity of the alginate solution increases with the molecular weight of the sodium alginate polymer, which is usually undesirable in processing. By using a combination of high molecular weight and low molecular weight alginate polymers, the elastic modulus of the gel can be increased significantly with minimal increase in the viscosity of the solution ^[1].

• Solubility

Alginates containing divalent or trivalent cations are insoluble in water, because alginates contain a terminal carboxyl ion (-COO^-), so these cations bind to them to produce an insoluble product. However, alginates containing monovalent cations can be dissolved in hot and cold water.

• Gelling

The most useful property of alginates is their ability to produce strong gels that can be used in the medical, cosmetic, textile, pharmaceutical and food industries. The formation of alginate gels can be achieved either by binding to cations, especially multivalent cations such as calcium ions (ionic gels) or by acid deposition (acidic gels).

• Stability

Dried alginates have very limited stability at ordinary temperatures due to intramolecular acid catalyzed degradation. For example, stored in a dry, cool place and not exposed to light, dried alginate powders have a shelf life of only a few months. In contrast, in deep freezers, alginates can be kept for several years without any significant reduction in molecular weight.

Applications

Alginates have many beneficial uses in a variety of industries. The main uses are described below.

Alfa Chemistry is passionate about marine biological resources. We have processed and manufactured a series of alginate products, which have been widely used in pharmaceutical, food, cosmetic and industrial fields. If you are also interested, please feel free to contact us. Let's create new possibilities together!

Reference

1. Kong, H. J.; et al. Decoupling the dependence of rheological/mechanical properties of hydrogels from solids concentration. Polymer. 2002; 43: 6239-6246.

For Research Use Only. Not for use in diagnostic or therapeutic procedures.