- Alginate is a naturally occurring polysaccharide predominantly found in the cell walls of brown algae (Phaeophyceae), where it serves as a structural component and helps maintain cell wall flexibility and integrity in marine environments.
- It is also produced by certain bacteria, such as Pseudomonas aeruginosa and Azotobacter vinelandii, as part of their extracellular polysaccharide matrix. Chemically, alginate is a linear copolymer composed of two uronic acids: β-D-mannuronic acid (M) and its C-5 epimer, α-L-guluronic acid (G). These monomers are linked through 1,4-glycosidic bonds and arranged in homopolymeric blocks of M (M-blocks), homopolymeric blocks of G (G-blocks), or alternating sequences of M and G residues (MG-blocks). The relative proportion and distribution of M and G residues vary depending on the source, giving alginates distinct physical and functional properties.
- One of the defining features of alginate is its ability to form gels in the presence of divalent cations, most notably calcium (Ca²⁺). The guluronic acid residues, particularly in G-blocks, align to form “egg-box” structures that tightly bind calcium ions, creating strong, stable gels even under mild conditions. This gel-forming ability is reversible, biocompatible, and tunable by altering the ratio of M- and G-blocks, making alginate highly versatile in both natural and applied contexts. Alginates with high G content form stronger, more brittle gels, while those with high M content form softer, more elastic gels.
- In nature, alginate plays a crucial role in enabling brown algae to thrive in fluctuating marine environments. Its hydrophilic character allows it to bind large amounts of water, contributing to tissue flexibility and resistance against desiccation. In bacteria such as Pseudomonas aeruginosa, alginate serves as a component of biofilms, where it provides structural stability, protection against environmental stresses, and resistance to host immune defenses. This bacterial alginate is of particular interest in clinical microbiology, as it contributes to the persistence of infections, especially in cystic fibrosis patients.
- Industrially, alginate is widely harvested from brown algae species such as Laminaria, Macrocystis, and Ascophyllum. It is used as a thickener, stabilizer, and gelling agent in food products like ice cream, yogurt, and sauces, where it improves texture and prevents phase separation. In the pharmaceutical and biomedical fields, alginate has gained prominence due to its biocompatibility, low toxicity, and mild gelation conditions. It is employed in wound dressings, drug delivery systems, tissue engineering scaffolds, and cell encapsulation technologies. Its ability to form hydrogels under physiological conditions allows for encapsulating living cells or bioactive molecules without compromising viability or activity.
- Beyond food and medicine, alginate also finds applications in textiles, paper manufacturing, and water treatment. In 3D bioprinting and regenerative medicine, alginate-based hydrogels are used as bioinks for fabricating tissue-like structures. In environmental engineering, alginate’s ability to chelate metal ions makes it useful for heavy metal removal and bioremediation. Its adaptability to chemical modification further enhances its utility, as derivatives can be tailored for specific functional or mechanical properties.
