- Carrageenan is a family of linear sulfated polysaccharides extracted from the cell walls of red seaweeds (Rhodophyta), where it functions as a structural component providing both rigidity and flexibility to marine plants.
- Chemically, carrageenan is composed of repeating disaccharide units of D-galactose and 3,6-anhydrogalactose, linked by alternating α-1,3 and β-1,4 glycosidic bonds, with varying degrees and patterns of sulfation. This sulfate substitution is what differentiates the major types of carrageenan—kappa (κ), iota (ι), and lambda (λ)—each of which exhibits distinct physicochemical and gelling properties.
- The structural differences between carrageenan types arise from the presence or absence of sulfate groups and the degree of 3,6-anhydrogalactose content. Kappa-carrageenan has one sulfate group per disaccharide and forms strong, rigid gels in the presence of potassium ions. Iota-carrageenan contains two sulfate groups per disaccharide and produces soft, elastic gels, especially in the presence of calcium ions. Lambda-carrageenan, with three sulfate groups per disaccharide, does not gel but acts as a thickener due to its high solubility and strong water-binding capacity. These differences allow carrageenan to serve a wide range of industrial purposes, tailored to specific textural or stabilizing requirements.
- One of the most remarkable features of carrageenan is its ability to form thermoreversible gels. Upon cooling, certain carrageenan types (notably κ and ι) undergo a coil-to-helix transition, which allows helices to aggregate and form three-dimensional networks that trap water. This gelling mechanism is highly influenced by ionic conditions, making carrageenan adaptable to different food and material systems. Its versatility has made it a cornerstone hydrocolloid in food technology, where it is used in dairy products (chocolate milk, cheese, ice cream), processed meats, and desserts to stabilize emulsions, improve mouthfeel, and prevent phase separation.
- In addition to food applications, carrageenan has important roles in pharmaceuticals, cosmetics, and biotechnology. Its biocompatibility and ability to form hydrogels under mild conditions make it valuable for drug delivery systems, wound dressings, and tissue engineering scaffolds. Carrageenan also exhibits antiviral and immunomodulatory properties, attributed to its sulfated nature, which can interfere with viral binding and replication. This has led to investigations into carrageenan-based formulations for antiviral therapies and as components of biomedical coatings.
- From a biological perspective, carrageenan contributes to the structural resilience of red algae, enabling them to withstand osmotic and mechanical stress in marine environments. Industrially, carrageenan is extracted from species such as Kappaphycus alvarezii, Eucheuma denticulatum, and Chondrus crispus (commonly known as Irish moss). The global carrageenan industry represents a major economic link between marine resources and biotechnology, with cultivation of red algae supporting livelihoods in coastal communities worldwide.
