Carrageenan is a type of sulfated polysaccharide extracted from red algae, with a sulfate content of approximately 22% to 35%. According to the content and position of the sulfate ester group, it can be divided into κ, ι, λ, θ, μ, ν and ζ, etc. Among them, κ-carrageenan is the most common and widely used. κ-Carrageenan is mainly extracted from the seaweed Kappaphycus auriculata. The sulfate content is 25%-30%. There is a sulfate ester group on the D-galactose unit connected to (1,3). group. κ-Carrageenan aqueous solution has thermally reversible properties and is sensitive to inorganic salts and pH. The viscosity of the solution will decrease exponentially with the increase of temperature, increase with the increase of the pH of the solution, and remain stable at pH=5.0~9.0; while the addition of inorganic salts will reduce the viscosity of the solution; currently, κ-kara Glue is mainly used in the food and pharmaceutical fields. When combined with other food glues, it can significantly improve the hardness, smoothness, chewiness and transparency of the product.
The Structure of κ-carrageenan
κ-Carrageenan is a sulfated polygalactose anionic polysaccharide composed of repeating α(1→3)-D-galactose-4-sulfate and β(1→4)-3,6-anhydro- Composed of D-galactose disaccharide units. There are two main conformations of κ-carrageenan molecular chain in aqueous solution: double helix structure (ordered state) and random coil chain (disordered state). The transition between these two conformations is significantly dependent on the external temperature. As the temperature increases, the double helix structure of the κ-carrageenan molecular chain will be destroyed and unwind to form random coils; when the temperature decreases, the random coils will re-assemble themselves to form a double helix, thus endowing κ-carrageenan with the glue solution system has good thermal reversibility. As an anionic polysaccharide, κ-carrageenan is very sensitive to salt ions, mainly because certain cations can affect the transition between single-chain and helical structures and the aggregation behavior of helical chains. Studies have shown that monovalent cations can induce the transformation of the random coil chain of carrageenan into a helical structure and promote the aggregation of spirochetes, thereby achieving the gelation transition of the solution. Usually, monovalent cations are more conducive to the formation of carrageenan double helix structure, and K+, Rb+, Cs+ are more effective than Li+ and Na+. As the radius of the metal cation increases, the charge density of the double helix will decrease, and the resulting shielding effect can significantly induce the aggregation of the double helix.
Application of κ-carrageenan
κ-carrageenan has a wide range of uses in the food field. For example, when added to dough, κ-carrageenan can interact with gluten protein to increase the thickness of the gluten network, effectively prevent the growth of ice crystals during refrigeration, and thus solve problems such as dough collapse and cracks during thawing; and κ-carrageenan as a cryoprotectant can prevent protein denaturation, extend the shelf life of frozen dough, and improve the taste of frozen dough. In view of the thermoreversible properties of κ-carrageenan, it can be used as a coagulant for biscuit sandwich jam, which can not only maintain the texture and taste of the jam, but also extend the shelf life. In addition, κ-carrageenan can also be used as a suspending agent and stabilizer for fruit pulp beverages, as well as a clarifier for beer and wine. κ-carrageenan is an anionic polysaccharide, which has a strong electrostatic physical interaction with molecules such as proteins, lipids and glucans, and can form polyelectrolyte complexes with them, promoting molecular coagulation, precipitation and precipitation. At the same time, κ-carrageenan can adsorb metal ions and pigment molecules, reduce the astringency of beer, and make the beer foam white and delicate.
κ-carrageenan is mainly used as a drug carrier in the biomedicine field, which is mainly attributed to the following advantages of its molecular chain structure: (1) κ-carrageenan is non-toxic and has excellent biocompatibility; (2) glycosidic bonds can be cleaved by hydrolases and have excellent biodegradability; (3) the sulfate groups in the molecular chain can greatly increase the drug loading through electrostatic interaction; (4) the presence of active hydroxyl groups in the molecular chain makes it easy to chemically modify. For example, κ-carrageenan can be used to prepare vaginal tablets loaded with acyclovir. Studies on the sustained release behavior of simulated vaginal fluid show that κ-carrageenan and hydroxypropyl methylcellulose components can not only achieve sustained release of drugs, but also help prevent genital herpes infection; for example, κ-carrageenan sustained-release beads loaded with non-steroidal anti-inflammatory drug mefenamic acid can reduce the daily dose of drugs, thereby significantly alleviating drug-induced gastrointestinal diseases.
Figure 1. Carrageenan applications in drug delivery systems and other biomedical applications. (Pacheco-Quito EM, et al.; 2020)
κ-carrageenan, as a natural polysaccharide, has a similar structure to glycosaminoglycans and shows good biological activity. It is considered to be an ideal bio-based material in the field of tissue engineering. For example, some researchers have constructed a type of photo-crosslinked κ-carrageenan gel material with controllable compression modulus, swelling ratio and pore size distribution based on methacrylated κ-carrageenan. By changing the physical and chemical crosslinking of the gel material, not only can the encapsulation of cells and the regulation of the biomechanical properties of the matrix be achieved, but the shape and spatial distribution of cell growth and differentiation in the matrix can also be regulated by micromolding, which has potential application prospects in the field of tissue engineering. κ-carrageenan can also be combined with some synthetic polymers, such as polyacrylamide, poly (N-acryloyl glycinamide), etc., through a double network structure design to form a high-strength functional hydrogel, which can be used as an implant material for some load-bearing tissues.
References
- Pacheco-Quito EM, et al.; Carrageenan: Drug Delivery Systems and Other Biomedical Applications. Mar Drugs. 2020, 18(11):583.
- Raghav N, et al.; Recent advances in cellulose, pectin, carrageenan and alginate-based oral drug delivery systems. Int J Biol Macromol. 2023, 244:125357.
