Thanks to its unique molecular structure and bioactive properties, alginate is gradually emerging as an indispensable "marine gem" in the fields of food, medicine, agriculture, and industry.

# Alginate: A Natural, Versatile Substance Derived from the Ocean

Alginic Acid is a natural polysaccharide aldaric acid extracted from the cell walls of brown algae such as kelp and giant kelp. Its chemical formula is (C₆H₈O₆)ₙ. This linear copolymer, composed of β-D-mannuronic acid (M) and α-L-guluronic acid (G) linked via 1,4-bonds, plays a crucial role in strengthening plant cell walls in nature. Since its first patent application by a British chemist in 1881, alginic acid has steadily emerged as an indispensable "marine treasure" across food, pharmaceutical, agricultural, and industrial sectors—thanks to its unique molecular structure and remarkable biological properties.

### Chemical Properties and Extraction Process

The molecular structure of alginate consists of three types of blocks: MM, GG, and MG segments, with the ratio of G to M directly influencing its gel-forming properties. For instance, alginates with a high G content readily cross-link with calcium ions to form rigid gels, whereas those rich in M produce elastic gels. This unique characteristic gives alginate a significant advantage when used to create foods with varying textures or medical dressings designed for specific applications.

Traditional extraction processes typically involve three steps: First, seaweed is treated with a dilute alkaline solution (such as sodium carbonate), converting insoluble alginates into soluble sodium salts. Next, impurities are removed via filtration, followed by the addition of hydrochloric acid or calcium chloride to precipitate and isolate the alginate. Finally, the product is dehydrated and dried to yield a powdered final product. In recent years, enzyme-assisted pretreatment techniques have significantly boosted extraction efficiency—for instance, treating brown algae powder with papaya enzyme at 55°C for 2 hours can maintain an alginate extraction rate consistently above 94%, producing a product that meets international standards. Additionally, bacterial fermentation methods using the nitrogen-fixing bacterium *Azotobacter vinelandii* offer a groundbreaking approach to alginate production. This method not only eliminates geographical and climatic constraints but also allows precise control over fermentation conditions to optimize the M/G ratio, paving the way for customized production tailored to specific needs.

### "Natural Thickeners" in the Food Industry

Alginic acid and its salts, such as sodium alginate, are among the most widely used natural additives in the food industry. The carboxyl and hydroxyl groups along its molecular chains give it exceptional water solubility and gel-forming properties, enabling it to create transparent, highly elastic gels. In ice cream, sodium alginate effectively inhibits ice crystal formation, enhancing the smoothness of the texture. In acidic dairy beverages, it forms a gel network cross-linked with calcium ions, stabilizing protein particles and preventing separation. Meanwhile, in jellies and puddings, the gel strength can be precisely controlled by adjusting the M/G ratio. Beyond these applications, alginic acid also serves as an emulsifier to stabilize salad dressings, acts as a coating agent to extend the shelf life of sausages, and even helps prevent protein precipitation during beer brewing. Globally, approximately 550,000 tons of alginic acid are used annually in food production, and its safety has been certified by both the FDA and the European Union.

### "Biocompatible Materials" in the Pharmaceutical Field

Alginate's excellent biocompatibility and low immunogenicity make it an ideal carrier for drug delivery systems. When cross-linked with divalent cations (such as calcium), it forms an open-lattice hydrogel that can encapsulate drug molecules, enabling controlled release. For instance, sodium alginate bisulfate (PSS), a well-established antithrombotic agent, is widely used in clinical practice; meanwhile, Gaoweiping tablets leverage alginate gel to create a protective barrier in gastric acid, effectively relieving heartburn. In the field of wound care, calcium alginate dressings work by absorbing exudates to form a gel-like structure, fostering a moist healing environment while simultaneously releasing calcium ions to promote clotting. In 2021, the global market for alginate-based wound dressings was valued at hundreds of millions of dollars, and it is projected to continue expanding through 2028 with a robust compound annual growth rate—particularly driven by the growing demand for chronic wound care solutions.

### The "Natural Growth Regulator" of Agricultural Production

Alginic acid fertilizer is the "green engine" of modern agriculture. Rich in algal polysaccharides, phenolic compounds, and plant hormones such as gibberellin and indole-3-acetic acid, it significantly boosts crop growth. Research from China Ocean University shows that alginic acid fertilizer can increase seed germination rates by 15%–20% and boost root biomass by more than 30%. By expanding vascular bundle cells in stems, it also accelerates nutrient transport, enhancing fertilizer efficiency. Moreover, the sugar alcohol compounds found in alginic acid—such as mannitol—can chelate heavy metal ions, reducing soil contamination, while its gel-like properties help improve soil structure and enhance water retention. With global annual production reaching tens of millions of tons, alginic acid fertilizer is driving agriculture toward a more sustainable future.

### "Green Solutions" for Industrial Applications

In the industrial sector, the environmental benefits of alginate are becoming increasingly evident. When reacted with calcium salts, it forms a high-molecular-weight resin that efficiently adsorbs heavy metal ions and organic pollutants from wastewater—boasting an adsorption capacity 2 to 3 times greater than traditional materials. In textile dyeing and printing, alginate serves as an active dye-printing paste, delivering not only exceptional print precision but also easy washability, thereby reducing water consumption. Moreover, alginate can be used to produce biodegradable plastics, nano-fertilizers, and smart release systems, providing critical technological support for a circular economy.

From the ocean to land, and from the lab to the production line, alginate is redefining the essence of "small molecules, big impact" through its diverse range of applications. As gene editing, nanotechnology, and artificial intelligence continue to converge and evolve, this ancient marine polysaccharide is poised to unlock even more groundbreaking innovations—bringing greater "blue power" to enhance human health and drive sustainable development for our planet.