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Alginate is named after the salts of alginic acid, all derivatives of alginic acid and itself. They are found in cell walls of brown algae. Phaeophyceae, Laminaria, Ecklonia, Ascophyllum, Durvillaea, Lessonia, Macrocystis, Sargassum and Turbinaria species are the sources for marine alginate [26, 27].

Alginate is a linear polysaccharide with an anionic polymeric and hydrocolloidal structure (Figure 4.3) and are composed of β-D-mannuronic acid (M) and α-L-guluronic acid (G). The chemical structure of the alginate varies from one genus to another brown seaweeds and also, the physical properties of alginates vary according to the ratio of mannuronic acid to guluronic acid, monomer sequence, and molecular weight of the chains. The more guluronic acid content means the more high-quality gelling property for alginate isolated from any seaweed. The physical properties of alginates also control the drug release rate from gels, and the phenotype and function of cells encapsulated in alginate gels as well as gelation [10, 35].

Alginate extraction can be examined under three steps: pre-extraction, neutralization and precipitation. By the precipitation stage, pathways are divided into two as seen in Figure 4.4. Sodium alginate is the main commercial form of alginate, with forms of soluble alginates such as alginic acid and alginic acid esters. Isolation and extraction process of alginates’ major disadvantage is the difficulty of the process from contaminated seaweed, where there are impurities in the final product because of the presence of cytotoxic materials in the contaminated seaweeds where further purification steps needed [36].

Figure 4.3 G blocks, M blocks and alternating blocks of alginate.

Figure 4.4 Isolation and extraction of pathways of alginate.

Alginate have several applications due to its gel-forming, thickening, stabilizing properties, bioactive and biodegradable functions and low toxicity [37]. For these reasons, it is widely used for food, textile, cosmetics, painting or dye and pharmaceutical industries. In food industry they have usage areas as thickeners, gelling agents, and as stabilizers of water-in-oil emulsions, suspensions like fruit juices. Especially in dairy products, alginates are using to obtain in non-sticky, non-softened and stable texture. Alginate matrices such as alginate-pectin or alginate-chitosan may also be used as an encapsulation agent for probiotics, proteins, pigments and volatile compounds [40–42]. Because of good film-forming properties for shelf life extension, reducing the browning rate, inhibiting the yeast and mold growing and maintaining the textural and color attributes they have been used in edible coating formulations [43–46]. Besides from the gelling property, they have applications to provide stable, longer lasting beer foam, to clarify the wine, also in restructured or re-formed food products [47–51].

In textile industry, alginate is also using for the thickening property for the paste containing the dye, because of its non-reactivity with the dye and easily washed out from the finished products [52]. Conventional pharmaceutical industry has been using alginate and its derivatives as thickening, stabilizing and gel-forming agents, as they have a significant role in controlled-release drug products [46] and has recently been used in the form of nanoparticles (e.g. hydrogels, beads) in drug delivery systems, especially in protein delivery [53–55].