forms. For the refined carrageenan, the carrageenan is precipitated with alcohol and in the second method (semi-refined carrageenan), it is dissolved in an alkali solution, like potassium chloride to form a strong gel which is then dried [35, 36].
Protein reactivity of carrageenan is an important property to be discussed for which application will be used of. Carrageenan is negatively charged, which means they are able to combine with positively charged particles, for example positively charged proteins, as in the three-dimensional gel network with the protein in milk (casein). Their main applications are in the food industry, especially in dairy products. As an emulsifier, carrageenan addition is necessary in dairy products to prevent separation of whey in cheese and ice creams and coffee whiteners. Carrageenan’s interactions with galactomannans are an important reason that it finds use in the production of fruit sorbet, poultry and meat products. Also, in pet foods semi-refined carrageenan are using for their gel forming structure. Carrageenan is found application areas in the structure of air freshener gels and toothpastes; also, biotechnological applications of carrageenan has been demonstrated as a medium for immobilizing enzymes or whole cells [32–39].
Figure 4.2 Chemical structure of carrageenan.
4.1.3 Alginate (Alginic Acid, Algin)
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].
4.1.4 Fucoidan
Fucoidans, also named as fucan or fucosan, are fucose-containing sulfated polysaccharides contain l-fucose and sulfate esters and placed in intracellular tissues of brown seaweeds [56]. Like other seaweed polysaccharides, fucoidans are also differ in structure among the species. Seaweed species which can have fucoidans are Laminaria, Fucus, Macrocystis and Himanthalia [56–60]. Some other species which have been studied in literature to obtain fucoidans are Cladosiphan, Adenocystis, Ascophyllum and Sargassum [56, 60–63]. Fucus vesiculosus is the most known fucoidan source, its chemical composition is relatively simple (Figure 4.5) as generally consists of, fucose linked sulfate groups, α-(1–3)-l-fucopyranose. Among the species the chemical composition is becoming complex where they contain various monosaccharides in small amounts (Table 4.1).
The earlier fucoidan extraction is based on hydrolyzing the non-fucoidan structure with acetic acid or hydrochloric acid. For the last seventy years many modifications were studied on the extraction and purification methodology for fucoidans [56, 60–62, 69, 70]. These studies obtained fucoidan with α-(1–3)-l-fucopyranosyls or α-(1–4)-l-fucopyranosyl residues which are sulfate substitutes and with different monosaccharides-linked structures. As Ale et al. [60] demonstrated the term “fucoidan” is a name of a wide family of fucosecontaining sulfated polysaccharides and corrected the name “fucoidan” as fucosecontaining sulfated polysaccharides. However, despite the different structured-last products obtained after the extraction, the earlier acidic extraction method with temperature elevation is still the preferred nowadays.
Figure 4.5 Fucoidan structure.
Table 4.1 Composition of fucoidans from different seaweed species.
| Species | Composition | References |
|---|---|---|
| Cladosiphon okamuranus | Fucose, glucose, urinic acid, sulfate | [62] |
| Fucus vesiculosus | Fucose, sulfate | [64, 65] |
| Macrocysstis pyrifera | Fucose–galactose, sulfate | [64] |
|
Fucus evanescens
|
