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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 Fucus serratus	Fucose–sulfate–acetate	[66, 67]
Laminaria angustata	Fucose–galactose–sulfate	[68]
Himanthalia lorea	Fucose, xylose, sulfate	[69]
Adenocytis utricularis	Fucose, galactose, mannose, sulfate	[70]

Fucoidan, like many seaweeds, has been consumed for a long time in Asian countries, and also used as a nutraceutical and cosmeceutical all around the world. Due to the biological activities, such as anticoagulant, antithrombotic, antitumor, antivirus, anti-proliferative, anti-inflammatory etc. their application interest is high in biological and life sciences. One of the application areas is as a dietary supplement as capsules and a powder supplement for beverages to enhance the immune system. In food industry, these sulfated polysaccharidecontained seaweeds, which have a prebiotic property, are used as a food supplementary for nutritional and functional food formulation. Anticoagulant, antimicrobial and anti-biofilm activities of fucoidans are used in dental applications. The ability to absorb directly by the human skin, as a cosmeceutical in topical cosmetics, fucoidans are used for whitening, preserving moisture, removing freckles in cosmetic industry [11, 60, 71–77].