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Fucoidan, or fucose-containing sulfated water soluble heteropolysaccharides, is in brown algae cell walls. Fucoidan would provide the cells with structural integrity and protect against dehydration [44, 45]. There are two groups of fucoidan based on the structures, one is composed of -L-fucopyranose (1→3) and the other is comprised of -L-fucopyranose residues (1→4). Sulfation or sulfate esters at 2,3 and/or 4 position are based on the glycosidic linkage and less than 10% are monosaccharides [46]. The exact composition varies according to the types of linkage, substitution, branching, sulfation, species, strain and geographical pattern; the biopolymer contains fucose, galactose, mannose, arabinose, xylose and sulfate. Algal fucoidans are low molecular weight (<30 kDa), formed by depolymerization [44, 47].

Fucus vesiculosus, a brown alga, contains 20% of its dry weight as fucoidans while algal cell walls are made up of 40% (w/w) of fucoidans. Strains commonly employed and used for the extraction of fucoidans are Ulva pertusa, Porphyra haitanensis, Laminaria sp., Sargassum glaucescens, S. horneri etc., as sulfated polysaccharides. The marine macroalgae are classified under mucopolysaccharides of brown macroalgae other than frame and storage polysaccharides [21].

Extraction of fucoidan carried out by several classical or novel methods, like, various chemical methods, water as solvent method, pretreatment, chromoatographic methods, microwave/ultrasound assisted extraction, enzyme extraction, etc. Pretreatments step is a requirement for removing chlorophyll, mannitol, salts and some compounds [48]. There is a long list role played and highlighted by fucoidan in human health applications, due its properties like anticancer, antiviral and anticoagulant. It is also found to stimulate immune systems in many ways like by altering the surface properties of cells or oral intake directly inhibiting, immunomodulating by promoting recovery of cells, acting as anti-inflammatory agents, etc. One assumption is that in fucoidans these bioactivity is because of presences of branched units within the sugar backbone [44].