Many types of brown seaweeds (Phaeophyceae) are available on
the Spanish coasts, such as Laminaria digitata and Ascophyllum
nodosum, both of which contain polysaccharides such as laminaran,
fucoidan and alginate. Alginates are normally present in algae cell
walls as insoluble calcium or magnesium salts, being responsible
for their strong, flexible tissue. Industrial alginate extraction is
basically divided into a first acid pre-treatment to convert insoluble
alginate salts into alginic acid, followed by an alkaline extraction to
convert insoluble alginic acid into soluble sodium alginate, which
passes into the aqueous phase; further alginate isolation requires
solid/liquid separation, precipitation and drying. Depending on the
species, the extraction can take several hours and repetitions
(Vauchel et al., 2009), and it has been demonstrated that after 2 h
alginates start depolymerizing