Technology comparison for sequential extraction of fucoidan and sodium alginate from Ascophyllum nodosum using a glycerol and choline chloride solvent

Brown algae are the main source of polysaccharides such as fucoidan and alginate, which can be used to develop a wide range of bioactive and polymer materials. In this study, sodium alginate and fucoidan were sequentially extracted using thermochemical, microwave, ultrasonic and sub critical water treatments of untreated and ethanol-pre-treated brown algae, Ascophyllum nodosum. Extraction was achieved using a solvent solution consisting of a 1:2 M ratio of choline chloride to glycerol (ChGl) in 70% water (w/w) for initial treatment to extract fucoidan, followed by Na₂CO₃ treatments for alginate extraction. Microwave extraction was shown to be the most advantageous treatment for alginate extraction, with the greatest biomass extracted (46.2%), purity (33.43% combined mannuronic and guluronic acid content), and molecular weight, whilst indicating an increased bioactive capacity associated with co-extracted polyphenolic content. However, using ChGl for fucoidan extraction resulted in a large fraction of the solvent remaining within the fucoidan. This is evidenced by up to 39% of the fucoidan consisting of glycerol. The extracted alginate has the potential as a bioactive polysaccharide, whilst the fucoidan would require further purification.