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

Abstract

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.