Optimisation of biorefinery production of alginate, fucoidan and laminarin from brown seaweed Durvillaea potatorum

Conventional alginate extraction from brown seaweed uses alkaline conditions to produce soluble sodium alginate as a single product. The objective of this study was to develop and optimise a seaweed biorefinery process to extract polysaccharides of alginate, fucoidan and laminarin from an Australian seaweed species Durvillaea potatorum (giant bull kelp). The addition of acid extraction as the first step and its optimisation have enabled the production of three polysaccharide products of fucoidan and laminarin (F/L), acidic extractable alginate (acid-A1), and alkaline extractable alginate (alkaline-A2). The two alginates have distinctively different biochemical properties compared to the conventional extracted alginate. The optimised acid extraction conditions (0.05 M HCl at 60 °C for 3 h) produced a higher yield (43.57%, w/w) of total polysaccharides (acid-A1, alkaline-A2, and F/L) than that of the conventional processing for single alginate product (38.97%, w/w). This novel biorefinery process yielded polysaccharides with different molecular weight, depending upon the extraction conditions. The molecular weight distribution of acid-A1 was in the size range of 250–500 kDa (93.6%) and <1 kDa (5.9%), alkaline-A2 was in the size range of 250–500 kDa (91.8%) and <1 kDa (8.1%) and F/L was in the size range of 750–1000 kDa (44.3%), 1–250 kDa (48.5%) and <1 kDa (8.8%). The M/G ratio, viscosity and pH solubility range properties of the two alginate products are distinctively different, as well as different from the conventional extracted alginate. The results establish a new biorefinery process incorporating an acid extraction step before alkaline extraction, thereby producing multiple valuable polysaccharide products from a single seaweed feedstock D. potatorum.