Sequential extraction and fractionation of four polysaccharides from cultivated brown algae Saccharina latissima and Alaria esculenta

Norway has a well-established seaweed industry based on extraction of alginates from wild harvested brown algae, Laminaria hyperborea (LH). However, further expansion of wild harvest is limited, and cultivated seaweed can contribute to meeting increasing demands for high value compounds in an environmentally sustainable manner. Herein, an integrated process for retrieving alginate, fucoidan, laminarin and cellulose was established for cultivated Saccharina latissima (SL) and Alaria esculenta (AE). Focus was to develop a process using mild chemical methods that do not compromise the molecular weights (MW) of the polysaccharides, particularly with respect to alginate. Response surface methodology (RSM) was applied to optimize the yield of fucoidan and laminarin and assess the effect of the applied extraction parameters: pH, temperature, and time, on the MW of subsequently extracted alginates. RSM confirmed that high yields of fucoidan and laminarin can be achieved while maintaining the alginate MW. Optimized conditions were applied in a pilot scale process, where all four polysaccharides were extracted. Purity (ranging from 40 up to 98 %) and composition of the components were evaluated combining several analytical techniques. Total yields of the polysaccharides were 23.4 % of the entering dry biomass from SL and 26.3 % from AE, representing around 55 % of the estimated maximal yield. However, all extractions were not optimized, and a mass balance revealed that <75 % more alginates could have been collected. The process can be adapted to simultaneously collect mannitol, which accounted for <15 % of the dry weight. The alginates were further examined by producing hydrogels, showing that the gel properties are comparable to alginates from LH fronds. The study demonstrated that mild chemical extraction techniques can be combined to extract all four polysaccharides from SL and AE, providing a foundation for a multicomponent biorefinery using cultivated brown algae.