Polysaccharides from red and green seaweed : Extraction, characterisation and applications

Sammanfattning: Cultivation of seaweed has been conducted for centuries in Asia, but is largely undeveloped in Sweden even though there is potential for this industry. Seaweed offers benefits compared with land-based biomass cultivation. Cultivation of seaweed does not occupy land areas and does not require irrigation or fertilizers, which contributes to avoid coastal eutrophication. Seaweed contains polysaccharides and is a potential feedstock for production of bio-based materials. The aim of this thesis was to extract and map the chemical structure of polysaccharides from macroalgae collected along the Swedish west coast. Another aim was to use the extracted polysaccharides to design new bio-based materials. In the first study, a fractionation strategy was developed to sequentially extract proteins and polysaccharides from the red macroalgae Porphyra. The fractionation yielded one protein fraction and three polysaccharide fractions. In the second study, the polysaccharide ulvan was extracted from two species of the green macroalgae Ulva. Two different extraction protocols were tested. Parameters such as the yield, molecular weight and monosaccharide composition of the extracted ulvan depended on the extraction protocol and the specie of Ulva used for the extraction. In the third study, ulvan extracted from Ulva was used to prepare hydrogels, which were tested as an adsorbent for heavy metals and the dye methylene blue. Ulvan was first oxidized into ulvan dialdehyde and mixed with gelatin, yielding hydrogels. The hydrogels showed high water-uptake capacity and a high adsorption capacity of methylene blue. The hydrogels also adsorbed heavy metal ions. In the fourth study, cellulose was extracted from Ulva and further used to prepare cellulose nanofibrils (CNF). Chemical analysis of the CNF showed that it contains mostly cellulose but also a smaller amount of a xylose-glucose copolymer. The CNF had a crystallinity index of 48% and showed typical peaks for the cellulose I allomorph.