Extraction, separation and purification of polyphenols, polysaccharides and pigments from British seaweed for high-value applications

Seaweed represents a valuable, underused sustainable resource. Current investment in seaweed farming will provide large quantities of biomaterial for a range of applications. The major focus of this thesis is on a class of polyphenols known as phlorotannin, of interest for their antioxidant and biomedical applications. Seaweed polyphenols have strong radical scavenging properties. Whilst there are many reported extraction methods for phlorotannin, it was not clear how different solvent systems affect the antioxidant capacity of the phlorotannin extracted. This work represents the first comparable study of its kind in which phlorotannin was isolated from seaweed using several extraction solvents and the antioxidant capacity evaluated using the DPPH radical scavenging assay. The structural profile and radical scavenging capacity of the phlorotannin did not change between the extracts. Water and ethanol-water mixtures were found to be the most suitable solvents for large-scale extraction of phlorotannin. The first study on the seasonal variation in phenolic content of industrially farmed seaweed grown on ropes was performed. The phenolic content of the two species studied, Fucus vesiculosus and Ascophyllum nodosum varied between 4-9 % dry mass and showed variation that could be attributed to the growth cycle of the seaweed. This demonstrates that the phenolic content is high enough all year round to allow viable extraction of phlorotannin. The radical scavenging capacity of Fucus vesiculosus was found to be 12% greater than Ascophyllum Nodosum. Given that the majority of farmed seaweed is destined for biofuel production, it was of interest to consider whether phlorotannin could be extracted during biofuel processing. A potential pre-treatment method proposed for processing seaweed for biofuel is the use of superheated water extraction. Phlorotannin was then extracted from superheated water, without impacting the radical scavenging capacity, demonstrating the potential for it to be integrated into future processing techniques.