The New Zealand government has recently allowed the harvest of Undaria pinnatifida (U. pinnatifida), an invasive alga, from human-made structures as it has potential commercial value. U. pinnatifida is a rich source of fucoidan, which has anticancer effects and can act as an antioxidant and anticancer agent. With the vast amounts of seaweed resources available in New Zealand, it was important to develop methods for extraction and purification of fucoidan from U. pinnatifida in order to further investigate its beneficial pharmaceutical properties.

The first part of this thesis involved the study of different methods of fucoidan extraction. This was followed by characterization of fractionated fucoidan, and investigation of its antioxidant activity. U. pinnatifida was harvested from mussel farms in the Marlborough Sounds, New Zealand. Three different fucoidan extraction techniques that included calcium chloride, hydrochloric acid and water extraction were used. The calcium chloride extraction gave the best quality fucoidan in terms of its yield, sulphate and fucose content while extraction with deionized water gave the least protein contamination out of the three methods. The calcium chloride extraction method was subsequently used for the extraction of fucoidan. It was also found that the sporophyll part of the alga contained more fucoidan than the blade.

As algae are subject to seasonal variations, monthly changes in the fucoidan content and composition of New Zealand U. pinnatifida were investigated. Crude fucoidan was extracted from the sporophyll of U. pinnatifida collected from July to October (from three different mussel farms). Fucoidan content increased significantly from July to September (25.4-26.3 to 57.3-70.0% dry weight) as sporulation occurred. At the same time, sulphate content increased significantly from 5.6-5.9 to 13.7-16.4% dry weight in sporophyll-derived fucoidan, and uronic acid increased from 1.4-2.1 to 2.1-3.6% dry weight in blade-derived fucoidan. These changes were probably related to the alga maturity and sporophyll synthesis.

The antioxidant activities of the fucoidan fractions were further investigated. Prior to this, fucoidan was separated into different fractions by means of ion-exchange chromatography. The fractions were tested for antioxidant activity using the DPPH and CUPRAC assays. Sulphate content in the three fractions isolated, F1, F2 and F3, were 6.96, 22.78 and 25.19%, respectively. The sulphate to fucose ratio also increased from F1 to F3 while the fucoidan fractions showed an increase in reducing ability towards both DPPH radicals and copper ions indicating a relationship between sulphate:fucose ratio with antioxidant activity. The molecular weight of the fractions was also determined. Crude fucoidan had the highest molecular mass of 1350 KDa with the strongest reducing ability. F1 had a molecular weight of 1067 KDa and the last two fractions, F2 and F3, had a mass of around 840 KDa. Results showed that the chemical composition and molecular weight greatly influenced the degree of bioactivity in fucoidan.