Abstract
Fucoxanthin (Fx) is the primary carotenoid found in some macro and microalgae, with light harvesting and photoprotective functions. Fx has attracted considerable attention in the pharmaceutical, food, feed, andcosmetic industries, due to its potential for preventing disease. Fx contents vary significantly between algae species and depend on environmental conditions and season. Stress induction has been reported as a technique for enhancing carotenoids in algae; however, not all studies find a positive correlation between stress exposure and Fx production, so this topic needs clarification. This thesis aims to investigate the potential of selected seaweeds and diatom species collected in New Zealand as Fx sources. The second aim was to study the correlation between oxidative stress and Fx production by using antioxidant enzyme activities and oxidative damage biomarkers in seaweed and diatom samples. The final aim was to investigate the relationship between the Fx content and the bioprotective capacity of the seaweed digest. Chapter 4 examined the effect of seasonal variation in Fx content and antioxidant status of nine brown seaweed species collected in different months from Brighton beach, Otago, New Zealand. The results showed a negative relationship between Fx content and high light conditions. Hence, the best time for harvesting seaweed with the maximum Fx is months with lower light levels (the end of winter and early spring in Brighton beach). Macrocystis pyrifera had the highest Fx concentration (0.78 mg g−1 DW in September) and is, therefore, the most promising species from a commercial viewpoint. Fx content and oxidative damage biomarkers showed a negative correlation, and a maximum level of oxidative damage biomarkers was observed in January when the Fx content was decreased. Chapter 5 examined the effect of light intensity and quality, and temperature on the Fx content and antioxidant status of the two marine diatoms Coscinodiscus radiatus and Cylindrotheca sp. The maximum Fx concentrations were 3.78 and 3.76 (mg g−1 DW), found in Cylindrotheca sp. grown at 12 °C and a light intensity of 12.5 μmol m−2 s−1 in the cool white and lumoflor treatments, respectively. Blue LED lights increased the Fx content of this species by 70.2% compared to the lumoflor reference light. As with the seaweed species, the correlation between oxidative stress and Fx production was negative in Cylindrotheca sp., and no correlation was observed in C. radiatus, indicating that stress induction strategies may not be an appropriate treatment for increasing Fx accumulation. The bioprotective capacities of six seaweed species with different concentrations of Fx (low-medium and high) on human intestinal Caco-2 cells exposed to hydrogen peroxide (H2O2)-induced oxidative stress were investigated in chapter 6. The result showed that seaweed digests could protect Caco-2 cells from oxidative stress, and there is a direct correlation between Fx content and the bioprotective capacities of seaweed digest. The highest protection against H2O2 was observed in digests of Cystophora scalaris and Macrocystis pyrifera, which contain high Fx concentrations. This thesis highlight the importance of considering species-specific differences and environmental /cultural conditions on Fx production in seaweeds and diatoms. The brown seaweed Macrocystis pyrifera and the diatom Cylindrotheca sp. produced more Fx than other species studied here and therefore show potential as a source for commercial Fx production. Moreover, a positive correlation between Fx content and bioprotective capacities of seaweed digests suggests that Fx concentration and factors that change Fx, such as seasonal variation or light treatment, should be addressed when investigating the antioxidant properties of brown seaweeds and diatom species.