Phlorotannins, current and future implications for the seaweed industry
Quéguineur, Benoît Louis Erwan
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This thesis focuses on phenolic compounds from brown macroalgae, named phlorotannins, and their current and future implication in the seaweed industry. After an examination of the phlorotannins content and in vitro antioxidant activity in 9 species of the West coast of Ireland, we selected Ascophyllum nodosum and Himanthalia elongata for their current uses in the seaweed industry and their traditional uses as food, respectively. The industrial process of Ascophyllum greatly reduced the total phenolic content and activity of phlorotannins, and therefore we provide some guidance on the best practices in their industrial extraction. In an attempt to facilitate standardisation of studies on phlorotannins, the monomer, phloroglucinol was chosen. Phloroglucinol exhibited antioxidant activities in non-biological assays, but was not a suitable standard in routine laboratory analysis. Moreover, high concentrations of phloroglucinol failed to protect against oxidative damages in biological assays. In order to assess the potential benefits of phlorotannins-rich extracts from Ascophyllum and Himanthalia for human food purposes, we performed various assays on biomarkers of cellular oxidative stress in cultured cell lines after a simulated digestion of the extracts. Our results demonstrate that the phlorotannins-rich extracts from Ascophyllum and Himanthalia have the ability to protect human HepG2 cells against an oxidative challenge by reducing free radical activity and enhancing antioxidant defences. In an attempt to link the structure of phlorotannins with their function, we developed an LC-MS method and suggested a molecular formula for various phlorotannins, allowing us to compare theoretical molecular formula with the observed mass spectra, and obtain a profile of the phlorotannins in various matrixes, which is especially useful in the food industry. Finally, large-scale cultivation of Phaeophyceae and the biorefinery concept were also discussed as a potential way to improve economical feasibility of biofuel from macroalgae. However, the scarcity of data and uncertainties about economics impede the development of a realistic study. Overall, This thesis provides experimental evidence that seaweed and seaweed-derived products enriched in phlorotannins may contribute to the dietary protection against diseases in which oxidative stress is implicated. The results support the industry in the move towards functional uses of phlorotannins. Phlorotannins can be valuable to the seaweed industry and its future challenges to come.
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