Biorefinery of the relevant brown algae Saccharina latissima and Ascophyllum nodosum towards novel, sustainable and functional ingredients

This doctoral thesis aims to provide fundamental and practical knowledge on the valorization of brown seaweeds. It has sought to understand the relationship between the structure and functionality of their polysaccharides and proteins, considering their functional, technological and bioactive properties. All this has been approached from a biorefinery perspective, focused on circular economy and sustainability. First, an optimization for extracting valuable compounds from brown seaweeds was carried out using various innovative technologies. A high-pressure pre-treatment of brown seaweeds (Ascophyllum nodosum and Saccharina latissima) to extract alginate was investigated and compared with the conventional extraction method. The purpose was to understand how initial differences in algal cell wall composition and structure affected the extraction of this polysaccharide and its technological properties, such as its ability as emulsifier and gelling agent. Likewise, the extraction of protein-polysaccharide conjugates was examined by sequential application of several extraction methods, as well as their functional properties (water, oil retention activity and emulsifying capacity) and bioactive properties (antioxidant activity and antihypertensive capacity). In these studies, differences were observed in the cell wall architecture of the algae, belonging to different orders, such as Fucales and Laminariales, which directly influenced the extracted compounds and their structural and technological properties. However, despite these differences, the results showed the potential of the extracted compounds as ingredients in the food and pharmaceutical industries. The second section of this thesis explored the valorization of by-products generated during alginate extraction. An exhaustive study of all the fractions and by-products produced in this process was carried out to identify the most promising fractions for valorization. The results showed that solid wastes had the most significant potential due to their physicochemical composition. Therefore, possible strategies to valorize these wastes were suggested, highlighting their high potential as bioactive, texturizing, or nutritional value-added ingredients for food, feed, cosmetic, and pharmaceutical applications. Besides, from this work, sequential and combined extraction by different methods was investigated to recover as much intracellular protein as possible from these solid wastes. It was found that the protein fraction of the extracts contained a high percentage of essential amino acids, adequate functional properties, and an interesting antihypertensive activity. Finally, the third part of this thesis focused on generating knowledge through the structural elucidation of alginate. For this purpose, a rapid method was developed to determine the M/G ratio of alginate, which showed values close to the reference method (1H NMR), demonstrating its accuracy. Overall, this PhD thesis represents a significant advance in generating knowledge and valorizing algal biomass and its residues into high-value compounds. Furthermore, these approaches are potentially applicable to other algal biomasses.

Peer reviewed