Production of hybrid protein-polysaccharide extracts from Ulva spp. seaweed with potential as food ingredients

This work explores the production of hybrid protein-polysaccharide extracts from the green seaweed Ulva spp. with potential for food-related applications by means of a pH-shifting method combined by a pre-treatment step. The optimum solubilization (pH = 12) and precipitation (pH = 3) conditions were first determined to maximize protein extraction; however, the extraction yield (21%) was still quite low. The application of a short (5 min) ultrasound pre-treatment prior to the solubilization step was seen to effectively disrupt the cell walls and facilitate protein release, hence increased up to 2-fold the protein extraction yields, and achieving a maximum of 47%. Interestingly, preservation of the seaweed biomass by freeze-drying caused a collapse in the cell wall structure, making protein extraction more difficult and giving rise to lower extraction yields (3-fold lower as compared to the frozen seaweed). The obtained extracts were composed mostly of proteins (21-40%) and carbohydrates (29-51%). The most abundant amino acids (AA) were alanine, glycine, aspartic acid and glutamic acid and the essential AA content accounted for 37-41%, superior to other proteins of non-animal origin. On the other hand, ulvans were the major polysaccharides found in the extracts, which may confer them interesting rheological and bioactive properties. As an important point for their application in the food industry, the low levels of metals and inorganic compounds in the extracts suggested low risk for human consumption. These results evidence the potential of Ulva spp. as a source of proteins with high interest for the production of novel food products based on alternative proteins.