Pilot-scale protein extraction of green seaweed (Ulva spp.) whole biomass and pulp – Investigating biochemical composition and protein digestibility in a rat trial

Ulva, a green seaweed, is gaining interest for food applications due to its high content of protein and well-balanced amino acid composition. However, protein extraction is necessary to reduce the ash content and increase the protein digestibility. In this study, pilot scale protein extraction from Ulva was obtained by a mechanical fractionation, creating a pulp and a juice. A second extraction of protein from the pulp was obtain after a pH shift to 8.5 and the proteins from the two juices were acid precipitated with and without a clearing step (decanting of the resulting juice). Extraction of protein from the whole biomass resulted in a higher content of crude protein (CP) (31.8–37.6 %), essential amino acids (EAA) (42.4 %), and nitrogen digestibility (59.5–63.3 %) than from the pulp (26.1–29.5 % CP of DM, 40.1–40.3 % EAA, 47.4±3.6 % nitrogen digestibility). Including the clearing step increased the protein content but not the nitrogen digestibility (59.5±4.8 % with clearing vs 63.3±3.4 % without). None of the extractions induced cross-linked AA of concern. However, elements were concentrated, where concentrations of arsenic might limit the utilization in food. These results indicate that upscaling of the protein extraction from Ulva is promising, but further improvement regarding toxic elements and protein digestibility is necessary.