Enrichment processes for the production of high-protein feed from the green seaweed Ulva ohnoi

New sources of protein are required to supplement current animal- and plant-protein. Here, we quantify the quality and yield of four protein-enriched biomass products (PEB-I to PEB-IV) and a protein isolate (PI) from the commercially produced seaweed Ulva ohnoi. To decrease the content of components of the biomass that may be undesirable in feed, we have developed a multi-step biorefinery process to produce salt, sulfated polysaccharides (ulvan), and protein products. The content of protein increased from 22.2 ± 0.4% dry weight (dw) in unprocessed biomass to between 39.5 ± 1.9% in the PEB-IV and 45.5 ± 0.8% in the PI. The quality (mol % of essential amino acids [EAA]) of the protein products was similar to soybean meal, with 41.6 ± 0.1 and 43.4 ± 0.1 mol% EAA in PEB-I and the PI, respectively. The yield of PEB products varied from 16.3 ± 0.8 to 41.0 ± 0.8% of the unprocessed biomass, with PEB-I > PEB-II = PEB-III > PEB-IV. The yield of all PEB products was more than four-fold greater than the PI (4.4%). Conservatively, the biomass productivity of U. ohnoi is 70 t dw ha−1 year−1 resulting in a projected annual production (t dw ha−1 year−1 ) of 24 t of salt, 4.3 t of ulvan, 29 t of PEB-I, or 3.2 t of PI using this biorefinery process. With nine-fold higher yield, and a protein product of similar quality to the PI, we recommend producing PEB-I by concentrating the protein through the extraction of salt and ulvan over the extraction of a PI for the development of food and feed products.