The nutritional value of seaweed for farm animals is, among other things, determined by the content of nutrients such as proteins, carbohydrates, and fats. This project investigated whether it is possibleto improve the digestibility and thus the accessibility of the seaweed components by means of biorefinery – in this case by mechanic and enzymatic treatment. Furthermore, it was investigated whether it is possible to isolate and separate peptides and amino acids (the building blocks of proteins). Animal studies with broilers were performed by Wageningen Livestock Research to investigate the effect of seaweed, with and without enzymatic treatment, on growth, feed conversion,digestibility and health (not reported here).The project was carried out together with Olmix. Olmix harvests green seaweed Ulva from the Atlantic Ocean off the coast of Brittany. The harvested seaweeds are pressed by Olmix, after which the liquid fraction is used for the production of a biostimulant (Seamel). In this project it was investigated whether it has added value to use the remaining solid seaweed fraction as an ingredient to animal feed, as such or after processing. The project investigated the use of enzymes and mechanical pretreatment to break down cell wall structures. Enzymes were selected based on chemical structures that occur in the cell wall; enzymes that break down carbohydrates into sugars (carbohydrases) and enzymes that break down proteins into peptides or amino acids (proteases). All the experiments were performed using Ulva that had been pressed once (Ulva Marc 1) and frozen afterwards, which was kindly provided by Olmix.For Ulva Marc 1 mechanical pre-treatment did not have an additional beneficial effect on dry matter and peptide release to the liquid fraction. It is recommended to test the effect of mechanical pre-treatment on fresh seaweed. The cells in fresh seaweed have a higher mechanical strength (turgor)and will be more vulnerable to mechanical disruption.The target dry matter release of >80% (as an indication for digestibility) and peptide release of >80%were not reached using enzymatic treatment (carbohydrases + proteases). Of all tested treatments the protease alcalase (60°C, pH as is) was the most effective (dry matter release ~53% DW, peptiderelease ~58%). A new process is proposed for obtaining an enriched protein fraction, in which the protease treatment is performed on the solid fraction obtained after carbohydrase treatment. This leads to selective release of peptides and a liquid fraction with a peptide content of 45% (N/DW) and apeptide recovery of 52%. The targeted peptide content of 45% (N/DW) can be reached in this manner.To further increase digestibility and peptide release, it is necessary to use enzymes that are even better able to break down the complex structures in seaweed cell walls. The enzymes used in this project come from organisms that can break down complex carbohydrates in land plants, such as cellulose and hemicellulose. However, seaweed contains other types of carbohydrates that require other types of enzymes that are not yet on the market. Such enzymes do exist and are present in fungi that naturally grow on seaweed: seaweed biomass is broken down in the marine environment.Together with NIOZ and Westerdijk Institute, a new project was started in 2022, aiming at isolating specific enzymes from marine fungi that are able to break down the cell walls in seaweeds. This project is part of the NWO program “From Sea to Society”.