High Digest SCP- Unlocking the Potential of Yeast Protein

Introduction As the global population grows, the demand for high-quality, protein-rich foods will continue to increase, and the aquaculture industry aims to help to fulfill this demand. Feed represents the major cost for farmed fish, and protein ingredients dominate the feed cost. Skretting, in collaboration with the NORCE and SINTEF, plan to explore a sustainable and digestible protein affordable for salmon feed. This new protein source is known as single cell protein (SCP), and refers to dead, non-viable and processed dry cells of microorganisms such as yeast, which grow on different carbon sources. One of the primary challenges is the high cost associated with SCP production. This makes it less economically viable compared to traditional feed ingredients. Additionally, SCP has been found to sometimes exhibit poor digestibility, which can limit its effectiveness and appeal in the aquaculture industry. While SCP holds great potential for enhancing salmon feed, addressing these cost and digestibility issues will be crucial for its future success in aquaculture. Researchers and industry stakeholders are actively exploring ways to overcome these challenges, aiming to make SCP a more attractive and sustainable option for fish farming. Achieved goals During the project, several yeast fermentation experiments were conducted, resulting in dry yeast production that can be used as a protein source in fish feed. SINTEF conducted microscale fermentations to compare different strains and evaluate their nutrient needs, scaling up to 1 liter volumes. Two yeast species, Saccharomyces cerevisiae and Cyberlindnera jadinii, were studied, with C. jadinii recommended for scale-up. High-pressure homogenization and autolysis were tested for cell disruption, with acetic acid proving most effective for C. jadinii. It was also proved that overexpressing lytic enzymes in S. cerevisiae improved autolysis. Skretting established a benchtop fermentation facility, producing up to 200 grams of dry yeast per campaign. The process was scaled up at NORCE, yielding 30 kg of non-autolyzed and 32 kg of autolyzed dry yeast from a 1500 liter fermentation. A biological trial where Atlantic salmon were fed diets with 20% dry yeast showed no significant differences in growth performance or nutrient digestibility compared to a fish meal-based diet. There were no significant differences in fish performance when fish were fed diets including non-autolyzed or autolyzed yeast. Techno-economic analysis indicated that producing dried yeast at scale could result in a viable protein source for salmon. Including autolysis in the production process did not add significant costs but showed no improvement in animal trials, suggesting it might not be necessary. Summary This research project is the result of an agreement between Skretting, SINTEF and NORCE for the development of the new single cell protein product. Today, Skretting predicts that new sustainable sources of feed ingredients will be increasingly important for securing the future production of aquaculture feed and it is then continuously scouting for alternative protein sources for aquaculture feed ingredients. Skretting has embarked upon a series of ambitious, company-wide strategies that aim to drive the aquaculture feeds expansion of the company, while following the principle to contribute to the reduction of the aquaculture industries’ reliance on marine ingredients and ingredients that have a high environmental footprint. The main idea of this project is to prepare for the future by developing yeast biomass into a high-quality protein source affordable to be used in salmon feeds. This can be achieved by development of a new processes for increasing protein digestibility and possibly increasing protein content of the yeast biomass. The knowledge created in this project will be used to scale-up and build an industrial process for the new yeast product.

Outcomes: • Microscale fermentation and scale-up: SINTEF conducted microscale fermentations to compare different production strains and evaluate their carbon sources and nutrient needs. These fermentations were scaled up to 1-liter volumes, achieving higher cell densities and identifying additional growth requirements. • Yeast species evaluation: Two yeast species, Saccharomyces cerevisiae and Cyberlindnera jadinii, were studied for their growth rates, biomass yields, and nutrient demands. C. jadinii was recommended for scale-up. • Cell disruption methods: High-pressure homogenization and accelerated autolysis were tested. Homogenization was effective for both strains. Acetic acid was the most effective inducer for C. jadinii, while ethanol and NaCl were more effective for S. cerevisiae. • Enzyme overexpression for autolysis: Six enzyme constructs were introduced into S. cerevisiae. The effectiveness of these enzymes was verified in microscale fermentations. The results confirmed that the enzymes were produced and active, suggesting that this approach could be used to achieve improved autolysis of the cell walls. • Knowledge transfer and facility establishment: Skretting established a benchtop fermentation facility capable of producing up to 200 grams of dry yeast per campaign • Large-scale fermentations: NORCE performed 15-liter and 1500-liter fermentations, yielding around 30 kg of non-autolyzed dry yeast and 32 kg of autolyzed dry yeast. • Animal trials: Feeds containing 20% dry yeast were tested in Atlantic salmon, showing no significant differences in growth performance compared to the fish meal based reference diet. Protein, fat, and amino acid digestibility were high across all diets. • Health and immunomodulatory effects: Plasma analysis suggested potential effects on mineral metabolism, but no treatment-related effects on the liver or distal intestine were observed. Cell culture assays indicated potential immunomodulatory effects. • Techno-economic analysis: Producing dried yeast at scale could make it a viable protein source for Atlantic salmon. Including autolysis did not add significant costs to production, but animal trials showed no improvement with autolyzed yeast. Impact: The project demonstrated advancements in optimizing yeast protein production for salmon feed. By successfully scaling up fermentation processes and evaluating various cell disruption methods, the project provided valuable insights into the feasibility and economic viability of using yeast as a protein source in aquaculture feed. The collaboration between industry and academic institutions facilitated knowledge transfer and innovation, paving the way for more sustainable and cost-effective solutions in fish farming. Despite the lack of improvement with autolyzed yeast in animal trials, the overall findings highlight the potential of dried yeast as a promising alternative to traditional fishmeal, contributing to the sustainability and efficiency of aquaculture.

This research project is the result of an agreement between Skretting, SINTEF and NORCE for the development of the new single cell protein product. Today, Skretting predicts that new sustainable sources of feed ingredients will be increasingly important for securing the future production of aquaculture feed and it is then continuously scouting for alternative protein sources for aquaculture feed ingredients. Skretting has embarked upon a series of ambitious, company-wide strategies that aim to drive the aquaculture feeds expansion of the company, while following the principle to contribute to the reduction of the aquaculture industries’ reliance on marine ingredients and ingredients that have a high environmental footprint. The main idea of this project is to prepare for the future by developing yeast biomass into a high-quality protein source affordable to be used in salmon feeds. This can be achieved by development of a new processes for increasing protein digestibility and possibly increasing protein content of the yeast biomass. The knowledge created in this project will be used to scale-up and build an industrial process for the new yeast product.