PhD defence about the potential of using brewer’s spent grain in fish feed

Fishmeal and soybean meal constitute the most common protein sources in feed used in aquaculture. Both ingredients are characterized by a high content of protein and an ideal amino acid composition. Yet, increasing demands and competition for resources have driven up the prices of these protein sources which has increased the need for implementing sustainable alternatives. 

PhD Student Freja Manø Busk Karlsen, DTU Aqua, has investigated whether brewer’s spent grain can be valorized to make it suitable as a protein source in fish feed. Brewer’s spent grain is the most abundant by-product from beer production and represents a potential protein source for feed in aquaculture due to its low market value, immense availability, and an initial protein content of 20-30% dry matter. 

However, inclusion of unrefined brewer’s spent grain in aquafeeds is hindered by its high levels of lignin, cellulose and hemicellulose which impair the protein digestion in fish. Furthermore, the protein content of unrefined spent grain is too low to meet the protein requirement of most fish species. 

Freja Manø Busk Karlsen has evaluated different refinement strategies for brewer’s spent grain that may allow for its incorporation in aquafeeds. She has used different biotechnological and chemical methods, including protein extraction and microbial fermentation, to remove or modify lignin, cellulose and hemicellulose and increase the protein content of the spent grain. 

In her thesis, Freja Manø Busk Karlsen concludes that her experiments show that it is possible to develop promising methods for processing brewer’s spent grain into a product that can be used in aquafeeds. Next step would be to optimize and upscale the methods to make them applicable at an industrial scale.  

About the defence

Freja Manø Busk Karlsen, DTU Aqua, will defend her PhD thesis "Evaluation of chemical and biological refinement strategies for transforming brewer’s spent grain into a high-quality protein source for fish feed” on Tuesday 20 December 2022, 13:00 on Zoom and at DTU Aqua in Hirtshals (find link and adress below).

Supervisors

• Principal supervisor: Associate Professor Peter Vilhelm Skov, DTU Aqua
• Co-supervisor: Senior Researcher Ivar Lund, DTU Aqua

Examiners

• Senior Researcher Anne Johanne Tang Dalsgaard, DTU Aqua (chair)
• Senior Research Scientist Elisabete Coelho, University of Aveiro, Portugal
• Senior Research Scientist Florbela Carvalheiro, National Laboratory of Energy and Geology, Portugal

Chairperson at defence

• Researcher Carlos Letelier-Gordo, DTU Aqua

Learn more

A copy of the thesis is available for reading at DTU Aqua. Please contact PhD Secretary Karin Stubgaard, stub@aqua.dtu.dk