Alternative Proteins Magazine ISSUE FOCUS October 2025 33 idues. Through fermentation, enzymatic hydrolysis, pyrolysis and other bioprocessing methods, industrial side-streams can be converted into high-value nutrition for livestock production and aquaculture. Rather than drawing on new land or ocean resources, they close the loop by transforming existing outputs into proteins, oils, and functional additives that can be incorporated into animal feed. WHAT ARE THE POTENTIAL CIRCULAR FEED SOLUTIONS? Single-cell proteins (SCPs) Single-cell proteins are ingredients produced by cultivating microbes, including bacteria, yeasts, or microalgae, on carbon-rich feedstocks. They can be processed to generate concentrated protein meals with balanced amino acids, or oils rich in omega-3 fatty acids, and are positioned as partial replacements for fishmeal and fish oil in diets for salmon and shrimp. Use cases are also emerging in piglet feeds and in pet food. In principle, SCPs can be cultivated on a wide range of side-streams, including waste gases such as biogenic methane, nutrient-rich wastewaters such as aquaculture effluents, lignocellulosic biomass such as woody agricultural residues, and food industry by-products like whey permeate. Circularity is already being demonstrated through several established pathways. Yeast SCPs produced on whey from cheese manufacturing and on molasses from sugar refining are already widely incorporated into animal feeds, demonstrating well-established circular pathways. Distillery residues are also being commercialised as substrates for cultivating microalgae rich in omega-3s, showing how nutrient-dense side streams can be upgraded into high-value ingredients, though adoption remains at an earlier stage. In parallel, bacterial SCPs produced on natural gas are entering commercial markets, where natural gas could eventually be replaced by biogenic methane as the feedstock. Research is also exploring additional lower-value substrates with greater circularity potential, including lignocellulosic residues, aquaculture effluents, and other nutrient-rich wastewaters. These approaches remain experimental but illustrate the scope for SCPs to redirect heavily underutilised outputs back into the food system. Regulatory frameworks are adapting, with approvals in the EU, US, and Japan showing that microbial proteins can be authorised when substrates are clearly defined and demonstrably safe. However, commercial production is concentrated on relatively clean co-products such as whey and molasses, or on defined inputs such as natural gas. Expanding the use of underutilised waste streams such as industrial effluents and wastewaters will require regulatory adaptation, new infrastructure to link residues with fermentation plants, and further cost reductions in large-scale bioprocessing. Photo: Freepik
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