New study: Stale bread can be converted into sustainable fish feed

The results show that the ingredient can contribute to both improved growth in farmed fish and reduced environmental impact.

Every year, large quantities of bread are discarded despite still containing valuable nutrients. In his research project, doctoral student Vahid Abbasi developed a method in which stale bread is fermented using fungi and transformed into a new ingredient, known as mycelium-bread, for use in fish feed.

"We wanted to investigate whether a major waste stream from the food sector could be transformed into a valuable resource for aquaculture. The results show that stale bread can be used to produce a nutrient-rich ingredient for fish feed production, while at the same time affecting environmental impact", explained Vahid Abbasi.

Through the fermentation process, the protein content of the bread increased from approximately 12 to 35 per cent. The process also added enzymes, antioxidants, and other bioactive substances that can support health and growth in fish, in this study the farming of rainbow trout.

The results showed that fish fed with feed containing mycelium bread grew better and utilised the feed more efficiently than fish fed with conventional feed. The quality of fillets of fish fed by mycelium-bread showed satisfied colour and antioxidants.

The entire chain was evaluated

The project included not only biological and nutritional studies but also analyses of environmental impact and economics. The raw material was sourced from a local supermarket, ICA City Knalleland in Borås, and the entire system was evaluated, from bread waste to the production of rainbow trout.

"An important part of the project was to investigate the entire value chain. Therefore, we combined laboratory studies and fish-farming trials with environmental and cost analyses to assess whether the solution is sustainable in practice."

The environmental analyses showed that the use of mycelium-bread in fish feed can reduce climate impact, land use, and eutrophication effects compared with conventional feed systems. Climate impact was reduced by up to 31 per cent, while land use was reduced by up to 43 per cent.

Contribution to a circular bioeconomy

Interest in alternative protein sources for aquaculture is increasing, and research is under way internationally into alternative protein resources including insects, algae, bacteria, yeast, and fungal products. Vahid Abbasi’s research contributes knowledge on how food waste can be transformed into a functional raw material for fish feed.

In the long term, the same type of fermentation technology could also be used for other waste streams from the food industry and agriculture.

The research project is linked to several of the United Nations Sustainable Development Goals, including responsible consumption and production, zero hunger, life below water, industry, innovation and infrastructure, and climate action.

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Vahid Abbasi defended his doctoral thesis on 18 September at the University of Borås.

Read the thesis Mycelium-Bread Feed Ingredient for a More Sustainable Aquaculture

Main supervisor: Amir Mahboubi Soufiani, Associate Professor

Research area: Resource Recovery