Could fish by-products improve plant-based food?

In Norway, fillets of cod and salmon are popular foods. But on the way from whole fish to fillet, up to 60% of the fish is discarded. These so-called side streams are currently used mainly for animal feed, fertiliser or biofuel. Since they contain valuable proteins, minerals and healthy fatty acids, they are also well suited as food. At the same time, many people want to cut down on meat, but plant-based products often lack important nutrients.

This PhD project therefore investigated whether marine side streams combined with plant proteins could be developed into nutritious, more sustainable food products. The aim was to examine how such ingredients affected product quality, with particular emphasis on texture.

Liv Helene Sickel of Nofima defended her PhD thesis at the University of Bergen in Norway, on 11 September 2026. The title of her thesis is “Marine side streams in high-moisture extrusion cooking”.

Softer texture with fish

Salmon- and cod-based ingredients from side streams were combined with pea protein and wheat gluten and processed using extrusion, a process that can produce a meat-like, fibrous texture. The study showed that a higher proportion of fish resulted in a softer texture, although the effect depended on both the type of ingredient and the processing conditions. In a salmon protein hydrolysate, the effect was explained by the processing method: during processing, the proteins had been broken down into small components (amino acids and small peptides) with properties similar to water molecules, giving them an effect comparable to adding water to a dough.

This suggests that water can be partly replaced with protein concentrate without significantly changing the texture, while increasing the nutritional value. When cod protein powder was added, a softer texture was likewise observed. A higher processing temperature compensated for this, so that products containing 25% fish had a texture similar to that of a plant-based reference sample.

The findings show that ingredients based on cod and salmon side streams have great potential in familiar food products. Combined with plant-based protein sources, they can produce products with high nutritional value, while making better use of marine resources.

Greater resource utilisation

In her PhD work, Liv Helene Sickel has worked on extensive processing of the fish raw material. Why did she want to research this topic?

“Ideologically, my choice comes down to resource utilisation. By creating opportunities to use more protein from fish we have already harvested, we could give the fishing industry an incentive to take better care of the raw material and use it in food. These side streams consist of valuable marine nutrients that can bring positive health benefits”, says Sickel.

Liv Helene Kolberg Sickel, age 29, holds a master’s degree in physical chemistry from the University of Bergen (2022). Her PhD, carried out at the food research institute Nofima and UiB, is part of the project “HybridFoods: Novel texturized hybrid foods targeting future sustainability and health challenges in the Anthropocene”. Her supervisors has been Tor Andreas Samuelsen and Åge Oterhals (Nofima), together with Tore Skodvin (UiB) and Atze van der Goot (Wageningen University, the Netherlands).

Main findings - Side streams from the fish industry, such as heads, backbones and skin, can be used to make plant-based food products more nutritious, thereby increasing the value of raw material that today largely goes to animal feed, biofuel and fertiliser. - The PhD thesis shows that fish-based ingredients can be combined with plant proteins and processed using extrusion to give products a better structure, texture and mouthfeel. - The research has identified which mixing ratios and processing conditions work best, making it easier for industry to adopt such ingredients. One example is that salmon hydrolysate can partly replace water while also increasing the nutritional content. - The findings could contribute to the development of new food products, such as burgers and nuggets, and represent an important step towards better use of marine side streams in food production.