Unlocking the hidden value of marine by-products

Rasmus Ree and Gro Bjerga, NORCE Research

FTA Issue No.2 2026

Marine by-products from fish processing are rich in valuable nutrients, yet are largely used for low-value purposes.

A major challenge is the development of fishy off-odours, which limits other uses. New biotechnological approaches offer ways to control and upgrade these resources into high-quality proteins for human consumption.

Norway is one of the world’s leading seafood nations (Figure 1). In 2024, Norwegian fisheries and aquaculture produced more than 3.2 million tons of seafood (1). Value creation in the seafood industry amounted to NOK 69 billion in 2024, and NOK 139 billion when spillover effects are included (2), accounting for 2% of Norwegian GDP. As the world’s largest producer and exporter of farmed Atlantic salmon and rainbow trout, Norway has a particular responsibility to ensure that its production contributes to a sustainable global food system. However, these impressive production figures represent, quite literally, only about two thirds of the story. 

Turning marine by-products into a national strategic resource

During fish processing, heads, backbones, skins, and trimmings are separated as so-called by-products. In Norwegian salmon processing, these can account for up to 40% of the total biomass. In 2024, more than 1 million tons of such material were generated (1). Although these resources are rich in valuable nutrients, their economic value remains relatively limited, with total revenue estimated at around NOK 3 billion (1).

About 65 percent of farmed salmon leaves the country without further processing, mainly due to high EU tariffs on processed products and the high cost of labour (Figure 2). Meanwhile, Norway relies heavily on imported protein ingredients, especially for fish feed, where there has been a shift from marine proteins to plant- and landbased sources driven by costs, availability and sustainability considerations. This creates a structural imbalance: while we export valuable marine nutrients or downgrade them to low value uses, we also depend on protein imports. 

If the necessary conditions are put in place, the seafood industry can play a bigger role in the Norwegian economy in the years ahead, not least as part of the green transition: It may have economic, ethical, environmental, and climate benefits (3).

Maximizing the value of marine by-products

Today, about two-thirds of Norwegian marine by-products are used in production of oils, protein and meal for feed applications (Figure 3). Roughly one-fifth is used as feedstock in energy production (1). According to the value pyramid framework, resources should be prioritized for the highest value purposes (4). Products intended for human consumption, such as protein powders, dietary supplements, and functional foods, are at the top of the pyramid because they deliver greater nutritional benefits and significantly higher economic returns than lower value uses like energy recovery or disposal.

Using all parts of the fish more efficiently is one of the most powerful ways to improve sustainability in the seafood sector (5). Turning underused raw materials into valuable food ingredients can reduce waste, strengthen food security, and lower dependence on imported resources. Moreover, it helps build new businesses and value chains and contributes to local jobs. From a broader perspective, ensuring that valuable nutrients stay in the food system supports climate goals (6). 

Upgrading by-products to premium proteins

One promising way to unlock this value is through a process known as enzymatic treatment. Enzymes are catalysts found in all living organisms that speed up specific reactions in a gentle and controlled way, without the need for harsh chemicals or extreme conditions. Once minced, fish trimmings are mixed with water and gently heated together with enzymes, in a process called hydrolysis (9). Over about an hour, the enzymes break large protein molecules into smaller building blocks of peptides and amino acids. 

Once the desired degree of hydrolysis is reached, higher temperatures are used to deactivates the enzyme and stop the reaction. The mixture is then separated into oil, solid material, and a liquid protein-rich fraction, which can be dried into a powder. Today, Norway has several advanced biorefineries based on this technology.

The main protein product of this process is known as fish protein hydrolysate. It contains typically above 70 percent protein, including all essential amino acids (10). Because the proteins are already broken down into small pieces, they are easily absorbed by the intestines. This makes them particularly suitable for people with increased nutritional needs, such as elderly people, people recovering from illness, or physically active individuals who benefit from fast protein uptake.

The relevance of such products is increasingly being recognised beyond niche or medical nutrition markets. In 2024, Indonesian president-elect Prabowo Subianto drew attention during the election campaign by proposing to replace cow’s milk with so-called fish milk in the national free school lunch programme – essentially a drink made from fish protein hydrolysate (11) (Figure 4).

Despite the recognition, fish protein hydrolysates are often used in non-food applications. Most of the product is sold to pet food producers and, to some extent, used in fish feed (1). This trend reflects both market dynamics and consumer preferences, with the main bottleneck for food applications being sensory quality (1,12).

«Smells like fish»

In sensory terms, fishy odours range from clean oceanlike, and slightly salty notes to grassy or seaweed-like nuances, which at low levels are often perceived as pleasant notes in fresh fish and seafood (13). These aromas are typically linked to volatile compounds that develop naturally in marine organisms. Problems arise when the smell becomes strong, sharp, or ammonia-like, which signals spoilage and chemical breakdown. Out of balance, fishy notes can indicate poor quality. However, the full mechanisms underlying fishy smell formation are not yet fully understood.

One of the key factors of fish odour is a compound that forms naturally in fish after harvest. This is a small molecule called trimethylamine (in short: TMA) (1,12). TMA has an extremely low odour threshold (14), which means that even at very low levels our noses can detect it. By itself, it has a somewhat ammonia- and crab-like smell. In hydrolysates TMA becomes concentrated, as it is water soluble. Over the past five years, research has begun to address sensory issues caused by TMA. 

Fixing the symptoms, not the cause

Masking is common in industry. Adding sugar during processing promotes the Maillard reaction, which provides a sweet notes and grilled odour. This was shown to mask the perception of fishy smell (16). Mixing in tea polyphenols likewise shows promise (17). At the same time, flavour masking can present its own challenges. Although President Subianto’s election campaign was successful and his plan to introduce free school lunches was widely supported, the suggestion of fish milk drew criticism for being strange and unappealing. Much of the reaction appeared to stem from the use of familiar flavours such as chocolate and strawberry to disguise the product’s fish-based origin. The inclusion of flavour-masking additives, including large amounts of sugar, could reasonably be seen as compromising the otherwise clear nutritional benefits of the fish-derived proteins. 

Some biorefineries have installed advanced filtration methods to remove TMA. This is an untargeted method which is known in scientific literature and industry to reduce the fishy smell. This method has the drawback of causing significant protein loss and altering the nutritional composition of the hydrolysate (15). Using nanofiltration, the perception of another undesirable attribute, bitterness, has been shown to increase. This is likely due to the retention of peptides known to contribute to bitter taste, yet another undesirable taste attribute. Consequently, other strategies beyond untargeted methods are being investigated. 

“You are what you eat”

Chemically speaking, TMA is a volatile amine which is formed postmortem from trimethylamine-N-oxide (TMAO), a naturally occurring metabolite in fish. The physiological role of TMAO is to act as an osmolyte, a small molecule that works to stabilize proteins and helps the cells cope with stress. TMA levels in raw materials vary depending on species, tissue, and processing (18). As a rule of thumb: the deeper the fish lives, with more pressure stress, the higher the TMAO levels are.

The food you digest releases volatile compounds that travel through your bloodstream, exit your pores as sweat or are exhaled by your lungs, often altering your natural body odour. Do people with seafood diet smell like TMA? 

Not always. After eating seafood, an enzyme in our liver turns TMA into the odourless TMAO. This is also one of the reasons why individuals don’t smell fishy after a seafood meal. At least most don’t.

From Shakespeare to science: Clues to a solution

In The Tempest, Shakespeare made the jester Trinculo examine Caliban and remark: «What have we here? A man or a fish? A fish: he smells like a fish; a very ancient and fish-like smell”. Caliban is the half-human offspring of a sea witch (Figure 5), suggesting the reason he should have such a marine scent, and leaving the molecular explanation of this phenomenon to modern geneticists. Caliban could, like Paul Giamatti’s character Paul Hunham in The Holdovers, suffer from fish odour syndrome, a rare metabolic condition in which the body cannot convert TMA and instead excretes it in sweat and urine. The patients lack the liver enzyme which oxidizes TMA to TMAO. 

For Caliban’s and Hunham’s part, their fishy body odour contributes to and is symbolic of their detachedness and alienation from other people. For researchers, the cause and symptom of this rare genetic syndrome yield a clue to a solution to the problem of fish-smelling byproducts. Could we use such an enzyme to remove this smell in fish protein hydrolysates? 

Targeted strategies are underway

Unlike filtration and masking, enzymes have the wonderful property of being highly specific. We have shown that an enzyme from a marine bacteria, which is very similar to our liver enzyme mentioned earlier, can be used to remove TMA from fish protein hydrolysates made from salmon (19). The enzyme basically reverts TMA back to the odourless TMAO (Figure 6). The enzyme oxidizes TMA using molecular oxygen and the NADPH molecule as a helper, leaving TMAO and the oxidized cofactor NADP+ as products (20,21).

Since this enzyme is of marine origin, it is adapted to relatively cold sea temperatures. However, biorefineries depend on moderate temperatures to run the hydrolysis process. Therefore, to improve the compatibility with industrial conditions, we made a new version of the enzyme that was able to cope with higher temperatures (22). Through protein engineering, targeted changes were introduced in the enzyme’s structure to enhance its stability at higher temperatures (Figure 7).

But it did not solve all issues. The helper molecule, NADPH, is very expensive. Enzyme-assisted removal of TMA in fish protein hydrolysates will not be industrially viable unless cofactor consumption is managed in a cost-effective manner. We therefore developed a system to recycle this helper molecule, so we would not need as much of it. The recycling part is handled by another type of enzyme, which makes NADPH from a cheaper molecule, NADP+. By combining these two enzymes, we were able to remove TMA from fish protein hydrolysates without spending a fortune on NADPH (23). Next, we needed to understand if the reduction in TMA levels we observed translated to a more appealing smell. An exceptionally welltrained panel of sensory experts were hired to sniff our samples. The sensory panel was able to detect a reduction in TMA levels compared to non-treated samples, proving to us that the method works. 

Thinking ahead

Although the enzyme system developed in this study is not yet ready for industrial implementation, it clearly demonstrates what targeted biotechnological solutions can offer. Enzymes can address specific quality challenges in a way that untargeted methods cannot. At the same time, the work highlights important trade-offs. Enzymes are precise but complex, and cost remains a key barrier. For now, preventive measures such as using fresh raw material, along with filtration and flavour masking, are likely to remain the most practical industrial solutions. Still, the enzymatic strategy illustrates a powerful concept: that carefully designed biological tools can open new pathways for upgrading underutilised marine resources. 

Looking forward, further development in enzyme engineering and process integration could gradually make such approaches more accessible. Even if enzymes are not always the final answer, they help point the way. In a sector like Norway’s marine industry, rich in raw materials, expertise, and innovation, this kind of targeted thinking may prove essential for creating new, higher-value products from resources we already have. What once smelled like a problem may ultimately help unlock new value.

The authors acknowledge funding from the Research Council of Norway through the Centre for Research-based Innovation in Industrial Biotechnology (SFI-IB, project no. 309558).

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