Process waters from the seafood industry contain valuable nutrients that could be used in food or aquaculture feed, but these process waters are currently treated as waste. A new research project from Chalmers University of Technology in Sweden shows the potential of recycling these nutrients back into the food chain.

During the seafood industry's preparation of herring, shrimp and mussels, large amounts of process water are continuously pumped out as waste, Chalmers said in an announcement. The water is used when boiling shrimp or mussels or when filleting, salting and marinating herring, for example.

Approximately 7,000-8,000 liters of water are used to prepare one ton of marinated herring, while 50,000 liters of water are needed per ton of peeled shrimp or per three tons of raw shrimp, the university reported.

However, these side stream waters contain proteins, peptides, fats and micronutrients that could be recycled and used, for example, by the food industry, as an ingredient in feed or for growing microalgae. In fact, the leftover boiled water from shrimp preparation is basically a ready-made stock, Chalmers noted.

The Nordic project Novaqua, coordinated by professor Ingrid Undeland of the Chalmers department of biology and biological engineering, has now shown the potential of extracting these important nutrients from the process waters.

"It's very important to help the industry understand that the side streams don't need to be wasted. Instead, they should be treated as really exciting raw material," she said.

"The backbone of our project is a circular approach. In the past, we had a more holistic view on handling of food raw materials, but today, so much is lost in side streams. Furthermore, we are in the middle of a protein shift, and there's a huge demand in society for alternative protein sources."

The university said research project started in 2015 with the aim to recover nutrients from seafood process waters and create innovative uses for them. A similar approach already has been successfully implemented in the dairy industry, where the residual liquid from cheese-making — whey — is used in sports nutrition as well as in different food and feed products.

The research team measured the composition of process waters and found that they contained up to 7% protein and 2.5% fat. In process waters from shrimp, astaxanthin — a red pigment and antioxidant often used as a dietary supplement — was also present.

"Our calculations show that in a primary processing plant for herring, as much as 15% of the herring protein coming into the industry leached out into the water and was treated as waste, thereby lost," Undeland explained.

Using a two-step process, the research team managed to recover up to 98% of the protein and 99% of the omega 3-rich fats. The process resulted in a semi-solid biomass and a nutrient-rich liquid. After dehydration, biomass from shrimp boiling water was shown to contain 66% protein and 25% fat.

Two tests were made, together with the University of Gothenburg and Skretting ARC, using this new biomass as an ingredient in feed for salmon, and the results were encouraging, the announcement said.

The nutritious liquid was used for glazing frozen fish, thereby protecting it from going rancid. It turned out to be slightly more protective than water, which is currently used for such glazing. The fluid was also tested as a substance for microalgae cultivation and was shown to enhance the growth of two types of algae. The algae biomass can subsequently be used as sources of protein or pigment.

Overall, the research project pointed out several different ways to recycle the nutrients that are currently lost in the seafood process waters. The next step is implementation in the seafood industry.

"A major challenge is to get the industry to manage the water side streams as food, beyond the stage when they are separated from the seafood product. Today, that is the point where the side streams start being handled as waste. This means there's a need for new routines for cooling and hygiene," Undeland said.

In Sweden, the waste waters are purified to some extent before they exit the factories. This means that many seafood producers already have the flotation technology needed in the second step of side stream recycling. However, there are also investments to be made, according to Bita Forghani Targhi, a post-doctoral researcher at the Chalmers division of food and nutrition science and colleague of Undeland.

"The main challenge would be cost-related issues," she said.

The work now continues within the new project AquaStream, funded by the European Maritime & Fisheries Fund.

Forghani pointed out that an important next step will include consulting with local businesses, interviewing them on generated side streams and verifying the current nutrient loss through a primary characterization of process waters.

She has a positive outlook on the future, saying, "I am quite positive on the fact that related industries, sooner or later, will be implementing these techniques. With ever-increasing awareness on the value of recycling nutrients, this facilitates industrial processes to adopt feasible approaches towards a circular economy."

Partners involved in the Novaqua project with Chalmers included Räkor & Laxgrossisten AB, Fisk Idag AB, Swemarc at the University of Gothenburg, DTU Foods, Bio-Aqua and Skretting ARC. Research on algae cultivation was done in collaboration with the researchers Eva Albers and Joshua Mayers with the Chalmers industrial biotechnology group. Scandic Pelagic AB and Klädesholmen Seafood AB were also affiliated to the project and played an important role in the new AquaStream project.