A matter of taste: a new solution for off-flavours in RAS systems

So-called “off-flavours” in fish and water mould cause significant economic losses to fish farming globally. They pose a particular problem for recirculating aquaculture systems (RAS).

Typically caused by the proliferation of microbes in the system, substances such as geosmin are not normally harmful to either people or fish, but they create an unpleasant, earthy flavour to which humans are extremely sensitive.

Water mould is also a common problem in fish farms globally. In salmonid farming, this has been estimated to cause production losses of up to 10% per year through all stages of production.

Now, the Natural Resources Institute Finland (Luke) and VTT Technical Research Centre of Finland have developed capture solutions based on chemically treated cellulose fibre materials to address these challenges.

 
As Luke’s Research Manager and Senior Scientist, Petra Lindholm-Lehto explains, cellulose fibres were originally used by VTT for hormone capture in wastewater*. The aim was to use the wood-based cellulose fibre yarn, coated with chemicals, to capture ethinylestradiol (EE2), a hormone used in contraceptive pills, and ensure it did not get into the water supply.

Lindholm-Lehto says: “Their group is our partner here and they are experts in modifying cellulose-based material. In this case, the fibre material was chemically modified to selectively capture the off-flavour compounds.”

The capture of off-flavour compounds was studied at Luke’s experimental aquaculture facility in Laukaa. The concentrations of 14 off-flavour compounds were tested in a recirculating aquaculture (RAS) environment, where part of the water was recirculated through a fibre material. The chemically treated fibre material accumulated up to 1,000 times higher concentrations of off-flavour compounds compared to those in untreated water. After the treatment, the concentrations of off-flavours in the fish remained below the sensory thresholds.

 
Petra Lindholm-Lehto says: “This is a very interesting result, as no new solutions have been introduced in recent years to reduce off-flavours in recirculating aquaculture systems.” 

At Luke’s Enonkoski aquaculture facility, a fibre material developed specifically for the capture of water mould spores was tested. The use of the fibre material significantly reduced the amount of mould spores in the water compared to a culture tank without the material.   

“Not enough is yet known about the behaviour of the water mould and studying it in fish farming is challenging.

Previously used treatments have proven to be unsafe or ineffective. The method we have developed is based on the use of harmless capture material and therefore the results of our experiments are interesting,” says Lindholm-Lehto. 

Hannes Orelma, Research Team Leader at VTT, adds: “These new cellulose-based capture materials will capture water mould spores and off-flavour compounds from the water, preventing them from accumulating in the fish.”

Patent applications have been filed for both of the innovations developed by Luke and VTT.  Could the idea be fully commercialised? Petra Lindholm-Lehto says: “We are open to all good options, we haven’t excluded any yet. Now we are looking for funding for further experiments to scale up and to develop the invention into a product.”

Jani Lehto, Director of Luke’s Bioeconomy and Environment Unit, says: “Our solutions can have a significant impact on the profitability of the industry. Our results are encouraging and show that these solutions have a lot of potential.

“Our next steps are to continue development of both technical solutions in commercial-scale farms and to move forward with commercialisation. We look forward to hearing from companies and operators who would like to develop these solutions further with us!”

* “Cyclodextrin-Functionalized Fiber Yarns Spun from Deep Eutectic Cellulose Solutions for Nonspecific Hormone Capture in Aqueous Matrices” (Biomacromolecules 2018, 19, 652−661) Orelma et al.