July 2022: Eliminating Off-Flavour – Making RAS Fish Taste Better

Last month, for an upcoming article, I received an interesting link from the editor of Hatchery International magazine: https://www.eitfood.eu/projects/just-add-water.
FishFrom Ltd, a land-based salmon farm in Scotland, is planning to raise Atlantic salmon from egg to 5kg using recirulating aquaculture systems (RAS) technology that improves animal welfare and product quality.

But what caught my eye in the link was the word bacteria. The new technology will not only reduce energy consumption and provide a host of other RAS benefits, but it will also eradicate particular bacteria, resulting in a product that is free from the muddy taste that is sometimes present in fish that are grown on land.

RAS is growing in leaps and bounds, and more fish are being produced in these systems every year. The practice allows fish to be raised in a controlled, healthy rearing environment and lowers the risk of negative environmental impacts. RAS is a positive step for fish farming, but mitigating the off-flavours that the system can impart on fish is a big challenge. Seen as a defect in quality, a muddy taste is bad for business and reduces market value.

This taste occurs when bacteria such as streptomyces, myxobacteria and actinomycetes build up in the water, producing organic compounds called geosmin (GSM) and 2-methylisoborneol (MIB). (GSM is the organic compound that causes the fresh, earthy smell we tend to detect after it rains). These are absorbed into the gills and tissues of the fish, accumulating in their flesh. Fish such as Arctic charr, barramundi and rainbow trout, as well as salmon, can all be affected. Off-flavours are usually removed by depurating fish in clean water, but this can take days to weeks depending on the concentrations of GSM and MIB, the species and their size, costs a lot in terms of equipment and energy requirement and can result in significant economic losses due to delays in harvest and high consumption of clean water. Fish are also not fed during depuration in order to ensure good water quality. This can result in weight loss.

Through the new technology it’s developing, FishFrom Ltd is aiming to combat issues associated with off-flavours and come up with solutions so it’s no longer a hot topic on RAS farms. The company has joined forces with the Universities of Trento and Bologna to develop a system that is based on photocatalytic ozonation — using light and ozone to purify water. Francesco Parrino, a University of Trento researcher who developed the system, told me this month that light can produce reactions that lead to the degradation of pollutants and the removal of pathogens such as viruses and bacteria. Could this method eventually replace depuration? Although it’s still not clear, the technology has shown some promise in that it appears to improve water quality parameters rather than alter them.

FishFrom Ltd is not the only company trying to counteract the effects of off-flavour. One study shows that methods such as advanced oxidation processes, algicides and activated carbon show promise in degrading the compounds that produce off-flavours. It’s also possible to add bacteria to the water that out-compete the bacteria that cause off-flavours. Biotechnology company Nova Q is exploring this very area, and their latest innovation is identifying a bacteria that will break down GSM and MIB. They’ve developed a product called RAS-Right, a liquid additive that contains a mix of bacteria that enhances the nitrification process in RAS farms. In the meantime, it may be possible one day to taste the fish before sending them out for analysis or shipping them to market. Scientifically, setting up a taste panel may not be easy due to the different taste thresholds of those involved. But matching up the science and data with taste information could prove to be insightful.

Interestingly and perhaps unexpectedly, feed firms are also looking at tackling off- flavour. KnipBio, whose focus is nutritional solutions for aquafeed, is investigating whether feed additives could reduce off-flavours. They say that fish fed a diet containing five percent of KnipBio Meal single-cell protein have significantly lower levels of GSM and MIB. As the first nutrition-based alternative to purging fish, the diet indicates that purging could potentially be eliminated, resulting in significantly better RAS economics, better process reliability and enhanced consumer satisfaction.

As their project evolves, FishFarm Ltd and the Universities of Trento and Bologna will also be taking into account the final stage of the process when the products hit the shelves — the behaviour of consumers, and their awareness in making responsible choices for the environment and their health. It’s important from the consumers’ point of view to know what they are buying, and with consumers trying to eat better and being more aware of issues such as aquaculture’s environmental impact, it is vital for farmers to know about consumer preference when it comes to such things as taste and texture and be able to deliver accordingly.

The inroads being made to address off-flavour are encouraging. It’s a topic that we don’t hear about so often in aquaculture circles but it’s one where everybody needs to have as much information as possible to try to mitigate the problem, so it’s great to see the efforts that are underway. Large-scale RAS facilities are continuing to develop, and one key to unlocking their growth potential could be in improving how they manage bacteria and ensure delicious taste and good quality. Technology providers have a key role here, and it will take the researchers and innovators out there to come up with that ideal solution, whether that’s a combination of technologies or just one.

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