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A surprise find: Soybean waste could be the future of fish feed


A surprise find: Soybean waste could be the future of fish feed

Researchers discovered that the wastewater from soybean processing can be converted into a nourishing, protein-rich food for farmed Asian sea bass
May 3, 2024

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New research finds a resource in the most unexpected of places—and with it, a solution to the mounting problem of unsustainable fish feed. The wastewater from soybean processing can be converted into a nourishing, protein-rich food for farmed Asian sea bass, a team of scientists has discovered.

Soybean processing to make milk, meat alternatives and other foods produces tons and tons of wastewater each year. But this water holds a valuable secret: a naturally-rich population of single-celled bacteria that are able to convert nutrients into high quantities of protein in their bodies—a talent that goes to waste when they are simply flushed down the drain.

The team of Singapore University researchers who produced the new study had a plan to divert them from this fate. They worked with a local food processing company to rescue hundreds of liters of soybean wastewater, which they discovered was rich in two types of protein-accumulating microbes in particular, known as Acidipropionibacterium and Propioniciclava. Then, they placed the wastewater into small bioreactors, and incubated it for several days at 30 ºC degrees to encourage the microbes’ growth, the wastewater providing the perfect nutritional medium. The final step was to harvest the protein-enriched bacteria from the sludge, then dry out the mix, combine it with water, and process it into a kind of mash that could be fed to fish.

This took them into the second phase of their experiment, which involved feeding one group of juvenile Asian sea bass a diet made up of 50/50 bacterial protein and regular fishmeal; while another received a traditional fishmeal diet, alone. After 24 days, the researchers looked at the two populations of fish, and measured percentage weight gain, feed conversion ratio, and mortality rates.


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What they noticed in this comparison was striking: regardless of diet, the sea bass grew well, and both diets met the juvenile fish’s protein, fat, and amino acid requirements (except for an amino acid called lysine, which in both diets occurred at lower rates than required, but which can be added to fish pens along with the feed, the researchers say.) The sea bass that were fed the alternative microbe protein diet did have significantly lower weight to begin with, but that evened out as they grew. And, notably, the group that received the traditional feed diet had greater variability in their weight gain as they grew—whereas those fed the alternative microbe protein diet showed a more even accumulation of weight over the experiment’s course. 

This suggests that the alternative feed diet could encourage more reliable and predictable growth of Asian sea bass, which would be a boon for the industry. But not only that, the effect of substituting 50% of regular fish feed with this alternative could have large environmental implications. 

Fish provide the largest source of protein to humans worldwide, and farms are now the largest, and fastest growing, source of that fish. This puts pressure on the wild stocks that are typically used to make the meal that sustains the fish in these burgeoning pens. What’s more, where soybean meal is used as a replacement for fish-based feed, it still comes with a huge cost in terms of land- and water-use. 

Meanwhile, the wastewater from other soybean uses goes unused—but according to the recent results, could feasibly tackle both of these sustainability challenges at once. Furthermore it’s not just soybean waste water, the researchers say: several agricultural processes create wastewater side streams that are rich in the combination of carbon, nitrogen, and phosphorus that’s needed to sustain a growing population of hungry, protein-accumulating bacteria. 

The study demonstrates the adage that one person’s trash could make another’s treasure—a principle that may also be crucial to reaching sustainability and a “transition to a circular bioeconomy,” the researchers say.

Wuertz. Et. al. “Microbial community‐based protein from soybean‐processing wastewater as a sustainable alternative fish feed ingredient.” Scientific Reports. 2024.

Image: ©Anthropocene Magazine/AI-generated

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