Steam it — don't boil it to reduce cyantoxin contamination

Back in 1979, 138 inhabitants of Palm Island, Queensland, were admitted to hospital, suffering from gastroenteritis. The gastro outbreak was eventually traced back to a local water supply — a dam that had experienced a significant bloom of Cylindrospermopsis raciborskii, an algae that had been treated with copper sulfate. The copper sulfate had caused the freshwater cyanobacteria to lyse and release cylindrospermopsin (a cyanotoxin) — this toxin was responsible for the disease outbreak.

The highly water soluble compound, which is produced by several cyanobacteria species, bioaccumulates in fish and other aquatic plants and animals. However, little is known about the extent of exposure via food in humans.

According to a recently released study, steaming freshwater fish for more than two minutes reduces the presence of cylindrospermopsin by up to 26% while if boiled, the reduction is only 18%.

The Toxicology and Legal Medicine at the University of Seville study also concluded that the biotoxins pass into the water that has been used for cooking.

In the study, published in Food Control, it was also observed that the concentration of this cyanotoxin after cooking would not have consequences for public health, as establish by the Provisional Tolerable Daily Intake established by the WHO.

Cyanotoxins can be found in plant-based foods, which have been watered with water that contains them. The same is true of cereals, fish and shellfish that have been contaminated before becoming part of the food chain. It has been shown that this cyanotoxin, which is increasingly more common globally, can affect organs like the liver, kidneys, heart, intestines, lungs and brain, among others, in animals. In humans, the effects of ingestion include hepatoenteritis, headaches, diarrhoea, dehydration and kidney damage, among others.

University of Seville researchers. Image credit: University of Seville.