The occurrence of Clostridium botulinum type E in Finnish trout farms and the prevention of toxin formation in fresh-salted vacuum-packed trout fillets.

The occurrence of C. botulinum on two Finnish rainbow trout farms were studied. C. botulinum type E toxin was detected from samples of fish intestines in 10% and 4% of the samples and in 0% and 100% of dam bottom sediments, respectively. The toxin formation of inoculated C. botulinum type E in three different brands of commercial fresh-salted vacuum-packed trout fillets was also investigated. In the brand with a salt concentration of 2.7% (a w = 0.96) and no nitrate, the toxin was formed in two weeks at 10 and 20 degrees C. If the pH of the product was lowed to 4.90 and NaCl concentration increased to 5.67% (a w = 0.94%) no toxin was formed even without the use of nitrate. By adding 0.1% of sodium nitrate to the curing solution (0.046% nitrate in the product) the toxin formation was brought to an end. According to the results of the study C. botulinum type E presents a potential health risk for man as well as for fish also in Finland. Trout products must be manufactured and stored in such a way that the possibility of toxin formation is eliminated.