Toxin Production by Clostridium botulinum Type E in Packaged Channel Catfish

Channel catfish were inoculated with 3 to 4 log spores/g of a mixed pool of four strains of C. botulinum type E (Beluga, Minnesota, G₂₁-5, and 070) and were packaged with an oxygen-permeable overwrap, in an oxygen-barrier bag with a modified atmosphere of CO₂-N₂ (80:20) or in a master bag with the same modified atmosphere. Packaged fish were stored at either 4°C and sampled at intervals over 30 days or at 10°C and sampled at intervals over 12 days. An additional master bag treatment in which overwrap-packaged catfish was stored first at 4°C, then removed from the master bags and stored at 10°C, was sampled at intervals over 18 days. Toxin production was evaluated using the mouse bioassay. Aerobic psychrotrophic and anaerobic populations were enumerated, and product spoilage characteristics were noted. Under abusive storage conditions of 10°C, there was no difference among the potential for toxin production in the packaged fish, with botulinum toxin detected on fish from each package type by day 6. At 4°C, toxin production was detected on day 9 in the overwrapped packages, while it was on day 18 in the modified atmosphere packaging. No toxin was found in the master bags held continually at 4°C. Toxin was detected on day 18 from samples initially held at 4°C in the master bag and subsequently held at 10°C. Spoilage preceded toxin production for samples stored at 4°C for each type of packaging. At 10°C, spoilage and toxin detection times coincided.