Production of Botulinum Toxin in Inoculated Pack Studies of Foil-Wrapped Baked Potatoes

Idaho Russet Burbank potatoes were surface or stab inoculated with 10 to 10⁵ spores of Clostridium botulinum type A strain, overwrapped in aluminum foil, baked at 204 C for 50 min or 96 C for 3 h and then held at 22 or 30 C. The shortest incubations resulting in the first botulinogenic potatoes were inversely related to spore doses and ranged from 3 to 7 days; potatoes inoculated with 10 spores were toxic after 5 to 7 days. Total toxin in individual potatoes incubated 3 to 5 days were 5 × 10³ to 5 × 10⁵ mouse mean lethal doses. Toxin was not found at distances greater than 1.6 cm from the spore inoculation site. Results indicate that left-over, foil-wrapped, baked potatoes are a perishable food that must be refrigerated.