Inactivation of botulinurn toxins was determined in selected acid and low acid foods and buffer systems. Heating at 74°C and 79°C gave a biphasic curve when the log of the inactivation of the toxins was plotted against the time of heating. At 74"C, the time for inactivation of 10' LD, ,, of type A toxin per gram of an acid food such as tomato soup to no detectable toxin by mouse assay was an hr. or more. At 85°C the inactivation was very rapid and approached exponential decrease with inactivation to no detectable toxin within 5 min. In general, the toxins were more stable in acid foods such as tomato soup at pH 4.2 than in low acid foods, such as canned corn at pH 6.2. Twenty minutes at 79°C or 5 min at 85°C is recommended as the minimum heat treatment for inactivation of 10' LD, 0 botulinurn toxins per gram of the foods tested.

Canned salmon is a low acid food. If all C. botulinum spores are not destroyed by proper processing in home canning, a potential hazard of botulism exists. Boiling will destroy the toxin, but will also affect the palatability and appearance of the salmon. To determine the minimum temperature and heating time to destroy toxin, type A, B, or E toxin was added to canned salmon. Two‐gram portions in small glass vials were heated at 68, 71, 74, 79 and 85°C for various lengths of time up to 20 minutes. To establish a heating procedure for cans and jars of salmon, spores of types A, B, and E C. botulinum were added to commercially canned salmon and to glass jars of home‐canned salmon and incubated for 10 days. Open cans and jars were oven‐heated at 350°F (177°C) to the same end‐point temperatures. Assays for toxin were carried out with mice. Inactivation of toxin in salmon heated in vials showed an initial rapid drop in toxicity followed by a leveling‐off of the rate so that 20‐minute heating at 68 or 71°C did not destroy all of the toxin. At 79 and 85°C, the inactivation was much more rapid and all detectable toxin was destroyed within 2 to 5 minutes. For the oven‐heating method for two sizes of cans and jars, an internal temperature of 85°C followed by a 30‐minute holding period at room temperature was effective in inactivating botulinum toxin.