HEAT INACTIVATION OF BOTULINUM TOXIN TYPE A IN SOME CONVENIENCE FOODS AFTER FROZEN STORAGE

ABSTRACT Crystalline type A toxin from the Hall Strain of Clostridium botulinum was added to beef pie fillings (pH 5.9), 0.05M phosphate buffer (pH 5.9), cream of mushroom soup (pH 6.2) or tomato soup (pH 4.1) and 1 ml placed in 2‐ml thin glass ampules. These were frozen and stored at ‐20°C for 180 days. At timed intervals a few ampules were thawed and the contents tested for toxicity and for the rate of heat inactivation of the toxin. The toxicity of type A in the contents remained the same throughout the frozen storage. Although the literature reports show a decrease in the heat stability of type E toxin after frozen storage, the heat inactivation rates for type A remained the same. pH is one of the important variables affecting the heat stability of type A toxin dissolved in various buffers.