Inactivation‐Rate Studies on a Radiation‐Resistant Spoilage Microorganism III. Thermal Inactivation Rates in Beef a, b

SUMMARY The thermal resistance of Micrococcus radiodurans R 1 , a spoilage bacterium highly resistant to ionizing radiation, was characterized. A modified “thermal‐death‐time tube” was used, with cells uniformly suspended in a raw meat puree reconstituted from freeze‐dried and powdered beef that had been screened to remove pipette‐plugging fibers and irradiated to eliminate viable aerobic organisms before use. Thermal death rate, unlike the radiation death rate, seemed to approximate an exponential form, as indicated by survival curves. A D 1A0 = 0.75 and z = 10.65 describes the heat resistance in beef. Simple calculations suggested that if all parts of the samples of beef reached 150° F, the lower level of the “medium‐done” range, a 1‐min hold at that temperature should reduce viable nymbers by a factor of 10 −10 and a 2‐min hold should reduce numbers by a factor of 10 −20 .