Comparative Radiation Death Kinetics of Clostridium botulinum Spores at Low-Temperature Gamma Irradiation

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Abstract
Spores of Clostridium botulinum 33A were irradiated with 60Co gamma rays in 0.067 M Sorensen phosphate buffer (pH 7.0) at −196, −140, −80, −30, or 5 C and incubated in recovery broth for 30 days at 30 C, thus simulating an inoculated pack and eliciting “partial spoilage” data. Resistance of the spores decreased linearly with increasing temperature. A simple empirical equation was derived to predict D values for any desired temperature. An Arrhenius plot of the D value—radiation temperature profile indicated that the death kinetics is not first order. Comparison of the data in this model system with those previously observed in beef indicates a similar radiation death pattern, except that resistance of the spores was somewhat more (1.6-fold) temperature dependent, although significantly more resistant, in the beef. A comparison of the D value-temperature relationship of Streptoccus faecium a21, obtained earlier, with strain 33A in the same model system indicated that the spores were considerably less resistant below −20 C and much more resistant above this radiation temperature.

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