Low-Temperature Irradiation of Beef and Methods for Evaluation of a Radappertization Process

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An inoculated, irradiated beef pack (1,240 cans) study was conducted for the determination of microbiological safety for unrestricted human consumption. Each can contained a mixture of 106 spores of each of 10 strains of Clostridium botulinum (5 type A and 5 type B), or a total of 107 spores/can. The cans were irradiated to various doses (100 cans/dose) with 60Co gamma rays at -30 ± 10 C, incubated at 30 ± 2 C for 6 months, and examined for swelling, toxicity, and recoverable botulinal cells. The minimal experimental sterilizing dose based on nonswollen, nontoxic sterile cans was 2.2 < experimental sterilizing dose ≤ 2.6 Mrad. Using recoverable cells as the most stringent criterion of spoilage, and assuming the conventional simple exponential (without an initial shoulder) rate of spore kill, the “12D” dose was 3.7 Mrad when estimated on the basis of a mixture of 10 strains totaling 107 spores/can, and 4.3 Mrad if it is assumed that each can of beef contained 106 spores of a single most resistant strain and all of these spores were of identical resistances. However, an analysis of the data by extreme value statistics indicated with 90% confidence that the spore death rate was not a simple exponential but might be a shifted exponential (with an initial shoulder), Weibull, lognormal, or normal, with a “12D” equivalent of about 3.0 Mrad regardless of the initial spore density per can. There was an apparent antagonism between the irradiated type A and B strains in the cans. Some of the cans contained type B toxin but did not include type B viable cells. Other cans had a mixture of type A and B toxins, but a large number of these cans did not yield recoverable type B cells. However, type A viable cells could always be demonstrated in those cans containing type A toxin.

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