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

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 10 6 spores of each of 10 strains of Clostridium botulinum (5 type A and 5 type B), or a total of 10 7 spores/can. The cans were irradiated to various doses (100 cans/dose) with 60 Co 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 7 spores/can, and 4.3 Mrad if it is assumed that each can of beef contained 10 6 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.