Suchergebnisse

"Screening" packs comprising 10 lots each of codfish cake, corned beef, and pork sausage, each lot containing about 106 spores of a different strain (five type A and five type B) of Clostridium botulinum per can, were irradiated at −30 ± 10 C with a series of increasing doses (20 replicate cans/dose) of 60Co gamma rays. The cans were incubated for 3 months at 30 C and examined for swelling, toxin, and recoverable botulinal cells. Based on the latter criterion of spoilage, median lethal dose (LD50) and D values were estimated for each strain in each food. The most resistant strain in codfish cake, corned beef, and pork sausage was, respectively, 53B, 77A, and 41B. There was no clear-cut trend in the comparative order of resistance between the two antigenic types among the three foods. LD50 values gave essentially the same order of resistances as the D values and may be used interchangeably with the latter for the 10 test organisms. "Clearance" packs consisting of the most resistant strain (about 107 spores/can) with its respective food were irradiated with a variety of doses at −30 ± 10 C, using 100 replicate cans/dose (about 109 spores/dose). These packs were incubated for 6 months at 30 C and assayed for the three types of spoilage. Based on recoverable cells, the experimental sterilizing doses (ESD) for codfish cake, corned beef, and pork sausage were 2.5< ESD ≤ 3.0, 2.0 < ESD ≤ 2.5, and 1.5 < ESD ≤ 2.0 Mrad, in that order. Assuming exponential spore death, the 12D values, or minimal radiation doses (MRD), were 3.24, 2.44, and 2.65 Mrad, respectively. Estimation of the MRD values by a method which assumes that spore death in the cans follows a normal distribution, yielded 3.09, 2.57, and 2.39 Mrad, respectively. Weibull analyis of the pooled 10-strain viable cell spoilage data of the screening packs for codfish cake or corned beef suggested that spore death in the cans follows a normal distribution yielded 3.09, 2.57, pooled data were not amenable to such analysis. Sublethal doses (0.5, 0.75 Mrad) ...

Ten lots of pork loin, packed in cans, were inoculated with approximately 106Clostridium botulinum spores per can. Each lot was seeded with a different strain; five type A and five type B strains were used. The pack comprised 5,690 cans, including controls, and contained about 109 spores per dose. The cans were irradiated with Co60 in the range of 0 to 5.0 Mrad (0.5 Mrad increments) at 5 to 25 C, incubated for 6 months at 30 C, and examined for swelling, toxicity, and recoverable C. botulinum. The minimal experimental sterilizing dose (ESD) based on nonswollen, nontoxic, but nonsterile end points was 2.5 < ESD ≤ 3.0 Mrad, and based on non-spoiled sterile cans was 3.5 < ESD ≤ 4.0 Mrad. The theoretical minimal radiation dose (MRD), the 12D equivalent, varied with the method of computation: 4.74, 4.33 ± 0.17, and 4.19 to 4.99 Mrad were obtained by the Weibull, Spearman-K̈arber, and Schmidt-Nank techniques, respectively. Calculation of D and MRD values by the conventional Schmidt-Nank method produced increasing values with rising dosage; this finding was compared with the data derived by the other two methods of calculation. Suggestions for estimating the MRD of a prototype radiation process are offered.

Ten lots of diced cured ham, packed in cans, were inoculated with approximately 106Clostridium botulinum spores per can. Each lot was seeded with a different strain (five type A and five type B strains). All cans were irradiated to various dose levels with Co60. Evidence provided by swelling, toxicity, and recoverable C. botulinum with 6,350 cans demonstrated that: (i) 4.5 Mrad was more than adequate as a sterilization dose; (ii) the minimal experimental sterilizing dose (ESD) based on nonswollen nontoxic endpoints was 2.0 < ESD ≤ 2.5 Mrad, and based on non-spoiled sterile cans was 3.0 < ESD ≤ 3.5 Mrad (the latter was supported by the computed theoretical 12D dose); (iii) D values calculated from botulinal survival data indicated that, as a group, the type A strains were more radioresistant than type B strains; strains 12885A and 41B, with respective D values of 0.242 and 0.175, represented the most resistant of each type; (iv) swollen cans did not always contain toxin, nor were toxic cans always swollen; (v) viable C. botulinum can exist for 6 months at 30 C without producing visible or toxic spoilage at doses of 3.0 Mrad and lower, including, in some instances, 0.0 Mrad; and (vi) a phenomenon similar to heat activation of spores occurred at sublethal radiation doses.

Sliced, cured bacon, packed in cans and seeded with 6 × 105 spores per can of Clostridium botulinum strains 33A or 41B, or with 3 × 106 spores per can of strains 36A, 12885A, 9B, or 53B, was irradiated to various dose levels with γ radiation. Evidence provided by swelling, toxicity, and recoverable C. botulinum with 2,200 inoculated, irradiated cans demonstrated that: (i) 4.5 Mrad were more than adequate as a sterilization dose; (ii) the experimental minimal sterilizing dose was 2.0 Mrad, and the theoretical 12-log reduction dose was 2.65 or 2.87 Mrad depending on the method of calculation; (iii) some spoilage occurred at dose levels below 2.0 Mrad; (iv) all visible spoilage of irradiated bacon was due to strains 33A and 12885A only, whose D values were, respectively, 0.141 and 0.177 Mrad based on spoilage data, and 0.221 and 0.188 Mrad, respectively, when based on recovery data; (v) toxic cans did not always result in swelling, nor did swollen cans always produce toxic spoilage; and (vi) viable C. botulinum can exist for at least 8 months in storage at 30 C without producing visible or toxic spoilage at doses below 2.0 Mrad.