Combined Irradiation-Heat Processing of Canned Foods

L. L. Kempe, J. T. Graikoski, P. F. Bonventre
1958 Applied microbiology  
If combined irradiation-heat processing is applied in the canned food processing industry, it could be desirable to preirradiate the products in the raw state. For example, it is conceivable that canned meat might be irradiated at one geographical location and heat processed in another. This idea prompted an investigation of the effectiveness of combined irradiation-heat processing of ground raw beef artificially contaminated with Clostridium botulinum 213B spores. MATERIALS AND METHODS Lean
more » ... AND METHODS Lean ground beef was purchased locally from the University of Michigan Food Stores. As soon as the meat was ground, it was spread in shallow enameled pans and placed in an evacuation chamber. Here the dissolved metabolic gases were removed by evacuation to about 25 in. of mercury after which the vacuum was released. This was repeated 3 times. Next the ground beef was packed into no. 1 picnic tin cans, being careful to avoid air pockets. Some of the cans were equipped with Ecklund (1949) thermocouples. The cans of meat were now placed in the evacuation chamber, where the degassing procedure was repeated 3 times. The meat was kept at about 40 F throughout this process. Following degassing, the meat was inoculated at the approximate geometrical center of each can with 1 ml of a spore suspension in distilled water. Finally the cans were sealed in a commercial type vacuum closing machine at a vacuum of about 26 in. of Hg. Experimental cans were then either irradiated or temporarily stored in a refrigerator; controls were immediately placed in an 85 F incubator. Following irradiation, the canned meat was heat processed to the desired F. value and then quickly cooled to the incubation temperature by immersion in cold water; after this, the processed experimental cans were also incubated at 85 F. During incu-bation, all cans were examined daily for gas development as evidenced by swelling. Since C. botulinum 213B spores were used as the inoculum, the development of toxin was also used as a criterion for C. botulinum growth in some of the cans showing gas production. Mouse inoculation was used for this purpose as previously described (Kempe et al., 1954) . Irradiation was carried out in the "center-well" of the large cobalt60 gamma radiation source at the University of Michigan. For this work, eight cans were placed in the "center-well" along with sufficient Dry Ice to refrigerate the canned meat. The irradiation was allowed to proceed for the required time, based upon a gamma ray field intensity of approximately 130,000 rep' per hr in the center of the cans at the time these studies were made. Periodic verification of the dosage rate was made by ferrous-ferric sulfate dosimetry (Weiss, 1952) using ferrous sulfate solutions in glass vials placed in the center of the cans (Kempe et al., 1954) . Seven cans at a time were processed in a steam heated autoclave as previously described . During heating, the cans were immersed in a pail of water located inside the autoclave. Temperatures at the center of three cans were measured by Ecklund thermocouples; the other four were the experimental cans whose temperature variations were assumed to parallel those found in the cans of meat containing thermocouples. F. values were calculated by a graphical modification of Ball's general method (Schultz and Olson, 1940) . The Z value was assumed to be 18 for these calculations. The C. botulinum 213B spores used in this study were I One rep is a dosage of ionizing radiation capable of producing energy adsorption of 93 ergs per g of tissue. Ferrousferric sulfate dosimetry was based on the oxidation of 15.4 micromols of ferrous ions per L per 1000 rep. 1958] 261 on May 7, 2020 by guest http://aem.asm.org/ Downloaded from
doi:10.1128/aem.6.4.261-263.1958 fatcat:7flr3vwm2fe7dpjhtqvrgczszu