Gamma Ray Sterilization of Canned Meat Previously Inoculated with Anaerobic Bacterial Spores1

Abstract

Before gamma irradiation can be evaluated as a technique for preserving food in tin cans, it is necessary that the amount of radiation required for sterilization be known. Although information is available concerning the sensitivity of bacterial spores in buffers (Proctor and Goldblith, 1951; Lawrence et al., 1953), such conditions are quite different from those existing in tin cans. It therefore seemed desirable to study the effectiveness of gamma radiation for killing the spores of anaerobic, food-spoilage bacteria that were inoculated into meat packed in No. 2 tin cans; data presented here correlate the quantity of gamma radiation from cobalt-60 required to produce sterility with the numbers of such spores present in the meat. MATERIALS AND METHODS Three anaerobic, spore-forming bacteria were used in this study. Putrefactive anaerobe no. 3679 came from the National Canner's Association Research Laboratory, while Clostridium botulinum, strains 62A and 213B, were furnished by the Hooper Foundation for Medical Research at the University of California. Spore suspensions were prepared according to procedures described by Reed et al. (1951); putrefactive anaerobe no. 3679 was grown in pork infusion broth, but Difco bacto-casitone was substituted for casein digest in the medium, specified by these workers, for clostridia. Stock spore suspensions were suspended in sterile distilled water and stored at 4 C. Samples of these suspensions were tested for heat resistance by C. W. Bohrer of the National Canner's Association

Comparative Resistance of Strains of Clostridium botulinum to Gamma Rays1

“…Unfortunately, PA 3679 has been shown to be significantly less tolerant to radiation than is C. botulinum (Morgan and Bohrer, 1953;Morgan TABLE 6. Resistance of PA 3679, strain S-2, to gamma rays in phosphate buffer (pH 7.0) and Reed, 1954; Kempe et al, 1954;Kempe, 1960). However, Brown, Vinton, and Gross (1960) reported that a strain of PA 3679, designated as S-2, was capable of surviving 8.0 Mrad in cured ham and 12.0 Mrad in fresh raw pork.…”

Combined Irradiation-Heat Processing of Canned Foods

“…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).…”

“…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).…”

“…L. L. KEMPE, J. T. GRAIKOSKI, AND P. F. BONVENTRE prepared and counted according to the procedures of Reed et al (1951) with the slight modifications described in previous studies from this laboratory (Kempe et al, 1954).…”

Biophysical Aspects of Clostridia

“…Numerous studies have demonstrated that proteinaceous solutions such as foods or microbiological growth media generally protect bacterial spores against radiation injury (e.g. Edwards, Peterson & Cummings, 1954;Pratt & Ecklund, 1954;Kempe et al, 1954). But exceptions to this generalization were noted as early as 1955 (Proctor, Goldblith, Oberle & Miller, 1955;Puld, Proctor & Goldblith, 1955) when it was reported that spores of B. subtilis were more radio-resistant in saline than in pea puree or evaporated milk.…”