DESTRUCTION OF CLOSTRIDIUM BOTULINUM BY IONIZING RADIATION PART II. PEAS, CHICKEN SOUP, AND PORK IN THE FROZEN STATE^a,b

Abstract

Determination of the radiation dose required to destroy spores of the toxin producing organism, Cl. botulinum, and produce a safe, sterile product is essential before irradiated foods can be introduced to consumers. The magnitude of cost and of such problems as changes in flavor, odor, texture, and nutrients, of course, depends very largely upon the radiation dose required for sterilization.Six-hundred cans each of peas, cream of chicken soup, and parboiled pork were inoculated with approximately 1,000,000 spores of CZ. botulinunz per can and subjected, in the frozen state, to various levels of gamma radiation from mixed fission products in spent fuel elements.Counts were made of surviving organisms in representative samplcs after irradiation and the remaining samples placed in incubation at 86" F. (30" C.) for one year.Counts of surviving spores, as well as tests for botulinum toxin, were made on flat cans surviving the year of incubation. E X P E R I M E N T A L P R O C E D U R EInoculum. Spore suspensions used throughout consisted of a mixture of 5 strains of C1. botzilinzm. Type A, and a mixture of 5 strains of Type B, all of which were grown separately on Wheaton's beef heart casein medium (7), concentrated, suspendcd in water, and heat shocked 10 minutes at 170" F. (77" C.) The 2 mixtures were provided by C. T.Townsend of the Western Laboratory of the National Canners Association. Dilutions of the original suspensions were made to permit inoculation of approximately 5,000 spores of cach type per gram of product.Peas for this pack, Perfection variety garden run, were blanched 3 minutes in boiling water, cooled, and frozen until ready for use. Sixty-one grams of peas were weighed into each 202 x 202 can and the mixed spore inoculum added by pipette. Cans were hrined with 36 ml. cold brine (1.4% sodium chloride, 4.8% sucrose) and close,d at 58-65°F. (14-18°C.) under 25 inches of mechanical vacuum.Chicken soup. Concentrated cream of chicken soup was removed from a commercial line without thermal processing and was returned frozen to Barrington for inoculation. Ninety-eight grams were filled into each 202 x 202 can and mixed spore inoculum added by pipette. Contents were stirred to insure distribution of spores, and the cans were closed at 5558°F. (13-14°C.) under 25 inches of mechanical vacuum.Peas.

Radioresistance of Five Strains of Clostridium Botulinum in Selected Food Productsa,b

“…In the first study (Denny et al, 1958;Pratt et a.l., 1959), the inoculum of CL botzlliwm spore suspensions con-sisted of mixed spores from 5 strains of Type A and from 5 strains of Type B. To gauge their radioresistance, the different strains were subjected to a screening test.…”

“…The program, undertaken in cooperation with the Quartermaster Food and Container Institute for the Armed Forces, was of such scope that the research laboratories of the National Canners Association, American Can Company, and Continental Can Company all collaborated in the work. The first two laboratories have published reports on their phases of the investigation, one by Denny et al (1958) and the other by Pratt et al (1959). Those papers described the over-all program and the results of work carried out using neutral phosphate and certain food products as the substrates during irradiation.…”

RADIATION STERILIZATION OF FOOD.I. PROCEDURES FOR THE EVALUATION OF THE RADIATION RESISTANCE OF SPORES OF CLOSTRIDIUM BOTULINUM IN FOOD PRODUCTSa

“…Dosimetry and calculation of exposure times to give the desired radiation dose were performed by Argonne personnel. Just prior to irradiation, each lot of 10 cans was warmed in water to approximately 80" F. Cans were placed in polystyrene foam holders and irradiated by the procedures described by Pratt et al (8) designed to equalize the dose received by each can. Following irradiation, cans were held at room temperature 1 or 2 days until returned to the laboratory for incubation at 85" F.…”

Radiation Resistance of Spores of Clostridium Species In Aqueous Suspension

“…sporogenes, generally the strain referred to as PA 3679, has been published (e.g. Morgan and Reed, 1954 ;Schmidt and Nank, 1960;Schmidt et al, 1962;Denny et al, 1959 ;Pratt et al, 1959;Anellis and Koch, 1962;Kempe et al, 1957). Cl.…”