Thermal destruction of the Salmonella group of micro-organisms, which are commonly present in commercially broken out raw egg pulp, is the prime objective of pasteurizing liquid egg in the manufacture of frozen and dried egg products. It is clearly recognized from Salmonella pathogenicity studies by McCullough and Eisele (24,25,26,27) and from other public health investigations that there is a need f o r eliminating these offending bacteria from egg products in order to prevent the occurrence of salmonellosis in institutional and 'military feeding and to minimize the latent "carrier state" of infectiousness, particularly among the food handlers. Adequacy of pasteurization depends on many factors, such as numbers and types of Salmonella present in the raw material, the pH of the liquid egg, and the time-temperature relationships involved in the heat resistance of these bacteria.Thermal process evaluations for food sterilization were established on a scientific basis in 1920 following the classical paper by Bigelow, Bohart, Richardson, and Ball (7). The ensuing three decades have brought many improvements in the technique of heat resistance determinations (1, 8, 14, 34, 37, 43, 4 8 ) and in the mathematical treatments of the thermal death time data secured (2, 3, 4, 7, 15, 16, 17, 20, 21, 22, 30, 32, 38, 39, 44, 45, 46). Although the literature concerning the thermal resistance of bacterial spores is rich in these advances, it is unfortunate that the same principles have not been as widely adopted by bacteriologists studying the Bansporulating organisms. I n connection with their investigation of t h e m 1 death time curves of coliform bacteria in milk, Olson, Macy, and Halvorson (29) stated recently: "With few exceptions the data on the thermal destruction of non-spore-forming bacteria are of such a nature that thermal death-time curves for the organisms studied cannot be constructed." A thermal death time curve defines the heat resistance of an organism at a given temperature (F value) as well as its sensitivity to changes in temperature ( z value). Such a curve, however, assumes the existence of absolute time-temperature relationships for the total destruction of a particular bacterial concentration. Hence, a sufficient change in the initial population of the suspension undergoing heat treatment would produce a change in the properties of the "absolute" thermal death time curve. A

Several statistical methods, including the conventional technique of Schmidt and Nank, were evaluated for estimating radiation resistance values of various strains of Clostridium botulinum by the use of partial spoilage data from an inoculated ham pack study. Procedures based on quantal response were preferred. The tedious but rigorous probit maximum likelihood determination was used as a standard of comparison. Weibull's graphical treatment was the method of choice because it is simple to utilize, it is mathematically sound, and its LD5 values agreed closely with the reference standard. In addition, it offers a means for analyzing the type of microbial death kinetics that occur in the pack (exponential, normal, log normal, or mixed distributions), and it predicts the probability of microbial death with any radiation dose used, as well as the dose needed to destroy any given number of organisms, without the need to assume the death pattern of the partial spoilage data. The Weibull analysis indicated a normal type kinetics of death for C. botulinum spores in irradiated cured ham rather than an exponential order of death, as assumed by the Schmidt-Nank formula. The Weibull 12D equivalent of a radiation process, or the minimal radiation dose (MRD), for cured ham was consistently higher than both the experimental sterilizing dose (ESD) and the Schmidt-Nank average MRD. The latter calculation was lower than the ESD in three of the five instances examined, which seems unrealistic. The Spearman-Karber estimate was favored as the arithmetic technique on the bases of ease of computation, close agreement with the reference method, and providing confidence limits for the LD5o values.

AN-ELLIS, A. (Quartermaster Food and Container Institute for the Armed Forces, U. S. Army, Chicago, Ill.) AND ROBERT B. KOCH. Comparative resistance of strains of Clostridiutn botulinunt to gamma rays. Appl. Microbiol. 10:326-330. 1962.-A total of 102 strains of Clostridiun botulinuml (56 strains of type A, 43 type B, and 3 nontoxigenic strains which could not be typed) was examined for resistance to gamma rays. When these organisms were suspended in neutral phosphate buffer in concentrations of 104 spores per tube, the threshold sterilizing dose appeared to be 1.4 'Mrad. Partial survival to 1.4 Mrad was shown by 10.70+c of the type A strains, 18.6 %/c of the type B strains, and one of three nontoxigenic strains. Overall , type A strains indicated higher radioresistance than type B strains, although there was overlapping. Representatives of the most resistant strains had D values of 0.317 to 0.336 Mrad; the D values of an intermediate group were 0.224 to 0.253 MIrad, and the most sensitive strain studied, ;1B, had a D value of 0.129 Mrad. The radioresistance of Putrefactive Anaerobe 3679, strain S-2, was comparable to the intermediate C. botulinum group (D = 0.209). ClostridiumI botulinumn appears to be the spore-forming food spoilage bacterium most resistant to ionizing radiation (Miorgan and Bohrer, 1953; Morgan and Reed, 1954). Since this organism is toxigenic, the acquiring of information on its radiation tolerance is important, for it must be completely destroyed if radiation is to be used for food preservation. The resistance of selected strains has been studied by several investigators. Denny et al. (1958), Pratt et al. (1958), and Schmidt and Nank (1960) determined the radiation dose necessary to sterilize different foods containing mixed cultures of C. botulinum. Morgan

Cans of ground cooked beef, inoculated with 106 or 108 spores per can of Clostridium botulinum 33A, were irradiated with 60Co gamma rays at a series of 14 temperatures ranging from −196 to 95C. The higher inoculum level required higher sterilizing doses. The D values, computed on the basis of recoverable C. botulinum, were independent of the inoculum level, and showed that spore resistance progressively decreased with increasing temperature. A statistical analysis of these data disclosed that the change in D values from −196 to 65C followed equally well a quadratic, exponential, or linear best-fit plot; above 65C radiation death was much more rapid. An equation was derived from the linear plot to predict D values for any desired temperature between −196 and 65C. Calculations of Ea and Q10 values, based on the linear curve, indicated a very small thermodynamic effect on radiation kill. An Arrhenius analysis of the temperature effect suggested that there was no simple physicochemical mechanism occurring in the inoculated beef pack which might explain the change in spore kill as a function of temperature. Theoretical commercial radiation processes for beef, based on the 12D concept and strain 33A spores, are presented for several easily controlled irradiation temperatures.