Cameron's Putrefactive Anaerobe 3679 is widely used as a test organism to evaluate process requirements f o r low-acid canned foods. Although the thermal resistance of this organism is known to vary with the substrate in which it is heated (2, 15, 18), until recently (10, 16) there were relatively few data in the literature that defined the constants of thermaldeath-time curves of the organism in vegetable substrates. Most of these data specify the resistance of spores when heated in liquid extracts or purCed vegetables. Townsend, Esty, and Baselt (18) have emphasized the need f o r information based on work with raw products rather than with brines from processed foods, and data reported more recently by Reed, Bohrer, and Cameron (10) indicate that heat resistance of spores in a given vegetable substrate may cliff e r considerably, depending on whether the substrate is prepared as a pt1ri.e or as larger piwrs sixspended in brine.With respect to processes f o r nonpurked vegetables, it seems reasonable to assume that the latter medium would be superior to the p r 4 e in providing environmental conditions that simulate conditioiis to which spores are exposed in containers of vegetables during processing.The study reported in this article, was undertaken to augment currently available data by determining the constants of thermal-death-time curves of P. A. 3679 spores heated in 13 low-and medium-acid vegetables, chopped or cut.Terms and nomenclature used in this paper are coiisistent with those used by Ball ( 3 ) , Townsend, Esty, and Baselt (18), Sognefest and Benjamin ( 1 4 ) , Reed, Bohrer, and Cameron (ZO), and others. E X P E R I M E N T A L METHODSPreparation of spore suspensions. Spore suspensions of P. A. 3679 were prepared by culturing the organism in 10% egg-meat medium (Difco) a t 3OoC.(86"F.) f o r 3 weeks, filtering the medium through glass wool, centrifuging the filtrate, and suspending the spores in a small volume of sterile 0.5% peptone solution. Concentrated suspensions, containing 3 X lo8 to 3 X lo8 spores per ml., were distributed in 2 t o 4 ml. quantities in TDT (thermal-death-time) tnhes. The tubes were sealed and heated for 20 minutes at 1OO0C.(212"P.) (12) and held under refrigeration until used.Preparation of substrates. Both commercially frozen and fresh food samples were used for preparing food substrates. Frozen foods were thawed; fresh vegetables were washed, trimmed, and blanched. All samples, with the exception of asparagus and spinach, were chopped in a hand food chopperb. Asparagus and spinach were chopped

No abstract

Previous evidence indicated that methionine in food proteins reacts with carbohydrates under the influence of heat to form complexes of obscure nature which are nutritionally inferior to methionine itself. In this study, to gain information which might elucidate the nature of this kind of complex, a model compound was synthesized from dextrose and meth-

C for six days, centrifuged to remove the bulk of the organisms, and the supernatants subsequently filtered through Coors porcelain filters. Flocculation units and the minimum lethal dose for guinea pigs were determined on each culture TABLE 1 Effect of the addition of L-tyrosine to the medium TOXIN MG L-TYROSINE PER 100 ML MEDIUM Lf pr ml Minimum lethMl lethal dose doeper ml thai dos 0 80

Information on the thermal resistance characteristics of specific spoilage organisms is needed t o estimate the lethalities of heat treatments applied in the pasteurization or sterilization of foods. Data now in the literature provide substantial basis for the assumption that, f o r a given organism under specified conditions, thermal death time is an exponential function of temperature. Thus, the resistance characteristics of a spoilage organism are designated by a thermal death time curve which, for practical purposes, is a straight line on semilogarithmic paper defined by a slope or z value and a point or F value (1). These data are also sufficient to demonstrate that the F value for a given organism depends upon the nature of the medium in which its determination i s made (5, 6).Slope or z value of the thermal death time curve also appears to be influenced b y the medium in which it is determined but relevant data are less conclusive. Thus, reported heat resistance data for spores of Cameron's Putrefactive Anaerobe 3679, a typical low-acid canned food spoilage organism, can be interpreted as evidence that z values of its thermal death time curves vary when determined in different food substrates (6). However, it is also notable that replicated determinations in a single food substrate have yielded z values exhibiting a range of variation comparable to that observed from determinations in several different substrates. For example, Townsend, Esty, and Baselt (14) using asparagus, peas, spinach, and milk as substrates, observed composite z values for P. A. 3679 spores varying from 16.9 to 21.1. At the same time individual determinations in asparagus yielded z values ranging from 16.6 to 30.0.In a previous paper, Reynolds, Kaplan, Spencer, and Lichtenstein (6) reported data on the characteristics of thermal death time curves for P. A. 3679 spores heated in 13 different vegetable substrates. The purpose of this report is to present additional thermal death time data on P. A. 3679 and Clostridiunz botulinum spores and to determine whether the variations in z values that were observed when spores were heated in a number of different substrates, represent real interactions between substrate and relative spore resistance or whether they can be attributed to uncontrolled variables in the experimental methodology 1ist.d. METHODSThe methods, media, techniques, and nomenclature used in this study mere tbose previously aescribea (6). Spore suspensions of Clostridim botulinum 313-B were prepared 173