THERMAL DESTRUCTION OF CAMERON'S PUTREFACTIVE ANAEROBE 3679 IN FOOD SUBSTRATES^a

Abstract

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

Clostridium sporogenes PA 3679 and Its Uses in the Derivation of Thermal Processing Schedules for Low-Acid Shelf-Stable Foods and as a Research Model for Proteolytic Clostridium botulinum

“…Among those characteristics that undoubtedly make PA 3679 a good thermal processing surrogate for proteolytic C. botulinum are its nontoxigenicity (31), the relative ease with which spore crops with a relatively high degree of heat resistance can be produced (30,113), its ready detection through off-odor and gas formation (33,73,88), and its genetic similarity with proteolytic strains of C. botulinum ((46) and as indicated by the present study).…”

“…During the mid-1900s, the resistance values of PA 3679 were used widely for designing processes for low-acid foods that enabled the processor to achieve economically acceptable levels of spoilage. Rapid cooling of the products subsequent to processing, and storage at temperatures inhibitory to growth, were relied upon to prevent the growth of any of the more heat-resistant thermophiles that might have survived the thermal process (73,94).…”

Significance of Variations in Observed Slopes of Thermal Death Time Curves for Putrefactive Anaerobes

“…The methods, media, techniques, and nomenclature used in this study mere tbose previously aescribea (6). Spore suspensions of Clostridim botulinum 313-B were prepared 173…”

Determination of a process time for a new product: canned low acid artichoke hearts

“…The thermal resistance of PA 3679 spores in artichoke puree with pH > 4.5 is not known, but the influence of substrate and pH on the thermal resistance in other products has been studied (e.g. Reynolds et al, 1951;Cameron, Leonard & Barret, 1980).…”