Synergistic Inactivation of Spores of ProteolyticClostridium botulinumStrains by High Pressure and Heat Is Strain and Product Dependent

Abstract

The combined high pressure and heat resistances of spores of five proteolytic Clostridium botulinum strains and of the nonpathogenic surrogate strain Clostridium sporogenes PA3679 were compared with their heat-only resistances on the basis of equivalent accumulated thermal lethality, expressed as equivalent minutes at a reference temperature of 105°C (F 105°C ). Comparisons were made with three model (i.e., diluted) products, namely, 30% (wt/wt) Bolognese sauce, 50% (wt/wt) cream sauce, and rice water agar. Pressure was determined to act synergistically with heat during high-pressure thermal (HPT) processing for C. botulinum FRRB 2802 (NCTC 7273) and C. botulinum FRRB 2804 (NCTC 3805 and 62A) in the Bolognese and cream sauces and for C. botulinum FRRB 2807 (213B) in the Bolognese sauce only. No synergy was observed for C. botulinum FRRB 2803 (NCTC 2916) or FRRB 2806 (62A) or C. sporogenes FRRB 2790 (NCTC 8594 and PA3679) in any of the model products. No significant protective effect of pressure against spore inactivation was determined for any Clostridium strain in any product. Because synergy was not consistently observed among strains of C. botulinum or among products, the prediction of inactivation of C. botulinum spores by HPT sterilization (HPTS) for the present must assume a complete lack of synergy. Therefore, any HPTS process for low-acid shelf-stable foods must be at least thermally equivalent to an F 0 process of 2.8 min, in line with current good manufacturing practices. The results of this study suggest that the use of C. sporogenes PA3679 as a surrogate organism may risk overestimating inactivation of C. botulinum by HPT processing.Low-acid shelf-stable products that are microbiologically safe and stable are not obtainable by high-pressure processing (HPP) at near-ambient temperatures, as bacterial spores can survive pressures above 1,500 MPa (3,6,16,35), which far exceed the pressure capabilities of current commercial HPP equipment. Extensive inactivation of bacterial spores by high pressure is likely only to be realized in combination with initial process temperatures that exceed 60°C (16,20,23,24,31,37,39; C. M. Roberts and D. G. Hoover, presented at the Institute of Food Technologists 1996 annual meeting). Of particular interest (and concern) for low-acid shelf-stable foods is the ability of a combined high pressure and heat process to synergistically inactivate spores of the major bacterial spore-forming pathogens of concern, which are proteolytic strains of the neurotoxigenic species Clostridium botulinum.The combined high pressure and heat resistances of spores of a number of proteolytic C. botulinum strains in a number of different matrices have been investigated. Proteolytic C. botulinum type A BS-A and 62A spores were inactivated by 2 and 3 log 10 , respectively, in phosphate buffer (0.067 M, pH 7.0) after 20 min at 827 MPa at 75°C and by 3.2 log 10 and 2.7 log 10 , respectively, in a crabmeat blend (pH 7.2 to 7.4) after 15 min (29). For mashed carrot, a 12-min process at 600 MPa and 80°C ...

Strong and Consistently Synergistic Inactivation of Spores of Spoilage-AssociatedBacillusandGeobacillusspp. by High Pressure and Heat Compared with Inactivation by Heat Alone

“…The Bolognese sauce, cream sauce, and rice were diluted to 30, 50, and 40% (wt/wt), respectively, with SDW and blended as described previously (7). The water from the blended rice mixture was combined 1:1 with 3% (wt/vol) molten agar as previously described (7). The addition of agar was required to provide greater control of the prepressurization heating process.…”

“…Previously, we have shown that, in laboratory scale experiments, the inactivation of spores of proteolytic Clostridium botulinum by HPT processing is similar to that achieved under thermal-only processing conditions compared on the basis of accumulated thermal lethality (F T z ) (7). While we have noted some synergy between heat and high pressure for the inactivation of spores of proteolytic C. botulinum, this synergy appears to be dependent on both the strain and the product (7). Contrary to the case for proteolytic C. botulinum, there are a number of published studies suggesting that the most heat-resistant spoilage bacterium of concern for LASSF, Geobacillus stearothermophilus, is not nearly as resistant to thermal processing under high pressure as its heat resistance would predict (2,14,17,21,24).…”

“…To date, the comparison of inactivation of spores by HPT and thermal-only processing on the basis of F T z at reference temperature (T ref ), and over the entire process, has been reported only for C. botulinum and Clostridium sporogenes spores (7). There is a need to comprehensively and systematically assess the HPT resistances of other spore-forming species of interest for LASSF using this approach.…”

Genetic Diversity of Clostridium sporogenes PA 3679 Isolates Obtained from Different Sources as Resolved by Pulsed-Field Gel Electrophoresis and High-Throughput Sequencing

“…However, a study by Bull et al (49) examined the resistance of NCTC8594 spores to combined high temperature and pressure in various food matrices and compared it with that of spores of C. botulinum strains 7273B, 62-A, 213B, and NCTC2916 under the same conditions. They found that NCTC8594 was more sensitive to combined high temperature and pressure than the majority of C. botulinum spores tested and concluded that NCTC8594 may not be a suitable surrogate for C. botulinum, at least for high-pressure thermal process validation studies (49).…”

“…Non-heat-treated controls were heat shocked at 80°C for 10 min and are reported as spore-forming units per milliliter. to batch as well as being strain dependent (9,26,49,57,58). Based on the results of this study, a reexamination and reevaluation of the thermal destruction data reported in the literature based on the "isolate" of PA 3679 used in a particular study are warranted.…”