High-pressure destruction kinetics of Clostridium sporogenes spores in ground beef at elevated temperatures.

High pressure (HP) is an alternative technique for thermal sterilization of foods with minimum quality loss. HP destruction kinetics of bacterial spores is essential to establishing sterilization process, but knowledge in this field is still very limited. In this study, destruction kinetics was investigated using Clostridium sporogenes PA 3679 (ATCC7955) spores in extra-lean ground beef (5 g each sealed in a sterile plastic bag). Duplicated samples were subjected to HP treatments at 700, 800 and 900 MPa in a HP system equipped with a Polyoxymethylene insulator to maintain constant temperatures at 80, 90 and 100 degrees C during pressure-holding time. The kinetic parameters of the spores (D- and Z-values) were evaluated at these pressures and temperatures. For the pressure from 700 to 900 MPa, D-values ranged from 15.8 to 7.0 and 1.5 to 0.63 min at 80 and 100 degrees C, respectively. The pressure resistance of Z(T)(P) value was 520-563 MPa at 80-100 degrees C. The temperature resistance of Z(P)(T) value was 19.1-19.7 degrees C at 700-900 MPa, much higher than that at atmospheric condition (12.4 degrees C). A regression model was generated which can be used to predict D-value or the death time of a minimum process under given pressure and temperature conditions. HP treatment with elevated temperatures can destroy bacterial spores with a shorter time or lower temperature than conventional thermal processing. This study provides useful information for the achievement of a safe HP sterilization process.

Heat inactivation of Listeria monocytogenes and Salmonella enterica serovar Typhi in a typical bologna matrix during an industrial cooking-cooling cycle.

The heat resistance of Salmonella enterica serovar Typhi PF-724 and Listeria monocytogenes 2812 was determined in a commercial bologna batter. The heat inactivation of the two bacterial species was also studied in a semiautomatic pilot smokehouse under cooking conditions that reproduced an industrial bologna process. S. enterica serovar Typhi PF-724 was less heat resistant than L. monocytogenes 2812. The D-values (times required to reduce the population by 1 logarithmic cycle) for S. enterica serovar Typhi PF-724 ranged from 10.11 to 0.04 min for temperatures of 50 to 70 degrees C, while for L. monocytogenes 2812, the D-values were 2.5-, 4.9-, 3.8-, 3.3-, and 2-fold higher at 50, 55, 60, 65, and 70 degrees C, respectively, than for S. enterica serovar Typhi PF-724. However, the z-value (temperature required to reduce log D by 1 logarithmic cycle) for S. enterica serovar Typhi PF-724 (5.72 degrees C) was not significantly different from the z-value for L. monocytogenes 2812 (7.04 degrees C), indicating that a given increase in temperature would have a similar effect on the decimal reduction time for both bacterial species in that meat emulsion. Our data on experimentally inoculated batter also showed that processing bologna at a cooking-cooling cycle commonly used in the industry resulted in a minimum 5-log reduction for both S. enterica serovar Typhi PF-724 and L. monocytogenes 2812.

Postprocessing in vitro digestion challenge to evaluate survival of Escherichia coli O157:H7 in fermented dry sausages.

Fermented dry sausages, inoculated with Escherichia coli O157:H7 during batter preparation, were submitted to an in vitro digestion challenge to evaluate the extent to which passage through the human gastrointestinal tract could inactivate the pathogenic cells, previously stressed by the manufacturing process. The numbers of surviving E. coli O157:H7 cells remained constant after a 1-min exposure of the finely chopped sausage to synthetic saliva or during the following 120-min exposure to synthetic gastric juice at an initial pH of 2.0. However, significant (P < or = 0.05) growth of the pathogen (1.03 to 2.16 log10 CFU/g) was observed in a subsequent 250-min exposure to a synthetic pancreatic juice at pH 8.0. In a different set of experiments, fractions from the gastric suspension were transferred into the synthetic pancreatic juice at 30-min intervals to mimic the dynamics of gastric emptying. Concurrently, the pH of the remaining gastric fluid was reduced to 3.0, 2.5, and 2.0 to simulate the gradual reacidification of the stomach contents after the initial buffering effect resulting from meal ingestion. Under these new conditions, pathogen growth during pancreatic challenge was observed for the first few fractions released from the stomach (90 min of exposure [pH 2.5]), but growth was no longer possible in the fractions submitted to the most severe gastric challenge (120 min of exposure [pH < 2.2]).

A model study of Escherichia coli O157:H7 survival in fermented dry sausages--influence of inoculum preparation, inoculation procedure, and selected process parameters.

The influence of inoculum preparation, inoculation level, and inoculation procedure on Escherichia coli O157:H7 inactivation during the manufacture of fermented sausage was evaluated in a model study. Prior growth in glucose-enriched tryptone soya broth, which provided exposure to mildly acidic conditions (pH 4.8), had no effect on the later survival of E. coli O157: H7 strains 5-1 and ATCC 43894 under extremely acidic conditions (pH 2), but the same strains became sensitive to acidity after 7 days of incubation on the surface of refrigerated beef (as per the normal contamination route from slaughter to further processing). In subsequent sausage production trials, the extent of destruction observed for E. coli O157:H7 strains F-90, 5-1, and ATCC 43894 inoculated directly into the meat batter was unchanged when the inoculation level was decreased from 7.3 to 4.7 log CFU/g, but the level of inactivation was ca. 1 log higher when the surfaces of beef cuts, rather than the batter, were inoculated 7 days prior to processing. Regardless of processing conditions (fermentation to a pH of < or = 5.0 at 24 or 37 degrees C, drying at 14 degrees C to a water activity [a(w)] value of 0.91 or 0.79), strains F-90, 5-1, and ATCC 43894 showed similar survival capacities during the manufacture of sausage. A approximately 2-log reduction in pathogen numbers was generally obtained after samples were dried to an a(w) of 0.91, irrespective of fermentation temperature. The addition of a 5-day predrying holding stage at the fermentation temperature significantly (P < 0.05) increased pathogen inactivation when fermentation was carried out at 37 degrees C (but not when it was carried out at 24 degrees C). However, significant pathogen reductions (4 to 5 log CFU/g) were achieved only for extensively dried products (a(w) = 0.79).