Influence of Cooling Rate on Outgrowth of Clostridium perfringens Spores in Cooked Ground Beef

The effect of low-temperature long-time (LTLT) cooking on survival of potentially pathogenic Clostridium perfringens in beef

Low-temperature long-time (LTLT) cooking may lead to risk of potential survival of pathogenic bacteria such as Clostridium perfringens in cooked meat. In this study, the effect of LTLT cooking on C. perfringens was investigated at temperatures commonly used by caterers. Brain heart infusion broth (BHIB) and meat cubes in pouches (vacuumed or non-vacuumed) were inoculated with C. perfringens (NCTC 8238) and heated at temperatures of 48 °C, 53 °C, 55 °C, 60 °C and 70 °C. The viability of C. perfringens in BHIB and meat was monitored using plate counting and the D-value of each thermal treatment was determined. The recovery of C. perfringens after thermal treatment was assessed using optical density measurements. Flow cytometry analysis was used to assess the physiological status (death/injury) of C. perfringens cells in BHIB. The results showed that the required log reduction (6-log) of C. perfringens can be achieved at 55 °C but not at 48 °C or 53 °C. The D-values at all temperatures were higher in meat compared to BHIB while the D-value at 55 °C was higher in non-vacuum compared to vacuum sealed meat. C. perfringens cells were able to recover and grow to pathogenic levels when thermal treatment was unable to achieve the required 6-log reduction. In BHIB, percentage of dead cells increased gradually at 48 °C, 53 °C and 55 °C while an immediate increase (>95%) was observed at 60 °C and 70 °C. These results are important to food safety authorities allowing to set the time-temperature combinations to be used in LTLT cooking to obtain safe meat.

Behavior and Inactivation of Enterotoxin-Positive Clostridium perfringens in Pork Picadillo and Tamales Filled with Pork Picadillo under Different Cooking, Storage, and Reheating Conditions

This study analyzed the behavior of Clostridium perfringens in individual ingredients and tamales containing different pathogen concentrations upon exposure to different temperatures and methods of cooking, storage, and reheating. In ground pork, C. perfringens cells were inactivated when exposed to 95°C for 30 min. Three lots of picadillo inoculated with 0, 3, and 5 log CFU/g C. perfringens cells, respectively, were exposed to different storage temperatures. At 20°C, cell counts increased 1 log in all lots, whereas at 8°C, counts decreased by 2 log. Four lots of tamales prepared with picadillo inoculated with 0, 2, 3, and 7 log CFU/g prior to the final cooking step exhibited no surviving cells (91°C for 90, 45, or 35 min). Four lots of tamales were inoculated after cooking with concentrations of 0, 0.6, 4, and 6 log CFU/g of the pathogen and then stored at different temperatures. In these preparations, after 24 h at 20°C, the count increased by 1.4, 1.7, and 1.8 log in the tamales inoculated with 0.6, 4, and 6 log inoculum, respectively. When they were stored at 8°C for 24 h, enumerations decreased to <1, 2.5, and 1.9 log in the tamales inoculated with 0.6, 4, and 6 log of C. perfringens cells, respectively. However, when the lots were exposed to 20°C and then 8°C, 0.8, 1.8, and 2.4 log changes were observed for the tamales inoculated with 0.6, 4, and 6 log, respectively. Microwaving, steaming, and frying to reheat tamales inoculated with 6 log CFU/g C. perfringens cells showed that the pathogen was inactivated after 2 min of exposure in the microwave and after 5 min of exposure to steam. In contrast, no inactivation was observed after 5 min of frying. The tamales inoculated with spores (7 log most probable number [MPN]/g) showed a decrease of 2 log after steaming or frying, and no survival was observed after microwaving. Tamales inoculated with spores (7 log MPN/g) after cooking were susceptible to microwaves, but 2.4 and 255 MPN/g remained after frying and steaming, respectively.

Alternative cooling procedures for large, intact meat products to achieve stabilization microbiological performance standards

Achieving the U. S. Department of Agriculture, Food Safety and Inspection Service (USDA-FSIS) stabilization microbiological performance standards for cooling procedures proves to be challenging for processors of large, whole-muscle meat products. This study was conducted to determine if slower cooling times than those provided by USDA-FSIS guidance will comply with the performance standard for Clostridium perfringens. Large (9 to 12 kg) cured bone-in hams (n = 110) and large (8 to 13 kg) uncured beef inside rounds (n = 100) were used. Stabilization treatments extended times to reduce internal product temperature from 54.4 to 26.7°C (hams and rounds) and from 26.7 to 7.2°C (for hams) and 26.7 to 4.4°C (for rounds). Control treatments, defined by current USDA-FSIS Appendix B guidelines, and a "worst-case scenario" treatment, in which products were cooled at room temperature (approximately 22.8°C) until internal product temperature equilibrated, were used. For both hams and rounds, stabilization showed less than 1-log growth of C. perfringens for all treatments, with the exception of the worst-case scenario for rounds. As expected for products cooled at room temperature, there was >1-log growth of C. perfringens reported for rounds, and the addition of curing ingredients to hams had an inhibitory effect on the growth of C. perfringens. The results demonstrate that industry may have increased flexibility associated with cooling large, whole-muscle cuts while still complying with the required stabilization microbiological performance standards.

Inhibition of Clostridium perfringens Spore Germination and Outgrowth by Buffered Vinegar and Lemon Juice Concentrate during Chilling of Ground Turkey Roast Containing Minimal Ingredients†

Inhibition of Clostridium perfringens spore germination and outgrowth in ground turkey roast containing minimal ingredients (salt and sugar), by buffered vinegar (MOstatin V) and a blend (buffered) of lemon juice concentrate and vinegar (MOstatin LV) was evaluated. Ground turkey roast was formulated to contain sea salt (1.5%), turbinado sugar (0.5%), and various concentrations of MOstatin V (0.75, 1.25, or 2.5%) or MOstatin LV (1.5, 2.5, or 3.5%), along with a control (without MOstatins). The product was inoculated with a three-strain spore cocktail of C. perfringens to obtain initial spore levels of ca. 2.0 to 0.5 log CFU/g. Inoculated products were vacuum packaged, heat shocked for 20 min at 75°C, and cooled exponentially from 54.4 to 4.0°C in 6.5, 9, 12, 15, 18, or 21 h. In control samples without MOstatin V or MOstatin LV, C. perfringens populations reached 2.98, 4.50, 5.78, 7.05, 7.88, and 8.19 log CFU/g (corresponding increases of 0.51, 2.29, 3.51, 4.79, 5.55, and 5.93 log CFU/g) in 6.5, 9, 12, 15, 18, and 21 h of chilling, respectively. MOstatin V (2.5%) and MOstatin LV (3.5%) were effective in inhibiting C. perfringens spore germination and outgrowth in ground turkey roast to &lt;1.0 log CFU/g during abusive chilling of the product within 21 h. Buffered vinegar and a blend (buffered) of lemon juice concentrate and vinegar were effective in controlling germination and outgrowth of C. perfringens spores in turkey roast containing minimal ingredients.

Evaluation of the microbial quality of Tajik sambusa and control of Clostridium perfringens germination and outgrowth by buffered sodium citrate and potassium lactate

Clostridium perfringens spore destruction, aerobic plate counts (APCs), and counts of Enterobacteriaceae, coliforms, and Escherichia coli during baking of sambusa (a traditional Tajik food) were evaluated. Control of germination and outgrowth of C. perfringens spores in sambusa during cooling at room or refrigerated temperatures was evaluated using organic acid salts (buffered sodium citrate [Ional] and 1 and 2% potassium lactate, wt/wt). Sambusa were prepared with 40 g of either inoculated or noninoculated meat and baked for 45 min at 180 degrees C. For evaluation of destruction of C. perfringens spores during heating and germination and outgrowth of spores during cooling, ground beef was inoculated and mixed with a three-strain cocktail of C. perfringens spores. Aerobic bacteria, Enterobacteriaceae, coliforms, and E. coli were enumerated in noninoculated sambusa before and after baking and after cooling at room or refrigeration temperatures. After baking, APCs and Enterobacteriaceae and coliform counts were reduced by 4.32, 2.55, and 1.96 log CFU/g, respectively. E. coli counts were below detectable levels in ground beef and sambusa samples. Enterobacteriaceae, coliform, and E. coli counts were below detectable levels (< 0.04 log CFU/g) in sambusa after cooling by both methods. Total C. perfringens populations increased (4.67 log CFU/g) during cooling at room temperature, but minimal increases (0.31 log CFU/g) were observed during cooling under refrigeration. Incorporation of 2% (wt/wt) buffered sodium citrate controlled C. perfringens spore germination and outgrowth (0.25 log CFU/g), whereas incorporation of up to 2% (wt/wt) potassium lactate did not prevent C. perfringens spore germination and outgrowth. Incorporation of organic acid salts at appropriate concentrations can prevent germination and outgrowth of C. perfringens in improperly cooled sambusa.

Predictive model for Clostridium perfringens growth in roast beef during cooling and inhibition of spore germination and outgrowth by organic acid salts

Spores of foodborne pathogens can survive traditional thermal processing schedules used in the manufacturing of processed meat products. Heat-activated spores can germinate and grow to hazardous levels when these products are improperly chilled. Germination and outgrowth of Clostridium perfringens spores in roast beef during chilling was studied following simulated cooling schedules normally used in the processed-meat industry. Inhibitory effects of organic acid salts on germination and outgrowth of C. perfringens spores during chilling and the survival of vegetative cells and spores under abusive refrigerated storage was also evaluated. Beef top rounds were formulated to contain a marinade (finished product concentrations: 1% salt, 0.2% potassium tetrapyrophosphate, and 0.2% starch) and then ground and mixed with antimicrobials (sodium lactate and sodium lactate plus 2.5% sodium diacetate and buffered sodium citrate and buffered sodium citrate plus 1.3% sodium diacetate). The ground product was inoculated with a three-strain cocktail of C. perfringens spores (NCTC 8238, NCTC 8239, and ATCC 10388), mixed, vacuum packaged, heat shocked for 20 min at 75 degrees C, and chilled exponentially from 54.5 to 7.2 degrees C in 9, 12, 15, 18, or 21 h. C. perfringens populations (total and spore) were enumerated after heat shock, during chilling, and during storage for up to 60 days at 10 degrees C using tryptose-sulfite-cycloserine agar. C. perfringens spores were able to germinate and grow in roast beef (control, without any antimicrobials) from an initial population of ca. 3.1 log CFU/g by 2.00, 3.44, 4.04, 4.86, and 5.72 log CFU/g after 9, 12, 15, 18, and 21 h of exponential chilling. A predictive model was developed to describe sigmoidal C. perfringens growth curves during cooling of roast beef from 54.5 to 7.2 degrees C within 9, 12, 15, 18, and 21 h. Addition of antimicrobials prevented germination and outgrowth of C. perfringens regardless of the chill times. C. perfringens spores could be recovered from samples containing organic acid salts that were stored up to 60 days at 10 degrees C. Extension of chilling time to > or =9 h resulted in >1 log CFU/g growth of C. perfringens under anaerobic conditions in roast beef. Organic acid salts inhibited outgrowth of C. perfringens spores during chilling of roast beef when extended chill rates were followed. Although C. perfringens spore germination is inhibited by the antimicrobials, this inhibition may represent a hazard when such products are incorporated into new products, such as soups and chili, that do not contain these antimicrobials, thus allowing spore germination and outgrowth under conditions of temperature abuse.

Validation of bacon processing conditions to verify control of Clostridium perfringens and Staphylococcus aureus

It is unclear how rapidly meat products, such as bacon, that have been heat treated but not fully cooked should be cooled to prevent the outgrowth of spore-forming bacterial pathogens and limit the growth of vegetative cells. Clostridium perfringens spores and vegetative cells and Staphylococcus aureus cells were inoculated into ground cured pork bellies with and without 1.25% liquid smoke. Bellies were subjected to the thermal profiles of industrial smoking to 48.9 degrees C (120 degrees F) and normal cooling of bacon (3 h) as well as a cooling phase of 15 h until the meat reached 7.2 degrees C (45 degrees F). A laboratory-scale bacon smoking and cooling operation was also performed. Under normal smoking and cooling thermal conditions, growth of C. perfringens in ground pork bellies was <1 log regardless of smoke. Increase of S. aureus was 2.38 log CFU/g but only 0.68 log CFU/g with smoke. When cooling spanned 15 h, both C. perfringens and S. aureus grew by a total of about 4 log. The addition of liquid smoke inhibited C. perfringens, but S. aureus still achieved a 3.97-log increase. Staphylococcal enterotoxins were detected in five of six samples cooled for 15 h without smoke but in none of the six samples of smoked bellies. In laboratory-scale smoking of whole belly pieces, initial C. perfringens populations of 2.23 +/- 0.25 log CFU/g were reduced during smoking to 0.99 +/- 0.50 log CFU/g and were 0.65 +/- 0.21 log CFU/g after 15 h of cooling. Populations of S. aureus were reduced from 2.00 +/- 0.74 to a final concentration of 0.74 +/- 0.53 log CFU/g after cooling. Contrary to findings in the ground pork belly system, the 15-h cooling of whole belly pieces did not permit growth of either pathogen. This study demonstrates that if smoked bacon is cooled from 48.9 to 7.2 degrees C (120 to 45 degrees F) within 15 h, a food safety hazard from either C. perfringens or S. aureus is not likely to occur.

Development of an integrated model for heat transfer and dynamic growth of Clostridium perfringens during the cooling of cooked boneless ham

Numerous small meat processors in the United States have difficulties complying with the stabilization performance standards for preventing growth of Clostridium perfringens by 1 log10 cycle during cooling of ready-to-eat (RTE) products. These standards were established by the Food Safety and Inspection Service (FSIS) of the US Department of Agriculture in 1999. In recent years, several attempts have been made to develop predictive models for growth of C. perfringens within the range of cooling temperatures included in the FSIS standards. Those studies mainly focused on microbiological aspects, using hypothesized cooling rates. Conversely, studies dealing with heat transfer models to predict cooling rates in meat products do not address microbial growth. Integration of heat transfer relationships with C. perfringens growth relationships during cooling of meat products has been very limited. Therefore, a computer simulation scheme was developed to analyze heat transfer phenomena and temperature-dependent C. perfringens growth during cooling of cooked boneless cured ham. The temperature history of ham was predicted using a finite element heat diffusion model. Validation of heat transfer predictions used experimental data collected in commercial meat-processing facilities. For C. perfringens growth, a dynamic model was developed using Baranyi's nonautonomous differential equation. The bacterium's growth model was integrated into the computer program using predicted temperature histories as input values. For cooling cooked hams from 66.6 degrees C to 4.4 degrees C using forced air, the maximum deviation between predicted and experimental core temperature data was 2.54 degrees C. Predicted C. perfringens growth curves obtained from dynamic modeling showed good agreement with validated results for three different cooling scenarios. Mean absolute values of relative errors were below 6%, and deviations between predicted and experimental cell counts were within 0.37 log10 CFU/g. For a cooling process which was in exact compliance with the FSIS stabilization performance standards, a mean net growth of 1.37 log10 CFU/g was predicted. This study introduced the combination of engineering modeling and microbiological modeling as a useful quantitative tool for general food safety applications, such as risk assessment and hazard analysis and critical control points (HACCP) plans.

Development of a model to predict growth of Clostridium perfringens in cooked beef during cooling

The objective of this work was to develop a new model to predict the growth of Clostridium perfringens in cooked meat during cooling. All data were collected under changing temperature conditions. Individual growth curves were fit using DMFit. Germination outgrowth and lag (GOL) time was modeled versus temperature at the end of GOL using conservative assumptions. Each growth curve was used to estimate a series of exponential growth rates at a series of temperatures. The squareroot model was used to describe the relationship between the square root of the average exponential growth rate and effective temperature. Predictions from the new model were in close agreement with the data used to create the model. When predictions from the model were compared with new observations, fail-dangerous predictions were made a majority of the time. When GOL time was predicted exactly, many fail-dangerous predictions shifted toward the fail-safe direction. Two important facts regarding C. perfringens should impact future modeling research with this organism and may have broader food safety policy implications: (i) the normal variability in the response of the organism from replicate to replicate may be quite large (1 log CFU) and may exceed the current U.S. Food Safety Inspection Service performance standard, and (ii) the accuracy of the GOL time model has a profound influence upon the overall prediction, with small differences in GOL time prediction (approximately 1 h) having a very large effect on the predicted final concentration of C. perfringens.

Effect of spices and organic acids on the growth of Clostridium perfringens during cooling of cooked ground beef

This study evaluated the effect of organic acids and spices, alone or combined, on Clostridium perfringens growth in cooked ground beef during alternative cooling procedures. Ground beef was inoculated with a three-strain cocktail of C. perfringens (ATCC 10388, NCTC 8238, and NCTC 8239) at 2 log spores per g and prepared following an industrial recipe (10% water, 1.5% sodium chloride, and 0.5% sodium triphosphate [wt/wt]). Treatments consisted of the base meat plus combinations of commercial solutions of sodium lactate or sodium citrate (0 or 2%, wt/wt) with chili, garlic and herbs, curry, oregano, or clove in commercial powder form (0 or 1%, wt/wt). Untreated meat was used as a control. Vacuum-packaged samples of each treatment were cooked (75 degrees C for 20 min) and cooled from 54.4 to 7.2 degrees C in 15, 18, or 21 h. Spore counts were estimated after inoculation, cooking, and cooling. All treatments containing sodium citrate reduced the population of C. perfringens about 0.38 to 1.14 log units during each of the three cooling procedures. No sodium citrate and spice treatment combinations showed antagonisms or synergisms. Regardless of the cooling time, the control ground beef or treatments with any of the five spices alone supported C. perfringens growth above the U.S. Department of Agriculture stabilization guidelines of 1 log unit. Except for the 21-h cooling period, addition of sodium lactate prevented C. perfringens growth over 1 log unit. Depending on the cooling time and spice, some combinations of sodium lactate and spice kept C. perfringens growth below 1 log unit.

Growth potential of Clostridium perfringens during cooling of cooked meats

Many meat-based food products are cooked to temperatures sufficient to inactivate vegetative cells of Clostridium perfringens, but spores of this bacterium can survive, germinate, and grow in these products if sufficient time, temperature, and other variables exist. Because ingestion of large numbers of vegetative cells can lead to concomitant sporulation, enterotoxin release in the gastrointestinal tract, and diarrhea-like illness, a necessary food safety objective is to ensure that not more than acceptable levels of C. perfringens are in finished products. As cooked meat items cool they will pass through the growth temperature range of C. perfringens (50 to 15 degrees C). Therefore, an important step in determining the likely level of C. perfringens in the final product is the estimation of growth of the pathogen during cooling of the cooked product. Numerous studies exist dealing with just such estimations, yet consensual methodologies, results, and conclusions are lacking. There is a need to consider the bulk of C. perfringens work relating to cooling of cooked meat-based products and attempt to move toward a better understanding of the true growth potential of the organism. This review attempts to summarize observations made by researchers and highlight variations in experimental approach as possible explanations for different outcomes. An attempt is also made here to identify and justify optimal procedures for conducting C. perfringens growth estimation in meat-based cooked food products during cooling.

Inhibitory effects of organic acid salts on growth of Clostridium perfringens from spore inocula during chilling of marinated ground turkey breast

Inhibition of Clostridium perfringens germination and outgrowth by salts of organic acids such as sodium lactate, sodium acetate, buffered sodium citrate and buffered sodium citrate supplemented with sodium diacetate was evaluated during continuous chilling of ground turkey. Turkey breast meat was injected with a brine-containing NaCl, potato starch and potassium tetra pyrophosphate to yield final in-product concentrations of 0.85%, 0.25% and 0.20%, respectively. The meat was ground, mixed with either sodium lactate (1%, 2%, 3% or 4%), sodium acetate (1% or 2%), buffered sodium citrate (Ional, 1%) or buffered sodium citrate supplemented with sodium diacetate (Ional Plus trade mark, 1%), in addition to a control that did not contain added antimicrobials. Each product was mixed with a three-strain C. perfringens spore cocktail to obtain final spore concentrations of ca. 2.8 log10 spores/g. Inoculated products (10 g) were packaged into cook-in-bags (2 x 3 in.), vacuum sealed, cooked at 60 degrees C for 1 h, and subsequently chilled from 54.4 to 7.2 degrees C in 15, 18 and 21 h following exponential chilling rates. Products were sampled immediately after cooking and then after chilling. Chilling of cooked turkey following 15, 18 and 21 h chill rates resulted in germination and outgrowth of C. perfringens spores to 6.6, 7.58 and 7.95 log10 CFU/g populations, respectively, from initial spore populations of ca. 2.80 log10 CFU/g. Incorporation of sodium lactate (1%), sodium acetate (1%), Ional or Ional Plus (1%) substantially inhibited germination and outgrowth of C. perfringens spores compared to controls. Final C. perfringens total populations of 3.12, 3.10, 2.38 and 2.92 log10 CFU/g, respectively, were observed following a 15-h exponential chill rate. Similar inhibitory effects were observed for 18 and 21 chill rates with the antimicrobials at 1% concentrations. While sodium lactate and sodium acetate concentrations of 1% were sufficient to control C. perfringens germination and outgrowth (<1.0 log10 CFU/g growth) following 15 h chill rates, higher concentrations were required for 18 and 21 h chill rates. Ional at 1% concentration was effective in inhibiting germination and outgrowth to <1.0 log10 CFU/g of C. perfringens for all three chill rates (15, 18 and 21 h) tested. Use of sodium salts of organic acids in formulation of ready-to-eat meat products can reduce the risk of C. perfringens spore germination and outgrowth during chilling.

Evaluation of a predictive model for Clostridium perfringens growth during cooling

Proper temperature control is essential in minimizing Clostridium perfringens germination, growth, and toxin production. The U.S. Department of Agriculture Food Safety and Inspection Service offers two options for the cooling of meat products: follow a standard time-temperature schedule or validate that alternative cooling regimes result in no more than a 1-log CFU/g increase of C. perfringens and no growth of Clostridium botulinum. The Juneja 1999 model for C. perfringens growth during cooling may be helpful in determining whether the C. perfringens performance standard has been achieved, but this model has not been extensively validated. The objective of this study was to validate the Juneja 1999 model under a variety of temperature situations. The Juneja 1999 model for C. perfringens growth during cooling is fail safe when low (<1 log CFU/ml) or high (>3 log CFU/ml) observed increases occur during exponential cooling. The Juneja 1999 model consistently underpredicted growth at intermediate observed increases (1 to 3 log CFU/ml). The Juneja 1999 model also underpredicted growth whenever exponential cooling took place at two different rates in the first and second portions of the cooling process. This error may be due to faster than predicted growth of C. perfringens cells during cooling or to an inaccuracy in the Juneja 1999 model.

Influence of several methodological factors on the growth of Clostridium perfringens in cooling rate challenge studies

Proper temperature control is essential in preventing Clostridium perfringens food poisoning. The U.S. Department of Agriculture Food Safety and Inspection Service cooling guidelines offer two options for the cooling of meat products: follow a standard time-temperature schedule or validate that alternative cooling regimens result in no more than a 1-log CFU/g increase of C. perfringens and no growth of Clostridium botulinum. The latter option requires laboratory challenge studies to validate the efficacy of a given cooling process. Accordingly, the objective of this study was to investigate the role of several methodological variables that might be encountered during typical C. perfringens challenge studies. Variables studied included plastic bag type (Whirlpak or Spiral Biotech), sealing method (Multivac or FoodSaver), initial spore inoculum size (1 to approximately 3 log CFU/g), and growth environment (ground beef or Trypticase-peptone-glucose-yeast extract [TPGY] broth). The major factors that affected growth were sample bag type and growth environment. Samples incubated in Whirlpak bags showed significantly less growth than those incubated in Spiral Biotech bags, which was likely due to the former bag's greater oxygen permeability. C. perfringens spores showed shorter germination, outgrowth, and lag times and C. perfringens cells showed faster growth rates in ground beef compared with TPGY broth. No significant difference was observed between two different sealing methods. Initial spore inoculum levels in the range studied had no significant effect on final C. perfringens cell concentration.

Evaluation of a Clostridium perfringens predictive model, developed under isothermal conditions in broth, to predict growth in ground beef during cooling

Proper temperature control is essential in minimizing Clostridium perfringens germination, growth, and toxin production. The U.S. Department of Agriculture (USDA) Food Safety and Inspection Service (FSIS) offers two options for the cooling of meat products: follow a standard time-temperature schedule or validate that alternative cooling regimens result in no more than a 1-log(10) CFU/g increase of C. perfringens and no growth of Clostridium botulinum. A mathematical model developed by Juneja et al. (Food Microbiol. 16:335-349, 1999) may be helpful in determining if the C. perfringens performance standard has been achieved, but this model has not been extensively validated. The objective of this study was to validate the Juneja 1999 model in ground beef under a variety of changing temperature and temperature abuse situations. The Juneja 1999 model consistently underpredicted growth of C. perfringens during exponential cooling of ground beef. The model also underpredicted growth of C. perfringens in ground beef cooled at two different rates. The results presented here show generally good agreement with published data on the growth of C. perfringens in similar products. The model error may be due to faster-than-expected exponential growth rates in ground beef during cooling or an error in the mathematical formulation of the model.

Effect of cooling on Clostridium perfringens in pea soup

Foods associated with Clostridium perfringens outbreaks are usually abused after cooking. Because of their short generation times, C. perfringens spores and cells can grow out to high levels during improper cooling. Therefore, the potential of C. perfringens to multiply in Dutch pea soup during different cooling times was investigated. Tubes of preheated pea soup (50 degrees C) were inoculated with cocktails of cells or heat-activated spores of this pathogen. The tubes were linearly cooled to 15 degrees C in time spans of 3, 5, 7.5, and 10 h and were subsequently stored in a refrigerator at 3 or 7 degrees C for up to 84 h. Cell numbers increased by 1-log cycle during the 3-h cooling period and reached their maximum after 10 h of cooling. Subsequent refrigeration hardly reduced cell numbers. Cooling of 3.75 liters of pea soup in an open pan showed that this amount of pea soup cooled from 50 to 15 degrees C in 5 h, which will allow a more than 10-fold increase in cell numbers. These findings emphasize the need of good hygienic practices and quick cooling of heated foods after preparation.

Growth of heat-treated enterotoxin-positive Clostridium perfringens and the implications for safe cooling rates

Clostridium perfringens 790-94 and 44071.C05 carrying a chromosomal and a plasmid cpe gene, respectively, were used to determine differences in heat resistance and growth characteristics between the genotypes. Heat inactivation experiments were conducted using an immersed coil apparatus. Spore germination, outgrowth, and lag phase, together named GOL time, as well as generation times were determined during constant temperatures in fluid thioglycollate (FTG) medium as well as in vacuum-packed, heat-treated minced turkey. GOL time and growth were also monitored during cooling scenarios from 65 to 10 degrees C for 3, 4, 5, 6, and 7 h in vacuum-packed, heat-treated minced turkey. Spores of strain 790-94 were approximately 10-fold more heat resistant at 85 degrees C than those of strain 44071.C05, and strain 790-94 also had a higher temperature growth range in FTG. The higher growth range for a chromosomal enterotoxin-producing CPE+ strain was confirmed using two other strains carrying a chromosomal (NCTC8239) and plasmid (945P) cpe gene. Moreover, strain 790-94 had shorter GOL times at 50 degrees C in turkey and approximately half the generation time compared with strain 44071.C05 at temperatures > or = 45 degrees C in both FTG and turkey. Strain 790-94 increased with 0.3, 1.0, 1.7, and 2.0 logs, respectively, during cooling from 65 to 10 degrees C in 4, 5, 6, and 7 h, which was significantly higher than for strain 44071.C05. A maximum acceptable cooling time of 5 h between 65 and 10 degrees C is suggested.

Dynamic computer simulation of Clostridium perfringens growth in cooked ground beef

The objective of this study was to develop a computer simulation algorithm to dynamically estimate and predict the growth of Clostridium perfringens in cooked ground beef. The computational algorithm was based on the implicit form of the Gompertz model, the growth kinetics of C. perfringens in cooked ground beef, and the fourth-order Runge-Kutta numerical method. This algorithm was validated using a cocktail of three strains of C. perfringens spores grown under isothermal, square-waved, linear cooling, and exponential cooling temperature profiles. In general, the results of computer simulation matched closely with the experimental data with the absolute errors less than 0.5 log(10) CFU/g. This method may be a useful tool for the food industry, regulatory agencies, distributors, and retailers to predict the effect of temperature abuse on the microbial safety of C. perfringens and other foodborne pathogens in processed meat products.

Influence of NaCl content and cooling rate on outgrowth of Clostridium perfringens spores in cooked ham and beef

The effect of NaCl concentration and cooling rate on the ability of Clostridium perfringens to grow from spore inocula was studied with the use of a process that simulates the industrial cooking and cooling of smoked boneless ham and beef roasts. NaCl was added to ground cooked hams A and B (which were commercially obtained) to obtain levels of 2.4, 3.1, 3.6, and 4.1% (wt/wt) and 2.8, 3.3, 3.8, and 4.3% (wt/wt), respectively, and to raw ground beef to obtain levels of 0, 1, 2, 3, and 4% (wt/wt). Ham C, a specially formulated, commercially prepared product, was supplemented with NaCl to obtain levels of 2.0, 2.5, 3.0, and 3.5%. The samples were inoculated with a three-strain mixture of C. perfringens spores to obtain concentrations of ca. 3 log10 CFU/g. Portions of meat (5 g each) were spread into thin layers (1 to 2 mm) in plastic bags, vacuum packaged, and stored at -40 degrees C. Thawed samples were heated at 75 degrees C for 20 min and subsequently cooled in a programmed water bath from 54.4 to < or = 8.5 degrees C in 15, 18, or 21 h. For the enumeration of C. perfringens, samples were plated on tryptose-sulfite-cycloserine agar and incubated in an anaerobic chamber at 37 degrees C for 48 h. Population densities for cooked ham and beef increased as cooling time increased, and NaCl exerted a strong inhibitory effect on the germination and outgrowth of C. perfringens. For beef, while 3% NaCl completely arrested growth, pathogen numbers increased by > or = 3, 5, and 5 log10 CFU/g in 15, 18, and 21 h, respectively, when the NaCl level was <2%. C. perfringens did not grow during cooling for 15, 18, or 21 h in ham samples containing > or = 3.1% NaCl. Results obtained in this study suggest that a 15-h cooling time for cooked ham, which is normally formulated to contain >2% NaCl, would yield an acceptable product (with an increase of <1 log10 CFU/g in the C. perfringens count); however, for beef containing <2% NaCl, C. perfringens populations may reach levels high enough to cause illness.

Use of organic acids for the control of Clostridium perfringens in cooked vacuum-packaged restructured roast beef during an alternative cooling procedure

This study was conducted to determine how well Clostridium perfringens spores germinate and grow in restructured roast beef treated with different commercial organic salts during an alternative chilling procedure. The meat was prepared according to an industrial recipe (10% water, 1.5% sodium chloride, and 0.5% sodium triphosphate). The base meat was treated with sodium citrate at 2 or 4.8% (wt/wt), buffered to a pH of 5.6, 5.0, or 4.4 (six treatments); a 60% (wt/wt) solution of sodium lactate at 2 or 4.8% (wt/wt); sodium acetate at 0.25% (wt/wt); or sodium diacetate at 0.25% (wt/wt). Untreated meat was used as a control. Meat samples were inoculated with a three-strain cocktail of C. perfringens spores (strains ATCC 10388, NCTC 8238, and NCTC 8239). Meat was vacuum packaged in bags and cooked in a stirred water bath to an internal temperature of 75 degrees C for 20 min, and then the bags were cooled from 54.4 to 4.4 degrees C within 18 h. Samples were taken after inoculation, after cooking, and after chilling. Spore and vegetative cell counts were obtained after incubation at 37 degrees C for 8 to 10 h in Fung's Double Tubes containing tryptose sulfite agar without egg yolk enrichment. Cooking was not sufficient to eliminate C. perfringens spores. Over the 18-h cooling period, sodium citrate, sodium lactate, and sodium diacetate reduced the growth of C. perfringens to < 1 log unit, a growth level that meets U.S. Department of Agriculture performance standards. The use of sodium citrate or sodium lactate at a concentration of > or = 2% (wt/wt) inhibited C. perfringens growth over the 18-h cooling period.

Impact of cooking, cooling, and subsequent refrigeration on the growth or survival of Clostridium perfringens in cooked meat and poultry products

In January 1999, the Food Safety and Inspection Service (FSIS) finalized performance standards for the cooking and chilling of meat and poultry products in federally inspected establishments. More restrictive chilling (stabilization) requirements were adopted despite the lack of strong evidence of a public health risk posed by industry practices employing the original May 1988 guidelines (U.S. Department of Agriculture FSIS Directive 7110.3). Baseline data led the FSIS to estimate a "worst case" of 10(4) Clostridium perfringens cells per g in raw meat products. The rationale for the FSIS performance standards was based on this estimate and the assumption that the numbers detected in the baseline study were spores that could survive cooking. The assumptions underlying the regulation stimulated work in our laboratory to help address why there have been so few documented outbreaks of C. perfringens illness associated with the consumption of commercially processed cooked meat and poultry products. Our research took into account the numbers of C. perfringens spores in both raw and cooked products. One hundred ninety-seven raw comminuted meat samples were cooked to 73.9 degrees C and analyzed for C. perfringens levels. All but two samples had undetectable levels (<3 spores per g). Two ground pork samples contained 3.3 and 66 spores per g. Research was also conducted to determine the effect of chilling on the outgrowth of C. perfringens spores in cured and uncured turkey. Raw meat blends inoculated with C. perfringens spores, cooked to 73.9 degrees C, and chilled according to current guidelines or under abuse conditions yielded increases of 2.25 and 2.44 log10 CFU/g for uncured turkey chilled for 6 h and an increase of 3.07 log10 CFU/g for cured turkey chilled for 24 h. No growth occurred in cured turkey during a 6-h cooling period. Furthermore, the fate of C. perfringens in cooked cured and uncured turkey held at refrigeration temperatures was investigated. C. perfringens levels decreased by 2.52, 2.54, and 2.75 log10 CFU/g in cured turkey held at 0.6, 4.4, and 10 degrees C, respectively, for 7 days. Finally, 48 production lots of ready-to-eat meat products that had deviated from FSIS guidelines were analyzed for C. perfringens levels. To date, 456 samples have been tested, and all but 25 (ranging from 100 to 710 CFU/g) of the samples contained C. perfringens at levels of <100 CFU/g. These results further support historical food safety data that suggest a very low public health risk associated with C. perfringens in commercially processed ready-to-eat meat and poultry products.

Control of Clostridium perfringens germination and outgrowth by buffered sodium citrate during chilling of roast beef and injected pork

Inhibition of the germination and outgrowth of Clostridium perfringens by buffered sodium citrate (Ional) and buffered sodium citrate supplemented with sodium diacetate (Ional Plus) during the abusive chilling of roast beef and injected pork was evaluated. Beef top rounds or pork loins were injected with a brine containing NaCl, potato starch, and potassium tetrapyrophosphate to yield final in-product concentrations of 0.85, 0.25, and 0.20%, respectively. Products were ground and mixed with Ional or Ional Plus at 0, 0.5, 1.0, and 2.0%. Each product was mixed with a three-strain C. perfringens spore cocktail to obtain final spore concentrations of ca. 2.5 log10 spores per g. Chilling of roast beef from 54.4 to 7.2 degrees C resulted in C. perfringens population increases of 1.51 and 5.27 log10 CFU/g for 18- and 21-h exponential chill rates, respectively, while chilling of injected pork resulted in increases of 3.70 and 4.41 log10 CFU/g. The incorporation of Ional into the roast beef formulation resulted in C. perfringens population reductions of 0.98, 1.87, and 2.47 log10 CFU/g with 0.5, 1.0, and 2.0% Ional, respectively, over 18 h of chilling, while > or = 1.0% Ional Plus was required to achieve similar reductions (reductions of 0.91 and 2.07 log10 CFU/g were obtained with 1.0 and 2.0% Ional Plus, respectively). An Ional or Ional Plus concentration of > or = 1.0% was required to reduce C. perfringens populations in roast beef or injected pork chilled from 54.4 to 7.2 degrees C in 21 h. Cooling times for roast beef or injected pork products after heat processing can be extended to 21 h through the incorporation of > or = 1.0% Ional or Ional Plus into the formulation to reduce the potential risk of C. perfringens germination and outgrowth.

Incidence of Clostridium perfringens in commercially produced cured raw meat product mixtures and behavior in cooked products during chilling and refrigerated storage

A total of 445 whole-muscle and ground or emulsified raw pork, beef, and chicken product mixtures acquired from industry sources were monitored over a 10-month period for vegetative and spore forms of Clostridium perfringens. Black colonies that formed on Shahidi-Ferguson perfringens (SFP) agar after 24 h at 37 degrees C were considered presumptive positive. Samples that were positive after a 15-min heat shock at 75 degrees C were considered presumptive positive for spores. Of 194 cured whole-muscle samples, 1.6% were positive; spores were not detected from those samples. Populations of vegetative cells did not exceed 1.70 log10 CFU/g and averaged 1.56 log10 CFU/g. Of 152 cured ground or emulsified samples, 48.7% were positive, and 5.3% were positive for spores. Populations of vegetative cells did not exceed 2.72 log10 CFU/g and averaged 1.98 log10 CFU/g; spores did not exceed 2.00 log10 CFU/g and averaged 1.56 log10 CFU/g. Raw bologna (70% chicken), chunked ham with emulsion, and whole-muscle ham product mixtures were inoculated with C. perfringens spores (ATCC 12916, ATCC 3624, FD1041, and two product isolates) to ca. 3.0 log10 CFU/g before being subjected either to thermal processes mimicking cooking and chilling regimes determined by in-plant temperature probing or to cooking and extended chilling regimes. Populations of C. perfringens were recovered on SFP from each product at the peak cook temperatures, at 54.4, 26.7, and 7.2 degrees C, and after up to 14 days of storage under vacuum at 4.4 degrees C. In each product, populations remained relatively unchanged during chilling from 54.4 to 7.2 degrees C and declined slightly during refrigerated storage. These findings indicate processed meat products cured with sodium nitrite are not at risk for the growth of C. perfringens during extended chilling and cold storage.

A probabilistic analysis of Clostridium perfringens growth during food service operations

The purpose of this study was threefold: first, the study was designed to illustrate the use of data and information collected in food safety surveys in a quantitative risk assessment. In this case, the focus was on the food service industry; however, similar data from other parts of the food chain could be similarly incorporated. The second objective was to quantitatively describe and better understand the role that the food service industry plays in the safety of food. The third objective was to illustrate the additional decision-making information that is available when uncertainty and variability are incorporated into the modelling of systems.

Cooling rate effect on outgrowth of Clostridium perfringens in cooked, ready-to-eat turkey breast roasts

The potential for Clostridium perfringens spores to germinate and grow in cooked, ready-to-eat turkey products was evaluated to determine a safe cooling rate within the critical temperatures of 48.9 C (120 F) through 12.8 C (55 F). Raw turkey deli breast roasts were inoculated with a cocktail of C. perfringens spores (NCTC 8238, NCTC 8239, and NCTC 10388) and cooked in a steam oven to an internal temperature of 72 C. The sample roasts were then cooled through the critical cooling range at rates yielding cooling times of 6, 8, and 10 h. Turkey roasts were analyzed for spore growth and multiplication using tryptose-sulfite-cycloserine agar and anaerobic incubation at 37 C for 48 h. Cooling times of 6 and 8 h showed no proliferation of C. perfringens that would violate the USDA/Food Safety Inspection Service safe cooling standard criteria, which would allow no more than a 1 log10 multiplication between 48.9 and 12.8 C. A 9.6-h cooling period between the designated temperatures at a 95% confidence interval was determined to be adequate for nonproliferation of C. perfringens. On the other hand, a 95% tolerance interval would be more stringent in that it suggests no more than an 8.9-h cooling period. Tolerance intervals required that 95% of all our observations did not exceed the limit of 1 log10 increase in C. perfringens. This study indicated that in cooked, ready-to-eat turkey deli breasts, a cooling period between 48.9 C (120 F) and 12.8 C (55 F) of no greater than 8.9 h should be utilized to prevent possible C. perfringens foodborne outbreaks.

Human disease associated with Clostridium perfringens enterotoxin

Clostridium perfringens continues to be a common cause of food-borne disease. Characteristics of this organism that contribute to its ability to cause food-borne illness include the formation of heat-resistant spores that survive normal cooking/heating temperatures, a rapid growth rate in warm food, and the production of enterotoxin (CPE) in the human gut. Time and temperature abuse associated with food preparation contributes to the majority of outbreaks of C. perfringens food-borne disease. CPE-induced diarrhea has been reported in the absence of a defined food vehicle. These cases have been typically associated with the elderly and following a course of antibiotic therapy. The incidence of CPE-induced diarrhea may be expected to increase with the growing population of immunocompromised (disease-, treatment-, or age-induced) individuals. Clostridium perfringens has been implicated as a possible contributor to the development of SIDS in susceptible individuals. Specifically, it has been hypothesized that CPE acts as a triggering agent, initiating the events associated with the development of SIDS. Continued refinement of both immunoassays and molecular methods for toxin and gene detection, respectively, will facilitate their eventual availability as commercial kits, providing rapid and simplified methods for the detection of C. perfringens isolates that produce or have the capacity to produce CPE as well as other toxins associated with this organism.