Influence of four retail food service cooling methods on the behavior of Clostridium perfringens ATCC 10388 in turkey roasts following heating to an internal temperature of 74 degrees C

The influence of four food service cooling methods (CM) on growth of Clostridium perfringens ATCC 10388 in cooked turkey roasts was evaluated. Raw whole turkey roasts were inoculated with C. perfringens spores (approximately 4.23 log CFU per roast), vacuum packaged, and heated to an internal temperature of 74 degrees C. The cooked roasts were cooled as follows: whole roast cut into four quarters and held at 4 degrees C (CM1); whole roast held in a blast chiller (CM2); whole roast loosely wrapped and held at 4 degrees C (CM3); and whole roasts (three per bag) held at 4 degrees C (CM4). The roasts were analyzed for C. perfringens using Shahidi-Ferguson perfringens agar and anaerobic incubation (37 degrees C, 24 h). None of the cooling methods met the amended 2001 U.S. Food and Drug Administration Food Code guidelines for safe cooling of potentially hazardous foods. Times taken for roasts to cool from 57 to 21 degrees C using CM1, CM2, CM3, and CM4 were 2.27, 3.11, 6.22, and 8.71 h, respectively. Times taken for roasts (21 degrees C) to reach 5 degrees C ranged from 6.33 (CM1) to 19.45 h (CM4). Based on initial numbers of C. perfringens, no growth occurred in roasts cooled by CM1 or CM2, whereas numbers increased by 1.5 and 4.0 log in whole roasts cooled via CM3 and CM4, respectively. These findings indicate that certain food service cooling methods for whole cooked turkey roasts may result in proliferation of C. perfringens and increase the risk of foodborne illness by this pathogen.

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.

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.

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.

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.

Increased inactivation of ozone-treated Clostridium perfringens vegetative cells and spores on fabricated beef surfaces using mild heat

Ozone treatment of beef surfaces enhanced the effectiveness of cooking temperatures ranging from 45 to 75 degrees C against enterotoxin-producing strains of Clostridium perfringens. Vegetative cells on beef surfaces at an initial concentration of 5.59 +/- 0.17 log CFU/g were reduced significantly (P < 0.05) to 4.09 +/- 0.72 log CFU/g and 3.50 +/- 0.90 log CFU/g after combined treatments with aqueous ozone (5 ppm) and subsequent heating at 45 and 55 degrees C, respectively. Spores on the beef surface were likewise significantly reduced from an initial concentration of 2.94 +/- 0.37 log spores per g to 2.07 +/- 0.38 log spores per g and 1.70 +/- 0.37 log spores per g after the combined treatment with aqueous ozone (5 ppm) and subsequent heating at 55 and 75 degrees C, respectively. Fluorescent nucleic acid stains were used with confocal fluorescence microscopy to show that spores remaining attached to the meat were protected from treatment-specific injury. This study provides evidence for the decreased resistance of both vegetative cells and spores of C. perfringens with ozone treatment that is followed by heat treatment at temperatures that would not otherwise be as effective, thus lowering the requirements for cooking beef while maintaining a margin of safety.

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.

An ultrastructural comparison of spores from various strains of Clostridium perfringens and correlations with heat resistance parameters

It has been shown that Clostridium perfringens isolates associated with food poisoning carry a chromosomal cpe gene, whereas nonfood-borne human gastrointestinal disease isolates carry a plasmid cpe gene. In addition, the chromosomal cpe gene isolates exhibit greater heat resistance as compared with the plasmid cpe strains. Therefore, the current study conducted ultrastructural measurements of spores from several plasmid and chromosomal cpe-positive C. perfringens isolates. In support of the dehydration mechanism of spore heat resistance, the C. perfringens spore core average size was found to show a negative correlation with D-values for spores obtained at 100 degrees C. Dipicolinic acid (DPA) concentrations assayed for the spores did not correlate well with C. perfringens spore core averages nor with D(10)-values at 100 degrees C. Spore core thickness might be a distinguishing phenotypic characteristic used to identify heat resistance and survival potential of C. perfringens in improperly cooked foods.

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.

Optimizing sporulation of Clostridium perfringens

Many sporulation media have been developed for Clostridium perfringens, but none stimulates sporulation for all strains. The aim of our experiments was to develop a sporulation method using Duncan and Strong (DS) medium, which supports sporulation of a wide variety of strains. Different inoculation levels were tested, and the effects of sporulation-promoting substances and acid shock were evaluated. Furthermore, DS medium was compared with other sporulation media. Highest spore numbers in DS medium were obtained with a 10% 24-h fluid thioglycollate broth inoculum (5.0 x 10(5)/ml). Addition of theophylline and replacement of starch by raffinose increased spore yields for some strains, but most strains were not affected (average increases in log N/ml of 0.2 and 0.3, respectively). One strain was enhanced by the addition of bile, but other strains were strongly inhibited (average decrease in log N/ml of 2.5); agar did not influence sporulation. Neither short-time acid exposure nor addition of culture supernatant fluids of well-sporulating strains resulted in higher spore numbers in DS medium. None of the tested methods enhanced sporulation in general; only strain-dependent effects were obtained. Peptone bile theophylline medium was the most promising sporulation medium tested; peptone bile theophylline starch medium yielded highest spore numbers (2.5 x 10(5)/ml), but some strains failed to sporulate. In conclusion, adding theophylline to DS medium may optimize sporulation of C. perfringens, but peptone bile theophylline medium with or without starch is most suitable.

Growth of Clostridium perfringens from spore inocula in sous-vide turkey products

Clostridium perfringens growth from a spore inoculum was investigated in vacuum-packaged, cook-in-bag ground turkey (pH 6) that included 0.3% (w/w) sodium pyrophosphate, and sodium chloride at 0, 1, 2, or 3% (w/w). The packages were processed to an internal temperature of 71.1 degrees C, ice chilled and stored at various temperatures. The total C. perfringens population was determined by plating diluted samples on tryptose-sulfite-cycloserine agar followed by anaerobic incubation at 37 degrees C for 48 h. At 28 degrees C, the addition of 3% salt in turkey was effective in delaying growth for 12 h. At 15 degrees C, growth occurred at a relatively slow rate in the presence of 1-2% salt. Vegetative cells were not observed even after 28 days of storage in the presence of 3% salt. C. perfringens growth was not observed at 4 degrees C regardless of salt levels. The D-values ranged from 23.2 min (no salt) to 17.7 min (3% salt). Cyclic and static temperature abuse of refrigerated products for 8 h did not lead to growth by C. perfringens from a spore inoculum.