Thermal destruction of Escherichia coli O157:H7 in beef and chicken: determination of D- and Z-values (original) (raw)
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Journal of Food Protection, 2009
We investigated the heat resistance of a four-strain mixture of Escherichia coli O157:H7 in raw ground beef in both the absence and presence of white and green tea powders and an apple skin extract. Inoculated meat was cooked using the sousvide technique, i.e., the meat was packaged in sterile bags and completely immersed in a circulating water bath at low temperature for a period of time. The bags were cooked for 1 h to an internal temperature of 55, 58, 60, or 62.5ЊC, and then held from 240 min at 55ЊC to 10 min at 62.5ЊC. The surviving bacteria were enumerated by spiral plating onto tryptic soy agar overlaid with sorbitol-MacConkey agar. Inactivation kinetics of the pathogens deviated from first-order kinetics. D-values (time, in minutes, required for the bacteria to decrease by 90%) in the control beef ranged from 67.79 min at 55ЊC to 2.01 min at 62.5ЊC. D-values determined by a logistic model ranged from 36.22 (D 1 , the D-value of a major population of surviving cells) and 112.79 (D 2 , the D-value of a minor subpopulation) at 55ЊC to 1.39 (D 1) and 3.00 (D 2) at 62.5ЊC. A significant increase (P Ͻ 0.05) in the sensitivity of the bacteria to heat was observed with the addition of 3% added antimicrobials. D-value reductions of 62 to 74% were observed with apple powder and 18 to 58% with tea powders. Thermal death times from this study will assist the retail food industry to design cooking regimes that ensure the safety of beef contaminated with E. coli O157:H7.
Journal of Food Science, 2011
This study evaluated inactivation of Escherichia coli O157:H7 in moisture-enhanced restructured nonintact beef cooked to 65 • C using different cooking appliances set at different temperatures. Batches (2 kg) of coarse-ground beef (approximately 5% fat) were mixed with an 8-strain composite (100 mL) of rifampicin-resistant E. coli O157:H7 (6.4 ± 0.1 log CFU/g) and a solution (100 mL) of sodium chloride plus sodium tripolyphosphate to yield concentrations (wt/wt) of 0.5% and 0.25%, respectively, in the final product. Beef portions of 2.54 cm thickness (15 cm dia) were prepared and were vacuum-packaged and frozen (−20 • C, 42 h). Partially thawed (−2.5 ± 1.0 • C) portions were pan-broiled (Presto R electric skillet and Sanyo R grill) or roasted (Oster R toaster oven and Magic Chef R kitchen oven) to 65 • C. The appliances were set at, and preheated before cooking to 149 or 204 • C (electric skillet), 149 or 218 • C (grill), 149 or 232 • C (toaster oven), and 149, 204, or 260 • C (kitchen oven). Temperatures of appliances and beef samples were monitored with thermocouples, and meat samples were analyzed for surviving microbial populations. In general, the higher the appliance temperature setting, the shorter the time needed to reach 65 • C, and the higher the edge and surface temperatures of the meat samples. Temperatures of 204 to 260 • C, regardless of appliance, resulted in greater (P < 0.05) pathogen reductions (3.3 to 5.5 log CFU/g) than those obtained at 149 • C (1.5 to 2.4 log CFU/g). The highest (P < 0.05) reduction (5.5 log CFU/g) was obtained in samples cooked in the kitchen oven set at 260 • C. The results should be useful to the food service industry for selection of effective nonintact beef cooking protocols, and for use in risk assessments for nonintact meat products.
Heat-Resistance of Escherichia Coli O157:H7 in Meat and Poultry as Affected by Product Composition
Journal of Food Science, 1995
The effects of fat level and low fat formulation on survival of Escherichiu coli 0157:H7 isolate 204P heated in ground beef [7%, 10% and 20% fat], pork sausage [7%, lo%, and 30% fat], chicken (3% and 11% fat), and turkey (3% and 11% fat) were determined by D-and z-values. D-values for E. coli 0157:H7 in lowest fat products were lower than in traditional beef and pork products (P < 0.05). Overall, higher fat levels in all products resulted in higher D-values. D,, values (min) ranged from 0.4550.47 in beef, 0.37-0.55 in pork sausage, 0.38-0.55 in chicken and 0.5550.58 in turkey. D,, and D,, values were respectively longer. Zvalues ranged from 4.44.8"C. Product composition affected lethality of heat to E. coli 0157:H7.
Journal of Food Science, 2009
This study evaluated the effects of meat binding or restructuring formulations, including salt/phosphate, algin/calcium, Activa TM RM, and Fibrimex R , with or without 0.27% (wt/wt) lactic acid, on thermal inactivation of internalized Escherichia coli O157:H7 in ground beef, serving as a model system for restructured products. Ground beef batches (700 g; approximately 5% fat) were mechanically mixed with a 5-strain composite of E. coli O157:H7 (7 log CFU/g) and then with the restructuring formulations. Product portions (30 g) were extruded into plastic test tubes (2.5 × 10 cm) and stored at 4 • C (18 h), before heating to 60 or 65 • C in a circulating water bath to simulate rare or medium-rare doneness of beef, respectively. Cooking to 60 or 65 • C reduced (P < 0.05) bacterial counts of control samples by 1.8 and 3.2 log CFU/g, respectively. Thermal destruction at 60 • C was not different (P > 0.05) among all treatments and the control. At 65 • C, greater (P < 0.05) thermal inactivation of E. coli O157:H7, as compared to the control, was obtained in samples treated with lactic acid alone (reductions of 4.9 log CFU/g), whereas for all other treatments, microbial destruction (reductions of 2.2 to 4.5 log CFU/g) was comparable (P > 0.05) to that of the control. Cooking weight losses were lower (P < 0.05) in salt/phosphate samples (<1%) compared to other formulations and the control (7.4% to 15.9%). Findings indicated that, under the conditions examined, restructuring of beef with salt/phosphate, algin/calcium, Activa TM RM, or Fibrimex R did not affect inactivation of internalized E. coli O157:H7 in undercooked (60 or 65 • C) samples, whereas inclusion of lactic acid (0.27%) in nonintact beef products enhanced pathogen destruction at 65 • C.
Foods
This study compared the quality variation and thermal inactivation of Escherichia coli O157:H7 in non-intact beef and veal. Coarse ground beef and veal patties (2.1 cm thick, 12.4 cm diameter, 180 g) inoculated with E. coli O157:H7, aerobically stored before double pan-broiling for 0-360 s without rest or to 55, 62.5, 71.1, and 76 • C (internal temperature) with 0.5-or 3.5-min rest. Microbial population and qualities including color, cooking losses, pH, water activity, fat, and moisture content, were tested. After cooking the beef and veal patties, the weight losses were 17.83-29%, the pH increased from 5.53-5.60 to 5.74-6.09, the moisture content decreased from 70.53-76.02% to 62.60-67.07%, and the fat content increased (p < 0.05) from 2.19-6.46% to 2.92-9.45%. Cooking beef and veal samples with increasing internal temperatures decreased a* and b* values and increased the L* value. Escherichia coli O157:H7 was more sensitive to heat in veal compared to beef with shorter D-value and "shoulder" time. Cooking to 71.1 and 76 • C reduced E. coli O157:H7 by >6 log CFU/g regardless of rest time. Cooking to 55 • C and 62.5 • C with a 3.5-min rest achieved an additional 1-3 log CFU/g reduction compared to the 0.5-min rest. Results should be useful for developing risk assessment of non-intact beef and veal products.
Journal of Food Science, 2008
In 19.1% fat ground beef, Escherichia coli O157:H7 was less heat-resistant at Ն Ն Ն Ն Ն58°C than the Salmonella typhimurium DT104 and Salmonella senftenberg, but at 55°C the D value was similar to DT104 strains and higher than an eight-strain Salmonella cocktail. Inactivation of E. coli O157:H7 was more temperature-dependent than the cocktail and DT104 strains. E. coli and DT104 strains were more heat-resistant in beef containing 19% fat than 4.8% fat. The cocktail was more thermally stable in stationary as compared to log phase. Freezing of inoculated raw meat decreased heat resistance of the cocktail. The pathogenic strain, growth phase of the organism, state of the meat (fresh or frozen) and meat composition must be considered when designing protocols to verify thermal processes.
International Journal of Food Microbiology, 2002
The effects of commercial beef burger production and product formulation on the heat resistance of Escherichia coli O157:H7 (NCTC 12900) in beef burgers were investigated. Fresh beef trimmings were inoculated with E. coli O157:H7 to approximately log 10 7.0 cfu g À 1 and subjected to standard beef burger production processes, including freezing, frozen storage and tempering. The tempered trimmings were processed in line with commercial practice to produce burgers of two formulations, a 'Quality' burger containing 100% beef and an 'Economy' burger containing 70% beef and 30% other ingredients (salt, seasoning, soya, onion and water). The burgers were then frozen and stored. Control 'unprocessed' burgers were produced to each of the above formulations using fresh beef trimmings. All burger types were heat-treated at 55, 60 or 65 jC. Samples were examined by plating on Tryptone Soya Agar (TSA), incubated at 37 jC for 2 h, before overlaying with SMAC (TSA/SMAC) and incubation at 37 jC. The resultant counts were used to derive D-values for E. coli O157:H7. At each treatment temperature, the D-values from each burger formulation using frozen tempered trimmings were significantly lower ( P < 0.001) than the D-values from that formulation using fresh trimmings. At each treatment temperature, the D-values from Economy burgers using processed trimmings were significantly higher ( P < 0.001) than the D-values from Quality burgers using processed trimmings. A similar trend of significantly higher ( P < 0.001) D-values for Economy burgers was observed using fresh trimmings. This study found that commercial processing and product formulation have profound effects on the heat resistance of E. coli O157:H7 in beef burgers. D
Food Research International, 2015
The objective of this study was to assess the combined effects of temperature, pH, sodium chloride (NaCl), and sodium pyrophosphate (SPP) on the heat resistance of Escherichia coli O157:H7 in minced beef meat. A fractional factorial design consisted of four internal temperatures (55.0, 57.5, 60.0 and 62.5°C), five concentrations of NaCl (0.0, 1.5, 3.0, 4.5 and 6.0 wt/wt.%) and SPP (0.0, 0.1, 0.15, 0.2 and 0.3 wt/wt.%), and five levels of pH (4.0, 5.0, 6.0, 7.0 and 8.0). The 38 variable combinations were replicated twice to provide a total of 76 survivor curves, which were modelled by a modified three-parameter Weibull function as primary model. The polynomial secondary models, developed to estimate the time to achieve a 3-log and a 5-log reduction, enabled the estimation of critical pH, NaCl and SPP concentrations, which are values at which the thermo-tolerance of E. coli O157:H7 reaches it maximum. The addition up to a certain critical concentration of NaCl (~2.7-4.7%) or SPP (~0.16%) acts independently to increase the heat resistance of E. coli O157:H7. Beyond such critical concentrations, the thermo-resistance of E. coli O157:H7 will progressively diminish. A similar pattern was found for pH with a critical value between 6.0 and 6.7, depending upon temperature and NaCl concentration. A mixed-effects omnibus regression model further revealed that the acidity of the matrix and NaCl concentration had a greater impact on the inactivation kinetics of E. coli O157:H7 in minced beef than SPP, and both are responsible for the concavity/convexity of the curves. When pH, SPP or NaCl concentration is far above or below from its critical value, the temperatures needed to reduce E. coli O157:H7 up to a certain log level are much lower than those required when any other environmental condition is at its critical value. Meat processors can use the model to design lethality treatments in order to achieve specific log reductions of E. coli O157:H7 in ready-to-eat beef products.
Journal of Food Science, 2010
Escherichia coli O157:H7 may become internalized during brine injection of meat. This study evaluated the effect of brining ingredients on E. coli O157:H7 in a meat model system after simulated brining, storage, and cooking. Fresh knuckles (5.3 ± 2.4% fat) or beef shoulder (15.3 ± 2.2% fat) were ground individually, mixed with an 8-strain composite of rifampicin-resistant E. coli O157:H7 (7 log CFU/g) and brining solutions. Treatments included no brining, distilled water, sodium chloride (NaCl, 0.5%), sodium tripolyphosphate (STP, 0.25%), sodium pyrophosphate (SPP, 0.25%), NaCl + STP, NaCl + SPP, NaCl + STP + potassium lactate (PL, 2%), NaCl + STP + sodium diacetate (SD, 0.15%), NaCl + STP + PL + SD, NaCl + STP + lactic acid (0.3%), NaCl + STP + acetic acid (0.3%), NaCl + STP + citric acid (0.3%), NaCl + STP + EDTA (20 mM) + nisin (0.0015%) or pediocin (1000 AU/g), NaCl + STP + sodium metasilicate (0.2%), NaCl + STP + cetylpyridinium chloride (CPC; 0.5%), and NaCl + STP + hops beta acids (0.00055%). Samples (30 g) were analyzed for pH, and total microbial and rifampicin-resistant E. coli O157:H7 (inoculum) populations immediately after mixing, storage (24 h at 4 • C), and cooking to 65 • C. Fat and moisture contents and water activity were measured after storage and cooking only; cooking losses also were determined. The effect of beef type on microbial counts, pH, and water activity was negligible. No reductions in microbial counts were obtained by the brining solutions immediately or after storage, except for samples treated with CPC, which reduced (P < 0.05) pathogen counts after storage by approximately 1 log cycle. Cooking reduced pathogen counts by 1.5 to 2.5 logs, while CPC-treated samples had the lowest (P < 0.05) counts compared to any other treatment. These data may be useful in developing/improving brining recipes for control of E. coli O157:H7 in moisture-enhanced beef products.
Journal of food protection, 2010
This study compared thermal inactivation of Escherichia coli O157:H7 in nonintact beefsteaks of different thicknesses by different cooking methods and appliances. Coarsely ground beef was inoculated with rifampin-resistant E. coli O157:H7 (eight-strain composite, 6 to 7 log CFU/g) and then mixed with sodium chloride (0.45%) plus sodium tripolyphosphate (0.23%); the total water added was 10%. The meat was stuffed into bags (10-cm diameter), semifrozen (-20 degrees C, 6 h), and cut into 1.5-, 2.5-, and 4.0-cm-thick steaks. Samples were then individually vacuum packaged, frozen (-20 degrees C, 42 h), and tempered (4 degrees C, 2.5 h) before cooking. Partially thawed (-2 +/- 1 degrees C) steaks were pan broiled (Presto electric skillet and Sanyo grill), double pan broiled (George Foreman grill), or roasted (Oster toaster oven and Magic Chef standard kitchen oven) to a geometric center temperature of 65 degrees C. Extent of pathogen inactivation decreased in order of roasting (2.0 to 4.2...