Thermal Inactivation of Salmonella spp. and Listeria innocua in the Chicken Breast Patties Processed in a Pilot-Scale Air-Convection Oven

A predictive model for the inactivation of Listeria innocua in cooked poultry products during postpackage pasteurization

Contamination of Listeria monocytogenes in ready-to-eat poultry products poses potential risk of listeriosis to the public. To control the level of Listeria contamination, attention has been focused on the postpackage pasteurization of fully cooked poultry products. In this study, we sought to develop a model to predict the thermal inactivation of L. monocytogenes in chicken drumettes during postpackage hot water pasteurization. Fully cooked chicken drumettes were inoculated with Listeria innocua as a surrogate microorganism for Listeria monocytogenes, vacuum packaged, and treated in hot water baths at 60, 70, 80, and 90°C for different heating times. Experimental results showed that a 7-log CFU/g reduction of L. innocua occurred at 54, 28, 18, and 10 min at 60, 70, 80, and 90°C, respectively. The Weibull model was used to fit the survival curves of L. innocua at each heating temperature. The root mean square errors and residual plots indicated good agreements between the predicted and observed values. The predictive model was further validated by predicting a new data set generated in the pilot-plant tests. Model performance was evaluated by the acceptable prediction zone method, and the results indicated that the percentages of acceptable prediction errors were 100, 100, 82.4, and 87.5% at 60, 70, 80 and 90°C, respectively, which were all greater than the threshold acceptable value of 70% , indicating good performance of the model. The developed predictive model can be used as a tool to predict thermal inactivation behaviors of L. monocytogenes in ready-to-eat chicken drumettes products.

Pathogen kinetics and heat and mass transfer-based predictive model for Listeria innocua in irregular-shaped poultry products during thermal processing

The increasing demand of ready-to-eat poultry products has led to serious concerns over product safety, and more emphasis has been placed on thorough cooking of products. In this study, processing conditions and thermal inactivation of Listeria innocua in chicken breast meats were evaluated during convection cooking in a pilot-plant scale air-steam impingement oven. A predictive model was developed by integrating heat and mass transfer models with a pathogen kinetics model to predict temperature, water content, product yield, and bacterial inactivation during air-steam impingement cooking. Skinless boneless chicken breasts were cooked at oven air temperatures of 177 and 200 degrees C for 2 to 10 min at a humidity of 70 to 75% (moisture by volume) and an air velocity of 1 m/s at the exit of the nozzles. The reduction in Listeria in chicken breasts after 2 to 5 min of cooking was from 0.3 to 1.4 log CFU/g and from 0.8 to 1.8 log CFU/g at 177 and 200 degrees C, respectively. After cooking for 10 min at both temperatures, no survivors were detected in any of the cooked chicken breasts from an initial bacterial concentration of 10(6) CFU/g. The standard errors of prediction for the endpoint center temperatures after 2 to 10 min of cooking were 2.8 and 3.0 degrees C for air temperatures of 177 and 200 degrees C, respectively. At 177 and 200 degrees C, the median relative errors of prediction for water content were 2.5 and 3.7% and those for product yield were 5.4 and 8.4%, respectively. The developed model can be used as a tool to assist in evaluating thermal processing schedules for poultry products cooked in an air-steam impingement oven.

Thermal process validation for Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes in ground turkey and beef products

At 55 to 70 degrees C, thermal inactivation D-values for Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes were 19.05 to 0.038, 43.10 to 0.096, and 33.11 to 0.12 min, respectively, in ground turkey and 21.55 to 0.055, 37.04 to 0.066, and 36.90 to 0.063 min, respectively, in ground beef. The z-values were 5.73, 5.54, and 6.13 degrees C, respectively, in ground turkey and 5.43, 5.74, and 6.01 degrees C, respectively, in ground beef. In both ground turkey and beef, significant (P < 0.05) differences were found in the D-values between E. coli O157:H7 and Salmonella or between E. coli O157:H7 and L. monocytogenes. At 65 to 70 degrees C, D-values for E. coli O157:H7, Salmonella, and L. monocytogenes were also significantly (P < 0.05) different between turkey and beef. The obtained D- and z-values were used in predicting process lethality of the pathogens in ground turkey and beef patties cooked in an air impingement oven and confirmed by inoculation studies for a 7-log (CFU/g) reduction of E. coli O157:H7, Salmonella, and L. monocytogenes.

Thermal lethality of salmonella in chicken leg quarters processed via an air/steam impingement oven

Chicken leg quarters were injected with 0.1 ml of the cocktail culture per cm2 of the product surface area to contain about 7 log(CFU/g) of Salmonella. The inoculated leg quarters were processed in an air/steam impingement oven at an air temperature of 232 degrees C, an air velocity of 1.4 m/s, and a relative humidity of 43%. The endpoint product temperatures were correlated with the cooking times. A model was developed for pathogen thermal lethality up to 7 log(CFU/g) reductions of Salmonella in correlation to the product mass (140 to 540 g) and cooking time (5 to 35 min). The results from this study are useful for validating thermal lethality of pathogens in poultry products that are cooked via impingement ovens.

Determination of thermal lethality of Listeria monocytogenes in fully cooked chicken breast fillets and strips during postcook in-package pasteurization

Fully cooked chicken breast fillets and strips were surface inoculated with a cocktail of Listeria monocytogenes culture. The inoculation level was 10(7) to 10(8) CFU/g meat. The inoculated products were vacuum packaged and pasteurized at 90 degrees C with a pilot-scale steam or hot water cooker. After heat treatment, the survivors of L. monocytogenes were enumerated. No significant difference was found on survivors of L. monocytogenes between steam- and hot water-treated products. To achieve a 7-log10 (CFU/g) reduction, approximately 5, 25, and 35 min were needed for single-packaged fillets, 227-g package strips, and 454-g strips, respectively. The results from this study were subsequently verified by a computer model that could predict the thermal lethality of pathogens in fully cooked meat and poultry products during postcook in-package pasteurization.

Lethality of Salmonella and Listeria innocua in fully cooked chicken breast meat products during postcook in-package pasteurization

The process lethality model was used to predict the thermal kill of Salmonella and Listeria innocua in fully cooked and vacuum-packaged chicken breast meat during hot-water postprocess pasteurization. Time-temperature profiles of the meat samples during treatment and D-values (decimal reduction times) and z-values (change in temperature required to change the D-value) for Salmonella and L. innocua in the same meat product were used in the prediction of lethality. The results of the model prediction were compared with those of the inoculation study for the same meat product at a 95% confidence level of up to 10(7) CFU/g for Salmonella and L. innocua. The thermal lethality predictions obtained with the process lethality model for Salmonella and L. innocua were within the 95% confidence level for the experimental data from the inoculation study, suggesting that the process lethality model was a useful tool for the determination of the kill of Salmonella or L. innocua at up to 10(7) CFU/g in fully cooked chicken breast meat products during postprocess pasteurization with hot water.

Thermal inactivation D- and Z-values of Salmonella and Listeria innocua in fully cooked and vacuum packaged chicken breast meat during postcook heat treatment

Studies were conducted to determine thermal inactivation D- and z-values of Salmonella and Listeria innocua in fully cooked and vacuum-packaged chicken breast meat. Fully cooked chicken breast meat products that were obtained from three different sources with differing formulations were uniformly inoculated with a cocktail of Salmonella (including Senftenberg, Typhimurium, Heidelberg, Mission, Montevideo, and California) or L. innocua at approximately 10(7) cfu/g. The inoculated meat samples were vacuum-packaged and then heat-treated at a temperature of 55 to 70 C for 5 to 90 min. After heat treatment, the samples were immediately cooled in an ice-water bath. Survivors of Salmonella and L. innocua were enumerated for each sample. D- and z-values of Salmonella and L. innocua were determined for each product and compared among the products. Source and formulation did not cause significant differences in the D- and z-values of Salmonella or L. innocua among the three fully cooked and vacuum-packaged chicken breast meat products.