Predictive model for growth of Clostridium perfringens during cooling of cooked ground pork

A predictive dynamic model for Clostridium perfringens spore germination and outgrowth in cooked pork products during cooling is presented. Cooked, ground pork was inoculated with C. perfringens spores and vacuum packaged. For the isothermal experiments, all samples were incubated in a water bath stabilized at selected temperatures between 10 and 51 °C and sampled periodically. For dynamic experiments, the samples were cooled from 54.4 to 27 °C and subsequently from 27 to 4 °C for different time periods, designated as x and y hours, respectively. The growth models used were based on a model developed by Baranyi and Roberts (1994), which incorporates a constant, referred to as the physiological state constant, q₀. The value of this constant captures the cells' history before the cooling begins. To estimate specific growth rates, data from isothermal experiments were used, from which a secondary model was developed, based on a particular form of Ratkowsky's 4-parameter equation. Using the data from dynamic experiments and the Ratkowsky model, an optimal value of q₀ (=0.01375) was derived minimizing the mean square error of predictions. However, using this estimate, the model had a tendency to over-predict relative growth when there was observed small amounts of relative growth, and under-predict relative growth when there was observed large relative growth. To provide more fail-safe estimates, rather than using the derived value of q₀, a value of 0.04 is recommended. The predictive model with this value of q₀ would provide more fail-safe estimates of relative growth and could aid producers and regulatory agencies with determining disposition of products that were subjected to cooling deviations.Industrial relevanceSafe time/temperature for cooling of cooked pork is very important to guard against the pathogen in cooked products. Predictive model will assist industry to determine compliance with regulatory performance standards and to ensure microbiological safety of cooked products.     

Proteolytic Clostridium botulinum growth at 12–48°C simulating the cooling of cooked meat: development of a predictive model

The objective of this study was to develop a model to predict the germination, outgrowth and lag (GOL), and exponential growth rates of Clostridium botulinum from spores at temperatures (12–48°C) applicable to the cooling of cooked meat products. The growth medium, Reinforced Clostridial medium (RCM) supplemented with oxyrase enzyme to create suitable anaerobic conditions, was inoculated with approximately 4 log₁₀spores ml⁻¹. Clostridium botulinum populations were determined at appropriate intervals by plating onto RCM. Clostridium botulinum growth from spores was not observed at temperatures <12°C or >48°C for up to 3 weeks. Growth curves were determined by fitting Gompertz functions to the data. From the parameters of the Gompertz function the growth characteristics, GOL times and exponential growth rates were calculated. These growth characteristics were subsequently described by Ratkowsky functions using temperature as the independent variable. Closed form equations were developed that allow for predicting relative growth for a general cooling scenario. By applying multivariate statistical procedures, the standard errors and confidence intervals were computed on the predictions of the amount of relative growth for a cooling scenario. The predictive model is capable of predicting spore outgrowth and multiplication for general cooling scenarios, for suitable but un-verified mathematical assumptions, and should aid in evaluating the safety of cooked products after cooling.     

Dynamic model for predicting growth of Salmonella spp. in ground sterile pork

A predictive model for Salmonella spp. growth in ground pork was developed and validated using kinetic growth data. Salmonella spp. kinetic growth data in ground pork were collected at several isothermal conditions (between 10 and 45 °C) and Baranyi model was fitted to describe the growth at each temperature, separately. The maximum growth rates (μ_max) estimated from the Baranyi model were modeled as a function of temperature using a modified Ratkowsky equation. To estimate bacterial growth under dynamic temperature conditions, the differential form of the Baranyi model, in combination with the modified Ratkowsky equation for rate constants, was solved numerically using fourth order Runge-Kutta method. The dynamic model was validated using five different dynamic temperature profiles (linear cooling, exponential cooling, linear heating, exponential heating, and sinusoidal). Performance measures, root mean squared error, accuracy factor, and bias factor were used to evaluate the model performance, and were observed to be satisfactory. The dynamic model can estimate the growth of Salmonella spp. in pork within a 0.5 log accuracy under both linear and exponential cooling profiles, although the model may overestimate or underestimate at some data points, which were generally < 1 log. Under sinusoidal temperature profiles, the estimates from the dynamic model were also within 0.5 log of the observed values. However, underestimation could occur if the bacteria were exposed to temperatures below the minimum growth temperature of Salmonella spp., since low temperature conditions could alter the cell physiology. To obtain an accurate estimate of Salmonella spp. growth using the models reported in this work, it is suggested that the models be used at temperatures above 7 °C, the minimum growth temperature for Salmonella spp. in pork.     

Predictive model for growth of Clostridium perfringens during cooling of cooked uncured meat and poultry

Comparison of Clostridium perfringens spore germination and outgrowth in cooked uncured products during cooling for different meat species is presented. Cooked, uncured product was inoculated with C. perfringens spores and vacuum packaged. For the isothermal experiments, all samples were incubated in a water bath stabilized at selected temperatures between 10 and 51 °C and sampled periodically. For dynamic experiments, the samples were cooled from 54.4 to 27 °C and subsequently from 27 to 4 °C for different time periods, designated as x and y hours, respectively. The growth models used were based on a model developed by Baranyi and Roberts (1994. A dynamic approach to predicting bacterial growth in food. Int. J. Food Micro. 23, 277-294), which incorporates a constant, referred to as the physiological state constant, q₀. The value of this constant captures the cells’ history before the cooling begins. To estimate specific growth rates, data from isothermal experiments were used, from which a secondary model was developed, based on a form of Ratkowsky’s 4-parameter equation. The estimated growth kinetics associated with pork and chicken were similar, but growth appeared to be slightly greater in beef; for beef, the maximum specific growth rates estimated from the Ratkowsky curve was about 2.7 log₁₀ cfu/h, while for the other two species, chicken and pork, the estimate was about 2.2 log₁₀ cfu/h. Physiological state constants were estimated by minimizing the mean square error of predictions of the log₁₀ of the relative increase versus the corresponding observed quantities for the dynamic experiments: for beef the estimate was 0.007, while those for pork and chicken the estimates were about 0.014 and 0.011, respectively. For a hypothetical 1.5 h cooling from 54 °C to 27° and 5 h to 4 °C, corresponding to USDA-FSIS cooling compliance guidelines, the predicted growth (log₁₀ of the relative increase) for each species was: 1.29 for beef; 1.07 for chicken and 0.95 log₁₀ for pork. However, it was noticed that for pork in particular, the model using the derived q₀ had a tendency to over-predict relative growth when the observed amount of relative growth was small, and under-predict the relative growth when the observed amount of relative growth was large. To provide more fail-safe estimate, rather than using the derived value of q₀, a value of 0.04 is recommended for pork.     

Effect of vacuum cooling followed by ozone repressurization on Clostridium perfringens germination and outgrowth in cooked pork meat under temperature-abuse conditions

The effect of combining vacuum cooling with an ozone-based inhibition process (InhVac) on Clostridium perfringens spore germination and outgrowth in cooked pork meat after exponential chilling (from 54.4 to 7.2 °C in 12, 15, 18, or 21 h) and isothermal storage (20, 25, 30, 36, or 45 °C) was evaluated. Ice cooling (IC) and vacuum cooling (VC) were used to compare the effects with InhVac. The samples were inoculated with a three-strain mixture of C. perfringens spores to obtain concentration of ca. 3 log₁₀ CFU/g. C. perfringens growth in samples treated by InhVac were 0.1, 0.37 and 0.9 log₁₀ CFU/g after 15, 18 and 21 h of cooling from 54.4 to 7.2 °C respectively, significantly lower (P<0.05) than those in samples subjected to IC (1.01, 2.10 and 2.8 log₁₀ CFU/g) and VC (0.56, 1.01 and 2.13 log₁₀ CFU/g). Compared to VC and IC, InhVac treatment increased the lag phase (λ), decreased the growth rates (μ_max), and extended the sample shelf-life (the time until a 1 log₁₀ CFU/g increase in C. perfringes from the initial concentration value) at all storage temperatures. InhVac-treated samples not only had a longer shelf-life than those treated by VC, but also exhibited almost two times longer shelf-life compared to those subjected to IC regardless of storage temperatures. Additionally, statistical indexes showed that a primary modified Gompertz model and a secondary Square Root model could fit the data well.Industrial relevanceIn this study, an innovative inhibition approach (InhVac) was found to show a better antimicrobial effect on C. perfringens germination and outgrowth in cooked pork meat compared to ice cooling and vacuum cooling under temperature-abuse conditions. A primary modified Gompertz model and a secondary Square Root model could be used to predict the C. perfringens growth in samples subjected to InhVac treatment.     

Selective recovery of proteolytic strains of Clostridium botulinum types A and B from model cured meat systems

A selective medium (SBM) containing a combination of antimicrobials was developed which allowed the quantitative isolation of inoculated proteolytic Clostridium botulinum types A, B and F from a simulated cured meat product (cured pork slurry) containing natural spoilage organisms. The medium effectively suppressed the growth of Cl. perfringens, Cl. butyricum, Cl. histolyticum and non-proteolytic strains of Cl. botulinum.Other proteolytic clostridia including putrefactive anaerobes and Cl. bifermentans were capable of growth in SBM but were rarely isolated from the inoculated cured pork slurry. From unheated slurries, inoculated with Cl. botulinum type A spores and stored at 27° or 35°C 356 of 384 (92·7%) colonies picked from SBM were confirmed as Cl. botulinum type A. Selectivity was greater at 27° or 35°C than 15° or 20°C but with experience presumptive Cl. botulinum colonies can be differentiated from other resistant organisms at the lower temperatures. When heated slurries were studied all 441 colonies picked from SBM were confirmed as Cl. botulinum type A.     

Quantitative assessment of the shelf life of ozonated apple juice

Sterile apple juice inoculated with S. cerevisiae ATCC 9763 (10³ CFU/mL) was processed in a bubble column with gaseous ozone of flow rate of 0.12 L/min and concentration of 33–40 μg/mL for 8 min. The growth kinetics of S. cerevisiae as an indicator of juice spoilage was monitored at 4, 8, 12 and 16 °C for up to 30 days. The kinetics was quantitatively described by the primary model of Baranyi and Roberts, and the maximum specific growth rate was further modeled as a function of temperature by the Ratkowsky type model. The developed model was successfully validated for the microbial growth of control and ozonated samples during dynamic storage temperature of periodic changes from 4 to 16 °C. Two more characteristic parameters were also evaluated, the time of spoilage of the product under static temperature conditions and the temperature quotient, Q ₁₀. At lower static storage temperature (4 °C), no spoilage occurred either for unprocessed or ozone-processed apple juice. In the case of ozone-processed apple juice, the shelf life was increased when compared with the controls, and the Q ₁₀ was found to be 7.17, which appear much higher than that of the controls, indicating the effectiveness of ozonation for the extension of shelf life of apple juice.     

Effects of cooked temperature on pork tenderness and relationships among muscle physiology and pork quality traits in loins from Landrace and Berkshire swine

The effect of, and associations between, loin muscle morphology and pork quality indicator traits were assessed at three cooked temperatures in loin chops from 38 purebred Berkshire and 52 purebred Landrace swine. Three loin chops from each pig were randomly assigned to cooked temperature treatments of 62, 71, or 79 °C and loin tenderness was assessed as Warner–Bratzler shear force (WBSF). Cooked temperature (P < 0.001), breed (P < 0.001) and breed × cooked temperature (P < 0.001) effects influenced loin chop WBSF, whereby WBSF increased as cooked temperature increased. Chops from Landrace pigs had greater WBSF at each cooked temperature compared with chops from Berkshire pigs. Chops from Landrace pigs became less tender with increasing cooked temperature, whereas chops from Berkshire pigs became less tender only when cooked to 79 °C. In loins from Landrace pigs, Minolta a1 at 62 °C (R² = 0.07), and average muscle fiber diameter at 71 °C and 79 °C (R² = 0.07 and 0.24, respectively), contributed to WBSF variation. In contrast, for loins from Berkshire pigs, loin ultimate pH and intramuscular fat percentage accounted for 27% and 30% of the variation in WBSF at 62 °C and 71 °C, respectively, and loin ultimate pH accounted for 7% of variation in WBSF at 79 °C. Results suggest that loins from Berkshire pigs have properties that resist toughening at greater cooked temperatures and that associations between quality measures and loin tenderness differ between Landrace and Berkshire pigs.     

Predictive model for growth of Clostridium perfringens during cooling of cooked ground chicken

Traditional methodologies for development of microbial growth models under dynamic temperature conditions do not take into account the organism's history. Such models have been shown to be inadequate in predicting growth of the organisms under dynamic conditions commonly encountered in the food industry. The objective of the current research was to develop a predictive model for Clostridium perfringens spore germination and outgrowth in cooked chicken products during cooling by incorporating a function to describe the prior history of the microbial cell in the secondary model. Incorporating an assumption that growth kinetics depends in an explicit way on the cells' history could provide accurate estimates of growth or inactivation.Cooked, ground uncured chicken was inoculated with C. perfringens spores, and from this chicken, samples were formed and vacuum packaged. For the isothermal experiments, all samples were incubated in a constant temperature water baths stabilized at selected temperatures between 10 and 51 °C and sampled periodically. The samples were cooled from 54.4 to 27 °C and subsequently from 27 to 4 °C at different time periods (cooling rates) for dynamic cooling experiments. The standard model provided predictions that varied from the observed mean log₁₀ growth values by magnitudes up to about 0.65 log₁₀. However, for a selected memory model, estimates of log₁₀ relative growth provided predictions within 0.3 log₁₀ of the mean observed log₁₀ growth values. These findings point to an improvement of predictions obtained by memory models over those obtained by the standard model. More study though is needed to validate the selected model.Industrial relevanceMention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.     

Inhibition of Clostridium botulinum by Antioxidants and Related Phenolic Compounds in Comminuted Pork

Antioxidants, esters of p-hydroxybenzoic acid and gallic acid, and related phenolic compounds were evaluated for their activity against growth and toxin production of C. botulinum types A and B in comminuted pork. With an inoculum level of 8,000 spores/g of meat most of the chemicals at a concentration of 1,000 ppm delayed first swell formation for less than 3 days beyond the control. For most compounds, the time to first swell formation beyond that of the control increased as the spore level per g of meat decreased. 8-Hydroxyquinoline at a concentration of 200 ppm or in combination with sodium nitrite (40 ppm) inhibited the growth and toxin production of C. botulinum in comminuted pork for 60 days at 27°C. 8-Hydroxyquinoline was more active in inhibition of growth and toxin production of C. botulinum in comminuted pork than in prereduced Thiotone-yeast extract-glucose broth.     

Analysis of mathematical models of Pseudomonas spp. growth in pallet-package pork stored at different temperatures

Pseudomonas of pallet-packaged raw pork grown at 0, 5, 10, 15, 20 and 25 °C has been studied in this paper. The modified Gompertz, Baranyi and Huang models were used for data fitting. Statistical criteria such as residual sum of squares, mean square error, Akaike's information criterion, and pseudo-R² were used to evaluate model performance. Results showed that there was an apparent decline in Pseudomonas growth at initial-storage phase at low temperatures. The modified Gompertz model outperformed the others at 5, 15, and 20 °C, while Baranyi model was appropriate for 0 and 25 °C. The Huang model was optimal at 10 °C. No single model can give a consistently preferable goodness-of-fit for all growth data. The Gompertz model, with the smallest average values of RSS, AIC, MSE and the biggest pseudo-R² at all temperatures, is the most appropriate model to describe the growth of Pseudomonas of raw pork under pallet packaging.     

Predictive model for growth of Clostridium perfringens during cooling of cooked cured chicken

Estimates of the growth kinetics of Clostridium perfringens from spores at temperatures applicable to the cooling of cooked cured chicken products are presented. A model for predicting relative growth of C. perfringens from spores during cooling of cured chicken is derived using a nonlinear mixed effects analysis of the data. This statistical procedure has not been used in the predictive microbiology literature that has been written for microbiologists. However, recently software systems have been including this statistical procedure. The primary growth curves, based on the stages of cell development, identify two parameters: (1) germination, outgrowth, and lag (GOL) time, or lag phase time; and (2) exponential growth rate, egr. The mixed effects model does not consider GOL and egr as constants, but as random variables that would, in all likelihood, differ for different cooling events with the same temperature. As such, it is estimated that the egr, for a given temperature, has a CV of approximately 19%. The model obtained by the mixed effects model is compared to the one obtained by the more traditional two-stage approach. The estimated parameters from the derived models are virtually the same. The model predicts, for example, a geometric mean relative growth of about 9·4 with an upper 95% confidence limit of 21·3 when cooling the product from 51°C to 12°C in 8 h, assuming log linear decline in temperature with time. C. perfringens growth from spores was not observed at a temperature of 12°C for up to 3 weeks.     

High pressure thermal processing for the inactivation of Clostridium perfringens spores in beef slurry

The spores of Clostridium perfringens can survive and grow in cooked/pasteurized meat, especially during the cooling of large portions. In this study, 600 MPa high pressure thermal processing (HPTP) at 75 °C for the inactivation of C. perfringens spores was compared with 75 °C thermal processing alone. The HPTP enhanced the inactivation of C. perfringens spores in beef slurry, resulting in 2.2 log reductions for HPTP vs. no reductions for thermal processing after 20 min. Then, the HPTP resistance of two C. perfringens spore strains in beef slurry at 600 MPa was compared and modeled, and the effect of temperature investigated. The NZRM 898 and NZRM 2621 exhibited similar resistance, and Weibull modeled well the log spore survivor curves. The spore inactivation increased when HPTP temperature was raised from 38 to 75 °C. The results confirm the advantage of high pressure technology to increase the thermal inactivation of C. perfringens spores in beef slurry.Industrial relevanceC. perfringens spores may cause food/meat poisoning as a result of improperly handled and prepared foods in industrial kitchens. Thermal processes at 100 °C or higher are generally carried out to ensure the elimination of these pathogenic spores. High pressure processing (HPP) is a food pasteurization technique which would help to maintain the sensorial and nutritional properties of food. Preservation of foods with HPP in conjunction with mild heat (HPTP) would enhance the spore inactivation compared to thermal processing alone at the same temperature, due to a known germination–inactivation mechanism. This technology, together with the application of Good Manufacturing Practices, including rapid cooling, is a good alternative to the traditional methods for producing safe processed meat and poultry products with enhanced sensory and nutritional quality.     

Effect of carbon monoxide in modified atmosphere packaging,storage time and endpoint cooking temperature on the internal color of enhanced pork

The objective of this research was to evaluate the effects of gas atmosphere, refrigerated storage time, and endpoint temperature on internal cooked color of injection-enhanced pork chops. Enhanced chops were packaged in 0.36% CO/20.34% CO₂ (CO-MAP), 80% O₂/20% CO₂ (HO-MAP), or PVC-overwrapped (PVC-OW; controls), stored at 4 °C for 0, 12, 19 or 26 days, displayed for 2 days then cooked to six endpoint temperatures (54, 60, 63, 71, 77, and 82 °C). L¹, a¹, and b¹ values, hue angle and chroma were determined on the internal cut surface of cooked chops. Chops packaged in CO-MAP had the highest a¹ values; a¹ value began increasing on day 14. The lowest hue angles occurred in chops cooked to lower endpoint temperatures. Chops in CO-MAP had lower hue angles and higher chroma than those in HO-MAP and PVC-OW. Above 71 °C, hue angle and chroma increased. Overall, CO-MAP packaged chops stored for longer time periods then cooked to lower endpoint temperatures appeared reddest. HO-MAP packaged chops were less red, did not change over time, and appeared more well done at lower endpoint temperatures than those in other gas atmospheres. CO-MAP packaged chops retained redness even after cooking at 82 °C.     

Changes in the texture,microstructures, colour and volatile compounds of pork meat loins during superheated steam cooking

We evaluated changes in the texture, colour, microstructure and volatile compounds of pork loins after superheated steam (SHS) cooking at 120, 140, 160 or 180 °C for 5, 10, 15 and 20 min. Results showed that the texture changed significantly with heating temperature and time. Hardness increased significantly with increasing temperature above 140 °C. Scanning electron microscopy micrographs showed that cooked pork with SHS had more complete muscle fibre bundle structure than that of pork in HA. The L* value indicating colour was significantly increased during the early period and then decreased, whereas the a* and b* values showed a continuous increase. Ninety-five volatile compounds were identified in cooked pork from SHS by gas chromatography/mass spectrometry with solid-phase microextraction. The amount of volatile compounds increased during cooking and decreased as cooking time increased and was well retained at 140 °C. Considering those variations, samples cooked at 140 °C showed better quality attributes.     

Incidence and Heat Resistance of Clostridium botulinum Type E Spores in Menhaden Surimi

Raw menhaden surimi (Brevoortia tyrannus) was examined to determine the incidence of Clostridium botulinum spores. Seven of 565 test portions (1.2%) were positive for type E spores. The thermal death time (TDT) tube method was used to determine the heat resistance of C. botulinum type E spores inoculated into the remaining 558 negative portions. Calculated mean D-values in mm were 8.66 at 73.9°C, 3.49 at 76.7°C, 2.15 at 79.4°C, and 1.22 at 82.2°C. The z-value of the phantom TDT curve was 9.78C^o. Our data indicate previously reported minimal time/temperature thermal processes used to set surimi gel provide an adequate margin of safety with regard to C. botulinum type E.     

Probability of growth and toxin production by nonproteolytic Clostridium botulinum in rockfish fillets stored under modified atmospheres

Whether toxin production by Clostridium botulinum precedes or follows spoilage of fish stored under modified atmospheres (MA), remains unclear. In this factorial design study we inoculated a pool of nonproteolytic C. botulinum spores (5 type E, 4 type B, and 4 type F strains) at 6 levels (10⁴ to 10⁻¹) between two rockfish fillets and then incubated the fillets at 4, 8, 12 and 30°C under vacuum, 100% CO₂ and 70% CO₂+30% air for 21 days. The probability of toxigenesis by one spore was significantly affected (P<0.005) by temperature (T) and storage time (S_t), and not (P>0.1) by MA, MA×T or MA×S_t. At the 10° spore/sample level, the earliest time to detect toxin production at 4,8,12 and 30°C under all MAs was >21, 15–21, 6–9 and 2 days, respectively. No toxin production was detected at 4°C. Only type B toxin was present in the toxic samples. At 30°C storage, spoilage of fillets followed toxigenesis. Using linear and logistic regression models, equations were derived that could estimate the lag phase and predict the probability of one spore initiating growth under a particular storage condition.     

“Blown pack” Probabilistic Modeling for C. Algidicarnis and C. Estertheticum under the Effects of Storage Temperature,Vacuum Level and Package Shrink Temperature

A model for ‘blown pack’ probability (BPP) caused by spores of C.estertheticum DSM8809 and C.algidicarnis, was developed as a function of vacuum packaging variables: storage temperature(ST:-2, 2, 4 and 15 °C), vacuum level(VL:6 and 9mBar) and heat shrink temperature(HST:83 and 87 °C). Beef meat pieces, were inoculated with spore suspensions individually at 10²spores/cm², packed and daily monitored up to 90 days. The lower BPP, estimated by the log-logistic model, for C.algidicarnis was 0.8% at:-1.5 °C/6mBar/87 °C while for C.estertheticum was 99.13% at the same conditions. For both organisms, tested variables were unable to eliminate the risk of blown packaged spoilage, at 10²spores/cm² contamination level.     

Microbiological conditions of moisture-enhanced pork before and after cooking

Substantial numbers of aerobic bacteria but few coliforms or Listeria spp. and no Escherichia coli were recovered from both swab samples and brines circulated in cleaned equipment used for injecting pork loins. After meat was processed for 30 or 60 min, the numbers of aerobic bacteria in brines had increased by >1 log unit, to about 4.5 log cfu ml⁻¹, but coliforms were <2 and E. coli and Listeria spp. were <1 log cfu ml⁻¹. The numbers of bacteria on the surfaces of pork loins before and after injection of the meat were similar. No bacteria were recovered from the deep tissues of the uninjected meat, but aerobic bacteria were recovered at log-mean numbers of 2.1 log cfu g⁻¹ and coliforms at log-total numbers of 1.2 log cfu 25 g⁻¹ from 25 samples of deep tissues of injected meat. Aerobic bacteria were recovered at log total numbers of 1.0 log cfu 25 g⁻¹ from 25 samples of injected pork cooked to a central temperature of 61 °C, but no bacteria were recovered from the deep tissues of meat cooked to 70 °C. The findings suggest that moisture-enhanced pork cooked to a medium rare condition can be microbiologically safe.     

Efficacy of plant extracts in inhibitingAeromonas hydrophilaandListeria monocytogenesin refrigerated,cooked poultry

Alcohol extracts of angelica root, banana purée, bay, caraway seed, carrot root, clove (eugenol), marjoram, pimento leaf and thyme were applied to cooked chicken to determine their antimicrobial activities against Aeromonas hydrophilaand Listeria monocytogenes.Skinless chicken breast meat was cooked to an internal temperature of 85°C, allowed to cool to c. 5°C, then treated by surface application with plant extracts. Low (10 cfu g⁻¹)or high (10⁵ cfu g⁻¹)populations of A. hydrophilaand L. monocytogeneswere applied and samples were stored at either 5 or 15°C for up to 14 or 7 days, respectively. Eugenol and pimento extracts were most effective in inhibiting growth of both bacteria. A. hydrophilawas the more sensitive to the two treatments, with 4 log₁₀ cfu g⁻¹less growth occurring at 14 days at 5°C on eugenol-treated breast meat than on control samples. These results suggested that plant extracts might be useful as antimicrobials in cooked, ready-to-eat chicken meat.