Surface carcass treatment with olive mill wastewater polyphenolic extract against Salmonella Enteritidis and Listeria monocytogenes: in vitro and in situ assessment

In recent years, there has been an increased interest in substances that could inhibit or reduce microbial growth in food products. Olive oil industry by-products, due to bioactive compounds with potential antimicrobial properties such as polyphenols, could be used in carcass treatment to enhance hygienic and quality traits. The assessment of the antimicrobial efficacy of bioactive molecules against pathogens should be determined with in vitro and in situ models since it is not possible to evaluate it directly on carcasses at the slaughterhouse. This study aimed to evaluate the effect of an olive mill wastewater polyphenolic extract against Salmonella Enteritidis and Listeria monocytogenes, simulating carcass surfaces using bovine dermis samples that were experimentally contaminated with the selected pathogens. The minimum inhibitory concentration and minimum bactericidal concentration were first determined for S. Enteritidis and L. monocytogenes. In situ, bactericidal activity assessment was performed using 20 cm2 derma samples contaminated with 5 Log CFU/20 cm2 of S. Enteritidis and L. monocytogenes in separate trials. Treatment with the polyphenolic extract was not effective for either microorganism. In order to establish the bacteriostatic activity of the polyphenolic extract, suspensions of about 2 Log CFU/20 cm2 of S. Enteritidis and L. monocytogenes were used. Polyphenolic extract treatment was not effective against Salmonella, while for Listeria it allowed microbial growth to delay (around 1 Log CFU/cm2 difference at 3, 7, and 14 days between treated and control groups). Further investigations are needed to evaluate the application of polyphenolic compounds on carcass surfaces and their effects on sensory traits.

Modeling the influence of propionic acid concentration and pH on the kinetics of Salmonella Typhimurium

Salmonella Typhimurium is a foodborne pathogen often found in the poultry production chain. Antibiotics have been used to reduce S. Typhimurium contamination in poultry aviaries and improve chicken growth. However, antibiotics were banned in several countries. Alternatively, organic acids, such as propionic acid (PA), can control pathogens. This study determined the PA minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and mathematically modeled S. Typhimurium growth/inactivation kinetics under the influence of PA at different pH values (4.5, 5.5, and 6.5) which are within the pH range of the chicken gastrointestinal tract. The PA MIC against S. Typhimurium was pH-dependent, resulting in 5.0, 3.5 and 9.0 mM undissociated PA at pH 4.5, 5.5, and 6.5, respectively. The Baranyi and Roberts and the Weibull model fit growth and inactivation data well, respectively. Secondary models were proposed. The validated model predicted 3-log reduction of S. Typhimurium in 3 h at 68.2 mM of undissociated PA and pH 4.5. The models presented a good capacity to describe the kinetics of S. Typhimurium subjected to PA, representing a useful tool to predict PA antibacterial action depending on the pH.

Salmonella spp. in poultry production-A review of the role of interventions along the production continuum

Salmonella is a significant pathogen of human and animal health and poultry are one of the most common sources linked with foodborne illness worldwide. Global production of poultry meat and products has increased significantly over the last decade or more as a result of consumer demand and the changing demographics of the world's population, where poultry meat forms a greater part of the diet. In addition, the relatively fast growth rate of birds which is significantly higher than other meat species also plays a role in how poultry production has intensified. In an effort to meet the greater demand for poultry meat and products, modern poultry production and processing practices have changed and practices to target control and reduction of foodborne pathogens such as Salmonella have been implemented. These strategies are implemented along the continuum from parent and grandparent flocks to breeders, the farm and finished broilers to transport and processing and finally from retail to the consumer. This review focuses on common practices, interventions and strategies that have potential impact for the control of Salmonella along the poultry production continuum from farm to plate.

Development of Shortened Enrichment Methods for Detection of Salmonella Typhimurium Spiked in Milk

Rapid and accurate testing of pathogenic Salmonella enterica in dairy products could reduce the risk of exposure to the bacterial pathogens for consumers. This study aimed to reduce the assessment time needed for enteric bacteria recovery and quantification in food using the natural growth properties of Salmonella enterica Typhimurium (S. Typhimurium) in cow's milk and efficiently using rapid PCR methods. Over 5 h of 37 °C enrichment, culture and PCR methods measured increases in the non-heat-treated S. Typhimurium concentration at similar rates, with an average increase of 2.7 log10 CFU/mL between the start of enrichment and 5 h. In contrast, no bacteria were recovered by culture after S. Typhimurium in milk received heat treatment, and the number of gene copies of heat-treated Salmonella detected by PCR did not increase with the enrichment time. Thus, comparing culture and PCR data over just 5 h of enrichment time can detect and differentiate between replicating bacteria and dead bacteria.

Effect of lysin EN4 in combination with sodium bicarbonate on reduction of Salmonella in chilled and thawed chicken meat

Lysin EN4 is a peptidoglycan-degrading enzyme. Like other lysins against Gram-negative bacteria, EN4 requires cell-wall destabilizing agents, such as ethylenediamine tetraacetic acid (EDTA) to facilitate it to the peptidoglycan layer. This study aimed to use EN4 in reducing Salmonella in chilled and thawed raw chicken meat. However, the use of EDTA is limited to some types of foods. An alternative to EDTA was explored. Sodium bicarbonate was identified as an effective alternative to EDTA. The combination of EN4 with 0.1 % NaHCO₃, pH 7.4 showed a wide lytic spectrum against Salmonella spp. The combination showed efficiency in reduction of Salmonella Enteritidis and Typhimurium in raw chicken meat during storage at 4 °C for 48 h, with the maximum reduction of 1.0-1.3log CFU/g. The efficiency of the combination against Salmonella was evaluated in frozen chicken meat during proper and improper defrosting. A significant reduction of Salmonella was observed in EN4-treated meat compared to the untreated control through 48 and 4 h of defrosting at 4 and 30 °C, respectively, with the greatest reduction of 1.2-1.6 log CFU/g. The results indicated that EN4 in combination with NaHCO₃ has a potential use for controlling growth of Salmonella in chilled and thawed chicken meat.

Salmonella Behavior in Meat during Cool Storage: A Systematic Review and Meta-Analysis

The aim of the present study was to investigate Salmonella behavior in meat stored in cool conditions (between 0 °C and 7.5 °C), by employing a systematic review and meta-analysis. The data were obtained from research articles published in SciELO, PubMed, the Web of Science, and Scopus databases. The results of the retrieved studies were obtained from meat (beef, chicken, pork, poultry, and turkey), fish, shellfish, and broth media samples The data were extracted as sample size (n), initial concentration (Xi), final concentration (Xf), standard deviation (SD), standard error (SE), and microbial behavior effects (reduction or growth). A meta-analysis was carried out using the metaphor package from R software. A total of 654 articles were initially retrieved. After applying the exclusion criteria, 83 articles were selected for the systematic review, and 61 of these were used for the meta-analysis. Most studies were conducted at 0 °C to 4.4 °C storage temperatures under normal atmosphere package conditions. Salmonella Typhimurium, S. Enteritidis, and a cocktail (strain mixture) were inoculated at 5.0 and 6.0 log CFU mL−1. Articles both with and without the addition of antimicrobial compounds were found. Salmonella concentration decreases were observed in most studies, estimated for all study combinations as −0.8429 ± 0.0931 log CFU g−1 (95% CI; −1.0254, −0.6604) (p < 0.001), varying for each subgroup analysis. According to this survey, Salmonella concentration decreases are frequent during cool storage, although concentration increases and no bacterial inactivation were observed in some studies.

Bacterial shifts on broiler carcasses at retail upon frozen storage

Freezing broiler carcasses, industrially or at home, not only delays spoilage, but also is expected to increase food safety by hampering growth of food pathogens. However, detailed knowledge on microbial changes after a short or longer freezing period of fresh broiler meat in home freezing setting is lacking and no comparison between different freezing periods has been published yet. The present study combined classical isolation techniques and identification by MALDI-TOF MS with 16S rRNA amplicon sequencing to assess bacterial contamination on broiler carcasses that were either bought fresh and then frozen for short periods (total n = 20) in home freezing, or industrial frozen one (total n = 4) at retail. Changes in total aerobic bacteria (TAB) were also studied on 78 freshly bought broiler carcasses that were then stored frozen for up to 6 months in domestic freezers. Salmonella and Campylobacter were examined to assess the effect of freezing on controlling common foodborne pathogens. The contamination level of mesophilic and psychrotrophic TAB was numerically equal on carcasses at retail, either fresh or frozen at different time points. After short and long freezing period, a decrease in counts of mesophilic TAB was observed, while changes in counts of psychrotrophic TAB were rarely observed. No correlation between home freezing period and TAB load, either mesophilic (R = -0.006, p = 0.949) or psychrotrophic (R = 0.080, p = 0.389), was observed. No Salmonella and Campylobacter was detected on industrial frozen carcasses but on fresh carcasses at retail, either pre-freezing or after freezing. The bacterial communities were influenced by freezing, in which some genera showed significantly changes in relative abundance after freezing. In conclusion, from a food safety point of view, freezing of meat products does not serve as safety hurdle, and freezing should only be considered as a method for extending shelf life compared with fresh chicken meat. Applying hygienic slaughter procedures to keep the initial contamination as low as possible, and the maintenance of the cold chain during further processing are the key factors in food safety.

Impact of sodium lactate, encapsulated or unencapsulated polyphosphates and their combinations on Salmonella Typhimurium, Escherichia coli O157:H7 and Staphylococcus aureus growth in cooked ground beef

Foodborne illnesses affect the health of consumers worldwide, and thus searching for potential antimicrobial agents against foodborne pathogens is given an increased focus. This research evaluated the influence of sodium lactate (SL), encapsulated (e) and unencapsulated (u) polyphosphates (PP; sodium tripolyphosphate, STP; sodium acid pyrophosphate, SPP), and their combinations on Salmonella Typhimurium, Escherichia coli O157:H7 and Staphylococcus aureus growth in cooked ground beef during 30 day storage at 4 or 10 °C. pH, water activity (a_w), oxidation-reduction potential (ORP) and S. Typhimurium, E. coli O157:H7 and S. aureus counts were determined. S. Typhimurium was not found in SPP-SL combination groups after 30 day storage at 4 °C (P <0.05). Lower S. Typhimurium levels were determined in only SL containing groups stored at 10 °C than group with only tested microorganism (MO, P < 0.05). Although there was no change in S. Typhimurium load in all SL incorporated groups during 10 °C storage, S. Typhimurium count increased in other groups (P < 0.05). E. coli O157:H7 in MO and STP groups showed an increase at 4 °C, whereas it decreased in SPP-SL combination groups (P < 0.05). A gradual increase in E. coli O157:H7 at 10 °C was determined in MO and only PP incorporated groups, whereas there was a decrease in STP-SL or SPP-SL combination groups (P < 0.05). E. coli O157:H7 count was stable in SL containing groups during 10 °C storage. A gradual decrease in S. aureus was determined in all treatments at 4 °C, whereas S. aureus count increased in MO and uSTP groups during 10 °C storage (P < 0.05). There was no change in S. aureus level in only eSTP or uSPP or ueSTP containing groups at 10 °C, meantime it decreased in other groups (P < 0.05). The lowest S. aureus load was achieved by uSPP-SL or eSPP-SL or ueSPP-SL combinations after 30 days at both storage temperatures (P < 0.05). In general, pH was higher in samples with STP than those with SPP and control (P < 0.05). The lowest a_w was generally obtained in all SL containing groups at both storage temperatures (P < 0.05). Lower ORP was determined in all PP incorporated groups during storage at both temperatures compared to others (P < 0.05). ORP in all treatments generally increased (P < 0.05) during storage at both storage temperatures. This study showed that encapsulation is not a factor affecting antimicrobial efficiency of PP and using PP-SL combinations have synergistic effect on reducing the viability of S. Typhimurium, E. coli O157:H7 and S. aureus and their subsequent growth ability in cooked ground beef.

Hyperbolastic type-III diffusion process: Obtaining from the generalized Weibull diffusion process

The modeling of growth phenomena has become a matter of great interest in many different fields of application and research. New stochastic models have been developed, and others have been updated to this end. The present paper introduces a diffusion process whose main characteristic is that its mean function belongs to a wide family of curves derived from the classic Weibull curve. The main characteristics of the process are described and, as a particular case, a diffusion process is considered whose mean function is the hyperbolastic curve of type III, which has proven useful in the study of cell growth phenomena. By studying its estimation we are able to describe the behavior of such growth patterns. This work considers the problem of the maximum likelihood estimation of the parameters of the process, including strategies to obtain initial solutions for the system of equations that must be solved. Some examples are provided based on simulated sample paths and real data to illustrate the development carried out.

Interventions Targeting Deep Tissue Lymph Nodes May Not Effectively Reduce the Risk of Salmonellosis from Ground Pork Consumption: A Quantitative Microbial Risk Assessment

The inclusion of deep tissue lymph nodes (DTLNs) or nonvisceral lymph nodes contaminated with Salmonella in wholesale fresh ground pork (WFGP) production may pose risks to public health. To assess the relative contribution of DTLNs to human salmonellosis occurrence associated with ground pork consumption and to investigate potential critical control points in the slaughter-to-table continuum for the control of human salmonellosis in the United States, a quantitative microbial risk assessment (QMRA) model was established. The model predicted an average of 45 cases of salmonellosis (95% CI = [19, 71]) per 100,000 Americans annually due to WFGP consumption. Sensitivity analysis of all stochastic input variables showed that cooking temperature was the most influential parameter for reducing salmonellosis cases associated with WFGP meals, followed by storage temperature and Salmonella concentration on contaminated carcass surface before fabrication. The input variables were grouped to represent three main factors along the slaughter-to-table chain influencing Salmonella doses ingested via WFGP meals: DTLN-related factors, factors at processing other than DTLNs, and consumer-related factors. The evaluation of the impact of each group of factors by second-order Monte Carlo simulation showed that DTLN-related factors had the lowest impact on the risk estimate among the three groups of factors. These findings indicate that interventions to reduce Salmonella contamination in DTLNs or to remove DTLNs from WFGP products may be less critical for reducing human infections attributable to ground pork than improving consumers' cooking habits or interventions of carcass decontamination at processing.

Microbial study of household hygiene conditions and associated Listeria monocytogenes infection risks for Peruvian women

OBJECTIVES

To develop an exposure and risk assessment model to estimate listeriosis infection risks for Peruvian women.

METHODS

A simulation model was developed utilising Listeria monocytogenes concentrations on kitchen and latrine surfaces in Peruvian homes, hand trace data from Peruvian women and behavioural data from literature. Scenarios involving varying proportions of uncontaminated, or 'clean', surfaces and non-porous surfaces were simulated. Infection risks were estimated for 4, 6 and 8 h of behaviours and interactions with surfaces.

RESULTS

Although infection risks were estimated across scenarios for various time points (e.g. 4, 6, 8 h), overall mean estimated infection risks for all scenarios were ≥ 0.31. Infection risks increased as the proportions of clean surfaces decreased. Hand-to-general surface contacts accounted for the most cumulative change in L. monocytogenes concentration on hands.

CONCLUSIONS

In addition to gaining insights on how human behaviours affect exposure and infection risk, this model addressed uncertainties regarding the influence of household surface contamination levels. Understanding the influence of surface contamination in preventing pathogen transmission in households could help to develop intervention strategies to reduce L. monocytogenes infection and associated health risks.

Effect of Chlorine-Induced Sublethal Oxidative Stress on the Biofilm-Forming Ability of Salmonella at Different Temperatures, Nutrient Conditions, and Substrates

The present study was conducted to evaluate the effect of chlorine-induced oxidative stress on biofilm formation by various Salmonella strains on polystyrene and stainless steel (SS) surfaces at three temperatures (30, 25 [room temperature], and 4°C) in tryptic soy broth (TSB) and 1/10 TSB. Fifteen Salmonella strains (six serotypes) were exposed to a sublethal chlorine concentration (150 ppm of total chlorine) in TSB for 2 h at the predetermined temperatures. The biofilm-forming ability of the Salmonella strains was determined in 96-well polystyrene microtiter plates by using a crystal violet staining method and on SS coupons in 24-well tissue culture plates. All tested strains of Salmonella produced biofilms on both surfaces tested at room temperature and at 30°C. Of the 15 strains tested, none (chlorine stressed and nonstressed) formed biofilm at 4°C. At 30°C, Salmonella Heidelberg (ID 72), Salmonella Newport (ID 107), and Salmonella Typhimurium (ATCC 14028) formed more biofilm than did their respective nonstressed controls on polystyrene ( P ≤ 0.05). At room temperature, only stressed Salmonella Reading (ID 115) in 1/10 TSB had significantly more biofilm formation than did the nonstressed control cells ( P ≤ 0.05). Salmonella strains formed more biofilm in nutrient-deficient medium (1/10 TSB) than in full-strength TSB. At 25°C, chlorine-stressed Salmonella Heidelberg (ATCC 8326) and Salmonella Enteritidis (ATCC 4931) formed stronger biofilms on SS coupons ( P ≤ 0.05) than did the nonstressed cells. These findings suggest that certain strains of Salmonella can produce significantly stronger biofilms on plastic and SS upon exposure to sublethal chlorine.

Overexpressing ovotransferrin and avian β-defensin-3 improves antimicrobial capacity of chickens and poultry products

Zoonotic and foodborne diseases pose a significant burden, decreasing both human and animal health. Modifying chickens to overexpress antimicrobials has the potential to decrease bacterial growth on poultry products and boost chicken innate immunity. Chickens overexpressing either ovotransferrin or avian β-defensin-3 (AvβD3) were generated using Tol-2 transposons. Transgene expression at the RNA and protein level was seen in egg white, breast muscle, and serum. There were significant differences in the immune cell populations in the blood, bursa, and spleen associated with transgene expression including an increased proportion of CD8+ cells in the blood of ovotransferrin and AvβD3 transgenic birds. Expression of the antimicrobials inhibited the in vitro growth of human and chicken bacterial pathogens and spoilage bacteria. For example, transgene expression significantly reduced growth of aerobic and coliform bacteria in breast muscle and decreased the growth of Salmonella enterica in egg white. Overall these results indicate that overexpression of antimicrobials in the chicken can impact the immune system and increase the antimicrobial capacity of poultry products.

Lauric acid as feed additive - An approach to reducing Campylobacter spp. in broiler meat

The increasing prevalence of Campylobacter spp. within broiler populations is a major problem for food safety and consumer protection worldwide. In vitro studies could already demonstrate that Campylobacter spp. are susceptible to lauric acid. The purpose of this study was to examine in vivo the influence of lauric acid as a feed additive on slaughter parameters, muscle fatty acid profile, meat quality traits and the reduction of Campylobacter coli in inoculated meat of Ross 308 (R308) and Hubbard JA 757 (HJA) broilers in three independent trials (n = 3). Although slaughter parameters did not show any significant differences, the fatty acid profile of both breeds revealed significantly higher lauric acid concentrations (P < 0.0001) in the Musculus pectoralis superficialis of treated broilers. Comparing both tested breeds, R308 test broilers had significantly higher lauric acid concentrations than HJA test broilers (P < 0.0001), indicating a higher conversion rate in those animals. The meat quality traits showed no differences in the R308 breed (P > 0.05), but HJA test broilers had higher values for drip loss, electrical conductivity, CIE color values L* and b*, and lower pH values. The inoculation trials of R308 showed that initial bacterial loads of 5.9 log10 cfu/g were reduced during six days of storage (4°C) to approximately 4.3 log10 cfu/g in the control groups compared to 3.5 log10 cfu/g in the treatment groups (P = 0.0295), which could be due to antimicrobial effects of lauric acid within the muscle. This study therefore suggests that lauric acid as a feed additive has the potential to improve food safety by reducing the numbers of Campylobacter coli in broiler meat. However, this effect seems to be dependent on the breed determining the feed intake capacity, the fat deposition and therefore the ability to incorporate lauric acid in the muscle.

Effects of Domestic Storage and Thawing Practices on Salmonella in Poultry-Based Meat Preparations

Among consumer food handling practices, time-temperature abuse has been reported as one of the most common contributory factors in salmonellosis outbreaks where the evidence is strong. The present study performed storage tests of burgers, sausages, and kebabs and investigated (i) the effect of refrigerator temperatures (4°C versus 8 or 12°C, which were the temperatures recorded in 33 and 3%, respectively, of domestic refrigerators in Italy), with or without prior temperature abuse (25°C for 2 h, simulating transport of meats from shop to home), and (ii) the impact of the thawing method (overnight in the refrigerator at 8°C versus on the kitchen countertop at 23°C) on the presence and numbers of Salmonella bacteria. Storage tests were carried out on naturally or artificially (Salmonella enterica serovar Typhimurium at ca. 10 CFU/g) contaminated products, while freezing-thawing tests were conducted only on artificially contaminated products (Salmonella Typhimurium at ca. 10, 100, and 1,000 CFU/g). The results from the artificially contaminated products showed significant (P < 0.05) growth of Salmonella Typhimurium at 12°C (i.e., from ca. 8 most probable number [MPN]/g to > 710 MPN/g) in kebabs after 7 and 10 days but more moderate growth in sausages (i.e., from ca. 14 MPN/g to a maximum of 96 MPN/g after 9 days of storage). Storage of naturally contaminated burgers or sausages (contamination at or below 1 MPN/g) at 4, 8, or 12°C and a short time of temperature abuse (2 h at 25°C) did not facilitate an increase in the presence and numbers of Salmonella bacteria. Thawing overnight in the refrigerator led to either a moderate reduction or no change of Salmonella Typhimurium numbers in burgers, sausages, and kebabs. Overall, this study showed that domestic storage and thawing practices can affect food safety and that time-temperature abuse can cause a substantial increase of Salmonella numbers in some types of poultry-based meat preparations, highlighting that efforts for the dissemination of consumer guidelines on the correct storage and handling of meats need to be continued.

Neural Network Model for Survival and Growth of Salmonella enterica Serotype 8,20:-:z6 in Ground Chicken Thigh Meat during Cold Storage: Extrapolation to Other Serotypes

Mathematical models that predict the behavior of human bacterial pathogens in food are valuable tools for assessing and managing this risk to public health. A study was undertaken to develop a model for predicting the behavior of Salmonella enterica serotype 8,20:-:z6 in chicken meat during cold storage and to determine how well the model would predict the behavior of other serotypes of Salmonella stored under the same conditions. To develop the model, ground chicken thigh meat (0.75 cm(3)) was inoculated with 1.7 log Salmonella 8,20:-:z6 and then stored for 0 to 8 -8 to 16°C. An automated miniaturized most-probable-number (MPN) method was developed and used for the enumeration of Salmonella. Commercial software (Excel and the add-in program NeuralTools) was used to develop a multilayer feedforward neural network model with one hidden layer of two nodes. The performance of the model was evaluated using the acceptable prediction zone (APZ) method. The number of Salmonella in ground chicken thigh meat stayed the same (P > 0.05) during 8 days of storage at -8 to 8°C but increased (P < 0.05) during storage at 9°C (+0.6 log) to 16°C (+5.1 log). The proportion of residual values (observed minus predicted values) in an APZ (pAPZ) from -1 log (fail-safe) to 0.5 log (fail-dangerous) was 0.939 for the data (n = 426 log MPN values) used in the development of the model. The model had a pAPZ of 0.944 or 0.954 when it was extrapolated to test data (n = 108 log MPN per serotype) for other serotypes (S. enterica serotype Typhimurium var 5-, Kentucky, Typhimurium, and Thompson) of Salmonella in ground chicken thigh meat stored for 0 to 8 days at -4, 4, 12, or 16°C under the same experimental conditions. A pAPZ of ≥0.7 indicates that a model provides predictions with acceptable bias and accuracy. Thus, the results indicated that the model provided valid predictions of the survival and growth of Salmonella 8,20:-:z6 in ground chicken thigh meat stored for 0 to 8 days at -8 to 16°C and that the model was validated for extrapolation to four other serotypes of Salmonella.

Control of Listeria species food safety at a poultry food production facility

Surveillance and control of food-borne human pathogens, such as Listeria monocytogenes, is a critical aspect of modern food safety programs at food production facilities. This study evaluated contamination patterns of Listeria species at a poultry food production facility, and evaluated the efficacy of procedures to control the contamination and transfer of the bacteria throughout the plant. The presence of Listeria species was studied along the production chain, including raw ingredients, food-contact, non-food-contact surfaces, and finished product. All isolates were sub-typed by pulsed-field gel electrophoresis (PFGE) to identify possible entry points for Listeria species into the production chain, as well as identifying possible transfer routes through the facility. The efficacy of selected in-house sanitizers against a sub-set of the isolates was evaluated. Of the 77 different PFGE-types identified, 10 were found among two or more of the five categories/areas (ingredients, food preparation, cooking and packing, bulk packing, and product), indicating potential transfer routes at the facility. One of the six sanitizers used was identified as unsuitable for control of Listeria species. Combining PFGE data, together with information on isolate location and timeframe, facilitated identification of a persistent Listeria species contamination that had colonized the facility, along with others that were transient.

Predictive thermal inactivation model for the combined effect of temperature, cinnamaldehyde and carvacrol on starvation-stressed multiple Salmonella serotypes in ground chicken

We investigated the combined effect of three internal temperatures (60, 65 and 71.1 °C) and four concentrations (0.0, 0.1, 0.5 and 1% vol/wt) of two natural antimicrobials on the heat resistance of an eight-strain cocktail of Salmonella serovars in chicken meat. A complete factorial design (3×4×4) was used to assess the effects and interactions of heating temperature and the two antimicrobials, carvacrol and cinnamaldehyde. The 48 variable combinations were replicated to provide a total of 96 survivor curves from the experimental data. Mathematical models were then developed to quantify the combined effect of these parameters on heat resistance of starved Salmonella cells. The theoretical analysis shows that the addition of plant-derived antimicrobials overcomes the heat resistance of starvation-stressed Salmonella in ground chicken meat. The influence of the antimicrobials allows reduced heat treatments, thus reducing heat-induced damage to the nutritional quality of ground-chicken products. Although the reported omnibus log-linear model with tail and the omnibus sigmoid model could represent the experimental survivor curves, their discrepancy only became apparent in the present study when lethality times (D-values and t7.0) from each of the models were calculated. Given the concave nature of the inactivation curves, the log-linear model with tail greatly underestimates the times needed to obtain 7.0 log lethality. Thus, a polynomial secondary model, based on the sigmoid model, was developed to accurately predict the 7.0-log reduction times. The three-factor predictive model can be used to estimate the processing times and temperatures required to achieve specific log reductions, including the regulatory recommendation of 7.0-log reduction of Salmonella in ground chicken.

Prediction of Listeria innocua survival in fully cooked chicken breast products during postpackage thermal treatment

The effectiveness of postpackage hot water thermal treatment on survival of Listeria innocua in fully cooked chicken breast products was investigated at 60, 70, 80, and 90°C. Primary models based on log-linear and Weibull models were used to fit bacterial survival curves at different temperatures. The prediction plot and fit statistics indicated that the Weibull model provided a better fit than the log-linear model and was selected as the primary model. A secondary model based on linear regression was developed to describe the effect of temperature on the kinetic parameters of Listeria innocua survival derived from the Weibull model. The root mean square error and coefficients of determination indicated a good fit of the secondary model. The models were validated by independent data from pilot plant tests, and the values of bias factor and accuracy factor fell into the acceptable range. The models developed in this study can assist poultry producers and risk managers in designing appropriate thermal treatment regimens to minimize the risk associated with Listeria in ready-to-eat poultry products.