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The effect of high pressure processing (HPP) at 450 MPa for 10 min, enterocins A and B, thymol, and their combinations on the inactivation of a four-strain cocktail of Listeria monocytogenes and the properties of sliced dry-cured ham during 30 days at 4 and 12 °C was investigated. Enterocins A and B initially reduced L. monocytogenes levels by more than 2.5 log units, but a regrowth was recorded during the storage. Individual treatments of thymol and HPP exhibited a low antimicrobial effect against the pathogen. A synergistic antibacterial activity against L. monocytogenes was observed when HPP was combined with enterocins A and B, preventing the recovery of the pathogen during all the storage period. Such combined treatment also maintained total viable counts (TVC) at low levels after 30 days at 4 and 12 °C. Minor changes were detected in pH, aw, color parameters, and shear strength values in dry-cured ham treated with enterocins A and B, thymol, HPP, and their combinations during the storage at both temperatures. Combination of HPP at 450 MPa for 10 min and enterocins A and B might be applied as a hurdle technology, since it reduced L. monocytogenes counts and spoilage bacteria, and slightly affected the characteristics of sliced dry-cured ham. [ABSTRACT FROM AUTHOR]

This work aims to evaluate the synergetic antimicrobial effects of cold nitrogen plasma (CNP) and lemongrass oil against L. monocytogenes on pork loin. Their possible effects on the physicochemical properties of pork were investigated as well. Lemongrass oil displayed anticipant antibacterial activities against L. monocytogenes at high dose, which could damage the bacterial membrane, leading to the losses of intracellular constituents, including DNA, protein and ATP. Compared with control groups, the number of L. monocytogenes on pork samples was reduced by 2.80 log10 steps after synergy treatment of CNP (500 W, 120 s) and lemongrass oil (5 mg/mL, 30 min). With the assistance of CNP, the satisfactory antibacterial effect for L. monocytogenes on pork was achieved after treatment for low concentration of lemongrass oil. In addition, the potential impacts on sensory attributes of pork were also minimized via combined treatment. Practical applications Under low concentration, lemongrass oil achieved the desired antibacterial effect for L. monocytogenes on pork loin with the assistance of CNP. The potential impacts on sensory attributes of pork loin were minimized via synergetic treatment as well. The synergetic treatment provides a new way for application of plant essential oil in food preservation. [ABSTRACT FROM AUTHOR]

The objective of this study was to directly construct a tertiary growth model for Listeria monocytogenes in a simulated comminuted, non-cured cooked pork product and simultaneously determine the kinetic parameters using a combination of dynamic and isothermal growth curves. Growth studies were conducted using a cocktail of 5 strains of L. monocytogenes in cooked pork under both dynamic and isothermal temperature profiles designed to examine the effect of temperature on bacterial growth. A direct kinetic analysis method was used to construct the growth models and determine the kinetic parameters. The bacterial growth was simulated by a set of differential equations, and the temperature effect was evaluated by the cardinal parameters model. A numerical analysis and optimization method was used to simultaneously solve the different equations and search for the best fits of kinetic parameters for the growth curves and models. The estimated minimum, optimum, and maximum growth temperatures were 0, 33.0, and 42.6 °C, matching well with typical growth characteristics of this microorganism. The root-mean-square error (RMSE) of curve-fitting was 0.42 log CFU/g. The growth models and kinetic parameters were validated using both independent dynamic and isothermal growth curves to check the accuracy of the models. The results showed that the RMSE of predicted growth was 0.49 log CFU/g. The residual errors of predictions follow a Laplace distribution, with 80.3% of the residual errors falling within ±0.5 log CFU/g of the observations. This study proves that the one-step dynamic analysis with both dynamic and isothermal temperature profiles can be an effective approach for simultaneously constructing a tertiary model and determining the kinetic parameters. [ABSTRACT FROM AUTHOR]

The potential of chitosan as a possible booster of the antimicrobial activity of Origanum vulgare EO (OEO) against spoilage bacteria and Listeria monocytogenes was investigated in fresh pork meat. Pork fillets were inoculated with 3 L. monocytogenes strains, dipped either in Origanum vulgare (oregano) Essential Oil (OEO) at 2 and 4%, or in chitosan 1% alone or added with 2 and 4% OEO, then packed under modified atmosphere (70% O 2 , 20% CO 2 , 10% N 2 ) and stored at 4 °C for 15 days. OEO did not reduce L. monocytogenes growth, while 2 Log decrease was obtained after 2 days of storage in treatments with chitosan alone or with OEO, with growth inhibition up to day 15 in samples with chitosan and OEO 4%. When OEO was combined with chitosan, total viable counts and spoilage bacteria were reduced and contained over time, particularly Pseudomonas (2.0 Log CFU/g at day 15) and Brochothrix thermosphacta (undetectable). All the treatments applied extended meat shelf-life with respect to control, whose commercial shelf-life was 10 days. Chitosan treatments enhanced L* and maintained a* values almost stable during storage. Chitosan and OEO singly applied reduced lipid oxidation (0.62–0.75 mg malondialdehyde/Kg meat) compared to control (0.99 mg malondialdehyde/Kg meat). Finally, chitosan treated samples were not recognized with respect to the control, whereas OEO gave bitter taste; chitosan with OEO instead mitigated the effect of OEO addition to meat. Chitosan combined with OEO boosts its antimicrobial activity and shows a potential for application in industrial production of fresh pork in MAP, to achieve shelf-life extension, control of L. monocytogenes growth, stability of color and protective effect from oxidation, with low sensory impact. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the basis of the putative persistence of Listeria monocytogenes in a new industrial facility dedicated to the processing of ready-to-eat (RTE) Iberian pork products. Quaternary ammonium compounds, which included benzalkonium chloride (BAC), were repeatedly used as surface disinfectants in the processing plant. Clean and disinfected surfaces were sampled to evaluate if resistance to disinfectants was associated with persistence. Of the 14 isolates obtained from product contact and non-product contact surfaces, only five different pulsed-field gel electrophoresis (PFGE) types were identified during the 27-month study period. Two of these PFGE types (S1 and S10-1) were previously identified to be persistent and BAC-resistant (BACr) strains in a geographically separate slaughterhouse belonging to the same company. The remaining three PFGE types, which were first identified in this study, were also BACr. Whole-genome sequencing and in silico multilocus sequence typing (MLST) analysis of five BACr isolates of the different PFGE types identified in this study showed that the isolate of the S1 PFGE type belonged to MLST sequence type 31 (ST31), a low-virulence type characterized by mutations in the inlA and prfA genes. The isolates of the remaining four PFGE types were found to belong to MLST ST121, a persistent type that has been isolated in several countries. The ST121 strains contained the BAC resistance transposon Tn6188. The disinfection-resistant L. monocytogenes population in this RTE pork product plant comprised two distinct genotypes with different multidrug resistance phenotypes. This work offers insight into the L. monocytogenes subtypes associated with persistence in food processing environments. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the prevalence of Listeria monocytogenes isolated from chilled pork from open-air markets and supermarkets in Nanjing and to characterize the isolates by serotyping, antibiotic resistance, and MLST subtyping analyses. The results showed that 26 of 476 samples (5.5%) were positive for L. monocytogenes . All the isolates belonged to three serotypes, with serotype 1/2a being dominant (53.8%), followed by serotype 1/2b (23.1%) and serotype 1/2c (23.1%). The antimicrobial susceptibility tests revealed that 5 isolates (19.2%) were susceptible to all antimicrobials used; the remaining strains were resistant to 1 (19.2%), 2 (34.6%), 3 (11.5%), 6 (3.85%) or even 9 (3.85%) different antimicrobials. All the isolates were susceptible to penicillin and vancomycin. Most of the isolates were susceptible to rifampicin and gentamicin (96.2%), cefotaxime (92.3%), streptomycin (92.3%) and trimethoprim/sulfamethoxazole (92.3%). MLST subtyping analyses revealed that 26 isolates were grouped into 10 sequence types (STs). Therefore, this study indicates the high percentage of serotypes 1/2a and 4b, which are associated with human listeriosis; and the high level of multi-resistance could be a public health hazard. [ABSTRACT FROM AUTHOR]

Two application methods were used to investigate the effect of plantaricin BM-1 on the control of Listeria monocytogenes and background spoilage bacteria in sliced vacuum-packaged cooked hant without the addition of any chemical preservatives, including sodium nitrite, during 35 days ot storage at 4°C. Regardless of the application method, plantaricin BM-1 treatment (320, 640, or 1,280 arbitrary units [AU]/g of sliced cooked ham) significantly (P < 0.05) reduced the survival of L. monocytogenes (inoculated at 4 log CFU/g of sliced ham) compared with its survival in the control during the first 21 days of storage at 4°C. The inhibitory effect of plantaricin applied to the surface of the ham was significantly better than the same concentration of plantaricin incorporated into the cooked ham (P < 0.0001 ) during storage. Even 320 AU/g plantaricin applied to the surface exhibited greater inhibition of L. monocytogenes than 1,280 AU/g plantaricin incorporated into the cooked ham on days 1, 14, and 28. A level of 1,280 AU/g plantaricin applied to the surface of the ham reduced L. monocytogenes counts to below the detection limit from the 1st to the 21st day of storage at 4°C. Afterwards, L. monocytogenes was able to reerow, and the viable counts of L. monocytogenes at the end of storage reached 2.76 log CFU/g (6.11 log CFU/g lower than in the control). In the control ham, the counts of background spoilage bacteria increased gradually and surpassed the microbiological spoilage limitation level on the 21st day of storage. However, plantaricin BM-1 treatment significantly (P < 0.05) reduced the survival of background spoilage bacteria in ham compared with their survival in the control from day 21 to 35 of storage at 4°C. A level of 1,280 AU/g plantaricin incorporated into cooked ham was the most effective, reducing the count of background spoilage bacteria count from an initial 2.0 log CFU/g to 1.5 log CFU/g on day 7. This was then maintained for another 14 days and finally increased to 2.76 log CFU/g at the end of the storage at 4°C (2.85 log CFU/g lower than in the control). In conclusion, plantaricin BM-1 application inhibited the growth of L. monocytogenes and background spoilage bacteria in cooked ham during storage at 4°C and could be used as an antimicrobial additive for meat preservation. [ABSTRACT FROM AUTHOR]

Ground pork meat with natural microbiota and inoculated with low initial densities (1-10 or 10-100 CFU/g) of Salmonella enterica or Listeria monocytogenes was stored under abusive temperature at 10C and thermally treated by a simulated home panfrying procedure. The growth and inactivation characteristics were also evaluated in broth. In ground pork meat, the population of S. enterica increased by less than one log after 12-days of storage at 10C, whereas L. monocytogenes increased by 2.3 to 2.8 log units. No unusual intrinsic heat resistance of the pathogens was noted when tested in broth at 60C although shoulders were observed on the inactivation curves of L.monocytogenes. After growth of S. enterica and L. monocytogenes at 10C for 5 days to levels of 1.95 log CFU/g and 3.10 log CFU/g, respectively, in ground pork meat, their inactivation in the burger subjected to a simulated home pan-frying was studied. After thermal treatment S. enterica was undetectable but L. monocytogenes was recovered in three out of six of the 25 g burger samples. Overall, the present study shows that data on growth and inactivation of broths are indicative but may underestimate as well as overestimate behavior of pathogens and thus need confirmation in food matrix conditions to assess food safety in reasonably foreseen abusive conditions of storage and usual home pan-frying of meat burgers in Belgium. [ABSTRACT FROM AUTHOR]

This study was conducted to develop a predictive model to estimate the growth of Listeria monocytogenes on fresh pork during storage at constant temperatures (5, 10, 15, 20, 25, 30, and 35°C). The Baranyi model was fitted to growth data (log CFU per gram) to calculate the specific growth rate (SGR) and lag time (LT) with a high coefficient of determination (R² > 0.98). As expected, SGR increased with a decline in LT with rising temperatures in all samples. Secondary models were then developed to describe the variation of SGR and LT as a function of temperature. Subsequently, the developed models were validated with additional independent growth data collected at 7, 17, 27, and 37°C and from published reports using proportion of relative errors and proportion of standard error of prediction. The proportion of relative errors of the SGR and LT models developed herein were 0.79 and 0.18, respectively. In addition, the standard error of prediction values of the SGR and LT of L. monocytogenes ranged from 25.7 to 33.1% and from 44.92 to 58.44%, respectively. These results suggest that the model developed in this study was capable of predicting the growth of L. monocytogenes under various isothermal conditions. [ABSTRACT FROM AUTHOR]

Essential oils and their constituents are reported to possess potent antimicrobial activity, but their use in food processing is limited because of low solubility in aqueous systems and volatilization during processing. Two proprietary noncommercial essential oil-containing phosphate blends were evaluated for antimicrobial activity against Salmonella enterica cocktail (SC)-and Listeria monocytogenes (Lm)-inoculated deli meat products made from pork, poultry, or beef. Four treatments were tested on restructured cured pork ham, emulsified chicken bologna, and restructured beef loaf: nonencapsulated essential oil with phosphate version 1 at 0.45% of final batch (EOV145; chicken and pork, or EEOV245 beef), micronized encapsulated essential oil with phosphate version 2 at 0.60% of final batch (EEOV260), a 2.0% potassium lactate (PL) control, and a negative control (CN) with no applied antimicrobial agent. Compared with the CN, none of the antimicrobial agents (EEOV260, EOV145, PL) successfully limited Lm or SC growth to <2.0 log cycles over 49 days or 35 days of refrigerated storage, respectively. The PL and EEOV260-treated ham loaves did show Lm growth limiting ability of up to 1 log cycle by days 35 and 42. On formed roast beef, the EEOV260 was able to extend the lag phase and inhibited the growth of Lm in the same manner as the PL. For SC- treated samples, the following effects were observed: in poultry bologna treated with EEOV260, a lag-phase extension was observed through 35 days of storage compared with the other samples. For pork deli loaves, the EEOV260 inhibited growth of SC at days 21 and 28 to the same level of efficacy as PL (0.5 log cycle). In roast beef samples, on day 35, the SC growth was inhibited ca. 0.5 log CFU/g by EEOV260 when compared with the CN. In conclusion the EEOV260 can function to replace PL to limit Salmonella and Lm growth in ready-to-eat deli products. Further testing is needed to ensure consumer acceptability. [ABSTRACT FROM AUTHOR]

In this study, mathematical models were developed to predict the growth probability and kinetic behavior of Listeria monocytogenes on fresh pork skin during storage at different temperatures. A 10-strain mixture of L. monocytogenes was inoculated on fresh pork skin (3 by 5 cm) at 4 log CFU/cm². The inoculated samples were stored aerobically at 4, 7, and 10°C for 240 h, at 15 and 20°C for 96 h, and at 25 and 30°C for 12 h. The Baranyi model was fitted to L. monocytogenes growth data on PALCAM agar to calculate the maximum specific growth rate, lag-phase duration, the lower asymptote, and the upper asymptote. The kinetic parameters were then further analyzed as a function of storage temperature. The model simulated growth of L. monocytogenes under constant and changing temperatures, and the performances of the models were evaluated by the root mean square error and bias factor (Bf). Of the 49 combinations (temperature x sampling time), the combinations with significant growth (P < 0.05) of L. monocytogenes were assigned a value of 1, and the combinations with nonsignificant growth (P ≥ 0.05) were given a value of 0. These data were analyzed by logistic regression to develop a model predicting the probabilities of L. monocytogenes growth. At 4 to 10°C, obvious L. monocytogenes growth was observable after 24 h of storage; but, at other temperatures, the pathogen had obvious growth after 12 h of storage. Because the root mean square error value (0.184) and Bf (1.01) were close to 0 and 1, respectively, the performance of the developed model was acceptable, and the probabilistic model also showed good performance. These results indicate that the developed model should be useful in predicting kinetic behavior and calculating growth probabilities of L. monocytogenes as a function of temperature and time. [ABSTRACT FROM AUTHOR]

In a 3-year study (2008 to 2011) to estimate the prevalence and the contamination sources of Listeria monocytogenes in pork meat in Sardinia, Italy, 211 samples were collected from five Sardinian swine slaughterhouses: 171 samples from slaughtered pigs and 40 from the slaughterhouse environment. Fifty L. monocytogenes isolates were characterized by PCR-based serotyping, presence of virulence-associated genes, and pulsed-field gel electrophoresis restriction analysis. The overall prevalence of L. monocytogenes was 33% in swine carcasses, 7% in cecal material, 23% on meat contact surfaces, and 25% on noncontact surfaces. Only two serotypes were detected: l/2c (78%) and l/2a (22%). In all, based on the presence of virulence-associated genes, eight pathogenic profiles were detected. Only 42% of all isolates carried the full complement of virulence-associated genes and were allotted to profile 1. Six pulsed-field gel electrophoresis profiles persisted in the slaughterhouses; restriction profiles appeared to be specific to each plant. [ABSTRACT FROM AUTHOR]

Abstract: Natural and organic food regulations preclude the use of sodium nitrite/nitrate and other antimicrobials for processed meat products. Consequently, processors have begun to use natural nitrate/nitrite sources, such as celery juice/powder, sea salt, and turbinado sugar, to manufacture natural and organic products with cured meat characteristics but without sodium nitrite. The objective of this study was to compare physio-chemical characteristics that affect Clostridium perfringens and Listeria monocytogenes growth in naturally cured and traditionally cured commercial frankfurters, hams, and bacon. Correlations of specific product characteristics to pathogen growth varied between products and pathogens, though water activity, salt concentration, and product composition (moisture, protein and fat) were common intrinsic factors correlated to pathogen growth across products. Other frequently correlated traits were related to curing reactions such as % cured pigment. Residual nitrite and nitrate were significantly correlated to C. perfringens growth but only for the ham products. [Copyright &y& Elsevier]

Objective. To determine the prevalence of L. monocytogenes in pork carcasses, meat cuts, and meat products ("chorizo", sausage and ham). Materials and methods. Stratified sampling was implemented in meat-processed products. We analyzed 566 (37%) carcasses, 472 (31%) meat cuts, and 481, (32%) meat-processed products, distributed as follows: 169 (11%) sausage, 163 (11%) ham, and 149 (10%) "chorizo" for a total of 1519 (100%) samples in a period of 18 months. The samples were processed using the ISO-17604, ISO-11290-1 and the USDA/FSIS (MLG-8.03) methods. Genus and species were confirmed by multiplex-PCR. Results. We obtained isolates of L. monocytogenes from 21 carcasses (10%), 160 (76%) from meat deboning, 10 (5%) from ham, 6 (3%) from "chorizo", and 13 (6%) from sausage. The prevalence found was 3.7% and 33.9% in carcasses and meat deboning respectively. The prevalence in the meat-processed products was 4.03% in "chorizo", 6.13% in ham and 7.69% in sausage. The overall prevalence of L. monocytogenes in the study was 13.82%. Conclusions. We found L. monocytogenes in different products analyzed, with particular interest in ham and sausage since both are consumed without previous heat treatment. [ABSTRACT FROM AUTHOR]

A correction to the article "Development of Predictive Models for the Growth Kinetics of Listeria monocytogenes on Fresh Pork under Different Storage Temperatures," that appeared in the 2015 issue is presented.