Listeria Monocytogenes In Ground Beef Research Articles

Optimizing the Effects of Nisin and NaCl to Thermal Inactivate Listeria monocytogenes in Ground Beef with Chipotle Sauce During Sous-vide Processing

Mild cooking thermal treatments, like sous-vide, can compromise ground meat entrees such as meatballs with chipotle sauce, especially when salt levels are reduced during its preparation. Listeria monocytogenes is a thermoresistant pathogen that can be in ready-to-eat food. On the other hand, nisin, due to its thermal stability, can be a good alternative to aid on the thermal inactivation of L. monocytogenes and ensure meat safety. The objective was to optimize the amount of nisin and salt concentrations to thermally inactivate L. monocytogenes during the sous-vide cooking of ground beef marinated in chipotle sauce, and to generate a predictive model. A four-strain cocktail was prepared and inoculated in ground beef in combination (3:2) with chipotle sauce added with nisin (0–150 IU) and salt (0–2%). After that, meat samples were sous-vide cooked at different temperatures, nisin, and salt concentrations, established by a central composite design. Depending on the levels of these factors, D-values ranged from 49.71 to 0.27 min. A predictive model (p < 0.05) was obtained by response surface, which described that D-values variation was explained by the linear effects of the three factors, the interaction between nisin and temperature, and the quadratic effects of salt and temperature. It was also observed that nisin presented a bactericidal effect while salt presented a protective effect during the thermal inactivation of L. monocytogenes. Adding 120 IU of nisin and 0.4% of salt to the meat product at 63°C temperature can help to ensure food safety by making L. monocytogenes cells more sensitive to the lethal effect of heat. The model developed in this study can be used by food processors for planning and designing effective levels of salt and nisin to thermally inactivate L. monocytogenes in ground beef products marinated with chipotle sauce to ensure their safety.

Assessment of the bioprotective potential of lactic acid bacteria against Listeria monocytogenes in ground beef.

Lactic acid bacteria can be considered as natural biopreservative and good biotechnological alternative to food safety. In this study, the antilisterial compounds produced by Enterococcus isolates from the Patagonian environment and their effectiveness for the control of Listeria monocytogenes in a food model were studied. Enterococcus isolates whose cell-free supernatant presented activity against Listeria monocytogenes were identified and evaluated for their virulence factors. The activity of the antimicrobial compounds produced by Enterococcus sp. against Listeria monocytogenes Scott A in meat gravy and ground beef during refrigerated storage was tested. The results indicated that ten Enterococcus isolates presented activity against Listeria monocytogenes and none of the selected strains presented virulence factors. L. monocytogenes in the food models containing the antilisterial compounds produced by Enterococcus sp. has decreased over the days, indicating that these compounds and cultures are an alternative to control the growth of L. monocytogenes in foods.

Use of cloves and cinnamon essential oil to inactivate Listeria monocytogenes in ground beef at freezing and refrigeration temperatures

The need for better control of foodborne pathogens has been of paramount importance in recent years as one of the major concerns to ensure food safety. This study was aimed to determine whether Cloves (Syzygium aromaticum) and Cinnamon (Cinnamomum cassia) derived essential oils (EOs) could be used to control Listeria monocytogenes in ground beef. When L. monocytogenes contaminated ground beef was exposed to 5% and 10% of crude and commercial clove EOs or 2.5% and 5.0% of crude and commercial cinnamon EOs and stored at refrigeration (8 °C), chilling (0 °C) temperatures for 7 days as well as at freezing (−18 °C) temperatures for 60 days, it was found that 10% clove (both crude and commercial) could completely inactivate L. monocytogenes in ground beef within 3 days of post inoculation, irrespective of storage temperature. However, 5.0% clove EOs (both crude and commercial) was not found effective in killing L. monocytogenes throughout the storage period. On the other hand, both 2.5% and 5.0% of crude and cinnamon EOs was not found effective in inactivating L. monocytogenes throughout the storage period. However, 5.0% commercial cinnamon EOs was able to reduce 3.5–4.0 log CFU/g of L. monocytogenes populations depending on the storage temperature and time. The 3.5–4.0 log CFU/g reduction of L. monocytogenes was achieved within 7 days at refrigeration and chilling temperatures but it takes 60 days while storage at freezing temperature. This finding suggested that the effectiveness of reducing L. monocytogenes populations in ground beef by chinamon EOs was influenced by storage temperature and time. On the other hand, this influence was not observed in clove EOs indicating that use of clove EOs is better in killing pathogen populations in ground beef, than that of cinnamon EOs. Hence, could be useful in controlling L. monocytogenes in ground beef meat and improve the safety of ground beef products.

The Relative Efficacy of Thermal and Acidification Stresses on the Survival of E. coli O157:H7, Salmonella, and Listeria Monocytogenes in Ground Beef

To provide additional insights on pathogen survival, we evaluated the relative efficacy of acidification (pH 2.7), thermophilic treatment (55 °C), and low temperature pasteurization (68 °C) on the inactivation of E. coli O157:H7, Salmonella, and Listeria monocytogenes in ground beef. A series of experiment was conducted under biosafety level 3 environments for assessing the impacts of heat and low pH on pathogen survival. Results showed that 5-log reductions of E. coli O157:H7 could take more than 2640 min at 55 °C, 134 min at 68 °C and 120 min under pH 2.7. Compared to E. coli O157:H7, the 5-log reduction of Salmonella was obtained in 4836, 126, 86 min at 55 °C, 68 °C, and pH 2.7, respectively. The 5-log reduction of Listeria was achieved in 4704, 200, and 115 min under 55 °C, 68 °C, and pH 2.7, respectively. The results of this study will provide additional insights for developing improved methods for controlling pathogens in ground beef.

Immunomagnetic nanobeads based on a streptavidin-biotin system for the highly efficient and specific separation of Listeria monocytogenes

Immunomagnetic separation was used to decrease the assay time for Listeria monocytogenes (LM) isolation. The coupling conditions and immunomagnetic bead (IMB) capture process were optimized. Results showed that the incubation time and separation time for 0.1 mg of 180 nm immunomagnetic nanobeads (IMB-S-180) coupled with monoclonal antibody using a streptavidin-biotin system was 45 and 3 min, respectively. Magnetic separation was affected by the separation medium and magnetic density of the magnetic separator. Capture efficiency (CE) was 94.12% when the magnetic density was 1.5 T, using 1 ml of PBS as separation medium. The IMBs exhibited highly specific binding with LM strains (CE > 90%) but low binding with non-target bacteria (CE < 5%). The CE of IMBs (0.1 mg/ml) against LM in ground beef and milk samples were 25.1% and 91.2%, respectively. These results can serve as a guide for the appropriate selection of IMBs for developing isolation processes for pathogens.

Predictive Thermal Inactivation Model for Effects and Interactions of Temperature, NaCl, Sodium Pyrophosphate, and Sodium Lactate on Listeria monocytogenes in Ground Beef

The effects and interactions of heating temperature (60 °C to 73.9 °C), salt (0.0 % to 4.5 % w/v), sodium pyrophosphate (0.0 % to 0.5 % w/v), and sodium lactate (0.0 % to 4.5 % w/v) on the heat resistance of a five-strain mixture of Listeria monocytogenes in 75 % lean ground beef were examined. Meat samples in sterile filtered stomacher bags were heated in a temperature controlled waterbath to determine thermal death times. The recovery medium was tryptic soy agar supplemented with 0.6 % yeast extract and 1 % sodium pyruvate. Weibull survival functions were employed to model the primary survival curves. Then, survival curve-specific estimated parameter values obtained from the Weibull model were used for determining a secondary model. The results indicate that temperature and salt have a large impact on the inactivation kinetics of L. monocytogenes, while sodium lactate (NaL) has an impact in the presence of salt. The model presented in this paper for predicting inactivation of L. monocytogenes can be used as an aid in designing lethality treatments meant to control the presence of this pathogen in ready-to-eat products.

Predictive model for the reduction of heat resistance of Listeria monocytogenes in ground beef by the combined effect of sodium chloride and apple polyphenols

We investigated the combined effect of three internal temperatures (57.5, 60, and 62.5°C) and different concentrations (0 to 3.0wt/wt.%) of sodium chloride (NaCl) and apple polyphenols (APP), individually and in combination, on the heat-resistance of a five-strain cocktail of Listeria monocytogenes in ground beef. A complete factorial design (3×4×4) was used to assess the effects and interactions of heating temperature, NaCl, and APP. All 48 combinations were tested twice, to yield 96 survival curves. Mathematical models were then used to quantitate the combined effect of these parameters on heat resistance of the pathogen. The theoretical analysis shows that compared with heat alone, the addition of NaCl enhanced and that of APP reduced the heat resistance of L. monocytogenes measured as D-values. By contrast, the protective effect of NaCl against thermal inactivation of the pathogen was reduced when both additives were present in combination, as evidenced by reduction of up to ~68% in D-values at 57.5°C; 65% at 60°C; and 25% at 62.5°C. The observed high antimicrobial activity of the combination of APP and low salt levels (e.g., 2.5% APP and 0.5% salt) suggests that commercial and home processors of meat could reduce the salt concentration by adding APP to the ground meat. The influence of the combined effect allows a reduction of the temperature of heat treatments as well as the salt content of the meat. Meat processors can use the predictive model to design processing times and temperatures that can protect against adverse effects of contaminated meat products. Additional benefits include reduced energy use in cooking, and the addition of antioxidative apple polyphenols may provide beneficial health affects to consumers.

Fractional Differential Equations Based Modeling of Microbial Survival and Growth Curves: Model Development and Experimental Validation

A fractional differential equations (FDEs)-based theory involving 1- and 2-term equations was developed to predict the nonlinear survival and growth curves of foodborne pathogens. It is interesting to note that the solution of 1-term FDE leads to the Weibull model. Nonlinear regression (Gauss-Newton method) was performed to calculate the parameters of the 1-term and 2-term FDEs. The experimental inactivation data of Salmonella cocktail in ground turkey breast, ground turkey thigh, and pork shoulder; and cocktail of Salmonella, E. coli, and Listeria monocytogenes in ground beef exposed at isothermal cooking conditions of 50 to 66 degrees C were used for validation. To evaluate the performance of 2-term FDE in predicting the growth curves-growth of Salmonella typhimurium, Salmonella Enteritidis, and background flora in ground pork and boneless pork chops; and E. coli O157:H7 in ground beef in the temperature range of 22.2 to 4.4 degrees C were chosen. A program was written in Matlab to predict the model parameters and survival and growth curves. Two-term FDE was more successful in describing the complex shapes of microbial survival and growth curves as compared to the linear and Weibull models. Predicted curves of 2-term FDE had higher magnitudes of R(2) (0.89 to 0.99) and lower magnitudes of root mean square error (0.0182 to 0.5461) for all experimental cases in comparison to the linear and Weibull models. This model was capable of predicting the tails in survival curves, which was not possible using Weibull and linear models. The developed model can be used for other foodborne pathogens in a variety of food products to study the destruction and growth behavior.

Thermal inactivation of Listeria monocytogenes in ground beef under isothermal and dynamic temperature conditions

The objective of this research was to compare the suitability of three kinetic models for describing the survival of a cocktail of Listeria monocytogenes in ground beef under both isothermal and dynamic temperature conditions. Ground beef (93% lean), inoculated with a 4-strain cocktail of L. monocytogenes, was subjected to heating at 57, 60, 63, or 66 °C to develop isothermal kinetic models. Experimental data showed that the isothermal survival curves were not strictly linear and were downwardly concaved. The isothermal inactivation of L. monocytogenes in ground beef was better described by two nonlinear kinetic models, the Weibull-type and the modified Gompertz models. Analytical results showed that root mean square error values (RMSE) of the Weibull-type and the modified Gompertz models were 0.19 and 0.20 log(CFU/g), both significantly smaller than that of the linear model (0.48 log(CFU/g)). Under linear heating dynamic conditions, however, only the modified Gompertz model, with a RMSE of only 0.71 log(CFU/g), was suitable for describing the survival of the pathogen. Both linear and Weibull-type models grossly underestimated the survival of L. monocytogenes in ground beef during dynamic heating.

Effects of Acetic-Lactic Acid Treatments Applied to Beef Trim on Populations of Escherichia coli O157:H7 and Listeria monocytogenes in Ground Beef

The efficacy of organic acid sprays for eliminating Escherichia coli O157:H7 and Listeria monocytogenes from beef trim used in a model ground beef production scheme was determined. Beef trim pieces with ca. 20% fat inoculated with E. coli O157:H7 or L. monocytogenes (ca. 3 log10 CFU/g) were utilized as controls or treated by spraying with 2 or 4% acetic and lactic acids. Propylene glycol (20%) was the carrier for each treatment. Following acid treatment, intact pieces were stored at 4°C for 12 or 24 h, ground, divided into 4 100-g retail packages and stored at 4°C for 0, 1, 2, or 4 days, at which time surviving populations of E. coli O157:H7 or L. monocytogenes were enumerated. High populations (>2.6 log10 CFU/g) of the pathogens persisted in all treatments. The 2% acid spray reduced (P < 0.01) the E. coli O157:H7 population by only 0.1 log10 CFU/g. The 2 and 4% acid sprays reduced (P < 0.001) the L. monocytogenes populations by 0.36 and 0.44 log10 CFU/g, respectively. Storing beef trim intact prior to grinding resulted in lower populations of E. coli O157:H7, and storage following grinding did not affect populations of either pathogen. The acid treatments tested were only slightly effective as sanitizers for beef trim destined for ground beef production.

Control of Listeria monocytogenes in ground beef by ‘Lactocin 705’, a bacteriocin produced by Lactobacillus casei CRL 705

The effectiveness of Lactobacillus casei CRL 705 as well as that of Lactocin 705, the associated bacteriocin produced, in reducing population levels and growth of Listeria monocytogenes in sterile and non-sterile ground beef was studied. Predetermined numbers of L. monocytogenes and concentrations of Lactocin 705 were added to the meat slurries. Listeria in the bacteriocin-treated and control samples during incubation at 20 °C were enumerated as CFU on Bacto blood agar base. Results indicated that reduction in numbers of Listeria was largest with high levels of Lactocin 705 and few initial cell numbers of the pathogen present in the meat slurry. However, when the producer strain was added to the slurry, no significant inhibition was detected. Furthermore, inhibition by listeria was shown to be greater when meat slurries were heat-treated.

Evaluation of FDA and USDA procedures for enumerating Listeria monocytogenes in ground beef

The suitability of FDA and USDA-FSIS methods for isolating Listeria monocytogenes from meat samples was evaluated and examined. The enrichment broths tested were Fraser broth (FB), Listeria enrichment broth (LEB), University of Vermont (UVM) broth, and UVM with extra acriflavine (UVMA). The agar media used included modified McBride agar (MMA), LiCl-phenylethanol-moxalactam (LPM) agar, modified Oxford (MOX) agar, and McBride agar (MA) as a control. The performance of 16 combinations of enrichment broth and plating agar media was examined to recover three strains of L. monocytogenes from pure culture suspension and a slurry of inoculated fresh ground beef (10 2–10 4 cfu ml −1). All media performed well; however, FDA-LEB combined with USDA-MOX agar was the most efficient for the detection of L. monocytogenes strains.

Survival of Listeria monocytogenes in Ground Beef or Liver During Storage at 4 and 25°C.

Survival and growth of three Listeria monocytogenes strains (Scott A, Brie-1, and ATCC 35152) were studied in ground beef or liver during storage from freshness to spoilage at 4 and 25°C. Cells were enumerated on Plate Count Agar, Trypticase Soy Agar, and selective media, including McBride Listeria Agar (MLA), Cyclohexanedione Nalidixic Acid Phenylethanol Agar (CNPA), LiCl Phenylethanol Moxalactam Agar (LPM), and LPM with potassium tellurite (LPMT). Aerobic natural microflora in the fresh uninoculated samples ranged from 102 to 104 CFU/g, and L. monocytogenes inocula were ca. 103 or 105 CFU/g. Total aerobes after 2 weeks at 4°C were >108 or >107/g in meat or liver respectively, while recovered numbers of L. monocytogenes remained unchanged during a storage of over 30 d in either ground meat or liver. Samples stored at 25°C confirmed recovery but absence of multiplication of the organism. LPM or LPMT provided the best selective environment for direct plating of meat. Despite differences in composition and spoilage pattern of meat and liver, no difference was observed in the fate of L. monocytogenes in these foods.

Survival of Listeria monocytogenes in ground beef

Listeria monocytogenes, due to its association with animals and animal products and its proven pathogenicity, is an organism of potential importance to the meat industry. The survival of L. monocytogenes in ground beef held at 4°C for 2 weeks was investigated. The ground beef was inoculated with L. monocytogenes type 1 or type 4 at a level of 5 × 10 5 to 7× 10 6 CFU/g and then packaged in either oxygen-permeable or oxygen-impermeable bags. Packages were sampled at random at 0, 2, 3, 5, 7, 11, and 14 days post-inoculation, and assayed for L. monocytogenes counts and pH. The number of L. monocytogenes in ground beef remained constant throughout the sampling period, and survival was not affected by package permeability to oxygen. Listeriae were not isolated from the control ground beef. The pH of the meat increased slightly during storage, but was always in the in the range pH 5.6 to 5.9. It appears that L. monocytogenes in ground beef can survive without any substantial increase or decrease in viable cell population during refrigerated storage for 14 days.