Inactivation Of Listeria Monocytogenes Research Articles

Inactivation of Listeria monocytogenes and Salmonella spp. on cantaloupe rinds by blue light emitting diodes (LEDs)

This study evaluated the potential of blue light-emitting diodes (LED) of wavelength 405 and 460 nm in combination with sodium chlorophyllin to inactivate Listeria monocytogenes and Salmonella spp. on cantaloupe rind. A cocktail culture of L. monocytogenes or Salmonella spp. strains was surface inoculated onto cantaloupe rinds to reach a final concentration of 4 log CFU/cm2 and dip-treated in a 100 μM sodium copper chlorophyllin solution. The cantaloupe samples were then exposed to 405 or 460 nm LEDs at a total dose of 1210 J/cm2 and 5356 J/cm2, respectively, at 4 and 20 °C. Results showed that the antibacterial efficacy against both pathogens on cantaloupe rinds between LED alone and LED with the chlorophyllin were statistically similar with bacterial inactivation ranging from 1.1 to 3 log CFU/cm2 in most of the cases or the difference was only minimal. A similar inactivation of 3 log CFU/cm2 was obtained in the case of L. monocytogenes and Salmonella spp. when illuminated by 405 nm LEDs while the inactivation of L. monocytogenes was higher than Salmonella spp. when illuminated by 460 nm LED. The δ value, a modified Weibull model parameter defined as the time (h) taken to reduce the bacterial population by 90%, was computed to compare the inactivation rates of the conditions. It was inferred that illumination with 405 nm LED required a lower δ value than 460 nm LED illumination (P < 0.05) for the inactivation of L. monocytogenes at 20 °C and Salmonella spp. at 4 °C. Thus the findings of this study indicate a promising application of blue LEDs to inactivate these pathogens on the surface of cantaloupe, minimizing the risk of listeriosis and salmonellosis by consumption of cantaloupe.

Combined effect of a positively charged cinnamon leaf oil emulsion and organic acid on the inactivation of Listeria monocytogenes inoculated on fresh-cut Treviso leaves

This study was performed to examine the inhibitory effect of combined treatments with a positively charged cinnamon leaf oil (P-CL) emulsion and various organic acids against Listeria monocytogenes inoculated on fresh-cut Treviso leaves. Combined treatments with a P-CL emulsion and an organic acid exhibited a higher inhibitory effect than treatment with each alone or NaOCl. The highest inhibitory effect was achieved by combined treatment with the P-CL emulsion and lactic acid (LA), which showed a 2.85-log reduction compared to distilled water washing. In addition, the inhibitory effect of the combined treatment was maintained during 6 days of subsequent storage, and showed a 3.24–3.39-log reduction compared to unwashed samples. Treviso leaves treated with the P-CL emulsion and LA also maintained their sensorial properties, including appearance, odor, hardness, freshness, and overall acceptability, during subsequent storage. Therefore, combined treatment with a P-CL emulsion and LA can be used to effectively ensure the microbial safety and organoleptic quality of fresh-cut Treviso leaves.

Mathematical approach for the Listeria monocytogenes inactivation during high hydrostatic pressure processing of a simulated meat medium

Abstract Based on a central composite experimental design, the effects of five factors: pH (4.6–6.6), sodium chloride (NaCl, 0–10%), sodium nitrite (NaNO2, 0–152 ppm), pressure (P, 300–600 MPa) and pressure-holding time (t, 0–10 min) on the inactivation of Listeria monocytogenes by high hydrostatic pressure processing on a simulated meat medium (SMM) were evaluated and quantified. Results showed that L. monocytogenes reductions during pressure treatments ranged from 0 to >6 log cfu/g. A polynomial inactivation model was developed being P, t and NaCl the only significant factors influencing HP-lethality (p ≤ 0.05). Inactivation on SMM increased with the increase in P and t, and a synergistic effect between both factors on process effectiveness was remarked. By increasing NaCl concentration (i.e. lowering aw values), a baroprotective effect on L. monocytogenes cells was evidenced. Besides the well-known effects of technological parameters, this study highlights the relevant influence of meat products formulations on the inactivation of L. monocytogenes induced by HHP processing.

Inactivation of Listeria monocytogenes on and within Apples Destined for Caramel Apple Production by Using Sequential Forced Air Ozone Gas Followed by a Continuous Advanced Oxidative Process Treatment

This study evaluated the efficacy of using sequential forced air ozone followed by an advanced oxidative process (AOP) treatment to inactivate Listeria monocytogenes on and within Empire apples. The forced air ozone treatment consisted of a reactor that introduced ozone (6 g/h) into an airstream that flowed through an apple bed (ca. 30 cm in depth). Before treatment, the apples were conditioned at 4°C to ensure that condensate had formed before the apples were transferred to the reactor. The condensate ensured sufficient relative humidity to enhance the antimicrobial action of ozone. Air was passed through the apple bed at 9.3 m/s, and the ozone was introduced after 10 min. The ozone concentration measured after exiting the apple bed reached a steady state of 23 ppm. A 20-min ozone treatment supported a 2.12- to 3.07-log CFU reduction of L. monocytogenes, with no significant effect of apple position within the bed. The AOP-based method was a continuous process whereby hydrogen peroxide was introduced as a vapor into a reactor illuminated by UV-C and ozone-emitting lamps that collectively generated hydroxyl radicals. Operating the AOP reactor with UV-C light (54-mJ cm2 dose), 6% (v/v) hydrogen peroxide, 2 g/h ozone, and a chamber temperature of 48°C resulted in a 3-log CFU reduction of L. monocytogenes on the surface of the apples and internally within the scar tissue. Applying a caramel coating, from a molten solution (at 80°C), resulted in a 0.5-log CFU reduction of L. monocytogenes on the apple surface. In apples treated with the sequential process, L. monocytogenes could only be recovered sporadically by enrichment and did not undergo outgrowth when the caramel apples were stored at 22°C for 19 days. However, growth of L. monocytogenes within the core, but not the surface, was observed from caramel apples prepared from nontreated control fruit.

Optimal characterization of thermal microbial inactivation simulating non-isothermal processes

In this paper, optimal experimental design is applied for the characterization of the microbial inactivation of Listeria monocytogenes under non-isothermal conditions, modelled by the Bigelow model. These conditions simulate industrial processes, where different temperature profiles can be applied for food processing. Here, the aim was to find the best time nodes for measurements given a fixed number of observations and a final time process. Results show that, compared to a “classic” uniform time distribution for the observations, the optimal distribution of observation times results in a more accurate description of the response of the microbial population. The OED resulted in a reduction in the relative standard errors for the estimated D and z-values of 25% and 80%, respectively.Prediction intervals of the microbial counts were calculated based on the parameters estimated with both designs (i.e., uniform and optimal design). The prediction interval generated using the parameters estimated from the optimal design is notably narrower than the one obtained when the “uniform” experiment is considered, thus providing a more accurate description of the thermal resistance of the microorganism. Although the Bigelow model has been used in this particular case, the functions developed have been wrapped in an R package (bioOED), which is freely available and can be used for any other type of microorganism and/or inactivation model.

The applicability of Weibull model for the kinetics inactivation of Listeria monocytogenes and Escherichia coli O157: H7 on soybean sprouts submitted to chemical sanitizers in combination with ultrasound at mild temperatures

This research was performed to evaluate the inactivation kinetics of slightly acidic electrolyzed water (SAEW), fumaric acid (FA) and their combination simultaneous with ultrasound (US) at a mild temperature against L.monocytogenes and E.coli O157:H7 on sprouts. The effects of combined treatments on sensory quality of sprouts were also examined. A t4D equal to 10 min was needed for the combined SAEW with FA (SAEW + FA) at 40 °C to reach 4 log reduction of L.monocytogenes; while the same combination simultaneous with ultrasound (SAEW + FA + US) provided the t4D value of 12; 7 and 3 min for L.monocytogenes at 23°, 30° and 40 °C respectively. For E.coli O157:H7, only (SAEW + FA + US) gave the t4D of 14; 9 and 3 min at 23°, 30°, and 40 °C respectively. The Weibull model provided a good fit with R2 ≥ 0.9 for both bacteria and the root mean square errors (RMSEs) were in the range of 0.01–0.48 for L.monocytogenes and 0.02–0.54 for E.coli O157:H7. The samples submitted to both combined treatments remained in good quality at the end of storage with slight deterioration due to ultrasound usage. This study suggests that the Weibull model could successfully be used to determine exact contact time for inactivating foodborne pathogens on food.

Influence of 405 nm light-emitting diode illumination on the inactivation of Listeria monocytogenes and Salmonella spp. on ready-to-eat fresh salmon surface at chilling storage for 8 h and their susceptibility to simulated gastric fluid

The aim of this study was to evaluate the antibacterial effect of 405 nm light-emitting diode (LED) against Listeria monocytogenes and Salmonella spp. on the surface of ready-to-eat (RTE) fresh salmon, and to determine the susceptibility of LED-illuminated bacterial cells to simulated gastric fluid (SGF). A cocktail culture of L. monocytogenes or Salmonella spp. was inoculated onto the freshly cut salmon surface and then illuminated by 405 nm LED (16 ± 2 mW/cm2) for 8 h at 4 and 12 °C. Illuminated cells were subsequently exposed to SGF at 37 °C. Results showed that the populations of LED-illuminated L. monocytogenes and Salmonella cells were significantly (P < .05) reduced by 0.4 and 0.5 log CFU/cm2 for 8 h compared to non-illuminated cells at 4 °C. At 12 °C, significant reductions of 0.3 and 0.4 log CFU/cm2 were observed for LED-illuminated cells, respectively. The D-values of LED-illuminated L. monocytogenes cells at 4 and 12 °C in SGF were 6.0 and 9.4 min, which were significantly lower than those of non-illuminated cells (14.4 and 15.6 min), respectively. Similarly, LED illumination also caused significant decreases in the D-values of Salmonella cells, resulting in 19.7 and 32.9 s of LED-illuminated cells at 4 and 12 °C, respectively, compared to those of non-illuminated cells (37.5 and 46.7 s). No significant color change was observed for LED-illuminated salmon for 8 h at both 4 and 12 °C. Although 405 nm LED illumination did not largely reduce the population of L. monocytogenes and Salmonella cells on fresh salmon during storage at chilling temperatures, these results indicate that 405 nm LED illumination might make them sensitive to gastric acid. Thus, this study suggests that the implementation of 405 nm LED in the storage of RTE fresh salmon products could be useful to minimize the risk of listeriosis and salmonellosis.

Reductionin Listeria monocytogenes, Salmonella enterica and Escherichia coli O157:H7 in vitro and on tomato by sophorolipid and sanitiser as affected by temperature and storage time

SummaryIncreased consumption of produce by consumers has been attributed to perceived health benefits of postharvest produce. Pathogen control is crucial because periodic occurrences and contamination of tomato and leafy greens have exacerbated food safety risks for consumers. We investigated the effects of temperatures (5 and 25 °C), storage time (30 min and 24 h) for inactivation of Listeria monocytogenes, Salmonella enterica and Escherichia coli O157:H7 by sophorolipid (SL‐p) produced fermentatively using palmitic acid as a co‐substrate at different concentrations in vitro. Reduction in pathogenic bacteria on grape tomato by SL‐p, sanitiser (Lovit) and combinations of SL‐p and sanitiser was determined. Temperature and storage time significantly (P &lt; 0.05) affected pathogen inactivations by SL‐p as pathogen reductions were greater at 25 °C and 24 h than at 5 °C and 30 min of storage. L. monocytogenes was the most sensitive to SL‐p treatment as reductions of 5 log relative to untreated controls were attained at 0.12% of SL‐p. Significant reductions in S. enterica (1.91–3.85 logs) and E. coli O157:H7 (0.87–4.09 logs) were recorded at 2–5% of SL‐p. Lower populations of Salmonella and E. coli O157:H7 were inactivated than L. monocytogenes. On grape tomato, pathogen populations inactivated increased at higher SL‐p levels at 25 °C. Sanitiser and sanitiser + SL‐p reduced bacterial populations on tomato by 5.29–5.76 logs and 0.71–3.3.66 logs, respectively. These results imply the interactions of temperature, storage time and SL‐p significantly (P &lt; 0.05) affected pathogen strain reductions. The combination of SL‐p with sanitiser led to synergistic effect on E. coli O157:H7, but not L. monocytogenes and S. enterica.

Effect of storage conditions in the response of Listeria monocytogenes in a fresh purple vegetable smoothie compared with an acidified TSB medium

In this study, growth and/or inactivation of Listeria monocytogenes 4032 at different inoculum levels in a vegetable smoothie with purple colour, (previously heat stabilised at 95 °C for 3 min) was evaluated. Growth/inactivation was compared with acidified TSB medium at the same pH level with HCl. Samples were stored at different temperatures (5, 10, 15 and 25 °C).All the smoothies stored at 15 and 25 °C showed growth up to 7.5–8.0 log CFU/mL and at 10 °C growth was only observed at the highest inoculum level. Growth was only observed at 25 °C in acidified TSB. In the case of the smoothies inoculated and stored at 5 °C, L. monocytogenes was not able to grow but survived for a long period of time, whereas at the lower inocula at 10 °C they presented a slow inactivation for an extended time. Acidified TSB inoculated and stored showed inactivation at 5, 10 and 15 °C. Best inactivation modelling alternatives are proposed. The differences between the smoothie and TSB medium about growth or survival in this study, even at relatively low pH values, were due to the favorable nutritional composition of the smoothie compared to a laboratory medium. Results in this study can allow to design safe conditions for smoothie production.

Thermal Inactivation of Listeria monocytogenes in Whole Oysters (Crassostrea belcheri) and Pasteurization Effects on Meat Quality

ABSTRACTThis study assesses the practical thermal inactivation of Listeria monocytogenes in whole oysters (Crassostrea belcheri) and the quality changes in meat caused by pasteurization (57.5–70.0°C). The D-value decreased from approximately 4 minutes to half a minute when the temperature was increased from 57.5 to 70.0°C. The z-value of L. monocytogenes was approximately 12.6°C. In the study of physical, chemical, microbiological, and sensory quality effects on pasteurized oyster meat, the 6D conditions for L. monocytogenes were used in processing at 57.5–70.0°C temperatures. It was found that the cooking loss and the b* color coordinate of oyster meat increased, whereas cutting strength, L*, a*, and moisture content decreased (P < 0.05) with treatment temperature. The pH of oyster meat was not significantly affected by the choice of treatment, and no total viable count (TVC) was found in any sample. In the sensory evaluation, odor, texture, and overall acceptability were not significantly affected by the treatment temperature. Only some specific descriptors related to oyster appearance and taste had significant differences between treatments in the sensory evaluation scores. Results from this study are useful for timing the thermal treatment of vacuum-packed whole oysters to inactivate L. monocytogenes.

Thermal Inactivation of Listeria monocytogenes and Salmonella during Water and Steam Blanching of Vegetables

Thermal inactivation of Listeria monocytogenes and Salmonella was evaluated on peas, spinach, broccoli, potatoes, and carrots that were treated with hot water and steam. One gram-positive bacterium, L. monocytogenes, and one gram-negative bacterium, Salmonella, were selected as pertinent human pathogens for evaluation. Samples were inoculated with a composite of five strains each of L. monocytogenes and Salmonella to achieve approximately 108 to 109 CFU/g. Inoculated samples were treated with hot water at 85 and 87.8°C and with steam at 85 and 96.7°C for up to 3.5 min. A greater than 5-log reduction of L. monocytogenes and Salmonella was achieved on all products within 0.5 min by hot water blanching at 85 and 87.8°C. Steam blanching at 85°C reduced Salmonella populations by greater than 5 log on spinach and peas within 2 min and on carrots and broccoli within 3.5 min. Populations of Salmonella were reduced by more than 5 log within 1 min on carrot, spinach, and broccoli and within 2 min on peas by steam blanching at 96.7°C. Steam blanching at 85°C reduced L. monocytogenes populations by more than 5 log on carrots and spinach within 2 min and on broccoli and peas within 3.5 min. L. monocytogenes populations were reduced more than 5 log within 1 min on carrot, spinach, peas and broccoli by steam blanching at 96.7°C. Longer treatment times and higher temperatures were required for steam-blanched samples than for samples blanched with hot water. Results suggest that hot water and steam blanching practices commonly used by the frozen vegetable industry will achieve the desired 5-log lethality of L. monocytogenes and Salmonella and will enhance microbiological safety prior to freezing.

Impact of Cooking Procedures and Storage Practices at Home on Consumer Exposure to Listeria Monocytogenes and Salmonella Due to the Consumption of Pork Meat.

The objective of this research was to analyze the impact of different cooking procedures (i.e., gas hob and traditional static oven) and levels of cooking (i.e., rare, medium, and well-done) on inactivation of Listeria monocytogenes and Salmonella in pork loin chops. Moreover, the consumer's exposure to both microorganisms after simulation of meat leftover storage at home was assessed. The results showed that well-done cooking in a static oven was the only treatment able to inactivate the tested pathogens. The other cooking combinations allowed to reach in the product temperatures always ≥73.6 °C, decreasing both pathogens between 6 log10 cfu/g and 7 log10 cfu/g. However, according to simulation results, the few cells surviving cooking treatments can multiply during storage by consumers up to 1 log10 cfu/g, with probabilities of 0.059 (gas hob) and 0.035 (static oven) for L. monocytogenes and 0.049 (gas hob) and 0.031 (static oven) for Salmonella. The key factors affecting consumer exposure in relation to storage practices were probability of pathogen occurrence after cooking, doneness degree, time of storage, and time of storage at room temperature. The results of this study can be combined with prevalence data and dose-response models in risk assessment models and included in guidelines for consumers on practices to be followed to manage cooking of pork meat at home.

Antibacterial effect of 460 nm light-emitting diode in combination with riboflavin against Listeria monocytogenes on smoked salmon

This study investigated the antibacterial effect of a 460 nm light emitting diode (LED) in combination with riboflavin on the inactivation of Listeria monocytogenes on smoked salmon. The influence of irradiance and temperature on this inactivation was examined. Smoked salmon fillets, surface-inoculated with a 4-strain cocktail of L. monocytogenes and topically administered with 25, 50 and 100 μM riboflavin, were illuminated by 460 nm LEDs at three different irradiances (15, 31 and 58 mW/cm2) and two temperatures (4 and 12 °C). Three conceptually different mathematical models - log-linear, modified Weibull and reduced Baranyi were used to fit the inactivation curves. The color of smoked salmon was also monitored during the illumination. A dosage of 2.4 kJ/cm2 LED illumination in combination with riboflavin caused 0.7–1.2 log CFU//cm2 reductions of L. monocytogenes at all irradiances and temperatures. Three-way ANOVA showed that all the three variables significantly influenced the inactivation of L. monocytogenes (P < 0.05). Significant interaction was observed between concentration and irradiance at 12 °C. Mathematical modeling suggested that the Weibull as well as the Baranyi model best fitted the inactivation curve and thus the Weibull model was subsequently used to compute the dose required for the first log reduction (δ). In most cases, the combination of LEDs and riboflavin was more effective than either treatment alone. The results of this study demonstrate the potential of 460 nm LEDs aided by riboflavin to minimize the risk of L. monocytogenes associated with smoked salmon during storage at food establishments.

Efficacy of radiant catalytic ionization to reduce bacterial populations in air and on different surfaces

Air contamination by biological agents is often observed in medical or veterinary facilities and industrial plants. Bioaerosols may sediment and pose the surface contamination. Microorganisms present on them may become a source of infections among humans and food contamination. This study determined the use of oxidative gases, including ozone and peroxide, generated by the Radiant Catalytic Ionization (RCI) cell for the inactivation of Acinetobacter baumannii, Escherichia coli, Enterococcus faecalis, Pseudomonas aeruginosa, Salmonella Enteritidis, Listeria monocytogenes, Staphylococcus aureus, Streptococcus epidermidis, Bacillus subtilis, Clostridium sporogenes, Candida albicans, Aspergillus niger and Penicillium chrysogenumon in air and on different surfaces. Results showed that oxidative gases produced by the RCI cell reduced all tested microorganisms. The full elimination of studied microorganisms from the air was obtained for E. coli and C. albicans. RCI also proved to be an effective method of eliminating microbes from the examined surfaces. Regarding of the species, strains origin and the type of surface, the reduction rate ranged from 19.0% for C. albicans to over 99% for A. baumanii. For both, air and surface, the most resistant to RCI was C. sporogenes spores, for which the percentage reduction rate ranged from –2.6% to 71.2% on the surfaces and was equal 71.7% in the air.

Trisodium phosphate enhanced phage lysis of Listeria monocytogenes growth on fresh-cut produce

Combination of bacteriophage and trisodium phosphate (TSP) to inactivate Listeria monocytogenes inoculated on fresh-cut produce was investigated. Fresh-cut tomato and watermelon inoculated with L. monocytogenes cocktail at log 107 CFU/g were treated with Listex P100 bacteriophage (108 PFU/g) alone, and in combination with TSP at 10, 30 and 60 mg/ml using chlorine at 200 mg/L as control. Treated samples were stored at 4 and 10 °C for 6 days. Effect of treatment on pH and colour of treated samples was evaluated. Phage treatment alone significantly (p < 0.05) reduced L. monocytogenes on fresh-cut tomato by approximately 0.5 and 0.6 log CFU/ml and on fresh-cut melon by 1.30 and 1.49 log CFU/ml at 4 and 10 °C respectively. Addition of phage-TSP at 10 mg/ml was only effective on fresh-cut melon, but phage-TSP at 30 and 60 mg/ml approximately reduced inoculated tomato by 1 and 2 logs, and melon by 2 and 5 logs at 4 and 10 °C respectively. Chlorine treatment showed 1–2 log reduction. Phage titer declined rapidly on tomato unlike melon, pH and colour parameters slightly increased with treatment combinations with no impairment on both samples. Phage-TSP combination could serve as effective tool to control listeriosis outbreak in fresh produce.

Thermal inactivation of Listeria monocytogenes and Salmonella spp. in sous-vide processed marinated chicken breast

The heat resistance of a cocktail of five Salmonella strains and five L. monocytogenes strains was determined in teriyaki-marinated chicken breasts. Inoculated meat, packaged in bags, were completely immersed in a circulating water bath and cooked to a final temperature of 55, 57.5 or 60°C in 1h, and then held for predetermined times. The surviving Salmonella and L. monocytogenes cells were enumerated by surface plating on XLD agar and Palcam agar, respectively. D-values, determined by linear regression, of Salmonella in chicken breast ranged from 47.65min at 55°C to 7.48min at 60°C; the values for L. monocytogenes ranged from 54.81min at 55°C to 10.39min at 60°C. Marination rendered the pathogen more sensitive to the lethal effect of heat. The results of this study will assist the food industry in ensuring microbiological safety of sous-vide processed marinated chicken breasts.

Synergistic Antimicrobial Combinations Inhibit and Inactivate Listeria monocytogenes in Neutral and Acidic Broth Systems

The use of antimicrobial compounds can be an effective approach to control Listeria monocytogenes in ready-to-eat foods, but it can also be limited by cost, restrictions on concentrations in foods, and potential changes to organoleptic properties. Combinatorial approaches that produce additive or synergistic effects allow for reductions in individual antimicrobial concentrations while achieving the same level of control. The present study determined the MIC and MBC of an antimicrobial compound when used alone or in binary combinations against L. monocytogenes in growth media adjusted to pH values 7.4 and 5.5 and characterized interactions as synergistic, additive, or antagonistic. Inhibitory and bactericidal concentrations were defined as changes in L. monocytogenes counts of ≤1.0 or ≥3.0 log CFU/mL compared with the starting inoculum, respectively. Individually, lauric arginate (LAE), hydrogen peroxide (HP), and ε-polylysine (EPL) inhibited L. monocytogenes growth at the lowest concentrations when applied alone in broth adjusted to pH 7.4. Similarly, LAE, EPL, and HP had the lowest MBCs in broth adjusted to both pH levels. The inhibitory efficacy of both caprylic acid and sodium caprylate (SC) increased at the lower pH, with reductions in MICs of >98%. In total, 35 and 19 additive or synergistic inhibitory and bactericidal combinations were identified at pH values 7.4 and 5.5, respectively. Combinations of acidified calcium sulfate with lactic acid (ACSL) and SC were among the most synergistic inhibitory groupings at both pH levels, whereas EPL+LAE were the most effective bactericides at pH 7.4. Combinations of SC with EPL or ACSL were also among the most effective bactericides at pH 5.5. These data serve as a foundation for developing more effective antimicrobial approaches for the control of L. monocytogenes in foods with different pH levels.

Model for Listeria monocytogenes inactivation by high hydrostatic pressure processing in Spanish chorizo sausage

A central composite design was implemented to study the effect of three factors on HHP-induced L. monocytogenes inactivation in Spanish chorizo sausage, in order to increase its effectiveness: product aw (0.79–0.92), pressure intensities (349–600 MPa, at 18 °C) and holding time (0–12.53 min). Response surface methodology was implemented with backward stepwise regression to generate a model that best fitted to the experimental data. All the three factors studied significantly influenced HHP inactivation of L. monocytogenes (p < 0.05). Pathogen reductions increased as the pressure and duration of HHP treatments rose. Low values of aw seemed to exert a protective effect on L. monocytogenes and pressures below 400 MPa did not lead to significant pathogen reductions. The model was validated with independent published data. Accuracy and bias factors were also determined to evaluate the performance of the developed model, which was considered acceptable for prediction purposes. The model generated represents a mathematical tool that will help food manufacturers to improve the efficacy of HHP processing of chorizo sausage and observe the regulatory authority’s specifications regarding L. monocytogenes levels while maintaining food safety.

Antimicrobial activity of safflower seed meal extract and its application as an antimicrobial agent for the inactivation of Listeria monocytogenes inoculated on fresh lettuce

This study examined the antimicrobial activity of safflower seed meal extract (SSME) against foodborne pathogens, and the microbial reduction effects of combined treatment with SSME and fumaric acid (FA) against Listeria monocytogenes inoculated on lettuce. Results with SSME showed antimicrobial activity against the pathogens, with the highest activity against L. monocytogenes. With 0.7% SSME treatment for 3 min, the reduction levels of total aerobic bacteria and L. monocytogenes in lettuce were 1.55 and 1.58 log CFU/g, respectively, compared with the control. In particular, the combined treatment with SSME and FA reduced the populations further by 1.14 and 1.66 log CFU/g compared to those in SSME treatment alone. The combined treatment did not affect quality indicators such as lettuce color. These results indicate that combined treatment of SSME and FA can be used as a novel antimicrobial agent for inactivating the pathogens in fresh produce.

Combination of endolysins and high pressure to inactivate Listeria monocytogenes

Outbreaks of listeriosis are often related to the consumption of low-processed ready-to-eat food products (e.g. soft cheeses or smoked fish) contaminated with Listeria monocytogenes. Traditional preservation techniques, such as heat treatment, cannot eliminate Listeria from these products without strongly affecting the quality of the foods. We therefore investigated the use of endolysin (PlyP40, Ply511, or PlyP825) in combination with high hydrostatic pressure processing to kill L. monocytogenes in buffer. The results demonstrated a more than additive effect when both treatments were combined. For example, whereas 0.16 μg/mL PlyP825 or 300 MPa (1 min, 30 °C) applied individually reduced the cell count by 0.2 and 0.3 log cfu, respectively, a combined treatment resulted in a reduction of 5.5 log cfu. Similar results were obtained for the other endolysins combined with high pressure processing. We also showed that the synergistic inactivation of cells by endolysin and HHP is possible at a pressure level of only 200 MPa (2 min, 30 °C). Thus, the application of endolysins did not only substantially increase the bactericidal effect of high pressure, but it also enabled the inactivation of bacterial cells at much lower pressure levels. This shows the potential of using such combined processes for the inactivation of L. monocytogenes and food preservation.