Growth Of Listeria Monocytogenes Research Articles

Modelling the Growth of Listeria monocytogenes on Fresh-Cut Cucumbers at Various Storage Temperatures

The primary objective of this study was to investigate the behavior of Listeria monocytogenes (L. monocytogenes) on fresh-cut cucumbers. Fresh-cut cucumber samples were inoculated with a mixture of six strains of L. monocytogenes. The inoculated samples were stored at 5, 10, 15, 20, 25, 30, and 35 °C. The results demonstrated that L. monocytogenes was able to grow on fresh-cut cucumbers at all the evaluated temperatures, although its growth decreased but was not inhibited at 5 °C. An extreme storage temperature of 35 °C considerably reduced the lag time. L. monocytogenes growth on fresh-cut cucumbers was controlled for several days by storage at a low temperature, mainly at 5 °C. Thus, this product should only be stored at low temperatures. The growth process was fitted by the Baranyi model, with the specific growth rates equally well-fitted to the Ratkowsky square-root model. The R-square and mean square error values for the corresponding Ratkowsky square-root models were 0.97 (R2 > 0.95) and 0.02, respectively. The Baranyi and Ratkowsky square-root models exhibited good relevancy. The predictive models developed in this study can be used to estimate the risk assessment of L. monocytogenes on fresh-cut cucumber.

Mozzarella cheese in Italy: Characteristics and occurrence of Listeria monocytogenes and coagulase-positive staphylococci at retail

Mozzarella cheese is a popular type of fresh cheese, originating from Mediterranean countries and worldwide consumed. As for other soft cheeses, its characteristics might support the growth of Listeria monocytogenes; therefore, the research's aim was to determine the occurrence of L. monocytogenes strains and Listeria spp. on mozzarella cheese at the time of purchase (T0) and at the end of shelf life (Tf). Given the relevance in dairy products, occurrence of coagulase-positive staphylococci was also explored. Retail batches (n = 106) collected in Italy, in supermarkets, discounts and small retailers, were analysed for pH and to detect L. monocytogenes, other Listeria spp. and coagulase-positive staphylococci. Three batches were positive for L. monocytogenes (2.8%; 3/106) and nine (9/106) for other species of Listeria spp. with an occurrence of 10.4% for Listeria spp. Coagulase-positive staphylococci were never detected. Mozzarella cheese showed variability in terms of pH (from 4.30 to 6.24 at T0) and residual shelf life (from 3 to 22 days). This research confirms that L. monocytogenes can be found in mozzarella cheese at retail. However, a low concentration of the pathogen (below the limit of quantification of 10 cfu g−1) was found in the contaminated products at the time of purchase and/or at the end of shelf life. This evidence is relevant since mozzarella cheese is not undergoing further treatment before consumption therefore thus represent the level of contamination to which the consumer might be exposed. Considering the technological steps of mozzarella production, preventing food contamination in food-processing and retail-handling environments is crucial to reduce the level of exposure to the consumer.

Interspecies Interaction of Bacteria Listeria monocytogenes, Yersinia pseudotuberculosis, and Marine Saprotrophs during Long-Term Culturing in Biofilms.

All bacterial strains studied retained the viability and ability to form both mono- and polycultural biofilms under conditions of long-term culturing in artificial seawater at 6°C and without addition of nutrients. Bacillus sp. and Pseudomonas japonica presumably stimulated the growth and reproduction of the pathogenic bacteria Listeria monocytogenes and Yersinia pseudotuberculosis. Preserved cell viability in a monoculture biofilm for a long period without adding a food source can indicate allolysis. At the same time, in a polycultural biofilm, the metabolites secreted by saprotrophic strains can stimulate the growth of L. monocytogenes and Y. pseudotuberculosis.

Antilisterial activity of olive-derived polyphenols: an experimental study on meat preparations

Pork meat and processed pork products have been linked to multiple listeriosis outbreaks worldwide during the past years. Specifically, it has been highlighted that minced pork meat is easily perishable and may increase the growth of Listeria monocytogenes, which could be harmful to the general public's health. This study aimed to investigate the potential application of olive oil mill wastewater polyphenolic and red beet extracts as natural antimicrobial agents for L. monocytogenes growth control in burgers. The minced pork meat was mixed with the extracts and experimentally inoculated with L. monocytogenes, then molded into vacuum-packaged and cold-stored (4±1°C) burgers kept under alternating exposure to fluorescent light. The L. monocytogenes enumeration was performed on burgers at 0, 2, 5, and 10 days of shelf life. In uninoculated burgers, physicochemical (pH, water activity, color) and sensory determination (descriptive sensory analysis) were also conducted. At the end of storage, the samples treated with olive-derived extract showed the lowest value of L. monocytogenes (approximately 1.3 Log CFU/g). The physicochemical and sensory traits of burgers have benefited from the addition of both olive-derived and red beet extracts. Results suggest that olive mill wastewater polyphenolic extracts could be added to minced pork meat products to act as a natural antimicrobial agent.

Inactivation efficacy of four commercial post-process treatments against Listeria monocytogenes and impact on the commercial quality of leafy greens

The problem of product contamination with human pathogenic microorganisms is still unsolved. Although prevention through the implementation of good agricultural practices and good manufacturing practices is the gold standard, product decontamination strategies can be used to complement preventive measures. Different bioprotective treatments have been suggested to reduce the risk of listeriosis in fresh produce, but more information is needed before industrial implementation. This study focused on the efficacy of four commercial treatments against Listeria monocytogenes growth and their effect on the organoleptic quality of baby spinach, cut romaine, cut iceberg, and shredded cabbage. The treatments included SafePro® (CHR Hansen, DK) and Holdbac® (DowDuPont, US), based on the use of lactic acid bacteria (LAB) cultures as well as two different bacteriophage solutions, ListShield (Intralytix, US) and PhageGuard Listex™ (PhageGuard, US). The selected treatments were tested under simulated commercial conditions. The application was performed after processing and before packaging using a fine mist spray. In all the trials, Listex™ showed the best results in reducing L. monocytogenes growth during shelf life in the four leafy greens chosen. Microbial reductions were close to 2 log units. L. monocytogenes reductions were observed 1 day after Listex™ application and the efficacy was maintained during storage (15 days at 7 °C). Organoleptic quality, including flavor, texture, browning/yellowing, decay, and visual appearance of the four leafy greens was not significantly affected by the application of Listex™ when compared to the untreated products. Post-process treatment with Listex™ based on bacteriophages effectively reduced L. monocytogenes and can be recommended as a control tool to reduce the risks for the presence of L. monocytogenes in leafy greens.

Extension of the gamma concept to handle changing environment during shelf-life. Applied to an example with Listeria monocytogenes in salads with changing pH.

Prediction of microbial growth is the main topic within the area of predictive microbiology. A commonly used framework is the so-called gamma concept which is to view the bacterial growth rate as a product of a bacteria- and medium specific maximum instantaneous factor, and several environmental factors. Traditionally environmental factors are assumed to be constant, leading to exponential growth. In the current study, we expand the gamma concept to include changing dynamic environmental factors, exemplified by pH, and show how this might affect estimates for Listeria monocytogenes growth rates and thereby predicted shelf-life. The study shows how substantial environmental changes might lead to large biases for the estimated growth and shelf-life, if not accounted for in the model. Finally, the study shed some light on how accuracy for the growth rate estimates might be improved by allocating more weight to observations prone to favorable than unfavorable environmental conditions.

Characterization of Antimicrobial Activities of Bifidobacterium lactis BB-12 and Their Inhibitory Effect Against Some Foodborne Pathogens.

Bifidobacterium animalis subsp. lactis BB-12, a probiotic, has shown potential to promote health benefits and control pathogens. This study aimed to investigate the effectiveness of BB-12 and its cell-free supernatant (CFS) in inhibiting the growth of Listeria monocytogenes and Salmonella enterica serovar Typhimurium. To assess the antimicrobial activity of BB-12, agar well diffusion, disk diffusion, and minimum inhibitory concentration (MIC) tests were conducted. The bicinchoninic acid (BCA) assay was performed to measure the protein concentration in CFS. The study's results indicated that the BB-12 strain inhibited the pathogens' growth. The disk diffusion test using BB-12 showed inhibitory results ranging from 11 to 14 mm for both bacteria. The agar well diffusion test reported the zone of inhibition ranging from 11.6 to 16 mm for both bacteria. The MIC test was conducted as a confirmatory test, which demonstrated the highest inhibitory zone using 2 McFarland (6 × 108 CFU/mL) concentrations of probiotics on L. monocytogenes (44.98%) and S. Typhimurium (66.41%). The disk diffusion test revealed that the probiotic CFS had a significant inhibitory impact on S. Typhimurium with a 16.6 mm zone of inhibition. The BCA test findings indicated that the 24- and 48-h CFSs exhibited inhibitory properties against infections. Notably, the 24-h CFS, including a protein level of 78.47 μg/mL, demonstrated a more pronounced inhibitory impact on both pathogens. The findings highlight that utilizing the BB-12 strain and its CFS can serve as a viable approach to battle infections, enhancing food safety and public health.

Lymph node stromal cells vary in susceptibility to infection but can support the intracellular growth of Listeria monocytogenes.

Lymph node stromal cells (LNSC) are an often overlooked component of the immune system, but play a crucial role in maintaining tissue homeostasis and orchestrating immune responses. Our understanding of the functions these cells serve in the context of bacterial infections remains limited. We previously showed that Listeria monocytogenes, a facultative intracellular foodborne bacterial pathogen, must replicate within an as-yet-unidentified cell type in the mesenteric lymph node (MLN) to spread systemically. Here, we show that L. monocytogenes could invade, escape from the vacuole, replicate exponentially, and induce a type I IFN response in the cytosol of two LNSC populations infected in vitro, fibroblastic reticular cells (FRC) and blood endothelial cells (BEC). Infected FRC and BEC also produced a significant chemokine and pro-inflammatory cytokine response after in vitro infection. Flow cytometric analysis confirmed that GFP+ L. monocytogenes were associated with a small percentage of MLN stromal cells in vivo following foodborne infection of mice. Using fluorescent microscopy, we showed that these cell-associated bacteria were intracellular L. monocytogenes and the number of infected FRC and BEC changed over the course of a three-day infection in mice. Ex vivo culturing of these infected LNSC populations revealed viable, replicating bacteria that grew on agar plates. These results highlight the unexplored potential of FRC and BEC to serve as suitable growth niches for L. monocytogenes during foodborne infection and to contribute to the pro-inflammatory environment within the MLN that promotes clearance of listeriosis.

Comparative Analysis of Growth, Survival, and Virulence Characteristics of Listeria monocytogenes Isolated from Imported Meat.

Listeria monocytogenes is an important foodborne pathogen with worldwide prevalence. Understanding the variability in the potential pathogenicity among strains of different subtypes is crucial for risk assessment. In this study, the growth, survival, and virulence characteristics of 16 L. monocytogenes strains isolated from imported meat in China (2018-2020) were investigated. The maximum specific growth rate (μmax) and lag phase (λ) were evaluated using the time-to-detection (TTD) method and the Baranyi model at different temperatures (25, 30, and 37 °C). Survival characteristics were determined by D-values and population reduction after exposure to heat (60, 62.5, and 65 °C) and acid (HCl, pH = 2.5, 3.5, and 4.5). The potential virulence was evaluated via adhesion and invasion to Caco-2 cells, motility, and lethality to Galleria mellonella. The potential pathogenicity was compared among strains of different lineages and subtypes. The results indicate that the lineage I strains exhibited a higher growth rate than the lineage II strains at three growth temperatures, particularly serotype 4b within lineage I. At all temperatures tested, serotypes 1/2a and 1/2b consistently demonstrated higher heat resistance than the other subtypes. No significant differences in the log reduction were observed between the lineage I and lineage II strains at pH 2.5, 3.5, and 4.5. However, the serotype 1/2c strains exhibited significantly low acid resistance at pH 2.5. In terms of virulence, the lineage I strains outperformed the lineage II strains. The invasion rate to Caco-2 cells and lethality to G. mellonella exhibited by the serotype 4b strains were higher than those observed in the other serotypes. This study provides meaningful insights into the growth, survival, and virulence of L. monocytogenes, offering valuable information for understanding the correlation between the pathogenicity and subtypes of L. monocytogenes.

The inhibitory effect of probiotic Lactococcus lactis on the growth and invasion of Listeria monocytogenes in Caco-2 cell line

The inhibitory effect of probiotic Lactococcus lactis on the growth and invasion of Listeria monocytogenes in Caco-2 cell line

Growth Control of Listeria monocytogenes in Raw Sausage via Bacteriocin-Producing Leuconostoc carnosum DH25.

The current study addresses the critical issue of Listeria monocytogenes growth in raw sausage/meat products leading to human infections, most commonly listeriosis, which is known for its high fatality rate. This research focuses on the isolation, identification, and screening of lactic acid bacteria from various meat and fish products in Switzerland. In total, 274 lactic acid bacteria strains were isolated from 30 different products and were screened for their ability to inhibit Listeria monocytogenes growth, with 51 isolates demonstrating anti-Listeria activity at 8 °C, 15 °C, 25 °C, and 37 °C. Further experiments, using a meat model and a raw sausage challenge test, demonstrated that Leuconostoc carnosum DH25 significantly inhibited Listeria monocytogenes growth during the ripening and storage of the tested meat/sausage. This inhibitory effect was found to be attributed to the bacteriocins produced by Leuconostoc carnosum DH25 rather than factors like pH or water activity. The stability of the anti-Listeria substances was examined, revealing their resistance to temperature and pH changes, making Leuconostoc carnosum DH25 a promising protective culture for raw sausages. The genome sequencing of this strain confirms its safety, with no antibiotic resistance genes or virulence factors detected, and reveals the presence of the structural genes for the production of the bacteriocin LeucocinB-Ta11a. This study underscores the potential of LAB strains and their bacteriocins as effective tools for enhancing food safety and preventing Listeria monocytogenes growth in meat products, offering valuable insights into biocontrol strategies in the food industry.

Reduction and Growth Inhibition of Listeria monocytogenes by Use of Anti-Listerial Nisin, P100 Phages and Buffered Dry Vinegar Fermentates in Standard and Sodium-Reduced Cold-Smoked Salmon.

Cold-smoked salmon are ready-to-eat products that may support the growth of pathogenic Listeria monocytogenes during their long shelf-life. Consumption of such contaminated products can cause fatal listeriosis infections. Another challenge and potential risk associated with CS salmon is their high levels of sodium salt. Excess dietary intake is associated with serious health complications. In the present study, anti-listerial bacteriocin (nisin), P100 bacteriophages (Phageguard L, PGL) and fermentates (Verdad N6, P-NDV) were evaluated as commercial bio-preservation strategies for increased control of L. monocytogenes in standard (with NaCl) and sodium-reduced (NaCl partially replaced with KCl) CS salmon. Treatments of CS salmon with nisin (1 ppm) and PGL (5 × 107 pfu/cm2) separately yielded significant initial reductions in L. monocytogenes (up to 0.7 log) compared to untreated samples. Enhanced additive reductions were achieved through the combined treatments of nisin and PGL. Fermentates in the CS salmon inhibited the growth of Listeria but did not lead to its eradication. The lowest levels of L. monocytogenes during storage were observed in nisin- and PGL-treated CS salmon containing preservative fermentates and stored at 4 °C, while enhanced growth was observed during storage at an abusive temperature of 8 °C. Evaluation of industry-processed standard and sodium-replaced CS salmon confirmed significant effects with up to 1.7 log reductions in L. monocytogenes levels after 34 days of storage of PGL- and nisin-treated CS salmon-containing fermentates. No differences in total aerobic plate counts were observed between treated (PGL and nisin) or non-treated standard and sodium-reduced CS salmon at the end of storage. The microbiota was dominated by Photobacterium, but with a shift showing dominance of Lactococcus spp. and Vagococcus spp. in fermentate-containing samples. Similar and robust reductions in L. monocytogenes can be achieved in both standard and sodium-replaced CS salmon using the bio-preservation strategies of nisin, PGL and fermentates under various and relevant processing and storage conditions.

Probiotic Bacillus strains inhibit growth, biofilm formation, and virulence gene expression of Listeria monocytogenes

This research aimed to evaluate the probiotic potential and anti-biofilm properties of Bacillus species isolated from dairy sludge, namely Bacillus subtilis GS3 (DS-1), Bacillus cereus BF2 (DS-2), Bacillus velezensis DM (DS-3), and Bacillus thuringiensis JB (DS-4). These strains exhibited tolerance to gastrointestinal fluids, bile salt, phenol, NaCl, and temperature variations. Moreover, they demonstrated notable cell surface hydrophobicity (70.80–89.30%), auto-aggregation (79.30–92.70%), and cholesterol removal (20.12–59.46%). Additionally, the strains displayed antioxidant activity and susceptibility to a wide range of antibiotics. The cell-free supernatants (CFS) of the strains exhibited inhibitory effects against Listeria monocytogenes ATCC 19115, with minimum inhibitory concentrations (MIC) observed at 12.5%, 25%, 25%, and 50% v/v for DS-1, DS-2, DS-3, and DS-4, respectively. The CFS also showed degradation and inhibition of L. monocytogenes biofilms, affecting adhesion, hydrophobicity, auto-aggregation, and exopolysaccharide production. Notably, DS-1 CFS suppressed the expression of genes associated with biofilm formation in L. monocytogenes, including those related to quorum sensing, virulence factors, and flagella. The antibacterial activity of CFS against L. monocytogenes was further confirmed by scanning electron microscopy. Particularly, the CFS of Bacillus spp., especially B. subtilis GS3, exhibited a strong inhibitory effect on the biofilm formation of L. monocytogenes.

Valorizing pomegranate wastes by producing functional silver nanoparticles with antioxidant, anticancer, antiviral, and antimicrobial activities and its potential in food preservation

The food sector generates massive amounts of waste, which are rich in active compounds, especially polyphenols; therefore, valorizing these wastes is a global trend. In this study, we produce silver nanoparticles from pomegranate wastes, characterized by enhanced antioxidant, anticancer, antiviral, and antimicrobial properties and investigated their potential to maintain the fruit quality for sixty days in market. The pomegranate waste-mediated silver nanoparticles (PPAgNPs) were spherical shape (measured by TEM), 20 nm (Zeta sizer), negatively charged −25.98 mV (Zeta potential), and surrounded by active groups (FTIR). The PPAgNPs scavenged 94 % of DPPH radicals and inhibited the growth of pathogens, i.e., Staphylococcus aureus, Listeria monocytogenes, Campylobacter jejuni, Salmonella typhi and Candida with inhibition zones diameters (16–45 mm). They impeded the development of breast and colon cancer cell lines by 80 and 78 %, increased the activity of apoptosis marker caspase 3, and inhibited 82 % of COVID-19. The PPAgNPs were added to the rat diet at 80, 160, and 320 µg/kg levels. PPAgNPs administered at a concentration of 160 µg/kg in the rat diet resulted in the best growth performance, normal liver and kidney parameters (p = 0.029–0.038), lowered lipid profile, malondialdhyde (MDA), and raised glutathion reduced (GSH), total protein (TP). Also, the reduced gene expression of Interleukin 6 (IL-6) and Tumor necrosis factor alpha (TNF-α) in albino rats' serum indicates the anti-inflammatory effect of PPAgNPs. PPAgNPs developed a functional coating to preserve mandarin fruit for 60 days by dipping technique. The active coat containing PPAgNPs can effectively preserve the fruit for 60 days.

Safety assurance assessment of palmito cheese: A Mesoamerican pasta filata unripe artisanal cheese

Use of acidification and kneading/stretching steps to ensure the safety of palmito cheese was evaluated. The pH (acidification) and temperature (kneading/stretching) kinetics were recorded during processing for three cheese batches from each of three artisanal producers and a pilot plant-produced cheese. The pH and water activity of cheeses were used to estimate the growth potential of pathogens of concern. F65 °C equivalent values for Coxiella burnetii were calculated using temperature kinetics. Theoretical logarithmic reductions for other foodborne pathogens were also estimated based on D and z values reported in literature. According to their pH and water activity, all produced cheeses may support the growth of Listeria monocytogenes, Salmonella, Escherichia coli O157:H7, and Staphylococcus aureus. Calculated F65 °C values for C. burnetii confirmed that the kneading/stretching operation cannot substitute milk pasteurisation. In no case was a 5-log reduction of all pathogens achieved. Hence, both steps should not be used as sole safety-assuring hurdles.

Vγ9+Vδ2+ T cell control of Listeria monocytogenes growth in infected epithelial cells requires butyrophilin 3A genes

Intracellular bacteria produce antigens, which serve as potent activators of γδ T cells. Phosphoantigens are presented via a complex of butyrophilins (BTN) to signal infection to human Vγ9+Vδ2+ T cells. Here, we established an in vitro system allowing for studies of Vγ9+Vδ2+ T cell activity in coculture with epithelial cells infected with the intracellular bacterial pathogen Listeria monocytogenes. We report that the Vγ9+Vδ2+ T cells efficiently control L. monocytogenes growth in such cultures. This effector function requires the expression of members of the BTN3A family on epithelial cells. Specifically, we observed a BTN3A1-independent BTN3A3 activity to present antigen to Vγ9+Vδ2+ T cells. Since BTN3A1 is the only BTN3A associated with phosphoantigen presentation, our study suggests that BTN3A3 may present different classes of antigens to mediate Vγ9+Vδ2+ T cell effector function against L. monocytogenes-infected epithelia.

Probabilistic modeling of the growth of Listeria monocytogenes: effect of nisin, temperature, and strain in the presence of potassium chloride or potassium sorbate

ABSTRACT The effects of temperature and nisin with either potassium chloride (KCl) or potassium sorbate on growth boundaries of three different Listeria monocytogenes strains in broth were studied. One ATCC7644 strain and two ready-to-eat food (RTE) isolates at different temperatures (4, 20, and 37°C) and nisin (0, 50, 100, 200, and 400 μg/mL) levels with either KCl (0, 1, 2, 3, and 4% w/v) or potassium sorbate (0, 0.05, 0.10, 0.15, and 0.20% w/v) were used. Highest and lowest growth probabilities were obtained for ATTC7644 and 120 (meat-based RTE isolate) strains, respectively with KCl and strain 137 (vegetable-based RTE isolate) was in between. However, the growth probabilities of the strains were just the opposite with the use of sorbate: strain 120 had the highest, whereas ATCC7644 strain had the lowest growth probability. Our results showed that nisin in combination with other preservatives may lead to diverse growth responses for different strains of L. monocytogenes. Validation studies performed in UHT whole milk and meat broth at 8 and 12°C and nisin levels of 25, 75, 150, and 250 μg/mL with either KCl (1.5%) or sorbate (0.125%) indicated 46% and 73% accurate predictions for milk and meat broth, respectively. Although a quick growth estimate was possible with the use of broth, we concluded that a model developed in a laboratory medium should not be extended in real food systems.

Effect of Commercial and Autochthonous Bioprotective Cultures for Controlling Listeria monocytogenes Contamination of Pecorino Sardo Dolce PDO Cheese.

The composition and physicochemical characteristics of short-aged Pecorino Sardo PDO (Protected Designation of Origin) cheese makes it permissive to Listeria monocytogenes growth. The PDO product specification stipulates that this cheese is produced with whole sheep's milk inoculated with cultures from the area of origin. Therefore, the use of bioprotective cultures for the inhibition of pathogens in PDO cheeses is allowed only if autochthonous microorganisms are used. Furthermore, bioprotective cultures are generally used on the cheese surface to prevent the outgrowth of L. monocytogenes, the application of which can be time-consuming and require specialist technical knowledge. In this study, we examine the direct addition of bioprotective cultures to the cheese vat and compare the activity of a commercial bioprotective culture (Lactiplantibacillus plantarum) and an autochthonous lactic acid bacterium with bioprotective properties (Lactobacillus delbruekii sups. sunkii), for the inhibition of L. monocytogenes in Pecorino Sardo PDO cheese. Three types of Pecorino Sardo PDO cheese were made with bioprotective cultures added directly to the cheese milk along with the starter inoculum: PSA, with the commercial bioprotective culture; PSB, with the autochthonous bioprotective culture; and a CTRL cheese with no bioprotective culture. A challenge test was performed on each of these cheeses by artificially contaminating the cheese surface with L. monocytogenes (2 Log10 CFU/g). Three batches of each cheese type were analyzed to enumerate mesophilic and thermophilic lactic acid bacteria and to investigate the growth potential of L. monocytogenes during manufacturing, at the end of ripening, at the end of shelf-life, and after 180 days from cheese production. Both bioprotective cultures tested in this study showed inhibitory action against the pathogen with 0.3-1.8 Log10 CFU/g (colony-forming unit per gram) reduction levels. The autochthonous organism, L. sunkii, was as effective as the commercially supplied culture, and the addition of the bioprotective cultures to the cheese-making procedure offered protection against L. monocytogenes. The direct addition of bioprotective cultures to the making procedure of Pecorino Sardo PDO cheese is a potentially innovative strategy to improve the safety of this product.

Effects of sodium nitrite reduction, removal or replacement on cured and cooked meat for microbiological growth, food safety, colon ecosystem, and colorectal carcinogenesis in Fischer 344 rats

Epidemiological and experimental evidence indicated that processed meat consumption is associated with colorectal cancer risks. Several studies suggest the involvement of nitrite or nitrate additives via N-nitroso-compound formation (NOCs). Compared to the reference level (120 mg/kg of ham), sodium nitrite removal and reduction (90 mg/kg) similarly decreased preneoplastic lesions in F344 rats, but only reduction had an inhibitory effect on Listeria monocytogenes growth comparable to that obtained using the reference nitrite level and an effective lipid peroxidation control. Among the three nitrite salt alternatives tested, none of them led to a significant gain when compared to the reference level: vegetable stock, due to nitrate presence, was very similar to this reference nitrite level, yeast extract induced a strong luminal peroxidation and no decrease in preneoplastic lesions in rats despite the absence of NOCs, and polyphenol rich extract induced the clearest downward trend on preneoplastic lesions in rats but the concomitant presence of nitrosyl iron in feces. Except the vegetable stock, other alternatives were less efficient than sodium nitrite in reducing L. monocytogenes growth.

Modeling and scenario-based risk estimation of Listeria monocytogenes in meatballs and Sundae, a Korean black pudding, under different packaging conditions

Vacuum packaging is known to be an effective way to limit the growth of food spoilage and food-poisoning bacteria. However, Listeria monocytogenes (LM) can survive under low-oxygen conditions and as well as refrigeration temperatures. This study was conducted to model the fate of LM-inoculated meatballs and Sundae, a Korean black pudding, and assess the effect of packaging (aerobic packaging, AP; vacuum packaging, VP) on risk. Meatballs and Sundae were spiked with LM and stored at temperatures ranging from 5 to 37 °C. Primary models were developed using the Baranyi model, and secondary models for the maximum growth rate (μmax) of meatballs and Sundae were developed using a square root model. The developed primary and secondary models were fitted well with a high goodness-of-fit (R2 ≥ 0.98). The bias factor (Bf) was 1.002–1.015, and the root mean square error (RMSE) was 0.002–0.051 1/h. Furthermore, dynamic models were developed and validated, with corresponding RMSE values < 0.851 ln CFU/g (<0.370 log CFU/g) and acceptable simulation zone (ASZ) values > 82%. Comparing the growth of LM according to the packaging, the lag phase duration of both samples was significantly shorter in VP than in AP; however, μmax of meatball at 10 °C was significantly faster in VP than in AP (p < 0.05). The probability of infection (Pinf) from the consumption of meatballs or Sundae with different packaging types was estimated using Monte Carlo simulations and scenario analysis. Simulation results showed that Pinf from the consumption of meat-based ready-to-eat foods with VP was not always lower than that with AP. There is a need to control the contamination of LM before packaging by placing efforts on implementing control measures during processing.