Reducing Listeria Monocytogenes Research Articles

Evaluation of the application of UV-C to reduce Listeria monocytogenes contamination under commercial conditions

Evaluation of the application of UV-C to reduce Listeria monocytogenes contamination under commercial conditions

Reduction of Listeria monocytogenes on chicken breasts by combined treatment with UV-C light and bacteriophage ListShield

The aim of this study was to determine the effect of a commercial bacteriophage (ListShield) against Listeria monocytogenes, alone or in combination with UV-C treatment, using artificially inoculated chicken breast. A mixture of three L. monocytogenes strains ATCC 19113, ATCC 19115, and ATCC 13932 was inoculated in chicken breast muscle (approximately 4.5 log CFU/g), followed by UV-C irradiation (at 600, 1200, 1800, and 2400 mWs/cm2), and/or phage treatment. Chicken breast samples were analyzed after 5 min and then stored for 72 h at 4 °C. Phage treatment was seen to reduce bacterial counts by up to 0.84 log units when applied alone, or 2.04 log units in combination with UV-C treatment during storage for 72 h. Additionally, the quality evaluation of chicken breast fillets such as thiobarbituric acid reactive substances (TBARS), pH, surface color as well as other sensory analysis were examined. There were no significant difference (p > 0.05) in color, pH (up to 48 h), TBARS and sensory quality (up to 24 h) due to phage and UV-C treatment (600–2400 mWs/cm2). In conclusion, our results demonstrate that a commercial bacteriophage preparation can be very effective for the control of L. monocytogenes in chicken fillets, either alone or in combination with UV-C treatment.

An assessment of the application of ultrasound in the processing of ready-to-eat whole brown crab (Cancer pagurus)

This study assesses the potential of incorporating ultrasound as a processing aid in the production of whole cooked brown crab (Cancer pagurus). The FDA recommended heat treatment to reduce Listeria monocytogenes by 6 log10 cycles in this product is a F707.5 of 2min. An equivalent F value was applied at 75°C in presence and absence of ultrasound in water alone or in water with 5% w/v NaCl added. Heat penetration, turbidity and conductivity of the cook water and also salt and moisture content of the crab meat (white and brown) were determined. Ultrasound assisted cooking allowed a reduction of the cooking time by up to 15% while still maintaining an F707.5 of 2min. Ultrasound also enhanced the rate and total amount of compounds released from the crab, which suggests that crabs cooked in the presence of ultrasound would be expected to be cleaner. Ultrasound also proved to be effective in reducing the salt content but hardly affected the final moisture content of the crab meat.

Growth Inhibitory Effects of Adhatoda vasica and Its Potential at Reducing Listeria monocytogenes in Chicken Meat.

The inhibitory effects of Adhatoda vasica ethanolic leaf extract (AVELE) against Listeria monocytogenes were examined to assess its potential to preserve minimally processed meat products safely. The total phenolic, flavonoid, and alkaloid levels in AVELE were 10.09 ± 4.52 mg of gallic acid equivalents (GAE)/g, 22.43 ± 1.62 mg of quercetin equivalents/g, and 19.43 ± 3.90 mg/g, respectively. AVELE (1, 5, 10, or 20%) had considerable antibacterial effects against L. monocytogenes NCIM 24563 in terms of the inhibitory zones (7.4–13.6 mm), MIC (100 mg/mL or 10% formulated solution), reduced cell viability, potassium ion efflux, and the release of 260-nm absorbing materials and extracellular ATP. AVELE was used as a rinse solution (5, 10, and 20%) for raw chicken breast meat. A 20% rinsing solution applied for 60 min inhibited the L. monocytogenes NCIM 24563 counts significantly on raw chicken breast meat. Moreover, L. monocytogenes NCIM 24563 did not grow in the meat sample when the rinse time was increased to 90 min at the same concentration. L. monocytogenes showed a greater reduction to ~3 CFU/g after rinsing with a 10 and 20% AVELE solution for 30 min than with a 5% AVELE solution. The rinsing processes with AVELE produced the final cooked chicken products with higher sensory attribute scores, such as taste, juiciness, and tenderness, compared to the control group along with a decrease in microbial contamination. Chicken meat rinsed with AVELE (rinsing time of 90 min) showed better sensory attribute scores of juiciness and tenderness, as well as the overall sensory quality compared to the untreated group. This research highlights the effectiveness of AVELE against L. monocytogenes NCIM 24563, suggesting that AVELE can be used as an effective antimicrobial marinade and/or a rinse for meat preservation.

Nonthermal pasteurization of tender coconut water using a continuous flow coiled UV reactor

A non-thermal pasteurization technology is desirable to naturally preserve nutrient and organoleptic properties of packaged tender coconut water (TCW) distributed under refrigeration. The goal of this research was to assess the antimicrobial effectiveness of ultraviolet light C (UVC) as a non-thermal pasteurization of TCW. A dean flow ultraviolet reactor was used with wavelength of 254 nm at the residence time of 14.0 s. The experimental variables were three Reynold numbers (Re = 198.8, 397.7 and 596.4) and two diameters of transparent PFA tubes (3.2 mm and 1.6 mm). TCW was inoculated with cultures of Escherichia coli W1485 and Listeria monocytogenes separately before passing through the UV reactor. UVC treatment yielded 5.27 and 4.74 log10 CFU/mL E. coli count reductions for 1.6 mm and 3.2 mm ID reactors, respectively, whereas the reduction of Listeria monocytogenes were 4.18 and 2.96 log10 CFU/mL, respectively at Re = 596.4. Furthermore, as the Reynold number increased, microbial reduction also increased. The physico-chemical changes of cold pasteurized TCW were not significantly different compared to the fresh TCW.

Inhibition of Escherichia coli O157:H7 and Listeria monocytognes growth in milk and cantaloupe juice by thymol nanoemulsions prepared with gelatin and lecithin

Thymol is an effective antimicrobial and is to be encapsulated for use in liquid foods. Previously, novel thymol nanoemulsions have been prepared with the emulsifier combination of gelatin-A (acid-hydrolyzed) or -B (base-hydrolyzed) and lecithin. The objective of this study was to characterize the antimicrobial activity of thymol nanoemulsified by gelatin and soy lecithin, using milk and cantaloupe juice as two model food systems at 21 °C. Nanoemulsions were overall more effective than free thymol in both media. Compared to the bacteriostatic effect of free thymol, 4.5 g/L nanoemulsified thymol gradually reduced Listeria monocytogenes by 5 and 3 log CFU/mL in 2% reduced fat and full fat milk after 48 h, respectively. In skim milk, the nanoemulsion with gelatin-A was overall more effective against L. monocytogenes than that with gelatin-B. Conversely, the nanoemulsion with gelatin-B reduced Escherichia coli O157:H7 to below the detection limit after 8 h in 2% reduced fat milk and 48 h in full fat milk, contrasting with the bacteria recovery for the nanoemulsion with gelatin-A after 48 h. The improved antimicrobial activities of thymol nanoemulsions were supported by the quantified increase of thymol concentration in the serum of milk. The nanoemulsion prepared with gelatin-B was more effective than that of gelatin-A in cantaloupe juice. The slight difference in bacterial recovery after treatment by nanoemulsions prepared with two types of gelatin suggests the impacts of droplet surface properties on interactions with bacteria membrane. The studied nanoemulsions have great potential for use as novel antimicrobial preservatives to improve food safety.

The effect of pulsed UV light on Escherichia coli O157:H7, Listeria monocytogenes, Salmonella Typhimurium, Staphylococcus aureus and staphylococcal enterotoxin A on sliced fermented salami and its chemical quality

Pulsed UV light (PL) applied at a fluence of 3 J/cm2 was effective to reduce Listeria monocytogenes, Escherichia coli 0157:H7, Salmonella Typhimurium and Staphylococcus aureus for 2.24, 2.29, 2.25 and 2.12 log CFU/g on the surface of dry fermented salami. Further increase in the fluence of PL treatment did not increase levels of microbial inactivation. However, the time interval between the contamination and PL treatment was found to have a significant impact on the efficacy of PL treatment and should be kept as short as possible. After initial PL treatment slices of fermented salami were packed in vacuum or in 80%CO2/20%N2 modified atmosphere and stored at 4 °C to investigate the effect of PL treatment on protein and lipid oxidation as the shelf life of fermented salami is not usually limited by microbial deterioration, but by chemical and sensory alterations. In this study observed lipid oxidation values for PL treated vacuum and modified atmosphere packed fermented salami slices fall within the acceptable threshold for the rancid odor, except for the sample treated with the highest fluence tested (15 J/cm2), packed in modified atmosphere and kept in cold storage for 9 weeks (1.23 mg MDA/kg). All values were below the threshold for rancid flavor, too. The significant rise in protein oxidation of PL treated fermented salami slices, perceived as 28% increase of carbonyl content compared to untreated samples, was observed only after 9 weeks of cold storage in both vacuum and modified atmosphere packed samples. The results of chemical analysis are in agreement with previously published results of sensory analysis. Current results show the applicability of PL to improve microbial safety of sliced fermented salami that are prone to cross-contamination without affecting quality attributes by lipid and protein oxidation.

Synergistic effect of a combination of ultraviolet–C irradiation and sodium hypochlorite to reduce Listeria monocytogenes biofilms on stainless steel and eggshell surfaces

The present study demonstrates the synergistic effect of treatment with a combination of ultraviolet (UV)C (300, 600, 1200, and 1800 mWs/cm2) irradiation and sodium hypochlorite (NaOCl) (50, 100, 150, and 200 ppm) on Listeria monocytogenes ATCC 19113 biofilms formed on stainless steel and eggshell surfaces. The synergistic effect was not dependent on the dose of UV–C irradiation or the concentration of NaOCl. Synergistic reductions of biofilms after UV–C/NaOCl treatment on stainless steel and eggshells were 0.95–3.68 log CFU/cm2 and –0.22 to 1.02 log CFU/cm2, respectively. The largest synergistic reductions of biofilms were 3.68 log CFU/cm2 using 1800 mWs/cm2 UV–C and 200 ppm NaOCl on stainless steel, and 1.02 CFU/cm2 using 600 mWs/cm2 UV–C and 50 ppm NaOCl on eggshells. The Hunter colors of L*, a*, and b* were not significantly (P > 0.05) changed on eggshell surfaces treated with all single and combined treatments. The results in this study indicate that the combination treatment of 1800 mWs/cm2 UV–C/200 ppm NaOCl could be feasible for use on stainless steel surfaces in industrial kitchens, facilities, and restaurants. In addition, the combination of 600 mWs/cm2 UV–C/500 ppm NaOCl could possibly be used in egg production, processing, and distribution processes to enhance food safety without causing changes to the eggshell surface color.

Inactivation of Listeria monocytogenes, Salmonella spp. and Escherichia coli O157:H7 on cantaloupes by octenidine dihydrochloride

The efficacy of a new generation disinfectant, octenidine dihydrochloride (OH), as wash and coating treatments for reducing Listeria monocytogenes (LM), Salmonella spp. (SAL), and Escherichia coli O157:H7 (EC) on cantaloupe was investigated. Cantaloupe rind plugs inoculated separately with the three bacterial species (∼8 log CFU/cm2) were washed for 1, 3, 5 min at 25 °C in water, or chlorine (200 ppm), ethanol (1%), OH (0.01, 0.05, 0.1%) and surviving populations were measured after treatment. Additionally, inoculated cantaloupe rind plugs were coated with 2% chitosan or chitosan containing OH (0.01, 0.05, 0.1%) and sampled for surviving pathogens. Subsequently, the antimicrobial efficacy of OH wash and coating (0.1, 0.2%) on whole cantaloupes was determined. All OH wash reduced LM, SAL, and EC on cantaloupe rinds by > 5 log CFU/cm2 by 2 min, and reduced populations to undetectable levels (below 2 log CFU/cm2) by 5 min (P < 0.05). Similarly, OH coating on cantaloupe rinds reduced the pathogens by 3–5 log /cm2 (P < 0.05). Washing and coating whole cantaloupes with OH reduced the three pathogens by at least 5 log and 2 log CFU/cm2, respectively (P < 0.05). Results suggest that OH could be used as antimicrobial wash and coating to reduce LM, SAL, and EC on cantaloupes.

Eugenol in combination with lactic acid bacteria attenuates Listeria monocytogenes virulence in vitro and in invertebrate model Galleria mellonella

Listeria monocytogenes is a human enteric pathogen that causes severe foodborne illness in high-risk populations. Crossing the intestinal barrier is the first critical step for Listeria monocytogenes infection. Therefore, reducing L. monocytogenes colonization and invasion of intestinal epithelium and production of virulence factors could potentially control listeriosis in humans. This study investigated the efficacy of sub-inhibitory concentration (SIC) of the plant-derived antimicrobial eugenol, either alone, or in combination with five lactic acid bacteria (LAB), namely Bifidobacterium bifidum (NRRL-B41410), Lactobacillus reuteri (B-14172), Lactobacillus fermentum (B-1840), Lactobacillus plantarum (B-4496) and Lactococcus lactis subspecies lactis (B-633) in reducing Listeria monocytogenes adhesion to and invasion of human intestinal epithelial cells (Caco-2). Additionally, the effect of the aforementioned treatments on Listeria monocytogenes listeriolysin production, epithelial E-cadherin binding and expression of virulence genes was investigated. Moreover, the in vivo efficacy of eugenol-LAB treatments in reducing Listeria monocytogenes virulence in the invertebrate model Galleria mellonella was studied. Eugenol and LAB, either alone or in combination, significantly reduced Listeria monocytogenes adhesion to and invasion of intestinal cells (P < 0.05). Moreover, eugenol-LAB treatments decreased Listeria monocytogenes haemolysin production, E-cadherin binding and virulence gene expression (P < 0.05). In addition, the eugenol-LAB treatments significantly enhanced the survival rates of G. mellonella infected with lethal doses of Listeria monocytogenes (P < 0.05). The results highlight the antilisterial effect of eugenol either alone or in combination with LAB, and justify further investigations in a mammalian model.

Combined effect of ultrasound and essential oils to reduce Listeria monocytogenes on fresh produce.

Salads prepared from contaminated fresh produce have a high risk of causing food-borne illnesses. Essential oils obtained from plants have antimicrobial activity and may provide a natural approach to reduce the pathogens on fresh produce. Additionally, ultrasound treatments have been shown to reduce the microbial counts on different foods. The objective of this study was to investigate the antimicrobial activities of cinnamon and lemon essential oils invitro and in food applications. Mixtures of lettuce, parsley and dill were inoculated with Listeria monocytogenes and then dip-treated for 5 min in one of the following treatments: sterile tap water, chlorinated water, 1% lemon essential oil, 2% cinnamon essential oil or 2% cinnamon essential oil + ultrasound. The samples were stored at 4 ℃ and collected at d 0, 1, 3, 5, 7 and 9 post inoculation. The 1% lemon (4 log) and 2% cinnamon (2 log) essential oil washes provided partial inhibition against L. monocytogenes by d 1. The combined application of 2% cinnamon oil and ultrasound resulted in only 0.85 log inhibition by d 1; however, the number of L. monocytogenes increased during storage and became nearly equal to the control at d 9. Therefore, different combinations of essential oils with other antimicrobials or novel technologies are required.

Efficacy of electrolyzed oxidizing water as a pretreatment method for reducing Listeria monocytogenes contamination in cold-smoked Atlantic salmon (Salmo salar)

Listeria monocytogenes contamination in ready-to-eat (RTE) fish products, in particular in cold-smoked salmon is an important food safety concern. This study evaluated the antimicrobial activity of electrolyzed oxidizing (EO) water as a pretreatment method during the process of cold-smoked salmon to inactivate L. monocytogenes. In addition, the effect of EO water treatment on the sensory and textural quality of the final product was also evaluated. Raw Atlantic salmon (Salmo salar) fillets were inoculated with L. monocytogenes (with an approximately cell number of 6 × 105 CFU/g L. monocytogenes ATCC 19114) and treated with EO water at three different temperatures (20, 30, and 40 °C) and at three different exposure time of 2, 6, and 10 min before the cold-smoking process. A combination of EO water and a mild temperature (40 °C) had reduced L. monocytogenes populations by 2.85 log10 CFU/g. The sensory as evaluated by a consumer panel (N = 71) and texture, which was measured by texture analysis showed no significant changes between EO and mild temperature treated samples and the control.

Decontamination of inoculated chicken carcasses by using some microbial decontaminators

This study was conducted to evaluate the efficacy of three decontaminators in reducing the level ofcontamination in chicken carcasses which had been artificially contaminated. A grand total of fortyrandom samples of raw chicken carcasses were purchased directly from local markets. Chicken sampleswere then dipped in cultures of the tested microorganisms (Salmonella spp., Staphylococcus aureus,E.coli O157:H7 and L. monoctogens) (10 samples for each microorganism). Then dipped intocontainers containing distilled water (control) , chlorine 30 ppm, 50 ppm and 70 ppm, trisodiumphosphate 3%, 5% an 8% and lactic acid 0.75%, 1.25% and 2% , where the reduction percentage ofSalmonella were 26.02 %, 26.57 %, 29.16 %, 34.88% , 36.78 %, 38.01 %, 35.42 %, 40.87 % and 54.50%, respectively, compared to control. while the reduction of Listeria monocytogenes was 16.64 %,20.60% , 30.43% , 21.74 %, 21.74 %, 25.14 %, 22.87 %, 30.24 % and 39.89 % respectively . Moreover, the reduction percentages of S. aureus was 14.29 %, 15.70 %, 19.58% , 8.11 %, 10.58 %, 27.69 %,17.28 %, 21.34 % and 27.87 % , respectively . Finally, the reduction percentage of E.coli O157:H7 was9.56 %, 16.61 %, 20.47 %, 17.45%, 21.48 %, 27.85 %, 18.12%, 19.97% and 29.70 %, respectively

Reduction of Listeria monocytogenes and Bacillus cereus in Milk by Zinc Oxide Nanoparticles.

Direct addition of antimicrobial materials to food during food processing is an effective method for controlling microbial contaminants of food and extending the shelf- life of food products. Objective of this research was to study the antimicrobial effect of zinc oxide (ZnO) nanoparticle and potential applications of ZnO nanoparticles in terms of controling two food-borne pathogens in milk. Toxicity of different concentration (0, 0.5, 2, 5, and 10 mM) of ZnO nanoparticles on Listeria monocytogenes and Bacillus cereus was studied in culture media and milk. Among the mentiond concentrations, treatment of 10 mM of ZnO nanoparticle was the most effective one for L. monocytogenes and B. cereus inhibition, which completely inhibited the growth of L. monocytogenes and B. cereus in 24h. These data revealed concentration-dependency of the antibacterial activity of ZnO. Therefore, 5 mM and 10 mM ZnO were selected for further studies, which were performed in milk, since they demonstrated significant growth inhibition. ZnO NPs were more capable in terms of reducing the initial growth counts of all the above-stated strains in milk. ZnO nanoparticles had an antimicrobial activity against L. monocytogenes and B. cereus in milk and the media. This work was a preliminary study that provided a starting point for determining whether the use of ZnO nanoparticles had the potential for being applied in food preservation or not.

A multi-sampling approach to evaluate an infrared surface treatment for reducing Listeria monocytogenes contamination on whole Gorgonzola cheese rinds

The microbial ecology of Gorgonzola cheese rind is the focus of many studies because the surface can be contaminated by pathogenic microorganisms. Among food-borne pathogens, particular attention is focused on the behaviour of Listeria monocytogenes that is able to grow at refrigeration temperatures and it could also grow during ripening. The Consortium for the Protection of Gorgonzola Cheese declares the rind not edible but the pathogen may also be transferred during cutting and portioning. Therefore, the decontamination of rinds is important to increasing cheese safety. To achieve this goal, many different strategies have been proposed. In this study, the application of an infrared surface treatment to decontaminate cheese rinds is proposed. The presence of L. monocytogenes, which was artificially inoculated in cheese rinds together with cheese rind microflora, and the cheese rind microflora were monitored before and after the treatment of 32 samples of Gorgonzola cheese rinds.The infrared surface treatment provided good reduction of the rind microflora, and L. monocytogenes was particularly affected by this. The treatment, applied to cheeses at the end of ripening, does not interfere with the ripening process and offers the advantages of short time exposures and easy installation of the equipment in cheese plants. Moreover, this study demonstrated that the sampling method affects the detection of cheese rind microflora. In fact, a non-destructive sampling method, based on a sponge and often used for surface sampling but never before applied to ready to eat food sampling, was compared with a traditional but destructive method, based on rind scraping. Regarding L. monocytogenes, the sponge method allowed to estimate even only 5.71 ± 0.79 log cfu g−1 of cells reduction after the treatment while the higher reduction when considering the rind scraping method was 4.06 ± 3.38 log cfu g−1. The sponge method, combined with the classic scraping one, besides offering the great advantage of not being destructive, allowed to differentiate the effect that the treatment has on the microflora located on the surface from those in deeper layers.

Effect of packaging and storage time on reduction of Listeria monocytogenes in RTE meat snacks

Effect of packaging and storage time on reduction of Listeria monocytogenes in RTE meat snacks

Comparison of post-lethality thermal treatment conditions on the reduction of Listeria monocytogenes and sensory properties of vacuum packed ricotta salata cheese

Ricotta salata is a whey protein cheese produced in Sardinia that in the last decades has been linked to several recalls and in 2012 to a severe human listeriosis outbreak. Contamination of ricotta salata with Listeria monocytogenes mainly occurs during post-process handling and generally origins from the processing environment. The application of water bath heat treatment in vacuum packed ricotta salata is a possible strategy to control L. monocytogenes superficial contamination. The objective of the present study was to select a heat treatment able to inactivate L. monocytogenes count of at least 5 log. Nine temperature time combinations, 75 °C, 85 °C and 90 °C applied for 15 min, 25 min and 40 min each were tested in ricotta wheels artificially contaminated with a mixture of 5 L. monocytogenes strains. Inactivation was assessed respectively one day and 30 days after heat treatment. The efficacy of treatments was evaluated based on the reduction in L. monocytogenes counts, on the impact on sensory properties and on the cost of the treatment. Two out of nine treatment combinations, i.e. 85 °C for 40 min and 90 °C for 40 min, were effective in reducing L. monocytogenes contamination level of 5 log. No significant difference was observed in sensory properties after the heat treatments. Therefore both combinations are eligible to conduct a successive study aimed to extend the shelf-life of ricotta salata up to several months.

Retardation of Listeria monocytogenes growth in mozzarella cheese using antimicrobial sachets containing rosemary oil and thyme oil.

An antimicrobial sachet containing microcellular foam starch (MFS) with embedded rosemary oil and thyme oil was developed to reduce bacterial growth in shredded mozzarella cheese. The efficacy of the volatiles of oils at various concentrations in reducing Listeria monocytogenes as well as the release of the oils from the MFS have been also determined in this study. The cheese, inoculated with a cocktail of 5 strains of L. monocytogenes (approximately 3 log CFU/g), was packaged in a Nylon/EVOH/PE bag. A paper sachet containing MFS embedded with rosemary oil and thyme oil, separately or together, was inserted into the bag. Rosemary and thyme oil volatiles released from the sachet restricted the growth of L. monocytogenes, resulting in a 2.5 log CFU/g reduction on day 9 at 10 °C. The volatile oils also showed inhibitory effects on the growth of lactic acid bacteria (LAB) and total aerobic bacteria (TAB). After 15 d at 10 °C, the numbers of LAB and TAB in the samples containing the sachet with both oils experienced a 1.2 and 1.4 log CFU/g reduction, respectively, compared to untreated samples. Nonetheless, the sachet treatment produced a distinct odor, unfavorably received by the panelists. The results suggest the potential for application of the sachet system for the reduction of growth of L. monocytogenes, LAB, and TAB in food products.

Control of Listeria monocytogenes in fresh cheese using protective lactic acid bacteria

In the past years, there has been a particular focus on the application of bacteriocins produced by lactic acid bacteria (LAB) in controlling the growth of pathogenic bacteria in foods. The aim of this study was to select LAB strains with antimicrobial activity, previously isolated from a traditional Azorean artisanal cheese (Pico cheese), in order to identify those with the greatest potential in reducing Listeria monocytogenes in fresh cheese. Eight bacteriocin producer strains identified as Lactococcus lactis (1) and Enterococcus faecalis (7) were tested. In general, the bacteriocin-producing strains presented a moderate growth in fresh cheese at refrigeration temperatures (4°C), increasing one log count in three days. They exhibited slow acidification capacity, despite the increased production of lactic acid displayed by some strains after 24h. Bacteriocin activity was only detected in the whey of fresh cheese inoculated with two Enterococcus strains, but all cheeses made with bacteriocin-producing strains inhibited L. monocytogenes growth in the agar diffusion bioassay. No significant differences were found in overall sensory evaluation made by a non-trained panel of 50–52 tasters using the isolates as adjunct culture in fresh cheese, with the exception of one Enterococcus strain. To test the effect of in situ bacteriocin production against L. monocytogenes, fresh cheese was made from pasteurized cows' milk inoculated with bacteriocin-producing LAB and artificially contaminated with approximately 106CFU/mL of L. monocytogenes. The numbers of L. monocytogenes were monitored during storage of fresh cheese at refrigeration temperature (4°C) for up to 15days. All strains controlled the growth of L. monocytogenes, although some Enterococcus were more effective in reducing the pathogen counts. After 7days, this reduction was of approximately 4 log units compared to the positive control. In comparison, an increase of 4logCFU/mL in pathogen numbers was detected over the same period, in the absence of bacteriocin-producing LAB. The combination of two bacteriocin producing Enterococcus sp. optimized the reduction of L. monocytogenes counts in fresh cheese, reducing by approximately 5logunits after 7days. The present work demonstrates that using bacteriocin-producing strains in the manufacture of fresh cheese might contribute to preventing the growth of undesirable pathogenic bacteria such as L. monocytogenes. A blend of two strains demonstrated great potential as a protective culture for the cheese making process.

Synergistic effects of ultrasound and sodium hypochlorite (NaOCl) on reducing Listeria monocytogenes ATCC19118 in broth, stainless steel, and iceberg lettuce.

This study was performed in order to determine whether a combined treatment of ultrasound and sodium hypochlorite (NaOCl) is more effective than individual treatment on reducing Listeria monocytogenes ATCC19118 on stainless steel and iceberg lettuce. The bactericidal effect of ultrasound and NaOCl was investigated in tryptic soy broth (TSB), on stainless steel and iceberg lettuce. Various concentrations of NaOCl (50, 100, 150, and 200 ppm) were tested along with various ultrasound treatment times (5, 20, 40, 60, 80, and 100 min). The combined treatment of ultrasound and NaOCl resulted in greater bacterial reductions than either treatment alone, without causing any significant changes in lettuce texture. The synergistic values of combined ultrasound and NaOCl treatments in TSB, on stainless steel, and on iceberg lettuce were 0.01-0.99 log10 colony-forming units (CFU)/mL, 0.01-0.62 log 10 CFU/g, and 0.12-1.66 log10 CFU/g, respectively. These results suggest that the combination of ultrasound and NaOCl was more effective than each treatment against Listeria monocytogenes, and that this combination can effectively sanitize fresh products such as iceberg lettuce.