Hudaa Neetoo

Control of Listeria monocytogenes on ham steaks by antimicrobials incorporated into chitosan-coated plastic films

Contamination of ready-to-eat (RTE) meat products such as ham steaks with Listeria monocytogenes has been a concern for the meat processing industry. The objective of this study was to evaluate the antilisterial efficacy of chitosan-coated plastic films alone or incorporating five generally recognized as safe (GRAS) antimicrobials. Effect of chitosan-coated plastic film on the growth of L. monocytogenes was first investigated in an aqueous system of culture medium broth and chitosan-coated films were able to inhibit the growth of L. monocytogenes in a concentration-dependent manner. However, chitosan-coated plastic films were not able to control the growth of L. monocytogenes on ham steaks. Therefore, five GRAS antimicrobials were subsequently incorporated into chitosan-coated plastic films to enhance their antilisterial effectiveness. Ham steaks were surface-inoculated with a five-strain cocktail of L. monocytogenes and then packaged in chitosan-coated plastic films containing 500 IU/cm(2) of nisin, 0.01 g/cm(2) of sodium lactate (SL), 0.0025 g/cm(2) of sodium diacetate, 0.003 g/cm(2) of potassium sorbate (PB), or 0.001 g/cm(2) of sodium benzoate (SB). The samples were stored at room temperature (ca. 20 degrees C) for 10 days. Incorporating antimicrobials into chitosan-coated plastic films slowed down or inhibited the growth of L. monocytogenes. The chitosan-coated plastic film containing SL was the most effective antimicrobial film and its efficacy against L. monocytogenes on ham steaks was evaluated during 12-week storage at 4 degrees C. The film showed excellent long-term antilisterial effect with the counts of L. monocytogenes being slightly lower than the initial inoculum. Chitosan-coated plastic films containing 0.001 g/cm(2) of SL have a potential to be used on ham steaks to control L. monocytogenes.

Effectiveness of chitosan-coated plastic films incorporating antimicrobials in inhibition of Listeria monocytogenes on cold-smoked salmon

The objective of this study was to evaluate the efficacy of chitosan-coated plastic films incorporating five Generally Recognized as Safe (GRAS) antimicrobials (nisin, sodium lactate (SL), sodium diacetate (SD), potassium sorbate (PS) and sodium benzoate (SB)) against Listeria monocytogenes on cold-smoked salmon. Salmon samples were surface-inoculated with a five-strain cocktail of L. monocytogenes and packaged in chitosan-coated plastic films containing 500 IU/cm(2) of nisin, 9 mg/cm(2) of SL, 0.5 mg/cm(2) of SD, 0.6 mg/cm(2) of PS, or 0.2 mg/cm(2) of SB, and stored at room temperature (ca. 20 degrees C) for 10 days. The film incorporating SL was the most effective, completely inhibiting the growth of L. monocytogenes during 10 days of storage. L. monocytogenes in samples packaged in the other four antimicrobial films grew, but the increase in counts was lower than the control. The antilisterial efficacy of films containing lower concentrations of SL (2.3 mg/cm(2) and 4.5 mg/cm(2)) and binary combinations SL, PS, SD, SB and nisin were subsequently evaluated. Among all the treatments, chitosan-coated plastic films with 4.5 mg/cm(2) SL, 4.5 mg/cm(2) SL-0.6 mg/cm(2) PS and 2.3 mg/cm(2) SL-500 IU/cm(2) nisin were the most effective. These three most effective antimicrobial films were then tested at refrigerated temperature. They completely inhibited the growth of L. monocytogenes on smoked salmon for at least 6 weeks. Chitosan-coated plastic films containing 4.5 mg/cm(2) SL can potentially assist the smoked-salmon processing industry in their efforts to control L. monocytogenes.

Inactivation of a Human Norovirus Surrogate by High-Pressure Processing: Effectiveness, Mechanism, and Potential Application in the Fresh Produce Industry

ABSTRACT Fresh produce is often a high-risk food for norovirus contamination because it can become contaminated at both preharvest and postharvest stages and it undergoes minimal or no processing. Currently, there is no effective method to eliminate the viruses from fresh produce. This study systematically investigated the effectiveness of high-pressure processing (HPP) on inactivating murine norovirus (MNV-1), a surrogate for human norovirus, in aqueous medium and fresh produce. We demonstrated that MNV-1 was effectively inactivated by HPP. More than a 5-log-PFU/g reduction was achieved in all tested fresh produce when it was pressurized at 400 MPa for 2 min at 4°C. We found that pressure, pH, temperature, and food matrix affected the virus survival in foods. MNV-1 was more effectively inactivated at 4°C than at 20°C in both medium and fresh produce. MNV-1 was also more sensitive to HPP at neutral pH than at acidic pH. We further demonstrated that disruption of viral capsid structure, but not degradation of viral genomic RNA, is the primary mechanism of virus inactivation by HPP. However, HPP does not degrade viral capsid protein, and the pressurized capsid protein was still antigenic. Overall, HPP had a variable effect on the sensorial quality of fresh produce, depending on the pressure level and type of product. Taken together, HPP effectively inactivated a human norovirus surrogate in fresh produce with a minimal impact on food quality and thus can provide a novel intervention for processing fruits intended for frozen storage and related products such as purees, sauces, and juices.

Potential antimicrobials to control Listeria monocytogenes in vacuum-packaged cold-smoked salmon pâté and fillets

In the wake of recent outbreaks associated with Listeria monocytogenes in ready-to-eat foods and an increasing desire for minimally processed foods, there has been a burgeoning interest in the use of natural antimicrobials by the food industry to control this pathogen. The minimum inhibitory concentrations (MICs) of nisin and salts of organic acids (sodium lactate (SL), sodium diacetate (SD), sodium benzoate (SB), and potassium sorbate (PS)) against twelve strains of L. monocytogenes in a TSBYE broth medium at 35 degrees C were determined. The MICs were strain-dependent and fell in the range of 0.00048-0.00190% for nisin, 4.60-5.60% for SL, 0.11-0.22% for SD, 0.25-0.50% for SB and 0.38-0.75% for PS, respectively. The two most antimicrobial-resistant strains were used as a cocktail in the following experiments to represent a worst case scenario. The five antimicrobials alone and in binary combinations were screened for their efficacy against the two-strain cocktail in TSBYE at sub-MIC and sub-legal levels at 35 degrees C. Seven effective antimicrobial treatments were then selected and evaluated for their long-term antilisterial effectiveness in cold-smoked salmon pâté and fillets during refrigerated storage (4 degrees C) of 3 and 6 weeks, respectively. The two most effective antimicrobial formulations for smoked salmon pâté, 0.25% SD and 2.4% SL/0.125% SD, were able to inhibit the growth of L. monocytogenes during the 3 weeks of storage. Surface application of 2.4% SL/0.125% SD was the most effective treatment for smoked salmon fillets which inhibited the growth of L. monocytogenes for 4 weeks. These antimicrobial treatments could be used by the smoked salmon industry in the U.S. and Europe in their efforts to control L. monocytogenes as they are effective against even the most antimicrobial-resistant strains tested in this study.

Bioactive alginate coatings to control Listeria monocytogenes on cold-smoked salmon slices and fillets

The relatively high incidence of Listeria monocytogenes in cold smoked salmon (CSS) is of concern as CSS is a ready-to-eat product. No post-processing measures are currently available to control this pathogen in CSS. The objective of this study was to develop an effective antimicrobial edible coating containing organic salts to control the growth of L. monocytogenes in CSS slices and fillets. An in-house made formulation consisting of sodium lactate (SL, 0-2.4%) and sodium diacetate (SD, 0-0.25%) as well as 2.5% OptiForm (a commercial formulation of SL and SD) were incorporated into five edible coatings: alginate, kappa-carrageenan, pectin, gelatin or starch. The coatings were applied onto the surface of CSS slices inoculated with L. monocytogenes to an inoculum level of 500 CFU/cm(2) ( approximately 3 log CFU/g) and stored at room temperature (22 degrees C) for 6 days. Alginate coating was found to be the most effective carrier for the various antimicrobial treatments in inhibiting the growth of L. monocytogenes. In the second phase of the study, CSS slices and fillets inoculated with the pathogen at a level of 500 CFU/cm(2) were coated with alginate incorporating the in-house made and the commercial (OptiForm) SL/SD based formulations and stored for 30 days at 4 degrees C. When cold-smoked salmon slices and fillets were stored at 4 degrees C, alginate coatings supplemented with 2.4%SL/0.25%SD and the commercial product OptiForm significantly delayed the growth of L. monocytogenes during the 30-day storage with final counts reaching 4.1 and 3.3 log CFU/g (slices) and 4.4 and 3.8 log CFU/g (fillets), respectively, while the counts in their untreated counterparts were significantly higher (P<0.05) reaching 7.3 and 6.8 log CFU/g for slices and fillets, respectively. Therefore, this study demonstrates the effectiveness of using an alginate-based coating containing lactate and diacetate to control the growth of L. monocytogenes to enhance the microbiological safety of filleted and sliced smoked salmon.

Pressure inactivation of Tulane virus, a candidate surrogate for human norovirus and its potential application in food industry

Human norovirus (HuNoV) is the leading causative agent for foodborne disease. Currently, studies of HuNoV usually rely on surrogates such as murine norovirus (MNV) due to the lack of a suitable cell culture system and a small animal model for HuNoV. Tulane virus (TV), a monkey calicivirus, is a cultivable enteric calicivirus that not only recognizes the same receptors as HuNoV, but is also genetically closely related to HuNoV. In this study, we determined the pH stability of TV and MNV-1, as well as the effect of high hydrostatic pressure (HHP) on inactivating both viruses in aqueous media, blueberries and oysters. We demonstrated that both TV and MNV-1 were very stable under an acidic environment. They were more resistant to pressure at an acidic environment than at neutral pH. Pressure treatment of 600 MPa for 2 min at different temperatures (4, 21 and 35 °C) barely caused any reduction of TV, as well as MNV-1, on un-wetted (dry) blueberries. However, both TV and MNV-1 on blueberries were successfully inactivated by a pressure of ≤400 MPa when blueberries were immersed in phosphate-buffered saline during HHP. Pressure inactivation of both TV and MNV-1 in blueberries and oysters increased as sample temperature decreased in the order of 4>21>35 °C. TV was more sensitive to pressure than MNV-1 for the three matrices tested, culture media, blueberries and oysters. This study provides important information on the use of TV as a surrogate for HuNoV study. Results obtained from this study lay a foundation for designing effective HHP treatments for inactivation of HuNoV in high-risk foods such as berries and oysters.

Potential application of high hydrostatic pressure to eliminate Escherichia coli O157:H7 on alfalfa sprouted seeds

Sprouts eaten raw are increasingly being perceived as hazardous foods as they have been implicated in Escherichia coli O157:H7 outbreaks where the seeds were found to be the likely source of contamination. The objective of our study was to evaluate the potential of using high hydrostatic pressure (HHP) technology for alfalfa seed decontamination. Alfalfa seeds inoculated with a cocktail of five strains of E. coli O157:H7 were subjected to pressures of 500 and 600 MPa for 2 min at 20 degrees C in a dry or wet (immersed in water) state. Immersing seeds in water during pressurization considerably enhanced inactivation of E. coli O157:H7 achieving reductions of 3.5 log and 5.7 log at 500 and 600 MPa, respectively. When dry seeds were pressurized, both pressure levels reduced the counts by <0.7 log. To test the efficacy of HHP to completely decontaminate seeds whilst meeting the FDA requirement of 5 log reductions, seeds inoculated with a ~5 log CFU/g of E. coli O157:H7 were pressure-treated at 600 and 650 MPa at 20 degrees C for holding times of 2 to 20 min. A >5 log reduction in the population was achieved when 600 MPa was applied for durations of > or =6 min although survivors were still detected by enrichment. When the pressure was stepped up to 650 MPa, the threshold time required to achieve complete elimination was 15 min. Un-inoculated seeds pressure-treated at 650 MPa for 15 min at 20 degrees C successfully sprouted achieving a germination rate identical to untreated seeds after eight days of sprouting. These results therefore demonstrate the promising application of HHP on alfalfa seeds to eliminate the risk of E. coli O157:H7 infections associated with consumption of raw alfalfa sprouts.

Inactivation of Salmonella and Escherichia coli O157:H7 on artificially contaminated alfalfa seeds using high hydrostatic pressure.

Alfalfa sprouts contaminated with Salmonella and Escherichia coli O157:H7 have been implicated in several outbreaks of foodborne illnesses in recent years. The seed used for sprouting appears to be the primary source of pathogens. Seed decontamination prior to sprouting presents a unique challenge for the sprouting industry since cells of the pathogenic survivors although undetectable after sanitizing treatments, can potentially multiply back to hazardous levels. The focus of this study was to therefore test the efficacy of high hydrostatic pressure to eliminate a approximately 5 log CFU/g load of Salmonella and E. coli O157:H7 on alfalfa seeds. Pressure treatment of 600 MPa for up to 25 min at 20 degrees C could not result in complete inactivation of Salmonella. High-pressure treatment was then carried out either at sub-ambient (4 degrees C) or elevated (40, 45 and 50 degrees C) temperatures to test the ability of high pressure to eliminate Salmonella. Pressure treatment at 4 and 20 degrees C did not deliver any satisfactory inactivation of Salmonella while high pressure at elevated temperatures achieved complete kill. Pre-soaking seeds prior to high-pressure treatment also enhanced pressure inactivation of Salmonella but at the expense of seed viability. High-pressure treatment of 500 MPa for 2 min at 45 degrees C was able to eliminate wild-type Salmonella and E. coli O157:H7 strains without bringing about any appreciable decrease in the seed viability.

Individual and combined application of dry heat with high hydrostatic pressure to inactivate Salmonella and Escherichia coli O157:H7 on alfalfa seeds

Alfalfa sprouts are recurrently implicated in outbreaks of food-borne illnesses as a result of contamination with Salmonella or Escherichia coli O157:H7. In the majority of these outbreaks, the seeds themselves have been shown to be the most likely source of contamination. The aims of this study were to comparatively assess the efficacy of dry heat treatments alone or in conjunction with high hydrostatic pressure (HHP) to eliminate a ∼5 log CFU/g load of Salmonella and E. coli O157:H7 on alfalfa seeds. Dry heat treatments at mild temperatures of 55 and 60 °C achieved ≤1.6 and 2.2 log CFU/g reduction in the population of Salmonella spp. after a 10-d treatment, respectively. However, subjecting alfalfa seeds to more aggressive temperatures of 65 °C for 10 days or 70 °C for 24 h eliminated a ∼5 log population of Salmonella and E. coli O157:H7. We subsequently showed that the sequential application of dry heating followed by HHP could substantially reduce the dry heating exposure time while achieving equivalent decontamination results. Dry heating at 55, 60, 65 and 70 °C for 96, 24, 12 and 6 h, respectively followed by a pressure treatment of 600 MPa for 2 min at 35 °C were able to eliminate a ∼5 log CFU/g initial population of both pathogens. Finally, we evaluated the impact of selected treatments on the seed germination percentages and yield ratios and showed that dry heating at 65 °C for 10 days did not bring about any considerable decrease in the germination percentage. However, the sprout yield of treated alfalfa seeds was reduced by 21%. Dry heating at 60 and 65 °C for 24 and 12 h respectively followed by the pressure treatment of 600 MPa for 2 min at 35 °C did not significantly (P > 0.05) affect the germination percentage of alfalfa seeds although a reduction in the sprouting yield was observed.

Application of an active alginate coating to control the growth of Listeria monocytogenes on poached and deli turkey products

The relatively high prevalence of Listeria monocytogenes in ready-to-eat (RTE) turkey products is of great concern. The overall objective of this study was to develop antimicrobial edible coating formulations to effectively control the growth of this pathogen. The antimicrobials studied were nisin (500IU/g), Novagard CB 1 (0.25%), Guardian NR100 (500ppm), sodium lactate (SL, 2.4%), sodium diacetate (SD, 0.25%), and potassium sorbate (PS, 0.3%). These were incorporated alone or in binary combinations into five edible coatings: alginate, kappa-carrageenan, pectin, xanthan gum, and starch. The coatings were applied onto the surface of home-style poached and processed deli turkey discs inoculated with ~3log CFU/g of L. monocytogenes. The turkey samples were then stored at 22 degrees C for 7days. For poached and processed deli turkey, the coatings were found to be equally effective, with pectin being slightly less effective than the others. The most effective poached turkey treatments seemed to be SL (2.4%)/SD (0.25%) and Nisin (500IU/g)/SL (2.4%), which yielded final populations of 3.0 and 4.9log CFU/g respectively compared to the control which was 7.9log CFU/g. For processed deli turkey, the most effective antimicrobial treatments seemed to be Nisin (500IU/g)/SD (0.25%) and Nisin (500IU/g)/SL (2.4%) with final populations of 1.5 and 1.7log CFU/g respectively compared to the control which was 6.5log CFU/g. In the second phase of the study, home-style poached and store-purchased roasted (deli) turkey inoculated with the pathogen at a level of ~3log CFU/g were coated with alginate incorporating selected antimicrobial combinations and stored for 8weeks at 4 degrees C. Alginate coatings supplemented with SL (2.4%)/PS (0.3%) delayed the growth of L. monocytogenes with final counts reaching 4.3log CFU/g (home-style poached turkey) and 6.5log CFU/g (roasted deli turkey) respectively while the counts in their untreated counterparts were significantly higher (P<0.05) reaching 9.9 and 7.9log CFU/g, respectively. This study therefore demonstrates the effectiveness of using alginate-based antimicrobial coatings to enhance the microbiological safety and quality of RTE poultry products during chilled storage.