Eliminate Listeria Monocytogenes Research Articles

PHYTOCHEMICAL PROFILE AND ANTIMICROBIAL ACTIVITY OF PLANT EXTRACTS AGAINST PATHOGENIC MICROORGANISMS OF IMPORTANCE TO THE LIVESTOCK INDUSTRY

Infections caused by pathogenic bacteria are a recurrent problem in the livestock sector, generating important economic losses in the livestock industry. One of the main strategies includes antibiotic therapy; however, its use is limited since pathogenic bacteria present resistance to these drugs, which makes treatment against microbial infections difficult. Therefore, the hypothesis proposed was that ethanolic extracts of native plants from the state of Sonora, Mexico, can inhibit the growth of Gram (+) and Gram (-) pathogenic bacteria related to common infections in the livestock industry. The objective was to evaluate the phytochemical and antimicrobial profile of native plants from the state of Sonora, Mexico. In this study, 17 ethanolic extracts were obtained from native plants of Sonora, and the antimicrobial activity was evaluated by the agar diffusion method and by the microdilution technique using reference bacteria from the ATCC collection. The phytochemical profile was evaluated by spectrophotometry and the experimental design used was completely randomized with three replicates per treatment at 95 % confidence. The results showed that extracts of Prosopis velutina, Ibervillea sonorae, Populus alba, Ambrosia ambrosioides, Krameria sonorae, and Leucaena leucocephala were effective in eliminating Listeria monocytogenes ATCC 19115, Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922 and Salmonella enterica serovar Typhimurium ATCC 14028 (p≤ 0.05). In addition, these extracts presented the highest concentration of total polysaccharides, flavones and flavonols, flavanones and dihydroflavonols, tannins and total chlorogenic acid (p ≤ 0.05). Therefore, plant extracts from Sonora, Mexico, represent a natural alternative for the control of Gram (+) and Gram (-) pathogens of importance to the livestock industry.

Antilisterial Potential of Lactic Acid Bacteria in Eliminating Listeria monocytogenes in Host and Ready-to-Eat Food Application

Listeriosis is a severe food borne disease with a mortality rate of up to 30% caused by pathogenic Listeria monocytogenes via the production of several virulence factors including listeriolysin O (LLO), transcriptional activator (PrfA), actin (Act), internalin (Int), etc. It is a foodborne disease predominantly causing infections through consumption of contaminated food and is often associated with ready-to-eat food (RTE) and dairy products. Common medication for listeriosis such as antibiotics might cause an eagle effect and antibiotic resistance if it is overused. Therefore, exploration of the use of lactic acid bacteria (LAB) with probiotic characteristics and multiple antimicrobial properties is increasingly getting attention for their capability to treat listeriosis, vaccine development, and hurdle technologies. The antilisterial gene, a gene coding to produce antimicrobial peptide (AMP), one of the inhibitory substances found in LAB, is one of the potential key factors in listeriosis treatment, coupled with the vast array of functions and strategies; this review summarizes the various strategies by LAB against L. monocytogenes and the prospect in development of a ‘generally regarded as safe’ LAB for treatment of listeriosis.

Inactivation of Listeria monocytogenes in raw and hot smoked trout fillets by high hydrostatic pressure processing combined with liquid smoke and freezing

High hydrostatic pressure (HHP; 200 MPa for 15 min), liquid smoke (0.50%, v/v) and freezing (−80 °C, overnight) was used to eliminate Listeria monocytogenes in BHI broth, raw and smoked trout. The bactericidal effect of liquid smoke solutions (L9 and G6), HHP and their combinations was evaluated against L.monocytogenes LO28, EGD-e and 10403S and further continued with the most resistant strain (10403S) to the combined treatment. For first time, a synergistic effect of liquid smoke and HHP was observed and was further enhanced by freezing prior to HHP. The effect of HHP and liquid smoke, prior to freezing was highest in BHI compared to raw and smoked trout. A major synergistic effect of HHP, liquid smoke and freezing was observed, reaching a 5.48 or 1.93 log CFU/g reduction when smoked or raw trout was used respectively. Furthermore, high injury levels occurred, among treatments reaching up to 55.98%. Industrial relevanceThis paper illustrates for first time, the possibility of using a very low pressure in combination with liquid smoke and freezing to eliminate L.monocytogenes. It was demonstrated that treatment of trout samples with liquid smoke followed by freezing prior to pressurization at 200 MPa for 15 min reduced the number of L.monocytogenes by more than 5-log CFU/g. Such a remarkable bacterial inactivation at a very low pressure (compared to common industrial practices) is a significant achievement that could allow production of safer and novel products by HHP at an affordable price, as the cost of equipment manufacture as well as the maintenance and running costs could be reduced substantially at lower operation pressures.

High Pressure Processing (HPP) Does Not Affect Texture and Sensory Attributes of Smoked Hams Cured by Conventional and Alternative Methods

ObjectivesHigh Pressure Processing (HPP) is a post-lethality treatment applied on RTE meats to reduce or eliminate Listeria monocytogenes. Previous research showed that HPP can affect texture and sensory attributes by modifying the myofibrillar structure and inducing lipid oxidation. Additionally, the increasing demand for natural and organic products created niche markets for uncured and alternatively cured hams. This experiment evaluated the effects of HPP on texture profile, WBSF, and sensory attributes of uncured, and conventionally and alternatively cured hams.Materials and MethodsThirty-two boneless pork top rounds (m. semimembranosus and m. adductor) were obtained from a commercial USDA inspected plant. Eight samples were assigned to 1 of 4 curing treatments. Treatments included conventional curing with nitrite (TRT1), alternative curing with celery powder (TRT2), uncured with apple cider, wine, and garlic (TRT3), and alternative curing with celery powder and buffered vinegar (TRT4). Samples were injected to 110% of green weight with a brine solution, immersed for 3 d, and smoked for 10 h at 107°C until the final product reached at least 71.1°C at the geometric center. From each sample, a total of four 2.54 cm thick slices were obtained. Two were treated with HPP at 87,000 psi for 3 min (HPP) and 2 were assigned as HPP control (NOHPP). Texture profile analysis (TPA) was performed on 3 cubes (2.54 cm2) from each slice and WBSF was analyzed from six 1.27 cm cores. A consumer sensory panel (480 panelists, 16 sessions, 30 panelists per session) evaluated color, odor, flavor, texture, and overall desirability by using a numerical scale (1 = Dislike extremely and 9 = Like extremely). Panelists also scored off-flavor intensity from 1 = No off-flavor to 9 = Off-flavor extremely intense. Data was analyzed by using PROC GLIMMIX of SAS (SAS Inst. Inc., Cary, NC) as a split plot design where curing treatment was the whole plot and HPP the sub plot.ResultsHPP did not affect hardness, adhesiveness, springiness, gumminess, chewiness and WBSF of smoked hams. However, a significant effect of HPP was observed for cohesiveness (0.38 for NOHPP and 0.34 for HPP; P < 0.0001). No interaction between TRT and HPP was observed for any texture profile attributes. Curing treatment only affected springiness (6.21a, 6.28a, 5.78b, and 5.90ab, for TRT1, 2, 3, and 4, respectively; P = 0.03). For sensory analysis, interaction between TRT and HPP main effects were observed on odor (P = 0.02) and off-flavor (P = 0.006). No single effect of HPP was observed on other sensory attributes. Curing treatment affected color, flavor, texture, and overall desirability (P < 0.0001). Overall TRT1 and TRT4 had better scores when compared to TRT2 and TRT3.ConclusionHPP did not affect texture and WBSF of smoked hams cured by conventional and alternative methods. Hams cured conventionally and alternatively with celery powder and buffered vinegar had better color, flavor, and overall desirability. Uncured hams had the lowest overall desirability when compared to cured hams.

Abstract A082: Identification of commensal bacterial strains that provide resistance to L. monocytogenes infection

Abstract Listeria monocytogenes is an important cause of foodborne infections, particularly in patients with hematologic malignancies, causing septicemia and meningoencephalitis. Although most strains of L. monocytogenes are antibiotic sensitive, antibiotic treatment is frustratingly ineffective at curing highly immunocompromised patients, resulting in a mortality rate of approximately 30%. The gut microbiota, which consists of commensal bacterial populations that inhabit the intestine, normally confers protection against orally acquired pathogens by exerting colonization resistance. Changes in microbiota composition induced by disease, pharmacological or antibiotic therapies can lead to dysbiosis, thereby impairing commensal-mediated colonization resistance and predisposing to infection. Our preliminary data show that bacterial species represented in a healthy microbiota can efficiently eliminate Listeria monocytogenes from the gut lumen, thus preventing the pathogen from translocating across the intestinal epithelium and spreading systemically. This mechanism of protection is particularly important in the context of congenic or acquired (chemotherapy-driven) immune deficiencies. Indeed, mice lacking T and B lymphocyets as well as innate lymphoid cells (Rag2/Il2rg Double Knockout mice, or Raggc), are highly susceptible to oral doses of Listeria that are non-lethal in WT mice. Although generally implicated in susceptibility to Listeriosis, the adaptive immune system is not involved in the in vivo clearance of the pathogen from the intestine, and the increased susceptibility to infection of these mice mainly results from the absence of innate immune cells producing interferon gamma at early stages, which leads to bacterial dissemination. Interestingly, Raggc mice are capable of surviving Listeria infection if challenged with low doses, which likely to mimicks the bacterial dosage acquired by immunocompromised patients. However, Raggc mice pre-treated with antibiotics experience uncontrolled intestinal growth of Listeria and subsequent systemic spread thus succumbing to low inoculum infection. This phenotype could be reproduced in mice treated with a combination of doxorubicin and cyclophosphamide, a cocktail often used in the treatment of cancer; although chemotherapy seemed to have an effect on the ability of the microbiota to restrict instestinal growth of Listeria, chemotherapy-treated mice became highly susceptible to low doses of Listeria only when pre-treated with antibiotics. Because antibiotics are often required for patients receiving cancer treatment, our these findings have potential clinical relevance. We are identifying specific commensal bacterial taxa and molecular mechanisms that mediate protection against L. monocytogenes. Our data indicate that Lactobacillus in the small intestine and Clostridium in the large intestine restrict Listeria growth in the gut lumen, thus lowering the bacterial burden and systemic spread. Germ-free (GF) mice reconstituted with a consortium of putative protective bacteria have greater resistance to infection than untreated GF mice or GF mice reconstituted with microbiota of antibiotic-treated mice, suggesting that gut commensals are independent and crucial contributors to host defense against Listeria. Our ultimate goal is to identify bacterial species that can be developed as probiotics for cancer patients to prevent intestinal L. monocytogenes carriage and infection. Combined shotgun sequencing and ex vivo assays on stool samples from cancer patients will be used to correlate loss of specific commensal bacteria with a predisposition to L. monocytogenes infection. Ultimately, this work will 1.) provide a novel approach to identifying subjects at high risk for L. monocytogenes infection and 2.) identify and characterize probiotic bacterial species to prevent and/or treat L. monocytogenes infections in cancer patients. Citation Format: Simone Becattini, Sohn G. Kim, Rebecca A. Carter, Lilan Ling, Ingrid M. Leiner, Eric G. Pamer. Identification of commensal bacterial strains that provide resistance to L. monocytogenes infection [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A082.

اثر عوامل محیطی بر روی خواص ضدلیستریایی نایسین

Nisin, belonged to type-A lantibiotcs, is a well-known bacteriocin that applied as natural preservative in food productions such as milk and cheese. This peptide has an inhibitory effect on many of Gram-positive bacteria. Using of nisin alone and in combination with other hurdles may serves as an effective method to eliminate listeria monocytogenes and other pathogens in food industries. This study was undertaken to evaluate the effect of nisin against listeria monocytogenes in different temperatures (4, 9 and 14°C), pH (5, 6 and 7) and NaCl concentrations (0, 1, 2 and 4). The minimum inhibitory concentration (MIC) of nisin was assessed using a broth micro-dilution method. Furthermore, for the effects of storage temperature, pH and sodium chloride concentration the Differences in Population (DP) assay were used. The MIC value of nisin was 320IU/ml. The effectiveness of nisin was pronounced at 14°C than at 9 and 4°C (P<0.016). nisin action increased in the presence of 2 and 4 g/100 ml of NaCl concentration (P<0.001). Also higher inactivation was observed after to pH 5 compared to pH 6 and 7 (P<0.001). Our results demonstrated that among different NaCl, pH, temperature and nisin values, the effect of NaCl was confounded than the effect of other factors at all prepared combinations (P<0.001).Our findings suggest the application of hurdle technology for achieving effective control of in most in food industries.

Use of E-beam radiation to eliminate Listeria monocytogenes from surface mould cheese.

Camembert and Brie soft cheese varieties were subjected to E-beam irradiation as a sanitation treatment. The effects of treatments on microbiota and selected physicochemical properties were also studied. The absorbed doses required to meet the food safety objective (FSO) according to EU and USDA criteria for Listeria monocytogenes were 1.27 and 2.59 kGy, respectively. The bacterial load, mainly lactic acid bacteria, was reduced by the treatment but injured cells were recovered during storage at 14°C. The radiation treatment gave rise to negligible changes in the pH and water activity at doses required to achieve microbial safety.

A biocontroller to eliminate Listeria monocytogenes from the food processing environment

Conventional disinfection methods have not been successful in eliminating Listeria monocytogenes from biofilms, which has caused difficulty in eradicating the pathogen from the food processing environment. The aim of this study was to formulate and design a biocontroller for application in the food processing environment and to evaluate its inhibitory capacity against biofilms from L. monocytogenes grown in vitro and in situ in floor gutters in a salmon processing plant. The biocontroller consisted of the thermally treated fermentate (TTF) from two Carnobacterium maltaromaticum strains (ATCC PTA 9380 and ATCC PTA 9381), a strain of Enterococcus mundtii (ATCC PTA 9382), plus nisin at a concentration of 1000 IU/mL. These components were entrapped in an alginate matrix supported by a mesh-type fabric. The activity of the biocontroller was analyzed during three weeks of storage at 4 °C by the plate antagonism test against a pool of five strains of L. monocytogenes. Effectiveness against L. monocytogenes was also tested on biofilms grown in vitro on stainless steel chips with coupons of the biocontroller placed on the chips and tested for 5 days. Loss of viability was confirmed by L. monocytogenes counts (cfu/cm2). Tests were also performed on biofilms grown in situ in floor gutters in a salmon processing plant. The biocontroller was fixed to the floor gutters for 48 h, and afterward, sampling by the sponge method for the presence of L. monocytogenes was performed. The results showed that the antagonistic activity of the biocontroller did not change significantly (p > 0.05) during the three weeks of storage at refrigeration temperature. The biocontroller coupons placed on a biofilm of five strains of L. monocytogenes grown on stainless steel chips reduced the counts from Log 3.7 cfu/cm2 to Log<1.0 cfu/cm2 after 24 h of contact, and no regrowth of the pathogen was observed for up to five days of contact. The in situ-tested biocontroller was able to inhibit or destroy L. monocytogenes in five out of seven trials, and the failures were due to loss of contact of the biocontroller with the side wall of the floor gutter. These in situ results confirmed the laboratory findings and proved the effectiveness of the biocontroller against L. monocytogenes.

Combined effect of benzalkonium chloride and ultrasound againstListeria monocytogenesbiofilm on plastic surface

This study was performed to evaluate the effectiveness of benzalkonium chloride combined with ultrasound in eliminating Listeria monocytogenes biofilm from polystyrene surface. The test strain of L. monocytogenes, previously classified as strong biofilm producer, was grown to form biofilm in tryptic soy broth at 20°C for 6 days in polystyrene specimen containers. The biofilms formed on surface of containers were treated with ultrasound alone, benzalkonium chloride (100 and 400 mg l(-1)) alone and their combination for three different exposure times (1, 5 and 15 min) at room temperature. Sonication was performed using an ultrasound bath at a constant ultrasound frequency of 35 kHz. After treatments, levels of biofilm biomass and viable cells in biofilm were determined using crystal violet staining and XTT assays, respectively. The combined treatment of ultrasound and benzalkonium chloride resulted in significant (P < 0·05) more decrease in the level of viable cells in the L. monocytogenes biofilm compared to individual treatments of benzalkonium chloride. Our results suggest that the combination of benzalkonium chloride with ultrasound is useful approach for the elimination of L. monocytogenes biofilms from plastic surfaces.

Comparative spatiotemporal analysis of the intrathecal immune response in natural listeric rhombencephalitis of cattle and small ruminants

This study examined the spatiotemporal immune response in listeric rhombencephalitis of ruminants in situ. Our data support the view that astrocytes facilitate the containment of infectious lesions. Results on the natural disease recapitulate observations in experimental rodent models and suggest that the mounted adaptive lymphocytic response of ruminants is effective in eliminating Listeria monocytogenes (LM). However, our data indicate earlier participation of the adaptive immune response, a stronger B lymphocyte contribution and a more protracted macrophage infiltration in the natural disease than it has been deduced from experimental models. Therefore, such models should be complemented by studies in natural host systems. Various macrophage and microglia subsets are involved in listeric rhombencephalitis and their differential contribution may account for species differences in clinical course and outcome of infection as might species differences in the B-cell response. Future functional ex vivo and in vitro studies are necessary to further investigate the findings obtained in the present study.

ELIMINATION OF LISTERIA MONOCYTOGENES ON COOKED CHICKEN BREAST MEAT SURFACES BY NEAR‐INFRARED SURFACE PASTEURIZATION PRIOR TO FINAL PACKAGING

ABSTRACTThe objective of this research was to develop a process to eliminate Listeria monocytogenes on ready‐to‐eat chicken meats by near‐infrared (NIR) surface pasteurization immediately prior to final packaging. Cooked chicken breast meats, surface‐inoculated with a cocktail of L. monocytogenes, were subjected to NIR treatment. The surface temperature of the inoculated samples was increased to and then maintained at a temperature set point (62, 68 or 75C) for up to 8 min, depending on the temperature. On average, the overall rates of bacterial inactivation were 0.35, 0.89 and 1.6 log cycles/min for the samples treated at 62, 68 or 75C, respectively. In contrast, the bacterial inactivation rates were only 0.21, 0.53, 0.63 or 0.95 log‐cycles/min for samples submerged under hot water maintained at 62, 68, 75 or 85C, respectively. NIR surface pasteurization process was convincingly more effective than the hot water immersion process to eliminate L. monocytogenes.PRACTICAL APPLICATIONSFar‐infrared (FIR) surface pasteurization, alone or in combination with hot water immersion (HWI) heating, has been used in the food industry to decontaminate ready‐to‐eat (RTE) meat surfaces immediately prior to final packaging. Near‐infrared surface pasteurization provides another potentially faster alternative to FIR and HWI to eliminate L. monocytogenes on RTE meats.

Spray application of liquid smoke to reduce or eliminate Listeria monocytogenes surface inoculated on frankfurters

In a simulated post process contamination scenario liquid smoke was sprayed on the frankfurters after peeling, and then inoculated with Listeria monocytogenes (Lm). Samples that did not receive a liquid smoke spray remained at approximately 2 log cfu/cm(2) during the 48h of storage while the levels on the liquid smoke treated frankfurters continued to decline until they were below detection level (1 cfu/100 cm(2)). A shelf-life study lasting 140 days indicated that liquid smoke suppressed the growth of Lm for up to 130 days. An application of 2 or 3 ml liquid smoke at packaging resulted in at least a 1 log reduction of Lm within 12h post packaging.

Efficacy of chlorine dioxide against Listeria monocytogenes in brine chilling solutions.

Chilled brine solutions are used by the food industry to rapidly cool ready-to-eat meat products after cooking and before packaging. Chlorine dioxide (ClO(2)) was investigated as an antimicrobial additive to eliminate Listeria monocytogenes. Several experiments were performed using brine solutions made of sodium chloride (NaCl) and calcium chloride (CaCl(2)) inoculated with L. monocytogenes and/or treated with 3 ppm of ClO(2). First, 10 and 20% CaCl(2) and NaCl solutions (pH 7.0) were inoculated with a five-strain cocktail of L. monocytogenes to obtain approximately 7 log CFU/ml and incubated 8 h at 0 degrees C. The results demonstrated that L. monocytogenes survived in 10% CaCl(2), 10 and 20% NaCl, and pure water. L. monocytogenes levels were reduced approximately 1.2 log CFU/ml in 20% CaCl(2). Second, inoculated ( approximately 7 log CFU/ml) brine solutions (10 and 20% NaCl and 10% CaCl(2)) treated with 3 ppm of ClO(2) resulted in a approximately 4-log reduction of the pathogen within 90 s. The same was not observed in a solution of 20% CaCl(2); further investigation demonstrated that high levels of divalent cations interfere with the disinfectant. Spent brine solutions from hot dog and ham chilling were treated with ClO(2) at concentrations of 3 or 30 ppm. At these concentrations, ClO(2) did not reduce L. monocytogenes. Removal of divalent cations and organic material in brine solutions prior to disinfection with ClO(2) should be investigated to improve the efficacy of the compound against L. monocytogenes. The information from this study may be useful to processing establishments and researchers who are investigating antimicrobials in chilling brine solutions.

Radiation sensitization and postirradiation proliferation of Listeria monocytogenes on ready-to-eat deli meat in the presence of pectin-nisin films.

In this study, the ability of pectin-nisin films in combination with ionizing radiation to eliminate Listeria monocytogenes and inhibit its postirradiation proliferation was evaluated. Pectin films containing 0.025% nisin were made by extrusion. The surface of a ready-to-eat turkey meat sample was inoculated with L. monocytogenes at 10(6) CFU/cm2 and covered with a piece of pectin-nisin film. The samples were vacuum packaged and irradiated at 0, 1, and 2 kGy. The treated samples were stored at 10 degrees C and withdrawn at 0, 1, 2, 4, and 8 weeks for microbial analysis. Reductions in L. monocytogenes viability of 1.42, 1.56, 2.85, 3.78, and 5.36 log CFU/cm2 were achieved for the treatments of 1 kGy, pectin-nisin film, 2 kGy, 1 kGy plus pectin-nisin film, and 2 kGy plus pectin-nisin film, respectively. The greatest reduction (5.5 log CFU/cm2) was observed at 1 week for the 2 kGy plus pectin-nisin film treatment, suggesting that nisin was further released from the film to the surface of meat samples. Pectin-nisin films used in this study did not prevent but did significantly slow (P < 0.05) the proliferation of the L. monocytogenes cells that survived irradiation during 8 weeks of storage at 10 degrees C. These data indicate the potential use of pectin-nisin films alone or in combination with ionizing radiation for preventing listeriosis due to postprocessing contamination of ready-to-eat meat products.

Optimization of E-beam irradiation treatment to eliminate Listeria monocytogenes from ready-to-eat (RTE) cooked ham

Abstract The inactivation kinetics of death of five Listeria monocytogenes and one Listeria innocua by E-beam irradiation have been studied in order to optimize the treatment for the sanitation of ready-to-eat (RTE) cooked ham. Treatments of 1 and 2.5 kGy were calculated to reach the food safety objective (FSO) according to the EU and USDA statements. These doses do not modify the sensory properties (appearance, odour and flavour) in such a way that they were detected by consumers, excepting the odour when 2.5 kGy are applied to meet the USDA criterion. Industrial relevance The application of E-beam irradiation at low dose (

Combining Organic Acid Treatment with Steam Pasteurization To Eliminate Listeria monocytogenes on Fully Cooked Frankfurters

An organic acid solution of 2% acetic, 1% lactic, 0.1% propionic, and 0.1% benzoic acids was combined with steam surface pasteurization to treat frankfurters during vacuum packaging to eliminate potential postcook contamination with Listeria monocytogenes. The thermal lethality of L. monocytogenes from steam was evaluated at an inoculation concentration of 1 to 6 log CFU/cm2. About 3-log reductions of L. monocytogenes were achieved when frankfurters were treated by steam for 1.5 s. Combining organic acid treatment with steam pasteurization further inhibited the growth of surviving L. monocytogenes cells for 19 and 14 weeks when the packaged frankfurters were stored at 4 and 7°C, respectively. The results from this study provide meat processors with useful information for controlling L. monocytogenes on ready-to-eat meats.

Impact of antimicrobial ingredients and irradiation on the survival of Listeria monocytogenes and the quality of ready-to-eat turkey ham

Irradiation is an effective technology in eliminating Listeria monocytogenes, but it induces quality changes in meat products at or above specific radiation doses. To minimize irradiation-induced quality changes, only low irradiation doses are recommended. However, low-dose irradiation provides a chance for some pathogens to survive and proliferate during prolonged storage. To solve this problem, antimicrobial ingredients [2% sodium lactate (SL), 0.1% sodium diacetate (SDA), 0.1% potassium benzoate (PB)] and low-dose irradiation were combined and tested for their effects on the growth of L. monocytogenes and meat quality. The log10 reductions of L. monocytogenes in hams following exposure to 1.0 to 2.5 kGy of irradiation ranged from 2.0 to 5.0. The D10 values were 0.52 kGy for control ham or ham with PB, SL, or PB + SL; 0.49 kGy for ham with SL+SDA; and 0.48 kGy for ham with PB + SL + SDA (PSS). Addition of SL + SDA or PB + SL in combination with 1.0 kGy of irradiation was effective in suppressing the growth of L. monocytogenes for about 6 wk when stored at 4 degrees C, whereas 2.0 kGy of irradiation was listeriostatic. Ham irradiated with 1 kGy in combination with PSS was listeriostatic throughout storage. SL increased firmness of turkey hams, and sensory panelists noted that the saltiness was a little higher in products containing SL, but its overall impact on quality was minimal. Amounts of benzene were detected in irradiated hams with PB, showing PB was not fit as an antimicrobial ingredient for irradiated foods. In conclusion, 2% SL and 0.1% SDA in combination with low-dose irradiation were effective in ensuring the safety of ready-to-eat meat products against L. monocytogenes.

Effectiveness of Irradiation Treatments in Inactivating Listeria monocytogenes on Fresh Vegetables at Refrigeration Temperature

Ionizing radiation can be effective in controlling the growth of food spoilage and foodborne pathogenic bacteria. This study reports on an investigation of the effectiveness of irradiation treatment to eliminate Listeria monocytogenes on laboratory-inoculated broccoli, cabbage, tomatoes, and mung bean sprouts. Irradiation of broccoli and mung bean sprouts at 1.0 kGy resulted in reductions of approximately 4.88 and 4.57 log CFU/g, respectively, of a five-strain cocktail of L. monocytogenes. Reductions of approximately 5.25 and 4.14 log CFU/g were found with cabbage and tomato, respectively, at a similar dose. The appearance, color, texture, taste, and overall acceptability did not undergo significant changes after 7 days of postirradiation storage at 4°C, in comparison with control samples. Therefore, low-dose ionizing radiation treatment could be an effective method for eliminating L. monocytogenes on fresh and fresh-cut produce.

Effects of High-Pressure Processing on the Safety, Quality, and Shelf Life of Ready-to-Eat Meats

Ready-to-eat (RTE) meats (low-fat pastrami, Strassburg beef, export sausage, and Cajun beef) were pressure treated at 600 MPa, 20°C, for 180 s to evaluate the feasibility of using high-pressure processing (HPP) for the safe shelf-life extension of these products. After processing, samples were stored at 4°C for 98 days during which time microbiological enumeration and enrichments were performed. Additionally, sensory analyses were undertaken to determine consumer acceptability and purchase intent over the duration of storage. Counts of aerobic and anaerobic mesophiles, lactic acid bacteria, Listeria spp., staphylococci, Brochothrix thermosphacta, coliforms, and yeasts and molds revealed that there were undetectable or low levels for all types of microorganisms throughout storage. Comparison of consumer hedonic ratings for unprocessed and processed meats revealed no difference in consumer acceptability, and no deterioration in the sensory quality was evident for any of the products tested during the study. Additionally, inoculated pack studies were conducted to determine if HPP could be used as a postlethality treatment to reduce or eliminate Listeria monocytogenes and thus assess the potential use of HPP in a hazard analysis critical control point plan for production of RTE meats. Inoculated samples (initial level of 104 CFU/g) were pressure treated (600 MPa, 20°C, for 180 s) and stored at 4°C, and survival of L. monocytogenes was monitored for 91 days. L. monocytogenes was not detected by plating methods until day 91, but selective enrichments showed sporadic recovery in three of the four products examined. The results show that HPP at 600 MPa, 20°C, for 180 s can extend the refrigerated shelf life of RTE meats and reduce L. monocytogenes numbers by more than 4 log CFU/g in inoculated product.

Control of Listeria monocytogenes by low-dose irradiation in combination with refrigeration in the soft whey cheese ‘Anthotyros’

Soft whey cheese ‘Anthotyros’ has the following characteristics: moisture content 65%, protein content 9·6%, fat content 16·6%, salt concentration in the aqueous phase below 1% and pH 6·4. The average counts of the product were 4·54, 3·80, and 1·2 log cfu g−1 for aerobic mesophilic bacteria, yeasts and Enterobacteriaceae, respectively. The feasibility of gamma radiation for eliminating Listeria monocytogenes Scott A inoculated into the freshly produced product, and following its counts during refrigerated storage at 4 and 10°C under vacuum packaging was investigated. Cheese samples were exposed to doses of 0·5, 2 and 4 kGy of gamma irradiation at 4°C. Irradiation at 0·5 kGy slightly reduced the aerobic mesophilic bacteria counts, while irradiation doses at 2 and 4 kGy reduced the microbial load by approximately 1–2 log cycles. Enterobacteriaceae could not be detected in irradiated samples. Irradiation decreased the yeast population which was detected during later stages of storage. Molds were not detected in any of the samples. The calculatedD10 -value for L. monocytogenes was 1.38 kGy. Surviving microbial cells could be detected throughout the entire period of 42 days storage. Sensory scores indicated that irradiation doses up to 4 kGy do not adversely affect ‘Anthotyros’ sensory properties.