Effect of pomegranate (Punica granatum) pomace extract as a washing agent on the inactivation of Listeria monocytogenes inoculated on fresh produce

Pomegranate pomace extract (PPE) was used as a substitute to chlorinated water for washing of fresh produce. PPE contained punicalagins and ellagic acids, and it had a good inhibitory effect against Listeria monocytogenes based on the results of disc diffusion test and time‐kill assay. Red chard, beet, chicon and red mustard leaves were treated with 7 mg mL^?1 PPE as a washing solution to inactivate L. monocytogenes inoculated on fresh produce and compared with 0.05 mg mL^?1 NaOCl treatment. After the treatment, L. monocytogenes population on the four leafy vegetables was reduced by 1.96–2.97 log CFU g^?1 compared to that on nontreated samples. The reductions in L. monocytogenes after PPE treatment were higher than those observed after NaOCl treatment. Further, the PPE treatment did not affect the surface colour of all fresh produce applied in this study. Thus, PPE can be used as an effective antimicrobial washing agent of fresh produce.     

Combined washing effect of noni extract and oregano essential oil on the decontamination of Listeria monocytogenes on romaine lettuce

Combined washing effect of noni extract (NE) and oregano essential oil (OE) on the decontamination of Listeria monocytogenes on romaine lettuce was examined. The fractional inhibitory concentration index (FICI) between NE and three different essential oils (cinnamon leaf, thyme and OE) was determined. Fractional inhibitory concentration index results indicated that OE only had an additive effect (FICI = 1). Noni extract/oregano essential oil combined washing resulted in the greatest reduction in viable cell numbers (3.42 log CFU g⁻¹) relative to non-washed samples. Furthermore, the combined washing was more effective than sodium hypochlorite washing in terms of reducing the microbial load (>1.44-log reduction). Washing treatment did not change the surface colour or total phenolic content in lettuce samples. These results suggest that NE/OE combined washing is applicable as a novel decontamination treatment to ensure the microbial safety of romaine lettuce without changing the quality.     

Antimicrobial activity of Ginkgo biloba leaf extract on Listeria monocytogenes

ABSTRACT: The antimicrobial activities of Ginkgo biloba leaf extract (GBE) and the combined effects of GBE and sodium EDTA (sodium Ethylenediaminetetraacetic acid) against Listeria monocytogenes were determined at 4 °C, 25 °C, and 37 °C. Listeria monocytogenes grown at 37 °C for 24 h was inoculated (6 to 7 log CFU/mL) into BHI broth containing either GBE or GBE and EDTA (1.6 mg/mL) with various GBE concentrations of 0.1, 0.25, 0.5, 1, 2.5, 5.0, 7.5, 10.0, 15.0, or 20.0% vol/vol and stored at 4 °C, 25 °C, and 37 °C. The inhibitory effect of the GBE was more pronounced at low temperature of 4 °C. GBE was effective in inhibiting microbial growth. Addition of EDTA enhanced antimicrobial activity of GBE.     

Evaluation of risk impact of consumers' behaviour in terms of exposure to Listeria monocytogenes in lettuce

The influence that consumers have on the exposure assessment due to the presence of Listeria monocytogenes in lettuce was studied. Four stages of the food chain were considered: transport home, storage, handling and washing. A survey provided information about family behaviour classified as: one adult living alone (n = 77), one adult with children (n = 21), two adults (n = 75), two adults with children (n = 139) and seniors (n = 157). Multiple correspondence analyses revealed only slight differences between one adult living alone (with or without children) and the other groups. The simulation results highlighted that in all groups, ‘transportation’ and ‘storage at home’ did not increase contamination. In the ‘handling’ stage, Listeria was able to increase an average of 1 log CFU g^?1, and in ‘washing’, consumers were able to reduce it to the values at retail. Finally, sensitivity analysis demonstrated that washing and surface contamination were the practices that had most influence on the risk.     

Characterization of Listeria monocytogenes and Listeria innocua from a vegetable processing plant by RAPD and REA

The incidence of Listeria monocytogenes in a vegetable processing plant was investigated over a 23-month period. Frozen ready-to-eat vegetable samples, well as the plant environment, were sampled. The molecular subtyping techniques, Random Amplified Polymorphic DNA (RAPD) and Restriction Endonuclease Analyses (REA), were performed to help investigate the origin and routes of Listeria dissemination.

The low and sporadic incidence of L. monocytogenes made it impossible to establish an epidemiological sequence in the processing plant, though a case of cross-contamination between tomato and ratatouille was detected. Listeria innocua subtyping, however, allowed us to determine the prevalence of several strains in vegetables, and their presence on machinery samples suggested the possibility of cross-contamination during processing.

The low incidence of L. monocytogenes indicated that the risk of listeriosis transmission by vegetable consumption is low. On the other hand, the isolation of the same strain of L. innocua in several surveys pointed out the risk of colonisation on surfaces and machinery. The persistence of Listeria spp. is a cause for concern as can lead to future contamination of vegetables processed in the plant and to a possible increased risk for health. Therefore, periodic controls for the presence of Listeria spp. and a further review of the cleaning and disinfection procedures used in frozen vegetable plants are recommended.     

Radiation Sensitivity of Listeria monocytogenes on Beef as Affected by Temperature

Longissimus dorsi from beef was inoculated with Listeria monocytogenes and the effect of gamma irradiation on the survival of this pathogen at ?60 to +15°C was determined. Radiation D-values were determined for inactivation of L. monocytogenes at 5°C intervals from ?20 to 5°C. These data were used to develop an equation to predict the response to gamma radiation within that range. An abrupt increase in resistance occurred at ?5°C. The radiation D-value was 0.45 kGy at 0°C, 0.77 kGy at ?5°C and 1.21 kGy at ?20°C. A straight line was obtained when the log₁₀ of the D-values from ?5 to ?20°C was plotted vs the reciprocal of the absolute temperature. This led us to calculate a value analogous to the Arrhenius activation energy for inactivation of L. monocytogenes by gamma radiation.     

Cross-contamination of fresh-cut lettuce after a short-term exposure during pre-washing cannot be controlled after subsequent washing with chlorine dioxide or sodium hypochlorite

Chlorine dioxide (ClO₂) has been postulated as an alternative to sodium hypochlorite (NaClO) for fresh-cut produce sanitization to avoid risks associated with chlorination by-products. Experiments were performed to determine the prevention of cross-contamination of fresh-cut lettuce by Escherichia coli using chlorine dioxide (3 mg/L) or sodium hypochlorite (100 mg/L) as sanitation agents. The efficacy of these sanitation solutions was evaluated simulating as much as possible the conditions of a fresh-cut processing line. Thus, to evaluate the potential risk of cross-contamination during pre-washing, inoculated fresh-cut lettuce was pre-washed and after that non-inoculated lettuce was then pre-washed in the same water. After this pre-washing, non-inoculated lettuce was cross-contaminated, changing from 0 to 3.4 log units of E. coli cells. During washing with sanitizers, none of the tested sanitation agents significantly reduced E. coli counts in both inoculated and cross-contaminated lettuce. These results suggest that when cross-contamination occurs, even if the event is recent, subsequent sanitation steps are inefficient for inactivating E. coli cells on the vegetable tissue. However, chlorine dioxide and sodium hypochlorite solutions were able to inactivate most E. coli cells that passed from inoculated product to wash water. Therefore, they might be able to avoid cross-contamination between clean and contaminated product during the washing step. Scanning electron microscopy micrographs indicated that bacterial cells were mainly located in clusters or tissue stomata where they might be protected, which explains the low efficacy of sodium hypochlorite and chlorine dioxide solutions observed in this study.     

Evaluation of a novel antimicrobial (lauric arginate ester) substance against biofilm of Escherichia coli O157:H7, Listeria monocytogenes,and Salmonella spp.

The purpose of this study was to evaluate the activity of a novel antimicrobial substance lauric arginate ester (LAE) against selected foodborne pathogens (Escherichia coli O157:H7, Listeria monocytogenes and Salmonella spp.) in biofilm. Minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were determined and showed that LAE exhibits a strong antimicrobial activity. Biofilms were grown on abiotic stainless steel, rubber, MBEC biofilm device) and biotic (lettuce) surfaces. The efficacy of LAE (50, 100 and 200 ppm) at reducing the biofilm cells on these surfaces was examined by applying LAE for 2 h. Results revealed that LAE exhibited the reduction in biofilm bacteria up to 7 log CFU cm^?2, 3.5 log CFU cm^?2, 4.0 log CFU peg^?1 and 1.5 log CFU cm^?2 on stainless steel, rubber, MBEC and lettuce surfaces, respectively. Overall, these results suggest that LAE has been shown to be a potential alternative to control bacteria in biofilm mode in food industry.     

Use of organic acids to inactivate Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on organic fresh apples and lettuce

Abstract: This study was undertaken to investigate the antimicrobial effect of organic acids against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on whole red organic apples and lettuce. Several studies have been conducted to evaluate organic acids as sanitizers. However, no studies have compared antimicrobial effects of various organic acids on organic fresh produce, including evaluation of color changes of produce. Apples and lettuce were inoculated with a cocktail of 3 strains each of 3 foodborne pathogens provided above and treated with 1% and 2% organic acids (propionic, acetic, lactic, malic, and citric acid) for 0, 0.5, 1, 5, and 10 min. With increasing treatment time and acid concentration, organic acid treatments showed significant reduction compared to the control treatment (distilled water), and differences in antimicrobial effects between organic acids were observed. After 10 min of treatment with 1% and 2% organic acids in apples, propionic (0.92 to 2.75 log reduction), acetic (0.52 to 2.78 log reduction), lactic (1.69 to >3.42 log reduction), malic (1.48 to >3.42 log reduction), and citric acid (1.52 to >3.42 log reduction) exhibited significant (P < 0.05) antibacterial effects against 3 foodborne pathogens compared to the control treatment. In lettuce, propionic (0.93 to 1.52 log reduction), acetic (1.13 to 1.74 log reduction), lactic (1.87 to 2.54 log reduction), malic (2.32 to 2.98 log reduction), and citric acid (1.85 to 2.86 log reduction) showed significant (P < 0.05) effects compared to the control treatment. Changes in sample color subjected to organic acids treatment were not significant during storage. Practical Application: It is suggested that organic acids have a potential as sanitizers for organic fresh produce. These data may help the organic produce industry provide safe fresh produce for consumers.     

Potential of a nisin-containing bacterial cellulose film to inhibit Listeria monocytogenes on processed meats

A bacterially produced cellulose film containing nisin was developed and used in a proof-of-concept study to control Listeria monocytogenes and total aerobic bacteria on the surface of vacuum-packaged frankfurters. Bacterial cellulose pellicles were produced by Gluconacetobacter xylinus K3 in Corn Steep Liquor-Mannitol Medium and were subsequently purified before nisin was incorporated into them. Investigations into the effect of nisin concentrations and contact times on incorporation of nisin into cellulose films showed that the lowest nisin concentration and shortest time needed for production of an effective antimicrobial cellulose film were 625IUml(-1) and 6h, respectively. The active cellulose films produced under these conditions did not, however, significantly reduce L. monocytogenes populations on frankfurters (P>0.05) during refrigerated storage for 14 days as compared to the controls. Films produced using a higher concentration of nisin (2500IUml(-1)) with the same exposure time (6h) resulted in a significant (P<0.05) decrease in L. monocytogenes counts on frankfurters of approximately 2logCFUg(-1) after 14 days of storage as compared to the control. Both the above-mentioned films showed a similar effectiveness in reducing total aerobic bacterial populations as measured by total aerobic plate counts on frankfurters. For both films, total aerobic bacterial levels were significantly (P>0.05) reduced by approximately 3.3logCFUg(-1) after 14 days of storage as compared to control samples. Bacterial cellulose films were demonstrated in this study to have potential applicability as antimicrobial packaging films or inserts for processed meat products.     

复配抑菌剂对单增李斯特菌的抑制作用及其保鲜效果

研究溶菌酶、甘氨酸和乙酸钠对单增李斯特菌的抑制效果,通过单因素抑菌率的结果,运用响应面法优化三种抑菌剂复配后对单增李斯特菌的抑制效果,并且将得到的最优浓度复配抑菌剂用来保鲜感染了单增李斯特菌的三文鱼,以细菌总数、单增李斯特菌数、pH、TBA值和TVB-N值为指标,研究复配抑菌剂的保鲜效果。结果表明:溶菌酶0.6 g/L、甘氨酸浓度为6.4 g/L、乙酸钠浓度为4.9 g/L为复合保鲜剂的最佳配比,此条件下对单增李斯特菌的抑菌率为80%±0.23%。冷藏条件下,经复配抑菌剂处理后的三文鱼品质优于未经处理的空白组,第7 d时,实验组细菌总数、单增李斯特菌数、pH、TBA值和TVB-N值分别为5.56 lg CFU/g、4.65 lg CFU/g、6.78、1.048 mg MDA/kg、18.03 mg N/100 g,相比空白组,能延长2 d的货架期。      

发酵火腿中单核细胞增生李斯特氏菌限量探讨与建议

在长期的发酵过程中,火腿表层的水分活度小于0.92;发酵火腿成品的水分活度也小于0.92。在此条件下,单核细胞增生李斯特氏菌不能生长,但仍能存活较长时间。发酵火腿成品无需冷藏即可贮存。目前的增菌培养检测法不适用于发酵火腿中单核细胞增生李斯特氏菌的检测。本文建议发酵火腿中单核细胞增生李斯特氏菌的限量为100CFU/g;或者,不将单核细胞增生李斯特氏菌列为发酵火腿中需要检测的项目。     

单核细胞增生李斯特氏菌实时荧光RPA检测方法的建立及应用

本研究旨在建立一种快速检测单核细胞增生李斯特氏菌(Listeria monocytogenes,LM)的实时荧光重组酶聚合酶扩增(real-time RPA)方法。基于LMhly A基因保守序列,设计合成特异性RPA引物和exo探针,所建立的LM real-time RPA方法能够在37℃等温条件下20 min内完成扩增。该方法仅对LM基因组DNA为阳性扩增,对其它20种致病菌基因组DNA的扩增均为阴性;以LM纯培养菌液的基因组DNA进行10倍列梯度稀释,并以之作为模板,其灵敏性可达到5×10-1 pg,与实验室已建立的real-time PCR方法一致。人工污染实验中,对于LM接菌量为3 CFU/25 g的羊肉和生菜样品,增菌14 h即可通过建立的real-time RPA方法检出,与传统培养方法和real-time PCR检测结果均一致,但是前者所需时间明显少于后者。本文建立的LM real-time RPA方法特异性强,灵敏性高,操作简单,反应迅速,并能够摆脱对价格昂贵的荧光PCR仪和专业实验室的需求,可应用于食品突发事件中LM的现场快速检测,对保障我国食品安全具有重要意义。     

Modeling the growth rate and lag time of different strains of Salmonella enterica and Listeria monocytogenes in ready-to-eat lettuce

The growth parameters (growth rate, μ and lag time, λ) of three different strains each of Salmonella enterica and Listeria monocytogenes in minimally processed lettuce (MPL) and their changes as a function of temperature were modeled. MPL were packed under modified atmosphere (5% O₂, 15% CO₂ and 80% N₂), stored at 7–30 °C and samples collected at different time intervals were enumerated for S. enterica and L. monocytogenes. Growth curves and equations describing the relationship between μ and λ as a function of temperature were constructed using the DMFit Excel add-in and through linear regression, respectively. The predicted growth parameters for the pathogens observed in this study were compared to ComBase, Pathogen modeling program (PMP) and data from the literature. High R² values (0.97 and 0.93) were observed for average growth curves of different strains of pathogens grown on MPL. Secondary models of μ and λ for both pathogens followed a linear trend with high R² values (>0.90). Root mean square error (RMSE) showed that the models obtained are accurate and suitable for modeling the growth of S. enterica and L. monocytogenes in MP lettuce. The current study provides growth models for these foodborne pathogens that can be used in microbial risk assessment.     

Nisin和柠檬酸对鲜切皇冠梨储藏期间单增李斯特菌生长的影响

分别采用0.05mg/m L乳酸链球菌素(Nisin)、0.3%柠檬酸复配溶液和自来水清洗接种单增李斯特菌(LM)的鲜切皇冠梨,将清洗后的鲜切皇冠梨分别于4、12、24℃的条件下储藏,以未清洗的样品为对照,测定储藏过程中LM的生长情况。结果显示Nisin和柠檬酸清洗能显著降低(p<0.05)鲜切皇冠梨中LM的初始带菌量。在4℃储藏过程中,Nisin和柠檬酸清洗的鲜切皇冠梨中LM数量没有明显变化(p>0.05),自来水清洗和未清洗的鲜切样品中LM数量略有升高。在12℃和24℃储藏期间,三种处理方式的鲜切皇冠梨LM数量均显著上升(p<0.05)。Nisin和柠檬酸复配清洗处理结合低温储藏能有效控制鲜切皇冠梨中LM的生长。      

Green tea extract as a natural antioxidant to extend the shelf-life of fresh-cut lettuce

Green tea extract (GT) was evaluated as a preservative treatment for fresh-cut lettuce. Different quality markers, e.g. respiration, browning, ascorbic acid and carotenoid content were evaluated. GT concentration (0.25, 0.5 and 1 g 100 mL^− 1) and temperature (20 °C and 50 °C) were tested. Optimal GT treatment (0.25 g 100 mL^− 1 at 20 °C) was compared with chlorine (120 ppm at 20 °C). High GT concentrations (0.5 g 100 mL^− 1 and 1.0 g 100 mL^− 1) maintained better prevent ascorbic acid and carotenoid loss than 0.25 g 100 mL^− 1 GT and chlorine. GT increased browning of samples, probably due to the content of polyphenols of the treatment; the use of heat-shock reduced this negative effect. GT and heat-shock combined also showed negative effects, reducing the antioxidant content (ascorbic acid and carotenoids). No significant differences were observed between chlorine and optimal GT (0.25 g 100 mL^− 1 at 20 °C) in browning appearance and sensory properties. GT better kept the antioxidant activity of the samples than chlorine.

Industrial relevance

An alternative treatment for minimally processed Iceberg lettuce is tested, based on its antioxidant capacity. Minimally processed industry is constantly looking for new treatments to avoid the use of chlorine which is a standard at the moment.     

ADSA Foundation Scholar Award--An integrated science-based approach to dairy food safety: Listeria monocytogenes as a model system

Transmission of food- and milkborne pathogens often involves complex interactions among the pathogen, the environment, and one or multiple host species. A complete understanding of these interactions is critical to allow the development of science-based, effective intervention strategies for foodborne infectious diseases. This article summarizes our studies on the transmission, ecology, pathogenesis and population genetics of Listeria monocytogenes, which we have used as model for a food- and milkborne pathogen that infects multiple hosts and also has considerable ability to survive and multiply in nonhost environments. Application of molecular subtyping tools in conjunction with phenotypic characterization of selected strains has allowed us to define distinct L. monocytogenes subtypes and clonal groups that appear to differ in relevant phenotypic characteristics that may affect their abilities to be transmitted through food systems. For example, a genetic group designated as lineage I has been shown to be not only more common among human listeriosis cases than among animal cases, but lineage I strains also appear to show an increased in vitro ability to spread intracellularly from host cell to host cell. These findings are consistent with the fact that while genetically diverse strains may be classified to one bacterial species, these strains often differ from one another in important genetic and phenotypic characteristics. I thus propose that evolutionary- and molecular subtyping-based definitions of bacterial subtypes and clonal groups will provide critical insight into the microbial ecology of dairy food systems, including not only foodborne pathogens, but also organisms important for dairy fermentation and spoilage.     

Development of a Steam Treatment to Eliminate Listeria monocytogenes From King Salmon (Oncorhynchus tshawytscha)

ABSTRACT: A pilot plant steam treatment system was developed to reduce L. monocytogenes contamination on exterior surfaces of King Salmon ( Oncorhynchus tshawytscha prior to processing. Numbers of surviving L. monocytogenes cells on the surface were determined using an enrichment-based Most Probable Number (MPN) technique. Inoculated L. monocytogenes cells were not recovered from the surface of salmon after exposure to the steam treatment for 8 sec. A 4-log reduction in L. monocytogenes numbers was obtained. Treated salmon could be processed into a high-yielding, high-quality cold smoked product. An in-plant system was subsequently shown to reduce "naturally" occurring L. monocytogenes numbers and produce a high quality final product.     

Behavior of Listeria monocytogenes inoculated on cantaloupe surfaces and efficacy of washing treatments to reduce transfer from rind to fresh-cut pieces

Attachment and survival of Listeria monocytogenes on external surfaces (rind) of inoculated cantaloupe, resistance of the surviving bacteria to chlorine or hydrogen peroxide treatments, transfer of the pathogen from unsanitized and sanitized rinds to fresh-cut tissues during cutting and growth, and survival of L. monocytogenes on fresh-cut pieces of cantaloupe were investigated. Surface treatment with 70% ethanol to reduce the native microflora on treated melon, followed by immersion in a four-strain cocktail of L monocytogenes (10(8) CFU/ml) for 10 min, deposited 4.2 log10 CFU/cm2 and 3.5 log10 CFU/cm2 of L monocytogenes on treated and untreated cantaloupe rinds, respectively. L. monocytogenes survived on the treated or untreated cantaloupe rinds for up to 15 days during storage at 4 and 20 degrees C, but populations declined by approximately 1 to 2 log10 CFU/cm2. Fresh-cut pieces prepared from inoculated whole cantaloupes stored at 4 degrees C for 24 h after inoculation were positive for L. monocytogenes. Washing inoculated whole cantaloupes in solutions containing 1,000 ppm of chlorine or 5% hydrogen peroxide for 2 min at 1 to 15 days of storage at 4 degrees C after inoculation resulted in a 2.0- to 3.5-log reduction in L. monocytogenes on the melon surface. Fresh-cut pieces prepared from the sanitized melons were negative for L. monocytogenes. After direct inoculation onto fresh-cut pieces, L. monocytogenes survived, but did not grow, during 15 days of storage at 4 degrees C. Growth was evident by 4 h of storage at 8 and 20 degrees C. It is concluded that sanitizing with chlorine or hydrogen peroxide has the potential to reduce or eliminate the transfer of L. monocytogenes on melon surfaces to fresh-cut pieces during cutting.     

基于FSO值对生熟食品交叉污染中单增李斯特菌的危害识别

为定性分析生熟食品中单增李斯特菌在不同案板材质上的交叉污染,选定木制、塑料及不锈钢案板为材质研究对象,设置4种常见场景,并测定各案板材质不同场景下卤猪舌、案板与黄瓜中单增李斯特菌的污染水平(lg CFU/g)。同时,选择一级Baranyi模型修改式,二级主参数模型对黄瓜中单增李斯特菌的生长进行模拟。此外,根据食品安全目标(FSO)计算整个交叉污染过程的污染水平,并以即食食品中单增李斯特菌的FSO值2(lg CFU/g)为标准,与12种交叉污染情景(4种场景×3种材质)比较,并进行风险等级排序。结果表明:木质案板场景1(S1w)、塑料案板场景1(S1p)和不锈钢案板场景1(S1s)风险等级最高;场景2、3和4下,木质案板风险等级分别为2、3和3,高出塑料和不锈钢案板(3、4和4)一个风险等级。本研究表明对案板不进行任何清洗处理最易引发交叉污染,木质案板相较于其他2种案板材质的风险较大。