Monocytogenes In Products Research Articles

New Term to Quantify the Effect of Temperature on pH min -Values Used in Cardinal Parameter Growth Models for Listeria monocytogenes.

The aim of this study was to quantify the influence of temperature on pHmin-values of Listeria monocytogenes as used in cardinal parameter growth models and thereby improve the prediction of growth for this pathogen in food with low pH. Experimental data for L. monocytogenes growth in broth at different pH-values and at different constant temperatures were generated and used to determined pHmin-values. Additionally, pHmin-values for L. monocytogenes available from literature were collected. A new pHmin-function was developed to describe the effect of temperatures on pHmin-values obtained experimentally and from literature data. A growth and growth boundary model was developed by substituting the constant pHmin-value present in the Mejlholm and Dalgaard (2009) model (J. Food. Prot. 72, 2132–2143) by the new pHmin-function. To obtain data for low pH food, challenge tests were performed with L. monocytogenes in commercial and laboratory-produced chemically acidified cheese including glucono-delta-lactone (GDL) and in commercial cream cheese. Furthermore, literature data for growth of L. monocytogenes in products with or without GDL were collected. Evaluation of the new and expanded model by comparison of observed and predicted μmax-values resulted in a bias factor of 1.01 and an accuracy factor of 1.48 for a total of 1,129 growth responses from challenge tests and literature data. Growth and no-growth responses of L. monocytogenes in seafood, meat, non-fermented dairy products, and fermented cream cheese were 90.3% correctly predicted with incorrect predictions being 5.3% fail-safe and 4.4% fail-dangerous. The new pHmin-function markedly extended the range of applicability of the Mejlholm and Dalgaard (2009) model from pH 5.4 to pH 4.6 and therefore the model can now support product development, reformulation or risk assessment of food with low pH including chemically acidified cheese and cream cheese.

Thermal Inactivation of Salmonella and Listeria monocytogenes in Peanut Butter–Filled Pretzels and Whole Wheat Pita Chips

Recent recalls and outbreaks due to foodborne pathogens in thermally processed low-moisture foods highlight the need for the food industry to validate their thermal process. The purpose of this study was to validate baking as an adequate lethality step in controlling Salmonella and Listeria monocytogenes during the production of peanut butter (PB)-filled pretzels and whole wheat (WW) pita chips. Two dough types, PB-filled pretzel and WW pita chip with varying water activities (0.96 to 0.98), were inoculated (target level, ∼108 to 109 CFU/g) with a multistrain cocktail of Salmonella and L. monocytogenes in separate trials and were baked at 300°F (148.9°C) and 350°F (176.6°C) for 0, 5, 10, 17, 25, and 30 min. Following baking, samples were rapidly cooled and analyzed for Salmonella and L. monocytogenes by the pour plate method. Uninoculated samples were analyzed for total viable aerobic plate count (APC) and Enterobacteriaceae counts. Water activity analysis was also performed. The experiment was replicated three times. Nonlinear regression was used to estimate the baking times required to achieve a minimum of 4- and 5-log reduction in APC, Salmonella, and L. monocytogenes. A 4- and 5-log reduction in APC was predicted following a treatment at 350°F for 3.3 and 5.6 min in WW pita chip product, respectively. Following a treatment of 350°F for 10 and 25 min, Enterobacteriaceae and APC counts were below the detection limit (<1 log CFU/g), respectively, in all of the PB-filled pretzel samples. Salmonella and L. monocytogenes counts decreased with increasing baking time regardless of the temperature used. Significant reductions (≥5-log reduction) were estimated in Salmonella and L. monocytogenes in product baked at 350°F for 15.5 and 17.5 min in WW pita chip dough and PB-filled pretzel dough, respectively. Both pathogens were below the detection limit (<1 log CFU/g) in PB-filled pretzel and WW pita chip products under baking conditions of 350°F for 25 and 30 min, respectively. This study demonstrates that PB-filled pretzel and WW pita chip products, when baked to saleable quality, will not present a public health risk from the standpoint of Salmonella or L. monocytogenes.

LISTERIA MONOCYTOGENES: OCORRÊNCIA EM PRODUTOS LÁCTEOS E SUAS IMPLICAÇÕES EM SAÚDE PÚBLICA

RESUMO Listeria monocytogenes é o agente causador da listeriose, uma grave doença de origem alimentar que causa severas infecções em humanos com altas taxas de mortalidade. O leite e seus derivados estão entre os produtos alimentícios mais frequentemente envolvidos na transmissão de L. monocytogenes. A listeriose acomete, sobretudo, indivíduos imunodeprimidos, grávidas, recém-nascidos e idosos, o que ressalta o caráter oportunista deste micro-organismo e sua importância para a saúde pública. No presente trabalho, faz-se uma revisão narrativa crítica sobre o risco à saúde humana decorrente da ingestão de leite e derivados contaminados por L. monocytogenes, bem como se discutem os fatores que determinam a contaminação por L. monocytogenes na cadeia de produção e distribuição de leite e derivados. São apresentados e avaliados os dados de ocorrência de L. monocytogenes em leite cru e em produtos lácteos no Brasil, tendo em vista seu potencial de envolvimento em casos de listeriose humana. Adicionalmente, são indicadas as principais áreas de pesquisa e atuação para prevenir a contaminação de L. monocytogenes em produtos lácteos.

Impact of storage temperature and product pH on the survival of Listeria monocytogenes in vacuum-packaged souse.

Souse is a fully cooked, ready-to-eat gelled pork product. There is a zero-tolerance policy for Listeria monocytogenes in ready-to-eat meat products. The survival and/or growth of L. monocytogenes in souse is unknown. The effectiveness of three different souse formulations (pH 4.3, 4.7, and 5.1) for controlling the growth of L. monocytogenes at two refrigerated storage temperatures (5 and 10 degrees C) was evaluated. All products were vacuum packaged. Uninoculated product was prepared as the control, and other products were artificially surface contaminated with a three-strain cocktail of L. monocytogenes (10(6) CFU/ cm2). Microbial counts were obtained on selective and nonselective media twice weekly through 8 weeks of storage. Souse did not support the growth of L. monocytogenes regardless of product formulation or storage temperature. At 5 degrees C, D-values for products with pH values of 4.7 and 5.1 were not different, but survival of L. monocytogenes in product with a lower pH (4.3) was decreased compared with survival in products with higher pH values (P < 0.05). Survival of L. monocytogenes was not impacted by storage temperatures (P > 0.05). Consumer acceptability (n = 75 souse consumers) of pH 4.3 products was not different from that for (typical) pH 4.7 products (P > 0.05). These results indicate that conventionally produced souse does not support the growth of L. monocytogenes and that inactivation of the organism is more likely in products formulated at a lower pH (< or = 4.3) without affecting consumer acceptance.

Survival, Growth, and Thermal Resistance of Listeria monocytogenes in Products Containing Peanut and Chocolate

Outbreaks of listeriosis associated with the consumption of ready-to-eat foods have raised interest in determining growth, survival, and inactivation characteristics of Listeria monocytogenes in a wide range of products. A study was undertaken to determine the thermal tolerance of L. monocytogenes in a peanut-based beverage (3.1% fat), whole-fat (3.5%) milk, whole-fat (4.0%) and reduced-fat (1.0%) chocolate milk, a chocolate-peanut spread (39% fat), and peanut butter (53% fat). The D60°C value (decimal reduction time at 60°C) in peanut beverage (3.2 min) was not significantly different (P > 0.05) than the D60°C value in whole-fat milk (3.3 min) or whole-fat chocolate milk (4.5 min) but significantly lower (P ≤ 0.05) than the D60°C value in reduced-fat chocolate milk (5.9 min). The pathogen was significantly more resistant to heat when enmeshed in chocolate-peanut spread (water activity [aw] of 0.46; D60°C = 37.5 min) and peanut butter (aw of 0.32; D60°C = 26.0 min) than in liquid products. At 10°C, the pathogen grew most rapidly in whole-fat chocolate milk and slowest in peanut beverage. At 22°C, populations increased significantly within 12 and 16 h in whole-fat milk and reduced-fat chocolate milk, respectively, and within 8 h in whole-fat chocolate milk and peanut beverage. Initial populations (3.37 to 4.42 log CFU/g) of L. monocytogenes in chocolate-peanut spread and peanut butter adjusted to an aw of 0.33 and 0.65 declined, but the pathogen was not eliminated during a 24-week period at 20°C. Survival was enhanced at reduced aw. Results indicate that a pasteurization process similar to that used for full-fat milk would be adequate to ensure the destruction of L. monocytogenes in peanut beverage. The pathogen survives for at least 24 weeks in chocolate-peanut spread and peanut butter at an aw range that encompasses that found in these products.

Thermal Inactivation of Salmonella and Listeria Monocytogenes in Ground Chicken Thigh/Leg Meat and Skin

Thermal inactivation D and z values of Salmonella and Listeria monocytogenes were obtained for chicken thigh and leg meat and skin. The D values of Salmonella at 55 to 70°C were 43.33 to 0.07 min in the meat and 43.76 to 0.09 min in the skin. The D values of L. monocytogenes at 55 to 70°C were 38.94 to 0.04 min in the meat and 34.05 to 0.05 min in the skin. The z value of Salmonella was 5.34°C in the meat and 5.56°C in the skin. The z value of L. monocytogenes was 5.08°C in the meat and 5.27°C in the skin. For Salmonella or L. monocytogenes, the z value of the meat was not different from that of skin. However, the z value of Salmonella in meat or skin was different from that of L. monocytogenes in meat or skin. The z value of Salmonella or L. monocytogenes in chicken thigh and leg meat was different from that in the skin. The results from this study are useful for predicting process lethality of Salmonella and L. monocytogenes in products that contain chicken thigh and leg meat or skin.

Listeria monocytogenes in Products of Animal Origin in Turkey

A study was carried out on 430 samples of different foodstuffs (soft cheese, raw chicken, minced beef, sausage, fish) and 400 carcase samples (sheep, young and adult cattle) for screening of Listeria monocytogenes. It was found that only one of the samples contained L. monocytogenes at > 10(3) cfu/ml in the initial examination, but another 42 samples contained L. monocytogenes following an enrichment process. L. monocytogenes was isolated most frequently from raw chicken samples (18%), but was not isolated from sausage samples. Forty-three isolates were defined as serotypes by using Bacto-Listeria-O-antisera Type 1 (Difco 2300-50-2) and Type 4 (Difco 2301-50-1) except that Type poly was not used. For these reasons, all isolates were classified as type 1 or type 4 and the other was termed untypeable. Twenty-one samples were type 1, 17 were untypeable, and 5 were both serotype 4 and untypeable.

Quantitative risk assessment for Listeria monocytogenes in smoked or gravad salmon and rainbow trout in Sweden

The objective of the present work was to develop a quantitative risk assessment model in which the exposure and risk of acquiring listeriosis from consumption of packaged smoked or gravad salmon and rainbow trout were estimated. An Excel spreadsheet model was constructed in which variables were represented by distributions based on surveys of L. monocytogenes in these food products, and on demographic and consumption data. Growth or inactivation was not included in the model. The model was run through Monte Carlo simulations using the @Risk software (Palisade Corporation). The probability of illness per serving was calculated using two dose-response models from the literature. The first was an exponential model in which the species specific constant R, that helps define the dose-response curve, previously has been estimated to be 1.18×10 −10 based on German data (GR). In this study, R was estimated to 5.6×10 −10 based on Swedish data. The second model was a flexible Weibull–Gamma model (WG), with different coefficients for high- and low-risk groups. The exponential model (GR), although conservative and generally overestimating the risk, still predicted a lower probability of illness than the WG-model. The estimated mean risk per serving was 2.8×10 −5 (GR, high-risk group), 2.0×10 −3 (WG, low-risk group) and 0.016 (WG, high-risk group), respectively. The average number of reported listeriosis cases in Sweden is 37 per year. In comparison, the mean number of annual cases predicted by the risk assessment model was 168 (range 47 to 2800, GR, high-risk group), and 95 000 (range 34 000 to 1.6×10 6, WG high-risk group), respectively. If 1 to 10% (uniform distribution) of strains, instead of all, were considered virulent, the mean number of predicted cases would decrease to nine (GR) and 5200 (WG), respectively. The mean annual cumulative individual risk in the high-risk group based on a monthly exposure was estimated to be 4.0×10 −4 (range 8.0×10 −8 to 5.4×10 −3, GR). This risk increased to 1.5×10 −3 (range 1.7×10 −5 to 9.2×10 −3, GR) based on a weekly exposure. The risk assessment model was most sensitive to the input distribution describing the level of contamination and to a lesser degree on the prevalence of L. monocytogenes, the proportion of virulent strains, and serving sizes. A lack of data on the prevalence and concentration of L. monocytogenes in these products, dose-response data and quantitative information on the proportion of virulent strains were identified.