Pathogens in low-moisture foods are an emerging food safety concern due to increased survival and thermotolerance in matrices with low water activity. However, limited data is publicly available for the thermotolerance of Listeria monocytogenes, Salmonella spp., and Enterococcus faecium NRRL B-2354 (a Salmonella surrogate). The aims of this study were to identify differences in thermal inactivation rates between these organisms in three different low-moisture foods. Three model low-moisture foods (peanut butter, powder infant formula, and wheat flour) were inoculated with either E. faecium, a Salmonella spp. cocktail, or a L. monocytogenes cocktail using a dry inoculation method for a total of 9 treatments. Samples were heat treated in a hot water bath at predetermined temperatures, and bacterial survival was detected via direct plating on tryptic soy agar with 0.6% yeast extract. In peanut butter and most of the powder infant formula treatments, Salmonella spp. had significantly higher D-values than L. monocytogenes using comparable temperatures (p < 0.05). However, D-values between Salmonella spp. and L. monocytogenes were comparable in wheat flour and one of the treatment temperatures in powder infant formula (p > 0.05). For all but one of the treatments at the same temperature, E. faecium had significantly higher D-values than L. monocytogenes and Salmonella spp. in each food matrix (p < 0.05). The observed matrix effect on thermotolerance for each of the bacteria was reported in descending order as powder infant formula > peanut butter > wheat flour in the majority of the comparable D-values. While Salmonella continues to be the pathogen of concern in low-moisture foods due to survival and outbreaks, these results indicate L. monocytogenes can exhibit similar thermotolerances in relevant model low-moisture foods matrices.

Vegetative, non-sporeforming foodborne pathogens show notable survival and uncanny thermotolerance in low water activity (aw) foods. Controlled studies on Listeria monocytogenes, Salmonella spp., and Enterococcus faecium NRRL B-2354 (a Salmonella surrogate) in a variety of food matrices support thermal process validation studies required to achieve global food safety objectives. In this study, we determined and compared thermal inactivation rates using independent six-strain cocktails of pathogens in three plant-based butters. Direct determinations of decimal reduction times (D-values) for L. monocytogenes, Salmonella, and E. faecium, in corresponding butters were inoculated using peanut oil, almond oil, or sunflower oil. Thermal Death Time (TDT) studies for the organisms were conducted in triplicate. Uniform bagged plant- based butter samples of Salmonella spp. or L. monocytogenes, or E. faecium alone were sandwiched in copper plates immobilized with recessed magnets. Samples underwent rapid heat treatments via water immersion under isothermal conditions ranging from 70°C to 85°C. Bacterial destruction in peanut butter (46% fat, 0.20 aw @ 25°C), almond butter, (50% fat, 0.32 aw @ 25°C), or sunflower butter (56% fat, 0.15 aw @ 25°C) was determined by direct plating. The TDT studies showed Salmonella spp. had consistently higher D-values than L. monocytogenes in all treatments, but pair-wise comparisons found no statistical difference when assessing the thermotolerance of the two pathogens in the individual plant-based butters tested (p > 0.005). These data support Salmonella as the primary pathogen of concern in low water activity foods and show the heat resistance of L. monocytogenes can approximate destruction kinetics observed for Salmonella spp. in low aw matrices. E. faecium exhibited the highest thermotolerance. This further supports the utility of this surrogate for Salmonella spp. and L. monocytogenes in high fat, low-moisture foods similar to the plant-based butters tested. Thermotolerance differences between a dry talc vs. peanut oil-based inoculation procedures in peanut butter were also evaluated. Surprisingly, the oil-based inoculations resulted in lower D- values (p > 0.01) for Salmonella spp. and the surrogate when compared to the dry inoculum.

<p>In recent years, numerous multistate foodborne outbreaks have been reported that are often associated with low moisture foods (LMFs). The survival of microorganisms in low moisture conditions has become one of the major concerns in the food industry. With the increasing number of recalls, it is necessary to ensure food safety by developing and validating the process parameters. Establishing a thermal process requires a detailed understanding of the inactivation kinetics of the target pathogen with respect to both the process (temperature, time, equipment) and the product conditions (water activity, composition). Along with the most widely used conventional thermal processing, there has been an increase in the demand for natural or minimally processed foods. As a result, many alternative non-thermal processing approaches that provide antimicrobial benefits while retaining the quality attributes of the food product are under investigation. This research focused on studying the inactivation kinetics of foodborne pathogens <em>Salmonella enteritidis</em> PT30 and <em>Cronobacter</em> <em>sakazakii</em> in powdered LMFs using both the thermal and non-thermal (cold plasma) processing technologies. The efficacy of a dielectric barrier discharge cold plasma equipment was tested against pathogens <em>Salmonella</em> <em>enteritidis</em> PT30 and <em>Cronobacter</em> <em>sakazakii</em> in LMFs at 70 kV, resulting in 3.8 log reduction in <em>Cronobacter</em>, and 4.41 log reduction in <em>Salmonella</em> after 5 min of cold plasma treatment in pea protein. The cellular damage to the pathogens was examined by transmission electron microscopy (TEM), and the reactive oxygen (ROS: OH, O) and nitrogen (RNS: N₂, N₂⁺) species were identified using optical emission spectroscopy. The RMSE for the model was found to be between 0.11 and 0.36 with the low standard error of the parameters (δ, n, and log N₀), which illustrated that the Weibull model was a good fit for the experimental inactivation data. </p> <p>In the thermal processing study, the inactivation kinetic parameters of these pathogens were estimated at 70, 80, and 90 °C at 0.11, 0.22, and 0.33 water activity in pea protein powder. The non-isothermal temperature profiles were simulated by building a two dimensional, axisymmetric heat transfer model of the test cell. The inactivation parameters D_ref, z_T, and z_aw were estimated in MATLAB by using a one-step non-linear regression analysis, which was a combination of the primary log-linear model with the secondary modified-Bigelow model. The model was found to be a good fit, showing lower root mean square error (RMSE) and residuals. Further, <em>Enterococcus</em> <em>faecium</em> was observed to have higher D-values at all the processing temperatures and water activity levels as compared to <em>Salmonella enteritidis</em> PT30 and <em>Cronobacter</em> <em>sakazakii</em>, which provides valuable evidence that <em>Enterococcus</em> <em>faecium</em> can be used as a surrogate microorganism for validating the thermal process for pea protein powder.</p>

Salmonella enterica serotypes have been linked to outbreaks associated with low water activity foods. The ability of biofilm forming pathogens, such as Salmonella, to survive thermal and chemical processes is improved; it is unclear if biofilms will also improve survival to desiccation and gastric stresses. The purpose of this study was to quantify the effect of physiological state (planktonic versus biofilm) and prior exposure to desiccation on Salmonella survival and gene expression after passage through an in-vitro digestion model. Cells of Salmonella enterica serotype Tennessee were deposited onto membranes for planktonic cells or on glass beads to create biofilms. The cells were subsequently dried at room temperature and stored in dried milk powder (aw = 0.3) for up to 30 days. Salmonella survival was quantified by serial dilution onto brilliant green agar before desiccation, after desiccation, after 1-day storage and after 30-day storage. At each sampling both physiological states were tested for survival through a simulated gastrointestinal system. RNA was extracted at the identical time points and relative gene expression determined for genes associated with stress response (rpoS, otsB), virulence (hilA, hilD, invA, sipC) and a housekeeping gene 16S rRNA using quantitative real-time PCR. The physiological state and length of storage effected the survival and gene expression of Salmonella within the desiccated milk powder environment and after passage through an in-vitro digestion system (p<0.05). Larger numbers of S. Tennessee were recovered by plate counts for biofilm cells, compared to planktonic cells. However, the numbers of 16S rRNA gene copies were not significantly different suggesting entry of S. Tennessee into a viable but non-culturable state. Prolonged storage in dry milk powder was not associated with increased cross-protection to gastric stress. Increased expression of stress response genes rpoS and otsB correlated with survival, indicating cross protection of low water activity and acid stress. Increased expression of virulence-associated genes was seen in cells exposed to short periods of dry storage, suggesting an increased virulence potential. / Master of Science in Life Sciences

No description available.

Hårdgörning av trä syftar till att göra materialet hårdare. Detta går att åstadkomma genom komprimering, det komprimerade materialet tenderar dock att återgå mot sin ursprungsform då materialet utsätts för fukt om ingen låsning sker. Låsningen kan ske mekaniskt i en treskiktskonstruktion som motverkar träets fuktrörelser. Dessa skivor har dock visat sig vara instabila och tidigare försök har uppvisat deformationer i form av kupning. Denna undersökning syftar till att utreda förutsättningarna för att använda komprimerad asp samt att ta fram underlag för framtagning av en kommersiell produkt. Praktiska tester har genomförts för att studera hårdhet, återfjädring och densitet hos det komprimerade virket. Vidare har treskiktsskivor tagits fram för att testa om det går att få en stabil konstruktion genom att variera tjockleken på spärrskiktet. Även skillnader i acklimatiseringstid och fuktkvotens inverkan för virkets återfjädring har studerats. Resultaten visar på att aspens hårdhet efter komprimering blir i samma nivå som bok och ask, en låg fuktkkvot vid komprimering av materialet ger en låg återfjädring, komprimerat material har en längre acklimatiseringstid till jämviktsfuktkvot och materialet går att låsa tvärs fiberriktningen i en treskiktskonstruktion. / To make wood harder it can be densified. This can be achieved by compression, the compressed material tends to return to the original shape when it is exposed to moisture fluxations and if no form of fixation occurs. The fixation can be done mechanically in a three-layer panel construction which reduce movements in the timber. These panels have been found to be unstable and previous attempts have shown deformations in form of cupping. This study aims to evaluate the conditions for using compressed aspen wood, and to provide a basis for development of a commercial product. Practical tests have been conducted to study hardness, springback and density of the compressed wood. In addition, three-layer panels have been developed to test whether it is possible to have a stable construction by varying the thickness of the buttom layer. Differences in acclimatisation time and the moisture contents effect on the springback has aslo been studied. The results show that the hardness of aspen wood after compression is in equal levels with beech and ashes, a low moisture contet provides a low springback, compressed timber have a longer time for acclimatisation and it is possible to fixate the material in the direction across the grain in a three-layer panel construction.

<p>Hårdgörning av trä syftar till att göra materialet hårdare. Detta går att åstadkomma genom komprimering, det komprimerade materialet tenderar dock att återgå mot sin ursprungsform då materialet utsätts för fukt om ingen låsning sker. Låsningen kan ske mekaniskt i en treskiktskonstruktion som motverkar träets fuktrörelser. Dessa skivor har dock visat sig vara instabila och tidigare försök har uppvisat deformationer i form av kupning. Denna undersökning syftar till att utreda förutsättningarna för att använda komprimerad asp samt att ta fram underlag för framtagning av en kommersiell produkt.</p><p>Praktiska tester har genomförts för att studera hårdhet, återfjädring och densitet hos det komprimerade virket. Vidare har treskiktsskivor tagits fram för att testa om det går att få en stabil konstruktion genom att variera tjockleken på spärrskiktet. Även skillnader i acklimatiseringstid och fuktkvotens inverkan för virkets återfjädring har studerats.</p><p>Resultaten visar på att aspens hårdhet efter komprimering blir i samma nivå som bok och ask, en låg fuktkkvot vid komprimering av materialet ger en låg återfjädring, komprimerat material har en längre acklimatiseringstid till jämviktsfuktkvot och materialet går att låsa tvärs fiberriktningen i en treskiktskonstruktion.</p> / <p>To make wood harder it can be densified. This can be achieved by compression, the compressed material tends to return to the original shape when it is exposed to moisture fluxations and if no form of fixation occurs. The fixation can be done mechanically in a three-layer panel construction which reduce movements in the timber. These panels have been found to be unstable and previous attempts have shown deformations in form of cupping. This study aims to evaluate the conditions for using compressed aspen wood, and to provide a basis for development of a commercial product.</p><p>Practical tests have been conducted to study hardness, springback and density of the compressed wood. In addition, three-layer panels have been developed to test whether it is possible to have a stable construction by varying the thickness of the buttom layer. Differences in acclimatisation time and the moisture contents effect on the springback has aslo been studied.</p><p>The results show that the hardness of aspen wood after compression is in equal levels with beech and ashes, a low moisture contet provides a low springback, compressed timber have a longer time for acclimatisation and it is possible to fixate the material in the direction across the grain in a three-layer panel construction.</p>