Present energy and environmental scenarios promote the incorporation of generation systems based on renewable sources into the distribution grids of electro-intensive industries, the benefits of ...which transcend the local generation of energy with minimal greenhouse gas emissions. In this regard, coordinated management of reactive power in a joint installation of a hot rolling mill plant and a wind farm can improve the immunity of both facilities against voltage sags. In this paper, the various factors influencing the response of the joint installation against voltage sags are analyzed. In this regard, special attention is paid to the wind farm location and, consequently, to the topology of the joint installation distribution network. The closer the wind farm and the rolling mill, the more relevant the shared impedances and the more significant the effect of the reactive power supplied by the wind farm. The main variables of interest are analyzed under actual rolling conditions both in normal operation and in the face of voltage sags to determine the most indicated distribution network topology.
In nature,
Listeria
may interact competitively and cooperatively with other organisms, resulting in unique spatial organization and functions for cells within the community. This study was undertaken ...to characterize the biofilm architecture of binary biofilms of
Listeria monocytogenes
and
Lactobacillus
species and to assess their effect on the survival of
Listeria
during exposure to hypochlorite. Three
L. monocytogenes
strains, ATCC 19115 (Lm5), ATCC 19117 (Lm7), and Coleslaw (LmC), were selected and combined individually with three
Lactobacillus
strains:
L. fermentum
(Lf),
L. bavaricus
(Lb), and
L. plantarum
(Lp). In binary Lm-Lp biofilms, the Lm cell counts were similar to single-species biofilms (8.5 log CFU/well), and the Lp cell numbers declined by 1.0 log CFU/well. In the presence of Lb, the Lm cell counts were reduced by 1.5 log CFU/well (
p
< 0.05), whereas the Lf cell counts increased at least by 3.5 log CFU/well. Confocal laser scanning microscopy (CLSM) determined that interspecies interactions significantly affected the spatial organization of three binary biofilms. Biofilm surface-to-volume ratio increased from 0.8 μm
2
/μm
3
for Lm5 in the monoculture to 2.1 μm
2
/μm
3
for Lm5-Lp in the dual-species model (
p
< 0.05), and was characterized by a thicker structure with a largely increased surface area. Biofilm roughness increased from 0.2 for Lm7 to 1.0 for Lm7-Lb biofilms (
p
< 0.05), which appeared as interspecific segregation. Biofilm thickness increased from 34.2 μm for LmC to 46.3 μm for LmC–Lf (
p
< 0.05), which produced flat and compact structures that covered the entire surface available. The biomass of the extracellular matrix was higher in the case of some binary biofilms (
p
< 0.05); however, this effect was dependent upon the species pair. When treated with hypochlorite, Lm5 in binary biofilms had an approximately 1.5 log CFU/well greater survival than individually. The unique spatial organization and greater protein production may explain the protective effect of Lp after hypochlorite exposure.
Salmonella can survive for long periods under extreme desiccation conditions. This stress tolerance poses a risk for food safety, but relatively little is known about the molecular and cellular ...regulation of this adaptation mechanism. To determine the genetic components involved in Salmonella's cellular response to desiccation, we performed a global transcriptomic analysis comparing S. enterica serovar Typhimurium cells equilibrated to low water activity (aw 0.11) and cells equilibrated to high water activity (aw 1.0). The analysis revealed that 719 genes were differentially regulated between the two conditions, of which 290 genes were up-regulated at aw 0.11. Most of these genes were involved in metabolic pathways, transporter regulation, DNA replication/repair, transcription and translation, and, more importantly, virulence genes. Among these, we decided to focus on the role of sopD and sseD. Deletion mutants were created and their ability to survive desiccation and exposure to aw 0.11 was compared to the wild-type strain and to an E. coli O157:H7 strain. The sopD and sseD mutants exhibited significant cell viability reductions of 2.5 and 1.3 Log (CFU/g), respectively, compared to the wild-type after desiccation for 4 days on glass beads. Additional viability differences of the mutants were observed after exposure to aw 0.11 for 7 days. E. coli O157:H7 lost viability similarly to the mutants. Scanning electron microscopy showed that both mutants displayed a different morphology compared to the wild-type and differences in production of the extracellular matrix under the same conditions. These findings suggested that sopD and sseD are required for Salmonella's survival during desiccation.
Leafy green vegetables have been identified as a source of foodborne illnesses worldwide over the past decade. Human enteric pathogens, such as Escherichia coli O157:H7 and Salmonella, have been ...implicated in numerous food poisoning outbreaks associated with the consumption of fresh produce. An understanding of the mechanisms responsible for the establishment of pathogenic bacteria in or on vegetable plants is critical for understanding and ameliorating this problem as well as ensuring the safety of our food supply. While previous studies have described the growth and survival of enteric pathogens in the environment and also the risk factors associated with the contamination of vegetables, the molecular events involved in the colonization of fresh produce by enteric pathogens are just beginning to be elucidated. This review summarizes recent findings on the interactions of several bacterial pathogens with leafy green vegetables. Changes in gene expression linked to the bacterial attachment and colonization of plant structures are discussed in light of their relevance to plant-microbe interactions. We propose a mechanism for the establishment and association of enteric pathogens with plants and discuss potential strategies to address the problem of foodborne illness linked to the consumption of leafy green vegetables.
and enterohemorrhagic
(EHEC) are of serious concern in wheat flour and its related products but little is known on their survival and thermal death kinetics. This study was undertaken to determine ...their long-term viability and thermal inactivation kinetics in flour. Inoculation was performed using mixtures of EHEC serogroups O45, O121, O145 and
followed by storage at room temperature (23°C) or 35°C (for
). Plate counting on tryptic soy agar (TSA) and enrichment were used to assess long-term survival. For thermal studies, wheat flour samples were heated at 55, 60, 65, and 70°C and cell counts of EHEC and
were determined by plating. The δ-values were calculated using the Weibull model. At room temperature, EHEC serovars and
were quantifiable for 84 and 112 days, and were detectable for the duration of the experiment after 168 and 365 days, respectively. The δ-values were 2.0, 5.54, and 9.3 days, for EHEC O121, O45, and O145, respectively, and 9.7 days for
. However, the only significant difference among all values was the δ-value for
and serogroup O121 (
≤ 0.05). At 35°C,
counts declined to unquantifiable levels after a week and were not detected upon enrichment after 98 days. Heat treatment of inoculated wheat flour at 55, 60, 65, and 70°C resulted in δ-value ranges of 20.0-42.9, 4.9-10.0, 2.4-3.2, and 0.2-1.6 min, respectively, for EHEC. The δ-values for
at those temperatures were 152.2, 40.8, 17.9, and 17.4 min, respectively. The δ-values obtained for
at each temperature were significantly longer than for EHEC (
≤ 0.05). Weibull model was a good fit to describe the thermal death kinetics of
and EHEC O45, O121 and O145 in wheat flour.
-EHEC and
can survive for extended periods of time in wheat flour.-Long-term storage inactivation curves of EHEC and
were similar.-EHEC was more sensitive to heat than
-Weibull model was a good fit to describe thermal death kinetics of EHEC and
-Flour storage at 35°C may be a feasible method for microbial reduction.
: Ricin is a potential bioterrisiom agent. There is a critical need for a method that can rapidly and simply detect ricin and other bioterrisiom agents in complex food matrices such as milk. In this ...study, we demonstrated a rapid method that combined immunomagnetic separation (IMS) and surface‐enhanced Raman spectroscopy (SERS) to detect ricin in whole milk. IMS was used to specifically capture the ricin out of the milk. Then, SERS was applied to analyze the IMS eluate mixed with silver dendrite nanosubstrates. This approach facilitated detection and quantification down to 4 μg/mL ricin in milk within 20 min, based on the results of principal component analysis and partial least squares analysis. The feasibility of using a portable Raman instrument shows great promise for on‐site detection in a processing facility.
Practical Application: The method described in this manuscript that combined IMS and SERS could be used for rapid detection of ricin and other protein toxins in complex food matrices such as milk within 20 min. The use of a portable Raman could facilitate the on‐site detection in a processing facility.
Microbiological analyses of fresh fruits and vegetables produced by organic and conventional farmers in Minnesota were conducted to determine the coliform count and the prevalence of Escherichia ...coli, Salmonella, and E. coli O157:H7. A total of 476 and 129 produce samples were collected from 32 organic and 8 conventional farms, respectively. The samples included tomatoes, leafy greens, lettuce, green peppers, cabbage, cucumbers, broccoli, strawberries, apples, and seven other types of produce. The numbers of fruits and vegetables was influenced by their availability at participating farms and varied from 11 strawberry samples to 108 tomato samples. Among the organic farms, eight were certified by accredited agencies and the rest reported the use of organic practices. All organic farms used aged or composted animal manure as fertilizer. The average coliform counts in both organic and conventional produce were 2.9 log most probable number per g. The percentages of E. coli-positive samples in conventional and organic produce were 1.6 and 9.7%, respectively. However, the E. coli prevalence in certified organic produce was 4.3%, a level not statistically different from that in conventional samples. Organic lettuce had the largest prevalence of E. coli (22.4%) compared with other produce types. Organic samples from farms that used manure or compost aged less than 12 months had a prevalence of E. coli 19 times greater than that of farms that used older materials. Serotype O157:H7 was not detected in any produce samples, but Salmonella was isolated from one organic lettuce and one organic green pepper. These results provide the first microbiological assessment of organic fruits and vegetables at the farm level.
The control of Salmonella in low water activity foods poses a challenge for the food industry because of its thermal resistance. The use of surrogate bacteria in a food plant is considered a critical ...component to validate processing steps. The objective of this study was to evaluate the use of Pediococcus acidilactici ATCC 8042, a generally recognized as safe bacterium (GRAS), as potential surrogate for Salmonella in commercial toasted oats cereal (TOC) and peanut butter. P. acidilactici was compared to a five-serovar cocktail of Salmonella and Enterococcus faecium NRRL-B2354, separately. Cultures were inoculated into TOC and thermal kinetic parameters (δ, β) were determined at 80, 85, 90, and 95 °C using the Weibull model. In peanut butter, δ and β parameters were obtained at 63, 68, 73, and 77 °C. In TOC, the δ values (initial decimal reduction time) of P. acidilactici were 63 and 7 min at 80 and 95 °C, respectively, and at all four temperatures they were not significantly different from δ values of E. faecium. The δ value of Salmonella at 80 °C (139 min) was two-fold greater than the other two bacteria's values (p < 0.05). In peanut butter, δ values of P. acidilactici ranged from 31 min at 63 °C to 2.6 min at 77 °C, and at all temperatures they were not significantly different from E. faecium's δ values. In peanut butter, all Salmonella cocktail's δ values were significantly smaller than P. acidilactici's with values of 2 min at 63 °C and 0.4 min at 77 °C. These results indicated that P. acidilactici was as heat tolerant as E. faecium in these food matrices. However, the thermal inactivation kinetic parameters suggested that P. acidilactici can only be considered a Salmonella surrogate in TOC at temperatures above 85 °C. Because of its greater thermal tolerance in peanut butter, P. acidilactici may be used as Salmonella surrogate if an additional safety factor is recommended.
•Pediococcus acidilactici ATCC 8042 survived heat in peanut butter and oats cereal.•Strain ATCC 8024 tolerated heat longer than Salmonella in peanut butter.•P. acidilactici had similar heat tolerance to Enterococcus faecium NRRL-B2354.•P. acidilactici had shorter heat survival at temperatures below 85 °C in oats cereal.
PDF
