AIMS: To evaluate the food safety and spoilage risks associated with psychrotrophic Bacillus cereus group bacteria for the egg product industry and to search for relevant risk markers. METHODS AND ...RESULTS: A collection of 68 psychrotrophic B. cereus group isolates, coming from pasteurized liquid whole egg products, was analysed through a principal component analysis (PCA) regarding their spoilage and food safety risk potentials. The principal component analysis showed a clear differentiation between two groups within the collection, one half of the isolates representing a safety risk and the other half a spoilage risk. CONCLUSIONS: Relevant risk markers were highlighted by PCA, that is (i) for the food safety risk, the presence of the specific 16S rDNA‐1m genetic signature and the ability to grow at 43°C on solid medium and (ii) for the spoilage risk, the presence of the cspA genetic signature. SIGNIFICANCE AND IMPACT OF THE STUDY: This work represents a first step in the development of new diagnostic technologies for the assessment of the microbiological quality of foods likely to be contaminated with psychrotrophic B. cereus group bacteria.
Lung-inspired, fractal flow-fields hold great potential in improving the performance of polymer electrolyte membrane fuel cells (PEMFCs) by providing uniform gas distribution across the electrodes ...and ensuring minimum entropy production in the whole system. However, the inherent susceptibility of the fractal flow-fields to flooding renders their use inadequate at high humidity conditions. In-depth understanding of water management in lung-inspired flow-fields is indispensable for the implementation of alternative outlet channel geometries or engineered water removal strategies to alleviate flooding. Here, liquid water formation and transport across the lung-inspired and serpentine flow-field based PEMFCs are evaluated using neutron radiography. The results reveal a propensity to flooding in the interdigitated outlet channels of the fractal flow-field with N = 4 generations as a result of slow gas velocity and narrow channel dimensions, which leads to significant performance deterioration. Neutron images also elucidate the importance of ensuring a well-defined internal channel structure of the fractal flow-fields to prevent backflow of liquid water via wicking and capillary pressure build-up arising from the narrow inlet gas channels and hydrophobic gas diffusion layer.
•Neutron radiographs are presented for the lung-inspired and serpentine flow-fields.•A well-defined channel structure of the fractal flow-field is indispensable.•Water removal strategies required to alleviate flooding in the fractal flow-field.
In-depth understanding of the dynamics of water formation, accumulation and removal is important for flow-field design optimization to ensure robust performance and durability of polymer electrolyte ...fuel cells (PEFCs). Here, in-operando neutron radiography is used to display and quantify liquid water distribution across the entire active area of single-, double- and quad-channel serpentine flow-fields. The results revealed that the water management and performance of PEFCs is strongly affected by the number of serpentine channels in the cathode flow-field. The single-channel serpentine-based PEFC exhibits both a better cell performance and uniformity in the local water distribution. The quad-channel based PEFC exhibits the largest voltage fluctuations caused by severe water flooding in the gas channels. However, the single-channel design leads to significantly larger pressure drop than the multiple-channel counterparts, which requires much higher parasitic power to pressurize and recirculate the reactants.
Three different regimes of operation can be defined based on the current density: gradually increasing hydration (<400 mA cm−2), flooding (400 mA cm−2 ≤ j ≤ 600 mA cm−2) and drying out (>600 mA cm−2). The reduced overall quantity of water in the channels with an increase in current density can be attributed to faster gas velocity and higher cell temperature.
•In-depth understanding of water dynamics through in-operando neutron radiography.•Single-, double- and quad-channel serpentine cathode flow-fields compared.•The single-channel exhibits better performance and water uniformity.•Three regimes identified: increasing hydration, flooding and drying out.
Abstract
Group B Streptococcus (GBS) is a leading cause of adverse pregnancy outcomes due to invasive infection. This study investigated longitudinal variation in GBS rectovaginal colonization, serum ...and vaginal GBS capsular polysaccharide (CPS)-specific antibody levels. Non-pregnant women were recruited in the UK and were sampled every 2 weeks over a 12-week period. GBS isolates were taken from recto-vaginal swabs and serotyped by polymerase chain reaction. Serum and vaginal immunoglobulin G (IgG) and nasal immunoglobulin A (IgA) specific to CPS were measured by Luminex, and total IgG/A by ELISA. Seventy women were enrolled, of median age 26. Out of the 66 participants who completed at least three visits: 14/47 (29.8%) women that were GBS negative at screening became positive in follow-up visits and 16/19 (84.2%) women who were GBS positive at screening became negative. There was 50% probability of becoming negative 36 days after the first positive swab. The rate of detectable GBS carriage fluctuated over time, although serum, vaginal, and nasal CPS-specific antibody levels remained constant. Levels of CPS-specific antibodies were higher in the serum of individuals colonized with GBS than in non-colonized, but similar in the vaginal and nasal mucosa. We found correlations between antibody levels in serum and the vaginal and nasal mucosa. Our study demonstrates the feasibility of elution methods to retrieve vaginal and nasal antibodies, and the optimization of immunoassays to measure GBS-CPS-specific antibodies. The difference between the dynamics of colonization and antibody response is interesting and further investigation is required for vaccine development.
In-depth understanding of water management is essential for the optimization of the performance and durability of polymer electrolyte fuel cells (PEFCs). Neutron imaging of liquid water has proven to ...be a powerful diagnostic technique, but it cannot distinguish between ‘legacy’ water that has accumulated in the system over time and ‘nascent’ water recently generated by reaction. Here, a novel technique is introduced to investigate the spatially resolved water exchange characteristics inside PEFCs. Hydro-electrochemical impedance imaging (HECII) involves making a small AC-sinusoidal perturbation to a cell and measuring the consequential water generated, using neutron radiographs, associated with the stimulus frequency. Subsequently, a least-squares estimation (LSE) analysis is applied to derive the spatial amplitude ratio and phase shift. This technique provides a complementary view to conventional neutron imaging and provides information on the source and ‘history’ of water in the system. By selecting a suitable perturbation frequency, HECII can be used to achieve an alternative image ‘contrast’ and identify different features involved in the water dynamics of operational fuel cells.
•Hydro-electrochemical impedance imaging applied to water management of PEFC.•HECII distinguish between 'legacy' and 'nascent' water in the PEFC.•The perturbation frequency of HECII affects water dynamics features.
The effect of oxidation on modification of single wall carbon nanotubes (SWCNTs) through successive purification steps has been studied. The efficient elimination of metal impurities has been ...followed by induced coupled plasma spectroscopy. Upon acid treatment, Raman spectroscopy clearly proofed that HNO
3 molecules were intercalated into the bundles of SWCNTs. At the same time, SWCNTs also have suffered a high degree of degradation and defects were introduced. The subsequent thermal processes led to the removal of further defect carbon materials and to the almost complete de-intercalation of the HNO
3 molecules. Changes in the structure of the SWCNT bundles have been observed by transmission electron microscopy. While bundles tend to separate upon acid treatment, after the complete purification process, the remaining SWCNTs tend to form thick bundles again. The existence of functional groups in the raw single wall carbon nanotubes material and their modification and almost complete removal after the final annealing step has been studied by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and temperature programmed desorption. Nitrogen adsorption isotherms analysed according to Brunauer–Emmet–Teller showed important changes in the pore volume and surface area through the purification steps.
Polymer electrolyte fuel cells (PEFC), although a promising technology for carbon free production of electricity, are penalized by system complexity, partly due to cooling and humidifying systems. ...These systems are necessary to avoid the heating up and drying of the membrane, which stop the electrochemical reaction. Here, we present an evaporative cooling concept for PEFC developed at Paul Scherrer Institute (PSI). Unlike other concepts, our approach does not require any additional layer in the cell structure. Water flows through dedicated anode flowfield channels, parallel to the gas channels, and is distributed over the cell area thanks to a modified gas diffusion layer (GDL). A synthesis method developed at Paul Scherrer Institut (PSI) transforms some portions of the GDL into hydrophilic patterns, which wick the water from the supply channels at low capillary pressure. These hydrophilic areas, parallel and equally spaced, define pathways for liquid water separated from the gases, which avoids flooding. A test cell was built to investigate both water transport with the help of neutron radiography and heat transport thanks to integrated heat flux sensors. Here, we will present how the evaporation can be controlled by the mass flow rates, temperatures, pressures of gases, and the geometry of the hydrophilic lines.
The aim of the present study was (i) to type, by genotypic and phenotypic methods, a collection of psychrotrophic bacteria belonging to the
Bacillus cereus group collected in a farm and in 6 egg ...breaking industries during a period covering a warm and a cold season, and (ii) to characterize the egg product spoilage (growth in liquid whole egg) and the sanitary risk potential (cytotoxic activity on Caco-2 cells and adhesion on stainless steel) of each isolate of the collection. The investigation of specific psychrotrophic and mesophilic signatures together with the study of ability to grow at 6
°C and/or at 43
°C on optimal agar medium allowed highlighting twelve profiles, the major one corresponding to the species
Bacillus weihenstephanensis (46.2% of the collection). The diversity of the profiles depended on the season and on the origin of the isolates. In terms of food spoilage, all the isolates were able to grow at the same level in liquid whole egg and in optimal medium, even at low temperature. Under the same conditions, the cytotoxic activity depended on the isolate, the medium and the temperature. At 10
°C, no isolate was cytotoxic at 10
°C in liquid whole egg and only one, belonging to the
Bacillus weihenstephansensis species, in the optimal medium. All the isolates were able to adhere on stainless steel at various levels, from 2.6
±
0.2
log cfu/cm
2 to 4.9
±
0.1
log cfu/cm
2. A large majority (80.8%) was strongly adhering and could lead to the formation of biofilms in industrial equipments.
A commercial 50 cm2 polymer electrolyte membrane (PEM) fuel cell with serpentine flow fields was operated at 2.0 bar and 60 °C with two orientations of the flow field channels with respect to ...gravity, i.e. horizontal and vertical channels. A 3 × 3 test matrix of anode and cathode reactants relative humidity was used for the performance assessment of the cell in both orientations. The cell performance and operating data, including cell voltage and resistance, were measured, and neutron radiographs were recorded during the entire operation in order to gain knowledge of the liquid water distributions within the cell for both orientations. A quantitative analysis of the results is presented in this work, comparing the cell operation for both flow field orientations. It is observed that the configuration with horizontal cathode flow field channels presents a better cell performance, and less amount of liquid water blocking the flow field channels. Thus, the results show that the selection of the cell orientation has an influence on the final performance, and it is therefore, a design parameter to be considered for a real application. The differences in the cell water content are quantitatively analyzed and discussed.
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