Using viscosity‐time plots of Escherichia coli cells undergoing chemical lysis to measure the impact of physiological changes occurring during batch cell growth

BACKGROUND: Viscosity–time plots for plasmid‐bearing E. coli cells undergoing alkaline lysis are reported in this study. The plots demonstrate generic features that reflect the progress of fermentation and allow an assessment of the genomic DNA denaturation following cellular release into the alkaline solution. This rheological analysis could offer useful insights to the state of fermentation or the selection of operational specifications and predictions of the performance of subsequent downstream operations. RESULTS: Studies showed a distinct change in the rheological profile throughout the batch fermentation, with different viscosity versus time profiles for lag, exponential and stationary microbial growth phases. The DNA denaturation time was found to increase with fermentation time from about 120 s after 3 h of fermentation to about 180 s after 7 h of fermentation. CONCLUSION: The increase of denaturation time was mainly caused by a rise in the genomic content of cells during the exponential growth phase. The viscosity–time profiles were found to provide a good indication of the cellular contents, reflecting the physiological changes occurring during a batch fermentation process. Copyright © 2009 Society of Chemical Industry     

DIAL–phoswich hybrid system for remote sensing of radioactive plumes in order to evaluate external dose rate

Radioactive pollutants which are released into the atmosphere are known to present a hazard to human health; therefore they must be identified and well protected. Here, an improved remote sensing system is investigated for monitoring radioactive plumes released into the atmosphere from nuclear sites. It is based on the combination of DIAL technique with a phoswich detector array. The DIAL, using a tunable UV/Vis laser, measures the concentration of the radionuclide and the plume distance, whereas the phoswich detects characteristic hard X/γ ray emissions. Here, we have shown the ability of a hybrid system for the prompt identification and quantification of the effluents containing the uranium radionuclide, using the parameters of uranium such as absorption cross-section, absorption spectrum and density.     

Efficacy of bacteriophage LISTEXP100 combined with chemical antimicrobials in reducing Listeria monocytogenes in cooked turkey and roast beef

The aim of this study was to verify the effectiveness of the commercially available anti-Listeria phage preparation LISTEX^™P100 in reducing Listeria monocytogenes on ready-to-eat (RTE) roast beef and cooked turkey in the presence or absence of the chemical antimicrobials potassium lactate (PL) and sodium diacetate (SD). Sliced RTE meat cores at 4 and 10 °C were inoculated with cold-adapted L. monocytogenes to result in a surface contamination level of 10³ CFU/cm². LISTEX^TMP100 was applied at 10⁷ PFU/cm² and samples taken at regular time intervals during the RTE product's shelf life to enumerate viable L. monocytogenes. LISTEX^™P100 was effective during incubation at 4 °C with initial reductions of L. monocytogenes of 2.1 log₁₀ CFU/cm² and 1.7 log₁₀ CFU/cm², respectively, for cooked turkey and roast beef without chemical antimicrobials (there was no significant difference to the initial L. monocytogenes reductions in the presence of LISTEX^TMP100 for cooked turkey containing PL and roast beef containing SD-PL). In the samples containing no chemical antimicrobials, the presence of phage resulted in lower L. monocytogenes numbers, relative to the untreated control, of about 2 log CFU/cm² over a 28-day storage period at 4 °C. An initial L. monocytogenes cell reduction of 1.5 log₁₀ CFU/cm² and 1.7 log₁₀ CFU/cm², respectively, for cooked turkey and roast beef containing no chemical antimicrobials was achieved by the phage at 10 °C (abusive temperature). At this temperature, the L. monocytogenes cell numbers of samples treated with LISTEX™ P100 remained below those of the untreated control only during the first 14 days of the experiment for roast beef samples with and without antimicrobials. On day 28, the L. monocytogenes numbers on samples containing chemical antimicrobials and treated with LISTEX^TMP100 stored at 4 and 10 °C were 4.5 log₁₀ CFU/cm² and 7.5 log₁₀ CFU/cm², respectively, for cooked turkey, and 1.2 log₁₀ CFU/cm² and 7.2 log₁₀ CFU/cm², respectively, for roast beef. In both cooked turkey samples with and without chemical antimicrobials stored at 10 °C, the phage-treated samples had significantly lower numbers of L. monocytogenes when compared to the untreated controls throughout the 28-day storage period (P < 0.0001). For roast beef and cooked turkey containing chemical antimicrobials treated with LISTEX^TMP100 and stored at 4 °C, no more than a 2 log CFU/cm² increase of L. monocytogenes was observed throughout the stated shelf life of the product. This study shows that LISTEX^™P100 causes an initial reduction of L. monocytogenes numbers and can serve as an additional hurdle to enhance the safety of RTE meats when used in combination with chemical antimicrobials.     

Sample preparation method for the analysis of some organophosphorus pesticides residues in tomato by ultrasound-assisted solvent extraction followed by dispersive liquid–liquid microextraction

A very simple and economic method for organophosphorus pesticides (OPPs) residues analysis in tomato by means of gas chromatography–flame photometric detection (GC–FPD) has been developed. The method involves a rapid and small-scale extraction. The sample was homogenised and extraction of the OPPs with acetone was carried out assisted by sonication. No clean-up or evaporation were required after extraction. Pre-concentration of the OPPs from the acetone extract was done by using dispersive liquid–liquid microextraction (DLLME) technique. Chlorobenzene was added in micro-level volume as extraction solvent and triphenylphosphate as internal standard in DLLME procedure. The method showed good linearity over the range assayed (0.5–1000 μg kg⁻¹) and the detection limits for the pesticides studied varied from 0.1 to 0.5 μg kg⁻¹. Repeatability studies resulted a relative standard deviation lower than 10% in all cases. The proposed method was used to determine pesticides levels in tomatoes grown in open field.     

Tailored Crumpling and Unfolding of Spray‐Dried Pristine Graphene and Graphene Oxide Sheets

For the first time, pristine graphene can be controllably crumpled and unfolded. The mechanism for graphene is radically different than that observed for graphene oxide; a multifaced crumpled, dimpled particle morphology is seen for pristine graphene in contrast to the wrinkled, compressed surface of graphene oxide particles, showing that surface chemistry dictates nanosheet interactions during the crumpling process. The process demonstrated here utilizes a spray‐drying technique to produce droplets of aqueous graphene dispersions and induce crumpling through rapid droplet evaporation. For the first time, the gradual dimensional transition of 2D graphene nanosheets to a 3D crumpled morphology in droplets is directly observed; this is imaged by a novel sample collection device inside the spray dryer itself. The degree of folding can be tailored by altering the capillary forces on the dispersed sheets during evaporation. It is also shown that the morphology of redispersed crumpled graphene powder can be controlled by solvent selection. This process is scalable, with the ability to rapidly process graphene dispersions into powders suitable for a variety of engineering applications.     

Mechanical properties of hybrid fiber reinforced lightweight aggregate concrete made with natural pumice

The purpose of this study is to improve the ductility of pumice lightweight aggregate concrete by incorporating hybrid steel and polypropylene fibers. The changes in mechanical properties and also bulk density and workability of pumice lightweight aggregate concrete due to the addition of hybrid steel and polypropylene fibers have been studied. The properties were investigated include bulk density and workability of fresh concrete as well as compressive strength, flexural tensile strength, splitting tensile strength and toughness of hardened concrete. Nine concrete mixtures with different volume fractions of steel and polypropylene fibers were tested. A large increase in compressive and flexural ductility and energy absorption capacity due to the addition of steel fibers was observed. Polypropylene fibers, on the other hand, caused a minor change in mechanical properties of hardened concrete especially in the mixtures made with both steel and polypropylene fibers. These observations provide insight into the benefits of different fiber reinforcement systems to the mechanical performance of pumice lightweight aggregate concrete which is considered to be brittle. These results provide guidance for design of concrete materials with reduced density and enhanced ductility for different applications, including construction of high-rise, earthquake-resistant buildings.