Inhibition by chelating agents of the formation of active extracellular proteinase by Pseudomonas fluorescens 32A

The effect of chelating agents on extracellular proteinase production by Pseudomonas fluorescens 32A was examined. Increasing concentrations of orthophosphate slightly stimulated growth while inhibiting proteinase synthesis. Fifty per cent inhibition was found at 35 and 28 mM-orthophosphate at 5 and 20 degrees C respectively. Extracellular protein concentration was reduced by 30% when cells were grown with 100 mM-orthophosphate. Polyacrylamide gel electrophoresis of the cell-free supernatants suggested that reduced enzyme synthesis had taken place as evidenced by the decrease in staining intensity of the protein band corresponding to the proteinase. Other phosphate compounds could replace orthophosphate as an inhibitor. Extent of inhibition was related to chain length; polyphosphates with 4-6 or 13-18 phosphorus atoms were the most effective inhibitors. EDTA (0.5 mM) completely inhibited proteinase synthesis. This inhibition could be partly reversed by Ca2+ and, to a lesser extent, Mn2+. Proteinase production at 5 degrees C in skim milk was completely inhibited by phosphate glass (P13-P18). Control experiments showed that loss of activity with chelators was not due to inhibition of preformed enzyme. The results suggest a possible role for polyphosphates in controlling proteinase production in stored milk.     

Ecotoxicology and residues of anthelmintic compounds

Anthelmintics and endectocides used for the treatment and prophylaxis of Ostertagia sp. in ruminants include benzimidazoles, levamisole, morantel and the avermectins and milbemycins. Most of these agents are excreted to some extent in the faeces of treated animals and it has been demonstrated that members of the avermectin/milbemycin group may have deleterious effects on non-target organisms utilising the faeces. The environmental impact of antiparasitic chemotherapy depends on the deleterious effect which the agent or its metabolites have on organisms in the locus of the excreta, the amount of active agent excreted, the temporal nature of the excretion and the stability of the ecotoxic residues. These have to be considered in the context of the overall proportion of excreted faeces from a herd which is contaminated and thus the availability of non-contaminated faeces which may act as refugia for dung utilising organisms. The contribution which weathering, faunal inhabitants, trampling by cattle and disturbance by birds have on the rate of dung degradation must also be considered. The greatest ecotoxicological risk is associated with sustained release delivery devices, delivering endectocides with potent activity against dipteran flies and coleopteran beetles. The relatively large proportion of most cattle herds excreting faeces with no endectocidal contamination is likely to reduce the impact that such treatment or prophylactic strategies have on non-target organisms.     

A combined discrete-continuous model describing the lag phase of Listeria monocytogenes

Food microbiologists generally use continuous sigmoidal functions such as the empirical Gompertz equation to obtain the kinetic parameters specific growth rate (mu) and lag phase duration (lambda) from bacterial growth curves. This approach yields reliable information on mu; however, values for lambda are difficult to determine accurately due, in part, to our poor understanding of the physiological events taking place during adaptation of cells to new environments. Existing models also assume a homogeneous population of cells, thus there is a need to develop discrete event models which can account for the behavior of individual cells. Time to detection (t(d)) values were determined for Listeria monocytogenes using an automated turbidimetric instrument, and used to calculate mu. Mean individual cell lag times (tL) were calculated as the difference between the observed t(d) and the theoretical value estimated using mu. Variability in tL for individual cells in replicate wells was estimated using serial dilutions. A discrete stochastic model was applied to the individual cells, and combined with a deterministic population-level growth model. This discrete-continuous model incorporating tL and the variability in tL (expressed as standard deviation; S.D.(L)) predicted a reduced variability between wells with increased number of cells per well, in agreement with experimental findings. By combining the discrete adaptation step with a continuous growth function it was possible to generate a model which accurately described the transition from lag to exponential phase. This new model may serve as a useful tool for describing individual cell behavior, and thus increasing our knowledge of events occurring during the lag phase.     

Photo-yellowing of a phenolic anti-oxidant in the presence of various stabilizer/titanium dioxide pigment combinations in polyethylene

The effect of various stabilizer and titanium dioxide (rutile) pigment combinations on the photo-yellowing and photo-oxidation of commercial polyethylene containing an antioxidant, 4,4′-thio-bis(6-tert-butyl-meta-cresol) is examined. The nature of various interacting mechanisms is discussed.     

Characterization of Apples and Apple Cider Produced by a Guelph Area Orchard

Thermal stability of food-borne pathogens in apple cider is influenced by the composition of the product. As a preliminary step to determining the effect of pasteurization of apple cider on survival of E. coli O157:H7, a study was carried out to characterize apples and unpasteurized apple cider produced by a guelph area orchard. Samples of commercial unpasteurized cider and the constituent apples were collected over 13 wk from August to November 1998, and unpasteurized laboratory cider was made from the individual apple varieties. pH, titratable acidity (TA), turbidity, total microbial counts, total solids and °brix for filtered and unfiltered samples were measured. The maximum, minimum, and average values for all unpasteurized commercial cider samples were found to be: pH, 3.71, 3.17, and 3.43; TA, 93.47, 49.46, and 69.95 mL of 0.1 N NaOH/100 mL; total solids, 13.21, 10.93, and 11.90%; °brix, 13.01, 11.17, and 12.02; turbidity, 238.1, 145.1, and 204.9 NTU; and total plate count, 4.91, 2.61, 3.75 log cfu·mL⁻¹. There were no significnat differences (P>0.05) between filtered and unfiltered samples. In addition, in commercial unpasteurized cider, there were no significant differences (P>0.05) with respect to any of the factors with time of processing. The composition of the unpasteurized laboratory cider made form individual apple varieties was dependent on the variety, but was generally within the ranges from published literature values. Mclntosh apples showed a significant (P≤0.05) decrease in TA with time of harvest. The results suggest that it is necessary to take the composition of commercial apple cider into account when developing thermal inactivation models for food-borne pathogens.     

Photostabilizing effect of Ni(II) chelates in polymers. I. Polystyrene

The photostabilizing effect of six Ni(II) chelates in films of polystyrene is compared with their efficiency in quenching triplet benzophenone and a correlation between the two established. In both polymer stabilizing and triplet quenching experiments, the diamagnetic chelates are more effective than the paramagnetic chelates, indicating that the structural arrangement of the ligand around the Ni atom is an important factor in both cases.     

Identification of the luminescent species in low-density polyethylene

The luminescence properties of two low-density polyethylene samples are examined, one prepared using oxygen and the other using a benzoyl-based initiator as catalysts. The fluorescence emission from both samples is assigned to the presence of an impurity, α,β-unsaturated carbonyl of the enone type. The phosphorescence emissions, on the other hand, are different. The phosphorescence emission from the sample prepared using oxygen as an initiator is assigned to the presence of a dienone impurity chromophore, whereas the emission from the sample prepared using a benzoyl-based initiator is assigned to benzoic acid residues.     

The Light Fastness of Anthraquinone Disperse Dyes on Poly(ethylene terephthalate)

The I.S.O. light-fastness grades of thirty-two anthraquinone disperse dyes on polyester fabric have been determined. High light fastness is exhibited by the 1- and 1,4-hydroxy derivatives and 1- or 1,4-sub-stituted amino derivatives possessing N-substituted electron-withdrawing groups. The 1- and 2-methoxyanthraquinones, 2-hydroxyanthraquinones and all the 2-amino derivatives examined, on the other hand, have poor light fastness. The high light stability of the 1-hydroxy- and 1-anilinoanthraquinones may be due to rapid de-activation of their photo-excited singlet states, while the poor light fastness of the 2-aminoanthraquinones is probably due to their ability to abstract electrons from their environment.