The bacteriology of fresh and spoiling Lake Victorian Nile perch (Lates niloticus)

A total of 177 bacterial cultures isolated from Lake Victorian Nile Perch (Lates niloticus) were investigated. The flora on newly caught Nile perch consisted of organisms belonging to the genera Moraxella, Alcaligenes, Acinetobacter, Pseudomonas, Aeromonas, Micrococcus and other Gram-positive organisms. 39% were identified as Gram-positive species and 61% were negative in the Gram-reaction. Three cultures out of 53 investigated caused weak rotten off-odours in sterile fish broth and one culture, an Aeromonas spp. produced strong rotten, fishy, hydrogen sulphide off-odours. From Nile perch spoiled at ambient temperature, 15 of the 42 strains isolated caused rotten, fishy, hydrogen sulphide off-odours. These specific spoilage bacteria were all identified as Aeromonas and all reduced trimethylamine oxide to trimethylamine and produced hydrogen sulphide. From spoiled iced Nile perch, 74 out of 82 (90%) of the bacteria isolated were identified as Pseudomonas. A small proportion of these (13 out of 74) produced off-odours in sterile fish broth resembling the spoiling fish. These specific spoilers could not be separated from the non-spoilers based on biochemical activities used in classical taxonomy. While the Pseudomonas spp. isolated did not produce trimethylamine or H₂S, a few of the remaining isolates (two Shewanella putrefaciens and five Aeromonas spp.) did produce these compounds. The role of Shewanella putrefaciens in the iced spoilage of Nile perch was, however, insignificant, since they only very late in the storage reached numbers where their spoilage could be detected.     

Investigation of airflow patterns in a microclimate by particle image velocimetry (PIV)

Problems with mould growth in dwellings usually occur in bedrooms in the microclimate behind closets placed next to exterior walls with poor insulation. It is anticipated that the problems are caused by lack of airflow behind the furniture in combination with a colder surface temperature and a high moisture production. The lack of air circulation decreases the surface temperature, which can cause problems. A particle image velocimetry (PIV) investigation was performed of the airflow patterns in such a microclimate. This paper describes the experimental set-up and the results. The results indicate that the flow rates behind the furniture will increase with increased distance between the closet and the wall, and even higher airflow rates are seen when the furniture is elevated by legs.     

Pressure effects on the hypervalent meat pigment ferrylmyoglobin

 Acid-catalyzed autoreduction of ferrylmyoglobin [MbFe(IV)=O] decreased with increasing hydrostatic pressure corresponding to a volume of activation of ΔV ^# = +7.2±0.8 ml mol^–1, as determined for pressures of up to 250 MPa at 15°C in acidic 0.16 M NaCl solution. For the non-catalyzed autoreduction, a significant increase in compressibility for the non-protonated heme pigment, corresponding to a compressibility coefficient of activation of Δκ^# = +(4.0±1.1)×10^–8 ml mol^–1 Pa^–1, moderates the effects of pressure, although the volume of activation determined at 30°C was comparable, i. e. ΔV ^# = +7.5±2.0 mol mol^–1. At pH relevant for meat, the effect of pressure on the transformation of ferrylmyoglobin to metmyoglobin [MbFe(III)] was approximately half that of the same pressure on the transformation of oxymyoglobin to metmyoglobin, when compared on a logarithmic basis. This result finds a surprising parallel in the temperature-dependence of the same acid-catalyzed processes to yield metmyoglobin. Received: 1 December 1997     

A comparative study of two food model systems to test the survival of Campylobacter jejuni at -18 degrees C

The survival of Campylobacter jejuni NCTC 11168 was tested at freezing conditions (-18 degrees C) over a period of 32 days in two food models that simulated either (i) the chicken skin surface (skin model) or (ii) the chicken juice in and around a broiler carcass (liquid model). In the skin model, cells were suspended in chicken juice or brain heart infusion broth (BHIB) and added to 4-cm2 skin pieces, which were subsequently stored at -18 degrees C. In the liquid model, cells were suspended in chicken juice or BHIB and stored at -18 degrees C. The decrease in the number of viable C. jejuni NCTC 11168 cells was slower when suspended in chicken juice than in BHIB. After freezing for 32 days, the reductions in the cell counts were 1.5 log CFU/ml in chicken juice and 3.5 log CFU/ml in BHIB. After the same time of freezing but when inoculated onto chicken skin, C. jejuni NCTC 11168 was reduced by 2.2 log units when inoculated in chicken juice and 3.2 log units when inoculated into BHIB. For both models, the major decrease occurred within the first 24 h of freezing. The results obtained in the liquid model with chicken juice were comparable to the reductions of Campylobacter observed for commercially processed chickens. The survival at -18 degrees C in the liquid model was also tested for three poultry isolates and three human clinical isolates of the serotypes 1.44, 2, and 4 complex. As observed for C. jejuni NCTC 11168, all the strains survived significantly better in chicken juice than in BHIB and were not notably influenced by serotype or origin. The findings indicate that the composition of the medium around the bacteria, rather than the chicken skin surface, is the major determining factor for the survival of C. jejuni at freezing conditions. The liquid model with chicken juice was therefore the best model system to study the freezing tolerance in Campylobacter strains.     

Prompt gamma rays from thermal-neutron capture

A catalog of γ-rays emitted following thermal-neutron capture in natural elements is presented. In Table I, γ-rays are arranged in order of increasing energy. Each line contains the γ-ray energy, intensity, element identification, thermal-neutron radiative-capture cross section, and the energies and intensities of two of the more abundant γ-rays associated with that element. In Table II, γ-rays are arranged by element and γ-ray energy; energy uncertainty and γ-ray intensity are given. The catalog is designed for use in high-resolution analytical prompt γ-ray spectroscopy.