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Biomedical subjects

J P Smelt

Publications and source records attributed to J P Smelt.

7 recordsLinked to original sources
PubMed1999

Effects of pulsed electric fields on inactivation kinetics of Listeria innocua.

The effects of pulsed electric field (PEF) treatment and processing factors on the inactivation kinetics of Listeria innocua NCTC 11289 were investigated by using a pilot plant PEF unit with a flow rate of 200 liters/h. The electric field strength, pulse length, number of pulses, and inlet temperature were the most significant process factors influencing the inactivation kinetics. Product factors (pH and conductivity) also influenced the inactivation kinetics. In phosphate buffer at pH 4.0 and 0.5 S/m at 40 degrees C, a 3. 0-V/microm PEF treatment at an inlet temperature of 40 degrees C resulted in > or = 6.3 log inactivation of strain NCTC 11289 at 49.5 degrees C. A synergistic effect between temperature and PEF inactivation was also observed. The inactivation obtained with PEF was compared to the inactivation obtained with heat. We found that heat inactivation was less effective than PEF inactivation under similar time and temperature conditions. L. innocua cells which were incubated for a prolonged time in the stationary phase were more resistant to the PEF treatment, indicating that the physiological state of the microorganism plays a role in inactivation by PEF. Sublethal injury of cells was observed after PEF treatment, and the injury was more severe when the level of treatment was increased. Overall, our results indicate that it may be possible to use PEF in future applications in order to produce safe products.

Electric Conductivity↗
PubMed1998

Effects of High Pressure on Inactivation Kinetics and Events Related to Proton Efflux in Lactobacillus plantarum.

Knowledge of the mechanism of pressure-induced inactivation of microorganisms could be helpful in defining an effective, relatively mild pressure treatment as a means of decontamination, especially in combination with other physical treatments or antimicrobial agents. We have studied the effect of high pressure on Lactobacillus plantarum grown at pH 5.0 and 7.0. The classical inactivation kinetics were compared with a number of events related to the acid-base physiology of the cell, i.e., activity of F(0)F(1) ATPase, intracellular pH, acid efflux, and intracellular ATP pool. Cells grown at pH 5.0 were more resistant to pressures of 250 MPa than were cells grown at pH 7.0. This difference in resistance may be explained by a higher F(0)F(1) ATPase activity, better ability to maintain a DeltapH, or a higher acid efflux of the cells grown at pH 5.0. After pressure treatment at 250 MPa, the F(0)F(1) ATPase activity was decreased, the ability to maintain a DeltapH was reduced, and the acid efflux was impaired. The ATP pool increased initially after mild pressure treatment and finally decreased after prolonged treatment. The observations on acid efflux and the ATP pool suggest that the glycolysis is affected by high pressure later than is the F(0)F(1) ATPase activity. Although functions related to the membrane-bound ATPase activity were impaired, no morphological changes of the membrane could be observed.

Journal Article↗
PubMed1990

A proposal for using previous experience in designing microbiological sampling plans based on variables.

A microbiological sampling system on the basis of variables is presented which requires only small numbers of replicates (n greater than or equal to 2). The system uses previous data on standard deviations of numbers of micro-organisms in batches and is particularly useful for in-plant situations. The discriminating power of the system is comparable to that of the current International Committee on Microbiological Specifications for Foods sampling schemes but uses more replicates.

Bacteriological Techniques↗
PubMed1986

Identification and grouping of Clostridium botulinum strains by numerical analysis of their electrophoretic protein patterns.

Strains of Clostridium botulinum type A, type E and both non-proteolytic and proteolytic types B and F were characterized by their electrophoretic protein patterns. As the protein pattern changes during sporulation, special attention was paid to the prevention of sporulation by selecting an appropriate medium (Strasdine's medium plus 1% w/v glucose) and a scheme of repeated subculturing. Ribosomal proteins, evolutionarily conservative and hence relatively similar in all types of bacteria, were removed to optimize the resolving power of the electrophoretic technique. Protein patterns were compared by computing correlation coefficients of normalized densitometric tracings. The method is highly reproducible and its resolving power is high: all protein patterns found were specific. The strains tested fall into two main groups: the proteolytic and the non-proteolytic cluster. Type A strains form a separate subgroup within the proteolytic cluster, the same applies to type E strains within the non-proteolytic group. Although time-consuming for spore-forming bacteria, this method is, to our knowledge, the only technique that recognizes individual strains of Cl. botulinum. For non-spore-forming micro-organisms the method is certainly much simpler and hence even more valuable.

Bacterial Proteins↗
PubMed1979

Clostridium botulinum can grow and form toxin at pH values lower than 4.6.

It is generally accepted that in Clostridium botulinum both growth and toxin formation are completely inhibited at pH values below 4.6. This critical pH value has been confirmed by many investigators using food as substrate or culture media. Occasionally growth of C. botulinum and toxin formation at pH values lower than 4.6 have been reported. In these cases the authors ascribed the unexpected outgrowth and toxin formation to local pH differences in inhomogeneous media and growth of C. botulinum before pH equilibration, or to the fact that fungi created microenvironments within or adjacent to the mycelial mat, where the pH was higher than 4.6 as was demonstrated by Odlaug and Pflug. We show here that the general assumption that C. botulinum does not grow below pH 4.6 is incorrect. We have observed that growth and toxin formation by C. botulinum can take place in homogeneous protein rich substrates (containing 3% or more soya or milk protein) at pH values lower than 4.6.

Botulinum Toxins↗