scholarly journals Growth Limits of Listeria monocytogenesas a Function of Temperature, pH, NaCl, and Lactic Acid

2000 ◽  
Vol 66 (11) ◽  
pp. 4979-4987 ◽  
Author(s):  
S. Tienungoon ◽  
D. A. Ratkowsky ◽  
T. A. McMeekin ◽  
T. Ross
Keyword(s):  
Experimental Data ◽  
Logistic Regression ◽  
Lactic Acid ◽  
Model Parameters ◽  
Food Borne ◽  
Food Borne Illness ◽  
Effects Of Temperature ◽  
Growth Limits ◽  
Food Safety Risk ◽  
Temperature Water

ABSTRACT Models describing the limits of growth of pathogens under multiple constraints will aid management of the safety of foods which are sporadically contaminated with pathogens and for which subsequent growth of the pathogen would significantly increase the risk of food-borne illness. We modeled the effects of temperature, water activity, pH, and lactic acid levels on the growth of two strains ofListeria monocytogenes in tryptone soya yeast extract broth. The results could be divided unambiguously into “growth is possible” or “growth is not possible” classes. We observed minor differences in growth characteristics of the two L. monocytogenes strains. The data follow a binomial probability distribution and may be modeled using logistic regression. The model used is derived from a growth rate model in a manner similar to that described in a previously published work (K. A. Presser, T. Ross, and D. A. Ratkowsky, Appl. Environ. Microbiol. 64:1773–1779, 1998). We used “nonlinear logistic regression” to estimate the model parameters and developed a relatively simple model that describes our experimental data well. The fitted equations also described well the growth limits of all strains of L. monocytogenesreported in the literature, except at temperatures beyond the limits of the experimental data used to develop the model (3 to 35°C). The models developed will improve the rigor of microbial food safety risk assessment and provide quantitative data in a concise form for the development of safer food products and processes.

scholarly journals Mechanism Analysis and Kinetic Modelling of Cu NPs Catalysed Glycerol Conversion into Lactic Acid

Catalysts ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 231 ◽  
Author(s):  
Sergey Zavrazhnov ◽  
Anton Esipovich ◽  
Sergey Zlobin ◽  
Artem Belousov ◽  
Andrey Vorotyntsev
Keyword(s):  
Experimental Data ◽  
Lactic Acid ◽  
Activation Barrier ◽  
Kinetic Modelling ◽  
Batch Reactor ◽  
Alkaline Media ◽  
Reaction Pathways ◽  
Model Parameters ◽  
Mechanism Analysis ◽  
Glycerol Conversion

Mechanism analysis and kinetic modeling of glycerol conversion into lactic acid in the alkaline media with and without heterogeneous catalyst Cu NPs are reported. The reaction pathways were determined in agreement with the experimental results and comprise several types of reactions, namely dehydrogenation, hydrogenolysis, dehydration and C–C cleavage. Experimental concentration-time profiles were obtained in a slurry batch reactor at different glycerol, NaOH and Cu NPs concentrations in a temperature range of 483–518 K. Power law, Langmuir–Hinshelwood (LH) and Eley–Rideal (ER) models were chosen to fit the experimental data. The proposed reaction pathways and obtained kinetic model adequately describe the experimental data. The reaction over Cu NPs catalyst in the presence of NaOH proceeds with a significantly lower activation barrier (Ea = 81.4 kJ∙mol−1) compared with the only homogeneous catalytic conversion (Ea = 104.0 kJ∙mol−1). The activation energy for glycerol hydrogenolysis into 1,2-propanediol on the catalyst surface without adding hydrogen is estimated of 102.0 kJ∙mol−1. The model parameters obtained in this study would be used to scale an industrial unit in a reactor modeling.

New parameters controlling the effect of temperature on enzyme activity

2007 ◽  
Vol 35 (6) ◽  
pp. 1543-1546 ◽  
Author(s):  
R.M. Daniel ◽  
M.J. Danson ◽  
R. Eisenthal ◽  
C.K. Lee ◽  
M.E. Peterson
Keyword(s):  
Experimental Data ◽  
Enzyme Activity ◽  
Thermal Behaviour ◽  
Equilibrium Model ◽  
Thermal Inactivation ◽  
Effect Of Temperature ◽  
Model Parameters ◽  
Effects Of Temperature ◽  
Activity Loss

Arising from careful measurements of the thermal behaviour of enzymes, a new model, the Equilibrium Model, has been developed to explain more fully the effects of temperature on enzymes. The model describes the effect of temperature on enzyme activity in terms of a rapidly reversible active–inactive (but not denatured) transition, revealing an additional and reversible mechanism for enzyme activity loss in addition to irreversible thermal inactivation at high temperatures. Two new thermal parameters, Teq and ΔHeq, describe the active–inactive transition, and enable a complete description of the effect of temperature on enzyme activity. We describe here the Model and its fit to experimental data, methods for the determination of the Equilibrium Model parameters, and the implications of the Model for the environmental adaptation and evolution of enzymes, and for biotechnology.

A consolidation model for a creeping clay

1999 ◽  
Vol 36 (4) ◽  
pp. 754-759 ◽  
Author(s):  
DFE Stolle ◽  
P A Vermeer ◽  
P G Bonnier
Keyword(s):  
Experimental Data ◽  
Weak Form ◽  
Model Parameters ◽  
One Dimensional ◽  
Secondary Compression ◽  
Compression Creep ◽  
Consolidation Model ◽  
Finite Element Procedure ◽  
Effects Of Temperature ◽  
Leda Clay

A nonlinear theory of consolidation is presented which takes into account secondary compression. The theory is incorporated into a weak form of equilibrium that is suitable for a finite element procedure. The model is used to interpret Crawford's experimental data on Leda clay. Limitations of the model are discussed, and a few thoughts on the effects of temperature on the evaluation of model parameters are briefly presented.Key words: secondary compression, creep, one-dimensional consolidation, modelling.

An Experimental Investigation of the Effects of Cycling Frequency and Temperature on the Fatigue Life of 60 Tin/40 Lead Solder

1996 ◽  
Vol 118 (4) ◽  
pp. 280-284 ◽  
Author(s):  
Gregory D. Leece ◽  
Ibrahim Miskioglu ◽  
David A. Nelson
Keyword(s):  
Experimental Data ◽  
Fatigue Life ◽  
Load Control ◽  
Model Parameters ◽  
Strong Correlations ◽  
Mechanical Fatigue ◽  
Fatigue Model ◽  
Cycling Frequency ◽  
Effects Of Temperature ◽  
Cycles To Failure

The effects of cycling frequency and temperature on the fatigue life of solder has been analyzed. Mechanical fatigue life experiments were conducted under load control while varying the temperature and cycling frequency. Using the experimental data, a fatigue model was formulated based on the Basquin and the Coffin-Manson relations, introducing the effects of temperature and frequency. The model parameters were obtained by a statistical method incorporating multiple linear regression. Using the model, estimated values of cycles to failure at each of the testing temperatures and frequency were calculated. Using the estimated values, an evaluation of each of the models was conducted, resulting in strong correlations between the model’s estimation and the experimental data.

Parameter Determination for Chloride and Tritium Transport in Undisturbed Lysimeters during Steady Flow

1992 ◽  
Vol 23 (2) ◽  
pp. 89-104 ◽  
Author(s):  
Ole H. Jacobsen ◽  
Feike J. Leij ◽  
Martinus Th. van Genuchten
Keyword(s):  
Experimental Data ◽  
Unsaturated Flow ◽  
Transport Model ◽  
Time Moment ◽  
Breakthrough Curves ◽  
Coarse Sand ◽  
Retardation Factor ◽  
Parameter Determination ◽  
Model Parameters ◽  
Water Fraction

Breakthrough curves of Cl and 3H2O were obtained during steady unsaturated flow in five lysimeters containing an undisturbed coarse sand (Orthic Haplohumod). The experimental data were analyzed in terms of the classical two-parameter convection-dispersion equation and a four-parameter two-region type physical nonequilibrium solute transport model. Model parameters were obtained by both curve fitting and time moment analysis. The four-parameter model provided a much better fit to the data for three soil columns, but performed only slightly better for the two remaining columns. The retardation factor for Cl was about 10 % less than for 3H2O, indicating some anion exclusion. For the four-parameter model the average immobile water fraction was 0.14 and the Peclet numbers of the mobile region varied between 50 and 200. Time moments analysis proved to be a useful tool for quantifying the break through curve (BTC) although the moments were found to be sensitive to experimental scattering in the measured data at larger times. Also, fitted parameters described the experimental data better than moment generated parameter values.

Food-borne Illness Surveillance and Etiology of Diarrhea in Bangladesh

2018 ◽  
Author(s):  
Mohammad Afzalur Rahman ◽  
M Flora ◽  
M Rahman ◽  
M Billah
Keyword(s):  
Food Borne ◽  
Food Borne Illness

scholarly journals In Silico Characterization of Toxin-Antitoxin Systems in Campylobacter Isolates Recovered from Food Sources and Sporadic Human Illness

Genes ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 72
Author(s):  
Bishoy Wadie ◽  
Mohamed A. Abdel-Fattah ◽  
Alshymaa Yousef ◽  
Shaimaa F. Mouftah ◽  
Mohamed Elhadidy ◽  
...  
Keyword(s):  
Environmental Conditions ◽  
In Silico ◽  
Antimicrobial Agents ◽  
Food Sources ◽  
Model Organisms ◽  
Food Borne ◽  
Food Borne Illness ◽  
Human Illness ◽  
Clonal Population Structure ◽  
In Silico Characterization

Campylobacter spp. represents the most common cause of gastroenteritis worldwide with the potential to cause serious sequelae. The ability of Campylobacter to survive stressful environmental conditions has been directly linked with food-borne illness. Toxin-antitoxin (TA) modules play an important role as defense systems against antimicrobial agents and are considered an invaluable strategy harnessed by bacterial pathogens to survive in stressful environments. Although TA modules have been extensively studied in model organisms such as Escherichia coli K12, the TA landscape in Campylobacter remains largely unexplored. Therefore, in this study, a comprehensive in silico screen of 111 Campylobacter (90 C.jejuni and 21 C.coli) isolates recovered from different food and clinical sources was performed. We identified 10 type II TA systems belonging to four TA families predicted in Campylobacter genomes. Furthermore, there was a significant association between the clonal population structure and distribution of TA modules; more specifically, most (12/13) of the Campylobacter isolates belonging to ST-21 isolates possess HicB-HicA TA modules. Finally, we observed a high degree of shared synteny among isolates bearing certain TA systems or even coexisting pairs of TA systems. Collectively, these findings provide useful insights about the distribution of TA modules in a heterogeneous pool of Campylobacter isolates from different sources, thus developing a better understanding regarding the mechanisms by which these pathogens survive stressful environmental conditions, which will further aid in the future designing of more targeted antimicrobials.

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