scholarly journals Effect of Challenge Temperature and Solute Type on Heat Tolerance of Salmonella Serovars at Low Water Activity

2001 ◽  
Vol 67 (9) ◽  
pp. 4128-4136 ◽  
Author(s):  
K. L. Mattick ◽  
F. Jørgensen ◽  
P. Wang ◽  
J. Pound ◽  
M. H. Vandeven ◽  
...  
Keyword(s):  
Water Activity ◽  
Heat Tolerance ◽  
Weibull Model ◽  
Microbial Inactivation ◽  
Published Data ◽  
Death Rates ◽  
Factors Affecting ◽  
Serovar Typhimurium ◽  
Death Kinetics ◽  
Fail Safe

ABSTRACT Salmonella spp. are reported to have an increased heat tolerance at low water activity (aw; measured by relative vapor pressure [rvp]), achieved either by drying or by incorporating solutes. Much of the published data, however, cover only a narrow treatment range and have been analyzed by assuming first-order death kinetics. In this study, the death ofSalmonella enterica serovar Typhimurium DT104 when exposed to 54 combinations of temperature (55 to 80°C) and aw (rvp 0.65 to 0.90, reduced using glucose-fructose) was investigated. The Weibull model (LogS = −btn ) was used to describe microbial inactivation, and surface response models were developed to predict death rates for serovar Typhimurium at all points within the design surface. The models were evaluated with data generated by using six different Salmonella strains in place of serovar Typhimurium DT104 strain 30, two different solutes in place of glucose-fructose to reduce aw, or six low-awfoods artificially contaminated with Salmonella in place of the sugar broths. The data demonstrate that, at temperatures of ≥70°C, Salmonella cells at low aw were more heat tolerant than those at a higher aw but below 65°C the reverse was true. The same patterns were generated when sucrose (rvp 0.80 compared with 0.90) or NaCl (0.75 compared with 0.90) was used to reduce aw, but the extent of the protection afforded varied with solute type. The predictions of thermal death rates in the low-aw foods were usually fail-safe, but the few exceptions highlight the importance of validating models with specific foods that may have additional factors affecting survival.

Predicting Survival of Salmonella in Low–Water Activity Foods: An Analysis of Literature Data

2014 ◽  
Vol 77 (9) ◽  
pp. 1448-1461 ◽  
Author(s):  
SOFIA M. SANTILLANA FARAKOS ◽  
DONALD W. SCHAFFNER ◽  
JOSEPH F. FRANK
Keyword(s):  
Influencing Factors ◽  
Water Activity ◽  
Predictive Models ◽  
Culture Media ◽  
Weibull Model ◽  
Factor Log ◽  
The Times ◽  
Time Required ◽  
Log Linear ◽  
Fail Safe

Factors such as temperature, water activity (aw), substrate, culture media, serotype, and strain influence the survival of Salmonella in low-aw foods. Predictive models for Salmonella survival in low-aw foods at temperatures ranging from 21 to 80°C and water activities below 0.6 were previously developed. Literature data on survival of Salmonella in low-aw foods were analyzed in the present study to validate these predictive models and to determine global influencing factors. The results showed the Weibull model provided suitable fits to the data in 75% of the curves as compared with the log-linear model. The secondary models predicting the time required for log-decimal reduction (log δ) and shape factor (log β) values were useful in predicting the survival of Salmonella in low-aw foods. Statistical analysis indicated overall fail-safe secondary models, with 88% of the residuals in the acceptable and safe zones (<0.5 log CFU) and a 59% correlation coefficient (R2 = 0.35). A high variability in log δ-values and log β-values was observed, emphasizing the importance of experimental design. Factors of significant influence on the times required for first log-decimal reduction included temperature, aw, product, and serotype. Log β-values were significantly influenced by serotype, the type of inoculum (wet or dry), and whether the recovery media was selective or not. The results of this analysis provide a general overview of survival kinetics of Salmonella in low-aw foods and its influencing factors.

scholarly journals New Mathematical Modeling Approach for Predicting Microbial Inactivation by High Hydrostatic Pressure

2007 ◽  
Vol 73 (8) ◽  
pp. 2468-2478 ◽  
Author(s):  
Bernadette Klotz ◽  
D. Leo Pyle ◽  
Bernard M. Mackey
Keyword(s):  
Microbial Inactivation ◽  
Inactivation Kinetics ◽  
Published Data ◽  
Model Parameters ◽  
Order Kinetic ◽  
Square Root ◽  
Additional Time ◽  
Decimal Reduction Time ◽  
First Order ◽  
Primary Model

ABSTRACT A new primary model based on a thermodynamically consistent first-order kinetic approach was constructed to describe non-log-linear inactivation kinetics of pressure-treated bacteria. The model assumes a first-order process in which the specific inactivation rate changes inversely with the square root of time. The model gave reasonable fits to experimental data over six to seven orders of magnitude. It was also tested on 138 published data sets and provided good fits in about 70% of cases in which the shape of the curve followed the typical convex upward form. In the remainder of published examples, curves contained additional shoulder regions or extended tail regions. Curves with shoulders could be accommodated by including an additional time delay parameter and curves with tails shoulders could be accommodated by omitting points in the tail beyond the point at which survival levels remained more or less constant. The model parameters varied regularly with pressure, which may reflect a genuine mechanistic basis for the model. This property also allowed the calculation of (a) parameters analogous to the decimal reduction time D and z, the temperature increase needed to change the D value by a factor of 10, in thermal processing, and hence the processing conditions needed to attain a desired level of inactivation; and (b) the apparent thermodynamic volumes of activation associated with the lethal events. The hypothesis that inactivation rates changed as a function of the square root of time would be consistent with a diffusion-limited process.

Biodynamic Modeling of a Pedestrian Impact With a Rigid Frontal Guard of a Utility Vehicle

2010 ◽  
Author(s):  
Rasoul Moradi ◽  
Chandrashekhar K. Thorbole ◽  
Michael McCoy ◽  
Hamid M. Lankarani
Keyword(s):  
Front Surface ◽  
Body Region ◽  
Computational Technique ◽  
Surface Model ◽  
Published Data ◽  
Factors Affecting ◽  
Light Trucks ◽  
Accident Data ◽  
Facet Surface ◽  
The Impact

Accident data reveals that in most pedestrian accidents, the pedestrian head and lower extremity are vulnerable to serious injuries. The vehicle front geometry profile as well as the impact speed are important factors affecting the pedestrian kinematics and injury potential. In the US, accident data also shows that the fatality rate for pedestrian/light trucks and vans (LTV) impact is greater than that for the pedestrian/passenger-car impact. Addition of a front guard on light trucks and sports utility vehicles to mitigate damage during off-road activity or to provide mounting points for extra lights, makes the pedestrian more vulnerable to the impact. In this paper, a computational technique is utilized to study the influence of the added front guard on the impacted pedestrian. A CAD model of a typical commercial frontal guard is developed and converted into a rigid facet model, and attached to the vehicle front. The validated standing dummy model in the MADYMO code is used to simulate a pedestrian, and the rigid facet-surface model of a pickup truck is used to generate a vehicle front surface. This computational model is validated by comparing the pedestrian kinematics with the published data. This study demonstrates that the pedestrian mid body region is more vulnerable with the addition of guard on the vehicle. The result from this study facilitates a better understanding of a guard design and its geometry profile as required to protect vulnerable road users.

Modeling the Effect of Water Activity, pH, and Temperature on the Probability of Enterotoxin A Production by Staphylococcus aureus

2016 ◽  
Vol 79 (1) ◽  
pp. 148-152 ◽  
Author(s):  
TIAN DING ◽  
YAN-YAN YU ◽  
CHENG-AN HWANG ◽  
QING-LI DONG ◽  
SHI-GUO CHEN ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Water Activity ◽  
Storage Temperature ◽  
Probability Model ◽  
Toxin Production ◽  
Factors Affecting ◽  
Model Predictions ◽  
And Storage ◽  
Storage Temperatures ◽  
Good Agreement

ABSTRACT The objectives of this study were to develop a probability model of Staphylococcus aureus enterotoxin A (SEA) production as affected by water activity (aw), pH, and temperature in broth and assess its applicability for milk. The probability of SEA production was assessed in tryptic soy broth using 24 combinations of aw (0.86 to 0.99), pH (5.0 to 7.0), and storage temperature (10 to 30°C). The observed probabilities were fitted with a logistic regression to develop a probability model. The model had a concordant value of 97.5% and concordant index of 0.98, indicating that the model satisfactorily describes the probability of SEA production. The model showed that aw, pH, and temperature were significant factors affecting the probability of toxin production. The model predictions were in good agreement with the observed values obtained from milk. The model may help manufacturers in selecting product pH and aw and storage temperatures to prevent SEA production.

Factors Affecting Choice of Working Stresses for High-Temperature Service

1933 ◽  
Vol 1 (3) ◽  
pp. 99-102
Author(s):  
P. G. McVetty
Keyword(s):  
High Temperature ◽  
Published Data ◽  
Creep Tests ◽  
Fundamental Study ◽  
Factors Affecting ◽  
Creep Characteristics ◽  
The Stability ◽  
Safe Working

Abstract This paper discusses the various methods which have been proposed to determine safe working stresses for high-temperature service. The question of the stability of alloys during the test and in subsequent service is considered, with particular emphasis upon probable changes in creep characteristics during long exposure to stress and temperature. It is shown that published data in general do not admit of extrapolation, and that attempts to estimate total creep in service from such data are not usually satisfactory. The author stresses the need for more fundamental study of the laws governing creep rather than creep tests of many different materials.

Analysing persistence of grass swards in terms of tiller birth and death

2011 ◽  
Vol 15 ◽  
pp. 63-68
Author(s):  
C. Matthew ◽  
Sackville Hamilton
Keyword(s):  
Abiotic Stresses ◽  
Birth Rate ◽  
Phleum Pratense ◽  
Leslie Matrix ◽  
Published Data ◽  
Population Stability ◽  
Death Rates ◽  
Timothy Grass ◽  
High Death ◽  
Bud Site

A methodology is developed to analyse the contribution to sward persistence of the processes tiller birth and tiller death, and variation in their rate over an annual cycle. The methodology is tested using previously published data for timothy grass (Phleum pratense). The analysis shows that high death rates of timothy tillers in summer present a problem for persistence in that tiller appearance rates required to maintain the tiller population in these conditions require tiller bud site usage statistics that are biologically unlikely in field swards. While it is not suggested that ryegrass has a naturally high tiller death rate in summer as demonstrated here for timothy, where abiotic stresses reduce ryegrass tiller survival, the same principles are likely to apply. Keywords: Leslie matrix, Phleum pratense, population stability, tiller birth rate, tiller survival rate, timothy grass

‘Quit while you are ahead – and smell the roses!’ A survey of retired Fellows of the Australian and New Zealand College of Anaesthetists

2021 ◽  
pp. 0310057X2110057
Author(s):  
Diana Strange Khursandi ◽  
Victoria Eley
Keyword(s):  
Clinical Practice ◽  
New Zealand ◽  
Standard Deviation ◽  
Response Rate ◽  
Common Factors ◽  
Published Data ◽  
Factors Affecting ◽  
Retirement Decisions ◽  
Zealand College ◽  
The Mean

There are no published data on the age of retirement of anaesthetists in Australia and New Zealand. We surveyed 622 retired Fellows of the Australian and New Zealand College of Anaesthetists to determine their ages of complete retirement from clinical practice, demographics, and whether they had retired at the age they had intended to retire. We also aimed to explore factors affecting the decision to retire, the practice of ‘winding down’, common post-retirement activities, and the arrangement of personal and professional affairs. Responses were received from 371 specialists (response rate 60%). The mean (standard deviation) age of retirement was 65.2 (6.9) years. The mean (standard deviation) retirement ages ranged from 62.0 (7.1) years (those who retired earlier than planned) to 68.0 (4.3) years (those who retired later than they had intended). The mean (standard deviation) age of retirement of the male respondents was 66.0 (6.5) years, and for female respondents was 62.7 (7.7) years. Two hundred and thirty-three respondents (63%) reported winding down their practice prior to retirement, and 360 (97%) had made a will. Poor health and loss of confidence were the two most common factors in the retirement decisions of those who retired earlier than they had planned. Our results may assist current practitioners plan for retirement, and suggest strategies to help health services, departments and private groups accommodate individuals in winding down their practice.

Shear strength of spruce glued—laminated timber beams

1985 ◽  
Vol 12 (3) ◽  
pp. 661-672 ◽  
Author(s):  
F. J. Keenan ◽  
J. Kryla ◽  
B. Kyokong
Keyword(s):  
Shear Strength ◽  
Cross Sections ◽  
Weibull Model ◽  
Longitudinal Shear ◽  
Douglas Fir ◽  
Published Data ◽  
Cross Sectional ◽  
Characteristic Value ◽  
Glued Laminated Timber ◽  
Timber Beams

The effect of size on longitudinal shear strength has been well established for Douglas-fir glued–laminated (glulam) timber beams. The present study examined whether this phenomenon exists in glulam beams made of spruce. The experiment consisted of three projects in which beams of various sizes were tested under concentrated mid-span load. The project A beams had clear spruce webs and white elm flanges with cross-sectional dimensions varying from 25 × 25 mm to 75 × 75 mm. The project B beams had spruce glulam webs with Douglas-fir flanges; cross sections ranged from 20 × 100 mm to 90 × 200 mm. In project C, three groups of 10 replications of commercially representative sizes of glulam beams were made from stiffness-rated spruce–pine–fir lumber. The beam cross sections were 76 × 200 mm, 76 × 400 mm, and 127 × 400 mm.The results indicated that depth, width, and shear plane had significant effects on the longitudinal shear strength of the beams in project A. Depth, width, and shear span of the small glulam beams in project B also had highly significant effects on shear strength. However, no effects of depth and width on the shear strength of glulam beams in project C were found. Regression analysis showed no dependence of shear strength on sheared volume for the beams of all three projects. The three-parameter Weibull model also failed to predict the near-minimum shear strength of spruce glulam beams. The results suggested that the lower-bound shear strength of spruce glulam beams is a constant (regardless of beam volume) and could be used as a single characteristic value for glulam design in shear. Further review of published data indicates that this may also be the case for Douglas-fir glulam but with a lower characteristic value than for spruce.

Modification of a Predictive Model To Include the Influence of Fat Content on Salmonella Inactivation in Low-Water-Activity Foods

2020 ◽  
Vol 83 (5) ◽  
pp. 801-815
Author(s):  
LISA M. TRIMBLE ◽  
JOSEPH F. FRANK ◽  
DONALD W. SCHAFFNER
Keyword(s):  
Water Activity ◽  
Survival Data ◽  
Peanut Butter ◽  
Weibull Model ◽  
Fat Content ◽  
Mitigation Strategies ◽  
Model Parameters ◽  
Least Squares Regression ◽  
Salmonella Spp ◽  
Model Predictions

ABSTRACT Low-water-activity (aw) foods (including those containing fat) are often implicated in outbreaks of Salmonella spp. The influence of fat content on survival in foods such as peanut butter remains unclear. Certain Salmonella serovars can survive for long periods in harsh temperatures and low moisture conditions. The objective of this study was to determine the influence of fat content on the survival of Salmonella in low-aw foods and expand an existing secondary inactivation model previously validated for lower-fat foods. Whey protein powder supplemented with peanut oil was equilibrated to five target aw values (aw < 0.60), inoculated with a dried four-strain cocktail of Salmonella, vacuum sealed, and stored at 22, 37, 50, 60, 70, and 80°C for 48 h, 28 days, or 168 days. Survival data were fitted to Weibull, Biphasic-linear, Double Weibull, and Geeraerd-tail models. The Weibull model was chosen for secondary modeling due to its ability to satisfactorily describe the data over most of the conditions under study. The influence of temperature, fat content, and aw on the Weibull model parameters was evaluated using nonlinear least squares regression, and a revised secondary model was developed based on parameter significance. Peanut butter, chia seed powder, toasted oat cereal, and animal crackers within the aw range of the model were used to validate the modified model within its temperature range. Fat content influenced survival in samples held at temperatures ≥50°C, whereas aw influenced survival at 37 and 70°C. The model predictions demonstrated improved % bias and % discrepancy compared with the previous model. Weibull model predictions were accurate and fail-safe in 38 and 58%, respectively, of the food and environmental conditions under study. Predictions were less reliable for peanut butter held at 80°C. This study provides data and a model that can aid in the development of risk mitigation strategies for low-aw foods containing fat. HIGHLIGHTS

Developing Safety Performance Functions for Railway Grade Crossings: A Case Study of Canada

2015 ◽  
Author(s):  
Shahram Heydari ◽  
Liping Fu
Keyword(s):  
Weibull Model ◽  
Safety Performance ◽  
Bayesian Hierarchical ◽  
Factors Affecting ◽  
Stop Sign ◽  
Technological Advances ◽  
Safety Performance Functions ◽  
Flashing Light ◽  
Grade Crossings ◽  
Safety Features

Although accident frequencies at railway grade crossings have shown a decreasing trend over the last two decades (partly due to implemented safety improvements and technological advances), safety at grade crossings is still a major concern since crossing accidents are usually associated with devastating consequences. This paper investigates the effect of various site attributes on railway crossing safety outcomes using recent Canada wide data from a 6-year period (2008–2013). The new data sets allow adjusting previous accident models according to latest circumstances (e.g., vehicles’ improved safety features) affecting safety dynamics at crossings. Employing Bayesian hierarchical models including the non-conventional Poisson-Weibull model, different safety performance functions were separately developed for crossings with the following major warning systems: (1) flashing light and bell (FLB), (2) flashing light, bell, and gate (FLBG), (3) standard reflectorized crossing sign (SRCS), and (4) standard reflectorized crossing sign and stop sign (SRCS & STOP). Among other findings, the results indicated that traffic exposure (product of train and vehicle), number of lanes, whistle prohibition, train speed, and road speed were the most important factors affecting accident frequencies at Canadian railway crossings. It should be also noted that safety performance functions vary, in terms of independent variables and their associated coefficients, between the aforementioned warning devices.

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