Response surface models for effects of temperature and previous growth sodium chloride on growth kinetics of Salmonella typhimurium on cooked chicken breast

Response surface models were developed and validated for effects of temperature (10 to 40 degrees C) and previous growth NaCl (0.5 to 4.5%) on lag time (lambda) and specific growth rate (mu) of Salmonella Typhimurium on cooked chicken breast. Growth curves for model development (n = 55) and model validation (n = 16) were fit to a two-phase linear growth model to obtain lambda and mu of Salmonella Typhimurium on cooked chicken breast. Response surface models for natural logarithm transformations of lambda and mu as a function of temperature and previous growth NaCl were obtained by regression analysis. Both lambda and mu of Salmonella Typhimurium were affected (P < 0.0001) by temperature but not by previous growth NaCl. Models were validated against data not used in their development. Mean absolute relative error of predictions (model accuracy) was 26.6% for lambda and 15.4% for mu. Median relative error of predictions (model bias) was 0.9% for lambda and 5.2% for mu. Results indicated that the models developed provided reliable predictions of lambda and mu of Salmonella Typhimurium on cooked chicken breast within the matrix of conditions modeled. In addition, results indicated that previous growth NaCl (0.5 to 4.5%) was not a major factor affecting subsequent growth kinetics of Salmonella Typhimurium on cooked chicken breast. Thus, inclusion of previous growth NaCl in predictive models may not significantly improve our ability to predict growth of Salmonella spp. on food subjected to temperature abuse.     

Extrapolation of a predictive model for growth of a low inoculum size of Salmonella Typhimurium DT104 on chicken skin to higher inoculum sizes

Validation of model predictions for independent variables not included during model development can save time and money by identifying conditions for which new models are not needed. A single strain of Salmonella Typhimurium DT104 was used to develop a general regression neural network (GRNN) model for growth of a low inoculum size (0.9 log) on chicken skin with native microflora as a function of time (0 to 8 h) and temperature (20 to 45°C). The ability of the GRNN model to predict growth of higher inoculum sizes (2, 3, or 4.1 log) was evaluated. When the proportion of residuals in an acceptable prediction zone (pAPZ) from -1 log (fail-safe) to 0.5 log (fail-dangerous) was ≥0.7, the GRNN model was classified as providing acceptable predictions of the test data. The pAPZ for dependent data was 0.93 and for independent data for interpolation was 0.88. The pAPZs for extrapolation to higher inoculum sizes of 2, 3, or 4.1 log were 0.92, 0.73, and 0.77, respectively. However, residual plots indicated local prediction problems with pAPZs of < 0.7 for an inoculum size of 3 log at 30, 35, and 40°C and for an inoculum size of 4.1 log at 35 and 40°C where predictions were fail-dangerous, indicating faster growth at higher inoculum sizes. The model provided valid predictions of Salmonella Typhimurium DT104 growth on chicken skin from inoculum sizes of 0.9 and 2 log at all temperatures investigated and from inoculum sizes of 3 and 4.1 log at some but not all temperatures investigated. Thus, the model can be improved by including inoculum size as an independent variable.     

Differences Between the Order Model and the Weibull Model in the Modeling of the Enzymatic Browning

This study was focused on a comparison between the first order model and the Weibull model regarding their suitability to fit the enzymatic browning kinetic data in samples of mushrooms, pears, apples, avocados, and bananas (based on the use of the L* luminosity, the ΔE*, and the BI as the browning indexes). In order to obtain statistically robust results, at least 900 points by curve kinetic were used to describe the enzymatic browning. A mean square error was used to measure the suitability of each model. In this study, 60 slices from each sample were analyzed in a computer vision system to calculate L* values. In the results, it was demonstrated that the Weibull model appears to be the best model for mushrooms, pears, apples, avocados, and bananas. According to that expected for a First order kinetic, the β values should be equal to one in the Weibull model. In this study, the β values observed were always less than one. Therefore, it is not possible to assert that the enzymatic browning always follows an empirical First order kinetic. According to the results of this investigation, it is recommended to use the Weibull model first to insure that enzymatic browning kinetic is of the first order.     

Efficiency of urease and nitrification inhibitors in reducing ammonia volatilization from diverse nitrogen fertilizers applied to different soil types and wheat straw mulching

BACKGROUND: Some authors suggest that the absence of tillage in agricultural soils might have an influence on the efficiency of nitrogen applied in the soil surface. In this study we investigate the influence of no‐tillage and soil characteristics on the efficiency of a urease inhibitor (N‐(n‐butyl)thiophosphoric triamide, NBPT) and a nitrification inhibitor (diciandiamide, DCD) in decreasing ammonia volatilization from urea and ammonium nitrate (AN), respectively. RESULTS: The results indicate that ammonia volatilization in soils amended with urea was significantly higher than in those fertilized with AN. Likewise, the main soil factors affecting ammonia volatilization from urea are clay and sand soil contents. While clay impedes ammonia volatilization, sand favours it. The presence of organic residues on soil surface (no‐tillage) tends to increase ammonia volatilization from urea, although this fact depended on soil type. The presence of NBPT in urea fertilizer significantly reduced soil ammonia volatilization. This action of NBPT was negatively affected by acid soil pH and favoured by soil clay content. CONCLUSION: The presence of organic residues on soil surface amended with urea increased ammonia volatilization, and was particularly high in sandy compared with clay soils. Application of NBPT reduced ammonia volatilization although its efficiency is reduced in acid soils. Concerning AN fertilization, there were no differences in ammonia volatilization with or without DCD in no‐tillage soils. Copyright © 2011 Society of Chemical Industry     

Prevalence of alcohol-impaired drivers based on random breath tests in a roadside survey in Catalonia (Spain)

Sobriety checkpoints are not usually randomly located by traffic authorities. As such, information provided by non-random alcohol tests cannot be used to infer the characteristics of the general driving population. In this paper a case study is presented in which the prevalence of alcohol-impaired driving is estimated for the general population of drivers. A stratified probabilistic sample was designed to represent vehicles circulating in non-urban areas of Catalonia (Spain), a region characterized by its complex transportation network and dense traffic around the metropolis of Barcelona. Random breath alcohol concentration tests were performed during spring 2012 on 7596 drivers. The estimated prevalence of alcohol-impaired drivers was 1.29%, which is roughly a third of the rate obtained in non-random tests. Higher rates were found on weekends (1.90% on Saturdays and 4.29% on Sundays) and especially at night. The rate is higher for men (1.45%) than for women (0.64%) and it shows an increasing pattern with age. In vehicles with two occupants, the proportion of alcohol-impaired drivers is estimated at 2.62%, but when the driver was alone the rate drops to 0.84%, which might reflect the socialization of drinking habits. The results are compared with outcomes in previous surveys, showing a decreasing trend in the prevalence of alcohol-impaired drivers over time.     

A light-weight authentication scheme for wireless sensor networks

Sensor networks are ad hoc mobile networks that include sensor nodes with limited computational and communication capabilities. They have become an economically viable monitoring solution for a wide variety of applications. Obviously, security threats need to be addressed and, taking into account its limited resources, the use of symmetric cryptography is strongly recommended. In this paper, a light-weight authentication model for wireless sensor networks composed of a key management and an authentication protocol is presented. It is based on the use of simple symmetric cryptographic primitives with very low computational requirements, which obtains better results than other proposals in the literature. Compared to SPINS and BROSK protocols, the proposal can reduce energy consumption by up to 98% and 67%, respectively. It also scales well with the size of the network, due to it only requiring one interchanged message, independently of the total number of nodes in the network.     

Charge Modified Cowpea Mosaic Virus Particles for Templated Mineralization

Surface charge modification of wild‐type Cowpea mosaic virus, a plant virus, is sufficient to promote the templated mineralization of metal and metal oxide. Surface negative charge is increased by the chemical introduction of succinamate on surface lysine groups. The cobalt and iron oxide templated nanoparticles subsequently obtained are monodisperse with a diameter of ca. 32 nm. Further, the iron oxide‐CPMV nanoparticles can be readily decorated with thiol‐containing molecules.     

Molecular and Electrophysiological Role of Diabetes-Associated Circulating Inflammatory Factors in Cardiac Arrhythmia Remodeling in a Metabolic-Induced Model of Type 2 Diabetic Rat

Background: Diabetic patients have prolonged cardiac repolarization and higher risk of arrhythmia. Besides, diabetes activates the innate immune system, resulting in higher levels of plasmatic cytokines, which are described to prolong ventricular repolarization. Methods: We characterize a metabolic model of type 2 diabetes (T2D) with prolonged cardiac repolarization. Sprague-Dawley rats were fed on a high-fat diet (45% Kcal from fat) for 6 weeks, and a low dose of streptozotozin intraperitoneally injected at week 2. Body weight and fasting blood glucose were measured and electrocardiograms of conscious animals were recorded weekly. Plasmatic lipid profile, insulin, cytokines, and arrhythmia susceptibility were determined at the end of the experimental period. Outward K⁺ currents and action potentials were recorded in isolated ventricular myocytes by patch-clamp. Results: T2D animals showed insulin resistance, hyperglycemia, and elevated levels of plasma cholesterol, triglycerides, TNFα, and IL-1b. They also developed bradycardia and prolonged QTc-interval duration that resulted in increased susceptibility to severe ventricular tachycardia under cardiac challenge. Action potential duration (APD) was prolonged in control cardiomyocytes incubated 24 h with plasma isolated from diabetic rats. However, adding TNFα and IL-1b receptor blockers to the serum of diabetic animals prevented the increased APD. Conclusions: The elevation of the circulating levels of TNFα and IL-1b are responsible for impaired ventricular repolarization and higher susceptibility to cardiac arrhythmia in our metabolic model of T2D.     

Metal contact properties of poly3-octylthiophene thin films

Chemically synthesized undoped poly3-octylthiophene (P3OT) was deposited as thin films on conducting glass substrates by drop casting. Doping state of P3OT was obtained by adding FeCl₃ into the original P3OT solution. A qualitative explanation of the electrical contact behavior of the P3OT films was given by a band diagram made from optical absorbance spectra and electrochemical current–voltage curves of the polymeric films. Gold contacts on both undoped and doped P3OT films give an ohmic contact. Silver/P3OT contact shows a rectifying behavior; the forward current is 500 times the reverse current at 0.5 V. Aluminum also forms rectifying contact with the two types of P3OT films, although the experimental rectification ratio is lower than that of the silver. The I–V curves of rectifying contacts were analyzed with Schottky equation and different diode parameters were obtained.