Modified Weibull Model Research Articles

Inactivation of Listeria monocytogenes and Salmonella spp. on cantaloupe rinds by blue light emitting diodes (LEDs)

This study evaluated the potential of blue light-emitting diodes (LED) of wavelength 405 and 460 nm in combination with sodium chlorophyllin to inactivate Listeria monocytogenes and Salmonella spp. on cantaloupe rind. A cocktail culture of L. monocytogenes or Salmonella spp. strains was surface inoculated onto cantaloupe rinds to reach a final concentration of 4 log CFU/cm2 and dip-treated in a 100 μM sodium copper chlorophyllin solution. The cantaloupe samples were then exposed to 405 or 460 nm LEDs at a total dose of 1210 J/cm2 and 5356 J/cm2, respectively, at 4 and 20 °C. Results showed that the antibacterial efficacy against both pathogens on cantaloupe rinds between LED alone and LED with the chlorophyllin were statistically similar with bacterial inactivation ranging from 1.1 to 3 log CFU/cm2 in most of the cases or the difference was only minimal. A similar inactivation of 3 log CFU/cm2 was obtained in the case of L. monocytogenes and Salmonella spp. when illuminated by 405 nm LEDs while the inactivation of L. monocytogenes was higher than Salmonella spp. when illuminated by 460 nm LED. The δ value, a modified Weibull model parameter defined as the time (h) taken to reduce the bacterial population by 90%, was computed to compare the inactivation rates of the conditions. It was inferred that illumination with 405 nm LED required a lower δ value than 460 nm LED illumination (P < 0.05) for the inactivation of L. monocytogenes at 20 °C and Salmonella spp. at 4 °C. Thus the findings of this study indicate a promising application of blue LEDs to inactivate these pathogens on the surface of cantaloupe, minimizing the risk of listeriosis and salmonellosis by consumption of cantaloupe.

Modeling Mayfly Nymph Length Distribution and Population Dynamics Across a Gradient of Stream Temperatures and Stream Types

We analyze a process-based temperature model for the length distribution and population over time of mayfly nymphs. Model parameters are estimated using a Markov Chain Monte Carlo parameter estimation method utilizing length distribution data at five different stream sites. Two different models (a standard exponential model and a modified Weibull model) of mayfly mortality are evaluated, where in both cases mayfly length growth is a function of stream temperature. Based on model-data comparisons to the modeled length distribution and the Bayesian Information Criterion, we found that approaches that length distribution data can reliably estimate 2–3 model parameters. Future model development could include additional factors include such as upstream environmental factors, abiotic conditions, interspecific competition, predation, or stream salinity. Outputs of this model could be applied to predict mayfly emergence across a geographic domain or to forecast mayfly population responses to climate change.

Convective Drying of Osmo-Treated Abalone (Haliotis rufescens) Slices: Diffusion, Modeling, and Quality Features

The focus of this research was based on the application of an osmotic pretreatment (15% NaCl) for drying abalone slices, and it evaluates the influence of hot-air drying temperature (40–80°C) on the product quality. In addition, the mass transfer kinetics of salt and water was also studied. The optimal time of the osmotic treatment was established until reaching a pseudo equilibrium state of the water and salt content (290 min). The water effective diffusivity values during drying ranged from 3.76 to 4.75 × 10−9 m2/s for three selected temperatures (40, 60, and 80°C). In addition, experimental data were fitted by Weibull distribution model. The modified Weibull model provided good fitting of experimental data according to applied statistical tests. Regarding the evaluated quality parameters, the color of the surface showed a change more significant at high temperature (80°C), whereas the nonenzymatic browning and texture showed a decrease during drying process mainly due to changes in protein matrix and rehydration rates, respectively. In particular, working at 60°C resulted in dried samples with the highest quality parameters.

The Impact of Water Activity on Storage Stability of a Newly Reformulated Salami A pilot scale study

Two formulations of salami were obtained: a conventional salami (50 % beef, 20 % pork and 30 % animal fat, w/w) and a reformulated one (50 % beef, 20 % pork and 30 % a mixture of olive and palm oil - 2.5:1, w/w). Storage studies were performed by accelerated shelf life testing at 20�C and different relative humidity, in comparison with 4 and 8�C after 22 days of storage. Halsey model was the best one to describe the desorption isotherms. The products stability was evaluated by TBA (thiobarbituric acid) index and colour changes. TBA increased with the increase of the environment relative humidity at 4 and 8�C. Modified Weibull model described the changes in colour as a function of TBA and water activity. Bound water characteristics have markedly changed at 20�C for both products. The results of this work can be used as reference in defining reformulated salami minimal durability.

Use of predictive model to describe sporicidal and cell viability efficacy of betel leaf (Piper betle L.) essential oil on Aspergillus flavus and Penicillium expansum and its antifungal activity in raw apple juice

The present study describes the effect of betel leaf (Piper betle L.) essential oil (BLEO) on spore inactivation and cell viability of Aspergillus flavus and Penicillium expansum using predictive model and its antifungal activity in raw apple juice. Survival curve of the spores under minimum fungicidal concentration of BLEO was modelled by a modified Weibull model: logN=logN0−(t/δ)β. The forward and side-scatter parameters of flow cytometer suggested differences in size and complexity of spores. Propidium iodide was used as fluorescent stain to distinguish between viable and non-viable spores. Scanning electron microscopic images revealed morphological alterations of treated spores. The cell viability effect of BLEO on mycelial matrix of A. flavus and P. expansum was measured using tetrazolium salt MTT and the inhibition was fitted to dose-response curves. Mycelial biomass of a selected mould in raw apple juice treated with BLEO based microemulsion (BLEO-ME) having different concentration of BLEO was determined based on ergosterol content. BLEO-ME exhibited fungal growth inhibition in raw apple juice, which suggests potential of BLEO as antifungal agent in food system.

Effects of Temperature and Moisture on Sporulation and Infection by Pseudoperonospora cubensis

Cucumber downy mildew, caused by Pseudoperonospora cubensis, is a worldwide disease that causes severe damage to cucumber production. The effects of temperature and moisture on sporulation and infection by P. cubensis were investigated by inoculating cucumber ('85F12') cotyledons with sporangia and examining the sporangia produced on the inoculated cotyledons under artificially controlled environments. The result showed that the temperature required for sporangium infection by P. cubensis and sporulation of the downy mildew lesions occurred at 5 to 30°C. The optimal temperature estimated by the fitted model was 18.8°C for sporangium infection and 16.2°C for downy mildew lesion sporulation. The pathogen formed plenty of sporangia when disease cotyledons were wetted or in the environment with relative humidity = 100%. The downy mildew lesions produced only a few sporangia when placed in the environment with relative humidity = 90%. The inoculated cotyledons, which incubated for 5 days at about 20°C in a dry greenhouse, began to form sporangia 4 h after being wetted when incubated in darkness. The quantity of sporangia produced on the downy mildew lesions increased with extension of incubating period (within 12 h), and the relationship between produced sporangia and the incubation period at 15, 20, and 25°C can be described by three exponential models. The observed minimum wetness durations (MWD) required for sporangia to complete the infection process and cause downy mildew were 12, 4, 2.5, 1, 1, and 6 h for 5, 10, 15, 20, 25, and 30°C, respectively. The effect of temperature and wetness duration on infection by sporangia of P. cubensis can be described by the modified Weibull model. The shortest MWD was 0.45 h, about 27 min, estimated by model. The experimental data and models will be helpful in the development of forecasting models and effective control systems for cucumber downy mildew.

Recovery of intact human norovirus from cabbage Kimchi stored at 4 °C and 10 °C during fermentation

This study aimed to evaluate the recovery of structurally intact human norovirus (NoV) during Kimchi fermentation at varying temperatures. Lactic acid bacteria (LAB), pH, and acidity during storage and fermentation were also measured to assess the correlation between NoV reduction and microbial or physicochemical property alterations. LAB number, NoV G titer, pH, acidity, and the ability of NoV GII.4 to persist in Kimchi stored at 4 °C and 10 °C (survivability) as determined using nano magnetic beads conjugated with poly(methyl vinyl ether-maleic anhydride) combined with quantitative real-time reverse transcription-polymerase chain reaction amplification were investigated up to 28 days post-inoculation. NoV was detected in all test samples after 28 days although the NoV recovery quantity was reduced to 1.31 (4 °C) and 1.66 (10 °C) log10 genomic copies/reaction. The time required to reduce the amount of virus by 2.57 log10 (td) on survival plots of NoV determined using a modified Weibull model was 2445 days at 4 °C and 138 days at 10 °C. These results indicate that NoV from food preparation or processing is able to persistently survive in Kimchi. Therefore, preventing NoV transmission is important for protecting Kimchi against NoV contamination.

Modeling of the microbial inactivation by high hydrostatic pressure freezing

This work aimed at investigating the effect of HPF processes on the inactivation kinetics of selected microbial strains, Escherichia coli O157:H7 ATCC 26 and Lactococcus lactis ssp. Cremoris suspended in McIlvine buffer. The effects of different processing conditions, namely pressure level (200–400 MPa), temperature (0, −10, −20 °C), treatment time (0, 2, 5, 7, 10 min) and number of phase transitions (single or multiple transitions) were investigated in the experimental trials. The mechanism of cell inactivation in complex processes, in which pressure and temperature are simultaneously changed, was also studied and the synergistic effect of the two processing parameters, if any, was identified. Experimental data were analyzed and fitted with mathematical models representing the kinetics of microbial inactivation in HPF processes.The results obtained so far demonstrated that the factor controlling the process efficiency is the pressure level at constant operating temperature. The level of inactivation obtained increased with decreasing the processing temperature at constant pressure or increasing the number of phase transitions, and with decreasing the size of ice crystals formed in the product. Finally, the kinetics of microbial death was described by a modified Weibull model, whose parameters are dependent on processing conditions.

Increasing Sorption Isotherms Accuracy: Weibull Modelling and Linear Regression

Relying on an adequate mathematical approach, two different mathematical procedures can be applied to the huge database produced during gas sorption isotherm experiments in order to obtain accurate data to be used in the industrial practice. To treat data determined from gas sorption isotherms without a careful mathematical support will produce inaccurate results, because all the determinations will be dependent on human decision. The minimum error reported since the first stage of a sorption isotherm determination, which corresponds to volume calibrations of reference and sample cells performed through the use of helium, will produce enormous inaccuracies on sorption isotherm behavior. These inaccurate behaviors may sometimes invalidate any Coalbed Methane recovery and CO2 injection programs. The study consisted on investigating gas sorption isotherm accuracies determined during the first part of the sorption process, which is mainly conducted by monitoring the pressure decline with time, in the reference and the sample cells (when both cells are not in contact), until the stabilization stage is achieved. Three samples from two different coals were selected in order to study their gas sorption behavior, in terms of a clear mathematical approach, when submitted to three different gas compositions, viz. 99.999% methane (CH4); 99.999% carbon dioxide (CO2); and a gas mixture containing 74.99% CH4 + 19.99% CO2 + 5.02% nitrogen (N2). Sorption experiments allow to conclude that the three samples present the same mathematical response during the first part of the sorption process. However, all gas sorption data (adsorption and desorption) collected from reference cell have a better fitting to a Modified Weibull Model, and all gas sorption data (adsorption and desorption) collected from sample cell respond in a trustworthy way to a Linear Regression Model. Confidence bands and prediction intervals (or bands) were also computed.

The effect of elementary fibre variability on bamboo fibre strength

Abstract Tensile strength of brittle fibres exhibits statistical distribution and size dependence. In this work, the average strength of bamboo fibre is found to decrease from 568 to 483 MPa as mean diameter increases from 196.6 to 584.3 μm. The morphologies of bamboo fibres with increasing diameters were investigated through Scanning Electron Microscopy (SEM) to demonstrate variations in the quantity of elementary fibres. The influence of elementary fibre distributions on the fibre strength was also studied. A modified Weibull model based on number of elementary fibres is proposed to perform scaling predictions for the fracture strength of the fibres at different between-fibre diameters. It was shown that the predicted results are in reasonable agreement with experimental data, highlighting the adequacies of the new analytical model for describing the diameter dependence of tensile strength.

Investigations on the structure and properties of palm leaf sheath fiber

As a natural cellulosic fiber, palm leaf sheath fiber (palm fiber) is widely-distributed and abundant cellulose and engineering fiber resource. To obtain essential information about palm fiber, its morphology, composition, chemical and crystal structure, tensile characteristic and adsorption property were investigated. Test results of palm fiber were compared with those of other natural cellulosic fibers. Palm fiber presents aligned Si-dots on the surface and abundant fiber cells with spiral vessel tissues at the cross section. The chemical composition reveals that palm fiber contains abundant lignin but smaller amount of cellulose (the content of 28.16 %). In addition, investigation illustrates that cellulose in palm fiber is Iβ-dominant type, which is also confirmed by FTIR analysis. X-ray diffraction study shows that the crystallinity (30.52 %), crystallinity index (36.5 %) and crystal size (2.5 nm) are all apparently lower than those of ramie, flax and bamboo fibers. Given the low crystallinity and cellulose content of palm fiber, its tensile strength and Young’s modulus are also lower than those of other fibers. Moreover, palm fiber exhibits excellent breaking elongation, high moisture regain, distinct yield characteristic, and variability in strength. The modified Weibull model was used to study the tensile behavior of palm fiber. This model accurately predicted fiber strength. The absorption volume in isotherm of carbonized palm fiber increases with rising pressure, thus indicating good porous structure of the fiber.

Modified Weibull Distribution for Analyzing the Tensile Strength of Bamboo Fibers

There is growing evidence that the standard Weibull strength distribution is not always accurate for the description of variability in tensile strength and its dependence on the gauge size of brittle fibers. In this work, a modified Weibull model by incorporating the diameter variation of bamboo fiber is proposed to investigate the effect of fiber length and diameter on the tensile strength. Fiber strengths are obtained for lengths ranging from 20 to 60 mm and diameters ranging from 196.6 to 584.3 μm through tensile tests. It is shown that as the within-fiber diameter variation increases, the fracture strength of the bamboo fiber decreases. In addition, the accuracy of using weak-link scaling predictions based on the standard and modified Weibull distribution are assessed, which indicates that the use of the modified distribution provides better correlation with the experimental data than the standard model. The result highlights the accuracy of the modified Weibull model for characterizing the strength and predicting the size dependence of bamboo fiber.

Quantifying variability on thermal resistance of Listeria monocytogenes

Knowledge of the impact of strain variability and growth history on thermal resistance is needed to provide a realistic prediction and an adequate design of thermal treatments. In the present study, apart from quantifying strain variability on thermal resistance of Listeria monocytogenes, also biological variability and experimental variability were determined to prioritize their importance. Experimental variability was defined as the repeatability of parallel experimental replicates and biological variability was defined as the reproducibility of biologically independent reproductions. Furthermore, the effect of growth history was quantified. The thermal inactivation curves of 20 L. monocytogenes strains were fitted using the modified Weibull model, resulting in total 360 D-value estimates. The D-value ranged from 9 to 30min at 55°C; from 0.6 to 4min at 60°C; and from 0.08 to 0.6min at 65°C. The estimated z-values of all strains ranged from 4.4 to 5.7°C. The strain variability was ten times higher than the experimental variability and four times higher than the biological variability. Furthermore, the effect of growth history on thermal resistance variability was not significantly different from that of strain variability and was mainly determined by the growth phase.

Inactivation and Sublethal Injury Kinetics of Staphylococcus aureus in Broth at Low Temperature Storage

Low temperatures are widely used to ensure food quality and safety. However, sublethally injured Staphylococcus aureus is an important microbiological safety concern in low temperature food. The objective of this study was to develop predictive inactivation kinetic models for the inactivation and sublethal injury of S. aureus in broth at different temperatures (4 to -18°C) and time points. S. aureus was diluted in tryptic soy broth plus 0.6% (wt/vol) yeast extract (TSBYE) to obtain approximately 10(8) CFU/ml and was stored separately at 4, -3, -11, and -18°C. After specific time points within 96 days, survival of S. aureus was determined on TSBYE and TSBYE agar plus 10% NaCl for enumeration of the total viable and noninjured cell numbers, respectively. Linear, Weibull, and modified Gompertz models were applied to determine survival curve regression. The combination of low temperature and time resulted in S. aureus inactivation, although the cells were able to survive in this sublethal state. Storage temperature was the critical parameter in survival of S. aureus. The modified Weibull model successfully described a second model of noninjured S. aureus cell survival at different low temperatures, whereas only the linear model was able to fit the total viable cells. The predictive model may be used to estimate the level of S. aureus contamination in food at low storage temperatures and times, and it provides new insight into the sublethally injured survival state of S. aureus in low temperature food.

Survival of hepatitis A virus on various food-contact surfaces during 28 days of storage at room temperature

Hepatitis A virus (HAV) infections constitute one of the leading causes of food-borne disease outbreaks. HAV spreads readily from one infected person to another through contaminated water or food, via the fecal–oral route. The prevention of HAV infection is therefore important in the preparation of food. The objective of this study was to investigate the survival of HAV on six different food-contact surfaces: ceramic, wood, rubber, glass, stainless steel and plastic. The survival of HAV was measured during storage at room temperature for 28days. On the food-contact surfaces, the greatest reduction in HAV was 2.3log10plaque-forming units (PFU)/coupon, observed on stainless steel, while the lowest HAV reduction was 1.4log10PFU/coupon, observed on wood. The values of dR (time required to reduce the virus by 99%) on survival plots of HAV determined by a modified Weibull model were 1396.9h (R2=0.97) on ceramic, 1676.4h (R2=0.98) on wood, 852.7h on rubber (R2=0.95), 1386.4h (R2=0.97) on glass, 428.6h (R2=0.96) on stainless steel and 833.0h (R2=0.97) on plastic. The infectivity of the virus on all six food-contact surfaces was maintained after 28days. Studies show that HAV from food preparation or processing will survive persistently on cookware. This study provides information useful for the control of HAV on different food-contact surfaces and the prevention of food-borne disease.

Survival of norovirus surrogate on various food-contact surfaces.

Norovirus (NoV) is an environmental threat to humans, which spreads easily from one infected person to another, causing foodborne and waterborne diseases. Therefore, precautions against NoV infection are important in the preparation of food. The aim of this study was to investigate the survival of murine norovirus (MNV), as a NoV surrogate, on six different food-contact surfaces: ceramic, wood, rubber, glass, stainless steel, and plastic. We inoculated 10(5) PFU of MNV onto the six different surface coupons that were then kept at room temperature for 28 days. On the food-contact surfaces, the greatest reduction in MNV was 2.28 log10 PFU/coupon, observed on stainless steel, while the lowest MNV reduction was 1.29 log10 PFU/coupon, observed on wood. The rank order of MNV reduction, from highest to lowest, was stainless steel, plastic, rubber, glass, ceramic, and wood. The values of d R (time required to reduce the virus by 90%) on survival plots of MNV determined by a modified Weibull model were 277.60 h (R(2) = 0.99) on ceramic, 492.59 h (R(2) = 0.98) on wood, 173.56 h on rubber (R(2) = 0.98), 97.18 h (R(2) = 0.94) on glass, 91.76 h (R(2) = 0.97) on stainless steel, and 137.74 h (R(2) = 0.97) on plastic. The infectivity of MNV on all food-contact surfaces remained after 28 days. These results show that MNV persists in an infective state on various food-contact surfaces for long periods. This study may provide valuable information for the control of NoV on various food-contact surfaces, in order to prevent foodborne disease.

Effect of power ultrasound application on aqueous extraction of phenolic compounds and antioxidant capacity from grape pomace (Vitis vinifera L.): Experimental kinetics and modeling

The kinetics of both conventional (mechanical stirring, 200rpm) and acoustic (55±5kHz, 435±5W/L) aqueous extraction of total phenolic content and antioxidant capacity from grape pomace by-products (Vitis vinifera L.) have been experimentally evaluated and modeled at different extraction temperatures (20, 35 and 50°C). A gradual and significant increase of total phenolic content and antioxidant capacity of the extracts was observed as the temperature increased, the highest values being obtained in the case of the extraction assisted acoustically. According to the results, the acoustic assistance of the extraction process led to aqueous extracts with phenolic and antioxidant characteristics similar to those obtained with mechanical stirring, working under lower temperature conditions and during less operating time. Specifically, the conventional extraction of total phenolics at 35 and 50°C did not differ significantly from extractions assisted with power ultrasound at 20 and 35°C, respectively; and the acoustic process required approximately 3, 4 and 8 times less time, at 20, 35 and 50°C, than the conventional extraction to obtain extracts with similar characteristics. The extraction curves obtained for total phenolic content and antioxidant capacity, measured by the ABTS and FRAP methods, were properly represented by a modified Weibull model for both conventional and acoustic extractions within the temperature range 20–50°C, presenting an average percentage of explained variance⩾97.9%, and an average mean relative error⩽7.0%. A high correlation (r2⩾0.992) was observed between the experimental and simulated values for all the quality attributes in study.

Tensile strength analysis of palm leaf sheath fiber with Weibull distribution

Palm leaf sheath fiber (palm fiber) was subjected to monotonic tensile load at four different gauge lengths, and its tensile behavior was investigated. The strength of palm fiber was studied by traditional Weibull models, compared with jute fiber. Modified Weibull model was also studied by considering the fiber diameter effect. The SEM graphics of breaking surfaces were obtained to study the fracture mechanism of palm fiber. Results show that palm fiber had a large diameter and excellent elongation properties. Weibull distribution was very suitable for strength analysis. Strength and Weibull modulus decreased, whereas Young’s modulus increased with the increase in gauge length and strength dispersion. The diameter had negative effect on palm fiber strength and modified Weibull model could predict strength accurately. Three main states of breaking surfaces were found and discussed. In addition, the strength of palm fiber was found more sensitive to gauge length than sisal fiber.

Inactivation Kinetics of Various Chemical Disinfectants on Aeromonas hydrophila Planktonic Cells and Biofilms

The present article focuses on the inactivation kinetics of various disinfectants including ethanol, sodium hypochlorite, hydrogen peroxide, peracetic acid, and benzalkonium chloride against Aeromonas hydrophila biofilms and planktonic cells. Efficacy was determined by viable plate count and compared using a modified Weibull model. The removal of the biofilms matrix was determined by the crystal violet assay and was confirmed by field-emission scanning electron microscope. The results revealed that all the experimental data and calculated Weibull α (scale) and β (shape) parameters had a good fit, as the R(2) values were between 0.88 and 0.99. Biofilms are more resistant to disinfectants than planktonic cells. Ethanol (70%) was the most effective in killing cells in the biofilms and significantly reduced (p<0.05) the biofilms matrix. The Weibull parameter b-value correlated (R(2)=0.6835) with the biofilms matrix removal. The present findings deduce that the Weibull model is suitable to determine biofilms matrix reduction as well as the effectiveness of chemical disinfectants on biofilms. The study showed that the Weibull model could successfully be used on food and food contact surfaces to determine the exact contact time for killing biofilms-forming foodborne pathogens.

Compressive Strength of Concrete Cores under High Strain Rates

A pulse-shaped split Hopkinson pressure (SHPB) was employed to determine the dynamic compressive mechanical responses of concrete cores. The loading pulses in SHPB experiments were precisely controlled to ensure that the core specimen deforms at a nearly constant strain rate under dynamically equilibrated stress during compression. A modified two-parameter Weibull distribution was used to analyze the test data. The Kolmogorov-Smirnov goodness-of-fit test was used to decide whether test data come from a population with this distribution. On the basis of the test data, Kolmogorov-Smirnov goodness-of-fit test, and probability plot, it is found that the modified Weibull model can be applied to compressive strength for concrete cores. In addition, the strain rate effect on the compressive strength of cores can be accurately predicted from the modified Weibull model.