Effect of pH on the heat resistance of spores Comparison of two models

International audienceAll published models describing the effect of pH on the heat resistance of spores can be regarded either as a linear first degree equation or a linear second degree equation. This work aimed to compare both models from 3 sets of published data for , Clostridium sporogenes and Bacillus stearothermophilus respectively. The relative quality of fit of each model with respect to the other depends on the species, the strain and the heating temperature. Parameter estimation was more reliable for the second degree model than for of the simple first degree equation. However, in the case of acidic foodstuffs, predictions obtained from the second degree model are more sensitive toward errors of parameter values. The second degree model is better from the point of view of safety at most frequent ranges of pH of foods. Moreover, for Clostridium botulinum , the goodness of fit of this model is clearly higher than that of the first degree equation. If this observation is confirmed by further work, the second degree model in application of standard calculations of heat processes of foods would be preferred

Survival curves of heated bacterial spores: effect of environmental factors on Weibull parameters

International audienceThe classical D-value of first order inactivation kinetic is not suitable for quantifying bacterial heat resistance for non-log linear survival curves. One simple model derived from the Weibull cumulative function describes non-log linear kinetics of micro-organisms. The influences of environmental factors on Weibull model parameters, shape parameter "p" and scale parameter "delta", were studied. This paper points out structural correlation between these two parameters. The environmental heating and recovery conditions do not present clear and regular influence on the shape the parameter "p" and could not be described by any model tried. Conversely, the scale parameter "delta" depends on heating temperature and heating and recovery medium pH. The models established to quantify these influences on the classical "D" values could be applied to this parameter "delta". The slight influence of the shape parameter p variation on the goodness of fit of these models can be neglected and the simplified Weibull model with a constant p-value for given microbial population can be applied for canning process calculations

Quantifying the effects of heating temperature, and combined effects of heating medium pH and recovery medium pH on the heat resistance of Salmonella typhimurium

International audienceThe influence of heating treatment temperature, pH of heating and recovery medium on the survival kinetics of Salmonella typhimurium ATCC 13311 is studied and quantified. From each non-log linear survival curve, Weibull model parameters were estimated. An average shape parameter value of 1.67 was found, which is characteristic of downward concavity curves and is in agreement with values estimated from other S. typhimurium strains. Bigelow type models quantifying the heating temperature, heating and recovery medium pH influences are fitted on scale parameter δ data (time of first decimal reduction), which reflects the bacterial heat resistance. The estimate of zT (4.64 °C) is in the range of values given in the literature for this species. The influence of pH of the heating medium on the scale parameter (zpH: 8.25) is lower than that of the recovery pH medium influence (z′pH: 3.65)

Validation of an overall model describing the effect of three environmental factors on the apparent D-value of Bacillus cereus spores

International audienceSeveral factorial models extending the famous Bigelow model to describe the influence of the heating and recovery pH and aw conditions on bacterial heat resistance have been developed. These models can be associated in an overall multifactorial model describing the influences of heating and recovery conditions on D values. For Bacillus cereus strain ADQP 407 the mo D el parameters characterising the environmental factor influences (pH, Temperature, aw) were evaluated. Determination of bacterial heat resistance in cream chocolate have been realised to validate these parameter values and to evaluate the level of the influence of food texture or different compounds not taken account of in the model

A Decision Support Tool based on microbial safety prediction for a better dimensioning of modified atmosphere packaging

Predicting microbial safety of fresh products in Modified Atmosphere Packaging (MAP) systems implies to take into account the dynamic of O2 and CO2 exchanges in the system and its effect on microbial growth. In this purpose we coupled mathematical models of gas transfer (permeation through packaging and solubilisation / diffusion within food) with predictive microbiology models that take into account the effect of CO2 and O2 partial pressure in headspace and corresponding dissolved concentrations in the food. This mechanistic model was validated in simplified and in real conditions using dedicated challenge-tests performed on poultry meat, fresh salmon and processed cheese, inoculated with either Listeria monocytogenes or Pseudomonas fluorescens.Once validated, this model could be used as a Decision Support Tool in order to optimize the initial packaging atmosphere (level of O2 and CO2) and / or the geometry (ratio headspace volume to food mass). This tool could also be used to identify the packaging gas permeability the most suitable for maintaining the targeted % of gas initially flushed in the pack within a given tolerance. This approach permits a better dimensioning of MAP of fresh produce by selecting the packaging material fitted to “just necessary” (and not by default the most barrier one). The connexion of this model with dedicated databases gathering gas permeabilities of commonly used packaging materials allows us to obtain as output a ranking of the most suitable materials. This tool would be very useful for all stakeholders of the fresh produce chain. A demonstration of this Decision Support Tool is here proposed with the pipeline between mathematical models and related databases

Prise en compte de l'influence du pH dans l'optimisation des traitements thermiques

Les traitements thermiques sont utilisés dans l'industrie de la conserve pour assainir les aliments et assurer leur stabilité microbiologique et biochimique. Cependant, les nombreux effets secondaires comme l'altération des qualités nutritives et organoleptiques, incitent les entreprises à réduire les barèmes à leurs minima, tout en maintenant la sécurité microbiologique. La recherche de ce barème optimum passe par l'étude de la résistance thermique des formes bactériennes sporulées. La première partie de ce manuscrit consiste en l'élaboration d'un modèle établi sur les spores de sept souches bactériennes (B. stearothermophilus, C. sporogenes, espèces acidophiles). Ce modèle décrit la thermorésistance en fonction de la température, mais surtout du pH de l'aliment que nous dédoublons en deux facteurs distincts : le pH du milieu de traitement thermique dont l'effet direct sur la thermorésistance est bien connu, et le pH du milieu d'incubation post-traitement qui affecte à la fois le taux de germes survivants susceptibles de se développer et la durée de réduction décimale apparente. La seconde partie est consacrée à l'application du modèle dans les calculs de barèmes de stérilisation. Les méthodes de Bigelow et de Ball sont étendues au multifactoriel par intégration du pH, conduisant ainsi à un nouveau protocole de détermination de barème de stérilisation. Pour appuyer cette démonstration, un produit industriel est choisi en exemple : ses barèmes sont redéterminés par cette nouvelle méthode.In canned food industry, heat treatments are used in order to produce healthier food and to maintain its microbiological and biochemical stability. However, the numerous side effects, such as deterioration of nutritious and organoleptical qualities, urge compagnies to reduce their scales down to a minimum that maintain, nevertheless, the microbiological stability. This Optimization research proceeds from the study of heat resistance of bacterial spores. In the first part of this work, we established a model on spores of seven bacterial strains (B. stearothermophilus, C. sporogenes, acidophilic species). In this model, the heat resistance of these spores is related to the temperature, and mainly to the food pH, which is devided into two distinct factors : The heat treatment medium pH whose direct effects on heat resistance are well known, and the post-treatment medium pH which affects both the rate of surviving spores likely to germinate and grow and the apparent decimal reduction time. The second part is assigned to the application of the model in sterilization time calculation methods. The Bigelow's and Ball's methods are enlarged by integration of pH, leading to a new protocol for sterilization time calculations. To check this demonstration, an industrial product is taken as an example and its scales are determined according to this new method.BREST-BU Droit-Sciences-Sports (290192103) / SudocSudocFranceF

Relationship between the apparent heat resistance of Bacillus cereus spores and the pH and NaCl concentration of the recovery medium

International audienceConventional heat resistance data , D values, were previously established by other workers at optimal condition for spores outgrowth. However, in canned food conditions of outgrowth are generally suboptimal in term of pH, salt concentration, water activity. Counts of survival spores after heat treatment are greatly influenced by the characteristics of the recovery medium. The selectivity of incubation conditions is enhanced by the injury of cells at sub-optimum recovery conditions. Both a decrease of number of viable cells being able to producing colonies and a decrease of the decimal reduction time is observed. The combined effects of pH and NaCl level of the recovery medium for the D value and ZpH value were studied. Spores of Bacillus cereus were heated at 95°C in phospho-citric buffer media at pH7. Cells were recovered at 25°C in nutritive agar with pH ranging from 5 to 7 and 1% to 4% NaCl concentration. For each condition D' values ( decimal reduction time associated with the recovery media characteristics) were determined. The results show a main influence of the recovery pH on the D' values. This effect is characterised by the z'pH values, distance of recovery medium pH from optimum recovery pH* medium (6.7) which leads to ten fold reduction time of D-value. The increase of the salt concentration leads to a slight decrease of D' value. However z'pH values are not significantly affected by the salt concentration. A simple three parameter model describing the effects of pH and NaCl concentration of the recovery medium upon the heat resistance of spores is proposed The interaction between pH and salt concentration is sufficiently low to be neglected by the model

Effect of pH on the heat resistance of spores Comparison of two models

International audienceAll published models describing the effect of pH on the heat resistance of spores can be regarded either as a linear first degree equation or a linear second degree equation. This work aimed to compare both models from 3 sets of published data for , Clostridium sporogenes and Bacillus stearothermophilus respectively. The relative quality of fit of each model with respect to the other depends on the species, the strain and the heating temperature. Parameter estimation was more reliable for the second degree model than for of the simple first degree equation. However, in the case of acidic foodstuffs, predictions obtained from the second degree model are more sensitive toward errors of parameter values. The second degree model is better from the point of view of safety at most frequent ranges of pH of foods. Moreover, for Clostridium botulinum , the goodness of fit of this model is clearly higher than that of the first degree equation. If this observation is confirmed by further work, the second degree model in application of standard calculations of heat processes of foods would be preferred

Modelling the overall effect of pH on the apparent heat resistance of Bacillus cereus spores

International audienceA simple overall model is proposed to describe the effect of both the pH of the heating menstruum and the pH of the recovery medium on the apparent spore heat resistance of Bacillus cereus. Applied to foods making up both heating and recovery media, the model can be reduced to only two parameters. Its goodness of fit and its robustness enable it to be applied to the optimisation of heat treatments. However. further experiments should be undertaken to validate the model for other species and to determine the parameters related to reference species such as Clostridium botulinum

Modelling the influence of the sporulation temperature upon the bacterial spore heat resistance, application to heating process calculation

International audienceEnvironmental conditions of sporulation influence bacterial heat resistance. For different Bacillus species a linear Bigelow type relationship between the logarithm of D values determined at constant heating temperature and the temperature of sporulation was observed. The absence of interaction between sporulation and heating temperatures allows the combination of this new relationship with the classical Bigelow model. The parameters zT and zTspo of this global model were fitted to different sets of data regarding different Bacillus species: B. cereus, B. subtilis, B. licheniformis, B. coagulans and B. stearothermophilus. The origin of raw products or food process conditions before a heat treatment can lead to warm temperature conditions of sporulation and to a dramatic increase of the heat resistance of the generated spores. In this case, provided that the temperature of sporulation can be assessed, this model can be easily implemented to rectify F values on account of possible increase of thermal resistance of spores and to ensure the sterilisation efficacy