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

Quantifying the combined effects of the heating time, the temperature and the recovery medium pH on the regrowth lag time of Bacillus cereus spores after a heat treatment

International audienceThe purpose of this study was to quantify the lag time of re-growth of heated spores of Bacillus cereus as a function of the conditions of the heat treatment: temperature, duration and pH of the recovery medium. For a given heating temperature, curves plotting lag times versus time of heating show more or less complex patterns. However, under a heating time corresponding to a decrease of 2 decimal logarithms of the surviving populations of spores, a linear relationship between the lag time of growth and the time of the previous heat treatment can be observed. The slope of this linear relationship followed itself a Bigelow type linear relationship, the slope of which yielded a - value very close to the observed conventional z-value. It was then concluded that the slope of the regrowth lag time versus the heating time followed a linear relationship with the sterilisation value reached in the course of the previous heat treatment. A sharp effect of the pH of the medium which could be described by a simple "secondary" model was observed. As expected, the observed intercept of the linear relationship between lag time and heating time (lag without previous heating) was dependent on only the pH of the medium and not on the heating temperature

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)

Modelling the influence of palmitic, palmitoleic, stearic and oleic acids on apparent heat resistance of spores of Bacillus cereus NTCC 11145 and Clostridium sporogenes Pasteur 79.3

International audienceHeat resistance of spores is affected by many factors such as temperature, pH, water activity (aw) and others. Previous studies have reported that free fatty acids can affect the germination and growth of bacterial spores. In this study, we investigated the influence of free fatty acids in heating medium or in recovery medium on the heat resistance of spores of Bacillus cereus NTCC 11145 and Clostridium sporogenes Pasteur 79.3. Four free fatty acids were studied: palmitic, palmitoleic, stearic and oleic acid. During thermal treatments, the impact of these FFA in heating media was generally low, but the presence of free fatty acids in the recovery medium highly decreases bacterial spore apparent heat resistance, particularly with unsaturated fatty acids. A mathematical model was developed to describe and quantify the influence of free fatty acids in recovery media on the D-values. The z'FFA parameter values which quantify the impact of free fatty acids were determined. The variation of this parameter value according to the free fatty acid type was compared with MIC value variation given in the literature. The model enables the decrease in D-values in the presence of free fatty acids to be estimated. The high concentrations of free fatty acids in liver or canned duck may explain the microbial stability with low sterilization values applied

An effective Matsusaka big theorem

Les auteurs ont étudié dans une population médiévale semi-rurale (nécropole de Digne, Alpes de Haute-Provence, France) les densités minérales osseuses au col fémoral et au triangle de Ward par absorptiométrie biphotonique à rayons X. Après vérification de l’absence de pathologie radiologiquement visible et vérification de l’absence de variation inter-mensurations et droite-gauche, les fémurs de 18 femmes d’âge au décès de moins de 30 ans et de 40 femmes de plus de 60 ans, réparties en deux périodes archéologiques, Xie-XIIIe et XVIe-XVIIe s. ont été mesurés. La comparaison des densités osseuses, indépendamment de la période archéologique, met en évidence une déperdition osseuse post-ménopausique dans la population médiévale et pré-moderne de la nécropole de Digne en Provence, entre le 11e et le 17e s., comparable à celle observée dans les populations industrialisées occidentales actuelles. Elle présente un caractère majeur chez certaines de ces femmes, évocateur d’une ostéoporose.The purpose of the study was to determine post-menopausal bone mineral content in women living in a semi-rural region at two different archaeological periods, i.e. Medieval 11th century and pre-modern 17th century. The femurs of 18 women under the age of 30 years at death and 40 women over the age of 60 at death were collected from the Notre Dame du Bourg Necropolis in Digne, Alpes-de-Haute-Provence, France. Measurements of the neck and Ward’s triangle regions were made by dual-energy X-ray absorptiometry after documenting the absence of radiologically detectable disease and of variations between two measurements and between right and left sides. Comparison of findings showed a decrease in bone mineral content between the two age groups (under 30 vs. over 60) in both the medieval and pre-modern population. Bone mineral content was comparable to that observed in the populations of present-day industrial nations. The extent of loss in some specimens were suggestive of osteoporosis

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

EFSA Panel on Biological Hazards (BIOHAZ); Scientific Opinion on public health risks represented by certain composite products containing food of animal origin

This Opinion reviews the factors that affect microbial survival and growth in composite products, and in foods in general. It concludes that the main factors to be considered are: water activity, pH, temperature and duration of storage, processing, and intensity and duration of other non-thermal physical processes applied. Prevalence and concentration of the pathogens in food are important to determine the risk for consumers. The opinion presents a review of the quantitative microbiology models and databases that can be used to provide quantitative estimations of the impact of the above factors on the survival and growth of the main bacterial pathogens. In composite products, migration and diffusion of moisture and substances among the ingredients may change their physico-chemical parameters, particularly at the interfaces. Therefore, the assessment of the risk posed by composite products needs to consider the combinations of parameters most permissive to survival and growth of pathogens. Two complementary approaches are proposed for the identification and profiling of microbiological hazards in different specific composite products. The first one is based on past outbreaks and prevalence of hazards in the products and leads to the conclusion that the most frequent hazard-composite product combinations are Salmonella in cakes and bakery products. The second one consists in decision tools based on the impact on the pathogens of food composition and food processing. Categorisation of the risk for composite products requires information on their composition, processing and further handling, which can largely differ for foods belonging to the same category. Further conditions may influence the risk and should be verified, i.e. hygienic conditions during preparation of the composite products and their ingredients, shelf-life conditions, and reliability of cooking by consumers to inactivate pathogens. The decision tools developed apply to all composite products considered by the mandate, as well as to all other foods. © European Food Safety Authority, 201

Recent Developments of Predictive Microbiology Applied to the Quantification of Heat Resistance of Bacterial Spores

International audienceAll conventional heat processing calculations are based on as few as two equations: a "primary" equation which corresponds to the first order kinetic of microbial inactivation represented by a log-linear survival curve, and a "secondary" equation which describes the effect of the heating temperature on the thermal resistance of target spores. Improvements of heat inactivation modelling consist in the extension of these equations into more general primary models which are able to fit typical non log-linear sur vival curves and multifactorial secondary models which take non only heating temperature, but also some new other environmental factors into account. A first models generation inputs only factors such as pH or water activity which are related to the heating phase regardless of recovery conditions. A second models generation further includes environmental factors linked to the recovery conditions of incubation for the calculation of heat resistance. These new trends lead to the main following consequences: i. the efficiency of a heat treatment is more suitably characterised by the bacterial inactivation ratio than by the traditional F-value which is no longer additive, ii. The lethality factor concept can be usefully extended to a more general function which would include not only heating temperature, but also main other environmental factors

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