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

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

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)

Physiological traits of Penicillium glabrum strain LCP 08.5568, a filamentous fungus isolated from bottled aromatised mineral water

International audiencePenicillium glabrum is an ubiquitous fungus distributed world wide. This fungus is a frequent contaminant in the food manufacturing industry. Environmental factors such as temperature, water activity and pH have a great influence on fungal development. In this study, a strain of P. glabrum referenced to as LCP 08.5568, has been isolated from a bottle of aromatised mineral water. The effects of temperature, aw and pH on radial growth rate were assessed on Czapeck Yeast Agar (CYA) medium. Models derived from the cardinal model with inflection (Rosso et al., 1993 An unexpected correlation between cardinal temperatures of microbial growth highlighted by a new model. J Theor. Bio. 162, 447-463) were used to fit the experimental data and determine for each factor, the cardinal parameters (minimum, optimum and maximum). Precise characterisation of the growth conditions for such a fungal contaminant, has an evident interest to understand and to prevent spoilage of food products

First report of an Ediacarian basement in the Western Alps: the Serre Chevalier crystalline unit (Briançonnais domain, France)

We report new LA-ICP-MS U-Pb zircon ages of varied crystalline rocks occurring in the Serre Chevalier crystalline terrain, an allochtonous basement unit located at the top of the Briançonnais nappes stack ∼5 km west of Briançon city. Mapped as an undifferentiated metasedimentary basement on the geological map at 1/50,000 scale, this unit actually displays varied lithologies including alternating micaschist, paragneiss, quartzite, coarse-grained conglomerate and felsic (leptynite) to mafic (amphibolite) gneiss of magmatic origin. All rocks were metamorphosed in response to a dominant pre-Alpine event under amphibolite facies conditions. Partial recrystallization under low-grade amphibolite to greenschist facies conditions was associated with alpine events. Zircon ages were obtained on four types of rocks: (i) a micaceous quartzite from the core of the metasedimentary unit displays a dominant age population around 610 Ma, with a minimal age of 580 Ma, and subordinated age populations at c. 940 Ma, 1825 Ma and 2100-2560 Ma ; (ii) a granite boulder from a coarse-grained conglomerate yields a well-defined age of 582 ± 5 Ma and subordinated inherited ages between 1800 and 2200 Ma. Zircon rims of probable metamorphic origin provide a concordant age of 492 ± 4 Ma ; (iii) a gneissic band in the vicinity of the conglomerate is dated at 597 ± 4 Ma ; (iv) a coarse-grained garnet amphibolite yields an age of 517 ± 3 Ma interpreted as the emplacement age of the protolith, either as intrusive unit cutting accross the sedimentary succession or lava intercalated within the sediments. The mainly Ediacarian record in the metasediments (quartzite and granite boulder in conglomerate) lead us to conclude that this material resulted from the erosion of a nearby Ediacarian (Cadomian ?) basement. The age of 517 Ma obtained on the amphibolite provides a minimum age for the sedimentary succession which deposition is therefore bracketed between 582 Ma and 517 Ma. This interval is comparable to that of the metasedimentary units of the Brioverian group of the Armorican Massif. Based on their low Th/U ratio, the 492 Ma-old zircon rims in the granite boulder are attributed to an Upper Cambrian metamorphic event

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