3D individual based model for simultaneous growth and interaction of L. Monocytogenes and lactic acid bacteria

International audienceBy interacting with pathogens, lactic acid bacteria (LAB) are able to contribute to food safety. By means of their lactic acid production which induces pH decrease, LAB influence the growth of pathogens. The aim of this study is to model and simulate lactic acid production, pH evolution, according to carbohydrate concentration in media, temperature, water activity and ratio of both population

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

Optimising food process and formulation on internet: the SYM'PREVIUS experience

International audienceThe Sym’Previus network started in 1999. Sym’Previus meets the French expertise in Predictive Microbiology of major food companies, technical centres and public research institute. This project aims at proposing an assisting tool in the management of food safety. The following dual (software) background is applied: firstly, a database where information on the behaviour of microorganisms in/on foods and natural contamination of foods are structured. A query system, called MIEL, specifically developed for the database, allows to formulate specific interrogation with a specific selection of food and microorganisms. Secondly, a user-friendly software simulates the growth of microorganisms in food matrix. Sym’Previus is a simpler access to predictive microbiology for food companies. At the present time the software describes the effects of temperature, pH and water activity on bacteria growth in a range of food commodities, such as cereals, egg products, dairy product, meat... Sym’Previus is available on www.symprevius.org

Sym'Previus. La microbiologie prévisionnelle, du laboratoire à l'industrie agroalimentaire = Predictive microbiology, from laboratory to food industry

International audienceL'industrie agroalimentaire et les pouvoirs publics sont contraints à une vigilance accrue sur la sécurité microbiologique des aliments proposés au consommateur en raison des graves conséquences (coût humain, pertes commerciales et pertes d'image) que peut entraîner une non-conformité sur une marque ou un type de produits. Les acteurs des filières agro-industrielles doivent répondre aux attentes du marché et être capables d'assumer pleinement leur responsabilité quant à la sécurité de leur fabrication. La sécurité microbiologique des produits alimentaires exige des connaissances solides et complexes sur la contamination naturelle des matières premières et des produits transformés, sur la capacité de survie des micro-organismes au cours des traitements de transformation, et leur développement aux différents stades de conservation. C'est dans ce contexte que s'inscrit le projet Sym'Previus ; il s'agit d'un outil d'aide à la prévision de l'évolution des populations microbiennes dans les aliments, à l'usage des professionnels de l'alimentation. Disponible sur Internet, cet outil rassemble d'une part, une base de données issues de la bibliographie, de l'industrie et de programmes de recherche, et d'autre part, un module de simulation du comportement microbien s'appuyant sur les outils actuels de la microbiologie prévisionnelle. Hormis la possibilité de prévoir le niveau de contamination d'un microorganisme à un instant de la vie d'un produit (de la fabrication à la consommation), Sym'Previus permet d'optimiser un procédé, une chaîne du froid, mais aussi d'accompagner la formulation et le développement d'un nouveau produit. = Predictive microbiology can be divided into two groups of models, named primary and secondary models. Primary models describe the evolution of the bacterial population with time. These models use parameters which may vary as the environmental factors change. Secondary models describe how those parameters vary with the environmental factors. Sym'Previus meets the French expertise in Predictive Microbiology of major food companies, technical centres and public research institutes. This project aims at proposing an assistance in the managing of the food safety. It is composed from two main softwares. Firstly, a database where information on the behaviour of microorganisms in/on foods and natural contamination of foods are structured. A query system, called MIEL, specifically developed for the database, allows to formulate specific interrogation with a specific selection of food and microorganisms. Secondly, a user-friendly software simulates the growth of microorganisms in food matrix

A software for Risk-Benefit based probabilistic assessment for heat processed foods

National audienceOBJECTIVE(S) The preservation of food quality during food processing is a key condition for food industries to remain competitive and respond to consumer demand. For that purpose, food industry must mediate among two objectives: preserve the nutritional benefits and ensure a high level of microbiological risk control. . The aim of this study is to develop a user friendly probabilistic tool able to assess quantitatively the risk and benefit of heat processed foods. The tool allows to appraise the risk (food spoilage) associated to survival Geobacillus Stearothermophilus and the benefit related to Vitamin C. In the end it proposes the best compromise to preserve vitamins and to control the microbiological risk of food. METHODS(S) The industrial risk considered in this study was that of the thermophilic bacterium Geobacillus stearothermophilus, recognized as a major source of spoilage in canned foods and frequently detected in cans presenting defects after 7-day incubation at 55°C (André et al., 2012). G. stearothermophilus heat resistance parameters (Dref, ZT and ZpH), used in this study, were estimated using hierarchical Bayesian modeling (Rigaux et al., 2012). Furthermore, nutritional benefit was that of vitamine C. The two bioactive forms of vitamin C were taken into account: DeHydroascorbic Acid (DHA) and Ascorbic Acid (AA). For both cases, activation Energy (Ea) and reaction rate (K) were considered. Monte Carlo based simulations were used in order to set up the destruction of G. Stearothermophilus and both AA and DHA of vitamin C (Rigaux et al., 2013). RESULTS The decision making tool developed in this study allows to quantify the risk due to G. stearothermophilus and displays the distribution based Monte-Carlo simulation of the decimal reduction number of the considered bacteria. The distribution is given with a target level user-defined. The probability to reach this known threshold is also calculated. At the same time, the tool displays the distribution based Monte-Carlo simulation of the vitamin C percentage reduction ([AA] and [DHA] concentrations). This distribution is given also with a user-specified allegation threshold for vitamin C. The probability to reach the allegation threshold is also given. Color codes are used to help users to decide on the risk-benefit compromise associated to a given heat processed food. CONCLUSIONS AND IMPACT OF THE STUDY A user friendly risk-benefit based probabilistic assessment tool for heat processed foods was developed in this study. The software allows to accurately evaluate and find the best compromise between nutritional quality and microbiological safety for heat processed food products. Monte-Carlo simulation method was performed in order to estimate the probability to reach both user-defined target levels of bacteria and allegation threshold of vitamin C. This statistical tool could have a significant industrial impact to better assess temperature profiles applied during heat processing, because not only a microbiological risk is put forth but also the nutritional benefit. This tool will be integrated to the heat inactivation module of Sym’Previus

Une diversité génétique importante révélée par les empreintes de PCR inter-LTR de souches de Debaryomyces hansenii et Kluyveromyces marxianus isolées de fromages traditionnels français.

The genetic diversity of two major yeast species found in cheese, Debaryomyces hansenii and Kluyveromyces marxianus, was analyzed within the yeast flora in French traditional cheesemaking. Based on the amplification of sequences separating long terminal repeat (LTR) retrotransposon sequences, a molecular typing method was developed for D. hansenii and K. marxianus. This method was applied to a total of 56 D. hansenii strains and 61 K. marxianus strains, mostly isolated during fermentation and ripening of traditional cheese from Normandy and Haute-Savoie (French Alps) regions. A total of 32 and 43 robust profiles were obtained for D. hansenii and K. marxianus, respectively. Cluster analysis confirmed the large genetic diversity already shown for D. hansenii and revealed an even larger diversity for K. marxianus. After its use with Saccharomyces cerevisiae, the inter-LTR PCR proved to be efficient to discriminate between strains of the two species, D. hansenii and K. marxianus, isolated from the same ecological niches, confirming the high intra-specific variability of species found in cheese. This strain typing could not correlate the analyzed strains with their origin, would it be the cheese type, the cheese-making facility or the cheese batch, showing a high discrimination power. The method described here will provide a fast and reliable tool for the biodiversity study of these two major cheese yeasts.La diversité génétique de deux levures majeures des fromages, Debaryomyces hansenii et Kluyveromyces marxianus, a été analysée dans la flore-levures de fromages français traditionnels. Basée sur l'amplification des séquences qui séparent les "Long Terminal Repeats" des rétrotransposons (LTR), une méthode de typage moléculaire a été développée pour D. hansenii et K. marxianus. La méthode a été appliquée à 56 souches de D. hansenii et 61 souches de K. marxianus, pour la plupart isolées pendant l'affinage de fromages traditionnels de Normandie et de Haute-Savoie. Un total de 32 et 43 profils robustes a été obtenu pour D. hansenii et K. marxianus, respectivement. Une analyse hiérarchique a confirmé la grande diversité génétique déjà observée pour D. hansenii et a révélé une grande diversité chez K. marxianus. Apres son utilisation chez Saccharomyces cerevisiae, la PCR inter-LTR s'est montrée très efficace pour discriminer entre isolats de D. hansenii et K. marxianus isolés des mêmes niches écologiques, confirmant ainsi la grande variabilité intra-spécifique des espèces présentes dans le fromage. Le typage de ces souches n'a pu être corrélé à la provenance des souches, que ce soit avec le type de fromage, la fromagerie ou le lot, indiquant un grand pouvoir de discrimination lors de ce typage. La méthode développée ici apporte un outil rapide et robuste pour étudier la biodiversité de ces deux espèces

Processing of reaction-bonded B4C–SiC composites in a single-mode microwave cavity

International audienceIn this study, the reaction sintering of boron carbide, which consists in doing reactive infiltration of molten silicon throughout a porous sample made of B4C and carbon graphite was investigated. Thus, it has been shown that a single-mode microwave cavity can be successfully used to produce reaction-bonded B4C–SiC composite. A specific package, consisting of a SiC based susceptor and a boron nitride based insulating container, was used to heat up the B4C–Si system using a single-mode microwaves cavity under an Ar–H2 atmosphere. Pore-free B4C–SiC composite successfully produced consists of a mixture of B4C and polygonal shaped β-SiC within a residual silicon matrix. The indentation technique permits to determine mechanical properties of the samples which are compared to those obtained conventionally. It appears that the average hardness (H≈22 GPa) value is quite constant all along the sample thickness which highlights good homogeneity of the samples obtained. Some aspects of the microstructure are also discussed and compared to those of samples conventionally obtained

Processing of reaction-bonded B4C-SiC composites in a single-mode microwave cavity

International audienceIn this study, the reaction sintering of boron carbide, which consists in doing reactive infiltration of molten silicon throughout a porous sample made of B4C and carbon graphite was investigated. Thus, it has been shown that a single-mode microwave cavity can be successfully used to produce reaction-bonded B4C-SiC composite. A specific package, consisting of a SiC based susceptor and a boron nitride based insulating container, was used to heat up the B4C-Si system using a single-mode microwaves cavity under an Ar-H-2 atmosphere. Pore-free B4C-SiC composite successfully produced consists of a mixture of B4C and polygonal shaped beta-SiC within a residual silicon matrix. The indentation technique permits to determine mechanical properties of the samples which are compared to those obtained conventionally. It appears that the average hardness (H approximate to 22 GPa) value is quite constant all along the sample thickness which highlights good homogeneity of the samples obtained. Some aspects of the microstructure are also discussed and compared to those of samples conventionally obtained. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved

Processing of reaction-bonded B4C-SiC composites in a single-mode microwave cavity

International audienceIn this study, the reaction sintering of boron carbide, which consists in doing reactive infiltration of molten silicon throughout a porous sample made of B4C and carbon graphite was investigated. Thus, it has been shown that a single-mode microwave cavity can be successfully used to produce reaction-bonded B4C-SiC composite. A specific package, consisting of a SiC based susceptor and a boron nitride based insulating container, was used to heat up the B4C-Si system using a single-mode microwaves cavity under an Ar-H-2 atmosphere. Pore-free B4C-SiC composite successfully produced consists of a mixture of B4C and polygonal shaped beta-SiC within a residual silicon matrix. The indentation technique permits to determine mechanical properties of the samples which are compared to those obtained conventionally. It appears that the average hardness (H approximate to 22 GPa) value is quite constant all along the sample thickness which highlights good homogeneity of the samples obtained. Some aspects of the microstructure are also discussed and compared to those of samples conventionally obtained

Validation of a predictive model coupling gas transfer and microbial growth in fresh food packed under modified atmosphere

Predicting microbial safety of fresh products in modified atmosphere packaging implies to take into account the dynamic of O2, CO2 and N2 exchanges in the system and its effect on microbial growth. In this paper a mechanistic model coupling gas transfer and predictive microbiology was validated using dedicated challenge-tests performed on poultry meat, fresh salmon and processed cheese, inoculated with either Listeria monocytogenes or Pseudomonas fluorescens and packed in commercially used packaging materials (tray + lid films). The model succeeded in predicting the relative variation of O2, CO2 and N2 partial pressure in headspace and the growth of the studied microorganisms without any parameter identification. This work highlighted that the respiration of the targeted microorganism itself and/or that of the naturally present microflora could not be neglected in most of the cases, and could, in the particular case of aerobic microbes contribute to limit the growth by removing all residual O2 in the package. This work also confirmed the low sensitivity of L. monocytogenes toward CO2 while that of P. fluorescens permitted to efficiently prevent its growth by choosing the right combination of packaging gas permeability value and initial % of CO2 initially flushed in the pack