Combined physico-chemical and water transfer modelling to predict bacterial growth during food processes

International audienceThe quality and safety of food products depend on the microorganisms, the food characteristics and the process. The prediction of conditions that prevent growth in complex situations due to the characteristics of the process and of the food cannot be obtained by predictive models of bacterial growth only. Thus, a combined modelling approach was developed by integrating three models, which were selected in a first step: (1) a bacterial model that predicts the bacterial growth from the physico-chemical properties of the media; (2) a water transfer model that predicts the effects of the drying process variables on the medium characteristics; and (3) a thermodynamic model that predicts the water activity (a(w)) and the pH of the media from its composition. A second step consisted in separately validating each selected model in which all of the physical, chemical or biological parameters appearing in the equations were previously measured. The third step combined the three knowledge models. The global model was validated on the basis of experimental results concerning the growth of Listeria innocua on the surface of a gelatine gel, the surface of which was submitted to a drying process (changes in relative humidity and air velocity). It was shown that bacterial growth models had to be modified: a specific model was set up to predict the maximum growth rate and another for the lag. Additionally, growth models set up in broth could not be applied in gelatine, leading to the development of a specific growth model on a solid surface. The thermodynamic model accurately predicted the pH and a(w) of bacterial broth in which high concentrations of solutes were added, and those of the solid media, the gelatine. The water transfer model was applied on gelatine data to predict the evolution of its surface a, during the drying process. The three models-bacterial, water transfer and thermodynamic, separately validated-were combined according to an integrated modelling strategy. The water transfer model coupled with the thermodynamic model predicted the a(w) on the gel surface. The predicted surface a, explained why growth inhibition was observed. Indeed, growth stopped at a predicted surface a(w)< 0.94, corresponding to L. innocua minimum a, during the drying process. The global model satisfactorily predicted L. innocua growth on the surface of the gel. This study proves the validity of the approach and shows that the combination of the water transfer and thermodynamic models compensates for the lack of a(w) measurement techniques

Study of mass transfer by condensation in humid air for life support systems

International audienc

Investigation of interfacial phenomena during condensation of humid air on a horizontal substrate

National audienc

Humid air condensation process on a horizontal solid substrate devoted to aerobic bioprocesses

International audienc

A fully predictive model for one-dimensional light attenuation by Chlamydomonas reinhardtii in a torus photobioreactor

International audienceThe light attenuation in a photobioreactor is determined using a fully predictive model. The optical properties were first calculated, using a data bank of the literature, from only the knowledge of pigments content, shape, and size distributions of cultivated cells which are a function of the physiology of the current species. The radiative properties of the biological turbid medium were then deduced using the exact Lorenz-Mie theory. This method is experimentally validated using a large-size integrating sphere photometer. The radiative properties are then used in a rectangular, one-dimensional two-flux model to predict radiant light attenuation in a photobioreactor, considering a quasi-collimated field of irradiance. Combination of this radiative model with the predictive determination of optical properties is finally validated by in situ measurement of attenuation profiles in a torus photobioreactor cultivating the microalgae Chlamydomonas reinhardtii, after a complete and proper characterization of the incident light flux provided by the experimental set-up

Axenic Cultures of Nitrosomonas europaea and Nitrobacter winogradskyi in Autotrophic Conditions: a New Protocol for Kinetic Studies

International audienc

A novel technique to evaluate interactions between Saccharomyces Cerevisiae cell wall and mycotoxins : application to zearalenone

International audienceThree models based on sigmoidal plotting were tested for their ability to describe zearalenone adsorption on Saccharomyces cerevisiae cell walls in vitro. All three models closely fitted the experimental data, but Hill's equation gave the most accurate parameters, and provided information on the physical and chemical mechanisms involved in the adsorption of mycotoxin on yeast cell walls

Adsorption of zearalenone by beta-D-glucans in the Saccharomyces Cerevisiae cell wall

International audienc

Influence of pH on complexing of model beta-D-Glucans with zearalenone

International audienc

HUMEX, a study on the survivability and adaptation of humans to long-duration exploratory missions, part II: Missions to Mars

Space exploration programmes, currently under discussion in the US and in Europe, foresee human missions to Mars to happen within the first half of this century. In this context, the European Space Agency (ESA) has conducted a study on the human responses, limits and needs for such exploratory missions, the so-called HUMEX study (ESA SP-1264). Based on a critical assessment of the limiting factors for human health and performance and the definition of the life science and life support requirements performed in the frame of the HUMEX study, the following major critical items have been identified: (i) radiation health risks, mainly occurring during the interplanetary transfer phases and severely augmented in case of an eruption of a solar particle event; (ii) health risks caused by extended periods in microgravity with an unacceptable risk of bone fracture as a consequence of bone demineralisation; (iii) psychological risks as a consequence of long-term isolation and confinement in an environment so far not experienced by humans; (iv) the requirement of bioregenerative life support systems complementary to physico-chemical systems, and of in situ resource utilisation to reach a closure of the life support system to the highest degree possible. Considering these constraints, it has been concluded that substantial research and development activities are required in order to provide the basic information for appropriate integrated risk managements, including efficient countermeasures and tailored life support. Methodological approaches should include research on the ISS, on robotic precursors missions to Mars, in ground-based simulation facilities as well as in analogue natural environments on Eart