Model-free estimation of mass fluxes based on concentration profiles. I. Presentation of the method and of a sensitivity analysis

International audienceAn approach to identify mass diffusion coefficients ( D) is presented, and applied to the case of a slab. It was based on a numerical exploitation of the concentration profiles to estimate the mass fluxes. The effect of the quality of the experimental data (spatial resolution, z D , temporal resolution, Fo D , of the concentration profiles, sampling) on the bias and sensitivity of the method was studied thanks to the use of simulated data (FoÎ[0,2 ] ), to which could be added Gaussian noise. Estimated D value were compared with the true solution (the one used for generating the simulated concentration data). The errors on D are large at low Fo 0.2 , D can be estimated with less than 1% of bias if DF

Model-free estimation of mass fluxes based on concentration profiles. II. Effect of noise on concentration profiles and of time resolution

International audienceAn extension of the approach adopted in Part I was developed to improve the identification of diffusivity (D) in relation to the inverse mass diffusion problem. It was based on an estimation of mass fluxes from concentration profiles previously fitted with smoothing spline functions. Data was smoothed to remove noise and to compensate for low spatial resolution. Estimated D values were compared with the true solution used to generate virtual concentration data. The error (er) on D was considerably reduced if the Fo domain was not uni- formly distributed but it verified uniform distribution of the average concentration. The effect of the quality of the experimental concentration data (spatial and temporal resolution, noise intensity) on er was also studied. Where D varied with concentration, er was minimal and close to the noise intensity if the numbers of concentration profiles or concentration data per profile were higher than 20

Understanding the physicochemical processes involved in cooking legumes to drive water transfer

International audienceThe cooking quality of pulses depends essentially on water transfers; they are thermally thin objects. These water transfers are driven by multiple thermal events related to starch (gelatinization, melting) and proteins (denaturations). The objective of this study was to understand the physicochemical processes involved in the cooking of legumes in order to propose technological ways of innovation (facilitating their preparation mode, ready to use...). This study identified, at steady state, the phase changes of starch and protein macronutrients of legumes (lentil, chickpea, bean), using differential scanning calorimetry (DSC) for the separation of thermal events (starch/protein). Modeling by de-summarization of DSC peaks and representation of binary water/starch and water/protein phase diagrams was developed. The combination of these two phase diagrams has made it possible, by adjustment, to represent the behaviour of the ternary water/starch/protein system and to propose a distribution of water between starch/proteins. For example, for chickpeas and beans, the amount of water attributed to the starch increases from less than 10% of the total water to about 35-45% at the end of cooking. The results of this work were able to model the water/starch/protein equilibrium states and will facilitate the representation of dynamic water transfer model in legumes during pre-soaking and cooking

Congélation d'un milieu poreux en contact avec un réfrigérant aqueux concentré : modélisation numérique du transfert de chaleur et de masse

International audienceThe authors have developed a model of coupled heat and mass transport within porous medium (sheet) saturated with an aqueous solution of initial non-zero solute concentration. The novel contribution of the present work is the resolution of the equations for simultaneous heat and mass flows at one of the interfaces for a wide range of temperatures and concentrations. Good agreement was noted between simulated and experimental data. The results presented also underline the fact that this knowledge model helps to clarify our understanding of the interaction mechanisms between heat and mass transport during the immersion freezing process.Les auteurs ont développé un model de transport couplant la chaleur et la masse dans un milieu poreux saturé avec une solution aqueuse avec une concentration initiale non égale à zéro en soluté. Les travaux présents apportent une nouvelle résolution des équations pour les écoulements simultanés de chaleur et de masse à un des interfaces pour diverses températures et concentrations. Les données simulées et expérimentales concordent. Les résultats présentés soulignent aussi le fait ce modèle de savoir aide à la compréhension des mécanismes d'interaction entre le transport de chaleur et de masse pendant le processus d'immersion réfrigérante

Effet du procédé de friture sur la répartition et l'état de l'eau mesurée par la RMN et IRM

The effects on frying on the water distribution and the starch granules of potatoes were studied using Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI). Potatoes slices, 5 cm diameter by 1.2 cm thickness were fried for 1, 3, 6 and 9 minutes at 170° C. The NMR relaxation results allowed to monitor the structural changes after frying. Into the sample core, the starch gelatinased and included changes on the water states and distribution. At the surface, the starch crystalline structure was confirmed and the water amount decrease and oil penetration were observed. The high sample heterogeneity induced by frying was confirmed by MRI measurements.Les effets du procédé de friture sur la répartition tissulaire de l'eau et dur les granules d'amidon sont étudiés par Résonance Magnétique Nucléaire (RMN) et Imagerie de Résonance Magnétique (IRM). Des tranches de pomme de terre de 5 cm de diamètre et 1,2 cm d'épaisseur sont frites pendant 1, 3, 6 et 9 minutes à 170° C. Les relaxations RMN permettent de caractériser les changements structuraux. A coeur, l'amidon gélatinise et modifie la relaxation des molécules d'eau et leur répartition. A la surface, la structure cristalline est confirmée, la teneur en eau diminue, tandis que la teneur en huile augmente. La forte hétérogénéité induite par le traitement est validée par les images IRM

Improvement of the in vitro digestible iron and zinc content of okra (Hibiscus esculentus L.) sauce widely consumed in Sahelian Africa

the effects of the formulation (okra, fish, soumbala, extract of wood ash) and cooking time of okra sauce on total iron and zinc content and on their in vitro digestibility were evaluated following a Doehlert uniform shell design with 5 factors and 33 trials. Cooking time had no significant effect on in vitro digestible iron and zine content, whereas formulation did. Each ingredient had a specific effect. Extract of wood ash, which is a source of soluble and digestible iron and zinc, is a good way of increasing the digestible ,ineral content of the dish. Okra, the main ingredient in this sauce, has a negative effect and should be added in moderate quantities ( 37.7% of the DM of the sauce). An optimization using the desirability function allows us to identify the optimal recipe that enable the quantity of digestible iron to be doubled and the quantity of digestible zinc to be increased by one third. This recipe calls for a mixture of 37.7% okra, 26.3% dried fish, 18.5% soumbala, and 3.7% extract of wood ash cooked for 25 min

Enseignements sur le procédé de friture-séchage de bois au travers d'une approche simplifié des phénomènes de transport de matière et d'énergie

International audienceLe procédé de friture-séchage de bois implique une ébullition intense. La pression au c½ur du bois peut atteindre 250 kPa. Dans de telles conditions, le transport de vapeur d'eau par perméation est considéré comme le mode de transport de matière principal dans un modèle simplifié de transport de matière et d'énergie. Celui-ci a été développé en l'absence de déformation et de pénétration d'huile dans une géométrie rectangulaire de longueur infinie et résolu numériquement avec un logiciel d'éléments finis commercial. L'eau libre et l'eau liée ont été distinguées dans l'équation de transport d'énergie. Bien que le flux de vapeur s'évacue principalement dans le sens orthogonal au plan considéré, l'utilisation de seulement deux perméabilités ajustées (9.10-15 et 9.10-16 m2) a permis de caractériser une quantité importante de bois quelles que soient leurs dimensions et leurs perméabilités. Ce modèle a été validé expérimentalement en pression et température au c½ur de l'échantillon, en température à trois endroits et en perte d'eau totale. Du hêtre (Fagus silvatica), du chêne (Quercus pedonculae) et du pin maritime (Pinus pinaster) ont été traités à l'échelle du dispositif de laboratoire (0.3 m) et à l'échelle d'un dispositif de dimension industrielle (3 m) dans une gamme de température allant de 103 à 180°C. L'apparition de fissurations a été mise en évidence par des chutes brutales de la température d'ébullition de l'eau