Modélisation de la viscosité de suspensions de particules molles végétales et observation directe des particules en milieu encombré

Les pure?es de pommes sont des suspensions concentre?es de particules non colloi?dales (180 ?m), non- sphe?riques et tre?s de?formables. Ces particules sont de?limite?es par une paroi cellulaire ve?ge?tale et remplies par la phase continue. Sous contrainte ou lorsque la concentration en particules augmente, elles se compriment, ce qui rend difficile la de?termination de leur fraction volumique re?elle et la compre?hension de leurs proprie?te?s rhe?ologiques. En ge?ne?ral, le comportement rhe?ologique des suspensions de particules ve?ge?tales est de?crit par trois domaines de concentration : un domaine dilue? dans lequel les particules interagissent peu (newtonien), un domaine interme?diaire marque? par l'apparition d'un re?seau entre les particules (comportement de fluide a? seuil, caracte?rise? par un module e?lastique a? faible de?formation qui augmente fortement avec la concentration en particules) et un domaine concentre? dans lequel les particules sont contraintes de se de?former pour s'adapter a? l'espace environnant et permettre l'e?coulement (le module e?lastique est de l'ordre de 103 Pa et la de?pendance a? la concentration en particules diminue). En combinant microscopie confocale et reconstruction 3D, nous avons de?veloppe?? un protocole pour de?terminer le volume de cellules dans des suspensions concentre?es de particules ve?ge?tales. Ce travail a permis de mettre en e?vidence que le volume des cellules diminue uniquement dans les suspensions fortement concentre?es. Par observation directe au sein de l'e?chantillon, nous apportons ainsi la preuve de la capacite?? des particules ve?ge?tales a? se comprimer et a? diminuer ainsi leur volume lorsque la concentration augmente. Dans ce travail, nous proposons e?galement un moyen d'acce?der a? la fraction volumique apparente des particules et un mode?le de?crivant la de?pendance de la viscosite? a? la concentration sur une large plage de concentrations. Le mode?le propose?, adapte? du mode?le de Mendoza (Mendoza 2013), s'ajuste avec pre?cision aux re?sultats expe?rimentaux obtenus sur des pure?es de pommes de distribution granulome?trique variable et sur des suspensions mode?les reconstitue?es dans plusieurs phases continues. Les parame?tres du mode?le refle?tent la rigidite? et l'asphe?ricite? des particules. Ce travail offre des perspectives inte?ressantes pour l'industrie des fruits et le?gumes transforme?s et a permis une avance?e vers la mode?lisation de ces syste?mes. Re?fe?rences : Day L., Xu M., Øiseth S.K., Hemar Y. & Lundin L. (2010). Control of Morphological and Rheological Properties of Carrot Cell Wall Particle Dispersions through Processing. Food and Bioprocess Technology, 3(6), 928?934. doi :10.1007/s11947-010-0346-0. Espinosa-Mun?oz L., Renard C., Symoneaux R., Biau N. & Cuvelier G. (2013). Structural parameters that determine the rheological properties of apple puree. Journal of Food Engineering, 119(3), 619?626. doi :10.1016/j.jfoodeng.2013.06.014. Mendoza C.I. (2013). Model for the Shear Viscosity of Suspensions of Star Polymers and Other Soft Particles. Macromolecular Chemistry and Physics, 214(5), 599?604. doi :10.1002/macp.201200551

How dimensional analysis allows to go beyond Metzner–Otto concept for non-Newtonian fluids

The concept of Metzner and Otto (1957) was initially developed for correlating power measurements in stirred vessels for shear-thinning fluids in the laminar regime with regard to those obtained for Newtonian liquids. To get this overlap, Metzner and Otto postulated and determined an “effective shear rate” which was proportional to the rotational speed of the impeller Although it was not based on a strong theoretical background, it was rapidly admitted as a practical engineering approach and was extended for seeking out a “Newtonian correspondence” with non-Newtonian results (i.e. different classes of fluids). This was applied in a variety of tank processes even for predicting heat transfer or mixing time, which stretches far away from the frame initially envisaged by Metzner and Otto themselves. This paper aimed to show how dimensional analysis offers a theoretically founded framework to address this issue without the experimental determination of effective quantities. This work also aimed to enlarge the underlying questions to any process in which a variable material property exists and impacts the process. For that purpose, the pending questions of Metzner and Otto concept were first reminded (i.e. dependence of the Metzner-Otto constant to rheological parameters, physical meaning of the effective shear rate, etc). Then, the theoretical background underlying the dimensional analysis was described and, applied to the case of variable material properties (including non-Newtonian fluids), by introducing in particular the concept of material similarity. Last, two examples were proposed to demonstrate how the rigorous framework associated with the dimensional analysis is a powerful method to exceed the concept of Metzner & Otto and, can be adapted beyond the Ostwald-de Waele power law model to a wide range of non-Newtonian fluids in various processes, without being restricted to batch reactor and laminar regime

Etude de la texture de suspensions de particules molles concentrées (relations entre la structure, la rhéologie et la perception sensorielle)

MASSY-AgroParisTech (913772301) / SudocSudocFranceF

Perception sensorielle de la texture de gels en France et au Vietnam et prédiction des profils sensoriels par des mesures instrumentales

MASSY-AgroParisTech (913772301) / SudocSudocFranceF

Prise en compte des e ets du produit et du procédé au cours de l'opération de foisonnement par battage en continu - Analyse dimensionnelle

L'objet de cette étude est de mieux formaliser et modéliser de façon générique le processus de structuration d'un produit par le procédé de foisonnement, en reliant les paramètres opératoires aux propriétés des mousses formées et de contribuer ainsi à un meilleur pilotage de l'opération. Une ligne de foisonnement par battage en continu a été instrumentée et l'évolution du diamètre des bulles en fonction des paramètres du produit et du procédé a été suivie pour des milieux modèles newtoniens et rhéofluidifiants. L'analyse dimensionnelle à l'échelle du procédé a permis d'aboutir à un modèle physique de l'opération, et donc d'avoir une compréhension des phénomènes en présence. Elle a aussi permis d'intégrer les paramètres du produit et du procédé et de simplifier la représentation des résultats expérimentaux. En n, la cohérence de ce modèle avec d'autres issus de la littérature et une première approche de validation avec un produit réel, semble justi er son caractère générique.The aim of this study is to better formalize and model in a generic way the structuring of a product by the foaming operation process, by linking the operating parameters to the foams properties and contribute to a better steering of the operation. A continuous whipping line was instrumented and the evolution of bubble diameter depending on both product and process parameters was characterized for Newtonian and shear-thinning model fluids. Dimensional analysis of the process has lead to a physical model of the operation, and therefore makes possible the understanding of the phenomena involved. It also helped to integrate the product and the process parameters and simplify the representation of experimental results. Finally, the consistency of this model with others from the literature and a first validation with a real product seems to justify his relevance.PARIS-AgroParisTech Centre Paris (751052302) / SudocSudocFranceF

A photographic method to measure food item intake. Validation in geriatric institutions

From both a clinical and research perspective, measuring food intake is an important issue in geriatric institutions. However, weighing food in this context can be complex, particularly when the items remaining on a plate (side dish, meat or fish and sauce) need to be weighed separately following consumption. A method based on photography that involves taking photographs after a meal to determine food intake consequently seems to be a good alternative. This method enables the storage of raw data so that unhurried analyses can be performed to distinguish the food items present in the images. Therefore, the aim of this paper was to validate a photographic method to measure food intake in terms of differentiating food item intake in the context of a geriatric institution. Sixty-six elderly residents took part in this study, which was performed in four French nursing homes. Four dishes of standardized portions were offered to the residents during 16 different lunchtimes. Three non-trained assessors then independently estimated both the total and specific food item intakes of the participants using images of their plates taken after the meal (photographic method) and a reference image of one plate taken before the meal. Total food intakes were also recorded by weighing the food. To test the reliability of the photographic method, agreements between different assessors and agreements among various estimates made by the same assessor were evaluated. To test the accuracy and specificity of this method, food intake estimates for the four dishes were compared with the food intakes determined using the weighed food method. To illustrate the added value of the photographic method, food consumption differences between the dishes were explained by investigating the intakes of specific food items. Although they were not specifically trained for this purpose, the results demonstrated that the assessor estimates agreed between assessors and among various estimates made by the same assessor. The results also revealed that the accuracy of this method was not dependent on the type of food studied, thus, the photographic method was not specific to a particular food type. Finally, the photographic method was able to provide more detailed data because it allowed differentiation between food item intakes. These findings clearly suggest that the photographic method is a valid and useful method to measure food intake in geriatric institutions

Influencia de las condiciones de proceso en las características físicas de masas de yuca

Las propiedades texturales de masas preparadas a partir de harina de yuca precocida fueron estudiadas con el fin de determinar el efecto de las condiciones de proceso en sus características físicas. El módulo de deformabilidad, la dureza, la cohesividad y la adhesividad de masas reconstituidas de harina de yuca se evaluaron utilizando un analizador de textura. Trozos de parénquima de yuca procesados a diferentes condiciones de cocción y almacenados a baja temperatura (-5 ºC y -20 ºC) por 24 h se emplearon para elaborar las harinas. Cuando la temperatura en el período de almacenamiento del parénquima cocinado disminuyó de -5ºC a -20ºC, el módulo de deformabilidad, la dureza y la cohesividad de la masa aumentaron significativamente. Se concluye que la temperatura en el período de reposo del parénquima cocinado es el factor más importante que afecta las propiedades texturales de la masa de yuca

Rheological properties of stabilizers at low temperatures in concentrated sucrose solutions

International audienceDuring the freezing of sorbets, the concentration of sucrose and stabilizing macromolecules increases in the unfrozen phase. Rheological properties of this unfrozen phase were studied, depending on nature and concentration of hydrocolloids in sucrose solutions at temperatures below zero. Three stabilizers were tested individually in sucrose-rich solutions: locust bean gum (LBG), hydroxypropylmethylcellulose (HPMC) and carboxymethylcellulose (CMC). The parameters of the Ostwald-de Waele model were determined and apparent viscosities of solutions were calculated at shear rates encountered during the process. Intrinsic viscosities and critical concentrations of entanglement were determined to evaluate the expansion of polymers in solutions and the transition of concentration regimes according to process conditions. Viscoelastic properties were also tested to study the possible cryogelation. For HPMC and LBG, the shear thinning behavior increased quite linearly with the concentration in stabilizer whereas CMC was highly shear thinning. Increasing sugar did not reveal large effect on these properties. The increase in apparent viscosity of the unfrozen matrix in process conditions was dependent on stabilizers; solutions containing LBG were less viscous than the others. Intrinsic viscosities revealed that HPMC and LBG became progressively less expanded as the concentration of sucrose increased whereas CMC tended to aggregate. Measurements of viscoelastic properties evidenced a dominant viscous behavior for HPMC and LBG systems whereas CMC systems showed dominant elastic behavior at frequencies higher than 0.1 Hz. The next challenge will be to better understand the potential link between the particular rheological behavior of hydrocolloids in process conditions and their possible influence on crystallization mechanisms

Influence of flavour enhancement on food liking and consumption in older adults with poor, moderate or high cognitive status

It is important to maintain adequate food consumption in older adults so as to prevent malnutrition, particularly among those with cognitive impairments who represent the majority of patients living in nursing homes. Indeed, these patients may reduce their food intake, which can be explained by a lack of pleasure in eating food. Few studies have tested the efficiency of strategies based on food pleasure to increase food intake in this population. To our knowledge, the influence of flavour enhancement has been widely investigated in non-cognitively impaired older adults, but not in those with cognitive impairments. Our objective was therefore to study the influence of flavour enhancement on food liking and then on food intake in older adults with different degrees of cognitive impairments. To achieve this, two food testing methods were compared: paired comparison and sequential monadic tests. 104 subjects were recruited in four nursing homes and clustered into three groups as a function of their cognitive impairments (severe, moderate and without marked cognitive impairments). Two different samples of an appetizer were formulated: a reference sample and a flavour-enhanced sample. These appetizers were offered to the participants before lunch in standardised small portions during three tasting sessions organised at intervals of one week. During one session, the participants received both samples at the same time (paired comparison test) and during the two others, they were given a single sample at each session (sequential monadic test). Food intake and food liking were then evaluated with respect to each participant and each sample. The results showed a positive correlation between food liking and food intake, and a positive influence of flavour enhancement on food intake, regardless of the cognitive status of the participants. The sequential monadic test produced results similar to those of the paired-comparison test in terms of the effects of flavour enhancement. These findings suggest that this method could be used to investigate the influence of food interventions at mealtimes in older adults with cognitive impairments. Finally, this study shows that food intake could be increased by optimising the sensory properties of foods served to cognitively impaired older patients