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International audience; The inner wall of the intestine has multiscale structures whose roles, beyond the increase of surface area for absorption, are yet to be discovered. In this study, the mixing process in a human duodenum with circular folds, driven by segmentation contraction, was simulated using a multiphysics model, making it possible to track the evolution of mixing level distributions and enabling quantitative evaluation ofthe structural role of folds in mixing intensification. It was found that, in a laminar flow regime, circular folds intensify both radial and axial mixing by synergistically offering prominent and long-lasting swirls/vortices, high fluid velocity and high shear rates. Tall and slim folds with enlarged segmentation amplitude,frequency and wavelength can enhance mixing. The maximum enhancement ratio can reach 6.18 under the investigated conditions. These findings will also be valuable for the improved design of biomimetic soft-elastic reactors for the chemical and pharmaceutical industries.

International audience; In humans, oral food intake is the ultimate stage of food supply chain and the beginning of food disintegration and digestion process. During aging, the oral health changes and sometimes eating food can be a real challenge as food can be hard to masticate, humidify or swallow. To meet this challenge, and as part of the AlimaSSenS project, a team of researchers from the Centre of taste and eating behaviour investigated the concept of “oral comfort” when eating a food in an elderly population. A group of 107 seniors aged 65 years and more participated in qualitative (focus group) and quantitative studies (tasting sessions) in order to explore the concept of oral comfort when eating, according to elderly people, and develop a questionnaire to evaluate the oral comfort when eating a food product. The results of the study highlighted that oral comfort when eating a food product is a multi-dimensional concept, which includes dimensions related to food oral processing, food sensory properties and, to a lesser extent, pain sensation. The concept of oral comfort when eating food should be taken into account by those who are willing to design food products tailored to the elderly population.; Chez l’homme, la mise en bouche d’un aliment est l’étape ultime de la chaîne alimentaire et le début du processus de dégradation et de digestion. Avec l’âge, la santé orale évolue et peut parfois rendre l’acte alimentaire difficile. Dans le cadre du projet AlimaSSenS, 107 personnes âgées ont participé à des études qualitatives (groupes de discussion) et quantitatives (séances de dégustation) afin de comprendre ce qu’est le confort en bouche et de développer un outil permettant d’évaluer ce concept. Les résultats de cette étude ont montré que le confort en bouche est un concept multidimensionnel qui inclut des dimensions de formation de bol alimentaire, de propriétés sensorielles de l’aliment et, dans une moindre mesure, de douleurs ressenties en bouche. De plus, cette étude a montré qu’un aliment inconfortable l’est pour l’ensemble des seniors interrogés, quelle que soit leur santé bucco-dentaire. Il semble essentiel, lors de développement de nouveaux produits à destination de la population senior, de recueillir l’évaluation du confort en bouche desdits produits avant toute commercialisation.

Cette étude s’intéresse à la problématique de la micronutrition. En effet, la qualité nutritionnelle des aliments constitue aujourd’hui un véritable enjeu de santé publique. Plus particulièrement, les micronutriments (vitamines, minéraux et oligo-éléments) semblent avoir un rôle important dans la prévention ou l’amélioration de pathologies majeures.Cependant, plutôt que d’étudier les quantités de micronutriments contenues dans un aliment, il semble plus pertinent de s’intéresser à leur biodisponibilité, c’est à dire la proportion disponible dans le plasma sanguin, après absorption intestinale (Parada et Aguilera, 2007). Cela implique de mieux appréhender tous les phénomènes qui interviennent jusqu’à la biodisponibilité des micronutriments.L’extraction de ces derniers de la matrice alimentaire ingérée représente la première étape de la digestion jusqu’à son absorption. La microstructure alimentaire joue donc un rôle dans la libération, la transformation et l’absorption de certains nutriments (Parada et Aguilera, 2007 ; Turgeon et Rioux, 2011). Néanmoins, le lien entre la matrice alimentaire et la biodisponibilité des micronutriments qu’elle contient, demeure peu connu.L’objectif de l’étude clinique MicroNut est donc de mieux comprendre comment la structure/texture de l’aliment impacte la biodisponibilité des micronutriments qu’elle contient. Elle avait également pour objectif secondaire d’étudier la déstructuration en bouche des matrices solides en un bol alimentaire et les conséquences éventuelles sur la bioaccessibilité des vitamines hydrosolubles libérées dans la salive, c’est à dire la quantité de micronutriments présents sous une forme disponible pour l’absorption intestinale, après leur extraction de la matrice alimentaire (Parada et Aguilera, 2007).

Dans le cadre de cette étude nationale financée par l’Institut Carnot Qualiment, l’Institut National de la Recherche Agronomique (INRA) et le Centre de Recherche en Nutrition Humaine (CRNH) ont pour objectif de comprendre comment la structure/texture des aliments impacte la biodisponibilité des micronutriments. En effet, qu’il s’agisse des glucides, des lipides ou des protéines, l’impact de la structure de l’aliment peut moduler la libération (bioaccessibilité) et/ou l’absorption (biodisponibilité) des nutriments, ainsi que leurs cinétiques respectives. Deux matrices alimentaires solides (biscuit et génoise) et deux matrices semi-solides (flan et crème anglaise), toutes quatre enrichies en vitamines D, B9, B12 et en lutéine, de composition constante mais de structures différentes, sont conçues et testées dans le cadre des deux protocoles qui constituent cette étude (Figure 1).Le premier protocole portant sur l’analyse de la biodisponibilité a pour but d’étudier la cinétique de biodisponibilité des micronutriments ciblés (vitamines B9, B12, D et lutéine) des quatre matrices alimentaires différentes. Chaque sujet volontaire doit réaliser quatre cinétiques, au cours desquelles il aura à consommer une des quatre matrices, dans un ordre aléatoire. Pendant chacune des séances de cinétique, d’une durée de 8h, des prélèvements sanguins à intervalle régulier seront réalisés.Le deuxième protocole portant sur l’analyse des propriétés physiques des bols alimentaires s’articulait autour de l’étude des propriétés rhéologiques et granulométriques des bols alimentaires des deux matrices solides. De plus une analyse biochimique de la libération des micronutriments d’intérêt (bioaccessibilité orale) était prévue sur les bols alimentaires collectés. Le travail de thèse présenté dans ce mémoire a été réalisé dans le cadre du 2ème protocole de l’étude MICRONUT.

International audience; Several studies demonstrated that oral health impairment, such as tooth loss or a decrease in salivary flow might lead elderly people to reduce their meat intake. The present study assessed the impact of culinary processes liable to improve meat texture and smooth down meat oral processing, in order to fulfil the oral capacities of elderly people. Four culinary processes were selected: cooking bag, blade tenderizer, marinade and low-temperature cooking. A panel of 40 elderly participants with good and poor dental status were asked to assess 5 chicken breast samples, 5 roast beef samples and 4 beefsteak samples prepared according to different process conditions by using an “oral comfort” questionnaire. Results highlighted the fact that oral impairment may alter food bolus formation as well as texture perception while eating meat in elderly people. Furthermore, they revealed that easy-to-do culinary processes may improve meat tenderness and juiciness as well as smooth down food bolus formation, in particular for the roast beef.

Theme 6 6.4 Impact of Food Oral Processing on health benefits Theme 6 6.4 Impact of Food Oral Processing on health benefitsTheme 6 6.4 Impact of Food Oral Processing on health benefits; The first stage of digestion of solid foods begins with the food oral processing. The way in which the food bolus formation is achieved during mastication will define further digestive steps and consequently nutrient bioavailability.This work was designed to study the impact of masticatory deficiency, frequently observed in elderlypopulation, combined with aged digestive characteristics on nutrients bioaccessibility after ingestion of a meat model food. Four combinations of oral and gastric digestive conditions were simulated: in vitro food boluses were obtained after normal or deficient mastication by programming the mastication simulator AM2 and were digested in an in vitro dynamic digester (DIDGI®) mimicking adult or elderly physiological gastric conditions. Physical characterization of food bolus material was obtained with granulometry and rheological measurements. Biochemical characteristics of the liquid phase of the bolus (lipids/proteins oxidation, free-iron/peptides release in liquid phase) were measured for nutrient bioaccessibility assessments. The kinetics of release of lipids, proteins and peptides from the food matrix during gastric digestion were assessed in digesta (collected after 30, 60, 90, 120 and 150min) and analyzed as the area under the curve of nutrient appearance. Results showed that (1) food bolus after deficient mastication were harder, more cohesive and less disorganized, and with a greater proportion of large particles (2) deficient mastication resulted in a reduced bolus ioaccessibility of free -iron and peptides (3) deficient mastication slightly impacted nutrient bioaccessibility in gastric digesta after adult digestive conditions, probably balanced by the gastric enzyme activity and acidic conditions (4) deficient mastication combined with the elderly digestive conditions delayed the release of nutrients in the gastric compartment and did not reach the threshold obtained during adult digestion. Obviously for designing specific food for elderly, the oral stage has to be carefully considered to fulfill the specific needs of the elderly population whom increase dramatically.

Pulse legumes (pea, lentil, faba bean) are excellent source of proteins (20-30% db), dietary fibers (10-30%), and starch (40-55%). The formulation of gluten-free extruded snacks made entirely from pulse legumes is an interesting way to introduce legumes to young people. Due to the reactivity of protein components under thermomechanical treatment, extrusion can produce cellular structures with various texture and starch-protein composite morphology. In turn, the morphology of parietal material governs masticatory performances. For the first time, the interaction coefficient between bolus and saliva was determined by taking into account multi-scale structure of high-protein solid foams. The pea flour was extruded using a twin-screw extruder to obtain solid foams adapted to human mastication. Some samples were selected for in-vitro chewing by mapping the main properties: density, cellular architecture, texture, water absorption index (WAI) of starch and solubility of protein aggregates linked by S-S bonds in the dithiothreitol (DTE) using Principal Component Analysis. The boluses were collected at 3 chewing steps, representing different chewing times (t) until swallowing. The size distribution of bolus fragments was determined by imaging technique. Bolus consistency and water (“saliva”) uptake were determined by an adapted capillary rheometer, and gravimetric method, respectively. For all samples, the bolus viscosity exhibited shear thinning behaviour and it decreased with chewing time. Bolus flow index was quite constant for all chewing conditions and samples. However, bolus consistency index was correlated negatively to bolus water uptake (∆W) through a plasticization coefficient. Furthermore, ∆W could be predicted from theoretical salivary flow and median particle size. The model parameters depending on foams absorption properties could be expressed in function of WAI and protein solubility in DTE. The results will enrich the database for mechanistic modelling of proteinaceous solid foams chewing.

In the elderly, masticatory function often presents failure in certain oral tasks due to impairment such as decline in muscular force, jaw or tongue motility, neuro-muscular coordination, tooth damage, malocclusion and saliva production. Great disparity is observed in the various and potentially cumulative oral declines that occur with ageing. Such difficulties may have an impact on food consumption and nutritional status. To obtain better understanding of the consequences of several oral deficiencies, a series of swallowable boluses were prepared in vitro with the AM2 masticator apparatus with normal and deficient programming. Physiological normal mastication (NM) was simulated using in vivo data from healthy subjects. Chewing deficiencies were reproduced by alteration of NM programming to perform different levels and combinations of force loss, lack of saliva and decrease in the motility of oral elements. Poultry meatballs were used as test-food. Particle size distribution in the food bolus was measured by sieving and rheological features (hardness, cohesiveness and elasticity) were assessed with a TPA test. Compared to the NM outcome, significant and gradual deterioration of the food bolus was observed and associated with alteration in force, saliva and motility. Combinations of several failures led to greater or cumulative deficiencies in swallowable bolus properties. For the elderly presenting a high prevalence of various oral injuries, tailoring textured food cannot be ignored as a solution for remedying deficiencies and favoring the formation of a safe-swallowable bolus, which is an essential vector of nutrients. Knowing the impacts of oral injuries on the food bolus is obviously a requisite for developing diet strategies, including nutritional items for specific populations.

Sarcopenia is a disease of ageing people which affects their muscle mass, strength and balance, and thus their autonomy. A way to slow down these effects is to improve the digestion of proteins, which can also be influenced by aging. However, the respective effect of the different phenomena involved in proteins digestion, and the effect of ageing on them, are difficult to determine experimentally in vivo or in vitro. Mathematical modelling offers an alternative approach that can provide information difficult or even impossible to obtain experimentally. This paper aims at quantifying the effect of the different phenomena involved in the gastric digestion of meat using a transfer-reaction modelling approach. Fick’s second law has been applied to determine the diffusion of protons and of pepsin from the gastric fluid into bolus particles issued from meat mastication. Meat buffering capacity was taken into account to calculate the local pH and pepsin activity into the meat particles. Local pepsin concentration and activity were used to determine the meat protein digestibility based on a previous model developed on myofibrils. The spatiotemporal evolution of pH, pepsin concentration and digestibility have been simulated numerically for various meat bolus particles sizes associated to different mastication performance, and for different physiological conditions in the stomach, including common functional deteriorations associated with ageing. The results show that while meat protein digestibility in the stomach is high in normal physiological conditions, it gets heavily reduced when masticatory capacity and/or hydrochloric acid secretion and/or gastric mobility in the stomach decline, ultimately preventing an efficient meat protein digestion. The results and model can be used to better assess the efficiency of different nutritional strategies proposed to increase meat proteins digestion, thus decreasing the problems associated to sarcopenia.

The first stage of digestion of solid foods begins with the food oral processing. The way in which the food bolus formation is achieved during mastication will define further digestive steps and consequently nutrient bioavailability. This work was designed to study the impact of masticatory deficiency, frequently observed in elderly population, combined with aged digestive characteristics on nutrients bioaccessibility after ingestion of a meat model food. Four combinations of oral and gastric digestive conditions were simulated: in vitro food boluses were obtained after normal or deficient mastication by programming the mastication simulator AM2 and were digested in an in vitro dynamic digester (DIDGI®) mimicking adult or elderly physiological gastric conditions. Physical characterization of food bolus material was obtained with granulometry and rheological measurements. Biochemical characteristics of the liquid phase of the bolus (lipids/proteins oxidation, free-iron/peptides release in liquid phase) were measured for nutrient bioaccessibility assessments. The kinetics of release of lipids, proteins and peptides from the food matrix during gastric digestion were assessed in digesta (collected after 30, 60, 90, 120 and 150min) and analyzed as the area under the curve of nutrient appearance. Results showed that (1) food bolus after deficient mastication were harder, more cohesive and less disorganized, and with a greater proportion of large particles (2) deficient mastication resulted in a reduced bolus ioaccessibility of free -iron and peptides (3) deficient mastication slightly impacted nutrient bioaccessibility in gastric digesta after adult digestive conditions, probably balanced by the gastric enzyme activity and acidic conditions (4) def icient mastication combined with the elderly digestive conditions delayed the release of nutrients in the gastric compartment and did not reach the threshold obtained during adult digestion. Obviously for designing specific food for elderly, the oral stage has to be carefully considered to fulfill the specific needs of the elderly population whom increase dramatically.

Background Fat perception and liking are the subjects of growing interest from industries and the scientific community to reduce the fat content in food products while maintaining consumers’ liking. Scope and Approach In this review, the different physiological parameters involved in fat perception and fat liking for food emulsions are explored, focusing on spreads. A deeper analysis of the physiological mechanisms occurring during the melting and inversion phases, followed by bolus formation, mouth coating and oral clearance, allows an examination of the links between food composition, food structure, oral physiological parameters, fat perception and liking. Key Findings and Conclusions Fat perception is a multimodal sensation involving olfactory, gustatory and tactile cues. The main sensory descriptors associated with fat liking are creaminess, spreadability and aroma perception. During the melting and inversion phases, oral volume, saliva flow and tongue-palate compression contribute to the heat transfer and cooling effect, leading to the first sensory perception. Global acceptability is also driven by the mouthfeel sensation perceived after swallowing. Mouthfeel is a consequence of the bolus formation, mouth coating and oral clearance processes that are dependent on both emulsion composition and oral physiological parameters (saliva flow, saliva composition, fungiform papillae). Understanding the physiological mechanisms controlling fat perception can lead to a better understanding of the consumer's preference and liking for food emulsions.

The liking of the bread by the consumers is largely impacted by its sensory properties, and notably the aroma and texture perceived during inmouth consumption. These perceptions cannot be only explained by the volatile composition of the bread or by its structure. In fact, they also depend on dynamic phenomena, resulting from the breakdown of the bread in mouth, which depends on each individual. This PhD project aims thus to better understand the determinants linked to the product and to the individual at the origin of the dynamics of aroma and texture perceptions of bread. A multidisciplinary strategy, based on the study of the oral processing in real conditions of mastication was set up to fulfill this objective. The results show firstly that the hydration capacity and the rigidity of the crumb have a main impact on the evolution of bolus properties and texture and aroma perceptions during consumption. In this way, the higher the hydration capacity of the bread is, the more easily broken and hydrated it will be. Moreover, a bread with a rigid crumb could cause a higher release of volatile compounds susceptible to interact with the sensory olfactive receptors. In addition, two types of masticatory behavior, based on masticatory duration, were highlighted between the individuals of the study. These behaviors lead to bolus with different properties at swallowing time and at different dynamics of aroma and texture perceptions.; L’appréciation du pain par le consommateur est largement impactée par ses propriétés sensorielles, notamment les perceptions d’arômes et de texture en bouche. Ces perceptions ne peuvent pas être uniquement expliquées par la composition aromatique du pain ou par sa structure. Elles dépendent également de phénomènes dynamiques, résultant de la déstructuration du pain en bouche, très dépendante de chaque individu. L’objectif de ce projet de thèse est donc de mieux comprendre les déterminants liés au produit et à l’individu à l’origine des dynamiques de perceptions d’arômes et de texture du pain. Une stratégie multidisciplinaire, basée sur l’étude du processus oral en conditions réelles de mastication, a été mise en place pour répondre à cet objectif. Les résultats de cette étude montrent d’une part que la capacité d’hydratation et la rigidité de la mie jouent un rôle majeur dans l’évolution des propriétés des bols et des perceptions de texture et d’arômes au cours de la consommation. Ainsi, plus un pain a une capacité d’hydratation élevée, plus il sera facilement déstructuré et hydraté. De plus, un pain avec une mie rigide provoquerait une plus grande libération des composés d’arômes susceptibles d’interagir avec les récepteurs olfactifs sensoriels. D’autre part, deux types de comportements masticatoires, basés sur la durée de mastication, ont été identifiés entre les individus participant à l’étude. Ces comportements conduisent à des bols aux propriétés différentes au moment de la déglutition et à des dynamiques différentes de perception de texture et d’arôme.

Mastication is essential to prepare food into a bolus ready to be swallowed safely, with no choking risk. Based on food bolus properties, a masticatory normative indicator was developed by Woda et al. (2010) to identify impaired masticatory function within good oral health population. The aim of the present study was to identify relevant parameters of bolus' structure to differentiate safe to unsafe bolus among elderly contrasting by their dental status.93 elderly, 58% with at least 7 posterior dental occlusions and 42% with less than 5 posterior dental occlusions were recruited. They masticated a piece of raw carrot and spit the food bolus ready to be swallowed. Particle size distribution of each individual bolus was evaluated using image analysis.Two parameters derived from the particles size distribution were considered: the median (d50) and the d99 (upper level with only 1% observed values higher). The parameters allowed identifying three groups: one group (n=45) with a food bolus made of many and small particles (d99 = 7.4 mm ± 1.2; d50 = 1.5 mm ± 0.3); one group (n=30) with food boluses containing medium particle size (d99 = 9.0 mm ± 1.4; d50 = 2.4 mm ± 0.4); and one group (n=18) whose food bolus is heterogeneous and contains big particles that seem unsafe to swallow (d99 = 10.3 mm ± 0.9; d50 = 1.7 mm ± 0.4). The links with oral health characteristics of each group were studied.

The preparation of a food bolus for swallowing is the main task of oral elements involved in the masticatory process. The combined events designed for that are perfectly adjusted to food structure. With a correct oral state and normal mastication, a follow-up to the bolus formation provides great information regarding mechanisms underlying food breakdown and other processing during which oral sensations and first steps of digestion take place. The food bolus is the result of matrix breakdown and saliva incorporation that favors particles agglomeration, combined outcome finally triggering swallowing. This work aimed at investigating the kinetics of bolus formation along the masticatory process regarding physical characteristics and oral bioaccessibility of nutrients. In vitro masticatory sequences were realized with the AM2 masticator apparatus programmed for normal mastication of Frankfurters thanks to in vivo data obtained during chewing the same food model. Normal masticatory sequences were experimentally stopped at different stages until the swallowing point (after 1/3, after 2/3 and at the end of the complete masticatory sequence). Frankfurters samples were prepared in cylindrical shape (6.5 ± 0.2 g). After liquid-solid phase separation, boluses were analyzed for physical (granulometry, rheological behavior) and chemical (protein/lipid oxidation, iron/peptides release in liquid phase) characteristics. From the beginning to the end of mastication, median particle size decreased from 9.38 ± 2.64 mm after 1/3 of the masticatory sequence to 5.02 ± 0.51 mm in the swallowable bolus. At the same time, the Frankfurter food bolus became softer, stickier, and less cohesive and elastic. The release of free-iron and peptides in the liquid phase significantly increased (63% and 16% respectively) from the first third of masticatory sequence to the masticatory endpoint due to progressive matrix disintegration. Protein oxidation also significantly increased in liquid phase of the bolus of Frankfurter model. This work highlighted significant changes in physical and chemical characteristics of food bolus throughout the masticatory sequence conferring emphasis on food matrix disruption and potential consequences to be considered both in terms of physical passage during swallowing and bioaccessibility of nutrients for example in case of impairment of this oral stage.

National audience

The authors want to thank O. François (University of Auvergne) for his involvement in the development of the AM2 apparatus and in preparing the figures; and P. Riordan for English revision; Developing masticatory apparatus, chewing robots or an artificial mouth is an old but ever more important goal in food science, nutrition or dental research fields, as reflected by the number of existing digital or biomechanical systems. Whatever the objective of the approach, basic knowledge of the physiology of mastication, adaptation and neurophysiological control is absolutely needed before conceiving an apparatus. Obviously, the final step in the development of a mastication simulator is its validation before performing food or food bolus characterization. This validation step is imperative to avoid biased interpretation and can be performed through in vivo–in vitro comparison of particle size distributions in food boluses obtained after normal mastication. This kind of validated machine offers the chance to produce boluses for other related uses such as nutrient bioaccessibility or digestion studies, for example. Such an apparatus can also be employed to simulate different dental states or ageing conditions

Session 10 : Meat, Nutrition and Health; National audience; This work was designed to study the effect of fibers addition in frankfurters on food bolus characteristics after mastication and on oral release of nutrients. Frankfurters were prepared with addition of fibers (psyllium and tapioca starch) in reduced-fat formulations. Food boluses were prepared during normal mastication programmed on a mastication simulator (AM2). After liquid-solid phase separation, boluses were analyzed for physical (granulometry, rheological behavior) and chemical (protein/lipid oxidation, iron/peptides release in bolus liquid phase) properties. Results showed that physico-chemical characteristics of food bolus after mastication depended on presence and fiber type. Matrix disruption during chewing is more important with fiber addition but significance was observed for psyllium fiber only. The bolus of psyllium-enriched frankfurter was softer, less cohesive than no-fiber and tapioca starch-enriched ones. Iron release from food matrix was significantly lower and peptide release significantly greater in frankfurters containing psyllium fibers compared to no-fibers and tapioca starch-enriched ones. In presence of fibers, liquid part of boluses contained fewer particles, which were of larger diameter with tapioca starch. Fibers used as fat-replacers in frankfurters formulation lead to significant changes in food bolus characteristic after mastication.

The challenge of this work is to carry out the rheological characterization of concentrated suspensions of viscoplastic objects suspended in a viscoelastic matrix. Three structural constraints are faced: the heterogeneity of the particles, the size of particle in relation to the size of the whole system studied, and the proximity between the consistency of the suspending phase and that the consistency of the particles. In the food context, some biological constraints are added: small lifetimes of bolus, in vivo sampling and test conditions of temperature and humidity. All these constraints lead to a compromise in rheometry, at the edge of continuum mechanics, aiming to measure useful rheological properties. To carry out the rheological characterizations quickly and efficiently, two original devices has been designed trough this work. Applied to food bolus from cheese, rheology comes to govern flows in the mouth and induce the creation of exchange area in the mouth, during the chewing process. Through these interfaces, the savors and flavors are released and transported to the sensory receptors. The results show the relationship between the yield stress of the bolus and flavors release of different hydrophobic aromas, depending on the firmness and fat content of the cheeses. Specifically, fluid suspending matrix appears to play a major role in the creation and persistence of exchange area.Applied to gastric juice from bread, the issue is whether changes in carbohydrate content could impact the rheology of gastric juice, modify the kinetics of stomach flow rate, and decrease the glycemic excursion. The results show the effect of amylose addition on increasing the viscosity for long digestion time, when the rheology is no longer governed by the jamming effect of the particles made of water-swollen bread. However, amylose does not seem to have any impact on the kinetics of emptying, which reinforces that the stomach flow rate is regulated by the caloric charge contained in the meal.; L'enjeu des travaux contenus dans cette thèse est la caractérisation rhéologique de suspensions concentrées d'objets viscoplastiques suspendus dans une matrice viscoplastique. Trois contraintes physiques se présentent : l'hétérogénéité des objets, la taille des objets au regard de la taille du système étudié, et la proximité entre la consistance de la phase suspendante et celle des objets. Dans notre contexte alimentaire, il faut ajouter des contraintes d'ordre biologique : les faibles durées de vie des produits, les prélèvements in vivo et la conservation des conditions de températures et d'humidité. L'ensemble de ces contraintes aboutit à une rhéométrie spécifique, aux frontières de la mécanique des milieux continues, avec pour objectif de mesurer des propriétés rhéologiques pertinentes. Pour cela, deux instrumentations originales ont été construites pour effectuer la caractérisation rhéologique le plus vite et au plus près de la génération des échantillons.Appliquée aux bols alimentaires issus de fromage, leur rhéologie vient gouverner les écoulements en bouche et induire la création de surface d'échange en bouche, au travers de la mastication. Au travers de ces interfaces, les arômes et les sapides sont libérés et transportés vers les récepteurs sensoriels. Les résultats montrent le lien entre le seuil de contrainte à l'écoulement du bol et la libération d'arômes de différents hydrophobicités, fonction de la fermeté et du taux de matières grasses du fromage. Plus particulièrement, la phase suspendante fluide, semble jouer un rôle majeur dans la création et la persistance des surfaces d'échanges. Appliquée aux jus gastriques issus de pain, l'enjeu est de savoir si des modifications des contenus en glucides pouvaient impacter la rhéologie des jus gastriques, modifier les cinétiques de vidange en sortie d'estomac, et diminuer l'excursion glycémique. Les résultats montrent l'effet d'un ajout d'amylose sur l'augmentation de la viscosité aux temps de digestion longs, lorsque la rhéologie n'est plus gouvernée par l'encombrement des particules de pain gonflées d'eau. Cependant, l'amylose ne semble pas avoir d'impact sur les cinétiques de vidange, ce qui vient conforter que le débit en sortie d'estomac est régulé par la charge énergétique contenue dans le repas.

The challenge of this work is to carry out the rheological characterization of concentrated suspensions of viscoplastic objects suspended in a viscoelastic matrix. Three structural constraints are faced: the heterogeneity of the particles, the size of particle in relation to the size of the whole system studied, and the proximity between the consistency of the suspending phase and that the consistency of the particles. In the food context, some biological constraints are added: small lifetimes of bolus, in vivo sampling and test conditions of temperature and humidity. All these constraints lead to a compromise in rheometry, at the edge of continuum mechanics, aiming to measure useful rheological properties. To carry out the rheological characterizations quickly and efficiently, two original devices has been designed trough this work. Applied to food bolus from cheese, rheology comes to govern flows in the mouth and induce the creation of exchange area in the mouth, during the chewing process. Through these interfaces, the savors and flavors are released and transported to the sensory receptors. The results show the relationship between the yield stress of the bolus and flavors release of different hydrophobic aromas, depending on the firmness and fat content of the cheeses. Specifically, fluid suspending matrix appears to play a major role in the creation and persistence of exchange area.Applied to gastric juice from bread, the issue is whether changes in carbohydrate content could impact the rheology of gastric juice, modify the kinetics of stomach flow rate, and decrease the glycemic excursion. The results show the effect of amylose addition on increasing the viscosity for long digestion time, when the rheology is no longer governed by the jamming effect of the particles made of water-swollen bread. However, amylose does not seem to have any impact on the kinetics of emptying, which reinforces that the stomach flow rate is regulated by the caloric charge contained in the meal.; L'enjeu des travaux contenus dans cette thèse est la caractérisation rhéologique de suspensions concentrées d'objets viscoplastiques suspendus dans une matrice viscoplastique. Trois contraintes physiques se présentent : l'hétérogénéité des objets, la taille des objets au regard de la taille du système étudié, et la proximité entre la consistance de la phase suspendante et celle des objets. Dans notre contexte alimentaire, il faut ajouter des contraintes d'ordre biologique : les faibles durées de vie des produits, les prélèvements in vivo et la conservation des conditions de températures et d'humidité. L'ensemble de ces contraintes aboutit à une rhéométrie spécifique, aux frontières de la mécanique des milieux continues, avec pour objectif de mesurer des propriétés rhéologiques pertinentes. Pour cela, deux instrumentations originales ont été construites pour effectuer la caractérisation rhéologique le plus vite et au plus près de la génération des échantillons.Appliquée aux bols alimentaires issus de fromage, leur rhéologie vient gouverner les écoulements en bouche et induire la création de surface d'échange en bouche, au travers de la mastication. Au travers de ces interfaces, les arômes et les sapides sont libérés et transportés vers les récepteurs sensoriels. Les résultats montrent le lien entre le seuil de contrainte à l'écoulement du bol et la libération d'arômes de différents hydrophobicités, fonction de la fermeté et du taux de matières grasses du fromage. Plus particulièrement, la phase suspendante fluide, semble jouer un rôle majeur dans la création et la persistance des surfaces d'échanges. Appliquée aux jus gastriques issus de pain, l'enjeu est de savoir si des modifications des contenus en glucides pouvaient impacter la rhéologie des jus gastriques, modifier les cinétiques de vidange en sortie d'estomac, et diminuer l'excursion glycémique. Les résultats montrent l'effet d'un ajout d'amylose sur l'augmentation de la viscosité aux temps de digestion longs, lorsque la rhéologie n'est plus gouvernée par l'encombrement des particules de pain gonflées d'eau. Cependant, l'amylose ne semble pas avoir d'impact sur les cinétiques de vidange, ce qui vient conforter que le débit en sortie d'estomac est régulé par la charge énergétique contenue dans le repas.

Understanding and modeling phenomena governing stimuli release during food consumption make it possible to respect both nutritional and sensorial criteria during its formulation. A model of salt release during the course of mastication was developed for "solid" products. The breakdown was comprehended by the generation of the area of contact between the product and the saliva that governs the transfers of stimuli. The area of contact was written as the product of two functions. The first was related to the subject and was function of his masticatory performance. The second was related to the product and depended on its breakdown behavior that can be determined by in vitro tests. During the pharyngeal stage, the biomechanics of swallowing governs pharyngeal mucosa coating and aroma compounds present in this layer. These phenomena are due to a thin film flow, stationary in a soft elastohydrodynamic contact whose the kinematics is equivalent to a forward roll coating process lubricated by saliva. Two sets of conditions were distinguished. When the saliva film is thin, food bolus viscosity has a strong impact on mucosa coating and on flavour release. When the saliva film is thick, the food bolus coating the mucosa is very diluted by saliva during the swallowing process and the impact of product viscosity on flavour release is weak. This second set of condition allowed us to explain the physical origin of in vivo observations on flavour release.; La compréhension et la modélisation des phénomènes régissant la libération des stimuli orosensoriels durant la consommation d'un aliment doit permettre de respecter des critères de conception à la fois nutritionnels et organoleptiques. Un modèle de libération du sel au cours de la mastication a été développé pour des produits " solides ". La déstructuration du produit a été appréhendée en terme de génération de surface de contact entre le produit et la salive qui gouverne les transferts de sel. La surface de contact a été considérée comme étant le produit de deux fonctions. La première est reliée au sujet et est fonction de son efficacité masticatoire. La seconde est reliée au produit et dépend de ses propriétés de déstructuration qui peuvent être déterminées par des tests in vitro. Durant la phase pharyngée, la biomécanique de la déglutition gouverne l'enduction des muqueuses par le bol alimentaire et ainsi la libération des composés d'arôme présents dans cette couche. Ces phénomènes sont régis par un écoulement en film mince, stationnaire, dans un contact élastohydrodynamique mou dont la cinématique équivaut à un processus d'enduction par des cylindres contrarotatifs lubrifiés par de la salive. Deux régimes ont été distingués. Lorsque le film de salive est fin, la viscosité du bol alimentaire a un grand rôle sur l'enduction et la libération des composés d'arôme. Lorsque le film de salive est épais, le bol est dilué par la salive durant le processus de déglutition et sa viscosité a un faible effet sur l'enduction et la libération des composés d'arôme. Ce second régime permet d'expliquer l'origine physique d'observations in vivo concernant la libération des composés d'arôme.

absent

International audience; The main goal of mastication is to prepare a food bolus suitable for deglutition. The bolus preparation consists in food breakdown and processing during which oral sensations are generated. This study was performed to examine the particle size distribution in the bolus formed by chewing 10 natural foods. Ten young subjects with normal dentition were asked to chew the food and to expectorate the bolus just before swallowing, while masticatory parameters were recorded. The particle size distribution of each bolus was evaluated by wet sieving. The number of cycles, sequence duration and masticatory frequency varied among subjects and foods. The particle size distributions differed among foods but were similar among subjects. The median particle size d(50) gave a range from 0.82 to 3.04 mm allowing a food classification based on the state of the bolus. The d(50) value reflected the fracturability and may be useful to describe food behaviour in the mouth during bolus preparation.

Dans l'ensemble des études qui contribue à la maîtrise des qualités sensorielles et nutritionnelles des produits issus de la filière viande, l'étape permettant de préciser la transformation de la viande en bol alimentaire est très peu documentée. Dans ce travail, nous avons cherché à mettre en évidence l'impact de la physiologie orale du consommateur et les propriétés structurales du produit sur la formation du bol alimentaire au cours de la mastication. L'efficacité masticatoire et les flux salivaires ont été évalués, afin de constituer des groupes de sujets adaptés aux hypothèses posées. Les relations entre flux et composition salivaires ont été caractérisées. Les bols alimentaires ont été prélevés à différents points de la mastication, enregistrée par électromyographie. Des mesures d'insalivation et de structures ont été réalisées par des méthodes validées. Lors de la consommation de viande, l'état bucco-dentaire du consommateur a des conséquences directes sur la dynamique de formation du bol et sur ses propriétés mécaniques. Chez les édentés complets appareillés, il a été non seulement observé une perte de capacité d'adaptation des paramètres de la mastication à l'évolution des propriétés de l'aliment mais aussi la formation de bols moins déstructurés qui se traduit par une diminution de l'utilisation des protéines pendant la digestion. En revanche, les différences de flux salivaires, restant dans un domaine physiologique, n'affectent pas les propriétés des bols au point de déglutition. Les modifications de composition de la salive totale observées après la mastication de différentes matrices alimentaires artificielles pourraient provenir d'une stimulation différentielle des différentes glandes salivaires. Les propriétés mécaniques de la viande influencent davantage la formation et les caractéristiques des bols alimentaires que sa composition