Electrical conductivity of dispersions: from dry foams to dilute suspensions

We present new data for the electrical conductivity of foams in which the liquid fraction ranges from two to eighty percent. We compare with a comprehensive collection of prior data, and we model all results with simple empirical formul\ae. We achieve a unified description that applies equally to dry foams and emulsions, where the droplets are highly compressed, as well as to dilute suspensions of spherical particles, where the particle separation is large. In the former limit, Lemlich's result is recovered; in the latter limit, Maxwell's result is recovered

An elasto-visco-plastic model for immortal foams or emulsions

A variety of complex fluids consist in soft, round objects (foams, emulsions, assemblies of copolymer micelles or of multilamellar vesicles -- also known as onions). Their dense packing induces a slight deviation from their prefered circular or spherical shape. As a frustrated assembly of interacting bodies, such a material evolves from one conformation to another through a succession of discrete, topological events driven by finite external forces. As a result, the material exhibits a finite yield threshold. The individual objects usually evolve spontaneously (colloidal diffusion, object coalescence, molecular diffusion), and the material properties under low or vanishing stress may alter with time, a phenomenon known as aging. We neglect such effects to address the simpler behaviour of (uncommon) immortal fluids: we construct a minimal, fully tensorial, rheological model, equivalent to the (scalar) Bingham model. Importantly, the model consistently describes the ability of such soft materials to deform substantially in the elastic regime (be it compressible or not) before they undergo (incompressible) plastic creep -- or viscous flow under even higher stresses.Comment: 69 pages, 29 figure

A standardised static in vitro digestion method suitable for food – an international consensus

peer-reviewedSimulated gastro-intestinal digestion is widely employed in many fields of food and nutritional sciences, as conducting human trials are often costly, resource intensive, and ethically disputable. As a consequence, in vitro alternatives that determine endpoints such as the bioaccessibility of nutrients and non-nutrients or the digestibility of macronutrients (e.g. lipids, proteins and carbohydrates) are used for screening and building new hypotheses. Various digestion models have been proposed, often impeding the possibility to compare results across research teams. For example, a large variety of enzymes from different sources such as of porcine, rabbit or human origin have been used, differing in their activity and characterization. Differences in pH, mineral type, ionic strength and digestion time, which alter enzyme activity and other phenomena, may also considerably alter results. Other parameters such as the presence of phospholipids, individual enzymes such as gastric lipase and digestive emulsifiers vs. their mixtures (e.g. pancreatin and bile salts), and the ratio of food bolus to digestive fluids, have also been discussed at length. In the present consensus paper, within the COST Infogest network, we propose a general standardised and practical static digestion method based on physiologically relevant conditions that can be applied for various endpoints, which may be amended to accommodate further specific requirements. A frameset of parameters including the oral, gastric and small intestinal digestion are outlined and their relevance discussed in relation to available in vivo data and enzymes. This consensus paper will give a detailed protocol and a line-by-line, guidance, recommendations and justifications but also limitation of the proposed model. This harmonised static, in vitro digestion method for food should aid the production of more comparable data in the future.COST action FA1005 Infogest22 (http://www.cost-infogest.eu/) is acknowledged for providing funding for travel, meetings and conferences

Bioavailability of Nutrients and Micronutrients: Advances in Modeling and In Vitro Approaches

International audienceThe bioavailability of food nutrients and microconstituents is recognized as a determinant factor for optimal health status. However, human and animal studies are expensive and limited by the large amount of potential food bioactive compounds. The search for alternatives is very active and raises many questions. On one hand, in vitro digestion systems are good candidates, but to date only bioaccessibility has been correctly assessed. To go further, to what degree should natural processes be reproduced? What techniques can be used to measure the changes in food properties and structures in situ in a noninvasive way? On the other hand, modeling approaches have good potential, but their development is time-consuming. What compromises should be done between food and physiology realism and computational ease? This review addresses these questions by identifying highly resolved analytical methods, detailed computer models and simulations, and the most promising dynamic in vitro systems

Bioaccessibility of Nutrients and Micronutrients from Dispersed Food Systems: Impact of the Multiscale Bulk and Interfacial Structures

International audienceMany food systems are dispersed systems, i.e. possess at least two immiscible phases. This is generally due to the coexistence of domains with different physicochemical properties separated by many interfaces which control the apparent thermodynamic equilibrium. This feature was and is still largely studied to design pharmaceutical delivery systems. In food science, the recent intensification of in vitro digestion tests to complement the in vivo ones holds promises in the identification of the key parameters controlling the bioaccessibility of nutrients and micronutrients. In this review, we present the developments of in vitro digestion tests for dispersed food systems (mainly emulsions, dispersions and gels). We especially highlight the evidences detailing the roles of the constituting multiscale structures. In a perspective section, we show the potential of structured interfaces to allow controlled bioaccessibility

Bioaccessibility of lipophilic micro-constituents from a lipid emulsion

International audienceDigestion is an important process, the first one in the conversion of food to energy. From this angle, digestion of nutrients was extensively studied, and this process was found to be very efficient. Nevertheless, many molecules contained in food do not bring energy but are essential as they allow maintaining normal body functions. These are the micro-nutrients, including vitamins and minerals. On top of that, recent nutrition research identified many other bioactive molecules (termed micro-constituents as they only represent a small part of the food) playing a role in the health status, e.g. contributing to the prevention of chronic diseases. However, it was shown that their digestion is much less efficient, especially that of lipophilic micro-constituents (such as lipophilic vitamins, carotenoids, cholesterol and other steroids) depending on food structure and composition. Enhancing their health effects through optimal absorption and bioavailability thus requires a comprehensive knowledge of their release from food within the gastrointestinal tract. To study this step, of which the endpoint is termed bioaccessibility, in vitro digestion methods proved to be well adapted to fundamental research. This review reports the effects of the physicochemical parameters controlling the bioaccessibility of various lipophilic micro-constituents from emulsion. Notably, it appears that this bioaccessibility is related to the bioaccessibility of lipid nutrients, as their kinetics are interrelated. This knowledge will enable the formulation of food in terms of structure and composition to obtain optimal bioaccessibility. As the latter likely controls bioavailability, prevention of some metabolic disorders could be targeted in the long term

Bioavailability of Nutrients and Micronutrients: Advances in Modeling and In Vitro Approaches

International audienceThe bioavailability of food nutrients and microconstituents is recognized as a determinant factor for optimal health status. However, human and animal studies are expensive and limited by the large amount of potential food bioactive compounds. The search for alternatives is very active and raises many questions. Onone hand, in vitro digestion systems are good candidates, but to date only bioaccessibility has been correctly assessed. To go further, to what degree should natural processes be reproduced? What techniques can be used to measure the changes in food properties and structures in situ in a noninvasive way? On the other hand, modeling approaches have good potential, but their development is time-consuming. What compromises should be done between food and physiology realism and computational ease? This review addresses these questions by identifying highly resolved analytical methods, detailed computer models and simulations, and the most promising dynamic in vitro systems

In vitro digestion of emulsions: mechanistic and experimental models

International audienceDigestion is a complex combination of physical, chemical and biological processes. In orderto investigate the impact of food structure on the digestion of lipids, we work on acontrollable triglyceride-based system: emulsion. In this study, the emulsion was composed ofa single triglyceride (tricaprylin or triolein), decanal as a model lipophilic micronutrient, and asingle emulsifier (-lactoglobulin or sodium oleate) at different concentrations. Weinvestigated the effects of these parameters on an in vitro intestinal static digestion, which wasmonitored using classic physicochemical methods: fatty acid titration, lipidsextraction/chromatography and sizing.To interpret the results, we developed several mechanistic models based on mass transferkinetics, which enable a direct comparison and identify the factors influencing the digestion.Those are the molar mass of the lipids, the initial interfacial area (droplet size) and dispersedvolume fraction, the interfacial tension and dilatational viscoelasticity.We also developed an experimental digestion model based on a single droplet usingtensiometry. This technique was able to monitor the kinetics of lipolysis and micellarsolubilization simultaneously.All methods confirmed the result from our previous study that the type of triglyceride is themajor parameter influencing the digestion. Moreover, the mechanistic and experimentalmodels allowed to evidence that digestion was usually faster for -lactoglobulinemulsions/droplets compared to sodium oleate ones. There was no clear effect of theemulsifier concentrati