Simulated 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.

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Standardised recommendations for a physiologically relevant, semi-dynamic in vitro simulation of upper GI tract digestion.

International audienceBy using simultaneously rheometry and a multiple light scattering technique, diffusing wave spectroscopy (DWS), we have studied the steady flows of three-dimensional aqueous foams. A number of parameters--the surfactants, the liquid volume fraction, and the roughness of the rheometer surfaces--are widely varied in order to determine which quantities have an impact on the macroscopic flow behaviors. By comparing to previous theoretical and experimental results, we show that flow regimes can either be slip or shear dominated. Two opposite slip regimes are identified; the transition from one to the other is obtained either by changing the surfactant or the liquid fraction, and we quantitately discuss which regime is selected for any given foam properties. Similarly, different shear regimes are also found, and we discuss the link between the macroscopic rheometry measurements, the nature of the flow, and the interfacial microscopic properties. Despite the occurrence of slip, we show how we can recover the actual shear rate by DWS, and how we can quantitatively explain the measured slip velocities

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 formulae. 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.

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Many food systems are dispersed systems, that is, they 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.

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