Béatrice Laroche

The heat treatment and the gelation are strong determinants of the kinetics of milk proteins digestion and of the peripheral availability of amino acids

This study aimed to determine the kinetics of milk protein digestion and amino acid absorption after ingestion of four dairy matrices by six minipigs: unheated or heated skim milk and corresponding rennet gels. Digestive contents and plasma samples were collected over a 7 h-period after meal ingestion. Gelation of milk slowed down the outflow of the meal from the stomach and the subsequent absorption of amino acids, and decreased their bioavailability in peripheral blood. The gelled rennet matrices also led to low levels of milk proteins at the duodenum. Caseins and β-lactoglobulin, respectively, were sensitive and resistant to hydrolysis in the stomach with the unheated matrices, but showed similar digestion with the heated matrices, with a heat-induced susceptibility to hydrolysis for β-lactoglobulin. These results suggest a significant influence of the meal microstructure (resulting from heat treatment) and macrostructure (resulting from gelation process) on the different steps of milk proteins digestion.

Acid and rennet gels exhibit strong differences in the kinetics of milk protein digestion and amino acid bioavailability

This study aimed at determining the kinetics of milk protein digestion and amino acid absorption after ingestion by six multi-canulated mini-pigs of two gelled dairy matrices having the same composition, similar rheological and structural properties, but differing by their mode of coagulation (acidification/renneting). Duodenal, mid-jejunal effluents and plasma samples were collected at different times during 7h after meal ingestion. Ingestion of the acid gel induced a peak of caseins and β-lactoglobulin in duodenal effluents after 20min of digestion and a peak of amino acids in the plasma after 60min. The rennet gel induced lower levels of both proteins in the duodenum (with no defined peak) as well as much lower levels of amino acids in the plasma than the acid gel. Plasma ghrelin concentrations suggested a potentially more satiating effect of the rennet gel compared to the acid gel. This study clearly evidences that the gelation process can significantly impact on the nutritive value of dairy products.

Impact of the Dairy Matrix Structure on Milk Protein Digestion Kinetics: Mechanistic Modelling Based on Mini-pig In Vivo Data

Beyond the individual content in nutrients, it is now established that the matrix structure is also to consider when evaluating the nutritional properties and possible health effects of a food material. The objective of this study was to gain knowledge on the effect of the structure of dairy products on the digestion of milk proteins as inferred from a mathematical modelling of mini-pig in vivo data. Six dairy matrices of the same composition but differing by their physicochemical and structural properties were investigated. They were manufactured using technological processes commonly used in the industry (heat treatment, rennet gelation, acid gelation and mixing). The experimental results cover a 7-h postprandial period and consist of plasmatic amino acid concentrations as well as dry matter contents and chromium concentrations (a marker of the liquid phase of the meal) of samples collected at the stomach exit. The model developed not only accounts for the main digestive events but also for phenomena that can occur within the stomach (milk clotting and aggregate syneresis). It provides a good fitting of all the experimental data and allows estimating parameter values that can be explained by considering the properties of the matrices investigated. The model has also been used to estimate quantities that cannot be observed experimentally (stomach volumes, endogenous secretions, gastric emptying half-time, etc.) in order to recover a better picture of all the results and validate the model predictions against the literature. It even appears that our simulations of gastric emptying and aminoacidemia superimpose very well with previously published data obtained using similar matrices and the same mini-pig species. This study shows that the great differences in the kinetics of amino acid absorption that were observed experimentally can be fully understood by considering the behaviour of the dairy matrices within the stomach. It therefore offers interesting perspectives for the integration of food structure parameters, and more particularly for dairy products, in the comprehensive view of the nutritional quality of food products.

Signatures of ecological processes in microbial community time series

BackgroundGrowth rates, interactions between community members, stochasticity, and immigration are important drivers of microbial community dynamics. In sequencing data analysis, such as network construction and community model parameterization, we make implicit assumptions about the nature of these drivers and thereby restrict model outcome. Despite apparent risk of methodological bias, the validity of the assumptions is rarely tested, as comprehensive procedures are lacking. Here, we propose a classification scheme to determine the processes that gave rise to the observed time series and to enable better model selection.ResultsWe implemented a three-step classification scheme in R that first determines whether dependence between successive time steps (temporal structure) is present in the time series and then assesses with a recently developed neutrality test whether interactions between species are required for the dynamics. If the first and second tests confirm the presence of temporal structure and interactions, then parameters for interaction models are estimated. To quantify the importance of temporal structure, we compute the noise-type profile of the community, which ranges from black in case of strong dependency to white in the absence of any dependency. We applied this scheme to simulated time series generated with the Dirichlet-multinomial (DM) distribution, Hubbell’s neutral model, the generalized Lotka-Volterra model and its discrete variant (the Ricker model), and a self-organized instability model, as well as to human stool microbiota time series. The noise-type profiles for all but DM data clearly indicated distinctive structures. The neutrality test correctly classified all but DM and neutral time series as non-neutral. The procedure reliably identified time series for which interaction inference was suitable. Both tests were required, as we demonstrated that all structured time series, including those generated with the neutral model, achieved a moderate to high goodness of fit to the Ricker model.ConclusionsWe present a fast and robust scheme to classify community structure and to assess the prevalence of interactions directly from microbial time series data. The procedure not only serves to determine ecological drivers of microbial dynamics, but also to guide selection of appropriate community models for prediction and follow-up analysis.

Reduction of Metabolic Models by Polygons Optimization Method Applied to Bioethanol Production with Co-Substrates

Abstract In literature metabolic stoichiometric matrix reduction is based on convex analysis by choosing the greatest triangle. This paper proposes a new methodology for the reduction of metabolic networks based on the concept of convex hull by optimization methods. Different polygons are tested to conjointly minimize the squared error (convex hull - experimental data) and maximize the convex hull area in order to reduce the set of metabolic reactions involved in the model. The advantage of this method relies on its ability to select different geometries in a simple manner with the knowledge of the elementary modes. A cybernetic model implementing the proposed optimization method is tested with data for bioethanol production by Saccharomyces cerevisiae growing on four substrates. Parameter estimation and model validation allow comparing the performance of the chosen polygons for reduction of metabolic pathways.

Computable convergence bounds of series expansions for infinite dimensional linear-analytic systems and application

This paper deals with the convergence of series expansions of trajectories for semi-linear infinite dimensional systems, which are analytic in state and affine in input. A special case of such expansions corresponds to Volterra series which are extensively used for the analysis, the simulation and the control of weakly nonlinear finite dimensional systems. The main results of this paper give computable bounds for both the convergence radius and the truncation error of the series. These results can be used for model simplification and analytic approximation of trajectories with a guaranteed quality. They are available for distributed and boundary control systems. As an illustration, these results are applied to an epidemic population dynamic model. In this example, it is shown that the truncation of the series at order?2 yields an accurate analytic approximation which can be used for time simulation and control issues. The relevance of the method is illustrated by simulations.

Controlling a non-linear epidemic PDE model with delayed detection: a model simplification approach

This paper investigates the problem of controlling an epidemic spread in an animal flock. The disease is characterized by a long and variable incubation period, during which individuals are infectious but do not show clinical signs. The disease detection is therefore delayed. The epidemic process and population dynamic in the flock are modelled by a system of non-linear integro-differential transport-reaction PDE, structured according to health status, age and time remaining before detection. We show that for realistic parameter values this system can be approximated with guaranteed error bounds by a simpler model, and use this simpler model to design flock management strategies.

Mathematical modelling of milk proteins digestion dynamics

Abstract The objective of this study is to better understand and model the effect of dairy matrix structure on the hydrolysis and transit rates of milk proteins during digestion. 2 dairy matrices having a similar composition but differing by their internal structure were manufactured: one solution and one acid gel which both contained a small amount of Cr-EDTA complex, a non-absorbable and non-hydrolysable water soluble marker. These matrices were given to six adult mini-pigs and, for each experiment, 9 samples were collected after the pylori, i.e. at the stomach exit. The first sample was collected before the meal and the 8 others at different times after the meal ingestion. Effluents were analysed to determine their residual concentration in milk proteins (β-lactoglobulin and caseins) and the Cr2+ concentration. A mathematical model describing the gastric emptying of Cr-EDTA and these proteins, as well as hydrolysis for proteins, is presented. This model provides a good fitting of the Cr-EDTA and proteins concentrations and allows estimating several unknown digestion parameters with a good accuracy.