Postprandial differences in the plasma metabolome of healthy Finnish subjects after intake of a sourdough fermented endosperm rye bread versus white wheat bread

<p>Abstract</p> <p>Background</p> <p>The mechanism behind the lowered postprandial insulin demand observed after rye bread intake compared to wheat bread is unknown. The aim of this study was to use the metabolomics approach to identify potential metabolites related to amino acid metabolism involved in this mechanism.</p> <p>Methods</p> <p>A sourdough fermented endosperm rye bread (RB) and a standard white wheat bread (WB) as a reference were served in random order to 16 healthy subjects. Test bread portions contained 50 g available carbohydrate. <it>In vitro </it>hydrolysis of starch and protein were performed for both test breads. Blood samples for measuring glucose and insulin concentrations were drawn over 4 h and gastric emptying rate (GER) was measured. Changes in the plasma metabolome were investigated by applying a comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry metabolomics platform (GC×GC-TOF-MS).</p> <p>Results</p> <p>Plasma insulin response to RB was lower than to WB at 30 min (P = 0.004), 45 min (P = 0.002) and 60 min (P < 0.001) after bread intake, and plasma glucose response was significantly higher at time point 90 min after RB than WB intake (P = 0.045). The starch hydrolysis rate was higher for RB than WB, contrary to the <it>in vitro </it>protein digestibility. There were no differences in GER between breads. From 255 metabolites identified by the metabolomics platform, 26 showed significant postprandial relative changes after 30 minutes of bread intake (p and q values < 0.05). Among them, there were changes in essential amino acids (phenylalanine, methionine, tyrosine and glutamic acid), metabolites involved in the tricarboxylic acid cycle (alpha-ketoglutaric, pyruvic acid and citric acid) and several organic acids. Interestingly, the levels of two compounds involved in the tryptophan metabolism (picolinic acid, ribitol) significantly changed depending on the different bread intake.</p> <p>Conclusions</p> <p>A single meal of a low fibre sourdough rye bread producing low postprandial insulin response brings in several changes in plasma amino acids and their metabolites and some of these might have properties beneficial for health.</p

Accuracy-based Simulation Strategies for Plasma Edge Simulations for Nuclear Fusion Devices

Nuclear fusion has the potential to provide the world's energy needs with safe, sustainable and virtually limitless energy. A key challenge in the realization of magnetically confined nuclear fusion is the power exhaust in the so-called divertor region near the reactor walls, which has to withstand enormous power loads. To predict and analyze divertor performance, accurate plasma edge simulations are indispensable. State-of-the-art plasma edge codes, such as B2-EIRENE, solve non-linear plasma and neutral transport equations iteratively. While plasma transport is modeled with fluid equations and implemented with a finite volume (FV) code, neutral transport requires a kinetic equation, implemented with a Monte Carlo (MC) code. In an MC code, particle trajectories are traced out to determine the average behavior of the particles. However, a statistical error remains on the result, which has a large impact on the convergence of the coupled FV-MC system. This complicates accuracy analysis and makes plasma edge simulations time-consuming. The goal of this PhD is to improve the speed and accuracy of B2-EIRENE simulations by optimizing the simulation strategy. Based on a detailed accuracy analysis, where all numerical error contributions are quantified, the coupling technique and the numerical parameters can be chosen more adequately. That way, a solution can be obtained in less computational time without losing accuracy. Or, similarly, a more accurate solution can be computed in the same computational time. First, we examine convergence and accuracy in a systematic way for several coupling techniques using a simplified 1D plasma edge model. Several error contributions are defined and methods to estimate these errors are proposed. We found the Random Noise coupling technique, where particle trajectories are uncorrelated between iterations, to be superior to Correlated Sampling, where trajectories are correlated, and Robbins Monro, where averaged values are used during the simulation. When the results of consecutive statistically stationary iterations are averaged in post-processing, an order of magnitude speed-up can be obtained without losing accuracy compared to the traditional simulation approach without averaging. Subsequently, we perform a first comprehensive accuracy analysis of B2-EIRENE simulation for a partially detached ITER divertor plasma. The speed-up obtained with averaging enabled simulations with on higher resolution discretization grids, which were previously unfeasible. A grid resolution study reveals that the discretization error in typical simulations is very large with some peak values increasing more than 40%. With a more suitable parameter choice, the total numerical error was limited to 15% within a feasible computational time. Finally, we extend the developed methodology for time-dependent FV-MC simulations and iterative MC codes using simplified 1D models. The extensions demonstrate the generality of the developed framework, which opens the way to accuracy analysis for many more applications within plasma edge simulations as well as in other fields where coupled stochastic-deterministic codes are emerging.status: publishe

Efficient code simulation strategies for B2-EIRENE

Plasma edge simulation codes are crucial for the interpretation of present experiments as well as for the assessment of new concepts and next generation nuclear fusion devices. These codes are most often based on a combined Finite Volume (FV) / Monte Carlo (MC) numerical approach to simulate coupled plasma and neutral particle transport. In this paper we apply recently derived error reduction analysis to assess numerical errors in a partially detached ITER case. We show that also for this strongly coupled FV/MC simulation case, statistical averaging over iterations provides an accurate means to achieve well reproducible and statistically accurate results. Moreover, the error reduction analysis with respect to numerical parameters provide a framework to achieve increased accuracy for a given computational cost. We also show how significant code speed-up can be achieved for a desirable accuracy compared to presently used simulation strategies. Keywords: Plasma edge modelling, Code speed-up, Error assessmen

Analytical study of statistical error in coupled finite-volume/Monte Carlo simulations of the plasma edge

© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Plasma and neutral transport in the plasma edge region of magnetic confinement fusion devices is often simulated by iteratively coupling a finite volume (FV) code for the plasma with a Monte Carlo (MC) code for the neutral particles. Because of the statistical MC noise, the iterative scheme defines a Markov process for the plasma states. We derived relations between the iterative scheme and the statistical distribution of the plasma states. In this paper, we study in detail, for random noise coupling and in a generalized scalar setting, the relation between the artificial time step used in the iterative scheme and the variance of the plasma states. We show numerically that our new insights, gained from the scalar setting, still hold when simulating a simplified 1D plasma edge model.status: publishe

Grid resolution study for B2-EIRENE simulation of partially detached ITER divertor plasma

© EURATOM 2018. This paper examines the effect of grid resolution on the solution of a B2-EIRENE simulation of a partially detached ITER divertor plasma. Due to the large amount of required computational time in coupled finite-volume/Monte-Carlo codes, simulations of the plasma edge are typically run on coarse grids. However, new averaging techniques make simulations with finer grids feasible. Starting from the original numerical grid, simulations are performed on two successively finer grids. Results of the numerical error analysis reveal that the discretization errors are large. Peak values are particularly sensitive to grid resolution and can increase more than for the same model input parameters. However, this effect is partially offset by a modification of the operational space of the ITER divertor in this case. By choosing the numerical parameters more adequately, a total numerical error of only has been achieved within a feasible computational time.status: publishe

(13)C-egg white breath test: a non-invasive test of pancreatic trypsin activity in the small intestine

BACKGROUND—The recent availability of egg white protein highly enriched with (13)C has allowed breath test technology to be adapted for the study of protein digestion and absorption. Pancreatic trypsin is considered to be the key enzyme in the proteolytic cascade.
AIM—To evaluate trypsin activity in the small intestine of healthy volunteers and patients with pancreatic disease by a recently developed (13)C-egg white breath test.
METHODS—A total of 48 healthy volunteers and 30 patients with pancreatic disease were studied after ingestion of a test meal consisting of 22 g (13)C-labelled egg protein. Breath samples were taken before and after ingestion of the meal and analysed for (13)CO(2) concentration. Moreover, pancreatic trypsin output after maximal stimulation was measured in 13 patients and nine healthy volunteers.
RESULTS—The six hour cumulative (13)CO(2) excretion in breath was significantly lower in patients than controls (mean (SEM): 6.23 (0.82)% v 19.16 (0.58)%, p<0.0001). An excellent correlation was found between the six hour cumulative (13)CO(2) excretion and trypsin activity after maximal pancreatic stimulation.
CONCLUSION—The non-invasive (13)C-egg white breath test is promising as an indirect pancreatic proteolytic function test.


Keywords: breath test; pancreatic disease; trypsin; protein; assimilatio