Functional imaging of plants: A nuclear magnetic resonance study of a cucumber plant

Functional magnetic resonance imaging was used to study transients of biophysical parameters in a cucumber plant in response to environmental changes. Detailed flow imaging experiments showed the location of xylem and phloem in the stem and the response of the following flow characteristics to the imposed environmental changes: the total amount of water, the amount of stationary and flowing water, the linear velocity of the flowing water, and the volume flow. The total measured volume flow through the plant stem was in good agreement with the independently measured water uptake by the roots. A separate analysis of the flow characteristics for two vascular bundles revealed that changes in volume flow of the xylem sap were accounted for by a change in linear-flow velocities in the xylem vessels. Multiple-spin echo experiments revealed two water fractions for different tissues in the plant stem; the spin-spin relaxation time of the larger fraction of parenchyma tissue in the center of the stem and the vascular tissue was down by 17% in the period after cooling the roots of the plant. This could point to an increased water permeability of the tonoplast membrane of the observed cells in this period of quick recovery from severe water los

Quantitative NME microscopy of iron transport in methanogenic aggregates

Transport of micronutrients (iron, cobalt, nickel, etc.) within biofilms matrixes such as methanogenic granules is of high importance, because these are either essential or toxic for the microorganisms living inside the biofilm. The present study demonstrates quantitative measurements of metal transport inside these biofilms using T1 weighted 3D RARE. It is shown that iron(II)-EDTA diffusion within the granule is independent of direction or the inner structure of the granules. Assuming position dependence of the spin-lattice relaxivity, Fick’s law for diffusion in a sphere can be applied to simulate the diffusion within the methanogenic granules under investigation. A relatively low diffusion coefficient of 2.5*10-11 m2·s-1 was obtained for iron diffusion within the methanogenic granul

Moisture distribution in broccoli: measurements by MRI hot air drying experiments

The internal moisture distribution that arise in food products during drying, is a key factor for the retention of quality attributes. To reveal the course of moisture content in a product, internal moisture profiles in broccoli florets are measured by MRI imaging during drying experiments with controlled air flow and temperature. The 3D images concern a matrix size of 64×64×64 elements. Signal intensity is converted to product moisture content with a linear relationship, while taking a minimum detectable moisture content of 0.3 kg water/ kg dry matter into account. Moisture content as a function of time is presented for a 2D cross sectional area in the middle of a broccoli sample. The average moisture contents for the cross sectional area obtained from the MRI imaging are compared with spatial model simulations for the moisture distribution. In that model the effective diffusion coefficient is based on the Free Volume Theory. This theory has the advantage that the changed mobility of water in the product during drying is taken into account and the theory also predicts the moisture transport in the porous broccoli floret. Key parameters for the Free Volume Theory are estimated by fitting to the experimental MRI results and the effective diffusion coefficient is given as a function of the product water content

Investigation on the influence of pre-treatments on drying behaviour of broccoli by MRI experiments

Abstract: Magnetic Resonance Imaging (MRI) allows the monitoring of internal moisture content of food products during drying non-destructively. In an experimental set-up with continuous and controlled hot air supply, the internal moisture distribution of broccoli with different pre-treatments are measured during drying. Moisture distribution, drying rate and shrinkage are compared and analyzed quantitatively. MRI results indicated that for fresh broccoli stalks the moisture content in the core of the sample increased after some hours of drying. With pre-treatments as peeling, blanching or freezing the moisture transport barrier in the skin of the broccoli sample was reduced. Shrinkage was uniform for most of the pre-treated samples and the moisture increment in the core did not occur. It was also found that with these pre-treatments progress of drying enhanced significantly. Therefore, from an drying efficiency and economic point of view, pre-treatments prior to drying offer important opportunities. Keywords: MRI, hot air drying, broccoli stalk, increased moisture content, pre-treatment

Soil - Plant - Atmosphere continuum studies by MRI

Understanding the way in which plants develop, grow, and interact with their environment requires tools capable of a high degree of both spatial and temporal resolution. Here we present an overview of noninvasive intact plant MRI, which is not a straight forward extension of the methods discussed for (bio)medical MRI. The combination of dedicated intact plant MRI hardware, methods of MRI flowmetry, and the interpretation of relaxation times and diffusion measurements in terms of water dynamics at the cell level provides an excellent and unique tool to study (the dynamics in) xylem and phloem water transport in relation to plant water balance, radial transport, root water uptake, and leaf evaporation/photosynthesis. Finally, a short overview of recently developed mobile NMR/MRI for in situ (greenhouses, field situation) applications is given

Influence of water content and drying on the physical structure of native hyaluronan

Hydration properties of semi-diluted hyaluronan were studied by means of time domain nuclear magnetic resonance. Based on the transverse proton relaxation times T2, the plasticization of hyaluronan which was precipitated by isopropylalcohol and dried in the oven have been determined at water content 0.4 g of water per g of hyaluronan. Above this water content, the relaxation times increased and levelled off around 0.8 g of water per g of hyaluronan which agrees well with values determined earlier by differential scanning calorimetry and dielectric relaxometry. The freeze dried and oven dried samples showed differences in their physical structure such as glass transition, plasticization concentration and sample topography which influenced their kinetics and mechanisms of hydration. Results confirmed earlier hypothesis that some native biopolymer structures can be easily modified by manipulation of preparation conditions, e.g. drying, giving fractions with specific physicochemical properties without necessity of their chemical modification

Stagnant mobile phase mass transfer in chromatographic media: Intraparticle diffusion and exchange kinetics

Pulsed field gradient nuclear magnetic resonance has been successfully applied to a direct and detailed experimental study of topological and dynamic aspects involved in the exchange of small, nonsorbed fluid molecules between the intraparticle pore network and the interparticle void space in chromatographic columns packed with spherical-shaped, porous particles. The approach provides quantitative data about the effective, intraparticle diffusion coefficients (and tortuosity factors) and about the associated, diffusion-limited mass transfer kinetics, including stagnant boundary layer contributions. In view of the recorded exchange kinetics, an analytical description for solute diffusion into/out of spherical particles is offered and addresses the influence of the particle size distribution and particle shape on the observed mass transfer rates and calculated diffusivities. The combined analyses of the steady-state intraparticle pore diffusion data and the associated exchange kinetics with Peclet numbers up to 500 reveals the existence of external stagnant fluid where all the interparticle fluid-side resistance to diffusion is localized. It is represented by a thin stagnant boundary layer around the particles and can be accounted for by the introduction of a hydrodynamically effective particle diameter which is found to depend on the Peclet number. The approach appears to be promising for a selective, detailed study of the boundary layer dynamics. Concerning the investigation of different chromatographic media and intraparticle morphologies, we demonstrate that the actual correlation (or randomness) of interconnection between intraparticle pores of different size has a profound effect on the observed tortuosity factors and the diffusion-limited stagnant mobile phase mass transfer kinetics. Compared to intraparticle pore networks with a random assignment of different pore sizes, hierarchically structured bidisperse porous particles offer a superior network topology, which can form the basis for an increased chromatographic performance

Gas and liquid distribution in the monolith film flow reactor

The gas-liquid distribution in a monolith film flow reactor is investigated in the scope of this work. Magnetic resonance imaging (MRI) and a customized liquid collection method hate been successfully applied to determine the liquid distribution over the monolith cross-section. Using a well-positioned spray nozzle liquid distributor, very uniform distributions are found which address the needs for applications that require high single-pass conversions. Due to the lack of radial convective flow in monoliths, the initial distribution propagates through the reactor. With a correct positioned spray nozzle distributor, a far more uniform distribution than the natural one for trickle beds is obtained. MRI, applied to study the local gas-liquid distribution in a monolith channel, clearly shows the accumulation of the liquid in the corners of the individual channel with an arc-shaped gas-liquid interface. Differences in local liquid holdup over the channel corners were found, which is described as channel scale nonuniformities. The experimental results are in good agreement with a fundamental hydrodynamic model based on the Navier-Stokes equations. The average liquid saturation is conveniently described with an engineering correlation ßL = 6.6 . (Fr2Ls/ReLs)0.46, as a function of the liquid phase Reynolds and Froude numbe

Stagnant mobile phase mass transfer in chromatographic media: Intraparticle diffusion and exchange kinetics

Pulsed field gradient nuclear magnetic resonance has been successfully applied to a direct and detailed experimental study of topological and dynamic aspects involved in the exchange of small, nonsorbed fluid molecules between the intraparticle pore network and the interparticle void space in chromatographic columns packed with spherical-shaped, porous particles. The approach provides quantitative data about the effective, intraparticle diffusion coefficients (and tortuosity factors) and about the associated, diffusion-limited mass transfer kinetics, including stagnant boundary layer contributions. In view of the recorded exchange kinetics, an analytical description for solute diffusion into/out of spherical particles is offered and addresses the influence of the particle size distribution and particle shape on the observed mass transfer rates and calculated diffusivities. The combined analyses of the steady-state intraparticle pore diffusion data and the associated exchange kinetics with Peclet numbers up to 500 reveals the existence of external stagnant fluid where all the interparticle fluid-side resistance to diffusion is localized. It is represented by a thin stagnant boundary layer around the particles and can be accounted for by the introduction of a hydrodynamically effective particle diameter which is found to depend on the Peclet number. The approach appears to be promising for a selective, detailed study of the boundary layer dynamics. Concerning the investigation of different chromatographic media and intraparticle morphologies, we demonstrate that the actual correlation (or randomness) of interconnection between intraparticle pores of different size has a profound effect on the observed tortuosity factors and the diffusion-limited stagnant mobile phase mass transfer kinetics. Compared to intraparticle pore networks with a random assignment of different pore sizes, hierarchically structured bidisperse porous particles offer a superior network topology, which can form the basis for an increased chromatographic performance

Soil - Plant - Atmosphere continuum studies by MRI

Understanding the way in which plants develop, grow, and interact with their environment requires tools capable of a high degree of both spatial and temporal resolution. Here we present an overview of noninvasive intact plant MRI, which is not a straight forward extension of the methods discussed for (bio)medical MRI. The combination of dedicated intact plant MRI hardware, methods of MRI flowmetry, and the interpretation of relaxation times and diffusion measurements in terms of water dynamics at the cell level provides an excellent and unique tool to study (the dynamics in) xylem and phloem water transport in relation to plant water balance, radial transport, root water uptake, and leaf evaporation/photosynthesis. Finally, a short overview of recently developed mobile NMR/MRI for in situ (greenhouses, field situation) applications is given