Henk Van As

Henk Van As
Wageningen University & Research | WUR · Faculty of Agrotechnology and Food Sciences

PhD

About

298
Publications
40,196
Reads
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6,536
Citations
Citations since 2016
41 Research Items
2509 Citations
20162017201820192020202120220100200300400
20162017201820192020202120220100200300400
20162017201820192020202120220100200300400
20162017201820192020202120220100200300400
Introduction
The research in Van As’ group is aimed at unravelling and understanding transport processes and water dynamics at different time and length scales in porous bio-systems to unravel structure-function relationships. For this, Time Domain NMR and (rheo-)MRI methods are developed. Applications are intact plants (xylem-phloem, source-sink, water limitation; first portable NMR to study flow in plants in 1986), plant-like materials, foods (composition, processing, structure, function) and food based materials (shear and flow behavior).
Additional affiliations
March 2013 - April 2013
Wageningen University & Research
Position
  • Advances in Magnetic Resonancne
February 2013 - March 2013
Wageningen University & Research
Position
  • Biophysical Imaging methods
Description
  • MRI, AFM, CLSM, FLIM
April 2012 - April 2016
Wageningen University & Research
Position
  • Can phloem be rate limiting between sink and source
Description
  • Source-sink effects on phloem transport are studied by MRI in intact plants.

Publications

Publications (298)
Article
Full-text available
Quantitative magnetic resonance imaging (qMRI) is a versatile, non-destructive and non-invasive tool in life, material, and medical sciences. When multiple components contribute to the signal in a single pixel, however, it is difficult to quantify their individual contributions and characteristic parameters. Here we introduce the concept of phasor...
Article
Full-text available
From the diffusional behavior of nanoparticles in heterogeneous hydrogels, quantitative information about sub-micron structural features of the polymer matrix can be derived. Pulsed-gradient spin-echo NMR is often the method of choice, because it measures diffusion of the whole ensemble of nanoparticles. However, in 1H diffusion-ordered spectroscop...
Article
Anoxic conditions should hamper the transport of sugar in the phloem, since this is an active process. The canopy is a carbohydrate source and the roots are carbohydrate sinks. By fumigating the shoot with N2 or flooding the rhizosphere, anoxic conditions in the source or sink, respectively, were induced. Volume flow, velocity, conducting area and...
Article
Full-text available
The importance and prospects for MRI as applied to intact plants and to foods are presented in view of one of humanity's most pressing concerns, the sustainable and healthy feeding of a worldwide increasing population. Intact plants and foods have in common that their functionality is determined by complex multiple length scale architectures. Intac...
Article
Full-text available
Water content and hydraulic conductivity, including transport within cells, over membranes, cell-to-cell, and long-distance xylem and phloem transport, are strongly affected by plant water stress. By being able to measure these transport processes non-invasely in the intact plant situation in relation to the plant (cell) water balance, it will be p...
Chapter
In this chapter, the authors discuss how magnetic resonance imaging (MRI) has thus far been deployed in a wide range of applications in plants and foods, and also outline future perspectives. The flow characterization of granular or fluid food products, often of non‐Newtonian nature, is crucial for designing and optimizing the quality and sensory p...
Article
Full-text available
p>This protocol describes a signal-to-noise ratio (SNR) calibration and sample preparation method for solenoidal microcoils combined with biological samples, designed for high-resolution magnetic resonance imaging (MRI), also referred to as MR microscopy (MRM). It may be used at pre-clinical MRI spectrometers, demonstrated on Medicago truncatula ro...
Article
Full-text available
Despite aerobic granular sludge wastewater treatment plants operating around the world, our understanding of internal granule structure and its relation to treatment efficiency remains limited. This can be attributed in part to the drawbacks of time-consuming, labor-intensive, and invasive microscopy protocols which effectively restrict samples siz...
Article
Full-text available
This work provides a systematic comparison of the signal-to-noise ratio (SNR), spatial resolution, acquisition times and metabolite limits-of-detection for magnetic resonance microscopy and spectroscopy at three different magnetic field strengths of 14.1 T, 17.6 T and 22.3 T (the highest currently available), utilizing commercially available hardwa...
Article
Full-text available
The mechanical properties of many supramolecular materials are often determined by noncovalent interactions that arise from an interplay between chemical composition and molecular microstructural organization. The reversible nature of noncovalent interactions gives supramolecular materials responsive properties that are otherwise difficult to obtai...
Preprint
Full-text available
The mechanical properties of many supramolecular materials are often determined by non-covalent interactions that arise from an interplay between chemical composition and molecular microstructural organization. The reversible nature of non-covalent interactions gives supramolecular materials responsive properties that are otherwise difficult to obt...
Article
Full-text available
Performing rheo-microMRI velocimetry at high magnetic field with strong pulsed field gradients has clear advantages in terms of (chemical) sensitivity and resolution in velocities, time and space. To benefit from these advantages some artefacts need to be minimized. Significant sources of such artefacts are chemical shift dispersion due to the high...
Article
Full-text available
Interactions between plants and the soil’s microbial & fungal flora are crucial for the health of soil ecosystems and food production. Microbe-plant interactions are difficult to investigate in situ due to their intertwined relationship involving morphology and metabolism. Here, we describe an approach to overcome this challenge by elucidating morp...
Article
Full-text available
Main conclusion Adaptation of the xylem under dehydration to smaller sized vessels and the increase in xylem density per stem area facilitate water transport during water-limiting conditions, and this has implications for assimilate transport during drought. Abstract The potato stem is the communication and transport channel between the assimilate...
Article
Changes in the physical state of cellular water and its interrelations with carbohydrate metabolism were studied during preplanting storage of tulip bulbs (Tulipa ges-neriana 'Apeldoorn'). • Magnetic resonance imaging, light and scanning electron microscopy and high-performance anion exchange chromatography with pulsed amperometric detection were u...
Article
Full-text available
The use of microbial fuel cells (MFCs) for wastewater treatment fits in a circular economy context, as they can produce electricity by the removal of organic matter in the wastewater. Activated carbon (AC) granules are an attractive electrode material for bioanodes in MFCs, as they are cheap and provide electroactive bacteria with a large surface a...
Article
Full-text available
Gastric digestion is crucial for protein breakdown. Although it has been widely studied with in vitro models, verification in vivo remains a big challenge. Magnetic resonance imaging (MRI) has the potential to bridge this gap. Our objective was to use the transverse relaxation time (T2) and rate (R2 = T2⁻¹) to monitor hydrolysis of protein-rich foo...
Article
Full-text available
Reactivation of axial water flow in ring-porous species is a complex process related to stem water content and developmental stage of both earlywood-vessel and leaf formation. Yet empirical evidence with non-destructive methods on the dynamics of water flow resumption in relation to these mechanisms is lacking. Here we combined in vivo magnetic res...
Article
A detailed investigation was carried out on the modulation of the coupling between network formation and recrystallisation of oil-dispersed micronized fat crystal (MFC) nanoplatelets by varying oil composition, shear and temperature. Sunflower (SF) and bean (BO) oils were used as dispersing media for MFC nanoplatelets. Already during MFC dispersion...
Article
Full-text available
A set of functionalized nanoparticles (PEGylated dendrimers, d = 2.8 - 9 nm) was used to probe the structural heterogeneity in Na+/K+ induced κ-carrageenan gels. The self-diffusion behavior of these nanoparticles as observed by 1H PFG NMR, FRAP and RICS revealed a fast and a slow compo nent, pointing towards microstructural heterogeneity in the gel...
Chapter
This chapter deals with the principles and the applications of magnetic resonance imaging (MRI) for assessment of the distribution and of the amount of intercellular gas-filled spaces and major metabolites in fruit and vegetable tissues. Combining this information with measurements of water characteristics could enable the use of MRI in an integrat...
Article
Dispersing micronized fat crystals (MFCs) in oil is a novel route to largely decouple fat crystallisation and network formation and thus to simplify the manufacture of fat-continuous food products. MFCs dispersed in oil form a weak interaction network, organized by crystal aggregates in a continuous net of crystalline nanoplatelets. The rough surfa...
Article
Full-text available
Chloroplast thylakoid membranes contain virtually all components of the energy-converting photosynthetic machinery. Their energized state, driving ATP synthesis, is enabled by the bilayer organization of the membrane. However, their most abundant lipid species is a non-bilayer-forming lipid, monogalactosyl-diacylglycerol; the role of lipid polymorp...
Article
Whey protein microparticles (CG MPs) were made with a cold gelation method. Without shearing or mixing during gelation spherical CG MPs were formed, while shearing or mixing resulted in smaller irregularly shaped CG MPs. The water-binding capacity of pellets (WBC-P) that were obtained after centrifuging CG MP dispersions was remarkably large (11–18...
Conference Paper
Full-text available
We use PFG NMR to measure hindered self-diffusion of spherical, monodisperse diffusionalnanoprobes in a polysaccharide network. These nanoprobes have different diameters in the 1–10 nm range, but identical inert (PEG) surfaces. We use Johnson’s model of particle self-diffusion in fibrous networks to estimate the polymerstrand thickness and to obtai...
Article
Full-text available
Some of the most striking features of Rhizophoraceae mangrove saplings are their voluminous cylinder-shaped hypocotyls and thickened leaves. The hypocotyls are known to serve as floats during seed dispersal (hydrochory) and store nutrients that allow the seedling to root and settle. In this study we investigate to what degree the hypocotyls and lea...
Article
We present a combined time domain NMR and rheology approach to quantify the water distribution in a phase separated protein blend. The approach forms the basis for a new tool to assess the microstructural properties of phase separated biopolymer blends, making it highly relevant for many food and non-food related applications. First, we determine t...
Article
Shear flow of microfibrillated cellulose dispersions is still not wholly understood as a consequence of their multi-length-scale heterogeneity. We added carboxymethyl cellulose, a charged polymer, to make cellulose microfibril dispersions more homogeneous at the sub-micron and macro scales. We then compared the yielding and flow behavior of these d...
Article
Full-text available
Description of processes such as bioaccumulation, bioavailability and biosorption of heavy metals in biofilm matrixes requires the quantification of their transport. This study shows 3D MRI measurements of the penetration of free (Fe2+, Co2+ and Gd3+) and complexed ([FeEDTA]2- and [GdDTPA]2-) metal ions in a single methanogenic granule. Interaction...
Article
Water-binding capacity (WBC) is commonly measured with a centrifugation method in which a sample is hydrated in excess water and the pellet weight after centrifugation defines the WBC. When a dispersion is being analyzed, here containing whey protein microparticles (MPs), the pellet consists of swollen particles and water between the particles. The...
Article
We present the design, preparation and characterization of two types of complex coacervate core micelles (C3Ms) with cross-linked cores and spectroscopic labels, and demonstrate their use as diffusional probes to investigate the microstructure of percolating biopolymer networks. The first type consists of poly(allylamine hydrochloride) (PAH) and po...
Article
In our studies on particle mobility in polymer solutions, we have investigated and determined self-diffusion coefficients of nanoparticles in semidilute solutions of poly(ethylene glycol) (PEG, Mw = 6, 20, 35, and 100 kDa). Specially designed PEGylated dendrimers with well-defined sizes (dh = 3.4–11.0 nm) and with internal 19F moieties allow for ba...
Article
Controlling self-assembly processes is of great interest in various fields where multifunctional and tunable materials are designed. We here present the versatility of lanthanide-complex-based micelles (Ln-C3Ms) with tunable coordination structures and corresponding functions (e.g. luminescence and magnetic relaxation enhancement). Micelles are pre...
Conference Paper
We designed complex coacervate micelles, internally labeled with 4 wt% 19F and functionalized with a PEO corona, for diffusional probing of heterogeneous biopolymer gels. The particles are spherical and monodisperse with a hydrodynamic diameter of 31 nm and can be used for NMR diffusion experiments with observation times of order 10-500 ms. We asse...
Conference Paper
Photosynthetic activity is directly coupled to changes in chloroplast volume and thylakoid membrane dynamics . Although chloroplast water amounts to around 10–30 % of the total leaf water, a very limited number of NMR studies of chloroplasts in vivo in relation to leaf water content has been published. The published approaches to discriminate chlor...
Article
Full-text available
At the submicron scale, food biopolymer networks can be visualized by a wide array of microscopic techniques, but these methods are mostly invasive and require careful image analysis in order to quantify network features. ‘Nanoparticle diffusometry’ provides a non-invasive alternative to infer quantitative submicron structural information about bio...
Article
Full-text available
Shrubs and trees with secondary phloem tissue produced by successive cambia mainly occur in habitats characterized by a periodical or continuous lack of water availability. The amount of this secondary phloem tissue in stems of Avicennia trees rises with increasing soil water salinity and decreasing inundation frequency. Hence, increased water stor...
Conference Paper
Full-text available
Several techniques have been employed to increase the efficiency of solar cells. Bio-mimic is one of them since plants use solar energy efficiently through photosynthesis. So, it is very inportant to understand the underlying mechanism of photosynthesis which takes place in a membrane called thylakoid, which is housed in the chloroplasts. The thyla...
Conference Paper
Several techniques have been employed to increase the efficiency of solar cells. Bio-mimic is one of them since plants use solar energy more efficiently through photosynthesis. So, it is very important to understand the underlying mechanism of photosynthesis which takes place in a plant membrane called thylakoid. The thylakoid membrane switches its...
Conference Paper
Full-text available
Complementary imaging techniques (µCT, SEM, MRI), NMR and quantitative image analysis methods were used to obtain multi-length scale information of the porous structure of carrots in their freeze-dried, rehydrating and rehydrated form. This work established a predictive relation between freezing rate and freeze damage. Water imbibition rates could...
Article
Full-text available
The effect of osmotic stress on plant water status and apical plant growth has been studied in six week old maize plants in well defined and controlled climate conditions using quantittative low filed NMR imaging. Simultaneous with NMR measurements several other techniques including water uptake measurements and photosynthetic activity measurements...