Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Pickering Emulsions for Food Applications: Background, Trends, and Challenges
Berton-Carabin, C.C. ; Schroën, C.G.P.H. - \ 2015
Annual Review of Food Science and Technology 6 (2015). - ISSN 1941-1413 - p. 263 - 297.
in-water emulsions - protein-stabilized emulsions - quinoa starch granules - colloidal particles - oxidative stability - lipid oxidation - o/w emulsions - silica nanoparticles - beta-lactoglobulin - physicochemical characteristics
Particle-stabilized emulsions, also referred to as Pickering emulsions, have garnered exponentially increasing interest in recent years. This has also led to the first food applications, although the number of related publications is still rather low. The involved stabilization mechanisms are fundamentally different as compared to conventional emulsifiers, which can be an asset in terms of emulsion stability. Even though most of the research on Pickering emulsions has been conducted on model systems, with inorganic solid particles, recent progress has been made on the utilization of food-grade or food-compatible organic particles for this purpose. This review reports the latest advances in that respect, including technical challenges, and discusses the potential benefits and drawbacks of using Pickering emulsions for food applications, as an alternative to conventional emulsifier-based systems.
Mechanical Characterization and pH Response of Fibril-Reinforced Microcapsules Prepared by Layer-by-Layer Adsorption
Rossier Miranda, F.J. ; Schroën, C.G.P.H. ; Boom, R.M. - \ 2010
Langmuir 26 (2010)24. - ISSN 0743-7463 - p. 19106 - 19113.
polyelectrolyte multilayers - industrial applications - colloidal particles - capsules - microencapsulation - stability - films - salt - nanocapsules - alginate
Despite the fair number of microencapsulation principles that have been developed, the actual protection and targeted delivery of sensitive ingredients remains a challenge in the food industry. A suitable technique should use food-grade and inexpensive materials, and ensure tight control over the capsule size and release trigger mechanism. For example, encapsulates may need to survive the low pH of the stomach to release their contents in the neutral environment of the small intestine. In this work we present layer-by-layer (LbL) microcapsules assembled from whey protein isolate (WPI), high-methoxyl pectin (HMP) and WPI-fibrils. The narrow size distribution of these capsules is determined by the oil-in-water droplets used as templates, and their mechanical properties and pH response can be tuned by the number of layers adsorbed. Capsules with more than eight layers have a mechanical strength comparable to chemically cross-linked polymer capsules, because of the reinforcement by the WPI-fibrils in combination with the shell completion. Typically, capsules with five layers survive pH 2 for more than 2 h, but dissolve within 30 min at pH 7. At higher number of layers, the capsules are even more stable. Contrary to other encapsulates, these capsules can be dried and are suitable for application in dry products.
Donnan Membrane Technique (DMT) for Anion Measurement
Alonso Vega, M.F. ; Weng, L.P. ; Temminghoff, E.J.M. ; Riemsdijk, W.H. van - \ 2010
Analytical Chemistry 82 (2010)7. - ISSN 0003-2700 - p. 2932 - 2939.
dissolved organic-matter - metal-ion concentrations - soil solution - chemical speciation - heavy-metals - sandy soil - colloidal particles - aqueous-solutions - water extracts - activity model
Donnan membrane technique (DMT) is developed and tested for determination of free anion concentrations. Time needed to reach the Donnan membrane equilibrium depends on type of ions and the background. The Donnan membrane equilibrium is reached in 1 day for Cl-, 1-2 days for NO3-, 1-4 days for SO42- and SeO42-, and 1-14 days for H2PO4- in a background of 2-200 mM KCl or K2SO4. The strongest effect of ionic strength on equilibrium time is found for H2PO4-, followed by SO42- and SeO42-, and then by Cl- and NO3-. The negatively charged organic particles of fulvic and humic acids do not pass the membrane. Two approaches for the measurement of different anion species of the same element, such as SeO42- and HSeO3-, using DMT are proposed and tested. These two approaches are based on transport kinetics or response to ionic strength difference. A transport model that was developed previously for cation DMT is applied in this work to analyze the rate-limiting step in the anion DMT. In the absence of mobile/labile complexes, transport tends to be controlled by diffusion in solution at a low ionic strength, whereas at a higher ionic strength, diffusion in the membrane starts to control the transport
Colloidosomes: Versatile microcapsules in perspective
Rossier Miranda, F.J. ; Schroën, C.G.P.H. ; Boom, R.M. - \ 2009
Colloids and Surfaces. A: Physicochemical and Engineering Aspects 343 (2009)1-3. - ISSN 0927-7757 - p. 43 - 49.
oil-water interface - emulsion droplet interface - latex-particles - composite tectocapsules - colloidal particles - pickering emulsions - shell structure - capsules - spheres - microspheres
Colloidal particles of different sizes and shapes can organize on suspended particles or emulsion droplets, forming hollow-porous microcapsules called colloidosomes. The potential of the colloidosomes to serve as targeted delivery/controlled release devices has been discussed many times in literature. However, obtaining well-defined colloidosomes at high yields is still an open challenge. We review and compare the different methods reported in literature to produce colloidosomes, not only to show the state of the art and the aspects requiring further development, but also to spot the possible future perspectives of research in this field
Residence time dependent desorption of Staphylococcus epidermidis from hydrophobic and hydrophilic substrata
Boks, N.P. ; Kaper, H.J. ; Norde, W. ; Busscher, H.J. ; Mei, H.C. van der - \ 2008
Colloids and Surfaces. B: Biointerfaces 67 (2008)2. - ISSN 0927-7765 - p. 276 - 278.
plate flow chamber - bacterial adhesion - colloidal particles - surfaces - deposition - forces - model - stiffness - kinetics
Adhesion and desorption are simultaneous events during bacterial adhesion to surfaces. although desorption is far less studied than adhesion. Here, desorption of Staphylococcus epidermidis from substratum surfaces is demonstrated to be residence time dependent. Initial desorption rate coefficients were similar for hydrophilic and hydrophobic dimethylclichlorosilane (DDS)-coated glass, likely because initial desorption is controlled by attractive Lifshitz-Van der Waals interactions, which are comparable on both substratum Surfaces. However, significantly slower decay times of the desorption rate coefficients are found for hydrophilic glass than for hydrophobic DDS-coated glass. This difference is suggested to be due to the acid-base interactions between staphylococci and these surfaces, which are repulsive on hydrophilic glass and attractive on hydrophobic DDS-coated glass. Final desorption rate coefficients are higher on hydrophilic glass than on hydrophobic DDS-coated glass, due to the so called hydrophobic effect, facilitating a closer contact on hydrophobic DDS-coated glass.
Classification and evaluation of microfluidic devices for continuous suspension fractionation
Kulrattanarak, T. ; Sman, R.G.M. van der; Schroën, C.G.P.H. ; Boom, R.M. - \ 2008
Advances in Colloid and Interface Science 142 (2008)1/2. - ISSN 0001-8686 - p. 53 - 66.
field-flow fractionation - deterministic lateral displacement - continuous particle separation - colloidal particles - dielectrophoretic separation - membrane - size - manipulation - microfiltration - filtration
Membrane processes are well-known for separating and fractionating suspensions in many industries, but suffer from particle accumulation on the membrane surface. Currently, there are new developments using microfluidic devices for cell/DNA sorting and fractionation. We anticipate these devices are also applicable to fractionation of polydisperse and concentrated suspensions (e.g. foods), and may potentially have fewer problems with particle accumulation compared to membranes. This review article presents an overview of relevant microfluidic devices. We focus on their performance with respect to concentrated suspensions, as one finds in food industry. We give quantitative estimates on their yield, selectivity, and the potential for large-scale application. From this evaluation follows that deterministic ratchets seem most promising.
Transmission and fractionation of micro-sized particle suspensions
Brans, G.B.P.W. ; Dinther, A.M.C. van; Odum, B. ; Schroën, C.G.P.H. ; Boom, R.M. - \ 2007
Journal of Membrane Science 290 (2007)1-2. - ISSN 0376-7388 - p. 230 - 240.
cross-flow microfiltration - colloidal particles - pore
In processes aimed at the fractionation of a multi-component feed stream, transmission of particles through the membrane is at least as important as retention of larger particles. In this paper, we describe the mechanisms of transmission of mono-disperse latex particles through a polymer membrane. The effects of process parameters, such as transmembrane pressure, cross flow velocity and feed concentration were investigated. In dead end filtration mode, we found that, depending on the transmembrane pressure, four particle transmission regimes could be distinguished. Particle deposition on polymer membranes and polymer microsieves was investigated in-line with confocal scanning laser microscopy (CSLM). It was observed that with the polymer membrane random depth deposition took place, while the microsieve exhibited in-pore fouling. In addition, bi-disperse particle suspensions were fractionated with dead end and cross flow membrane filtration, and various effects were charted. Based on the phenomena observed, it is concluded that the design of a fractionation process starts with defining a stable transmission regime for small particles, and subsequently choosing the process conditions for minimal deposition of the larger particles
Role of lactobacillus cell surface hydrophobicity as probed by AMF in adhesion to surfaces at low and high ionic strength
Vadillo-Rodriguez, V. ; Busscher, H.J. ; Meij, H.C. van der; Vries, J. de; Norde, W. - \ 2005
Colloids and Surfaces. B: Biointerfaces 41 (2005)1. - ISSN 0927-7765 - p. 33 - 41.
scanning force microscopy - plate flow cell - colloidal particles - bacterial adhesion - functional-groups - escherichia-coli - layer proteins - image-analysis - deposition - adsorption
The S-layer present at the outermost cell surface of some lactobacillus species is known to convey hydrophobicity to the lactobacillus cell surface. Yet, it is commonly found that adhesion of lactobacilli to solid substrata does not proceed according to expectations based on cell surface hydrophobicity. In this paper, the role of cell surface hydrophobicity of two lactobacillus strains with and without a surface layer protein (SLP) layer has been investigated with regard to their adhesion to hydrophobically or hydrophilically functionalized glass surfaces under well-defined flow conditions and in low and high ionic strength suspensions. Similarly, the interaction of the lactobacilli with similarly functionalized atomic force microscope (AFM) tips was measured. In a low ionic strength suspension, both lactobacillus strains show higher initial deposition rates to hydrophobic glass than to hydrophilic glass, whereas in a high ionic strength suspension no clear influence of cell surface hydrophobicity on adhesion is observed. Independent of ionic strength, however, AFM detects stronger interaction forces when both bacteria and tip are hydrophobic or hydrophilic than when bacteria and tip have opposite hydrophobicities. This suggest that the interaction develops in a different way when a bacterium is forced into contact with the tip surface, like in AFM, as compared with contacts developing between a cell surface and a macroscopic substratum under flow. In addition, the distance dependence of the total Gibbs energy of interaction could only be qualitatively correlated with bacterial deposition and desorption in the parallel plate flow chamber.
Humic substances are soft and permeable : evidence from their electrophoretic mobilities
Duval, J.F.L. ; Wilkinson, K.J. ; Leeuwen, H.P. van; Buffle, J. - \ 2005
Environmental Science and Technology 39 (2005)17. - ISSN 0013-936X - p. 6435 - 6445.
fluorescence correlation spectroscopy - ion complexation equilibria - fulvic-acids - proton-binding - physicochemical description - polyelectrolyte properties - diffusion-coefficients - colloidal particles - organic-matter - ph
Due to the complexity of the humic substances (HS), mathematical models have often been employed to understand their roles in the environment. Since no consensus exists with respect to the structure and conformation of the HS, models have alternatively given them properties corresponding to impermeable hard spheres or fully permeable polyelectrolytes. In this study, the hydrodynamic permeability of standard HS (Suwannee River fulvic, humic, and peat humic acids) are evaluated as a function of pH and ionic strength. A detailed theoretical model is used to determine the softness parameter (lambda0), which characterizes the degree of flow penetration into the HS on the basis of measured values of electrophoretic mobilities, diffusion coefficients, and electric charge densities. Their motion in an electric field is evaluated by a rigorous numerical evaluation of the governing electrokinetic equations for soft particles. The hydrodynamic impact of the polyelectrolyte chains is accounted for by a distribution of Stokes resistance centers and partial dissociation of the hydrodynamically immobile ionogenic groups distributed throughout the polyelectrolyte. The results demonstrate thatthe studied HS are small (radius ca. 1 nm), highly charged (500-650 C g(-1) when all sites are dissociated), and very permeable (typical flow penetration length of 25-50% of the radius, depending on pH). The HS also coagulate slightly when lowering the pH of the solution. Modeling of the HS as hard spheres with a charge and slip plane located at the surface is thus physically inappropriate, as are a number of analytical theories for soft particles that hold for low to moderate electrostatic potentials and large colloids. The shortcomings of these simpler approaches, when interpreting the electrophoretic mobilities of HS, are highlighted by comparison with rigorous theoretical predictions.
Analysis of the interfacial properties of fibrillated and nonfibrillated oral streptococcal strains from electrophoretic mobility and titration measurements : Evidence for the shortcomings of the classical soft-particle approach
Duval, J.F.L. ; Busscher, H.J. ; Belt-Gritter, B. van de; Mei, H.C. van der; Norde, W. - \ 2005
Langmuir 21 (2005)24. - ISSN 0743-7463 - p. 11268 - 11282.
atomic-force microscopy - colloidal particles - cell-wall - surface characteristics - protein antigens - network method - salivarius - electrokinetics - suspensions - recognition
Chemical and structural intricacies of bacterial cells complicate the quantitative evaluation of the physicochemical properties pertaining to the cell surface. The presence of various types of cell surface appendages has a large impact on those properties and therefore on various interfacial phenomena, such as aggregation and adhesion. In this paper, an advanced analysis of the electrophoretic mobilities of fibrillated and nonfibrillated strains (Streptococcus salivarius HB and Streptococcus salivarius HB-C12, respectively) is performed over a wide range of pH and ionic strength conditions on the basis of a recent electrokinetic theory for soft particles. The latter extends the approximate formalism originally developed by Ohshima by solving rigorously the fundamental electrokinetic equations without restrictions on the bacterial size, charge, and double layer thickness. It further allows (i) a straightforward implementation of the dissociation characteristics, as evaluated from titration experiments, of the ionogenic charged groups distributed throughout the bacterial cell wall and/or the surrounding exopolymer layer and (ii) the inclusion of possible specific interactions between the charged groups and ions from the background electrolyte other than charge-determining ions. The theory also enables an estimation of possible swelling/shrinking processes operating on the outer polymeric layer of the bacterium. Application of the electrokinetic model to HB and HB-C12 clearly shows a significant discrepancy between the amount of surface charges probed by electrophoresis and by protolytic titration. This is ascribed to the specific adsorption of cations onto pristine charged sites in the cell wall. Physicochemical parameters pertaining to the hydrodynamics (softness degree) and electrostatics of the bacterial cell wall (HB-C12) and soft polymeric layer (HB) are quantitatively derived
Atomic force microscopic corroboration of bond ageing for adhesion of Streptococcus thermophilus to solid substrata
Vadillo-Rodriguez, V. ; Busscher, H.J. ; Norde, W. ; Vries, J. de - \ 2004
Journal of Colloid and Interface Science 278 (2004)1. - ISSN 0021-9797 - p. 251 - 254.
plate flow chamber - bacterial adhesion - particle deposition - colloidal particles - polymers - surfaces - adsorption
Initial bacterial adhesion is considered to be reversible, but over time the adhesive bond between a bacterium and a substratum surface may strengthen, turning the process into an irreversible state. Microbial desorption has been studied in situ in controlled flow devices as a function of the organisms resident time on the surface (J. Colloid Interface Sci. 164 (1994) 355). It appeared that desorption of Streptococcus thermophilus decreased strongly within approximately 50 s after initial adhesion due to bond aging. In this paper, bond aging between the S. thermophilus cell surface and the silicon nitride tip of an AFM (atomic force microscope) is corroborated microscopically and related to the macroscopic, residence time-dependent desorption of the organism under flow. AFM indicated bond strengthening between the tip and the cell surface within 100 s of contact, which is on the same order of magnitude as bond aging inferred from residence time-dependent desorption. Comparison of the interaction energies derived from AFM and macroscopic desorption indicate that bond strengthening arises as a result of multiple attachments of extracellular polymeric substances to a substratum surface.
Electrostatic interactions between immunoglobulin (IgG) molecules and a charged sorbent
Bremer, M.G.E.G. ; Duval, J.F.L. ; Norde, W. ; Lyklema, J. - \ 2004
Colloids and Surfaces. A: Physicochemical and Engineering Aspects 250 (2004)1-3. - ISSN 0927-7757 - p. 29 - 42.
colloidal particles - hydrophobic surfaces - adsorption - proteins - forces - reflectometry - polystyrene - antibodies - interfaces - fragments
The influence of electrostatic interactions on the adsorption of IgG is examined both theoretically and experimentally. The long-range interaction between IgG and the charged sorbent surface is treated in terms of the DLVO theory taking into account the possibility of charge- and potential regulation upon approach of IgG towards the surface. The relevant electrostatic and van der Waals interactions are a combination of interactions between IgG molecules and the sorbent surface (hetero-interaction part) and interactions between adsorbed and incoming IgG molecules (homo-interaction part). Experiments are performed on hydrophilic surfaces, namely negatively charged silica and positively charged amine-functionalised silica. It is concluded that electrostatic interactions have a strong influence on the adsorption behaviour. Excellent agreement was found between experiment and theory with respect to the dependence of the adsorption kinetics on pH and ionic strength. Furthermore, the steady-state adsorbed amount as a function of these variables is satisfactorily accounted for
Brownian particles in supramolecular polymer solutions
Gucht, J. van der; Besseling, N.A.M. ; Knoben, W. ; Bouteiller, L. ; Cohen Stuart, M.A. - \ 2003
Physical Review. E, Statistical nonlinear, and soft matter physics 67 (2003). - ISSN 1539-3755 - p. 051106/1 - 051106/10.
diffusing-wave-spectroscopy - stokes-einstein behavior - probe particles - light-scattering - spherical-particles - colloidal particles - viscoelastic moduli - actin solutions - latex spheres - dynamics
The Brownian motion of colloidal particles embedded in solutions of hydrogen-bonded supramolecular polymers has been studied using dynamic light scattering. At short times, the motion of the probe particles is diffusive with a diffusion coefficient equal to that in pure solvent. At intermediate time scales the particles are slowed down as a result of trapping in elastic cages formed by the polymer chains, while at longer times the motion is diffusive again, but with a much smaller diffusion coefficient. The influence of particle size and polymer concentration was investigated. The experimental data are compared to a theoretical expression for the mean-square displacement of an embedded particle in a viscoelastic medium, in which the solvent is explicitly taken into account. Differences between the friction and elastic forces experienced by the particle and the macroscopic viscosity and elasticity are explained by the inhomogeneity of the medium on the length scale of the particle size.
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