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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Nanospheres of alginate prepared through w/o emulsification and internal gelation with nanoparticles of CaCO3
Paques, J.P. ; Sagis, L.M.C. ; Rijn, C.J.M. van; Linden, E. van der - \ 2014
Food Hydrocolloids 40 (2014). - ISSN 0268-005X - p. 182 - 188.
drug-delivery - beads - microcapsules - release - calcium - islets - encapsulation - particles - chitosan - size
Gelled nanospheres of alginate are prepared through a single step technique involving emulsification and gelation. CaCO3 nanoparticles, together with glucono delta-lactone (GDL), are dispersed in an alginate solution, which is subsequently dispersed in an oil phase and followed by gelation of the alginate spheres. Rheology and pH time dependence are determined during gelation of macroscopic alginate gels. The results are used to optimize CaCO3/alginate mass ratio and GDL/CaCO3 molar ratio in the recipe for formation of the alginate spheres. It is found that nanoparticles of CaCO3 result in smaller alginate spheres and reduces the gelation time significantly, compared to microparticles of CaCO3. Cryo-SEM and light microscopy confirmed the formation of gelled alginate spheres below 10 µm with majority of spheres smaller than 2 µm and even spheres below 200 nm are observed. The extension into the nano range, the reduction in gelation time, and the possibility of a final internal pH around 6 all significantly extend the range of applications for these alginate nanospheres.
A Descriptive Force-Balance Model for Droplet formation at microfluidic Y-junctions
Steegmans, M.L.J. ; Ruiter, J. de; Schroën, C.G.P.H. ; Boom, R.M. - \ 2010
AIChE Journal 56 (2010)10. - ISSN 0001-1541 - p. 2641 - 2649.
membrane emulsification - device - flow - microchannel - viscosity - motion - sphere - beads - wall
In a previous article, we studied the basics of emulsification in microfluidic Y-junctions, however, without considering the effect of viscosity of the disperse phase. As it is known from investigations on many different microstructures that viscosity and viscosity ratio are governing parameters for droplet size, we here investigate whether this is also the case for microfluidic Y-junctions and do so for a wide range of process conditions. The investigated Y-junctions have a width of 19.9 or 12.8 µm and a depth of 5.0 µm, and the formed monodisperse droplets (CV <1%) are between 3 and 20 µm. We varied the disperse-phase viscosity using different oils (1–105 mPa s), and continuous-phase viscosity using glycerol–water and ethanol–water mixtures (1.0–6.2 mPa s), which corresponds to disperse-to-continuous-phase viscosity ratios from 0.4 to 105.0. Through the variation of the liquids, also a range in interfacial tensions (12–55 mN m-1) is assessed. The disperse-phase flow rate is varied from 0.039 to 18.0 µL h-1, the continuous-phase flow rate from 1.39 µL h-1 to 0.41 mL h-1, and this corresponds to flow rate ratios from 1.1 × 10-3 to 0.14, which is once again based on wide range of conditions. For all these conditions, in which droplets are formed in the dripping and jetting regime, the droplet size could be described with a model based on the existing force-balance model, but now extended to incorporate the cross-sectional area of the droplet and the resistance with the wall. Surprisingly enough, it was found that the droplet size is not influenced by the disperse-phase viscosity, or the viscosity ratio, but it is dominated by the resistance with the wall and the continuous-phase properties. Because of this, emulsification with Y-junctions is intrinsically simpler than any other shear-based method as droplet size is only determined by the continuous phase
Impact of pH on CdII partitioning between alginate gel and aqueous media
Kalis, E.J.J. ; Davis, T.A. ; Town, R.M. ; Leeuwen, H.P. van - \ 2009
Environmental Chemistry 6 (2009)4. - ISSN 1448-2517 - p. 305 - 310.
ion-exchange resin - ca-alginate - equilibrium-model - donnan potentials - acidic conditions - metal sorption - heavy-metals - biosorption - beads - adsorption
Many microorganisms exist in a biogel-mediated micro-environment such as a cell wall or a biofilm, in which local concentrations of ionic nutrients and pollutants differ from those in the surrounding bulk medium. The local concentration is the relevant parameter for considerations of bioavailability. These modified concentrations arise as a consequence of the negative charges within biogels which may induce a Donnan potential inside the biogel phase. For metals, the net effect on the speciation within the biogel, relative to the bulk medium, is an enhancement of the concentration of free cations. Since the structural charge in the biogel arises from protolytic functional groups, the Donnan potential is pH dependent. Here we apply in situ voltammetry to measure the free metal ion concentration inside alginate gel as a function of pH. In the pH range 3 to 7, the speciation of CdII within this model biogel can be explained by specific binding to carboxylic functional groups and electrostatic binding resulting from the Donnan potential
Deacylation of antibiotic A40926 by immobilized Actinoplanes teichomyceticus cells in an internal-loop air-lift bioreactor
Jovetic, S. ; Bresser, L. de; Tramper, J. ; Marinelli, F. - \ 2003
Enzyme and Microbial Technology 32 (2003)5. - ISSN 0141-0229 - p. 546 - 552.
carrageenan - beads
A40926 is a natural glycopeptide antibiotic. It is a precursor of dalbavancin, a semi-synthetic second-generation glycopeptide in clinical development for the treatment of ß-lactam-resistant Staphyloccous aureus and Staphylococcus epidermidis infections. Deacylation of A40926, producing an intermediate useful for the synthesis of novel derivatives, can be carried out by the action of Actinoplanes teichomyceticus cells. Kinetics parameters for this particular deacylation reaction were obtained by fitting the experimental data to a Michaelis¿Menten kinetic model. The feasibility of A40926 deacylation by immobilized A. teichomyceticus cells in an air-lift bioreactor was examined. A single continuously operated air-lift reactor (ALR) was evaluated by a model describing diffusion and reaction in the biocatalyst beads. Model estimates were in a good agreement with experimental results. The system was operated continuously for 21 days with overall conversion above 60%.
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