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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    Elucidating the relationship between the spreading coefficient, surface-mediated partial coalescence and the whipping time of artificial cream
    Hotrum, N.E. ; Cohen Stuart, M.A. ; Vliet, T. van; Avino, S.F. ; Aken, G.A. van - \ 2005
    Colloids and Surfaces. A: Physicochemical and Engineering Aspects 260 (2005)1-3. - ISSN 0927-7757 - p. 71 - 78.
    in-water emulsions - air/water interface - dairy emulsions - oil droplets - destabilization - manufacture - stability
    We studied the whipping of artificial creams composed of a blend of sunflower oil and hydrogenated palm fat stabilized by protein or a mixture or protein and low molecular weight (lmw) surfactant. It was found that an increased whipping speed, decreased protein concentration, and the addition of lmw surfactant leads to shorter whipping times. Further, shorter whipping times were observed for WPI-stabilized cream compared to cream stabilized by sodium caseinate. In all cases, the decrease in whipping time was due to a decrease in the length of the second stage of whipping, the stage characterized by the adhesion of fat droplets to the air bubble surface. The decrease in whipping time could be accounted for by considering the influence of the experimental variables on the fraction of bubble surface area at which fat droplet spreading is possible. The same changes in parameters that promote droplet spreading at the air/water interface cause a decrease in the whipping time of our model creams. Correlating the whipping time of cream with the spreading behavior of fat droplets at the air/water interface represents a new insight into the mechanisms involved in the whipping of cream.
    Scaling Behavior of Delayed Demixing, Rheology, and Microstructure of Emulsions Flocculated by Depletion and Bridging
    Blijdenstein, T.B.J. ; Linden, E. van der; Vliet, T. van; Aken, G.A. van - \ 2004
    Langmuir 20 (2004)26. - ISSN 0743-7463 - p. 11321 - 11328.
    diffusing-wave spectroscopy - in-water emulsions - colloid-polymer mixtures - confocal microscopy - beta-lactoglobulin - disordered solids - elastic networks - transient gels - particle gels - casein gels
    Abstract: This paper describes an experimental comparison of microstructure, rheology, and demixing of bridging- and depletion-flocculated oil-in-water emulsions. Confocal scanning laser microscopy imaging showed that bridging-flocculated emulsions were heterogeneous over larger length scales than depletion-flocculated emulsions. As a consequence, G' as determined from diffusing wave spectroscopy (DWS) corresponded well with G' as measured macroscopically for the depletion-flocculated emulsions, but this correspondence was not found for the bridging-flocculated emulsions. The heterogeneity of bridging-flocculated emulsions was confirmed by DWS-echo measurements, indicating that their structure breaks up into large fragments upon oscillatory shear deformation larger than 1%. Depletion- and bridging-flocculated emulsions showed a different scaling of the storage modulus with the volume fraction of oil and a difference in percolation threshold volume fraction. These differences will be discussed on the basis of the two types of droplet-droplet interactions studied. Gravity-induced demixing occurred in both emulsions, but the demixing processes differed. After preparation of bridging-flocculated emulsions, serum immediately starts to separate, whereas depletion-flocculated systems at polysaccharide concentrations in the overlap regime usually showed a delay time before demixing. The delay time was found to scale with the network permeability, B; the viscosity, , of the aqueous phase; and the density difference between oil and water, , as tdelay ~ B-1-1. The results are in line with the mechanism proposed by Starrs et al. (J. Phys.: Condens. Matter 2002, 14, 2485-2505), where erosion of the droplet network leads to widening of the channels within the droplet networks, facilitating drainage of liquid.
    Influence of dynamic interfacial tension on droplet formation during membrane emulsification
    Graaf, S. van der; Schroën, C.G.P.H. ; Sman, R.G.M. van der; Boom, R.M. - \ 2004
    Journal of Colloid and Interface Science 277 (2004)2. - ISSN 0021-9797 - p. 456 - 463.
    in-water emulsions
    Membrane emulsification is a promising and relatively new technique for producing emulsions. The purpose of this study was to better understand the influence of interfacial tension on droplet formation during membrane emulsification. Droplet formation experiments were carried out with a microengineered membrane; the droplet diameter and droplet formation time were studied as a function of the surfactant concentration in the continuous phase. These experiments confirm that the interfacial tension influences the process of droplet formation; higher surfactant concentrations lead to smaller droplets and shorter droplet formation times (until 10 ms). From drop volume tensiometer experiments we can predict the interfacial tension during droplet formation. However, the strong influence of the rate of flow of the to-be-dispersed phase on the droplet size cannot be explained by the predicted values. This large influence of the oil rate of flow is clarified by the hypothesis that snap-off is rather slow in the studied regime of very fast droplet formation. (C) 2004 Elsevier Inc. All rights reserved.
    Serum separation and structure of depletion- and bridging-flocculated emulsions: a comparison
    Blijdenstein, T.B.J. ; Winden, A.J.M. van; Vliet, T. van; Aken, G.A. van - \ 2004
    Colloids and Surfaces. A: Physicochemical and Engineering Aspects 245 (2004)1-3. - ISSN 0927-7757 - p. 41 - 48.
    in-water emulsions - protein-stabilized emulsion - beta-lactoglobulin - polysaccharide - suspensions - carrageenan - interfaces - polymers - behavior - rheology
    Stability against demixing, rheology and microstructure of emulsions that were flocculated by depletion or bridging were compared. Flocculation by depletion and bridging was induced by addition of the polysaccharide carboxy-methylcellulose (CMC) to emulsions that were stabilised by ß-lactoglobulin (ß-lg) at pH 6.7 and 3.0, respectively. Depletion-flocculated emulsions generally have a lower initial demixing rates than bridging-flocculated emulsions, but after long times they are compressed to a higher oil content by gravity. Differences in the initial demixing rate are shown to be caused by differences in porosity between the gels. In bridging-flocculated emulsions, large irreversible flocs are formed by flow during mixing, resulting in larger permeability than in depletion-flocculated emulsions. Rheological measurements showed that bridging-flocculated emulsions could withstand larger stresses than depletion-flocculated emulsions. Greater network strength and a lower probability of rearrangements explain why bridging-flocculation systems can retain more water at longer times. Keywords: Emulsions; Depletion; Bridging; Structure; Serum separation
    Status of cross-flow membrane emulsification and outlook for industrial application
    Gijsbertsen-Abrahamse, A.J. ; Padt, A. van der; Boom, R.M. - \ 2004
    Journal of Membrane Science 230 (2004)1-2. - ISSN 0376-7388 - p. 149 - 159.
    shirasu-porous-glass - in-water emulsions - microchannel emulsification - droplet formation - ceramic membranes - microspheres - size - pore
    Cross-flow membrane emulsification has great potential to produce monodisperse emulsions and emulsions with shear sensitive components. However, until now, only low disperse phase fluxes were obtained. A low flux maybe a limiting factor for emulsion production on a commercial scale. Therefore, the effects of membrane parameters on the disperse phase flux are estimated. Besides, the effects of these parameters on the droplet size and droplet size distribution are qualitatively described. Wetting properties, pore size and porosity mainly determine the droplet size (distribution). Membrane morphology largely determines the disperse phase flux. As an example, industrial-scale production of culinary cream was chosen to evaluate the required membrane area of different types of membranes: an SPG membrane, an alpha-Al2O3 membrane and a microsieve. Due to the totally different morphologies of these membranes, the fraction of active pores is I for a microsieve and is very low for the other membranes. The choice of the optimal membrane did not depend on the production strategy: either to produce large quantities or to produce monodisperse emulsions, the best suitable was a microsieve with an area requirement of around I m(2). In general, the total membrane resistance should be low to obtain a large disperse phase flux. In contrast, the membrane resistance should be high to obtain monodisperse emulsions when using membranes with a high porosity. (C) 2003 Elsevier B.V. All rights reserved.
    Control of strength and stability of emulsion-gels by a combination of long- and short-range interactions
    Blijdenstein, T.B.J. ; Hendriks, W.P.G. ; Linden, E. van der; Vliet, T. van; Aken, G.A. van - \ 2003
    Langmuir 19 (2003)17. - ISSN 0743-7463 - p. 6657 - 6663.
    in-water emulsions - beta-lactoglobulin - colloidal systems - calcium-binding - aggregation - ph - polysaccharide - flocculation - dispersions - behavior
    This paper discusses the change in phase behavior and mechanical properties of oil-in-water emulsion gels brought about by variation of long- and short-range attractive interactions. The model system studied consisted of oil droplets stabilized by the protein -lactoglobulin (-lg). A long-range depletion attraction was obtained by addition of dextran. At short distances, the interaction is dominated by electrostatic repulsion between the adsorbed layers of -lg. This interaction was varied by addition of Ca2+ ions and by changing the NaCl concentration. Combination of long- and short-range attraction resulted in a substantial decrease in the rate of serum separation and an increase in the emulsion gel modulus at small deformations compared to depletion attraction alone. The flocculation process and the morphology of the flocs were investigated by diffusing wave spectroscopy and confocal scanning laser microscopy. Above a minimum concentration, dextran induced fast depletion flocculation, leading to a network of emulsion droplets. This network quickly collapsed due to gravity. Addition of Ca2+ ions above a minimum concentration induced slow flocculation, and the flocs creamed before a network was formed. Addition of both dextran and Ca2+ ions resulted in a two-step mechanism of emulsion gel formation. A network is quickly formed by depletion flocculation and subsequently the bonds between the emulsion droplets are reinforced by Ca2+ ions. Due to this reinforcement, rearrangements of this network were suppressed resulting in a smaller rate of serum separation.
    Colloidal destabilisation mechanisms in protein-stabilised emulsions
    Aken, G.A. van; Blijdenstein, T.B.J. ; Hotrum, N.E. - \ 2003
    Current Opinion in Colloid and Interface Science 8 (2003)4-5. - ISSN 1359-0294 - p. 371 - 379.
    in-water emulsions - highly concentrated emulsions - film trapping technique - air/water interface - beta-lactoglobulin - conformational aspects - molecular-diffusion - dextran sulfate - thin-films - flocculation
    Over the past decade important new insights have been gained into the functionality of proteins as emulsion and foam stabilisers. This paper reviews important new findings in the fields of emulsion stabilisation by polysaccharide thickeners, coalescence in highly concentrated and dilute aggregated emulsions and emulsion droplet–air interaction. These new findings will be discussed in terms of recent improved understanding of the surface rheological behaviour and thin film behaviour of proteins. These insights may lead to an improved use of the special properties that proteins have as emulsion stabilisers compared to other stabilisers, such as low-molecular-weight surfactants or polyelectrolytes.
    Effects of spray drying on physicochemical properties of milk protein-stabilised emulsions
    Sliwinski, E.L. ; Lavrijsen, B.W.M. ; Vollenbroek, J.M. ; Stege, H.J. van der; Boekel, M.A.J.S. van; Wouters, J.T.M. - \ 2003
    Colloids and Surfaces. B: Biointerfaces 31 (2003). - ISSN 0927-7765 - p. 219 - 229.
    in-water emulsions - whey proteins - interfacial properties - exchange-reactions - ionic-strength - adsorption - caseins - heat - behavior - systems
    The effect of spray drying and reconstitution has been studied for oil-in-water emulsions (20.6% maltodextrin, 20% soybean oil, 2.4% protein, 0.13 M NaCl, pH 6.7) with varying ratios of sodium caseinate and whey protein, but with equal size distribution (d(32) = 0.77 mum). When the concentration of sodium caseinate in the emulsion was high enough to entirely cover the oil-water interface, the particle size distribution was hardly affected by spray drying and reconstitution. However, for emulsions of which the total protein consisted of more than 70% whey protein, spray drying resulted in a strong increase of the droplet size distribution. The adsorbed amount of protein ranged from 3 mg m(-2) for casein-stabilised emulsions to 4 mg m(-2) for whey protein-stabilised emulsions with a maximum of 4.2 mg m(-2) for emulsions containing 80% whey protein on total protein, which means that for all these emulsions about one quarter of the available protein was adsorbed at the oil-water interface. The adsorbed amount of protein was hardly affected by spray drying. After emulsion preparation casein proteins adsorbed preferentially at the oil-water interface. As a result of spray drying, the relative amount of beta-lactoglobulin in the adsorbed layer increased strongly at the expense of alpha(s1)-casein and beta-casein. Percentages of alpha(s2)-casein and kappa-casein in the adsorbed layer remained largely unchanged. The changes in the protein composition of the adsorbed layer as a result of spray drying and reconstitution were the largest when beforehand hardly any whey protein was present in the adsorbed layer and hardly any sodium caseinate in the aqueous phase. Apparently, during spray drying conditions have been such that beta-lactoglobulin could unfold, aggregate, and react with other cystein-containing proteins changing the particle size distribution of the emulsions and the composition of the adsorbed layer. It seemed, however, that non-adsorbed sodium caseinate in some way was able to protect the adsorbed casein proteins from being displaced by aggregating whey protein. (C) 2003 Elsevier B.V. All rights reserved.
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