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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    Modeling interfacial dynamics using nonequilibrium thermodynamics frameworks
    Sagis, L.M.C. - \ 2013
    The European Physical Journal. Special Topics 222 (2013)1. - ISSN 1951-6355 - p. 105 - 127.
    extended irreversible thermodynamics - scanning angle reflectometry - in-water emulsions - adsorption layers - surface rheology - 2-dimensional suspensions - superficial viscosity - reciprocal relations - general formalism - polymer-solutions
    In recent years several nonequilibrium thermodynamic frameworks have been developed capable of describing the dynamics of multiphase systems with complex microstructured interfaces. In this paper we present an overview of these frameworks. We will discuss interfacial dynamics in the context of the classical irreversible thermodynamics, extended irreversible thermodynamics, extended rational thermodynamics, and GENERIC framework, and compare the advantages and disadvantages of these frameworks.
    Editorial: Dynamics of complex fluid-fluid interfaces
    Sagis, L.M.C. ; Fischer, P. ; Anderson, P.D. - \ 2013
    The European Physical Journal. Special Topics 222 (2013)1. - ISSN 1951-6355 - p. 1 - 5.
    in-water emulsions - liquid interfaces - bending rigidity - rheology - fibrils - viscoelasticity - permeability - particles - mixtures - behavior
    Generalized surface momentum balances for the analysis of surface dilatational data
    Sagis, L.M.C. - \ 2013
    The European Physical Journal. Special Topics 222 (2013)1. - ISSN 1951-6355 - p. 31 - 38.
    in-water emulsions - interfacial permeability - superficial viscosity - bending rigidity - lipid-bilayers - fluid - dynamics - liquid - microbubbles - mixtures
    Dilatational rheological properties of interfaces are often determined using drop tensiometers, in which the interface of the droplet is subjected to oscillatory area changes. A dynamic surface tension is determined either by image analysis of the droplet profile or by measuring the capillary pressure. Both analysis modes tend to use the Young-Laplace equation for determining the dynamic surface tension. For complex fluid-fluid interfaces there is experimental evidence that this equation does not describe the response of the interface to deformations adequately. Generalizations of this equation are available, and in this comment we will discuss these generalizations, and the conditions for which they reduce to the Young-Laplace equation.
    Surface rheological properties of liquid-liquid interfaces stabilized by protein fibrillar aggregates and protein-polysaccharide complexes
    Humblet-Hua, K.N.P. ; Linden, E. van der; Sagis, L.M.C. - \ 2013
    Soft Matter 9 (2013)7. - ISSN 1744-683X - p. 2154 - 2165.
    in-water emulsions - egg-white lysozyme - air/water interface - beta-lactoglobulin - amyloid fibrils - oil/water interface - bending rigidity - sodium caseinate - dextran sulfate - food systems
    In this study we have investigated the surface rheological properties of oil-water interfaces stabilized by fibrils from lysozyme (long and semi-flexible and short and rigid ones), fibrils from ovalbumin (short and semi-flexible), lysozyme-pectin complexes, or ovalbumin-pectin complexes. We have compared these properties with those of interfaces stabilized by the native proteins. The surface dilatational and surface shear moduli were determined using an automated drop tensiometer and a stress controlled rheometer with biconical disk geometry. Results show that interfaces stabilized by complexes of these proteins with high-methoxyl pectin have higher surface shear and dilatational moduli than interfaces stabilized by the native proteins only. The interfaces stabilized by ovalbumin and lysozyme complexes have comparable shear and dilatational moduli though ovalbumin-pectin complexes are twice as large in radius as lysozyme-pectin complexes. Under most of the experimental conditions, interfaces stabilized by fibrils have the highest surface rheological moduli. The difference between long semi-flexible lysozyme fibrils or short rigid lysozyme fibrils is not pronounced in interfacial dilation rheology but significant in interfacial shear rheology. The complex surface shear moduli of interfaces stabilized by long semi-flexible fibrils are about 10 times higher than those of interfaces stabilized by short rigid fibrils, over a range of bulk concentrations. Interfaces stabilized by short and more flexible ovalbumin fibrils have a significantly higher surface shear modulus than those stabilized by longer and more rigid lysozyme fibrils. This study has shown that the use of such supra-molecular structural building blocks creates a wider range of microstructural features of the interface, with higher surface shear and dilatational moduli and a more complex dependence on strain.
    Enhancement of Emulsifying Properties of Cuttlefish Skin Gelatin by Modification with N-hydroxysuccinimide Esters of Fatty Acids
    Aewsiri, T. ; Benjakul, S. ; Visessanguan, W. ; Encarnacion, A.B. ; Wierenga, P.A. ; Gruppen, H. - \ 2013
    Food Bioprocess Technology 6 (2013)3. - ISSN 1935-5130 - p. 671 - 681.
    in-water emulsions - fish gelatin - proteins - stability - surface - adsorption
    Cuttlefish (Sepia pharaonis) skin gelatin modified with N-hydroxysuccinimide esters of various fatty acids including capric acid (C10:0), lauric acid (C12:0), and myristic acid (C14:0) at different molar ratios was characterized and determined for emulsifying property. Fatty acid esters were incorporated into gelatin as indicated by the decrease in free amino group content. Gelatin modified with fatty acid ester had the increased surface hydrophobicity and emulsifying property with coincidental decrease in surface tension. Gelatin modified with fatty acid ester of C14:0 showed the highest surface activity, especially with the high degree of modification. Emulsion stabilized by gelatin modified with fatty acid ester of C14:0 had a smaller mean particle diameter with higher stability, compared with that stabilized by the control gelatin (without modification). Emulsion stabilized by modified gelatin remained stable at various pH (3–8) and salt concentrations (NaCl 0–500 mM). Emulsion was also stable after being heated at 50–90 °C for 30 min.
    Emulsion properties of algae soluble protein isolate from Tetraselmis sp.
    Schwenzfeier, A. ; Helbig, A. ; Wierenga, P.A. ; Gruppen, H. - \ 2013
    Food Hydrocolloids 30 (2013)1. - ISSN 0268-005X - p. 258 - 263.
    in-water emulsions - diffusing wave spectroscopy - whey-protein - physicochemical properties - stabilized emulsions - flocculation - emulsifiers - adsorption - microalgae - pectin
    To study possible applications of microalgae proteins in foods, a colourless, protein-rich fraction was isolated from Tetraselmis sp. In the present study the emulsion properties of this algae soluble protein isolate (ASPI) were investigated. Droplet size and droplet aggregation of ASPI stabilized oil-in-water emulsions were studied as function of isolate concentration (1.25–10.00 mg/mL), pH (3–7), and ionic strength (NaCl 10–500 mM; CaCl2 0–50 mM). Whey protein isolate (WPI) and gum arabic (GA) were used as reference emulsifiers. The lowest isolate concentrations needed to reach d32 = 1 µm in 30% oil-in-water emulsions were comparable for ASPI (6 mg/mL) and WPI (4 mg/mL). In contrast to WPI stabilized emulsions ASPI stabilized emulsions were stable around pH 5 at low ionic strength (I = 10 mM). Flocculation only occurred around pH 3, the pH with the smallest net droplet ¿-potential. Due to the charge contribution of the anionic polysaccharide fraction present in ASPI its droplet ¿-potential remained negative over the whole pH range investigated. An increase in ionic strength (=100 mM) led to a broadening of the pH range over which the ASPI stabilized emulsions were unstable. GA emulsions are not prone to droplet aggregation upon changes in pH or ionic strength, but much higher concentrations are needed to produce stable emulsions. Since ASPI allows the formation of stable emulsions in the pH range 5–7 at low protein concentrations, it can offer an efficient natural alternative to existing protein–polysaccharide complexes.
    Properties of emulsions stabilised by sodium caseinate–chitosan complexes
    Zinoviadou, K. ; Scholten, E. ; Moschakis, T. ; Biliaderis, C.G. - \ 2012
    International Dairy Journal 26 (2012)1. - ISSN 0958-6946 - p. 94 - 101.
    in-water emulsions - whey-protein isolate - beta-lactoglobulin-pectin - high-methoxyl pectin - polysaccharide interactions - bioactive components - particle tracking - dextran sulfate - o/w emulsions - interfaces
    Oil-in-water emulsions (10%, w/w, oil) were prepared at pH 5.7 by using electrostatically formed complexes of 0.5% (w/w) sodium caseinate (Na-CAS) and 0–0.6% (w/w) chitosan. Emulsions stabilized by complexes with increased levels of chitosan (>0.2% w/w) had a smaller average droplet size and exhibited greater stability during storage. All chitosan containing emulsions exhibited a slight shear thinning behaviour with increased high-shear-rate viscosity at higher chitosan levels. Even though complexing of Na-CAS with chitosan resulted in a delay of the adsorption of the surface active components at the oil/water interface, the presence of chitosan did not significantly influence the rheological properties of the formed interfaces. Acid-induced aggregation was observed only for the emulsion that was stabilized solely by Na-CAS when the pH dropped close to the isoelectric point of the protein component, resulting in flocculation and large increase in the storage modulus.
    Green-Kubo relations for dynamic interfacial excess properties
    Sagis, L.M.C. - \ 2012
    Physica A 391 (2012)15. - ISSN 0378-4371 - p. 3805 - 3815.
    in-water emulsions - extended irreversible thermodynamics - fourier-transform rheology - permeability
    In this paper we analyze the fluctuations of the in-plane interfacial excess fluxes in multiphase systems, in the context of the extended irreversible thermodynamics formalism. We derive expressions for the time correlation functions of the surface extra stress tensor, the surface mass flux vector, and the surface energy flux vector, and use these expressions to derive Green–Kubo relations for the surface shear viscosity, the surface dilatational viscosity, the surface diffusion coefficient, and the surface thermal conductivity. These Green-Kubo relations can be used to compute these excess transport coefficients using for example molecular dynamics simulations
    Spontaneous droplet formation techniques for monodisperse emulsions preparation – Perspectives for food applications
    Maan, A.A. ; Schroën, C.G.P.H. ; Boom, R.M. - \ 2011
    Journal of Food Engineering 107 (2011)3-4. - ISSN 0260-8774 - p. 334 - 346.
    in-water emulsions - through microchannel emulsification - silicon-nitride surfaces - membrane emulsification - polymeric microspheres - interfacial-tension - channel structure - aspect-ratio - oil - generation
    Spontaneous droplet formation through Laplace pressure differences is a simple method for making monodisperse emulsions and is claimed to be suited for shear and temperature sensitive products, and those requiring high monodispersity. Techniques belonging to this category include (grooved) microchannel emulsification, straight-through microchannel emulsification, and EDGE (Edge-based Droplet GEneration). In this paper, an overview is given of the process, and design parameters that play a role in microchannel emulsification including their effect on droplet size and distribution. Besides, various products made by microchannel emulsification are discussed. Industrial microchannel emulsification is still not possible due to the low production rates. The new EDGE mechanism seems an interesting development, since it promises larger throughputs per droplet formation unit, better scalability, and shows robust operation with practical, food-grade components. However, for spontaneous emulsification techniques to be used on large scale, improvements in construction materials (including surface modification) are expected to be of essence.
    Textural perception of liquid emulsions: Role of oil content, oil viscosity and emulsion viscosity
    Aken, G.A. van; Vingerhoeds, M.H. ; Wijk, R.A. de - \ 2011
    Food Hydrocolloids 25 (2011)4. - ISSN 0268-005X - p. 789 - 796.
    in-water emulsions - sensory perception - stabilized emulsions - oral conditions - food emulsions - saliva - flocculation - polysaccharide - dispersions - creaminess
    This work describes a study on the in-mouth textural perception of thickened liquid oil-in-water emulsions. The variables studied are oil content, oil viscosity, and the concentration of polysaccharide thickener. Gum arabic was chosen as the thickener because of the nearly Newtonian behavior of its solutions and special care was taken to suppress aroma clues. Based on the experimental results and findings from previous studies, this work shows that the emulsion droplets influence textural sensory perception of liquid emulsions by three main mechanisms, each of which relate to changes in specific sensory attributes, and none of which were found to be significantly dependent on the viscosity of the oil: 1) by increasing the viscosity, 2) by becoming incorporated in the mucous oral coating, and 3) by spreading oil at the oral surfaces. Based on these results, the possibility for replacement of emulsified fat by a polysaccharide thickener is evaluated.
    EDGE emulsification for food-grade dispersions
    Dijke, K.C. van; Schroën, C.G.P.H. ; Padt, A. van der; Boom, R.M. - \ 2010
    Journal of Food Engineering 97 (2010)3. - ISSN 0260-8774 - p. 348 - 354.
    in-water emulsions - microchannel emulsification - interfacial-tension - droplet formation - membrane - array
    In this paper, we use the Edge-based Droplet GEneration (EDGE) emulsification method to produce food-grade emulsions (including double emulsions) and foams. This newly developed mild technology proved to be very stable and robust in the production of all these products. The products are made with food-grade components in an up-scaled micro device, which does not show any changes in time in wettability and fouling. The size of the droplets and bubbles is as needed for food stuffs. Air bubbles generated with EDGE were much larger than emulsion droplets, which could be explained through the viscosity ratio of the phases and changes in interfacial free energy caused by dynamic interfacial tension effects. In the outlook section of this paper, the obtained results are related to the dimensions of the devices, which are in a practically feasible range, also due to the simplicity of the EDGE structure and its operation. Preliminary estimations show that a 300L system can produce 1 m/h 4% (v/v) emulsion
    Antioxidative activity and emulsifying properties of cuttlefish skin gelatin modified by oxidised phenolic compounds
    Aewsiri, T. ; Benjakul, S. ; Visessanguan, W. ; Eun, J.B. ; Wierenga, P.A. ; Gruppen, H. - \ 2009
    Food Chemistry 117 (2009)1. - ISSN 0308-8146 - p. 160 - 168.
    in-water emulsions - whey-protein isolate - stability - collagen - surfactant - foams - acids - assay - gum
    Antioxidative activity and emulsifying properties of cuttlefish skin gelatin modified by different oxidised phenolic compounds including caffeic acid, ferulic acid and tannic acid at different concentrations were investigated. Oxidised phenolic compounds were covalently attached to gelatin as indicated by the decrease in amino groups. Fourier transform infrared spectroscopic studies indicated the presence of an aromatic ring and a hydroxyl group in gelatin after modification. Modified gelatin had the increased antioxidative activity but the decreased surface hydrophobicity. Gelatin modified with 5% oxidised tannic acid had no change in emulsifying properties. Emulsion stability and oxidative stability of menhaden oil-in-water emulsion stabilised by 0.5% and 1.0% gelatin without and with modification by 5% oxidised tannic acid were studied. Both gelatins at a higher concentration (1.0%) yielded an emulsion with a smaller particle size. Modified gelatin inhibited the formation of TBARS in the emulsion more effectively than the control gelatin throughout the 12 days of storage.
    A Geometric Model for the Dynamics of Microchannel Emulsification
    Zwan, E.A. van der; Schroën, C.G.P.H. ; Boom, R.M. - \ 2009
    Langmuir 25 (2009)13. - ISSN 0743-7463 - p. 7320 - 7327.
    in-water emulsions - droplet formation - array - channel - cfd - microspheres - prediction - diameter - plate
    Microchannel emulsification is an interfacial tension driven method to produce monodisperse microdroplets, or microspheres. In this paper we introduce a model for describing the dynamics of microchannel emulsification based on simple time dependent geometric shape analysis. The model is based on mechanistic principles that simultaneously predicts both process and microchannel geometry effects. The model contains no adjustable (fit) parameters and is thus fully predictive for oil in water emulsification. The model is easy to use and does not require extensive computational time and/or memory. The model was validated by comparison with the experimental results published by Sugiura and co-workers and we found excellent agreement. It was found that the droplet size of oil in water emulsions could be fully predicted using only two dimensionless numbers, an adapted capillary number that also comprises effects of terrace width and height, and the ratio of terrace length over terrace height. Based on these findings, a dimensionless design map could be constructed for a wide range of process conditions and microchannel dimensions
    Partial coalescence as a tool to control sensory perception of emulsions
    Benjamins, J. ; Vingerhoeds, M.H. ; Zoet, F.D. ; Hoog, E.H.A. de; Aken, G.A. van - \ 2009
    Food Hydrocolloids 23 (2009)1. - ISSN 0268-005X - p. 102 - 115.
    in-water emulsions - protein-stabilized emulsions - fat-content - destabilization - aggregation - temperature - crystals - phase - films - shear
    This study evaluates the role of partial coalescence of whey protein-stabilized emulsions on sensory perception. The selection of fats was restricted to vegetable fats that are essentially melted at oral temperatures. The sensitivity to partial coalescence was controlled by a variation in the fat melting curve and by addition of unsaturated monoglyceride. Most fat-related sensory attributes appear to be well-correlated to an increase in viscosity and coalescence in the mouth due to partial coalescence. Moreover, it was found that in-mouth aeration induces extra coalescence, which increases the perception of fat-related sensory attributes significantly. Monoglyceride addition induces a shift of the sensory perception of fattiness and other fat-related attributes. There are clear indications that monoglyceride addition affects sensory perception not only by promoting partial coalescence, but also by an additional effect such as its surface activity.
    Rheological Behavior of Food Emulsions Mixed with Saliva: Effect of Oil Content, Salivary Protein Content, and Saliva Type
    Silletti, E. ; Vingerhoeds, M.H. ; Aken, G.A. van; Norde, W. - \ 2008
    Food Biophysics 3 (2008)3. - ISSN 1557-1858 - p. 318 - 328.
    in-water emulsions - transmission electron-microscopy - human glandular salivas - micelle-like structures - stabilized emulsions - depletion-flocculation - beta-lactoglobulin - sodium caseinate - oral behavior - polysaccharide
    In this paper, we studied the effect of saliva on the rheological properties of ß-lactoglobulin- and lysozyme-stabilized emulsions, prepared at pH¿=¿6.7 in relation to variation of emulsions- and saliva-related parameters. The effect of oil¿volume fraction (2.5% w/w to 10% w/w), salivary protein concentration (0.1 to 0.8 mg ml¿1), and the use of both stimulated and unstimulated saliva was investigated. Viscosity and storage modulus were measured before (¿ emul and G¿emul, respectively) and after addition of saliva (¿ mix and G¿mix). To better estimate the changes due to saliva-induced flocculation of the emulsions, the ratios ¿ mix/¿ emul, G¿mix/G¿emul were calculated. In addition, tan ¿ (=the ratio of the loss and storage moduli) was investigated to evaluate the viscoelastic behavior of the emulsion/saliva mixtures. Increasing the oil¿volume fraction and salivary protein concentration resulted in an increase in ¿ mix/¿ emul and G¿mix/G¿emul, while a decrease in tan ¿ of the emulsion/saliva mixtures is occurring. When compared with unstimulated saliva, mixing ß-lactoglobulin-stabilized emulsions with stimulated saliva led to a reduction in ¿ mix/¿ emul and G¿mix/G¿emul, and an augment of tan ¿ at all measured deformations. In case of lysozyme-stabilized emulsions, the use of stimulated saliva increased G¿mix/G¿emul for ¿¿
    Direct observation of adhesion and spreading of emulsion droplets at solid surfaces
    Dresselhuis, D.M. ; Aken, G.A. van; Hoog, E.H.A. de; Cohen Stuart, M.A. - \ 2008
    Soft Matter 4 (2008). - ISSN 1744-683X - p. 1079 - 1085.
    in-water emulsions - o/w emulsions - lubrication - tribology - friction - coalescence - chocolate - membrane - tissue - layers
    Sensory perception of fat is related to orally perceived in-mouth friction. From this perspective, we investigate adhesion and spreading of emulsion droplets on solid surfaces and connect it to the ability of food emulsions to lower friction. Furthermore, we study what the contribution is of the separate colloidal forces on droplet adhesion. The effect of saliva on adhesion and spreading is also briefly investigated.Using a flow cell in combination with light microscopy and video imaging allowed us to clearly distinguish between adhered and spread emulsion droplets. The capability to make this distinction between adhesion and spreading experimentally is new and provided us with the insight that the occurrence of spreading is essential for lowering friction. Mainly electrostatic, steric and hydrophobic interactions of the droplets with solid surfaces are found to determine adhesion and subsequent spreading of emulsion droplets. This was investigated by varying the adsorbed amount of protein, the ionic strength of the emulsion as well as the hydrophobicity of the solid surface. Especially the hydrophobic interaction between droplet and surface is shown to be crucial for droplet adhesion and spreading. Saliva is of minor importance for adhesion and spreading. This work gives insight in the way emulsion droplets interact with solid surfaces and the type of colloidal interactions that play a role. The information it provides can be used to develop emulsions that are reasonably stable during the shelf life of the product, but do spread on oral surfaces, thus lowering friction and enhancing fat perception
    Application of oral tissue in tribological measurements in an emulsion perception context
    Dresselhuis, D.M. ; Hoog, E.H.A. de; Cohen Stuart, M.A. ; Aken, G.A. van - \ 2008
    Food Hydrocolloids 22 (2008)2. - ISSN 0268-005X - p. 323 - 335.
    in-water emulsions - dairy-products - human tongue - lubrication - creaminess - behavior - chocolate - texture - cavity - saliva
    Tribological measurements are indicated to be a tool in predicting the creamy in-mouth sensation of a food product. Tribological measurements relating lubricational behaviour of a food product to perception are often conducted with artificial surfaces. In this work we used pig's tongue to mimic the human tongue, which has the advantage of having surface characteristics similar to a human tongue. Using biological material has also some drawbacks. The most important drawbacks are the limited availability, the individual differences between the tongues, and the relative fast degradation of the tissue. The aim of this study was to identify the characteristics of the tongue in terms of surface roughness, deformability and wetting properties. The knowledge on these characteristics can serve as reference when using modified poly dimethyl siloxane (PDMS) in tribological experiments relating perception to in-mouth friction. Furthermore, we demonstrated that these characteristics are crucial in tribological studies to draw rightful conclusions. Tribological measurements were performed with an experimental set-up combining friction measurement with confocal scanning laser microscope (CSLM) observations. We identified the importance of these characteristics for tribology measurements performed in relation to sensory perception. It is shown that the tongue surface has some very typical characteristics, including the presence of papillae and a hydrophilic mucus layer, and an elastic modulus that is at least two orders of magnitude smaller than that of smooth PDMS surfaces. The different surface characteristics appear to lead to completely different lubricational behaviour of the food emulsions between these surfaces. Furthermore, for food emulsions differences in the occurrence of coalescence were found between shearing with pig's tongue and PDMS surfaces. Therefore, we conclude that for studies relating sensory properties of food systems to lubricational behaviour, a careful choice of representative surfaces is essential and that modification of smooth PDMS can result in surfaces having characteristics closer to tongue tissue
    Tribology of o/w emulsions under mouth-like conditions: determinants of friction
    Dresselhuis, D.M. ; Klok, H.J. ; Cohen Stuart, M.A. ; Vries, R.J. de; Aken, G.A. van; Jongh, H.H.J. de - \ 2007
    Food Biophysics 2 (2007)4. - ISSN 1557-1858 - p. 158 - 171.
    in-water emulsions - lubrication mechanism - boundary lubrication - surface modification - protein adsorption - behavior - saliva - flocculation - perception - chocolate
    Fat-perception is thought to be related to a complex interplay between fat-associated flavor release and mouth-feel. Friction sensed between the tongue and the palate seems to play a prominent role: in previous work, we have shown that emulsions that are more sensitive toward coalescence give rise to a lowering of the orally perceived and experimentally measured friction and, probably as a consequence, to an enhanced fat-perception. In this paper, we study in detail the factors determining friction of protein-stabilized emulsions using a novel mouth-mimicking tribometer and model surfaces consisting of PDMS modified in various ways (hydrophobicity, deformability, roughness). We show that unlike in many technological applications where lubrication is essentially hydrodynamic, for physiologically relevant loads, the modified PDMS is boundary and/or mixed lubricated, which is like in-mouth lubrication. We find that an increased sensitivity of the emulsions toward coalescence results in a lower friction, confirming previous results obtained with pig¿s tongue. Surface-induced coalescence (or spreading of emulsion droplets) seems to be very important in this, surface hydrophobicity being the dominant trigger. Viscosity of the dispersed phase does not have such a strong influence on both the measured friction and the oral perceived friction. We do find a strong influence of the presence of bulk proteins and saliva on friction. Finally, hardly any dependence of measured friction on fat content of the emulsion was observed, indicating that only a small amount of fat is needed to alter the friction.
    The role of electrostatistics in saliva-induced emulsion flocculation
    Silletti, E. ; Vingerhoeds, M.H. ; Norde, W. ; Aken, G.A. van - \ 2007
    Food Hydrocolloids 21 (2007)4. - ISSN 0268-005X - p. 596 - 606.
    in-water emulsions - human glandular salivas - human whole saliva - depletion flocculation - mucin mg1 - complex coacervation - food hydrocolloids - beta-lactoglobulin - protein-components - whey proteins
    Upon consumption food emulsions undergo different processes, including mixing with saliva. It has been shown that whole saliva induces emulsion flocculation [van Aken, G. A., Vingerhoeds, M. H., & de Hoog, E. H. A. (2005). Colloidal behaviour of food emulsions under oral conditions. In E. Dickinson (Eds.), Food colloids 2004: Interactions, microstructure and processing (pp. 356¿366). Cambridge: The Royal Society of Chemistry; Vingerhoeds, M. H., Blijdenstein, T. B. J., Zoet, F. D., & van Aken, G. A. (2005). Emulsion flocculation induced by saliva and mucin. Food Hydrocolloids, 19, 915¿922]. It was hypothesized that depletion flocculation was responsible for the observed flocculation. To further unravel the mechanism, we investigated the role of electrostatics on the behavior of emulsion/saliva mixtures. Emulsions stabilized with differently charged surfactants and proteins were mixed with saliva. Strongly negatively charged emulsions (SDS and Panodan) do not flocculate, likely because the electrostatic repulsion between the droplets overcomes the attractive depletion and van der Waals interactions. Neutral and weakly negatively charged emulsions (Tween 20 and ß-lactoglobulin pH 6.7) undergo flocculation, which is reversible upon dilution with water. This is probably due to depletion interactions, induced by large salivary protein like mucins, in combination with the van der Waals interaction and the sufficiently low electrostatic repulsion between the droplets. Positively charged emulsions (CTAB, lysozyme and ß-lactoglobulin pH 3.0) show irreversible flocculation leading to rapid phase separation. These findings point to a role of electrostatic attraction between the negatively charged proteins present in saliva and the positively charged surfaces of the emulsion droplets. The results indicate that the sign and the density of the charge on the surface of the droplets contribute significantly to the behavior of an emulsion when mixed with saliva. Depending on the charge, saliva-induced emulsion flocculation is driven by two different main mechanisms: depletion flocculation and electrostatic attraction.
    Lattice Boltzmann simulations of droplet formation in a T-shaped microchannel
    Graaf, S. van der; Nisisako, T. ; Schroën, C.G.P.H. ; Sman, R.G.M. van der; Boom, R.M. - \ 2006
    Langmuir 22 (2006)9. - ISSN 0743-7463 - p. 4144 - 4152.
    in-water emulsions - membrane emulsification - numerical-simulation - complex fluids - liquid-gas - model - flows - interface - dynamics - mixture
    We investigated the formation of a droplet from a single pore in a glass chip, which is a model system for droplet formation in membrane emulsification. Droplet formation was simulated with the lattice Boltzmann method, a method suitable for modeling on the mesoscale. We validated the lattice Boltzmann code with several benchmarks such as the flow profile in a rectangular channel, droplet deformation between two shearing plates, and a sessile drop on a plate with different wetting conditions. In all cases, the modeling results were in good agreement with the benchmark. A comparison of experimental droplet formation in a microchannel glass chip showed good quantitative agreement with the modeling results. With this code, droplet formation simulations with various interfacial tensions and various flow rates were performed. All resulting droplet sizes could be correlated quantitatively with the capillary number and the fluxes in the system.
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