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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    Towards predicting the stability of protein-stabilized emulsions
    Delahaije, R.J.B.M. ; Gruppen, H. ; Giuseppin, M.L.F. ; Wierenga, P.A. - \ 2015
    Advances in Colloid and Interface Science 219 (2015). - ISSN 0001-8686 - p. 1 - 9.
    in-water emulsions - random sequential adsorption - equation-of-state - beta-lactoglobulin - light-scattering - latex-particles - quantitative description - exposed hydrophobicity - globular-proteins - diffusing wave
    The protein concentration is known to determine the stability against coalescence during formation of emulsions. Recently, it was observed that the protein concentration also influences the stability of formed emulsions against flocculation as a result of changes in the ionic strength. In both cases, the stability was postulated to be the result of a complete (i.e. saturated) coverage of the interface. By combining the current views on emulsion stability against coalescence and flocculation with new experimental data, an empiric model is established to predict emulsion stability based on protein molecular properties such as exposed hydrophobicity and charge. It was shown that besides protein concentration, the adsorbed layer (i.e. maximum adsorbed amount and interfacial area) dominates emulsion stability against coalescence and flocculation. Surprisingly, the emulsion stability was also affected by the adsorption rate. From these observations, it was concluded that a completely covered interface indeed ensures the stability of an emulsion against coalescence and flocculation. The contribution of adsorption rate and adsorbed amount on the stability of emulsions was combined in a surface coverage model. For this model, the adsorbed amount was predicted from the protein radius, surface charge and ionic strength. Moreover, the adsorption rate, which depends on the protein charge and exposed hydrophobicity, was approximated by the relative exposed hydrophobicity (QH). The model in the current state already showed good correspondence with the experimental data, and was furthermore shown to be applicable to describe data obtained from literature.
    Aqueous foams stabilized by chitin nanocrystals
    Tzoumaki, M. ; Karefyllakis, D. ; Moschakis, T. ; Biliaderis, C.G. ; Scholten, E. - \ 2015
    Soft Matter 11 (2015). - ISSN 1744-683X - p. 6245 - 6253.
    in-water emulsions - pickering emulsions - silica nanoparticles - polymer microrods - fluid interfaces - particles - cellulose - behavior - bubbles - microparticles
    The aim of the present study was to explore the potential use of chitin nanocrystals, as colloidal rod-like particles, to stabilize aqueous foams. Chitin nanocrystals (ChN) were prepared by acid hydrolysis of crude chitin and foams were generated mainly by sonicating the respective dispersions. The foamability of the chitin nanocrystals was evaluated and the resulting foams were assessed for their stability, in terms of foam volume reduction and serum release patterns, during storage. Additionally, the samples were studied with light scattering and optical microscopy in order to explore the bubble size distribution and morphology of the foam. Nanocrystal concentration and charge density was varied to alter the packing of the crystals at the interface. At low concentrations of ChNs, foams were stable against coalescence and disproportionation for a period of three hours, whereas at higher concentrations, the foams were stable for several days. The enhanced stability of foams prepared with ChNs, compared to surfactant-stabilized foams, can be mainly attributed to the irreversible adsorption of the ChNs at the air-water interface, thereby providing Pickering stabilization. Both foam volume and stability of the foam were increased with an increase in ChNs concentration, and at pH values around the chitin's pKa (pH 7.0). Under these conditions, the ChNs show minimal electrostatic repulsion and therefore a higher packing of the nanocrystals is promoted. Moreover, decreased electrostatic repulsion enhances network formation between the ChNs in the aqueous films, thereby providing additional stability by gel formation. Overall, ChNs were proven to be effective in stabilizing foams, and may be useful in the design of Pickering-stabilized food grade foams.
    Properties of Oil/Water Emulsions Affecting the Deposition, Clearance and After-Feel Sensory Perception of Oral Coatings
    Camacho, S. ; Hollander, E.L. de; Velde, E. van de; Stieger, M.A. - \ 2015
    Journal of Agricultural and Food Chemistry 63 (2015)8. - ISSN 0021-8561 - p. 2145 - 2153.
    in-water emulsions - flavor perception - sodium caseinate - oil content - viscosity - flocculation - saliva - tongue - retention - behavior
    The aims of this study were to investigate the influence of (i) protein type, (ii) protein content, and (iii) viscosity of o/w emulsions on the deposition and clearance of oral oil coatings and after-feel perception. Oil fraction (moil/cm2tongue) and after-feel perception differed considerably between emulsions which do not flocculate under in mouth conditions (Na-caseinate) and emulsions which flocculate under in mouth conditions (lysozyme). The irreversible flocculation of lysozyme stabilized emulsions caused slower oil clearance from the tongue surface compared to emulsions stabilized with Na-caseinate. Protein content had a negative relation with oil fraction for lysozyme stabilized emulsions and no relation for Na-caseinate stabilized emulsions immediately after expectoration. Viscosity differences did not affect oil fraction, although the presence of thickener decreased deposition of oil on tongue. We conclude that after-feel perception of o/w emulsions is complex and depends on the deposited oil fraction, the behavior of proteins in mouth, and thickeners.
    Aqueous fractionation yields chemically stable lupin protein isolates
    Berghout, J.A.M. ; Marmolejo-Garcia, C. ; Berton-Carabin, C.C. ; Nikiforidis, C.V. ; Boom, R.M. ; Goot, A.J. van der - \ 2015
    Food Research International 72 (2015). - ISSN 0963-9969 - p. 82 - 90.
    in-water emulsions - seed oil bodies - oxidative stability - antioxidant properties - lipid oxidation - physicochemical properties - functional-properties - quality - acids - polysaccharides
    The chemical stability of lupin protein isolates (LPIs) obtained through aqueous fractionation (AF, i.e. fractionation without the use of an organic solvent) at 4 °C or 20 °C was assessed. AF of lupin seeds results in LPIs containing 2 wt.% oil. This oil is composed of mono- and poly-unsaturated fatty acids and the isolate may thus be prone to lipid and protein oxidation. Lipid and protein oxidation marker values of LPIs obtained at 4 °C and at 20 °C were below the acceptability limit for edible vegetable oils and meat tissue protein; the level of lipid oxidation markers was lower at 20 °C than at 4 °C. The fibre-rich pellet and the protein-rich supernatant obtained after AF also had lower levels of oxidation markers at 20 °C than at 4 °C. This is probably the result of a higher solubility of oxygen in water at lower temperature, which could promote lipid oxidation. The differences between fractions can be explained by the differences in their composition; the fibre-rich pellet contains polysaccharides that potentially have an anti-oxidative effect, while the protein-rich supernatant is rich in sulphur-rich proteins that may scavenge metal ions and free radicals from the aqueous phase. Additionally, the differences in solubility of metal ions and metal-chelating properties of protein at pH 4.5 and pH 7.0 explain the higher level of oxidation in the LPI at pH 4.5 compared with the LPI at pH 7.0. The application of a heat treatment to reduce oxidation decreased the protein and oil recovery values, and increased oxidation values above the acceptability limit. Therefore, AF at 20 °C is the most suitable process to obtain chemically stable LPIs.
    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.
    Composition, properties and potential food applications of natural emulsions and cream materials based on oil bodies
    Nikiforidis, C.V. ; Matsakidou, A. ; Kiosseoglou, V. - \ 2014
    RSC Advances : An international journal to further the chemical sciences 4 (2014)48. - ISSN 2046-2069 - p. 25067 - 25078.
    assisted aqueous extraction - in-water emulsions - oxidative stability - soybean oil - maize germ - rheological characteristics - physicochemical stability - physical stability - sodium caseinate - lipid droplets
    Oil bodies are micron- or submicron-sized organelles found mainly in parts of plants such as seeds, nuts or some fruits and their main role is to function as energy stores. Their structure is made up of a core of triglycerides covered by a protein–phospholipid layer which protects the oil bodies against external chemical/mechanical stresses. Following treatment with aqueous media of the rich-in-oil raw materials, an extract of oil bodies, dispersed in a solution of exogenous plant proteins, is obtained. Effective recovery of oil droplets from the initial extract, which is in effect a relatively dilute natural emulsion, leads to the preparation of either a more concentrated natural emulsion with a composition in terms of oil and protein close to that of animal milk or, alternatively, to a concentrated oil droplet-based “cream”. Both the natural emulsion and the “cream” can be exploited in the development of a number of novel food products by suitably substituting the oil/fat droplets of the traditionally-prepared food product with natural oil droplets.
    Effect of interfacial properties on the reactivity of a lipophilic ingredient in multilayered emulsions
    Chaprenet, J. ; Berton-Carabin, C.C. ; Elias, R. ; Coupland, J. - \ 2014
    Food Hydrocolloids 42 (2014)part1. - ISSN 0268-005X - p. 56 - 65.
    in-water emulsions - whey-protein isolate - solid lipid nanoparticles - oxidative stability - beta-lactoglobulin - surfactant micelles - delivery-systems - chemical-stability - oil - droplets
    The aim of this work was to investigate the location and reactivity of a lipophilic spin probe, 4-phenyl- 2,2,5,5-tetramethyl-3-imidazoline-1-oxyl nitroxide (PTMIO) in multilayered, biopolymer-based emulsions stabilized with a primary anionic layer (sodium caseinate) and a secondary cationic layer (lysozyme or diethylaminoethyl (DEAE) dextran). A broad range of ¿-potential values, from ca. -55 mV to 35 mV, was achieved. Emulsions with good physical stability were achieved when the magnitude of the net charge on the droplets was sufficiently great, otherwise some physical destabilization (flocculation) could be observed, especially in the case of caseinate-lysozyme-stabilized emulsions. The analysis of electron paramagnetic resonance (EPR) spectra of PTMIO in emulsion systems showed that probe molecules partitioned between the oil droplet core (ca. 73%) and the aqueous phase (ca. 27%), independently of the interfacial composition. Surprisingly, the rate of reduction of the nitroxide group of PTMIO by ascorbate anions remained unchanged when secondary interfacial layers were added, showing that the droplet surface charge was not the prevalent factor controlling the interactions between lipophilic compounds and aqueous phase reagents. Instead we argue that the reduction of PTMIO occurs in the aqueous phase.
    Physical characteristics of submicron emulsions upon partial displacement of whey protein by a small molecular weight surfactant and pectin addition
    Kaltsa, O. ; Paximada, P. ; Mandala, I. ; Scholten, E. - \ 2014
    Food Research International 66 (2014). - ISSN 0963-9969 - p. 401 - 408.
    in-water emulsions - protein/surfactant interfacial interactions - competitive adsorption - sodium caseinate - plus surfactant - rheological properties - stabilized emulsions - nonionic surfactant - chitosan complexes - milk-proteins
    O/W emulsions (6% wt olive oil) were prepared at pH 3.3 using different WPI:Tween 20 weight ratios (1:0, 3:1, 1:1, 1:3, 0:1) at 1% wt total concentration. The emulsion droplet size was found to decrease with an increase in Tween 20. A minimum droplet size of d3,2 300 nm was found for Tween systems alone, similar to that found (360 nm) for a 1:1 WPI:Tween 20 combination (p <0.05). This specific composition showed a value for the interfacial tension close to that of Tween 20 alone. However, the emulsions presented low stability regardless of the WPI:Tween 20 ratio. To increase their stability, pectin was added, in various concentrations (0.2, 0.4 and 0.6% wt), using the Layer by Layer technique. In the presence of pectin, the ¿-potential of the oil droplets became negative; indicating that negatively charged pectin was absorbed onto the positively-charged droplet surface forming a secondary layer. The additional layer resulted in a wide range of emulsion stability. For all pectin concentrations, the 1:1 ratio of WPI:Tween 20 showed the highest stability. In most emulsions, extensive aggregation of oil droplets was observed, and their viscosity increased. Insufficient amounts of pectin to form the secondary layers led to bridging flocculation phenomena of oppositely charged pectin and proteins, leading to aggregation of the oil droplets. The higher the concentration of pectin, the greater the stability of the emulsion due to higher viscosity. All in all, the addition of a second layer consisting of pectin can be used to increase the stability of an emulsion containing emulsion droplets in the sub-micron range.
    Characterisation and use of ß-lactoglobulin fibrils for microencapsulation of lipophilic ingredients and oxidative stability thereof
    Serfert, Y. ; Lamprecht, C. ; Tan, C.P. ; Rossier Miranda, F.J. ; Schroen, C.G.P.H. ; Boom, R.M. - \ 2014
    Journal of Food Engineering 143 (2014). - ISSN 0260-8774 - p. 53 - 61.
    in-water emulsions - spray-drying behavior - emulsifying properties - interfacial rheology - antioxidant activity - lipid oxidation - protein fibrils - amyloid fibrils - ionic-strength - whey proteins
    There is a growing interest in using fibrils from food grade protein, e.g. ß-lactoglobulin, as functional ingredients. In the present study, the functionality of fibrillar ß-lactoglobulin from whey protein isolate (WPI) was compared to native WPI in terms of interfacial dilatational rheology and emulsifying activity at acidic conditions (pH 2.0 and 3.0). We report here for the first time data on microencapsulation of fish oil by spray-drying as well as oxidative stability of the oil in emulsions and microcapsules in dependence of WPI conformation. WPI fibrils exerted a significantly higher elasticity at the oil–water (o/w) interface and a better emulsifying activity at a fixed oil content compared to native WPI. Microencapsulation efficiency was also higher with fibrillar WPI (>95%) compared to native WPI (~90%) at pH 2.0 and a total oil and protein content of 40% and 2.2%, respectively, in the final powder. The oxidative deterioration was lower in emulsions and microcapsules prepared with fibrillar than with native WPI. This was attributed to improved interfacial barrier properties provided by fibrils and antioxidative effects of coexisting unconverted monomers, particularly hydrophilic peptides
    Influence of the emulsion formulation in premix emulsification using packed beds
    Nazir, A. ; Boom, R.M. ; Schroën, C.G.P.H. - \ 2014
    Chemical Engineering Science 116 (2014). - ISSN 0009-2509 - p. 547 - 557.
    in-water emulsions - droplet break-up - membrane emulsification - multiple emulsions - microchannel emulsification - interfacial-tension - drug-delivery - static mixers - homogenization - surfactant
    Premix emulsification was investigated using packed beds consisting of micron-sized glassbeads, a system that avoids fouling issues, unlike traditional premix membrane emulsification. The effects of emulsion formulation were investigated, most notably the viscosity and the surfactant. The dropletsize was reduced by increased shea rstress in the emulsion. This was stronger at low viscosity ratios than at high ratios. As expected the flux was proportional to the overall emulsion viscosity, and emulsions with small droplet size (Sauter mean droplet diameter o5 µm) could still be produced at up to 60% of dispersed phase provided that sufficient surfactant was available. More uniform emulsions(spanE0.75) were produced withTween-20(nonionic )and SDS(anionic) as surfactants than with CTAB (acationic surfactant), possibly due to acombination of a low equilibrium interfacia ltension and electrostatic attractions with the glass surface. Scaling relations were proposed taking into account all investigated product properties that can describe the dropletsize successfully.
    Improved emulsion stability by succinylation of patatin is caused by partial unfolding rather than charge effects
    Delahaije, R.J.B.M. ; Wierenga, P.A. ; Giuseppin, M.L.F. ; Gruppen, H. - \ 2014
    Journal of Colloid and Interface Science 430 (2014). - ISSN 0021-9797 - p. 69 - 77.
    in-water emulsions - protein-exposed hydrophobicity - beta-lactoglobulin - drop size - adsorption - flocculation - interface - stabilization - ph - dependence
    This study investigates the influence of succinylation on the molecular properties (i.e. charge, structure and hydrophobicity) and the flocculation behavior of patatin-stabilized oil-in-water emulsions. Patatin was succinylated to five degrees (0% (R0) to 57% (R2.5)). Succinylation not only resulted in a change of the protein charge but also in (partial) unfolding of the secondary structure, and consequently in an increased initial adsorption rate of the protein to the oil–water interface. The stability against salt-induced flocculation showed two distinct regimes, instead of a gradual shift in stability as expected by the DLVO theory. While flocculation was observed at ionic strengths > 30 mM for the emulsions stabilized by the variants with the lowest degrees of modification (R0–R1), the other variants (R1.5–R2.5) were stable against flocculation ¿ 200 mM. This was related to the increased initial adsorption rate, and the consequent transition from a protein-poor to a protein-rich regime. This was confirmed by the addition of excess protein to the emulsions stabilized by R0–R1 which resulted in stability against salt-induced flocculation. Therefore, succinylation of patatin indirectly results in stability against salt-induced flocculation, by increasing the initial adsorption rate of the protein to the oil–water interface, leading to a shift to the protein-rich regime.
    High throughput production of double emulsions using packed bed premix emulsification
    Sahin, S. ; Sawalha, H.I.M. ; Schroen, C.G.P.H. - \ 2014
    Food Research International 66 (2014). - ISSN 0963-9969 - p. 78 - 85.
    release rate profiles - in-water emulsions - multiple w/o/w emulsions - droplet break-up - membrane emulsification - microchannel emulsification - interfacial-tension - food applications - drug-delivery - nickel sieves
    We explored the potential of packed bed premix emulsification for homogenizing coarse food grade W/O/W emulsions, prepared with sunflower oil. Using packed beds with different glass bead sizes (30–90 µm) at different applied pressures (200–600 kPa), emulsions with reasonably uniform droplet size (span ~ 0.75) were produced successfully at high fluxes (100–800 m3 m- 2 h- 1). Sodium chloride was used as a release marker: after five homogenization cycles, the produced emulsions were found to retain almost all of their initial content (99%). As was previously found for single emulsions, the packed bed system proved to be effective in breaking up the W/O/W emulsion droplets, with droplet to pore size ratios as low as 0.3. Results were analysed through the pore Reynolds number, Rep, which characterizes the flow inside the packed bed, and were related back to the droplet break-up mechanisms occurring. At high Rep, droplet break-up was expected to be governed by shear forces while at low Rep, there is a shift from shear based to spontaneous droplet break-up.
    Complex interfaces in food: Structure and mechanical properties
    Sagis, L.M.C. ; Scholten, E. - \ 2014
    Trends in Food Science and Technology 37 (2014)1. - ISSN 0924-2244 - p. 59 - 71.
    in-water emulsions - by-layer technique - polyelectrolyte capsules - rheological properties - air/water interfaces - dilatational rheology - pickering emulsions - droplet deformation - protein adsorption - liquid interfaces
    Multiphase food systems (emulsions, foam) often have interfaces with a complex microstructure, formed by interfacial self-assembly of proteins, lipids, or colloidal particles. The response of these interfaces to deformations tends to be highly nonlinear and far more complex than the response of interfaces stabilized by simple low molecular weight surfactants. In this review we present an overview of various types of complex interfaces encountered in food products, and discuss their microstructure and mechanical properties. We also discuss how to properly characterize the nonlinear behavior of these interfaces, using surface rheological techniques, droplet deformation studies, and structural characterization methods.
    Dynamic behavior of interfaces: Modeling with nonequilibrium thermodynamics
    Sagis, L.M.C. - \ 2014
    Advances in Colloid and Interface Science 206 (2014). - ISSN 0001-8686 - p. 328 - 343.
    liquid-vapor interface - curved fluid interfaces - in-water emulsions - surface-diffusion coefficient - scanning angle reflectometry - extended thermodynamics - latex-particles - amyloid fibrils - air-water - 2-dimensional suspensions
    In multiphase systems the transfer of mass, heat, and momentum, both along and across phase interfaces, has an important impact on the overall dynamics of the system. Familiar examples are the effects of surface diffusion on foam drainage (Marangoni effect), or the effect of surface elasticities on the deformation of vesicles or red blood cells in an arterial flow. In this paper we will review recent work on modeling transfer processes associated with interfaces in the context of nonequilibrium thermodynamics (NET). The focus will be on NET frameworks employing the Gibbs dividing surface model, in which the interface is modeled as a twodimensional plane. This plane has excess variables associated with it, such as a surface mass density, a surface momentum density, a surface energy density, and a surface entropy density. We will review a number of NET frameworks which can be used to derive balance equations and constitutive models for the time rate of change of these excess variables, as a result of in-plane (tangential) transfer processes, and exchange with the adjoining bulk phases. These balance equations must be solved together with mass, momentum, and energy balances for the bulk phases, and a set of boundary conditions coupling the set of bulk and interface equations. This entire set of equations constitutes a comprehensive continuummodel for amultiphase system, and allows us to examine the role of the interfacial dynamics on the overall dynamics of the system. With respect to the constitutive equations we will focus primarily on equations for the surface extra stress tensor.
    Effect of charged polysaccharides on the techno-functional properties of fractions obtained from algae soluble protein isolate
    Schwenzfeier, A. ; Wierenga, P.A. ; Eppink, M.H.M. ; Gruppen, H. - \ 2014
    Food Hydrocolloids 35 (2014). - ISSN 0268-005X - p. 9 - 18.
    in-water emulsions - diffusing wave spectroscopy - tetraselmis sp - adsorption - microalgae - dissociation - hydrolysis - stability
    It has been suggested previously that charged polysaccharides present in algae soluble protein isolate (ASPI) contribute to its foaming and emulsifying properties. In this study ASPI was fractioned into one fraction enriched in uronic acids (the building blocks of charged polysaccharides, [ASPI-UA]), one enriched in protein (ASPI-P) and one containing small, dissociated (glyco-)proteins (ASPI-S). Emulsions prepared using ASPI-UA were stable against flocculation between pH 3e7, while ASPI-P and ASPI-S showed decreased emulsion stabilities around pH 5. This indicates the importance of the charged polysaccharides present in ASPI for emulsion stability at pH 5. For the foaming properties of ASPI no effect of charged polysaccharides was observed. Instead, ASPI-S showed considerably higher foam stabilities at pH 5e7 than the other fractions. These results suggest that dependent on the application charged polysaccharides or dissociated (glyco-) proteins can contribute to ASPI’s techno-functional properties. Its further fractionation yields a fraction with improved emulsion stability and a fraction with improved foaming properties.
    Dynamics of multiphase systems with complex microstructure. I. Development of the governing equations through nonequilibrium thermodynamics
    Sagis, L.M.C. ; Öttinger, H.C. - \ 2013
    Physical Review. E, Statistical nonlinear, and soft matter physics 88 (2013)2. - ISSN 1539-3755 - 13 p.
    scanning angle reflectometry - in-water emulsions - superficial viscosity - general formalism - bending rigidity - lipid-bilayers - interfaces - surface - fluid - rheology
    In this paper we present a general model for the dynamic behavior of multiphase systems in which the bulk phases and interfaces have a complex microstructure (for example, immiscible polymer blends with added compatibilizers, or polymer stabilized emulsions with thickening agents dispersed in the continuous phase). The model is developed in the context of the GENERIC framework (general equation for the nonequilibrium reversible irreversible coupling). We incorporate scalar and tensorial structural variables in the set of independent bulk and surface excess variables, and these structural variables allow us to link the highly nonlinear rheological response typically observed in complex multiphase systems, directly to the time evolution of the microstructure of the bulk phases and phase interfaces. We present a general form of the Poisson and dissipative brackets for the chosen set of bulk and surface excess variables, and show that to satisfy the entropy degeneracy property, we need to add several contributions to the moving interface normal transfer term, involving the tensorial bulk and interfacial structural variables. We present the full set of balance equations, constitutive equations, and boundary conditions for the calculation of the time evolution of the bulk and interfacial variables, and this general set of equations can be used to develop specific models for a wide range of complex multiphase systems.
    Dynamics of multiphase systems with complex microstructure. II. Particle-stabilized interfaces
    Sagis, L.M.C. - \ 2013
    Physical Review. E, Statistical nonlinear, and soft matter physics 88 (2013)2. - ISSN 1539-3755 - 9 p.
    fourier-transform rheology - in-water emulsions - superficial viscosity - bending rigidity - surface - liquid - viscoelasticity - liquid/liquid - fluid - gas/liquid
    In this paper we use the GENERIC (general equation for nonequilibrium reversible-irreversible coupling) nonequilibrium thermodynamics framework to derive constitutive equations for the surface extra stress tensor of an interface stabilized by a two-dimensional suspension of anisotropic colloidal particles. The dependence of the surface stress tensor on the microstructure of the interface is incorporated through a dependence on a single tensorial structural variable, characterizing the average orientation of the particles. The constitutive equation for the stress tensor is combined with a time-evolution equation describing the changes in the orientation tensor as a result of the applied deformation field. We examine the predictions of the model in in-plane steady shear flow, in-plane oscillatory shear flow, and oscillatory dilatational flow. The model is able to predict the experimentally observed shear thinning behavior in surface shear flow, and also the experimentally observed emergence of even harmonics in the frequency spectrum of the surface stress in oscillatory dilatational flow. Our results show that the highly nonlinear stress-deformation behavior of interfaces with a complex microstructure can be modeled well using simple structural models like the one presented here.
    Reactants encapsulation and Maillard Reaction
    Troise, A.D. ; Fogliano, V. - \ 2013
    Trends in Food Science and Technology 33 (2013). - ISSN 0924-2244 - p. 63 - 74.
    model dough systems - in-water emulsions - n-epsilon-carboxymethyllysine - polyunsaturated fatty-acids - ascorbic-acid - acrylamide formation - lipid oxidation - high-pressure - amino-acid - microencapsulated ingredients
    In the last decades many efforts have been addressed to the control of Maillard Reaction products in different foods with the aim to promote the formation of compounds having the desired color and flavor and to reduce the concentration of several potential toxic molecules. Encapsulation, already applied in food industry for different purposes, can be used as a strategy to get the controlled release of some compounds promoting the Maillard Reaction development in order to mitigate the formation of some undesired compounds. In this review the underneath reaction mechanism, the activity of various reactants, the encapsulation strategies and some possible applications in food processing were discussed highlighting the potentialities of encapsulated ingredients in the modulation of Maillard Reaction.
    Normal stresses in surface shear experiments
    Sagis, L.M.C. - \ 2013
    The European Physical Journal. Special Topics 222 (2013)1. - ISSN 1951-6355 - p. 99 - 103.
    in-water emulsions - interfacial permeability - general formalism - bending rigidity - complex fluids - dynamics - viscoelasticity - thermodynamics - liquid/liquid - gas/liquid
    When viscoelastic bulk phases are sheared, the deformation of the sample induces not only shear stresses, but also normal stresses. This is a well known and well understood effect, that leads to phenomena such as rod climbing, when such phases are stirred with an overhead stirrer, or to die swell in extrusion. Viscoelastic interfaces share many commonalities with viscoelastic bulk phases, with respect to their response to deformations. There is however little experimental evidence that shear deformations of interfaces can induce in-plane normal stresses (not to be confused with stresses normal to the interface). Theoretical models for the stress-deformation behavior of complex fluid-fluid interfaces subjected to shear, predict the existence of in-plane normal stresses. In this paper we suggest methods to confirm the existence of such stresses experimentally.
    Protein transfer to membranes upon shape deformation
    Sagis, L.M.C. ; Bijl, E. ; Antono, L. ; Ruijter, N.C.A. de; Valenberg, H.J.F. van - \ 2013
    The European Physical Journal. Special Topics 222 (2013)1. - ISSN 1951-6355 - p. 61 - 71.
    blood-cell deformability - in-water emulsions - fat globule size - interfacial permeability - flow - drops - milk - dissolution - infections - adsorption
    Red blood cells, milk fat droplets, or liposomes all have interfaces consisting of lipid membranes. These particles show significant shape deformations as a result of flow. Here we show that these shape deformations can induce adsorption of proteins to the membrane. Red blood cell deformability is an important factor in several diseases involving obstructions of the microcirculatory system, and deformation induced protein adsorption will alter the rigidity of their membranes. Deformation induced protein transfer will also affect adsorption of cells onto implant surfaces, and the performance of liposome based controlled release systems. Quantitative models describing this phenomenon in biomaterials do not exist. Using a simple quantitative model, we provide new insight in this phenomenon. We present data that show convincingly that for cells or droplets with diameters upwards of a few micrometers, shape deformations induce adsorption of proteins at their interface even at moderate flow rates.
    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.
    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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