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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    Nonlinear shear and dilatational rheology of viscoelastic interfacial layers of cellulose nanocrystals
    Berg, Merel van den; Kuster, Simon ; Windhab, E.J. ; Sagis, L.M.C. ; Fischer, P. - \ 2018
    Physics of Fluids 30 (2018)7. - ISSN 1070-6631 - 11 p.
    compressibility - contact angle - Hydrophobicity - nanomechanics - nanoparticles - polymers - Rheology - softening - viscoelasticity - work hardening
    We present a nonlinear rheological investigation of model rod-like particles at the air/water interface in dilatation and shear. Cellulose nanocrystals were modified to vary their surface hydrophobicity, creating a range of surface-active particles with varying contact angle. The interfacial rheological properties were studied using a series of frequency sweeps in small amplitude oscillatory shear as well as strain sweeps under large amplitude oscillatory shear (LAOS) and large amplitude oscillatory dilatation (LAOD) to include the nonlinear behavior. A multi-mode Maxwell model was used to fit the frequency sweeps that were obtained during formation of the interfacial layer. A shift toward longer
    relaxation times was found, more pronounced for particles with higher hydrophobicity. Lissajous plots in LAOS revealed strain stiffening, yielding, and unconstrained flow of the interfacial layers.
    Lissajous plots in LAOD revealed strain hardening in compression and strain softening in expansion, increasing with surface pressure and with particle hydrophobicity. While interfacial layers commonly show gel or solid-like behavior, our findings imply a weakly aggregated system. The rheological
    behavior indicates the formation of larger clusters for particles with high hydrophobicity compared to smaller clusters for particles with low hydrophobicity. The particle-particle interactions therefore vary with hydrophobicity, suggesting that capillary interactions are important for the formation of these microstructures.
    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.
    Non-linear surface dilatational rheology as a tool for understanding microstructures of air/water interfaces stabilized by oligofructose fatty acid esters
    Kempen, S.E.H.J. van; Schols, H.A. ; Linden, E. van der; Sagis, L.M.C. - \ 2013
    Soft Matter 9 (2013)40. - ISSN 1744-683X - p. 9579 - 9592.
    air-water-interface - monolayers - layers - shear - viscoelasticity - adsorption - systems - foams
    In this paper, the rheological response of air/water interfaces, stabilized by various oligofructose fatty acid esters, to oscillatory dilatational deformations was studied and compared to the response of interfaces stabilized by sucrose esters. We have followed a traditional approach to surface rheology, where the development of the modulus as a function of time is studied as well as the frequency dependence of the modulus. We also adopted a different approach where we investigate in detail the amplitude dependence of the modulus. Finally, we studied the temperature dependence. We show that for an accurate characterization of the dilatational rheology of fluid-fluid interfaces with a complex microstructure, a protocol should be used that not only involves variations of surface pressure, frequency, and temperature, but also establishes amplitude dependence. We show that Lissajous plots of surface pressure versus deformation can be useful tools to help interpret surface dilatational behavior in terms of interfacial microstructure. The rheological response of interfaces stabilized by oligofructose esters differed significantly from the response of those stabilized by sucrose esters. Sucrose esters behaved like typical low molecular weight surfactants, and gave interfaces with relatively low moduli, a frequency scaling of the dilatational modulus with an exponent close to 0.5, and displayed no asymmetries in Lissajous plots. In contrast, the oligofructose esters gave, depending on the fatty acid tail, relatively high moduli, almost independent of frequency. Significant asymmetries were observed in the Lissajous plots, with strain hardening during compression and strain softening during extension. Our results suggest that the unusual rheological properties of interfaces stabilized by oligofructose esters may be the result of the formation of a two-dimensional soft glass phase by the oligofructose part of the ester.
    The effect of diesters and lauric acid on rheological properties of air/water interfaces stabilized by oligofructose lauric acid monoesters
    Kempen, S.E.H.J. van; Schols, H.A. ; Linden, E. van der; Sagis, L.M.C. - \ 2013
    Journal of Agricultural and Food Chemistry 61 (2013)32. - ISSN 0021-8561 - p. 7829 - 7837.
    enzymatic-synthesis - esters - esterification - oligosaccharides - viscoelasticity - lipase - shear
    In this study, the rheological properties of interfaces stabilized by oligofructose fatty acid esters were elucidated. First, the properties of interfaces stabilized by monoesters (ME), diesters (DE), lauric acid (LA), oligofructose (OF), and mixtures of ME with DE, LA, or OF were studied. Second, the properties of interfaces stabilized by the crude product (CP) containing ME, DE, LA, and OF were studied. The dependency of the dilatational modulus on frequency and deformation amplitude indicated the possible formation of a soft glass phase for ME, and a viscous interface for DE. When ME and DE were mixed at a ratio of 0.8/0.2, the experimental results suggest that the interfacial structure consists of islands of a glass phase formed by ME, dispersed in a 2D viscous phase of DE. CP stabilized interfaces, where the ratio ME/DE was higher, lead to a different rheological response. The ratio ME/DE plays an important role in the surface properties of the CP. This may have significant consequences for applications in macroscopic systems such as foams.
    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.
    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
    Bacterial cell surface deformation under external loading
    Chen, Y. ; Norde, W. ; Mei, H.C. van der; Busscher, H.J. - \ 2012
    mBio 3 (2012)6. - ISSN 2150-7511 - 8 p.
    atomic-force microscopy - staphylococcus-aureus - mechanical-properties - adhesion - biofilms - model - viscoelasticity - peptidoglycan - contact - removal
    Viscoelastic deformation of the contact volume between adhering bacteria and substratum surfaces plays a role in their adhesion and detachment. Currently, there are no deformation models that account for the heterogeneous structure and composition of bacteria, consisting of a relatively soft outer layer and a more rigid, hard core enveloped by a cross-linked peptidoglycan layer. The aim of this paper is to present a new, simple model to derive the reduced Young’s modulus of the contact volume between adhering bacteria and substratum surfaces based on the relationship between deformation and applied external loading force, measured using atomic force microscopy. The model assumes that contact is established through a cylinder with constant volume and does not require assumptions on the properties and dimensions of the contact cylinder. The reduced Young’s moduli obtained (8 to 47 kPa) and dimensions of the contact cylinders could be interpreted on the basis of the cell surface features and cell wall characteristics, i.e., surfaces that are more rigid (because of either less fibrillation, less extracellular polymeric substance production, or a higher degree of cross-linking of the peptidoglycan layer) had shorter contact cylinders and higher reduced Young’s moduli. Application of an existing Hertz model to our experimental data yielded reduced Young’s moduli that were up to 100 times higher for all strains investigated, likely because the Hertz model pertains to a major extent to the more rigid peptidoglycan layer and not only to the soft outer bacterial cell surface, involved in the bond between a bacterium and a substratum surface.
    Does size matter? Elasticity of compressed suspensions of colloidal- and granular-scale
    Menut, P. ; Seiffert, S. ; Sprakel, J.H.B. ; Weitz, D.A. - \ 2012
    Soft Matter 8 (2012)1. - ISSN 1744-683X - p. 156 - 164.
    complex fluids - rheology - emulsions - pastes - viscoelasticity - particles - glasses - slip
    We investigate the mechanics of dense packing of very small, colloidal-scale, and larger, granular-scale microgel particles. At low particle concentration, thermally induced Brownian motion of the particles is important for the colloidal-scale systems; in contrast, such Brownian motion is irrelevant at particle packing fractions beyond jamming. As a consequence, colloidal and granular systems behave very similarly under these conditions. At sufficiently high compression of the microgel particles, their polymeric nature sets the scale of the osmotic pressure and shear modulus of the whole packing, in direct analogy with macroscopic, continuous polymer gels. This observation suggests that the particulate nature of microgels is inconsequential for their linear elasticity in a highly packed state. In contrast, the particulate nature of the microgels does become essential when the packed suspensions are forced to yield and flow; here, the differences between colloidal- and granular-scale particles are marked.
    Physical gels based on charge-driven co-assembly
    Lemmers, M. - \ 2012
    Wageningen University. Promotor(en): Martien Cohen Stuart, co-promotor(en): Jasper van der Gucht. - [S.l. : s.n. - ISBN 9789461731180 - 187
    gels - zelf-assemblage - visco-elasticiteit - ladingskenmerken - gels - self assembly - viscoelasticity - charge characteristics

    Gels are used in a variety of products ranging from personal care products and food products to explosives. An important area where aqueous physical gels are applied is the water-based coatings industry. Currently, classical associative thickeners are used to form transient networks based on hydrophobic interactions. Although this technology has greatly improved the properties of water-based coatings, there remain some problems related to the use of these classical associative thickeners.

    In this Thesis we investigate aqueous physical gels based on interconnected polyelectrolyte complex micelles, as a new two-component associative thickener. The physical gels are prepared from an ABA triblock copolymer, with charged A-blocks and a neutral hydrophilic B-block, mixed with either an oppositely charged homopolymer or nanoparticle. Electrostatic interaction is the driving force for association of the oppositely charged components, leading to transient networks of interconnected flowerlike micelles or particles, depending on the origin of the oppositely charged component. The fact that we deal with a two-component system, as well as a completely different driving force for association, could potentially solve some of the current problems related to the use of the classical associative thickeners.

    Throughout this Thesis we have tried to link the microstructure of the gels to the macroscopic properties. We do so by combining microscopic experimental techniques, such as (dynamic) light scattering, small-angle X-ray scattering and (cryo-) scanning electron microscopy with macroscopic experimental techniques such as rheometry.

    In chapter 2 we show that we successfully prepared an aqueous multi-responsive reversible gel based on the bridging of polyelectrolyte complex micelles. At low concentrations these two oppositely charged polymers co-assemble spontaneously to form flowerlike polyelectrolyte complex micelles. If two micelles come close enough to each other, the micelles can become connected to each other, because a triblock copolymer can stick both end-blocks in two different micellar cores. This bridging is reversible, meaning that the micelles are continuously connected and disconnected. At high concentrations enough micelles become interconnected to form a percolating path through the sample, hence the solution becomes a physical gel. Due to the electrostatic driving force for the co-assembly of micelles, these gels are truly multi-responsive.

    The influence of the charge ratio on the formation of polyelectrolyte complex micelles and their networks is studied in detail in chapter 3. Our measurements suggest an asymmetry, with respect to the charge stoichiometric point, in the shape and size of the co-assembled complexes.

    In chapter 4 we take a closer look at the network topology and how this is influenced by total polymer concentration and salt concentration.

    In chapter 5 we show that it is possible to use charged inorganic nanoparticles as nodes in a transient network bridged by triblock copolymers with charged end-blocks. Since gels of this kind have never been described before, we named this class of gels 'Complex Composite Gels'.

    Rheology of interfaces stabilized by a 2D suspension of anisotropic particles: a classical irreversible thermodynamics theory
    Sagis, L.M.C. - \ 2011
    Soft Matter 7 (2011)17. - ISSN 1744-683X - p. 7727 - 7736.
    nonequilibrium thermodynamics - superficial viscosity - general formalism - latex-particles - complex fluids - liquid - liquid/liquid - dynamics - viscoelasticity - gas/liquid
    Surface rheological properties have a significant impact on the stability of particle-stabilized emulsions and foams. Interfaces stabilized by anisotropic particles display a highly nonlinear surface rheology, even at relatively small deformation rates. The nonlinearity of the response is the result of changes in the microstructure of the interface, induced by the applied deformation. The particles are oriented in the direction of the imposed flow field, and this leads to a decrease in the surface shear viscosity (shear thinning). In this paper we derive nonlinear constitutive equations for the surface stress tensor of an interface stabilized by a mixture of anisotropic particles and low molecular weight surfactants, using the classical irreversible thermodynamics formalism. These equations are valid in the low shear regime, where departures from linear behavior are still small. The effect of the microstructure of the interface on the rheological response is incorporated through the particle orientation tensor Qs. The constitutive equations are able to predict the shear thinning behavior observed experimentally for this type of interface.
    The formation and deformation of protein structures with viscoelastic properties
    Riemsdijk, L.E. van - \ 2011
    Wageningen University. Promotor(en): Rob Hamer; Remko Boom, co-promotor(en): Atze Jan van der Goot. - S.l. : s.n. - ISBN 9789085858638 - 239
    eiwitten - nieuwe eiwitten - visco-elasticiteit - wei-eiwit - chemische structuur - moleculaire structuur - deeg - proteins - novel proteins - viscoelasticity - whey protein - chemical structure - molecular conformation - doughs

    This study describes the formation of a gluten substitute.

    Chapter 1 describes the properties that are necessary to obtain a gluten substitute.

    Chapter 2 describes the formation and properties of protein particle suspensions. Two proteins with different intrinsic properties, gelatin and whey protein, were selected as model materials.

    Chapter 3 describes the effects of simple shear flow on the formation and properties of gelatin particle suspensions. The application of well-defined simple shear flow during phase separation was used to control the protein particle size in a gelatin–dextran system.

    Chapter 4 describes the formation and properties of whey protein particle suspensions having different particle sizes and different abilities to form disulphide bonds. Application of shear during their formation was used.

    Chapter 5 describes a novel concept for making elastic dough through combining a whey protein particle suspension with native wheat starch. Three differently structured whey protein suspensions were evaluated.

    Chapter 6 discusses the use of the whey protein particle suspensions prepared and used in chapter 5 for baking bread.

    Chapter 7 describes the role of molecular properties on the final dough and bread that were discussed in chapters 5 and 6.

    Chapter 8 summarizes the main findings of the project on “The formation and deformation of protein structures with viscoelastic properties”.

    Modelling Surface Rheology of Complex Interfaces with Extended Irreversible Thermodynamics
    Sagis, L.M.C. - \ 2010
    Physica A 389 (2010)4. - ISSN 0378-4371 - p. 673 - 684.
    superficial viscosity - dilational properties - liquid interface - protein layers - equation - fluids - viscoelasticity - monolayer - dynamics - behavior
    The rheological properties of the interfaces in complex multiphase systems often play a crucial role in the dynamic behavior of these systems. For example, these properties affect the dynamics of emulsions, of dispersions of vesicles, of biological fluids, or of free surface flows. In the past three to four decades a vast amount of literature has been produced dealing with the rheological properties of interfaces stabilized by low molecular weight surfactants, proteins, (bio)polymers, lipids, colloidal particles, and various mixtures of these surface active components. The data of these surface rheological experiments are often analyzed with ad hoc generalizations of rheological models used for the analysis of rheological properties of bulk phases. The validity of these generalizations is in general not discussed. Here we show how the extended irreversible thermodynamics (EIT) formalism can be used to generate a wide range of thermodynamically admissible constitutive models for the surface stress tensor, which not only encompass currently used constitutive models, but also suggest several new ones, particularly useful for modelling the nonlinear response of interfaces
    Diffusing Wave Spectroscopy Used to Study the Influence of Shear on Aggregation
    Ruis, H.G.M. ; Venema, P. ; Linden, E. van der - \ 2008
    Langmuir 24 (2008)14. - ISSN 0743-7463 - p. 7117 - 7123.
    multiple light-scattering - sol-gel transition - gelation - flow - suspensions - emulsions - milk - viscoelasticity - dispersions - dynamics
    In this study, diffusing wave spectroscopy (DWS) is used to investigate the effect of shear on a food-related aggregating emulsion. The principle of the method is validated using a nonaggregating, nearly monodisperse latex suspension. In general, with increasing shear rate the diffusive motion of the scatterers becomes negligible compared to the convective motion. This causes a decrease in the decay time of the autocorrelation curves and a change in the form of the autocorrelation curves from nearly exponential to Gaussian. This is reflected in the exponent of the mean square displacement that changes from 1 to 2. The effect of shear on the acidification of a sodium caseinate-stabilized emulsion was studied by DWS and by rheometry. The emulsion droplets in the food-related emulsion were uniformly dispersed at neutral pH. Upon acidification down to a pH of 5.2 0.05, the emulsion showed Newtonian behavior with constant viscosity over the whole pH range. At pH 5.17 0.05, independent of the applied shear rate during acidification, the viscosity suddenly increased. From this point on, the emulsion showed shear-thinning behavior. The photon-transport mean free path (l*) was not influenced by the applied shear rate and did not change down to pH 5.2 0.05. Close to this pH, l* increased, and the decay of the autocorrelation curves shifted to longer correlation times when shear rates smaller than 1 s¿1 were applied. At lower pH (5.05 0.05), l* started to fluctuate, and the autocorrelation curves no longer decayed to zero, indicating that at these shear rates the system behaved nonergodicly. Assuming that the convective motion and the Brownian motion are independent of each other, the mean square displacement as a result of Brownian motion was determined. From this, the sol¿gel point and the radius of the aggregates at this point as a function of the shear rate was determined. The results indicated that the radius of the aggregates at the sol¿gel transition decreased with increasing shear rate and suggested that shear will result in a more open structure of the network formed by the aggregates
    Rheological studies of thermosensitive triblock copolymer hydrogels
    Vermonden, T. ; Besseling, N.A.M. ; Steenbergen, M.J. van; Hennink, W.E. - \ 2006
    Langmuir 22 (2006)24. - ISSN 0743-7463 - p. 10180 - 10184.
    aqueous-solutions - gel point - poly(ethylene glycol) - polymeric micelles - viscoelasticity - dependence - systems
    Hydrogel formation by physical cross-linking is a developing area of research toward materials suitable for pharmaceutical and biomedical applications. Polymers exhibiting lower critical solution temperature (LCST) behavior in aqueous solution are used in this study to prepare hydrogels. Four triblock copolymers (ABA) with thermosensitive poly(N-(2-hydroxypropyl) methacrylamide lactate) A-blocks and a hydrophilic poly(ethylene glycol) B-block have been synthesized. The molecular weight of the hydrophilic PEG block was fixed at 10 kDa, whereas the molecular weight of the pHPMAm - lactate block was varied between 10 and 20 kDa. The rheological characteristics of these polymer hydrogels were studied as a function of temperature, concentration, and the length of the thermosensitive blocks. Gelation occurred rapidly upon increasing the temperature to 37°C, which makes this system suitable as an injectable formulation. The gels became stronger with increasing temperature and concentration, and moreover they behaved as critical gels, which means that G¿ and G¿ follow power laws over the entire frequency range. Surprisingly, with increasing length of the thermosensitive blocks, weaker hydrogels were formed. This trend can be explained by the cross-link density of the physical network, which increases with decreasing length of the thermosensitive blocks
    The effect of shear flow on the percolation concentration of fibrillar protein assemblies
    Veerman, C. ; Sagis, L.M.C. ; Venema, P. ; Linden, E. van der - \ 2005
    Journal of Rheology 49 (2005)2. - ISSN 0148-6055 - p. 355 - 368.
    rod-like macromolecules - rodlike chains subject - rheooptical response - transition-temperatures - collagen protein - light-scattering - gels - ovalbumin - viscoelasticity - birefringence
    The objective of this study was to investigate the effect of shear flow on the percolation concentration (cp) for solutions of fibrillar protein assemblies. Theoretical calculations were performed to obtain cp versus Peclet number. They were based on a random contact model for rodlike particles, making use of a shear dependent excluded volume per fibril. We found cp to increase with increasing Peclet number. Results of flow birefringence measurements were used to obtain the rotational diffusion coefficient at cp, which enables one to transform the theoretically obtained cp(Pe) into a prediction for cp versus shear rate. This prediction was used to fit viscosity measurements as a function of shear rate, near the percolation threshold. A satisfactory fit was found indicating that the percolation threshold, cp, as function of shear rate can be predicted by combining theory and optical measurements.
    Equilibrium polymers in solution and at interfaces
    Gucht, J. van der - \ 2004
    Wageningen University. Promotor(en): Gerard Fleer; Martien Cohen Stuart, co-promotor(en): N.A.M. Besseling. - [S.I.] : s.n. - ISBN 9789058089632 - 293
    polymeren - hydrofiele polymeren - evenwicht - grensvlak - waterstofbinding - reologische eigenschappen - visco-elasticiteit - polymers - hydrophilic polymers - equilibrium - interface - hydrogen bonding - rheological properties - viscoelasticity - cum laude
    cum laude graduation (with distinction)
    Extruder goed toepasbaar voor continue extractie en deegkneden
    Stegeman, D. ; Luyten, H. - \ 2000
    Voedingsmiddelentechnologie 33 (2000)7. - ISSN 0042-7934 - p. 30 - 32.
    uitpersing - verwerking - broodbereiding - brood - vloeistofmechanica - prestatieniveau - kwaliteit - reologie - visco-elasticiteit - uitrusting - voedselindustrie - voedseltechnologie - productieprocessen - machines - extrusion - processing - breadmaking - bread - fluid mechanics - performance - quality - rheology - viscoelasticity - equipment - food industry - food technology - production processes - machines
    De voortdurende ontwikkeling van de apparatuur zorgt voor een continue uitbreiding van de toepassingsmogelijkheden van de extrusietechnologie. De werking van het extrusie-extractieproces is behandeld en schematisch weergegeven
    Mechanical properties of fats in relation to their crystallization
    Kloek, W. - \ 1998
    Agricultural University. Promotor(en): P. Walstra; T. van Vliet. - S.l. : Kloek - ISBN 9789054859475 - 241
    plantaardige oliën - plantaardige vetten - kristallisatie - vloeistofmechanica - reologie - visco-elasticiteit - plant oils - plant fats - crystallization - fluid mechanics - rheology - viscoelasticity - cum laude

    Crystallization in bulk fats is always initiated by a heterogeneous nucleation process. Homogeneous nucleation conditions for fully hydrogenated palm oil (HP) in sunflower oil (SF) could be obtained by emulsifying the fat phase into very fine droplets and using sodium caseinate as an emulsifier. The crystallization kinetics of such a dispersion was determined by means of ultra-sound velocity measurements and could be modeled by a classical nucleation model. The temperature dependency of the kinetics yielded a surface free energy for nucleus formation of about 4mJ×m -2and almost the whole triglyceride molecule should be in the right conformation for incorporation in a nucleus.

    The isothermal crystallization kinetics of bulk solutions of HP in SF in theβ' polymorph could be described well by combination of a classical nucleation function and an empirical crystal growth rate equation taking into account the decrease of supersaturation during crystallization. This yielded a surface free energy for heterogeneous nucleus formation of 3.8 mJ×m -2and about 80 % of the triglyceride molecule to be in the right conformation for incorporation in a nucleus.

    Fat crystals in oil exhibit Brownian motion and attract each other due to van der Waals attraction that results in dispersions with fat crystal aggregates. The structure of the fat crystal aggregates could be described well by a fractal approach as was shown by light scattering and modeling of the viscosity as function of shear rate. Low volume fraction HP/SF dispersion yielded fractal dimensionalities of about 1.7 - 1.8 which is indicative for rapid diffusion limited aggregation and increased with increasing shear rate. Volume fraction of solids of about 0.005 appeared to be sufficient to form a weak gel built from aggregates with a dimensionality of about 1.7 - 1.8.

    Simultaneous crystallization and aggregation of high volume fraction HP/SF dispersion leads to compaction of aggregates after primary network formation. The elastic moduli of these dispersion can be described by higher apparent dimensionalities. Crystallization after gelation also makes the stress carrying strands less flexible and leads to sintering of the fat crystals. The latter occured more easily for fats having a broad fatty acid distribution. Sintering of fat crystals was shown by comparison of elastic moduli and loss tangents before and the development of moduli after mechanical treatment. From model calculations, it was shown that for dispersions in which van der Waals forces are the only interaction forces, crystals can easily bend on deformation of the crystal network.

    Application of shear during crystallization leads to more compact crystal aggregates as was shown by determination of elastic moduli in compression on dispersions that were crystallized in a surface scraping heat exchanger.

    Oppervlakte-reologische eigenschappen bepalen vorming en stabiliteit schuim.
    Kalsbeek, H.K.A.I. van; Aken, G.A. van; Bos, M. ; Prins, A. - \ 1997
    Voedingsmiddelentechnologie 30 (1997)6. - ISSN 0042-7934 - p. 11 - 14.
    deformatie - vloeistofmechanica - voedselindustrie - voedseltechnologie - verbetering - innovaties - materialen - modernisering - eigenschappen - eiwitten - reologie - visco-elasticiteit - deformation - fluid mechanics - food industry - food technology - improvement - innovations - materials - modernization - properties - proteins - rheology - viscoelasticity
    Het onderzoek naar het schuim- en emulgeergedrag van eiwitten en peptiden. Het Innovatiegericht Onderzoeks Programma Industriele Eiwitten wordt in projecten uitgevoerd door de Landbouwuniversiteit te Wageningen en het Nederlands Instituut voor Zuivelonderzoek (NIZO)
    Biochemical parameters of gluten in relation to fundamental rheological properties.
    Sliwinski, E. ; Kolster, P. ; Vliet, T. van - \ 1996
    Industrial Proteins 3 (1996)1. - ISSN 1381-0022 - p. 9 - 11.
    gluten - graaneiwitten - tarwegluten - reologische eigenschappen - mechanische eigenschappen - veerkracht - plasticiteit - visco-elasticiteit - bakkwaliteit - broodbereiding - gluten - cereal proteins - wheat gluten - rheological properties - mechanical properties - elasticity - plasticity - viscoelasticity - baking quality - breadmaking
    Dit IOP Industriële Eiwitten project is gericht op het leggen van relaties tussen biochemische karakteristieken van tarwegluten en hun reologisch gedrag. Op deze wijze wordt inzicht verkregen in structuurfunctie relaties van tarwegluten, met name gericht op bakkerijtoepassingen. Voor dit onderzoek zijn zes Europese tarwe-variëteiten geselecteerd, die vergelijkbare eiwitgehaltes hebben, maar een groot verschil in bakkwaliteit vertonen. Kwaliteitsverschillen tussen deze variëteiten uiten zich het meest in de benodigde kneedtijd om optimale bakkwaliteit te bereiken. Er zijn duidelijke aanwijzingen dat hieraan een aantal biochemische factoren ten grondslag liggen zoals de hoeveelheid van het glutenine polymeer, de polymerisatie ervan en de mate van fysische interacties tussen de gluten-eiwitten
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