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Temperature controlled sequential gelation in composite microgel suspensions
Appel, J. ; Lange, N. de; Kooij, H.M. van der; Laar, T.X. van de; Hove, J.B. ten; Kodger, T.E. ; Sprakel, J.H.B. - \ 2015
Particle and Particle Systems Characterization 32 (2015)7. - ISSN 0934-0866 - p. 764 - 770.
attractive particles - liquid - gels
Depending on the volume fraction and interparticle interactions, colloidal suspensions can exhibit a variety of physical states, ranging from fluids, crystals, and glasses to gels. For microgel particles made of thermoresponsive polymers, both parameters can be tuned using environmental parameters such as temperature and ionic strength, making them excellent systems to experimentally study state transitions in colloidal suspensions. Using a simple two-step synthesis it is shown that the properties of composite microgels, with a fluorescent latex core and a responsive microgel shell, can be finely tuned. With this system the transitions between glass, liquid, and gel states for suspensions composed of a single species are explored. Finally, a suspension of two species of microgels is demonstrated, with different transition temperatures, gels in a sequential manner. Upon increasing temperature a distinct core–sheath structure is formed with a primary gel composed of the species with lowest transition temperature, which acts as a scaffold for the aggregation of the second species.
Organogel formation via supramolecular assembly of oleic acid and sodium oleate
Nikiforidis, C.V. ; Gilbert, E.P. ; Scholten, E. - \ 2015
RSC Advances : An international journal to further the chemical sciences 5 (2015)59. - ISSN 2046-2069 - p. 47466 - 47475.
system - solvent - liquid - amphiphiles - particles - micelles - lecithin - bilayers - laurate - water
To create materials with novel functionalities, the formation of gels within hydrophobic media has become popular. This is often accomplished through the assembly of low molecular weight organogelators into a variety of complex phases through intermolecular interactions. In the case of edible materials, the assembly of saturated fatty acids to form fat crystal networks is often used for structuring. Here, the first example of structuring with unsaturated fatty acids is reported, namely mixtures of oleic acid and sodium oleate, to structure edible lipid phases. Small-angle scattering demonstrates that the resultant structures, which vary with oleic acid and sodium oleate molar ratio, comprise either inverse micellar or lamellar phases, combined with the formation of crystalline space-filling networks. Network formation was found for filler concentrations above 10 wt%. Rheological measurements show that gel strength depends on the ratio of oleic acid to sodium oleate, and is greater when only oleic acid is used. The addition of up to 1.5 wt% of water enhanced the strength of the organogels, probably through supplementary hydrogen bonding but, for concentrations greater than 2.0 wt%, the assembly was inhibited leading to collapse of the gel.
Multiphysics pore-scale model for the rehydration of porous foods
Sman, R.G.M. van der; Vergeldt, F.J. ; As, H. van; Dalen, G. van; Voda, A. ; Duynhoven, J.P.M. van - \ 2014
Innovative Food Science and Emerging Technologies 24 (2014). - ISSN 1466-8564 - p. 69 - 79.
moisture transport - mass-transfer - water - imbibition - quality - media - pressure - lattice - liquid - fruits
In this paper we present a pore-scale model describing the multiphysics occurring during the rehydration of freeze-dried vegetables. This pore-scale model is part of a multiscale simulation model, which should explain the effect of microstructure and pre-treatments on the rehydration rate. Simulation results are compared to experimental data, obtained by MRI and XRT. Time scale estimates based on the pore-scale model formulation agree with the experimental observations. Furthermore, the pore-scale simulation model provides a plausible explanation for the strongly increased rehydration rate, induced by the blanching pre-treatment. Industrial relevance The increased insight in the physical processes governing the rehydration of porous or freeze-dried foods gives more rationale for optimizing all processing steps. Industry is seeking for means to give dried fruits and vegetables more convenience, but also higher quality concerning health and texture. This study shows that blanching pretreatment prior to freeze-drying strongly enhances the rehydration, while the loss of nutrients is hardly affected.
Hydrodynamic Interactions between Two Equally Sized Spheres in Viscoelastic Fluids in Shear Flow
Snijkers, F. ; Pasquino, R. ; Vermant, J. - \ 2013
Langmuir 29 (2013)19. - ISSN 0743-7463 - p. 5701 - 5713.
spherical-particles - boger fluids - suspensions - rheology - alignment - microstructure - aggregation - evolution - liquid
The effect of using a viscoelastic suspending medium, on the;in-plane hydrodynamic interaction between two equally sized spheres in shear flow is studied experimentally to understand flow-induced assembly behavior (i.e., string formation). A counterrotating device equipped with a Couette geometry is used together with quantitative videomicroscopy. To evaluate the effects of differences in rheological properties of the suspending media, fluids have been selected that highlight specific constitutive feature's. These include a reference Newtonian fluid (N), a,constant-viscosity, high-elasticity Boger fluid (BF), a wormlike micellar surfactant solution with a, single dominant relaxation time (WMS), and a broad spectrum shear-thinning elastic polymer solution (ST). As expected, the trajectories are symmetric in the Newtonian fluid. In the BF, the midpoints. of the spheres are observed to remain in the same plane before and after,the interaction, as in the Newtonian fluid, although the path lines are in this case no longer symmetric. Interactions in the, ST and WMS are highly asymmetric. Two, fundamentally different kinds of path lines are Observed in the WMS and ST: reversing and Open trajectories: The type of trajectory depends on the initial Configuration of the spheres with respect to:each,other and on the shear rate. On the basis of the obtained results, shear-thinning of the viscosity seems to be the key rheological parameter that determines the overall nature of, the interactions rather than the relative magnitude of the normal stress differences.
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.
Supported La2O3 and MgO nanoparticles as solid base catalysts for aldol reaction while suppressing dehydration at room temperaure
Frey, A.M. ; Kumar Karmee, S. ; Jong, K.P. de; Bitter, J.H. ; Hanefeld, U. - \ 2013
ChemCatChem 5 (2013). - ISSN 1867-3880 - p. 594 - 600.
platinum catalysts - carbon nanofibers - liquid - hydrotalcites - oxide - hydrogenation - condensation - hydrocarbons - chemicals - basicity
La2O3 and MgO nanoparticles (3–4 nm) supported on carbon nanofibers were evaluated as solid base catalysts for the aldol reaction of benzaldehyde and acetone at room temperature. Both catalysts were found to be highly active and selective with respect to 4-hydroxy-4-phenylbutan-2-one, thus suppressing the elimination of H2O, which is a challenge for this reaction. La2O3 nanoparticles were more stable towards water, which makes them more applicable than MgO nanoparticles as a solid base catalyst for this reaction.
Sporulation environment of emetic toxin-producing Bacillus cereus strains determines spore size, heat resistance and germination capacity
Voort, M. van der; Abee, T. - \ 2013
Journal of Applied Microbiology 114 (2013)4. - ISSN 1364-5072 - p. 1201 - 1210.
wet-heat - bacterial-spores - dipicolinic acid - subtilis spores - atcc-14579 - thuringiensis - radiation - anthracis - kinetics - liquid
Aim Heat resistance, germination and outgrowth capacity of Bacillus cereus spores in processed foods are major factors in causing the emetic type of gastrointestinal disease. In this study, we aim to identify the impact of different sporulation conditions on spore properties of emetic toxin-producing B. cereus strains. Methods and Results Spore properties of eight different emetic toxin-producing strains were tested, with spores produced in five different sporulation conditions: aerated liquid cultures, air–liquid biofilms, 1·5% agar plates, 0·75% agar plates and swarming colonies. Model food studies revealed spores from emetic toxin-producing strains to germinate efficiently on meat broth- and milk-based agar plates, whereas germination on rice-based agar plates was far less efficient. Notably, spores of all strains germinated efficiently when 0·1% meat broth was added to the rice plates. Analysis of spores derived from different environments revealed large diversity and showed biofilm spores for the strains tested to be the largest in size, the most heat resistant and with the lowest germination capacity. Conclusions Sporulation in complex conditions such as biofilms and surface swarming colonies increases heat resistance and dormancy of spores. Significance and impact of the study The results obtained imply the importance of sporulation conditions on spore properties of emetic toxin-producing B. cereus strains, as occur for instance in food processing. Keywords Bacillus cereus; biofilm; food poisoning; heat resistance; spore germination; swarming
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.
Mechanism of perforation based on spreading properties of emulsified oils
Hilz, E. ; Vermeer, A.W.P. ; Cohen Stuart, M.A. ; Leermakers, F.A.M. - \ 2012
Atomization and Sprays 22 (2012)12. - ISSN 1044-5110 - p. 1053 - 1075.
fan spray nozzles - surfactant solutions - hydraulic nozzles - drift reduction - droplet-size - liquid - formulation - emulsions - adjuvants - breakup
During an agricultural application, sprays are formed by atomization through a hydraulic nozzle. Fine spray droplets can cause off-target contamination with agrochemicals when they move by air from the application site. Dilute oil-in-water emulsions create coarser sprays than water, when atomized through a flat fan nozzle, and are therefore interesting for drift control purposes. However, different emulsions influence the spray droplet size to a different extent and this effect is not yet well understood. With an aim to develop products with drift reduction properties it is necessary to comprehend the mechanism of interactions between emulsion droplets and the continuous aqueous phase. In this study, we analyze systematically the effects of different physical properties of oils on the spray formation process and investigate how the type of the emulsified oil, the concentration of emulsifier, emulsion droplet size, the spreading properties of the emulsified oil, and its viscosity influence the spray droplet size. Based on the experimental data, we propose a spray formation mechanism of dilute oil-in-water emulsions. We argue that when the liquid sheet leaves the nozzle, some emulsion droplets might merge with the air/water interface of the liquid sheet, spread there and induce a subphase flow, which, reinforced by perturbations in a turbulent flow, will initiate spray atomization. In mixtures of a dilute emulsion and a water soluble surfactant, dynamic surface tension at the interface of the liquid sheet controls the spray formation process. Surfactants located at the interface form a kinetic barrier for the spreading emulsion droplets and thus delay the atomization onset.
Ternary fluid mixture confined between surfaces: Surface-induced phase transition and long-range oscillatory forces
Banerjee, S. ; Mulder, P. ; Kleijn, J.M. ; Cohen Stuart, M.A. - \ 2012
Chemistry Letters / Chemical Society of Japan 41 (2012)10. - ISSN 0366-7022 - p. 1113 - 1115.
capillary condensation - lamellae formation - liquid - systems
Surface forces between a soft cellulose surface and a hard silica particle were measured in wet hexane with or without the addition of a surfactant. In the absence of a surfactant, the adhesion force was enhanced as a result of capillary condensation of water. The effect of the surfactant in reducing the adhesion force with increasing water content in a ternary fluid mixture of a surfactant, hexane, and water was systematically studied. Long-range oscillations of the force–distance curves are discussed in the light of various mesophase compositions in the bulk.
Effect of surface roughness and softness on water capillary adhesion in apolar media
Banerjee, S. ; Mulder, P. ; Kleijn, J.M. ; Cohen Stuart, M.A. - \ 2012
The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment, & General Theory 116 (2012)25. - ISSN 1089-5639 - p. 6481 - 6488.
atomic-force microscope - lamellae formation - phase-separation - mica surfaces - thin-film - condensation - kinetics - liquid - alkanes - pore
The roughness and softness of interacting surfaces are both important parameters affecting the capillary condensation of water in apolar media, yet are poorly understood at present. We studied the water capillary adhesion between a cellulose surface and a silica colloidal probe in hexane by AFM force measurements. Nanomechanical measurements show that the Young’s modulus of the cellulose layer in water is significantly less (7 MPa) than in hexane (7 GPa). In addition, the cellulose surface in both water and hexane is rather rough (6–10 nm) and the silica probe has a comparable roughness. The adhesion force between cellulose and silica in water-saturated hexane shows a time-dependent increase up to a waiting time of 200 s and is much (2 orders of magnitude) lower than that expected for a capillary bridge spanning the whole silica probe surface. This suggests the formation of one or more smaller bridges between asperities on both surfaces, which is confirmed by a theoretical analysis. The overall growth rate of the condensate cannot be explained from diffusion mediated capillary condensation alone; thin film flow due to the presence of a wetting layer of water at both the surfaces seems to be the dominant contribution. The logarithmic time dependence of the force can also be explained from the model of the formation of multiple capillary bridges with a distribution of activation times. Finally, the force–distance curves upon retraction show oscillations. Capillary condensation between an atomically smooth mica surface and the silica particle show less significant oscillations and the adhesion force is independent of waiting time. The oscillations in the force–distance curves between cellulose and silica may stem from multiple bridge formation between the asperities present on both surfaces. The softness of the cellulose surface can bring in additional complexities during retraction of the silica particle, also resulting in oscillations in the force–distance curves.
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.
Monitoring the development of a microbial electrolysis cell bioanode using an electrochemical quartz crystal microbalance
Kleijn, J.M. ; Lhuillier, Q. ; Jeremiasse, A.W. - \ 2010
Bioelectrochemistry 79 (2010)2. - ISSN 1567-5394 - p. 272 - 275.
polymer-films - hydrogen - surface - frequency - operation - adhesion - biofilms - systems - liquid
In this paper we explored the use of an electrochemical quartz crystal microbalance (QCM) to follow the development of electrochemically active biofilms on electrodes. With this technique it should be possible to monitor simultaneously the increase in biomass and the current generated by the electrogenic bacteria in the biofilm. We monitored the adsorption and the subsequent growth of bacteria that are used in microbial electrolysis cells, on a gold electrode (anode). After attachment it took about 3 h for the bacteria to start to grow and develop a biofilm. Although the current was still relatively low, there is a clear correlation with the increase in biomass. The method is promising for the further investigation of the development of biofilms on electrodes (bioelectrodes).
Effect of viscosity on appetite and gastro-intestinal hormones
Zijlstra, N. ; Mars, M. ; Wijk, R.A. de; Westerterp-Plantenga, M.S. ; Holst, J.J. ; Graaf, C. de - \ 2009
Physiology and Behavior 97 (2009)1. - ISSN 0031-9384 - p. 68 - 75.
food-intake - physical state - eating behavior - meal viscosity - body-weight - satiety - humans - carbohydrate - liquid - hunger
In previous studies we showed that higher viscosity resulted in lower ad libitum intake and that eating rate is an important factor. In this study we aimed to explore the effect of viscosity on the gastro-intestinal hormones ghrelin, CCK-8 and GLP-1. Thirty-two subjects (22 ± 2 y, BMI 21.9 ± 2.2 kg/m2) participated in this cross-over study. Subjects received a fixed amount of a chocolate flavored milk-based liquid or semi-solid product similar in energy density and macronutrient composition. Before intake and 15, 30, 60 and 90 min thereafter, appetite was rated and blood was drawn to determine glucose, CCK-8, active ghrelin, desacyl ghrelin and GLP-1 concentrations. After the last blood withdrawal, subjects were offered a chocolate cake meal to consume ad libitum. In the appetite ratings we observed a small effect showing that the semi-solid product is apparently considered as more satisfying than the liquid. There was a significant product effect for fullness (p 0.03), desire to eat (p 0.04), appetite something sweet (p 0.002) and prospective consumption (p 0.0009). We observed no clear effect of viscosity on gastro-intestinal hormones. Only for desacyl ghrelin there was a significant product effect (p 0.004). Concentrations were consistently higher after intake of the semi-solid product. Ad libitum intake of the chocolate cake was 102 ± 55 g after the liquid and 96 ± 46 g after the semi-solid product (ns). The results of our study show a similar response of the gastro-intestinal hormones CCK-8, ghrelin and GLP-1 after a fixed preload of a liquid and semi-solid product similar in energy- and macronutrient composition.
The effect of viscosity on ad libitum food intake
Zijlstra, N. ; Mars, M. ; Wijk, R.A. de; Westerterp-Plantenga, M. ; Graaf, C. de - \ 2008
International Journal of Obesity 32 (2008). - ISSN 0307-0565 - p. 676 - 683.
sugar-sweetened beverages - body-weight - physical state - human-milk - satiety - humans - consumption - ratings - liquid - hunger
Background: Energy-yielding liquids elicit weak suppressive appetite responses and weak compensatory responses, suggesting that liquid calories might lead to a positive energy balance. However, data is often derived from foods differing in many characteristics other than viscosity. Objective: To investigate the effect of viscosity on ad libitum food intake in real-life setting and to investigate whether a difference in ad libitum intake is related to eating rate and/or eating effort. Design: In real-life setting 108 nonrestrained subjects (267 years, BMI 22.72.4 kg m-2) received a chocolate flavored liquid, semi-liquid and semi-solid milk-based product, similar in palatability, macronutrient composition and energy density. In laboratory setting 49 nonrestrained subjects (246 years, BMI 22.22.3 kg m-2) received the liquid or semi-solid product. Effort and eating rate were controlled by means of a peristaltic pump. Results: In real-life setting the intake of the liquid (809396 g) was respectively 14 and 30% higher compared to the semi-liquid (699391 g) and semi-solid product (566311 g; P
PROP sensitivity reflects sensory discrimination between custard desserts
Wijk, R.A. de; Dijksterhuis, G. ; Vereijken, P.H. ; Prinz, J.F. ; Weenen, H. - \ 2007
Food Quality and Preference 18 (2007)4. - ISSN 0950-3293 - p. 597 - 604.
taster status - texture - 6-n-propylthiouracil - perception - bitterness - intensity - ptc/prop - liquid - foods
Sensitivity to 6-n-propylthiouracil (PROP) for a group of 180 naïve consumers was related to their perception of 16 commercially available vanilla custard desserts. Rated intensities of taste and texture attributes varied moderately and inconsistently with PROP sensitivity. In contrast, discriminative ability increased with PROP sensitivity resulting in higher numbers of significant differences between pairs of custards. In terms of signal/noise theory, the results indicate that PROP sensitivity enhances the separation of the response signals but does not reduce their noise. The naïve consumers were also compared with highly trained panelists to test whether effects of PROP sensitivity resemble the effects of experience and training. Naïve consumers and trained panelists responded similarly with respect to taste and texture sensations such as creaminess and thickness, but were clearly different with respect to others such as heterogeneity and fattiness. Trained panelists demonstrated even stronger discriminative abilities than consumers with high PROP sensitivities for some attributes but weaker abilities for others. A practical implication of these findings is that selection criteria for participation in sensory panels should include PROP sensitivity, if the panel is aimed at maximum discriminative performance.
Perceived creaminess of semi-solid foods
Wijk, R.A. de; Terpstra, M.E.J. ; Janssen, A.M. ; Prinz, J.F. - \ 2006
Trends in Food Science and Technology 17 (2006)8. - ISSN 0924-2244 - p. 412 - 422.
oral texture - custard desserts - sensory perception - creamy mouthfeel - attributes - liquid - milk - fat
Results of sensory, physiological and physico-chemical studies from our laboratory on perceived creaminess of semi-solids foods are reviewed. Most results stem from studies using model vanilla custard desserts, allowing systematic variation of fat, flavor and thickener properties. The generalizability of the custard results was verified for yogurts, mayonnaises, white sauces and other semi-solid foods. Creaminess sensations could be decomposed into sensations reflecting either properties of the bulk or of the surface of the oral food bolus. Bulk properties related to the rheological properties of the bolus whereas surface properties related to lubrication and flavor release. Creaminess was inversely related to enzymatic and mechanical induced break-down during oral processing. Starch thickeners generally enhanced creaminess although they suffered from enzymatic break-down compared to non-starch thickeners. It is suggested that the negative effects of break-down were off-set by positive effects of fat migrating to the surface of the bolus. The surfaced fat enhances lubrication and the release of fat-soluble flavors enhance creaminess, especially in low fat starch-based semi-solids. Bulk-related properties were measured by rheological measurements, surface-related properties were measured by friction, and mechanical- and enzymatic break-down properties were measured with a modified rheometer.
Sensory sub-attributes of creamy mouthfeel in commercial mayonnaises, custard desserts and sauces
Weenen, H. ; Jellema, R.H. ; Wijk, R.A. de - \ 2005
Food Quality and Preference 16 (2005)2. - ISSN 0950-3293 - p. 163 - 170.
least-squares regression - semi-solids - texture - creaminess - liquid - perception - acceptance - foods
The sensory components of creamy mouthfeel in commercial mayonnaises, custard desserts and sauces were determined, using multi-variate analysis of the mean sensory ratings obtained from a quantitative descriptive analysis (QDA) panel. Creamy is a particularly interesting attribute, as it is generally well correlated with consumer preference. Texture attributes which were found to contribute positively to creamy mouthfeel included thick, airy, smooth and fatty mouth- or afterfeel, negative contributions were found for rough, heterogeneous, grainy and melting mouth- or afterfeel. Odour (assessed before ingestion) and non-texture trigeminal attributes had little or no effect on creamy mouthfeel, taste/flavour attributes (assessed while the product is in the mouth) did affect creamy mouthfeel, in some cases positively (caramel flavour) and in some cases negatively (broth and cheese flavour). The use of noseclips or the addition of a flavouring substance, confirmed that olfactory cues and/or intranasal sensations have an effect on creamy mouthfeel