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.