Laboratory of Physical Chemistry and Colloid Science

Wageningen, Netherlands

Laboratory of Physical Chemistry and Colloid Science

Wageningen, Netherlands

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Li Y.,Laboratory of Physical Chemistry and Colloid Science | Li Y.,Beijing University of Chemical Technology | Norde W.,Laboratory of Physical Chemistry and Colloid Science | Norde W.,University of Groningen | Kleijn J.M.,Laboratory of Physical Chemistry and Colloid Science
Langmuir | Year: 2012

The interaction of biocompatible polyelectrolytes (chargeable poly(amino acids)) with oxidized starch microgel particles has been studied. The aim was to form a polyelectrolyte complex layer around the outer shell of microgel particles filled with functional ingredients to slow down the release of the ingredients from the gel and make this process less sensitive to salt. First, the distribution of positively charged poly(l-lysine) (PLL) of two different molecular weights ("small", 15-30 kDa, and "large", 30-70 kDa) in the negatively charged gel particles was measured. The small PLL distributes homogeneously throughout the gel particles, but the large PLL forms a shell; i.e., its concentration at the outer layer of the particles was found to be much higher than in their core. This shell formation does not occur at a relatively high salt concentration (0.07 M). The large PLL was selected for further study. It was found that upon addition of PLL to lysozyme-loaded gel particles the protein is exchanged by PLL. The exchange rate increases with increasing pH, in line with the increasing electrostatic attraction between the gel and the polyelectrolyte. Therefore, it was decided to use also a negatively charged poly(amino acid), poly(l-glutamic acid) (PGA), to form together with PLL a stable polyelectrolyte complex shell around the gel particles. This approach turned out to be successful, and the PLL/PGA complex layer effectively slows down the release of lysozyme from the microgel particles at 0.05 M salt. In addition, it was found that the PLL/PGA layer protects the gel particle from degradation by α-amylase. © 2011 American Chemical Society.


Li Y.,Laboratory of Physical Chemistry and Colloid Science | Kleijn J.M.,Laboratory of Physical Chemistry and Colloid Science | Cohen Stuart M.A.,Laboratory of Physical Chemistry and Colloid Science | Slaghek T.,TNO | And 3 more authors.
Soft Matter | Year: 2011

The aim of this paper is to determine the mobility of protein molecules inside oxidized potato starch polymer (OPSP) microgel particles (spherical, 10-20 m in diameter). This provides relevant information for controlled uptake and release applications of such systems. The mobility of Alexa-488 labelled lysozyme inside the microgel is measured by fluorescence recovery after photobleaching (FRAP) in combination with confocal laser scanning microscopy (CLSM). CLSM images show that the protein molecules distribute quite homogeneously over the microgel particles. By fitting the FRAP data with a model based on exchange between bleached and unbleached protein molecules inside the gel, we identified several protein fractions of different mobility. Increasing the salt concentration (NaCl) or the pH causes a shift in the distribution towards the more mobile fractions. This is consistent with earlier uptake and release measurements, which showed that the binding affinity decreases with increasing salt concentration and pH. At low protein concentrations, at which the microgel is not saturated with protein, the mobility of the bound protein molecules is more restricted than at protein concentrations where the uptake is complete. This is attributed to binding of the protein molecules to multiple binding sites. The model explains reasonably the mechanism of protein mobility inside the microgel, indicating that embedded ingredients with charge properties comparable to those of lysozyme can be protected at low salt concentration and low pH. Increasing the salt concentration or the pH triggers the release. © 2011 The Royal Society of Chemistry.


Trappmann B.,University of Cambridge | Gautrot J.E.,University of Cambridge | Connelly J.T.,University of Cambridge | Connelly J.T.,Queen Mary, University of London | And 14 more authors.
Nature Materials | Year: 2012

To investigate how substrate properties influence stem-cell fate, we cultured single human epidermal stem cells on polydimethylsiloxane (PDMS) and polyacrylamide (PAAm) hydrogel surfaces, 0.1 kPa-2.3 MPa in stiffness, with a covalently attached collagen coating. Cell spreading and differentiation were unaffected by polydimethylsiloxane stiffness. However, cells on polyacrylamide of low elastic modulus (0.5 kPa) could not form stable focal adhesions and differentiated as a result of decreased activation of the extracellular-signal- related kinase (ERK)/mitogen-activated protein kinase (MAPK) signalling pathway. The differentiation of human mesenchymal stem cells was also unaffected by PDMS stiffness but regulated by the elastic modulus of PAAm. Dextran penetration measurements indicated that polyacrylamide substrates of low elastic modulus were more porous than stiff substrates, suggesting that the collagen anchoring points would be further apart. We then changed collagen crosslink concentration and used hydrogel-nanoparticle substrates to vary anchoring distance at constant substrate stiffness. Lower collagen anchoring density resulted in increased differentiation. We conclude that stem cells exert a mechanical force on collagen fibres and gauge the feedback to make cell-fate decisions. © 2012 Macmillan Publishers Limited. All rights reserved.


Zhulina E.B.,RAS Institute of Macromolecular Compounds | Leermakers F.A.M.,Laboratory of Physical Chemistry and Colloid Science | Borisov O.V.,University of Pau and Pays de l'Adour
Macromolecules | Year: 2015

We predict theoretically that in contrast to composite brushes of end-tethered linear polymers that exhibit vertical stratification, chemically identical branched macromolecules with different molecular weights and selected architectures can distribute their free ends all over the volume of composite brush and produce a unified polymer density profile. As a result of this, we expect the presence of terminal end-groups of all constituent macromolecular species in the vicinity of the external boundary of such composite brush. The predictions of the analytical theory are supported by numerical self-consistent field calculations. Unified brushes offer new possibilities in the design of polymer-decorated surfaces and might improve our understanding of natural biointerfaces. © 2015 American Chemical Society.


Saglam D.,Top Institute Food and Nutrition | Saglam D.,Wageningen University | Venema P.,Wageningen University | de Vries R.,Laboratory of Physical Chemistry and Colloid Science | And 2 more authors.
Food Hydrocolloids | Year: 2013

In this work heat stability and rheological properties of concentrated whey protein particle dispersions in different dispersing media are studied. Whey protein particles (protein content ∼20% w/v) having an average size of a few microns were formed using a combination of two-step emulsification and heat-induced gelation. Particles were dispersed (volume fraction of particles ∼0.35) in solutions of Na-caseinate, whey protein isolate or gum arabic at different concentrations. The microstructure, particle size distribution and flow behaviour of the dispersions were analyzed before and after heating at 90 °C for 30 min. All dispersions were liquid-like and no significant change in the microstructure was observed after heat treatment. Viscosity measurements showed that both the type and the concentration of the stabilizer influenced the viscosity changes after heat treatment. When 1% (w/w) gum arabic was used as stabilizer no change in the viscosity was observed after heat treatment. However, when Na-caseinate or whey protein isolate was used, viscosity increased in low-shear regime and shear-thickening was observed in high-shear regime. Heat treatment did not significantly alter the zeta potential of the particles, whereas the size of the particles increased after heating due to swelling. The results show that swelling of the particles plays a significant role in the heat stability and rheological properties of these dispersions. © 2012 Elsevier Ltd.


Saglam D.,Top Institute Food and Nutrition | Saglam D.,Wageningen University | Venema P.,Top Institute Food and Nutrition | Venema P.,Wageningen University | And 4 more authors.
Langmuir | Year: 2012

Whey protein particles have several applications in modulating food structure and for encapsulation, but there is a lack of methods to prepare particles with a very high internal protein content. In this study whey protein particles with high internal protein content were prepared through emulsification and heat gelation of 25% (w/w) whey protein isolate solution at different pH (6.8 or 5.5) and NaCl concentrations (50, 200, or 400 mM). Particles formed at pH 6.8 were spherical, whereas those formed at pH 5.5 were irregular and had a cauliflower-like appearance. Both particles had an average size of few micrometers, and the particles formed at pH 5.5 had higher protein content (∼39% w/v) than the particles formed at pH 6.8 (∼18% w/v). Similarly, particle morphology and protein density were also affected by initial NaCl concentration: particles formed at 50 mM NaCl (pH 6.8) were spherical, whereas particles formed at either 200 mM NaCl (pH 6.7) or 400 mM NaCl (pH 6.6) were irregular and protein density of the particles increased with increasing initial NaCl concentration. Whey protein particles formed at pH 5.5 showed an excellent heat stability: viscosity of the suspensions containing approximately 30% of protein particles formed at pH 5.5 did not show any change after heating at 90 °C for 30 min while the viscosity of suspensions containing protein particles prepared at other conditions increased after heating. In summary, whey protein particles with varying microstructure, shape, internal protein density, and heat stability can be formed by using heat-induced gelation of whey protein isolate at different gelling conditions. © 2012 American Chemical Society.


Saglam D.,Top Institute Food and Nutrition | Saglam D.,Wageningen University | Venema P.,Wageningen University | de Vries R.,Laboratory of Physical Chemistry and Colloid Science | van der Linden E.,Wageningen University
Food Hydrocolloids | Year: 2014

Due to aggregation and/or gelation during thermal treatment, the amount of whey proteins that can be used in the formulation of high protein foods e.g. protein drinks, is limited. The aim of this study was to replace whey proteins with whey protein particles to increase the total protein content and heat stability. For this purpose whey protein particles with a size of a few micrometers were formed through emulsification and heat gelation of a 25% (w/w) whey protein isolate (WPI) solution at either pH 5.5 or at pH 6.8. Dispersion of whey protein particles formed at pH 5.5 showed an exceptional heat stability (at pH~7); the viscosity of the dispersions containing a total protein concentration around 18% (w/w) did not change after heating at 90°C for 30min, while a WPI solution already gelled under same heating conditions at protein concentrations around 11% (w/w). Additionally, no gelation was observed in the dispersions prepared by pH 5.5 particles, when the total protein concentration was increased above 20% (w/w). However, due to the increased particle concentration shear-thickening was observed in these samples. Whey protein particles prepared at pH 6.8 showed rather weak stability against heat treatment, mainly as a result of swelling. Protein particles were not resistant to gastric digestion and complete degradation of the particles was observed after a short incubation time under pancreatic conditions. In conclusion, the use of dense whey protein particles has been shown to be a useful strategy to counter aggregation and/or gelation problems in high protein foods. © 2012 Elsevier Ltd.


Saglam D.,Top Institute Food and Nutrition | Saglam D.,Wageningen University | Venema P.,Wageningen University | de Vries R.,Laboratory of Physical Chemistry and Colloid Science | And 2 more authors.
Food Hydrocolloids | Year: 2014

We have studied the influence of dense whey protein particles on the mechanical properties of whey protein isolate (WPI) gels at high protein concentrations (16-22% (w/w)). Incorporation of dense whey protein particles in the gel, while keeping the total protein concentration constant, leads to a considerably lower storage modulus. By adding protein particles, the total protein concentration of the WPI gels could be increased by 25-55% (w/w), without increasing the storage modulus of the gel. The large deformation properties of the WPI gels were also influenced by the presence of dense protein particles. Gels containing protein particles fractured at a lower strain than pure WPI gels at the same protein concentration. We conclude that protein particles can be used to modulate mechanical properties of WPI gels and are promising candidates for the development of high protein foods with improved textural properties. © 2013 Elsevier Ltd.


Saglam D.,Wageningen University | Saglam D.,Top Institute Food and Nutrition | Venema P.,Wageningen University | Venema P.,Top Institute Food and Nutrition | And 4 more authors.
Food Hydrocolloids | Year: 2011

We have developed a robust procedure for preparing protein micro-particles with a high internal protein content (∼20% w/w). Such protein micro-particles, having controlled size, protein content, and surface composition can be useful in the development of novel food products with high protein content. Protein particles were formed through emulsification of a WPI (whey protein isolate) solution (25% w/w) in sunflower oil containing 2.5% (w/w) PGPR (Polyglycerol Polyricinoleate) as an oil-soluble emulsifier. The emulsion (w/o) was heated to induce gelation of the protein inside the emulsion droplets. Oil was removed through successive centrifugation and washing steps. This resulted in micron-sized protein particles dispersed in an aqueous phase. The average diameter of the particles was in the order of a few μm, depending on the mixing speeds applied in the primary emulsification step. CLSM (Confocal laser scanning microscopy) analysis of protein particles indicated that there is oil associated with the particles, either surrounding the particles and/or distributed throughout the particles. NMR analysis showed that this amount of oil does not exceed 1.8% (w/w). © 2010 Elsevier Ltd.


Saglam D.,Top Institute Food and Nutrition | Saglam D.,Wageningen University | Venema P.,Wageningen University | De Vries R.,Laboratory of Physical Chemistry and Colloid Science | Van Der Linden E.,Wageningen University
Soft Matter | Year: 2013

We have studied swelling properties and stability of protein particles prepared through emulsification and heat-induced gelation of whey proteins under different conditions. The protein particles themselves are stable over a wide pH range, but around pH 5 aggregation was observed, presumably because of a weakened electrostatic repulsion close to the protein iso-electric point. Protein leakage from the particles was found not to be higher than 8% (w/w) in most of the pH range, but increased significantly at alkaline pH. The pore size of the particles is in the range of 4 to 20 nm at neutral pH and the particles show a pH- and salt-responsive swelling, due to their polyampholytic character, as shown by confocal scanning electron microscopy analysis. These results indicate that these whey protein particles could be used as targeted delivery vehicles. The pH sensitive swelling of the particles may also result in significant changes in the volume of the particles, thereby influencing the rheological properties of dispersions made out of these particles, especially in concentrated systems. This journal is © 2013 The Royal Society of Chemistry.

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