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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    Comparing foam and interfacial properties of similarly charged protein–surfactant mixtures
    Lech, F.J. ; Meinders, M.B.J. ; Wierenga, P.A. ; Gruppen, H. - \ 2015
    Colloids and Surfaces. A: Physicochemical and Engineering Aspects 473 (2015). - ISSN 0927-7757 - p. 18 - 23.
    sodium dodecyl-sulfate - bovine serum-albumin - air-water interfaces - beta-lactoglobulin - titration calorimetry - binding - sds - adsorption - rheology - layers
    The foam stability of protein–surfactant mixtures strongly depends on the charge of the protein and the surfactant, as well as on their mixing ratio. Depending on the conditions, the mixtures will contain free proteins, free surfactants and/or protein–surfactant complexes. To be able to compare different protein–surfactant mixtures, generic knowledge about the occurrence of each of these states and their relative contribution to foam stability is essential. In this work, the foam stability and interfacial properties of bovine serum albumin (BSA) mixed with sodium dodecyl sulphate (SDS) as well the binding of SDS to BSA as are studied at different molar ratios (MR). A comparison is made with ß-lactoglobulin (BLG) mixed with SDS. Both proteins and SDS are negatively charged at pH 7. The foam stability in the presence of small amounts (up to MR 1) of SDS is half the value of the pure protein solutions. The foam stability for both protein surfactant mixtures reaches a minimum at MR 20. A further increase of the MR leads to an increase of foam stability. The foam stability of BLG–SDS at MR >20 follows the foam stability of pure SDS solutions at equivalent concentrations, while BSA–SDS mixtures have an offset and begin to increase from MR >50. This behaviour was also reflected in the surface pressure and complex dilatational elastic moduli, and could be linked to the binding of the surfactant to the proteins. Both proteins bind SDS at high and low affinity binding sites. BSA's high affinity binding sites have a binding stoichiometry of 5.5 molSDS/molprotein, and BLG's high affinity binding site has a stoichiometry of 0.8 molSDS/molprotein (determined by isothermal titration calorimetry). Binding to the low affinity binding sites, occurs with a binding ratio, leading to an accumulation of free surfactants. While the basic mechanisms underlying the foam properties of mixed systems are not explained in detail by this approach, the foam stability plots of both protein surfactant mixtures could be superimposed using the concentration of free SDS.
    Disintegration of protein microbubbles in presence of acid and surfactants: a multi-step process
    Rovers, T.A.M. ; Sala, G. ; Linden, E. van der; Meinders, M.B.J. - \ 2015
    Soft Matter 11 (2015)32. - ISSN 1744-683X - p. 6403 - 6411.
    bovine serum-albumin - microspheres - nanoparticles - fabrication - stability
    The stability of protein microbubbles against addition of acid or surfactants was investigated. When these compounds were added, the microbubbles first released the encapsulated air. Subsequently, the protein shell completely disintegrated into nanometer-sized particles. The decrease in the number of intact microbubbles could be well described with the Weibull distribution. This distribution is based on two parameters, which suggests that two phenomena are responsible for the fracture of the microbubble shell. The microbubble shell is first weakened. Subsequently, the weakened protein shell fractures randomly. The probability of fracture turned out to be exponentially proportional to the concentration of acid and surfactant. A higher decay rate and a lower average breaking time were observed at higher acid or surfactant concentrations. For different surfactants, different decay rates were observed. The fact that the microbubble shell was ultimately disintegrated into nanometer-sized particles upon addition of acid or surfactants indicates that the interactions in the shell are non-covalent and most probably hydrophobic. After acid addition, the time at which the complete disintegration of the shell was observed coincided with the time of complete microbubble decay (release of air), while in the case of surfactant addition, there was a significant time gap between complete microbubble decay and complete shell disintegration.
    Quantitative description of the parameters affecting the adsorption behaviour of globular proteins
    Delahaije, R.J.B.M. ; Gruppen, H. ; Giuseppin, M.L.F. ; Wierenga, P.A. - \ 2014
    Colloids and Surfaces. B: Biointerfaces 123 (2014). - ISSN 0927-7765 - p. 199 - 206.
    air-water-interface - bovine serum-albumin - beta-lactoglobulin - rheological properties - air/water interface - surface rheology - kinetics - ovalbumin - charge - denaturation
    The adsorption behaviour of proteins depends significantly on their molecular properties and system conditions. To study this relation, the effect of relative exposed hydrophobicity, protein concentration and ionic strength on the adsorption rate and adsorbed amount is studied using ß-lactoglobulin, ovalbumin and lysozyme. The curves of surface elastic modulus versus surface pressure of all three proteins, under different conditions (i.e. concentration and ionic strength) superimposed. This showed that the interactions between the adsorbed proteins are similar and that the adsorbed proteins retain their native state. In addition, the adsorption rate (kadsorb) was shown to scale with the relative hydrophobicity and ionic strength. Moreover, the adsorbed amount was shown to be dependent on the protein charge and the ionic strength. Based on these results, a model is proposed to predict the maximum adsorbed amount (Gmax). The model approximates the adsorbed amount as a close-packed monolayer using a hard-sphere approximation with an effective protein radius which depends on the electrostatic repulsion. The theoretical adsorbed amount was in agreement with experimental Gmax (±10%).
    Effect of Glycation on the Flocculation Behavior of Protein-Stabilized Oil-in-Water Emulsions
    Delahaije, R.J.B.M. ; Gruppen, H. ; Nieuwenhuijzen, N.H. van; Giuseppin, M.L.F. ; Wierenga, P.A. - \ 2013
    Langmuir 29 (2013)49. - ISSN 0743-7463 - p. 15201 - 15208.
    bovine serum-albumin - beta-lactoglobulin - physicochemical properties - adsorption dynamics - disjoining pressure - alpha-lactalbumin - interfaces - particles - thickness - size
    Glycation of proteins by the Maillard reaction is often considered as a method to prevent flocculation of protein-stabilized oil-in-water emulsions. The effect has been suggested, but not proven, to be the result of steric stabilization, and to depend on the molecular mass of the carbohydrate moiety. To test this, the stabilities of emulsions of patatin glycated to the same extent with different mono- and oligosaccharides (xylose, glucose, maltotriose, and maltopentaose) were compared under different conditions (pH and electrolyte concentration). The emulsions with non-modified patatin flocculate under conditions in which the zeta potential is decreased (around the iso-electric point and at high ionic strength). The attachment of monosaccharides (i.e., glucose) did not affect the flocculation behavior. Attachment of maltotriose and maltopentaose (Mw > 500 Da), on the other hand, provided stability against flocculation at the iso-electric point. Since the zeta potential and the interfacial properties of the emulsion droplets are not affected by the attachment of the carbohydrate moieties, this is attributed to steric stabilization. Experimentally, a critical thickness of the adsorbed layer required for steric stabilization against flocculation was found to be 2.29–3.90 nm. The theoretical determination based on the DLVO interactions with an additional steric interaction coincides with the experimental data. Hence, it can be concluded that the differences in stability against pH-induced flocculation are caused by steric interactions.
    Influence of buffer composition on the distribution of inkjet printed protein molecules and the resulting spot morphology
    Mujawar, L.H. ; Amerongen, A. van; Norde, W. - \ 2012
    Talanta 98 (2012). - ISSN 0039-9140 - p. 1 - 6.
    bovine serum-albumin - antibody microarrays - surfaces - performance - adsorption
    Producing high quality protein microarrays on inexpensive substrates like polystyrene is a big challenge in the field of diagnostics. Using a non-contact inkjet printer we have produced microarrays on polystyrene slides for two different biotinylated biomolecules, bovine serum albumin (BSA–biotin) and immunoglobulin-G (IgG–biotin), and studied the influence of buffer (composition and pH) on the spot morphology and signal intensity. Atomic force microscopy revealed the morphological pattern of the (biomolecule) spots printed from phosphate buffer (pH 7.4), phosphate buffered saline (pH 7.4) and carbonate buffer (pH 9.6). The spots showed an irregular crust-like appearance when printed in phosphate buffered saline (pH 7.4), mainly due to the high NaCl content, whereas spots of biomolecules printed in carbonate buffer (pH 9.6) showed a smooth morphology. In addition, the rinsing of these dried spots led to the loss of a considerable fraction of the biomolecules, leaving behind a small fraction that is compatible with the (mono)layer. It was confirmed by confocal laser microscopy that the quality of the spots with respect to the uniformity and distribution of the biomolecules therein was superior when printed in carbonate buffer (pH 9.6) as compared to other buffer systems. Particularly, spotting in PBS yielded spots having a very irregular distribution and morphology.
    Speciation analysis of aqueous nanoparticulate diclofenac complexes by solid-phase microextraction
    Zielinska, K. ; Leeuwen, H.P. van; Thibault, S. ; Town, R.M. - \ 2012
    Langmuir 28 (2012)41. - ISSN 0743-7463 - p. 14672 - 14680.
    bovine serum-albumin - walled carbon nanotubes - drug binding-sites - capillary-electrophoresis - aquatic environment - antiinflammatory drugs - mass-spectrometry - metal-complexes - water samples - nd-spme
    The dynamic sorption of an organic compound by nanoparticles (NPs) is analyzed by solid-phase microextraction (SPME) for the example case of the pharmaceutical diclofenac in dispersions of impermeable (silica, SiO(2)) and permeable (bovine serum albumin, BSA) NPs. It is shown that only the protonated neutral form of diclofenac is accumulated in the solid phase, and hence this species governs the eventual partition equilibrium. On the other hand, the rate of the solid/water partition equilibration is enhanced in the presence of the sorbing nanoparticles of SiO(2) and BSA. This feature demonstrates that the NPs themselves do not enter the solid phase to any appreciable extent. The enhanced rate of attainment of equilibrium is due to a shuttle-type of contribution from the NP-species to the diffusive supply of diclofenac to the water/solid interface. For both types of nanoparticulate complexes, the rate constant for desorption (k(des)) of bound diclofenac was derived from the measured thermodynamic affinity constant and a diffusion-limited rate of adsorption. The computed k(des) values were found to be sufficiently high to render the NP-bound species labile on the effective time scale of SPME. In agreement with theoretical prediction, the experimental results are quantitatively described by fully labile behavior of the diclofenac/nanoparticle system and an ensuing accumulation rate controlled by the coupled diffusion of neutral, deprotonated, and NP-bound diclofenac species.
    Protein-Repellent Silicon Nitride Surfaces: UV-Induced Formation of Oligoethylene Oxide Monolayers
    Rosso, M. ; Nguyen, A.T. ; Jong, E. de; Baggerman, J. ; Paulusse, J.M.J. ; Giesbers, M. ; Fokkink, R.G. ; Norde, W. ; Schroën, C.G.P.H. ; Rijn, C.J.M. van; Zuilhof, H. - \ 2011
    ACS Applied Materials and Interfaces 3 (2011)3. - ISSN 1944-8244 - p. 697 - 704.
    self-assembled monolayers - transfer radical polymerization - low-temperature plasma - bovine serum-albumin - c linked monolayers - poly(ethylene glycol) - organic monolayers - molecular simulation - ultrafiltration membranes - oligo(ethylene glycol)
    The grafting of polymers and oligomers of ethylene oxide onto surfaces is widely used to prevent nonspecific adsorption of biological material on sensors and membrane surfaces. In this report, we show for the first time the robust covalent attachment of short oligoethylene oxide-terminated alkenes (CH3O(CH2CH2O)3(CH2)11-(CH-CH2) [EO3] and CH3O(CH2CH2O)6(CH2)11-(CH-CH2) [EO6]) from the reaction of alkenes onto silicon-rich silicon nitride surfaces at room temperature using UV light. Reflectometry is used to monitor in situ the nonspecific adsorption of bovine serum albumin (BSA) and fibrinogen (FIB) onto oligoethylene oxide coated silicon-rich silicon nitride surfaces (EOn-SixN4, x > 3) in comparison with plasma-oxidized silicon-rich silicon nitride surfaces (SiOy-SixN4) and hexadecane-coated SixN4 surfaces (C16-SixN4). A significant reduction in protein adsorption on EOn-SixN4 surfaces was achieved, adsorption onto EO3-SixN4 and EO6-SixN4 were 0.22 mg m-2 and 0.08 mg m-2, respectively. The performance of the obtained EO3 and EO6 layers is comparable to those of similar, highly protein-repellent monolayers formed on gold and silver surfaces. EO6-SixN4 surfaces prevented significantly the adsorption of BSA (0.08 mg m-2). Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray reflectivity and static water contact angle measurements were employed to characterize the modified surfaces. In addition, the stability of EO6-SixN4 surfaces in phosphate-buffered saline solution (PBS) and alkaline condition (pH 10) was studied. Prolonged exposure of the surfaces to PBS solution for 1 week or alkaline condition for 2 h resulted in only minor degradation of the ethylene oxide moieties and no oxidation of the SixN4 substrates was observed. Highly stable antifouling coatings on SixN4 surfaces significantly broaden the application potential of silicon nitride-coated microdevices, and in particular of microfabricated filtration membranes
    Grafted ionomer complexes and their effect on protein adsorption on silica and polysulfone surfaces
    Brzozowska, A.M. ; Keizer, A. de; Detrembleur, C. ; Stuart, M.A.C. ; Norde, W. - \ 2010
    Colloid and Polymer Science 288 (2010)16-17. - ISSN 0303-402X - p. 1621 - 1632.
    coacervate core micelles - pyridinium-type polymers - bovine serum-albumin - polyelectrolyte multilayers - polyvinyl pyridine - ultrafiltration membranes - antibacterial activity - polystyrene surfaces - aqueous-solutions - block-copolymer
    We have studied the formation and the stability of ionomer complexes from grafted copolymers (GICs) in solution and the influence of GIC coatings on the adsorption of the proteins beta-lactoglobulin (beta-lac), bovine serum albumin (BSA), and lysozyme (Lsz) on silica and polysulfone. The GICs consist of the grafted copolymer PAA(28)-co-PAPEO(22) {poly(acrylic acid)-co-poly[acrylate methoxy poly(ethylene oxide)]} with negatively charged AA and neutral APEO groups, and the positively charged homopolymers: P2MVPI(43) [poly(N-methyl 2-vinyl pyridinium iodide)] and PAH center dot HCl160 [poly(allylamine hydrochloride)]. In solution, these aggregates are characterized by means of dynamic and static light scattering. They appear to be assemblies with hydrodynamic radii of 8 nm (GIC-PAPEO(22)/P2MVPI(43)) and 22 nm (GIC-PAPEO(22)/PAH center dot HCl160), respectively. The GICs partly disintegrate in solution at salt concentrations above 10 mM NaCl. Adsorption of GICs and proteins has been studied with fixed angle optical reflectometry at salt concentrations ranging from 1 to 50 mM NaCl. Adsorption of GICs results in high density PEO side chains on the surface. Higher densities were obtained for GICs consisting of PAH center dot HCl160 (1.6 divided by 1.9 chains/nm(2)) than of P2MVPI(43) (0.6 divided by 1.5 chains/nm(2)). Both GIC coatings strongly suppress adsorption of all proteins on silica (>90%); however, reduction of protein adsorption on polysulfone depends on the composition of the coating and the type of protein. We observed a moderate reduction of beta-lac and Lsz adsorption (>60%). Adsorption of BSA on the GIC-PAPEO(22)/ P2MVPI(43) coating is moderately reduced, but on the GIC-PAPEO(22)/ PAH center dot HCl160 coating it is enhanced.
    Reduction of protein adsorption on silica and polysulfone surfaces coated with complex coacervate core micelles with poly(vinyl alcohol) as a neutral brush forming block
    Brzozowska, A.M. ; Zhang, Q. ; Keizer, A. de; Norde, W. ; Cohen Stuart, M.A. - \ 2010
    Colloids and Surfaces. A: Physicochemical and Engineering Aspects 368 (2010)1-3. - ISSN 0927-7757 - p. 96 - 104.
    bovine serum-albumin - polyelectrolyte multilayers - ultrafiltration membranes - poly(ethylene glycol) - polyvinyl pyridine - aqueous-solution - assembled monolayers - aquatic environment - organic pollutants - polymeric micelles
    We have studied the formation and stability of complex coacervate core micelles (C3Ms) in solution, and the influence of C3M coatings on the adsorption of the proteins ß-lactoglobulin (ß-lac), bovine serum albumin (BSA), and lysozyme (Lsz) on silica and polysulfone surfaces. The C3Ms consist of a block copolymer PAA50-65-b-PVA445 (poly(acrylic acid)-b-poly(vinyl alcohol)), with a neutral PVA block, and the positively charged homopolymers: P2MVPI (poly(N-methyl 2-vinyl pyridinium iodide), or PAH·HCl (poly(allylamine hydrochloride)). In solution at pH 7 these micelles disintegrate if the salt concentration exceeds 100 mM NaCl. Adsorption of C3Ms and proteins was studied by fixed angle optical reflectometry at salt concentrations ranging from 1 to 50 mM NaCl. C3M consisting of PAH·HCl strongly suppresses protein adsorption on silica, also at low salt concentration. However, at high salt concentrations it enhances adsorption of BSA on hydrophobic polysulfone, probably due to the formation of complexes between BSA and PAH·HCl. Much smaller reduction of protein adsorption on silica and polysulfone was obtained by C3Ms consisting of P2MVPI.. In this case the effectiveness of the coating strongly depends on the type of protein. On polysulfone at 50 mM NaCl we have observed only reduction of Lsz adsorption whereas adsorption of the negatively charged proteins is enhanced rather than reduced by the coating. We relate the results obtained for C3M with P2MVPI to the low density of the PVA chains on the surfaces, partial segregation of polymer chains within coacervate layer, and penetration of the adsorbed layer by the proteins.
    Grafted block complex coacervate core micelles and their effect on protein adsorption on silica and polystyrene
    Brzozowska, A.M. ; Keizer, A. de; Norde, W. ; Detrembleur, C. ; Cohen Stuart, M.A. - \ 2010
    Colloid and Polymer Science 288 (2010)10-11. - ISSN 0303-402X - p. 1081 - 1095.
    bovine serum-albumin - beta-lactoglobulin - polymeric micelles - chain stiffness - surfaces - binding - dependence - monolayers - reduction - copolymer
    We have studied the formation and the stability of grafted block complex coacervate core micelles (C3Ms) in solution and the influence of grafted block C3M coatings on the adsorption of the proteins ß-lactoglobulin, bovine serum albumin, and lysozyme. The C3Ms consist of a grafted block copolymer PAA21-b-PAPEO14 (poly(acrylic acid)-b-poly(acrylate methoxy poly(ethylene oxide)), with a negatively charged PAA block and a neutral PAPEO block and a positively charged homopolymer P2MVPI (poly(N-methyl 2-vinyl pyridinium iodide). In solution, these C3Ms partly disintegrate at salt concentrations between 50 and 100 mM NaCl. Adsorption of C3Ms and proteins has been studied with fixed-angle optical reflectometry, at salt concentrations ranging from 1 to 100 mM NaCl. In comparison with the adsorption of PAA21-b-PAPEO14 alone adsorption of C3Ms significantly increases the amount of PAA21-b-PAPEO14 on the surface. This results in a higher surface density of PEO chains. The stability of the C3M coatings and their influence on protein adsorption are determined by the composition and the stability of the C3Ms in solution. A C3M-PAPEO14/P2MVPI43 coating strongly suppresses the adsorption of all proteins on silica and polystyrene. The reduction of protein adsorption is the highest at 100 mM NaCl (>90%). The adsorbed C3M-PAPEO14/P2MVPI43 layer is partly removed from the surface upon exposure to an excess of ß-lactoglobulin solution, due to formation of soluble aggregates consisting of ß-lactoglobulin and P2MVPI43. In contrast, C3M-PAPEO14/P2MVPI228 which has a fivefold longer cationic block enhances adsorption of the negatively charged proteins on both surfaces at salt concentrations above 1 mM NaCl. A single PAA21-b-PAPEO14 layer causes only a moderate reduction of protein adsorption.
    Field theoretical analysis of driving forces for the uptake of proteins by like-charged polyelectrolyte brushes: Effects of charge regulation and patchiness
    Vos, W.M. de; Leermakers, F.A.M. ; Keizer, A. de; Cohen Stuart, M.A. ; Kleijn, J.M. - \ 2010
    Langmuir 26 (2010)1. - ISSN 0743-7463 - p. 249 - 259.
    bovine serum-albumin - poly(acrylic acid) brush - complex micelles - aqueous-solution - polymer brushes - adsorption - particles - molecules - density - layer
    At the moment two competing explanations exist for the experimental finding that net negatively charged proteins adsorb on or absorb in negatively charged polyelectrolyte brushes. One explanation is based on the possibility of charge regulation. The idea is that a protein can reverse its charge when it is in the presence of the high electrostatic potential of the brush and then can be inserted. The other explanation relies on the charge anisotropy of proteins, that is, that it carries positively charged and negatively charged patches. The positively charged region gains more energy from interacting with the negative brush than the negative charged patch loses, especially when the charge densities and electrostatic potentials are high, thus providing a net attraction. We present a model in which both mechanisms are combined. We confirm that both charge anisotropy and charge regulation effects on their own can be responsible for protein uptake at the "wrong" side of the isoelectric point (IEP). In addition, we find that the respective effects are additive. Indeed, taking both effects into account results in a stronger attraction between a PE brush and protein at the IEP, and the attraction is found further above the IEP than the individual effects would have made possible. Still, for patchiness to have a strong contribution, the patches need very high charge densities. Therefore, we argue that for most types of protein charge reversal will be the main driving force for adsorption on the wrong side of the IEP, while patchiness will contribute less
    Reduction of protein adsorption on silica and polystyrene surfaces due to coating with Complex Coacervate Core Micelles
    Brzozowska, A.M. ; Hofs, P.S. ; Keizer, A. de; Fokkink, R.G. ; Stuart, M.A.C. ; Norde, W. - \ 2009
    Colloids and Surfaces. A: Physicochemical and Engineering Aspects 347 (2009)1-3. - ISSN 0927-7757 - p. 146 - 155.
    bovine serum-albumin - poly(ethylene glycol) chains - competitive adsorption - assembled monolayers - polymeric micelles - block-copolymer - polyacrylamide - kinetics - brushes - forces
    The reduction of protein adsorption by a polymer brush formed upon adsorption of Complex Coacervate Core Micelles (C3Ms), consisting of a charged copolymer containing a neutral block and an oppositely charged homopolymer, on silica and polystyrene surfaces has been studied in situ using fixed angle optical reflectometry. Four proteins were used: lysozyme, beta-lactoglobulin, bovine serum albumin,and fibrinogen. The C3M coating is responsive to changes in pH and salt concentration, and can be completely removed from the surface by rinsing with a concentrated salt solution (>2 M NaCl) or an acidic solution (pH <2). The same surface can be subsequently coated with a fresh micellar layer. The reduction of protein adsorption by C3Ms was found to be influenced by the surface chemical composition, surface charge, hydrophobicity and salt concentration. C3M adsorption was higher on hydrophobic polystyrene than on hydrophilic silica, but stronger reduction of protein adsorption was observed on silica. The protein resistance of the brush is enhanced by increasing the salt concentration from 5 to 100 mM as a consequence of the stronger screening of excess charges. The stoichiometric charge composition, at which stable C3Ms are formed in bulk, is not the optimal one to create an effective coating on charged surfaces. On the silica surface higher reduction of protein adsorption was observed when micelles carry an excess charge opposite to the charge of the native surface.
    Interactions between globular proteins and procyanidins of different degrees of polymerization
    Prigent, S.V.E. ; Voragen, A.G.J. ; Koningsveld, G.A. van; Baron, A. ; Renard, C.M. ; Gruppen, H. - \ 2009
    Journal of Dairy Science 92 (2009). - ISSN 0022-0302 - p. 5843 - 5853.
    bovine serum-albumin - precipitating capacity - condensed tannins - haze formation - binding - grape - milk - polyphenols - products - quality
    Interactions of proteins with phenolic compounds occur in food products containing vegetable sources, such as cocoa, cereals, or yogurts containing fruit. Such interactions can modify protein digestion and protein industrial properties. Noncovalent interactions between globular proteins (proteins important in industry) and procyanidins (phenolic compounds present in large quantity in fruits) were studied. The affinity constants between procyanidins of various average degrees of polymerization () and lysozyme or -lactalbumin were measured by isothermal titration calorimetry. The effects of these interactions on protein solubility and foam properties were examined using -lactalbumin and BSA. Weak interactions were found with epicatechin and procyanidin dimers. Procyanidins of n = 5.5 and n = 7.4 showed medium (1.5 x 105 M–1) and high (8.69 x 109 M–1) affinities, respectively, for -lactalbumin at pH 5.5, with n the average number of subunits per oligomer. A positive cooperativity of binding at low procyanidin:protein molar ratios was observed. The affinities of -lactalbumin and lysozyme for procyanidins increased when the pH was close to the isoelectric pH. Solubility of lysozyme was strongly decreased by procyanidins of n = 5.5, whereas -lactalbumin and BSA were less affected. Protein solubility in the presence of procyanidins was not affected by increased ionic strength but increased slightly with temperature. Procyanidins of n = 5.5 and n = 7.4 stabilized the average bubble diameter of foam formed with -lactalbumin but had no effect on foam made from BSA. These results indicate that procyanidins of medium can lead to an undesirable decrease of protein solubility, but may play a positive role in foam stability.
    The Production of PEO Polymer Brushes via Langmuir-Blodgett and Langmuir-Schaeffer Methods: Incomplete Transfer and Its Consequences
    Vos, W.M. de; Keizer, A. de; Kleijn, J.M. ; Cohen Stuart, M.A. - \ 2009
    Langmuir 25 (2009)8. - ISSN 0743-7463 - p. 4490 - 4497.
    bovine serum-albumin - diblock copolymer - polyelectrolyte brushes - poly(ethylene glycol) - polystyrene brushes - poly(acrylic acid) - protein adsorption - silica surfaces - density - temperature
    Using fixed-angle ellipsometry, we investigate the degree of mass transfer upon vertically dipping a polystyrene surface through a layer of a polystyrene-poly(ethylene oxide) (PS-PEO) block copolymer at the air water interface (Langmuir-Blodgett or LB transfer). The transferred mass is proportional to the PS-PEO grafting density at the air-water interface, but the transferred mass is not equal to the mass at the air-water interface. We find that depending on the chain length of the PEO block only a certain fraction of the polymers at the air-water interface is transferred to the solid surface. For the shortest PEO chain length (PS36-PEO148), the mass transfer amounts to 94%, while for longer chain lengths (PS36-PEO370 and PS38-PEO770), a transfer of, respectively 57% and 19%, is obtained. We attribute this reduced mass transfer to a competition for the PS surface between the PEO block and the PS block. Atomic force microscopy shows that after transfer the material is evenly spread over the surface. However, upon a short heating of these transferred layers (95 °C, 5 min) a dewetting of the PS-PEO layer takes place. These results have a significant impact on the interpretation of the results in a number of papers in which the above-described transfer method was used to produce PEO polymer brushes, in a few cases in combination with heating. We briefly review these papers and discuss their main results in light of this new information. Furthermore, we show that, by using Langmuir-Schaeffer (LS, horizontal) dipping, much higher mass transfers can be reached than with the LB method. When the LB or LS methods are carefully applied, it is a very powerful technique to produce PEO brushes, as it gives full control over both the grafting density and the chain length
    Influence of the overall charge and local charge density of pectin on the complex formation between pectin and beta-lactoglobulin
    Sperber, B.L.H.M. ; Schols, H.A. ; Cohen Stuart, M.A. ; Norde, W. ; Voragen, A.G.J. - \ 2009
    Food Hydrocolloids 23 (2009)3. - ISSN 0268-005X - p. 765 - 772.
    bovine serum-albumin - whey proteins - aqueous-solution - acid - polyelectrolytes - coacervation - stabilization - conformation - carrageenan - dependence
    The complex formation between ß-lactoglobulin (ß-lg) and pectin is studied using pectins with different physicochemical characteristics. Pectin allows for the control of both the overall charge by degree of methyl-esterification as well as local charge density by the degree of blockiness. Varying local charge density, at equal overall charge is a parameter that is not available for synthetic polymers and is of key importance in the complex formation between oppositely charged (bio)polymers. LMP is a pectin with a high overall charge and high local charge density; HMPB and HMPR are pectins with a low overall charge, but a high and low local charge density, respectively. Dynamic light scattering (DLS) titrations identified pHc, the pH where soluble complexes of ß-lg and pectin are formed and pH, the pH of phase separation, both as a function of ionic strength. pHc decreased with increasing ionic strength for all pectins and was used in a theoretical model that showed local charge density of the pectin to control the onset of complex formation. pH passed through a maximum with increasing ionic strength for LMP because of shielding of repulsive interactions between ß-lg molecules bound to LMP, while attractive interactions were repressed at higher ionic strength. Potentiometric titrations of homo-molecular solutions and mixtures of ß-lg and pectin showed charge regulation in ß-lg¿pectin complexes. Around pH 5.5¿5.0 the pKas of ß-lg ionic groups are increased to induce positive charge on the ß-lg molecule; around pH 4.5¿3.5 the pKa values of the pectin ionic groups are lowered to retain negative charge on the pectin. Since pectins with high local charge density form complexes with ß-lg at higher ionic strength than pectins with low local charge density, pectin with a high local charge density is preferred in food systems where complex formation between protein and pectin is desired.
    Complex formation in mixtures of lysozyme-stabilized emulsions and human saliva
    Silletti, E. ; Vingerhoeds, M.H. ; Norde, W. ; Aken, G.A. van - \ 2007
    Journal of Colloid and Interface Science 313 (2007)2. - ISSN 0021-9797 - p. 485 - 493.
    transmission electron-microscopy - phase-ordering kinetics - micelle-like structures - high-pressure treatment - bovine serum-albumin - egg-white lysozyme - rheological properties - beta-lactoglobulin - ionic-strength - whey proteins
    In this paper, we studied the interaction between human unstimulated saliva and lysozyme-stabilized oil-in-water emulsions (10 wt/wt% oil phase, 10 mM NaCl, pH 6.7), to reveal the driving force for flocculation of these emulsions. Confocal scanning laser microscopy (CSLM) showed formation of complexes between salivary proteins and lysozyme adsorbed at the oil¿water interface and lysozyme in solution as well. To assess the electrostatic nature of the interaction in emulsion/saliva mixtures, laser-diffraction and rheological measurements were conducted in function of the ionic strength by adding NaCl to the mixture in the range between 0 and 168 mM. Increasing the ionic strength reduced the ability of saliva to induce emulsion flocculation as shown by the decreased floc size and the effect on the viscosity. Turbidity experiments with varying pH (3¿7) and ionic strength also showed decreased complex formation in mixtures between saliva and lysozyme in solution upon NaCl addition up to 200 mM. Decreasing the pH increased the turbidity, in line with the increase of the positive net charge on the lysozyme molecule. We conclude that electrostatic attraction is the main driving force for complex formation between saliva components and lysozyme adsorbed at the oil droplets and in solution.
    Covalent interactions between proteins and oxidation products of caffeoylquinic acid (chlorogenic acid)
    Prigent, S.V.E. ; Voragen, A.G.J. ; Visser, A.J.W.G. ; Koningsveld, G.A. van; Gruppen, H. - \ 2007
    Journal of the Science of Food and Agriculture 87 (2007)13. - ISSN 0022-5142 - p. 2502 - 2510.
    bovine serum-albumin - physicochemical characterization - proteolytic digestion - polyphenol oxidase - model solutions - caffeic acid - derivatives - tyrosine - systems - peroxidase
    BACKGROUND: The interactions between phenolic compounds and proteins can modify protein properties important in the food industry. To understand the effects of these interactions, the covalent interactions between caffeoylquinic acid (chlorogenic acid, CQA) oxidised by polyphenol oxidase (PPO) at acidic pH 6 (pH 6) and -lactalbumin, lysozyme and bovine serum albumin (BSA) were compared with non-enzymatically induced covalent interactions at alkaline pH (pH 9). The effects of these modifications on protein properties were examined. RESULTS: Both ways of modification seemed to result in protein modification mainly via dimeric rather than monomeric CQA quinones. These modifications led to a decrease in the number of free primary amino groups of the proteins. Modification with CQA alone induced a low degree of protein dimerisation, which also occurred through the action of PPO alone. Modification drastically reduced the solubility of lysozyme over a broad pH range, whereas that of -lactalbumin was strongly reduced only at pH values close to its pI. The solubility of BSA was much less affected than that of the other proteins and only at acidic pH. CONCLUSION: These results indicate some similarities between modifications at pH 6 and 9 and that both modifications clearly change the functional properties of globular proteins.
    Protein-polysaccharide interactions: The determination of the osmotic second virial coefficients in aqueous solutions of ß-lactoglobulin and dextran
    Schaink, H.M. ; Smit, J.A.M. - \ 2007
    Food Hydrocolloids 21 (2007)8. - ISSN 0268-005X - p. 1389 - 1396.
    bovine serum-albumin - phase-separation - depletion - mixtures - pressure - lysozyme - systems - model - size - dimerization
    Solutions containing dextran and solutions containing mixtures of dextran +ß-lactoglobulin are studied by membrane osmometry. The low concentration range of these solutions is considered. From the measured osmotic pressures the virial coefficients are obtained. These are analyzed using the osmotic virial coefficient of ß-lactoglobulin solutions published earlier by us [Schaink, H.M., & Smit, J. A.M. (2000). Determination of the osmotic second virial coefficient and the dimerization of beta-lactoglobulin in aqueous solutions with added salt at the isoelectric point. PCCP, 2, 1537¿1541]. The second cross-virial coefficient A12 is found to be positive indicating a repulsive and probably mainly steric interaction between neutral in nature dextran and and practically uncharged ß-lactoglobulin (pH=5.18). The measurements show that the ß-lactoglobulin has only a small tendency to form multimers in the presence of dextran. The phase diagram of solutions of dextran+Whey Protein Isolate (appr. 60% ß-lactoglobulin) is also presented. The McMillan¿Mayer equation of state that considers only the second virial coefficients is found to be unreliable for the extrapolation up to the concentrations at which phase separation is expected Keywords: Proteins; Polysaccharides; Osmotic pressure; Virial coefficients; Phase separation
    Phase behavior of mixtures of oppositely charged nanoparticles: Heterogeneous Poisson-Boltzmann cell model applied to lysozyme and succinylated lysozyme
    Biesheuvel, P.M. ; Lindhoud, S. ; Vries, R.J. de; Stuart, M.A.C. - \ 2006
    Langmuir 22 (2006)3. - ISSN 0743-7463 - p. 1291 - 1300.
    bovine serum-albumin - protein solutions - colloidal crystals - osmotic-pressure - polyelectrolytes - sedimentation - adsorption - separation - complexation - equilibrium
    We study the phase behavior of mixtures of oppositely charged nanoparticles, both theoretically and experimentally. As an experimental model system we consider mixtures of lysozyme and lysozyme that has been chemically modified in such a way that its charge is nearly equal in magnitude but opposite in sign to that of unmodified lysozyme. We observe reversible macroscopic phase separation that is sensitive not only to protein concentration and ionic strength, but also to temperature. We introduce a heterogeneous Poisson-Boltzmann cell model that generally applies to mixtures of oppositely charged nanoparticles. To account for the phase behavior of our experimental model system, in addition to steric and electrostatic interactions, we need to include a temperature-dependent short-ranged interaction between the lysozyme molecules, the exact origin of which is unknown. The strength and temperature dependence of the short-ranged attraction is found to be of the same order of magnitude as that between unmodified lysozyme molecules. The presence of a rather strong short-ranged attraction in our model system precludes the formation of colloidal liquid phases (or complex coacervates) such as those typically found in mixtures of globular protein molecules and oppositely charged polyelectrolytes.
    The adsorption and unfolding kinetics determines the folding state of proteins at the air-water interface and thereby the equation of state
    Wierenga, P.A. ; Egmond, M.R. ; Voragen, A.G.J. ; Jongh, H.H.J. de - \ 2006
    Journal of Colloid and Interface Science 299 (2006)2. - ISSN 0021-9797 - p. 850 - 857.
    bovine serum-albumin - neutron reflectivity - air/water interface - beta-casein - liquid interfaces - structural conformation - surface pressure - competitive adsorption - infrared-spectroscopy - circular-dichroism
    Unfolding of proteins has often been mentioned as an important factor during the adsorption process at air-water interfaces and in the increase of surface pressure at later stages of the adsorption process. This work focuses on the question whether the folding state of the adsorbed protein depends on the rate of adsorption to the interface, which can be controlled by bulk concentration. Therefore, the adsorption of proteins with varying structural stabilities at several protein concentrations was studied using ellipsometry and surface tensiometry. For beta-lactoglobulin the adsorbed amount (Gamma) needed to reach a certain surface pressure (Pi) decreased with decreasing bulk concentration. Ovalbumin showed no such dependence. To verify whether this difference in behavior is caused by the difference in structural stability, similar experiments were performed with cytochrome c and a destabilized variant of this protein. Both proteins showed identical Pi-Gamma, and no dependence on bulk concentration. From this work it was concluded that unfolding will only take place if the kinetics of adsorption is similar or slower than the kinetics of unfolding. The latter depends on the activation energy of unfolding (which is in the order of 100-300 kJ/mol), rather than the free energy of unfolding (typically 10-50 kJ/mol).
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