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.

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    Foam properties of proteins, low molecular weight surfactants and their complexes
    Lech, F.J. - \ 2016
    Wageningen University. Promotor(en): Harry Gruppen; Peter Wierenga; Marcel Meinders. - Wageningen : Wageningen University - ISBN 9789462576247 - 122
    surfactants - proteins - bovine serum albumin - beta-lactoglobulin - lysozyme - foams - chemical properties - stability - mixtures - food chemistry - oppervlaktespanningsverlagende stoffen - eiwitten - runderserumalbumine - bèta-lactoglobuline - lysozym - schuim - chemische eigenschappen - stabiliteit - mengsels - voedselchemie

    This thesis shows the effects that the addition of low molecular weight surfactants (LWMS) to proteins has on the foam stability of the mixture. For this, the bulk, interfacial, thin liquid films and foam properties are determined for different protein-LWMS mixtures at different molar ratios (MR). It was shown that the MR as well as the charge of the protein and LMWS determine the foam stability of the mixtures. For all mixtures it was found that the proteins have a select number of high affinity binding sites. So, the concentration of free LMWS in the solution is 0 until a critical MR (MRcr), at which all high affinity binding sites are saturated. Above this MRcr, part of the LMWS binds to low affinity binding sites of the proteins. The low affinity binding sites have a binding ratio < 1, which determines the concentration of bound and free LMWS. For similarly charged protein-LMWS mixtures (i.e. b-lactoglobulin (BLG) and sodium dodecyl sulphate (SDS) and bovine serum albumin (BSA) and SDS at pH 7) the foam stability typically decreases from the foam stability of the pure protein solution (MR 0) until MRcr is reached. At MR > MRcr the foam stability is dominated by the amount of free LMWS. For oppositely charged protein-LMWS mixtures, the binding of the LMWS to the proteins can be described in a similar way, although the number of high affinity sites and low affinity binding ratio are different. There is also a regime of MRs in which the protein-LMWS complexes form large aggregates. These aggregates were in some cases found to increase foam stability (lysozyme (LYS) and SDS and BLG-SDS at pH 3), while in another case (BLG and cetyltrimethylammonium bromide (CTAB)) they lead to decreased foam stability. Still, in all cases it was found that above MRD the aggregates dissociate and the foam stability becomes dominated by free surfactants, equivalent to what was observed for similarly charged protein-LMWS mixtures.

    A multi-scale model was developed to describe the stability of thin liquid films in terms of rupture time and thickness. Initially, the model was used to predict the stability of surfactant free films of water and electrolyte solutions. Later, it was used to predict the foam stability in LYS-SDS mixtures. For that purpose, the model was combined with a foam drainage model to provide theoretical estimations of foam stability. This model is the basis to understand coalescence of bubbles in foam. Finally, the concept of the critical MRs and the free LMWS was introduced. Using this, the foam properties of protein-LMWS mixtures can partly be predicted by relative charge of the components and the binding to both high and low affinity binding sites.

    Are antimicrobial defences in bird eggs related to climatic conditions associated with risk of trans-shell microbial infection?
    Horrocks, N.P.C. ; Hine, K. ; Hegemann, A. ; Ndithia, H.K. ; Shobrak, M. ; Ostrowski, S. ; Williams, J.B. ; Matson, K.D. ; Tieleman, B.I. - \ 2014
    Frontiers in Zoology 11 (2014). - ISSN 1742-9994 - 10 p.
    bacterial loads - life-history - maternal exposure - barn swallow - avian egg - incubation - diversity - eggshells - temperature - lysozyme
    Introduction All bird eggs are exposed to microbes in the environment, which if transmitted to the developing embryo, could cause hatching failure. However, the risk of trans-shell infection varies with environmental conditions and is higher for eggs laid in wetter environments. This might relate to generally higher microbial abundances and diversity in more humid environments, including on the surface of eggshells, as well as the need for moisture to facilitate microbial penetration of the eggshell. To protect against microbial infection, the albumen of avian eggs contains antimicrobial proteins, including lysozyme and ovotransferrin. We tested whether lysozyme and ovotransferrin activities varied in eggs of larks (Alaudidae) living along an arid-mesic gradient of environmental aridity, which we used as a proxy for risk of trans-shell infection. Results Contrary to expectations, lysozyme activity was highest in eggs from hotter, more arid locations, where we predicted the risk of trans-shell infection would be lower. Ovotransferrin concentrations did not vary with climatic factors. Temperature was a much better predictor of antimicrobial protein activity than precipitation, a result inconsistent with studies stressing the importance of moisture for trans-shell infection. Conclusions Our study raises interesting questions about the links between temperature and lysozyme activity in eggs, but we find no support for the hypothesis that antimicrobial protein deposition is higher in eggs laid in wetter environments.
    Designing microcapsules based on protein fibrils and protein - polysaccharide complexes
    Hua, K.N.P. - \ 2012
    Wageningen University. Promotor(en): Erik van der Linden, co-promotor(en): Leonard Sagis. - S.l. : s.n. - ISBN 9789461733801 - 136
    lysozym - ovalbumine - pectinen - aggregatie - inkapseling in microcapsules - lysozyme - ovalbumin - pectins - aggregation - microencapsulation

    Keywords: encapsulation, microcapsule, protein, fibril, protein-polysaccharide complex, controlled release, interfacial rheology, lysozyme, ovalbumin

    This thesis describes the design of encapsulation systems using mesostructures from proteins and polysaccharides. The approach was to first investigate the physical properties of the encapsulating materials (protein fibrils and protein – polysaccharide complexes). Subsequently, microcapsules with tunable release rate and mechanical strength were developed.

    Firstly, the effect of steady shear and turbulent flow on the formation of protein fibrils from lysozyme was studied. We determined the conversion and size distribution of fibrils obtained by heating lysozyme solutions at pH 2. The formation of fibrils was quantified using flow-induced birefringence. The size distribution was fitted using decay of birefringence measurements and Transmission Electron Microscopy. The morphology of Lys fibrils and kinetics of their formation varied considerably depending on the flow applied. With increasing shear or stirring rate, more rod-like and shorter fibrils were obtained, and the conversion into fibrils was increased.

    Secondly, we have investigated the surface rheological properties of oil – water interfaces stabilized by fibrils from lysozyme (long and semi-flexible, and short and rigid ones), fibrils from ovalbumin (short and semi-flexible), lysozyme – pectin complexes, or ovalbumin – pectin complexes. We have compared these properties with those of interfaces stabilized by the native proteins. The surface dilatational and surface shear moduli were determined using an automated drop tensiometer, and a stress controlled rheometer with biconical disk geometry. Results show that interfaces stabilized by protein – pectin complexes have higher surface shear and dilatational moduli than interfaces stabilized by the native proteins only. At most of the experimental conditions, interfaces stabilized by protein fibrils have the highest surface rheological moduli. The difference between long semi-flexible lysozyme fibrils or short rigid lysozyme fibrils is not pronounced in interfacial dilation rheology but significant in interfacial shear rheology. The complex surface shear moduli of interfaces stabilized by long semi-flexible fibrils are about ten times higher than those of interfaces stabilized by short rigid fibrils, over a range of bulk concentrations. Interfaces stabilized by short and more flexible ovalbumin fibrils have a significantly higher surface shear modulus than those stabilized by the somewhat longer and more rigid short lysozyme fibrils.

    Finally, encapsulation systems are developed using layer-by-layer adsorption of food-grade polyelectrolytes on an emulsion droplet template. The first encapsulation system was built with alternating layers of ovalbumin fibrils and high methoxyl pectin. By varying the number of layers, the release of active ingredients can be controlled: increasing the number of layers of the shell from four to eight, decreases the release rate by a factor six.

    The other encapsulation systems were built with alternating layers of protein – pectin complexes and protein fibrils. Two types of proteins (ovalbumin and lysozyme) and three types of fibrils were used: short and semi-flexible from ovalbumin, short and rod-like, and long and semi-flexible from lysozyme. At low number of layers (less than five), microcapsules from ovalbumin complexes and fibrils were stronger than microcapsules prepared from lysozyme complexes and fibrils. Increasing the number of layers, the mechanical stability of microcapsules from lysozyme complexes and fibrils increased significantly, and capsules were stronger than those prepared from ovalbumin complexes and fibrils with the same number of layers. The contour length of the Lys fibrils did not have a significant effect on mechanical stability of the lysozyme complexes and fibrils capsules. These results show that mechanical properties of this type of capsule can be tuned by varying the flexibility of the protein fibrils.

    Pathogen pressure puts immune defense into perspective
    Horrocks, N.P.C. ; Matson, K.D. ; Tieleman, B.I. - \ 2011
    Integrative and Comparative Biology 51 (2011)4. - ISSN 1540-7063 - p. 563 - 576.
    microbial communities - molecular techniques - eggs - diversity - soil - populations - antibodies - lysozyme - proteins - disease
    The extent to which organisms can protect themselves from disease depends on both the immune defenses they maintain and the pathogens they face. At the same time, immune systems are shaped by the antigens they encounter, both over ecological and evolutionary time. Ecological immunologists often recognize these interactions, yet ecological immunology currently lacks major efforts to characterize the environmental, host-independent, antigenic pressures to which all animals are exposed. Failure to quantify relevant diseases and pathogens in studies of ecological immunology leads to contradictory hypotheses. In contrast, including measures of environmental and host-derived commensals, pathogens, and other immune-relevant organisms will strengthen the field of ecological immunology. In this article, we examine how pathogens and other organisms shape immune defenses and highlight why such information is essential for a better understanding of the causes of variation in immune defenses. We introduce the concept of “operative protection” for understanding the role of immunologically relevant organisms in shaping immune defense profiles, and demonstrate how the evolutionary implications of immune function are best understood in the context of the pressures that diseases and pathogens bring to bear on their hosts. We illustrate common mistakes in characterizing these immune-selective pressures, and provide suggestions for the use of molecular and other methods for measuring immune-relevant organisms.
    Smart microgels for controlled uptake and release
    Li, Y. - \ 2011
    Wageningen University. Promotor(en): Martien Cohen Stuart; Willem Norde, co-promotor(en): Mieke Kleijn. - [S.l.] : S.n. - ISBN 9789085859994 - 173
    gels - zetmeel - colloïden - lysozym - gecontroleerde afgifte - gels - starch - colloids - lysozyme - controlled release

    This dissertation describes a systematic study on oxidized starch microgel particles. It begins with the preparation and characterization of oxidized starch gels in terms of some important physical-chemical properties, with the aim to select an optimum gel for further investigation of protein uptake. The gel with the highest degree of oxidation DO100% is chosen for lysozyme uptake because of its high protein uptake capacity and low swelling capacity. In addition, DO30% gels have been used in many experiments, since DO30% starch allows for preparation of well-defined spherical microgel particles and because it is enzymatically degradable. The two main aspects of interest are the protein binding affinity and protein saturation. Neutral pH and low salt concentration are found to be the optimum protein uptake conditions for high protein saturation. For more detailed studies, spherical microgels with a narrow size distribution have been made by optimizing the preparation process. The mobility of lysozyme molecules inside those microgel particles has been investigated. The main conclusion is that high salt and high pH increase the mobility of lysozyme in the gel particles. It implies that high pH and high salt concentration are potential triggers for lysozyme release from the gel. Subsequently, the kinetics of protein release by high pH and high salt concentration is presented. For the aim of application, the antimicrobial activity of lysozyme containing starch gel particles against some bacterial strains is determined. Finally, the deposition of poly-lysine/poly-glutamic acid complex layer around microgel surface is used to stabilize the microgel particle and optimize our system.

    Influence of Protein Hydrolysis on the Growth Kinetics of ß-lg Fibrils
    Kroes-Nijboer, A. ; Venema, P. ; Bouman, J. ; Linden, E. van der - \ 2011
    Langmuir 27 (2011)10. - ISSN 0743-7463 - p. 5753 - 5761.
    lactoglobulin gels - amyloid fibrils - ph 2 - aggregation - heat - lysozyme - amyloidogenesis
    Recently it was found that protein hydrolysis is an important step in the formation of ß-lactoglobulin fibrils at pH 2 and elevated temperatures. The objective of the present study was to further investigate the influence of hydrolysis on the kinetics of fibril formation. Both the hydrolysis of ß-lactoglobulin and the growth of the fibrils were followed as a function of time and temperature, using SDS polyacrylamide gel electrophoresis and a Thioflavin T fluorescence assay. As an essential extension to existing models, the quantification of the effect of the hydrolysis on the fibrillar growth was established by a simple polymerization model including a hydrolysis step.
    Size-exclusion chromatographic protein refolding: Fundamentals, modelling and operation
    Freydell, E.J. ; Wielen, L. van der; Eppink, M.H.M. ; Ottens, M. - \ 2010
    Journal of Chromatography. A, Including electrophoresis and other separation methods 1217 (2010)49. - ISSN 0021-9673 - p. 7723 - 7737.
    refractive-index detectors - nonlinear chromatography - diffusion-coefficients - liquid-chromatography - light-scattering - human proinsulin - aggregation - lysozyme - mechanism - media
    Size-exclusion chromatography (SEC) has proven its capability to refold a variety of proteins using a range of gel filtration column materials, demonstrated in the growing body of experimental evidence. However, little effort has been allocated to the development of mechanistic models describing size-exclusion chromatographic refolding reactors (SECRR). Mechanistic models are important since they provide a link between process variables like denatured and reduced protein feed concentration (C(f,D&R)), flow rate, column length, etc., and performance indicators like refolding yield (Y(N)), thereby opening the possibility for in silico design of SECRRs. A critical step, in the formulation of such models, is the selection of an adequate reaction mechanism, which provides the direct link between the separation and the refolding yield. Therefore, in this work we present a methodology using a SEC refolding reactor model, supported by a library of reaction mechanisms, to estimate a suitable reaction scheme using experimental SEC refolding data. SEC refolding data is used since it provides information about the mass distribution of monomers and aggregates after refolding, information not readily available from batch dilution refolding data alone. Additionally, this work presents (1) a systematic analysis of the reaction mechanisms considered using characteristic time analysis and Damköhler maps, revealing (a) the direct effect of a given reaction mechanism on the shape of the SEC refolding chromatogram (number of peaks and resolution) and (b) the effect that the competition between convection, refolding and aggregation is likely to have on the SEC refolding yield; (2) a comparison between the SECR reactor and the batch dilution refolding reactor based on mechanistic modeling, quantitatively showing the advantages of the former over the latter; and (3) the successful application of the modeling based strategy to study the SEC refolding data of an industrially relevant protein. In principle, the presented modeling strategy can be applied to any protein refolded using any gel filtration material, providing the proper mass balances and activity measurements are available.
    Size-exclusion simulated moving bed chromatographic protein refolding
    Freydell, E. ; Bulsink, Y. ; Hateren, S. van; Wielen, L. van der; Eppink, M.H.M. ; Ottens, M. - \ 2010
    Chemical Engineering Science 65 (2010)16. - ISSN 0009-2509 - p. 4701 - 4713.
    hydrophobic interaction chromatography - ion-exchange chromatography - escherichia-coli - human proinsulin - oxidative renaturation - inclusion-bodies - lysozyme - aggregation - purification - polymerization
    Size-exclusion chromatographic refolding (SECR) has successfully proven its capability to refold a variety of proteins using a range of gel filtration column materials. Several approaches have also been undertaken to improve the refolding yield of these systems, mostly under batch operation. Although, these approaches may lead to an increase on refolding yield, it is not expected that they will lead to significant increases in other important process indicators, such as volumetric productivity, specific eluent consumption and product concentration in the product stream; as these indicators are strongly dependent on the mode of operation. To overcome the shortcomings of batch chromatography, the size-exclusion refolding reactor may be operated in a continuous mode, with the aid of Simulated Moving Bed (SMB) technology. Albeit, SMB technology has inherent advantages over batch chromatography, these have been proven mainly in the context of conventional purifications and are still to be addressed in the context of chromatographic refolding reactors. In this work we report the on-column refolding of an industrially relevant protein, produced in inclusion bodies, by batch size-exclusion chromatography (SEC) and simulated moving bed size-exclusion chromatography (SMBSEC). The presented study encompasses: (1) a statistical design of experiments (DOE) to study the combined effect of the mobile phase pH (9.0–11.20) and the feed concentration of denatured and reduced protein (Cf,D&R=2.50–7.50 mg ml-1) on the refolding yield of the model protein; (2) a mechanistic analysis of the SMBSECR data, using a detailed model that accounts for both separation and refolding; and (3) a detailed comparison of the SMBSECR against the SECR, based both on quantitative and qualitative criteria. Our work showed that: (1) refolding yields of 50% are attainable by tuning pH and Cf,D&R, and that the positive effect of pH is strongly dependent on the Cf,D&R; (2) the modeling tool captured well the SMBSECR behavior, based solely on the effect that Cf,D&R has on the reaction rates; and (3) the volumetric productivity of the SMBSECR is about 53 times higher than that of the SECR, the specific solvent consumption is approximately 1/10th of that of the SECR, and the concentration of the product (i.e., native protein), leaving the SMBSECR, is roughly 4.5-fold higher than the one leaving the SECR. Accordingly, the comparison revealed the significant advantages that SMB technology has to offer to the design of chromatographic refolding reactors
    Complex coacervate core micelles from iron-based coordination polymers
    Wang, J.Y. ; Keizer, A. de; Fokkink, R.G. ; Yan, Y. ; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2010
    The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical 114 (2010)25. - ISSN 1520-6106 - p. 8313 - 8319.
    diblock copolymer - block-copolymers - polyelectrolyte - nanoparticles - stability - lysozyme - ionomers - delivery - design - length
    Complex coacervate core micelles (C3Ms) from cationic poly(N-methyl-2-vinyl-pyridinium iodide)-b-poly(ethylene oxide) (P2MVP41-b-PEO205) and anionic iron coordination polymers are investigated in the present work. Micelle formation is studied by light scattering for both Fe(II)- and Fe(III)-containing C3Ms. At the stoichiometric charge ratio, both Fe(II)-C3Ms and Fe(III)-C3Ms are stable for at least 1 week at room temperature. Excess of iron coordination polymers has almost no effect on the formed Fe(II)-C3Ms and Fe(III)-C3Ms, whereas excess of P2MVP41-b-PEO205 copolymers in the solution can dissociate the formed micelles. Upon increasing salt concentration, the scattering intensity decreases. This decrease is due to both a decrease in the number of micelles (or an increase in CMC) and a decrease in aggregation number. The salt dependence of the CMC and the aggregation number is explained using a scaling argument for C3M formation. Compared with Fe(II)-C3Ms, Fe(III)-C3Ms have a lower CMC and a higher stability against dissociation by added salt.
    Self-consistent-field calculations of proteinlike incorporations in polyelectrolyte complex micelles
    Lindhoud, S. ; Cohen Stuart, M.A. ; Norde, W. ; Leermakers, F.A.M. - \ 2009
    Physical Review. E, Statistical nonlinear, and soft matter physics 80 (2009)5. - ISSN 1539-3755 - 15 p.
    interacting chain molecules - entrapping enzyme molecules - coacervate core micelles - neurofilament brush - diblock copolymers - polymeric micelles - statistical-theory - block-copolymer - lysozyme - adsorption
    Self-consistent field theory is applied to model the structure and stability of polyelectrolyte complex micelles with incorporated protein (molten globule) molecules in the core. The electrostatic interactions that drive the micelle formation are mimicked by nearest-neighbor interactions using Flory-Huggins X parameters. The strong qualitative comparison with experimental data proves that the Flory-Huggins approach is reasonable. The free energy of insertion of a proteinlike molecule into the micelle is nonmonotonic: there is (i) a small repulsion when the protein is inside the corona; the height of the insertion barrier is determined by the local osmotic pressure and the elastic deformation of the core, (ii) a local minimum occurs when the protein molecule is at the core-corona interface; the depth (a few kBT's) is related to the interfacial tension at the core-corona interface and (iii) a steep repulsion (several kBT) when part of the protein molecule is dragged into the core. Hence, the protein molecules reside preferentially at the core-corona interface and the absorption as well as the release of the protein molecules has annealed rather than quenched characteristics. Upon an increase of the ionic strength it is possible to reach a critical micellization ionic (CMI) strength. With increasing ionic strength the aggregation numbers decrease strongly and only few proteins remain associated with the micelles near the CMI
    The Critical Aggregation Concentration of ß-Lactoglobulin-Based Fibril Formation
    Kroes-Nijboer, A. ; Venema, P. ; Bouman, J. ; Linden, E. van der - \ 2009
    Food Biophysics 4 (2009)2. - ISSN 1557-1858 - p. 59 - 63.
    heat-induced denaturation - amyloid fibrils - globular-proteins - whey-protein - ionic-strength - low ph - gels - gelation - ovalbumin - lysozyme
    The critical aggregation concentration (CAC) for fibril formation of ß-lactoglobulin (ß-lg) at pH 2 was determined at 343, 353, 358, 363, and 383 K using a Thioflavin T assay and was approximately 0.16 wt%. The accuracy of the CAC was increased by measuring the conversion into fibrils at different stirring speeds. The corresponding binding energy per mol, as determined from the CAC, was 13 RT (~40 kJ mol¿1) for the measured temperature range. The fact that the CAC was independent of temperature within the experimental error indicates that the fibril formation of ß-lg at pH 2 and the measured temperature range is an entropy-driven process.
    Relating the effect of saliva-induced emulsion flocculation on rheological properties and retention on the tongue surface with sensory perception
    Vingerhoeds, M.H. ; Silletti, E. ; Groot, J. de; Schipper, R.G. ; Aken, G.A. van - \ 2009
    Food Hydrocolloids 23 (2009)3. - ISSN 0268-005X - p. 773 - 785.
    oil-in-water - custard desserts - alpha-amylase - oral texture - creaminess - protein - tannin - model - viscosity - lysozyme
    Perception of food emulsions can often not be directly related to the structure of the products before consumption. Taking into account the changing product structure upon oral processing might increase understanding of the relation between perception and product properties. This study aims to gain insight in the effect of saliva-induced flocculation on perception of emulsions at neutral pH. Whey protein (WPI)-stabilized emulsions flocculating in a reversible manner with saliva were compared with lysozyme-stabilized emulsions that irreversible flocculate with saliva. The main emulsion variables, besides the emulsifying protein, were oil content (2.5% oil vs 10% oil), and the effect of emulsion thickening with guar gum (at 10% oil). To relate perception to processes occurring in the oral cavity, the emulsions were characterized before and after oral processing with respect to morphology and rheological properties (viscosity, storage and loss moduli). In addition, insight in retention of emulsion droplets on the tongue surface was obtained by measuring emulsifier and oil content in tongue swabs. Saliva-induced emulsion flocculation clearly shows a large effect on perception of the here studied emulsions. WPI-stabilized emulsions showed little retention on the tongue surface and perception was characterized by creaminess, fattiness and thickness. Guar gum thickening further increased perception of these attributes. On the other hand, for lysozyme-stabilized emulsions perception was largely related to attributes like dryness, roughness and astringency. In addition, a large viscosity increase upon oral processing and clear retention of emulsion droplets on the tongue surface was observed. Guar gum thickening decreased the effects of irreversible flocculation, likely because of its lubricating properties and increased viscosity. Although the amount of mucins recovered from the tongue surface was unaffected by orally processing of lysozyme-stabilized emulsions, the sensory characteristics of these emulsions reminds one of astringency perception of e.g. tannins that precipitate salivary proteins.
    Salt-induced release of lipase from polyelectrolyte complex micelles
    Lindhoud, S. ; Vries, R.J. de; Schweins, R. ; Cohen Stuart, M.A. ; Norde, W. - \ 2009
    Soft Matter 5 (2009)1. - ISSN 1744-683X - p. 242 - 250.
    charged block-copolymers - entrapping enzyme molecules - angle neutron-scattering - coacervate core micelles - drug-delivery - diblock copolymer - polymeric micelles - protein complexes - stability - lysozyme
    With the aim to gain insight into the possible applicability of protein-filled polyelectrolyte complex micelles under physiological salt conditions, we studied the behavior of these micelles as a function of salt concentration. The micelles form by electrostatically driven co-assembly from strong cationic block copolymers poly(2-methyl vinyl pyridinium)41-block- poly(ethylene oxide)205, weak anionic homopolymers poly(acrylic acid)139, and negatively charged lipase molecules. The formation and disintegration of these micelles were studied with dynamic light scattering (DLS), by means of composition and salt titrations, respectively. The latter measurements revealed differences between disintegration of lipase-filled and normal polyelectrolyte complex micelles. These data, together with small angle neutron scattering (SANS) measurements provide indications that lipase is gradually released with increasing salt concentration. From the SANS data a linear relation between the intensity at q = 0 and the volume of the cores of the micelles at different salt concentrations was derived, indicating a loss of volume of the micelles due to the release of lipase molecules. It was estimated that beyond 0.12 M NaCl all lipase molecules are released
    Stability of complex coacervate core micelles containing metal coordination polymer
    Yan, Y. ; Keizer, A. de; Cohen Stuart, M.A. ; Drechsler, M. ; Besseling, N.A.M. - \ 2008
    The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical 112 (2008)35. - ISSN 1520-6106 - p. 10908 - 10914.
    block ionomer complexes - entrapping enzyme molecules - diblock copolymer - physicochemical properties - polyelectrolyte - nanoparticles - lysozyme - delivery - surface - length
    We report on the stability of complex coacervate core micelles, i.e., C3Ms (or PIC, BIC micelles), containing metal coordination polymers. In aqueous solutions these micelles are formed between charged-neutral diblock copolymers and oppositely charged coordination polymers formed from metal ions and bisligand molecules. The influence of added salt, polymer concentration, and charge composition was investigated by using light scattering and cryo-TEM techniques. The scattering intensity decreases strongly with increasing salt concentration until a critical salt concentration beyond which no micelles exist. The critical micelle concentration increases almost exponentially with the salt concentration. From the scattering results it follows that the aggregation number decreases with the square root of the salt concentration, but the hydrodynamic radius remains constant or increases slightly. It was concluded that the density of the core decreases with increasing ionic strength. This is in agreement with theoretical predictions and is also confirmed by cryo-TEM measurements. A complete composition diagram was constructed based on the composition boundaries obtained from light scattering titrations
    When emulsions meet saliva : a physical-chemical, biochemical and sensory study
    Silletti, E. - \ 2008
    Wageningen University. Promotor(en): Willem Norde, co-promotor(en): G.A. van Aken; Monique Vingerhoeds. - S.l. : s.n. - ISBN 9789085048213 - 243
    emulsies - eigenschappen - sensorische evaluatie - speeksel - uitvlokking - lysozym - eiwitexpressieanalyse - emulsions - properties - sensory evaluation - saliva - flocculation - lysozyme - proteomics
    Keywords: Emulsion, flocculation, bridging, saliva, salivary protein, salivary peptides, lysozyme, -lactoglobulin, complex formation, LC-MS, SELDI-TOF-MS, proteomics.

    Upon consumption food emulsions undergo various structural and compositional changes in the mouth. One of these changes is that mixing of an emulsion with saliva induces droplet flocculation
    In the study described in this thesis we investigated the influence of saliva on emulsions properties, the mechanism of flocculation and the role in sensory perception. Firstly, we started with evaluating the effect of parameters related to emulsions on flocculation (i.e. differently charged surfactants and proteins such as -lactoglobulin and lysozyme used as emulsifiers and oil-volume fraction). Among the obtained results, we observed that the sign and the density of the charge on the surface of the droplets determine the (ir-)reversibility of flocculation upon dilution with water and shearing. Secondly, the effect of saliva-related parameters was analyzed. Among other aspects, it appeared that an increase in salivary protein concentration increased emulsion flocculation, and that extensive flocculation is typically found for unstimulated saliva. This approach shows that both emulsion and saliva properties affect the flocculation behavior of emulsions/saliva mixtures.
    To investigate the nature of the flocculation, we characterized the salivary protein composition in both the continuous phase of the emulsion/saliva mixture and on the emulsion droplets. Different physical-chemical and biochemical techniques were used. For this approach, we focused on -lactoglobulin and lysozyme stabilized emulsions, which flocculated reversibly and irreversibly, respectively, upon mixing with saliva. A large number of salivary proteins and peptides in the molecular mass (Mr) range between 0.8 kDa and 100 kDa and the salivary mucins MUC5B and MUC7 (Mr > 200 kDa) associated with emulsion droplets of the emulsions. The results also indicate that the emulsifying protein at the oil-water interface determines which salivary components associate with the droplets in the flocs. A hypothesis is formulated that emulsion flocculation is mainly driven by a complex formation involving specific interactions and electrostatic attraction between salivary peptides/proteins and the emulsifying proteins at the droplets surface.
    The importance of the saliva-induced droplet flocculation was demonstrated with a sensory paneling study. Emulsions stabilized by whey protein isolate, (predominantly composed of -lactoglobulin) showed reversible flocculation and were perceived as creamy. In contrast, emulsions stabilised by lysozyme showed irreversible flocculation and were perceived as dry, rough and astringent.
    To conclude, this thesis shows that saliva-induced emulsion flocculation is driven mainly by association of salivary peptides and proteins to the droplets surface. Because of this, flocculation is determined by the composition of the droplet interface as well as the composition of the saliva, and can be controlled by variation of emulsion parameters (charge, pH, ionic strength). This interaction between emulsions and saliva may help to improve our understanding an control the sensory perception of emulsions.
































    Characteristic differences in the formation of complex coacervate core micelles from neodymium and zinc-based coordination polymers
    Yan, Y. ; Besseling, N.A.M. ; Keizer, A. de; Cohen Stuart, M.A. - \ 2007
    The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical 111 (2007)21. - ISSN 1520-6106 - p. 5811 - 5818.
    diblock copolymer - block-copolymers - metal-ions - polyelectrolyte - recognition - stability - lysozyme
    In this paper we compare the formation of complex coacervate core micelles (C3Ms) from two different tricompontent mixtures, namely neodymium, the bisligand L2EO4 and the poly(cation)-block-poly(neutral) diblock copolymer P2MVP41-b-PEO205, and zinc, L2EO4 and P2MVP41-b-PEO205 mixed systems. Three sets of titration experiments were carried out for each system: (i) titration of diblock copolymer P2MVP41-b-PEO205 with the stoichiometric mixture of metal ions and bisligands, (ii) titration of a mixture of diblock copolymer and bisligand with metal ions, and (iii) titration of a mixture of diblock copolymer and metal ions with bisligands. In all the above three cases, micelles are found to form either in a broad range of charge ratios or in a broad range of metal/bisligand ratios. Upon addition of Nd2-(L2EO4)3 coordination polymer to P2MVP41-b-PEO205 solution, and upon addition of Nd3+ to a mixture of L2EO4 and P2MVP41-b-PEO205, micelles are found to form immediately after the first addition, whereas micelles show up in the similar zinc system only after a certain threshold Zn-(L2EO4) or Zn2+ concentration. This difference can be traced to the different structures of the Nd2-(L2EO4)3 and Zn-(L2EO4) coordination compounds. At very low concentrations, Zn-(L2EO4) are ring-like oligomers, but Nd2-(L2EO4)3 are larger networks. The network structure favors the formation of coacervate micellar core with P2MVP41-b-PEO205. Moreover, excess of Nd3+ ions will break up the C3Ms, while the same amount of Zn2+ has hardly any effect on the C3Ms. The breakdown of C3Ms by Nd3+ is due to the charge inversion of the coordination complex with increasing [Nd3+]/[L2EO4] ratio, which results in repulsive interaction between the coordination complex and the diblock copolymer, whereas no such interaction can occur in the zinc system.
    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
    Hierarchical Self-Assembly in Solutions Containing Metal Ions, Ligand, and Diblock Copolymer
    Yan Yun, ; Besseling, N.A.M. ; Keizer, A. de; Marcelis, A.T.M. ; Drechsler, M. ; Cohen Stuart, M.A. - \ 2007
    Angewandte Chemie-International Edition 46 (2007)11. - ISSN 1433-7851 - p. 1807 - 1809.
    coordination polymers - block-copolymer - micelles - core - polyelectrolyte - recognition - complexes - lysozyme
    Structure and rheological properties of acid-induced egg white protein gels
    Weijers, M. ; Velde, F. van de; Stijnman, A. ; Pijpekamp, A. van de; Visschers, R.W. - \ 2006
    Food Hydrocolloids 20 (2006)2-3. - ISSN 0268-005X - p. 146 - 159.
    heat-induced aggregation - induced gelation - beta-lactoglobulin - functional-properties - light-scattering - denatured whey - disulfide bond - ionic-strength - ovalbumin - lysozyme
    This study compares the rheological properties of acid-induced gels prepared of industrial spray-dried egg white proteins (EWP) with the acid-induced gels prepared of ovalbumin (OA) and whey protein isolate (WPI). Also we aimed to form transparent gels of EWP by means of the cold-gelation process. We showed that it was not possible to prepare cold-set gels because ovotransferrin (OT), present in EWP, was found to interfere with fibril formation. Therefore, we developed a new purification method in which first Or was selectively denatured by a heating step, subsequently precipitated by acidification and removed by centrifugation. Finally, the supernatant was desalted by ultra filtration. This resulted in a preheated EWP preparation, which mainly contains OA (> 80%). By removing OT using this new preheat procedure transparent gels were obtained after acid-induced gelation. Fracture properties of various EWP preparations were determined and compared with those of acid-induced gels of OA and WPI. Gels formed from different EWP preparations were weak (fracture stress 1-15 kPa, fracture strain 0.3-0.7), and the networks consisted of thin strands with hardly any additional disulphide bonds formed during the gelation step. In conclusion, the microstructure of the aggregates formed in the first step of the cold-gelation process and the amount of additional disulphide bonds formed during the second step appeared to be the determining factors contributing to the hardness and deformability of acid-induced gels of egg white proteins.
    Shear pulses nucleate fibril aggregation
    Akkermans, C. ; Venema, P. ; Rogers, S.S. ; Goot, A.J. van der; Boom, R.M. ; Linden, E. van der - \ 2006
    Food Biophysics 1 (2006)3. - ISSN 1557-1858 - p. 144 - 150.
    beta-lactoglobulin gels - globular-proteins - mechanism - lysozyme - gelation - ph
    We have studied the effect of shear flow on the formation of amyloid fibrils of the whey protein ß-lactoglobulin. ß-Lactoglobulin aggregates into long, thin, and semiflexible fibrils upon heating at low pH and low ionic strength. Solutions with a protein concentration of 0.5% (w/w) were used, and the formation of fibrils was quantified with flow-induced birefringence, a proportional measure of the length concentration of the fibrils. From the decay of the birefringence after cessation of the flow, a length distribution could be fitted. Pulsed and continuous shear treatment of the samples resulted in a comparable enhancement of the fibrillar growth as compared to the fibrillar growth under quiescent conditions. This indicates that the onset of shear flow is the key parameter for the enhancement of fibrillar growth and not the continuous shear flow itself. This behavior is comparable to a nucleation-like process, during which preaggregates of the fibrils are induced during the onset of the flow and orthokinetic coagulation is absent. However, a difference was present in the length distribution between the pulsed and continuously sheared samples, which can be explained by the homogenizing effect of shear flow.
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