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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    Protein–Peptide Interaction: Study of Heat-Induced Aggregation and Gelation of ß-Lactoglobulin in the Presence of Two Peptides from Its Own Hydrolysate
    Kosters, H.A. ; Wierenga, P.A. ; Vries, R.J. de; Gruppen, H. - \ 2013
    Journal of Agricultural and Food Chemistry 61 (2013)18. - ISSN 0021-8561 - p. 4218 - 4225.
    rheological properties - alpha-lactalbumin - gels - isolate - acid - ovalbumin - fractions - soy
    Two peptides, [f135–158] and [f135–162]-SH, were used to study the binding of the peptides to native ß-lactolobulin, as well as the subsequent effects on aggregation and gelation of ß-lactoglobulin. The binding of the peptide [f135–158] to ß-lactoglobulin at room temperature was confirmed by SELDI-TOF-MS. It was further illustrated by increased turbidity of mixed solutions of peptide and protein (at pH 7), indicating association of proteins and peptides in larger complexes. At pH below the isoelectric point of the protein, the presence of peptides did not lead to an increased turbidity, showing the absence of complexation. The protein–peptide complexes formed at pH 7 were found to dissociate directly upon heating. After prolonged heating, extensive aggregation was observed, whereas no aggregation was seen for the pure protein or pure peptide solutions. The presence of the free sulfhydryl group in [f135–162]-SH resulted in a 10 times increase in the amount of aggregation of ß-lactoglobulin upon heating, illustrating the additional effect of the free sulfhydryl group. Subsequent studies on the gel strength of heat-induced gels also showed a clear difference between these two peptides. The replacement of additional ß-lactoglobulin by [f135–158] resulted in a decrease in gel strength, whereas replacement by peptide [f135–162]-SH increased gel strength.
    Comparison of xanthans by the relative abundance of its six constituent repeating units
    Kool, M.M. ; Gruppen, H. ; Sworn, G. ; Schols, H.A. - \ 2013
    Carbohydrate Polymers 98 (2013)1. - ISSN 0144-8617 - p. 914 - 921.
    xanthomonas-campestris - rheological properties - pyruvate content - polysaccharide - gum - acetyl - chromatography - hydrolysis - transition
    Five xanthans were hydrolyzed to their repeating units using cellulases. Hydrophilic interaction chromatography with online electrospray ionization ion trap mass spectrometry and evaporative light scattering detection was used to analyze the oligomers released. It was concluded that six different pentamer repeating units (RUs) exists within a xanthan sample. The most abundant RU shows acetylation on the inner mannose and pyruvylation on the outer mannose. The second most abundant RU shows acetylation on both the inner and the outer mannose. It becomes clear that more variations in the xanthan structure exist than generally recognized. Comparison of five different xanthan samples revealed that, although the molecular composition of xanthan samples can be exactly the same, the ratio in which the RUs occur can differ significantly. It is, therefore, concluded that xanthan samples should be characterized for both, their molecular composition and the relative abundance of the RUs present
    Pasta highly enriched with vegetables: from microstructure to sensory and nutritional aspects
    Vicente Da Silva, E.M. - \ 2013
    Wageningen University. Promotor(en): Erik van der Linden, co-promotor(en): Leonard Sagis; Elke Scholten; Matthijs Dekker. - S.l. : s.n. - ISBN 9789461736864 - 167
    deegwaren - broccoli - voedselverrijking - reologische eigenschappen - sensorische evaluatie - voedingswaarde - pasta - broccoli - food enrichment - rheological properties - sensory evaluation - nutritive value

    A lifestyle that combines poor food choices with very low or no physical activity can result in the development of diseases such as obesity, and this is affecting a growing number of children. One of the most effective strategies to fight obesity combines physical activity and the consumption of low energy-dense foods, such as vegetables. Vegetables are known to have health benefits but are often non-appealing to children/adolescents due to their bitterness, undesired texture, and their low satiating capacity. One of the possible solutions to increase vegetable intake by children is to incorporate vegetables in a food matrix they like. Several studies have shown that pasta is very much appreciated by children, making it an ideal candidate for the development of vegetable-enriched foods. In this work, dried broccoli powder (BP) was used to enrich pasta-like products. We have investigated aspects that are important to sensorial properties and aspects related to possible health benefits. One aspect relevant to sensorial properties is rheology. The rheology of sweet potato starch (SPS) dough was drastically affected by high volume fractions of BP. This was caused by the swelling of the broccoli powder, up to a maximum of 7.6 times their original volume. In order to control this high swelling capacity of the particles two approaches were followed and both resulted in the prevention of particle swelling. The first was the use of hydrocolloids with high water binding capacity (e.g. xanthan gum) and the second was the use of a different matrix (durum wheat semolina (DWS)). DWS pasta did not show to be greatly affected by the incorporation of high amounts of broccoli powder. The acceptability of pasta products was assessed using a test panel. The results showed that all samples tested (0 – 30%BP) were acceptable, where 30% BP turned out to be on the limit of acceptability. Glucosinolates (GLs) are phytochemicals that are associated with the health benefits of broccoli. An increasing volume fraction of broccoli powder resulted in an increasing content of glucosinolates in dried cooked pasta. At volume fractions higher than 20% BP this effect levels off. From this work, we can conclude that as much as 20% BP can be added to DWS pasta to improve nutritional properties (in terms of GLs) while maintaining acceptable sensorial properties.

    Nanostructure development during peroxidase catalysed cross-linking of a-lactalbumin
    Saricay, Y. ; Wierenga, P.A. ; Vries, R.J. de - \ 2013
    Food Hydrocolloids 33 (2013)2. - ISSN 0268-005X - p. 280 - 288.
    whey-protein isolate - microbial transglutaminase - horseradish-peroxidase - beta-lactoglobulin - conformational properties - rheological properties - thermal-stability - laccase - oxidation - enzyme
    Whereas extensive work has been done on the food functional and chemical aspects of enzymatic protein cross-linking, relatively little is known about the nanostructure and physical-chemical properties of enzymatically cross-linked protein. We investigate how nanostructure develops during enzymatic cross-linking of the 4 tyrosine residues of the globular protein apo a-lactalbumin. Protein cross-linking is catalysed by Horseradish Peroxidase, under the periodic addition of peroxide. We use on-line static and dynamic light scattering, combined with on-line UV-spectroscopy to simultaneously probe the development of nanostructure, the extent of dityrosine formation, and the catalytic state of the enzyme, as a function of the number of peroxide additions. It is found that initially, the rate of dityrosine formation is high, whereas the increase in the solution size of the cross-linked protein is limited. At later stages, the increase in solution size is significant whereas dityrosine formation slows down. Finally, the reaction stops due to enzyme inactivation. Off-line size exclusion chromatography shows that the initial phase corresponds to a fast cross-linking of monomers into small oligomers, followed by a slower joining of oligomers into large protein polymers. Consistent with this, Atomic Force Microscopy shows very heterogeneous polymers, apparently consisting of subunits that we identify with the oligomers formed in the first phase of the reaction. The dependence of the solution size on the molar mass of the cross-linked protein is determined using static and dynamic light scattering on fractionated reaction products. For sizes ranging from 30 nm to 80 nm, the protein polymers consist of 100–1000 a-lactalbumin subunits, and have molar masses of 106–107 g/mol. Apparent internal protein densities of the protein polymers calculated from these numbers are only a few weight percent, indicating a very dilute, open architecture of the cross-linked protein.
    Rheology and Fracture Mechanics of Foods
    Vliet, T. van - \ 2013
    Boca Raton, FL, USA : CRC Press - ISBN 9781439827031 - 363
    reologie - mechanische eigenschappen - voedingsmiddelen - mechanica - voedselproducten - meettechnieken - reologische eigenschappen - rheology - mechanical properties - foods - mechanics - food products - measurement techniques - rheological properties
    The mechanical properties of food play an important role during manufacturing, storage, handling, and last but not least, during consumption. For an adequate understanding of the mechanical properties of liquid, liquid-like, soft solid, and solid foods, a basic understanding of relevant aspects of rheology and fracture mechanics is essential. Focusing on basic principles, Rheology and Fracture Mechanics of Foods examines how rheological and fracture behavior in food relates to product structure. Divided into three parts, the book reviews basic concepts and emphasizes aspects relevant for studying food products, raw materials, and intermediate products. It then introduces measuring methods and the equipment used for studying mechanical properties of food products, highlighting tests that deliver reproducible and interpretable data. The final part investigates the relation between rheological and fracture behavior of matter and physical structure at the relevant molecular, mesoscopic, and macroscopic length scales. In addition to the basics of rheology and fracture mechanics, the book explores the relationship between measured mechanical properties and the structure of the different types of food and how they may determine texture perception
    Protein micro-structuring as a tool to texturize protein foods
    Purwanti, N. ; Peters, J.P.C.M. ; Goot, A.J. van der - \ 2013
    Food & Function 4 (2013)2. - ISSN 2042-6496 - p. 277 - 282.
    amino-acids - dietary-protein - rheological properties - statistical-mechanics - high-carbohydrate - elderly people - whey - requirements - muscle - microstructure
    Structuring protein foods to control the textural properties receives growing attention nowadays. It requires decoupling of the product properties such as water holding capacity and the mechanical properties from the actual protein concentration in the product. From an application point of view, both increasing and lowering the protein content in the food are interesting. Foods enriched with proteins are important due to their reported health benefits, but increasing the protein content in food products generally leads to products that are firmer and have a more rubbery mouth-feel than the regular products, making them less attractive. A reduced protein content, for example in meat- or cheese-analogues, is relevant because it leads to a lower caloric intake per serving and it enhances its economic potential. Decoupling of the protein concentration and product properties can be obtained by changing the internal structure of those food products. This paper outlines the use of protein aggregates and particles in a protein matrix as a tool to obtain different textural properties of a model protein product. Whey protein isolate (WPI) was taken as a model protein. However, further investigation of WPI microparticles should focus on a better understanding of their swelling behaviour in the protein matrix to fully use the potential of those protein particles as a tool to decouple product properties and actual protein concentration.
    Interfacial properties of air/water interfaces stabilized by oligofructose palmitic acid esters in the presence of whey protein isolate
    Kempen, S.E.H.J. van; Maas, K. ; Schols, H.A. ; Linden, E. van der; Sagis, L.M.C. - \ 2013
    Food Hydrocolloids 32 (2013)1. - ISSN 0268-005X - p. 162 - 171.
    air-water-interface - beta-lactoglobulin - competitive adsorption - rheological properties - surfactant systems - dynamic properties - foaming properties - liquid interfaces - mixed films - displacement
    To study the applicability of oligofructose palmitic acid esters (OF-C16) as novel surfactants in food systems, the functional properties of OF-C16 were studied in the presence of whey protein isolate (WPI). Surface tension measurements, surface dilatational rheology, foam stability tests and Brewster Angle Microscopy were used to study the competitive adsorption of WPI and OF-C16 and the displacement of WPI by OF-C16. Pure WPI stabilized interfaces had a moderate surface tension (48 mN/m) and a dilatational modulus of 90 mN/m, while pure OF-C16 stabilized interfaces had a low surface tension (30 mN/m) and a dilatational modulus of 50 mN/m. The stabilization mechanisms of WPI (elastic network formation) and of OF-C16 (surface solidification) are very different, and the combined adsorption of these two components led to a structure with a much lower dilatational modulus. At the lowest WPI concentrations (0.5% and 1%), the equilibrium surface tension was similar to a pure OF-C16 stabilized interface, pointing to a low WPI surface concentration. However, apparently still sufficient WPI had adsorbed either at or just below the interface, to prevent the OF-C16 from solidifying. Despite the low moduli, the foam stability for the mixed systems was high. The interfaces were probably stabilized by the Gibbs-Marangoni mechanism. In contrast, at the highest WPI concentration (2%), the equilibrium surface concentration of WPI was sufficiently high to decrease the interfacial mobility of OF-C16, which decreased the Gibbs-Marangoni effect and resulted in decreased foam stability. Finally, OF-C16 could also displace a fully developed WPI network from the interface.
    Structuring of expanded snacks based on patato ingredients : a review
    Sman, R.G.M. van der; Broeze, J. - \ 2013
    Journal of Food Engineering 114 (2013)4. - ISSN 0260-8774 - p. 413 - 425.
    glass-transition temperature - damaged starch granules - physical-properties - extruded products - bubble-growth - semicrystalline polymers - rheological properties - extrusion behavior - sodium-chloride - foaming process
    In this paper we review the current knowledge on the structuring via bubble expansion of starchy snacks, which are formulated on the basis of potato ingredients. These snacks are rarely discussed in scientific literature, but there are a scant number of patents dealing with various formulations and process descriptions. The general trends in the snack processing, we have described in a formal way using the Complex Dispersed Systems notation, augmented with a depiction of the processing pathway in the supplemented state diagram of starch. With this general framework in mind, we have compared the information given in the patents with scientific literature on cereal-based snacks. Based on this comparison we have formulated hypotheses about the functionality of the various ingredients with respect to the structuring of the potato snacks.
    Reducing the stiffness of concentrated whey protein isolate (WPI) gels by using WPI microparticles
    Purwanti, N. ; Moerkens, A. ; Goot, A.J. van der; Boom, R.M. - \ 2012
    Food Hydrocolloids 26 (2012)1. - ISSN 0268-005X - p. 240 - 248.
    rheological properties - water-absorption - powders - aggregation - composites - starch - shear - flow
    Concentrated protein gels were prepared using native whey protein isolate (WPI) and WPI based microparticles. WPI microparticles were produced by making gel pieces from a concentrated WPI suspension (40% w/w), which were dried and milled. The protein within the microparticles was denatured and the protein concentration after drying was similar to the native WPI powder. WPI microparticles had irregular shape with an average size of about 70 mm. They absorbed water when dispersed in water, but the dispersion did not gel upon heating. Replacing part of the native WPI powder with WPI microparticles in the protein gel resulted in lower gel stiffness compared with a gel with the same overall protein concentration but without microparticles. However, microparticles also strengthened the continuous phase because they take up water from this phase. This might increase gel stiffness more than would be expected from an inert particle/filler. There was also good bonding between the microparticles and the WPI continuous phase in the gel, which contributed to gel stiffness.
    Formation of oil droplets in plasticized starch matrix in simple shear flow
    Emin, M.A. ; Hardt, N.A. ; Goot, A.J. van der; Schuchmann, H.P. - \ 2012
    Journal of Food Engineering 112 (2012)3. - ISSN 0260-8774 - p. 200 - 207.
    polymer blends - rheological properties - newtonian drop - thermoplastic starch - extrusion-cooking - molecular-weight - sunflower oil - steady shear - corn starch - deformation
    This paper describes the effect of simple shear flow on the formation of triglyceride oil droplets in a plasticized starch matrix. An in-house developed shearing device was used that enabled the application of controlled shear flow and rheological characterization of the native maize starch–triglyceride blends at shear stresses of up to 37 kPa. Due to the high viscosity of starch matrix, the viscosity ratio of the continuous starch phase and the dispersed triglyceride phase varied between 10-7 and 10-5. It was possible to create small droplets with a droplet diameter of 2.1 µm using simple shear flow only. An increase in shear rate had no influence on droplet diameter. However, an increase in oil content led to a vast increase in droplet diameter indicating the occurrence of coalescence. The results further show that the maximum stable droplet size in plasticized starch is significantly smaller (up to 100 times) than the predicted values for a Newtonian matrix. The differences of plasticized starch to Newtonian matrices are discussed in detail.
    Soft matter approaches to food structuring
    Sman, R.G.M. van der - \ 2012
    Advances in Colloid and Interface Science 176-177 (2012). - ISSN 0001-8686 - p. 18 - 30.
    lattice-boltzmann simulations - protein-polysaccharide interactions - brownian dynamics simulation - free-volume theory - glass-transition - phase-transitions - mass-transfer - rheological properties - beta-lactoglobulin - casein micelles
    We give an overview of the many opportunities that arise from approaching food structuring from the perspective of soft matter physics. This branch of physics employs concepts that build upon the seminal work of van der Waals, such as free volume, the mean field, and effective temperatures. All these concepts aid scientists in understanding and controlling the thermodynamics and (slow) dynamics of structured foods. We discuss the use of these concepts in four topics, which will also be addressed in a forthcoming Faraday Discussion on food structuring.
    Improved creaminess in stirred yoghurt through amylomaltase-treated starch domains
    Kanning, M.W. ; Velde, F. van de; Alting, A.C. ; Buwalda, P.L. - \ 2012
    International Dairy Journal 27 (2012)1-2. - ISSN 0958-6946 - p. 86 - 91.
    rheological properties - milk - protein - impact - gels
    Amylomaltase-treated starch (ATS) has been described as an excellent fat-replacer in set yoghurt. Its functionality as a creaminess enhancer relates to the ability to form domains, which have melting and yielding characteristics in the mouth. This study was intended to understand the functionality of ATS in stirred yoghurt. Sensory evaluation of reduced fat stirred yoghurt samples showed that the creaminess perception of stirred yoghurt with 1.5% fat and 0.5% ATS was comparable with the reference full fat yoghurt containing 3% fat. This showed that ATS was even more effective as a creaminess enhancer in stirred yoghurt than in set yoghurt. This was related to the higher effectiveness of domain formation during storage after cooling in a dispersed system, as a result of stirring of the yoghurt gel, compared with a gelled set-yoghurt system.
    Structuring high-protein foods
    Purwanti, N. - \ 2012
    Wageningen University. Promotor(en): Remko Boom, co-promotor(en): Atze Jan van der Goot. - S.l. : s.n. - ISBN 9789461731913 - 188
    eiwitten - structuur - gelering - reologische eigenschappen - wei-eiwit - proteins - structure - gelation - rheological properties - whey protein

    Increased protein consumption gives rise to various health benefits. High-protein intake can lead to muscle development, body weight control and suppression of sarcopenia progression. However, increasing the protein content in food products leads to textural changes over time. These changes result in product hardening over time and several negative sensorial attributes such as rubbery and dry mouth feel.

    This thesis describes the role of structuring to control the rheological and mechanical properties of high-protein model foods. By altering the internal structure of the model systems, textural properties of the model systems at initial stage (fresh products) can be improved.

    Content of this thesis can be distinguished into four parts. The first part reviews existing studies related to high-protein foods. The effects of ingredients and processing were evaluated with respect to food products having a high protein content. Some studies indicated typical problems occurring in products or model systems with an increased protein content such as product hardening over time. Ingredients that might be added to ameliorate product properties were plasticizers, peptides made from whey proteins, disulphide reducing agents, and components that block the free thiol groups in proteins. This part provides guidelines for structuring high-protein foods aimed at avoiding or reducing the unfavourable changes in properties over time. Concentrated proteins in their native (unmodified) form can be replaced by protein domains or structural elements with altered properties. These domains or elements mitigate the changes in product structure, resulting in a product that is softer than the one made from native proteins only.

    The second part focuses on the structural elements made from whey protein isolate (WPI), namely WPI aggregates and WPI microparticles. WPI aggregates were formed by different heating conditions at neutral pH. Generally, a higher concentration and a higher temperature resulted in bigger and less dense aggregates. A higher temperature also resulted in a higher reactivity (a larger number of available thiol groups). Heating an aggregate suspension led to a weaker gel than a gel made from native protein at similar. This result was hypothesized to originate from the lower number of contact points formed with larger aggregates. It was concluded that the most pronounced weakening effect could be obtained with aggregates that are large, dense, and non-reactive. That is why WPI microparticles were created. The particles were formed by gelling a concentrated WPI solution, and subsequent drying the gel and milling it into small particles. Partial replacement of native WPI with WPI microparticles resulted in a weaker gel than a gel made from native WPI only at the same total protein concentration. This result was attributed to the inability of the microparticles to form a gel. However, the weakening effect of these particles in the model system was limited due to water redistribution and the good bonding between the particles and the protein continuous phase.

    The third part describes how the properties of high-protein gels containing WPI microparticles change over time. A high-protein gel made from native WPI was used as a reference. The firmness and fracture stress of the gel made from WPI only increased during the first few days and then stabilized. The gel consisting of WPI microparticles in WPI or in a mixture of locust bean gum (LBG)–xanthan gum (XG) tended to harden for a longer period. Most likely, water redistribution is responsible for this observation.

    The influence of charge ratio on transient networks of polyelectrolyte complex micelles
    Lemmers, M. ; Spruijt, E. ; Beun, L.H. ; Fokkink, R.G. ; Leermakers, F.A.M. ; Portale, G. ; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2012
    Soft Matter 8 (2012)1. - ISSN 1744-683X - p. 104 - 117.
    coacervate core micelles - transfer radical polymerization - associative polymers - diblock copolymers - block-copolymers - rheological properties - methyl-methacrylate - aqueous-solutions - phase-behavior - water
    We study the influence of charge ratio on the transient network formation of bridged polyelectrolyte complex micelles. The polyelectrolyte complex micelles are based on mixing an ABA triblock copolymer in which the A-blocks are positively charged and the B-block is neutral and hydrophilic, and a negatively charged homopolymer. We investigate the microstructure of our samples with (dynamic) light scattering and small-angle X-ray scattering, and the mechanical properties by rheometry. At charge stoichiometric conditions, we obtain flowerlike polyelectrolyte complex micelles. These micelles become interconnected at high concentrations, leading to a sample-spanning transient network. For excess negative charge conditions, we obtain so-called ‘soluble complexes’ which are small aggregates carrying the excess negative charge on the polyelectrolyte complex parts. For excess positive charge conditions, micelles stay intact, because the triblock copolymers can localize the excess positive charge at the periphery of the micellar corona. This structural asymmetry is not reflected in the mechanical properties, which show a strong decrease in viscosity on either side of the charge stoichiometric point.
    Colloids and interfaces in life sciences and bionanotechnology
    Norde, Willem - \ 2011
    CRC Press - ISBN 9781439817186 - 466 p.
    colloids - colloidal properties - interface - surface tension - emulsions - foams - rheological properties - textbooks - surface chemistry

    Colloidal systems occur everywhere-in soils, seawater, foodstuff, pharmaceuticals, paints, blood, biological cells, and microorganisms. Colloids and Interfaces in Life Sciences and Bionanotechnology, Second Edition, gives a concise treatment of physicochemical principles determining interrelated colloidal and interfacial phenomena. New in the Second Edition: New topics, including phase separations in polymer systems, electrokinetics of charged permeable surface coatings, and polymer brush coatings to control adsorption and adhesion of particles. Emphasis on inter-particle interactions and surface phenomena in (bio)nanotechnology. Full solutions to over 100 updated and additional exercises are presented in the Appendix. Focusing on physicochemical concepts that form the basis of understanding colloidal and interfacial phenomena-rather than on experimental methods and techniques-this book is an excellent primer for students and scientists interested in colloidal and interfacial phenomena, their mutual relations and connections, and the fascinating role they play in natural and man-made systems.

    Colloidal Protein Particles Can Be Used to Develop a Gluten-free Bread
    Riemsdijk, L.E. van; Goot, A.J. van der - \ 2011
    Cereal Foods World 56 (2011)5. - ISSN 0146-6283 - p. 201 - 204.
    rheological properties - celiac-disease - cold gelation - quality - flour - dough - batters - formulations - impact
    This paper presents a novel approach for the production of gluten-free breads. Rather than mimicking the molecular structure and properties of gluten, gluten functionality was mimicked by creating a colloidal protein particle network (based on whey protein). The addition of this protein particle network transformed a starch slurry into a material with dough-like properties that could be used in a standard baking process to produce gluten-free breads. An overview of the potential and limitations of this novel technology is given.
    Polyelectrolyte complexes: Bulk phases and colloidal systems
    Gucht, J. van der; Spruijt, E. ; Lemmers, M. ; Cohen Stuart, M.A. - \ 2011
    Journal of Colloid and Interface Science 361 (2011)2. - ISSN 0021-9797 - p. 407 - 422.
    oppositely charged polyelectrolytes - coacervate core micelles - highly aggregating systems - electrostatic free-energy - aqueous-solutions - multilayer films - rheological properties - diblock copolymer - cell model - coordination polymers
    When aqueous solutions of polycations and polyanions are mixed, polyelectrolyte complexes form. These are usually insoluble in water, so that they separate out as a new concentrated polymer phase, called a complex coacervate. The behavior of these complexes is reviewed, with emphasis on new measurements that shed light on their structural and mechanical properties, such as cohesive energy, interfacial tension, and viscoelasticity. It turns out that stoichiometric complexes can be considered in many respects as pseudo-neutral, weakly hydrophobic polymers, which are insoluble in water, but become progressively more soluble as salt is added. In fact, the solubility-enhancing effect of salt is quite analogous to that of temperature for polymers in apolar solvents. Since two-phase systems can be prepared in colloidal form, we also discuss several kinds of colloids or 'microphases' that can arise due to polyelectrolyte complexation, such as thin films, 'zipper' brushes, micelles, and micellar networks. A characteristic feature of these charge-driven two-phase systems is that two polymeric ingredients are needed, but that some deviation from strict stoichiometry is tolerated. This turns out to nicely explain how and when the layer-by-layer method works, how a 'leverage rule' applies to the density of the 'zipper brush', and why soluble complexes or micelles appear in a certain window of composition. As variations on the theme, we discuss micelles with metal ions in the core, due to incorporation of supramolecular coordination polyelectrolytes, and micellar networks, which form a new kind of physical gels with unusual properties
    Transient network topology of interconnected polyelectrolyte complex micelles
    Lemmers, M. ; Voets, I.K. ; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2011
    Soft Matter 7 (2011)4. - ISSN 1744-683X - p. 1378 - 1389.
    transfer radical polymerization - diblock copolymer micelles - coacervate core micelles - rheological properties - aqueous-solutions - associating polymers - poly(ethylene oxide) - telechelic polymers - methyl-methacrylate - triblock copolymer
    In this paper we study transient networks formed by co-assembly of an ABA triblock copolymer with charged A blocks and neutral water-soluble B blocks, and an oppositely charged homopolymer. Above the CMC, the polymers associate into flowerlike micelles consisting of a polyelectrolyte complex core and a neutral corona of loops formed by the middle blocks. At higher concentrations, the micelles become connected to each other by bridging middle-blocks, leading to a physical network with visco-elastic properties. We use a combination of (dynamic) light scattering, small-angle X-ray scattering and rheometry, to characterize how the network structure changes with polymer concentration and ionic strength, and how these changes affect the macroscopic elastic properties of the network. We find that an increase in ionic strength leads to a decrease in aggregation number and size of the individual micelles, which simultaneously leads to an increase in the number density of micelles. These two effects compensate each other such that the probability of bridge formation is equal at all salt concentrations, meaning that the elastic modulus of the gels is independent of salt concentration
    A novel method to prepare gluten-free dough using a meso-structured whey protein particle system
    Riemsdijk, L.E. van; Pelgrom, P.J.M. ; Goot, A.J. van der; Boom, R.M. ; Hamer, R.J. - \ 2011
    Journal of Cereal Science 53 (2011)1. - ISSN 0733-5210 - p. 133 - 138.
    rheological properties - bread quality - simple shear - microstructure - hydrocolloids - formulations - behavior - flow
    This paper presents a novel concept for making an elastic dough using a structured protein suspension. The idea behind it is based on the hypothesis that a number of gluten properties originate from a particle structure present in the gluten network. Three different mesoscopically structured whey protein suspensions were produced: whey protein aggregates, a whey protein cold set gel and whey protein particles. Dough mixtures or batters were prepared by mixing the structured protein particle suspension with starch. Farinograph curves, small and large deformation experiments showed that the presence of a mesoscopic protein structure had a large impact on the properties of gluten-free starch mixtures. The whey protein that was structured into a mesoscopic particle suspension changed the starch mixture from a liquid into a cohesive material, having strain hardening properties.
    Preparation of gluten-free bread using a meso-structured whey protein particle system
    Riemsdijk, L.E. van; Goot, A.J. van der; Hamer, R.J. ; Boom, R.M. - \ 2011
    Journal of Cereal Science 53 (2011)3. - ISSN 0733-5210 - p. 355 - 361.
    rheological properties - gas retention - dough - flour - stabilization - formulations - quality
    This article presents a novel method for making gluten-free bread using mesoscopically structured whey protein. The use of the meso-structured protein is based on the hypothesis that the gluten structure present in a developed wheat dough features a particle structure on a mesoscopic length scale (100 nm–100 µm). Whey protein particles were prepared by cold gelation of soluble whey protein aggregates during phase separation. The addition of a 2.4% whey protein particle suspension to wheat starch resulted in a dough that could be baked into a leavened bread with a specific volume up to 3.7 ml/g and a bubble size comparable with a normal bread. The relevance for structuring the whey protein into mesoscopic particles was confirmed by tests in which only a homogeneous whey protein gel or a whey protein solution was used. The protein particle system gave better results after proving and baking compared with these systems.
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