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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Structuring oil by protein building blocks
Vries, Auke de - \ 2017
Wageningen University. Promotor(en): Erik van der Linden, co-promotor(en): Elke Scholten. - Wageningen : Wageningen University - ISBN 9789463430760 - 167
gelation - gels - proteins - mechanical properties - oils - solidification - gelering - gels - eiwitten - mechanische eigenschappen - oliën - hardwording

Over the recent years, structuring of oil into ‘organogels’ or ‘oleogels’ has gained much attention amongst colloid-, material,- and food scientists. Potentially, these oleogels could be used as an alternative for saturated- and trans fats in food products. To develop oleogels as a suitable replacement for saturated fats, the requirements go beyond merely providing a solid appearance to an otherwise liquid oil. For food applications, the gelator should be a well-known ingredient for food manufacturers, have a good nutritional value, and contribute to ‘clean labelling’. Proteins meet all these requirements and could therefore be of high potential. The general concept of protein-based oil gelation fits well into the growing general interest to reduce solid fats from food products along with increase in flexibility in terms of choice of ingredients. In this thesis, the suitability of proteins as a structuring agent for liquid oil was investigated and the rheological behaviour was described. To create protein oleogels, heat-set whey protein gels and protein aggregates, or ‘building blocks’, are created in an aqueous environment. Then, the aqueous phase is exchanged for a liquid oil phase via an intermediate solvent. It was show that by using this procedure, the created protein building blocks are highly efficient in creating oleogels. It is encouraging to see that the interactions between proteins can be altered by simple changes to the system, such as changing the oil type, water addition, or applying a heat treatment. This leads to the possibility to effectively and substantially tune the rheological properties of the final oleogel, such as its gel strength or yielding behaviour.

Supramolecular networks of telechelic polymers
Bohdan, M.A. - \ 2016
Wageningen University. Promotor(en): Jasper van der Gucht, co-promotor(en): Joris Sprakel. - Wageningen : Wageningen University - ISBN 9789462578678 - 117
supramolecular chemistry - networks - polymerization - gels - mechanical properties - separation technology - rheology - supramoleculaire chemie - netwerken - polymerisatie - gels - mechanische eigenschappen - scheidingstechnologie - reologie

This thesis focuses on the fundamental understanding of phenomena associated with the gelation of end-functionalized polymers and the dynamic processes occurring inside of the gel network. To address particular questions we use two types of telechelic polymers, in which the assembly occurs due to the solvophobic interactions and due to the metal-ligand coordination, respectively. In this research we employ a number of methods, mostly rheology and light scattering.

In Chapter 2 we revealed new insights into the complex microscopic dynamics of transient networks, assembled by hydrophobic forces. Using light scattering experiments we show how these materials exhibit complex multimodal relaxation spectra. To shed light on the nature of such relaxation processes we systematically changed the network architecture by gradually reducing the network connectivity while keeping the polymer concentration constant. This strategy allows us to disentangle the roles of concentration and connectivity on the dynamic modes of these systems.

In Chapters 3 and Chapter 4 we experimentally explored the pathways of network formation from telechelic polymers association by means of metal-ligand complexation. Interestingly, while some networks exhibit near-ideal Maxwellian behavior, as expected for transient networks, we find certain cases where we observe scale-free critical mechanics. To date this latter behavior was only identified close to a covalent percolation transition. The critical behavior observed for these end-functional self-assembled polymer networks, however, is robust to changes in concentration, temperature and crosslinking degree. Our studies show that such a self-organized and robust critical state is the results of arrested phase separation that kinetically traps the network-forming system at its percolation point. The system thus remains trapped in a critical state resulting in robust power-law scaling of shear and relaxation moduli. We also show how this state depends sensitively on the relaxation kinetics of the nodes by demonstrating an intermediate case where initial critical behavior slowly relaxes over the course of several days to the ideal linear Maxwell case. With our research we highlight the complex pathway where self-assembling systems reach their equilibrium ground state, involving persistent and long-lived kinetically arrested states which give rise to unusual mechanics and highly heterogeneous spinodal structures.

Chapter 5 brought us towards more applicable materials where we develop a highly tunable composite network based on orthogonal supramolecular interactions. For such a design we generate multivalent nanoparticle tectons, which are subsequently linked together into network structures, using metal-coordination interactions. Materials built this way are highly tunable with moduli and viscosities spanning many orders of magnitude.

In the remainder of this chapter, we focus on some unresolved and outstanding questions regarding the physical chemistry and properties of supramolecular networks and we will discuss some preliminary data obtained in our efforts to resolve them.

Fibrillar structures in mixed systems
Peng, Jinfeng - \ 2016
Wageningen University. Promotor(en): Erik van der Linden, co-promotor(en): Paul Venema; K.P. Velikov. - Wageningen : Wageningen University - ISBN 9789462578265 - 284
cellulose - bacteria - fibres - protein isolates - whey - mixtures - emulsions - mechanical properties - cellulose - bacteriën - vezels - eiwitisolaten - wei - mengsels - emulsies - mechanische eigenschappen

Fibrillar structures are important structuring elements for food products. Understanding the behaviour of fibrillar structures in complex food systems is essential for successful industrial applications. This thesis presents the behaviour of two different fibrillar structures, i.e. whey protein isolate (WPI) fibrils and bacterial cellulose (BC) microfibrils in mixtures under various conditions. The WPI fibrils are prepared from WPI and the BC microfibrils are extracted from commercial available ‘Nata de Coco’ by high-energy de-agglomeration. In Chapter 1, a general introduction is given, where we introduce two different fibrillar structures that were studied in this thesis. Also, the aim and the outline of the thesis are presented. In Chapter 2, 3, 4 and 5, the behaviour of mixtures containing WPI and BC microfibrils under different conditions are investigated. By varying the concentration ratios, pH, NaCl concentration and further applying heating treatment, their physico-chemical properties in mixed solutions, mixed solutions after heating and further heat-induced mixed gels are investigated and characterized at both pH 2 and pH 7. In general, both mixing WPI and BC microfibrils without heating and subsequently applying heating treatment lead to stable and homogeneous mixtures at pH 7, as long as BC microfibril concentration is above a critical value. Microscopic images showed that the WPI aggregates and BC microfibrils co-existed in the system. WPI denatured and aggregated in the mixture in the same way as when it is heated alone. Upon gelation, the WPI and BC microfibrils form a duplex gel consisting of two independent and homogeneous networks spanning the whole system. At pH 2, the WPI and BC microfibrils also form stable and homogeneous mixtures in the liquid state, both before and after heating. Microscopic images showed two fibrillar structures that are uniformly and independently present. Upon gelation at higher WPI concentration, a bi-fibrillar gel is formed consisting of a WPI fibrilllar gel and BC microfibrillar gel that co-exist. In Chapter 6 and 7, the behaviour of WPI fibrils at pH 2 in dispersions containing spheres, i.e. emulsions and polystyrene latex dispersions are studied. When WPI and spheres are both positively charged (i.e. WPI-stabilized emulsion), we observed depletion flocculation and depletion stabilization when the WPI fibril concentration increases. When WPI and the spheres are oppositely charged (i.e. polystyrene latex dispersions), bridging flocculation and steric/electrostatic stabilization were observed at low WPI fibril concentration, followed by depletion flocculation and depletion stabilization upon increasing WPI fibril concentrations. In Chapter 8 the stability of emulsions at pH 2 in the presence of only BC microfibrils and in the presence of both BC microfibrils and WPI fibrils was studied. When only BC microfibrils added at a sufficiently high concentration, the emulsions are stabilized by the presence of a yield stress as generated by the BC network. When both WPI fibrils and BC microfibrils are added to the emulsions, the networks they form behave in the same way, as when they are added to the emulsions separately. The WPI fibrils induced depletion flocculation and stabilization of the emulsions, despite the presence of the BC microfibrils. However, at high enough BC microfibril concentrations, the emulsions can be stabilized against depletion flocculation as induced by the WPI fibrils. The competition between stabilization and/or de-stabilization induced by the BC microfibrils and the WPI fibrils can lead to emulsions with different microstructures and rheological properties. A general discussion on the results obtained in this thesis is presented in Chapter 9, which includes recommendations for further research and concluding remarks.

Composite hydrogels of bio-inspired protein polymers : mechanical and structural characterization
Rombouts, W.H. - \ 2015
Wageningen University. Promotor(en): Jasper van der Gucht. - Wageningen : Wageningen University - ISBN 9789462575721 - 172
gels - formation - proteins - polymers - networks - mechanical properties - gels - formatie - eiwitten - polymeren - netwerken - mechanische eigenschappen

In this thesis we presented various combinations of custom-designed protein polymers that formed composite hydrogels. In chapter 2, composite hydrogels were prepared by mixing silk-like block copolymers (CP2SE48CP2) with collagen-like block copolymers (T9CR4T9). We found that by adding the collagen-like protein polymer the storage modulus, the critical stress and critical strain values of the composite hydrogels were significantly improved in comparison to the single networks. With cryo-transmission electron microscopy (cryo-TEM) we observed that the silk-like fibers were bundled in the presence of the collagen-like protein polymer, probably due to depletion attraction interactions. In follow-up research on these composite hydrogels in chapter 3, we tried to get more insight into the exact toughening mechanism and self-healing capabilities of the composite network by performing cyclic loading/unloading tests. We found that mechanical hysteresis occurred in these composite hydrogels. The energy that was dissipated could be split into two contributions: a part belonging to the permanent rupture of silk-like fibers, and a viscoelastic part belonging to the assembly and disassembly of collagen-like triple helices. Both these contributions increased as the concentration of the collagen-like protein polymer in the composite network was increased, resulting in toughening of the composite network. Furthermore, it was observed that the silk-like fiber network was not able to recover, while the composites could recover up to 70% of the original storage modulus after failure. In chapter 4 we studied composite networks of silk-like block copolymers (CP2SE48CP2) and a FMOC-functionalized dipeptide (FMOC-LG) which could both form fibers. With cryo-TEM and atomic force microscopy (AFM) we found that two different types of fibers were formed, indicating that orthogonal self-assembly occurred in this system. We found with rheology that the storage moduli of the composite fiber networks were significantly higher (75 kPa vs. 400 kPa) than that of the single networks. Strain-hardening present in the FMOC-LG fiber network disappeared when the silk-like protein polymer was present. In chapter 5 hydrogels with both physical and chemical crosslinks were prepared from collagen-like protein polymers (T9CRT9). The chemical crosslinks were introduced by crosslinking lysine residues present in the random-coil middle blocks with glutaraldehyde. We found with rheology that the order in which the physical and chemical networks were formed did not influence the final storage modulus of the hydrogel. Depending on the amount of glutaraldehyde added we found an increase of up to an order of magnitude in the storage modulus for the collagen-like hydrogels. To investigate effects on the nonlinear rheological properties cyclic loading/unloading tests were performed. It was observed that before hydrogel failure occurred no hysteresis was observed between consecutive cycles. Both physical and chemical crosslinks ruptured when the hydrogel was fractured. In chapter 6 we studied hydrogels formed by the co- assembly of an asymmetric silk-collagen-like protein polymer (SH8CR4T9) with a symmetric oppositely charged silk-like protein polymer (CP2SE48CP2). This was done in a step-wise approach: (1) the S blocks were co-assembled into silk-like fibers. (2) the T blocks were assembled into triple helical nodes by reducing the temperature. We confirmed with confocal laser scanning microscopy and NMR that both monomers were present in the same fibers. With rheology we found that these composite hydrogels did respond in a reversible manner to temperature changes, with which the mechanical strength of the hydrogel can be tuned. In chapter 7 hydrogel formation of a modified silk-like protein polymer with a cysteine-residue attached to the C-terminal side (CP2SH48CP2-Cys) was studied. With rheology we showed that hydrogels that were formed in oxidizing conditions, where disulfide-bridges could form, were much stronger than those formed in reducing conditions. Both hydrogels formed in oxidizing and reducing conditions showed a scaling of modulus versus concentration consistent with entangled semi-flexible networks. This result implied that the disulfide-bridges formed between cysteine-residues formed loops in the coronae of the fibers. The increase in mechanical strength of the fibers was related to the increase in persistence length of the fibers in oxidizing conditions observed with AFM. With self-consistent field theory-simulations it was shown that the formation of loops in the corona resulted in a slight reduction of the lateral pressure in the corona of the fibers. However, this effect is by itself not sufficient to cause a significant change in persistence length. Due to the reduction in lateral pressure, the stacking of monomers into fibers is probably influenced: fibers with a more crystalline structure and with less detects are formed, resulting in improved mechanical properties of the hydrogels. In the general discussion in chapter 8, we reflect on our work, discuss about future directions of research, and possible applications of protein polymers.

Functionality-driven fractionation of lupin seeds
Berghout, J.A.M. - \ 2015
Wageningen University. Promotor(en): Remko Boom, co-promotor(en): Atze Jan van der Goot. - Wageningen : Wageningen University - ISBN 9789462572287 - 165
lupinen - eiwitisolaten - fractionering - scheiding - mechanische eigenschappen - voedselproducten - lupins - protein isolates - fractionation - separation - mechanical properties - food products
Functionality-driven fractionation of lupin seeds

The growth in the world population requires an increase in the production of protein-rich foods from plant-based materials. Lupin seeds have potential to become a novel plant protein source for food products because they are rich in protein (about 37 wt%) and they can be grown in moderate temperature climates as in north-western Europe. Besides a high protein content, lupin seeds are rich in dietary fibres (soluble and insoluble), contain about 7-10 wt% oil, and are low in starch. To optimally use the proteins present in lupin, a fractionation process has to be developed. For other legumes, refining of protein is usually performed through wet fractionation techniques. However, wet fractionation methods are resource-intensive, as a result of which the potential reduction in environmental impact when using plant-based materials for foods decreases.

The aim of this thesis is to obtain understanding of the production of functional, protein-rich material from lupin seeds in a more efficient manner. In this thesis, it is shown that focus on functionality rather than purity can lead to simplified fractionation processes, which is a concept referred to as functionality-driven fractionation (Figure 1). The influence of these simplifications on protein functionality and on physical and chemical stability of the protein isolates was explored. Furthermore, we performed a sustainability assessment of fractionation processes, from which we concluded that focus on a dry product with high purity has a large impact on energy use. In case of lupin, avoiding the oil extraction step as well as the drying step could lead to large gains in sustainability.

Figure 1 Upper scheme: conventional ingredient production and product processing route, focusing on protein and yield. Lower scheme: novel approach, focusing on functionality and sustainability.

The results presented in this thesis provide steps towards more sustainable production of functional fractions for food applications obtained with simplified fractionation processes. This work provides future perspectives for functionality-driven fractionation processes that may be extended to other legumes and pulses as well. This approach leads to the development of ingredients and fractions of seeds and legumes that can be used for plant-based food products.

Dry fractionation for sustainable production of plant protein concentrates
Pelgrom, P.J.M. - \ 2015
Wageningen University. Promotor(en): Remko Boom, co-promotor(en): Maarten Schutyser. - Wageningen : Wageningen University - ISBN 9789462572355 - 202
fractionering - peulvruchten (groente) - mechanische eigenschappen - eiwitextractie - voedselverrijking - fractionation - vegetable legumes - mechanical properties - protein extraction - food enrichment

The global demand for protein-rich foods is expected to double in the coming decades due to the increasing prosperity and world population. To keep up with the demand, the transition from an animal to a plant-based protein supply is desirable from long-term economic and environmental perspectives. In particular, legumes such as pea and lupine are of interest due to their nutritional profile and high protein content. Legume proteins are commonly purified by wet fractionation, which consumes large amount of water and energy and alters the native functionality of the proteins. Therefore, this thesis describes a sustainable, dry fractionation method for legumes to obtain functional protein-enriched fractions. Firstly, experiments have been performed to increase understanding of both the material properties of legume seeds and of the process conditions relevant to dry fractionation. Dedicated milling settings were selected for starch-rich and oil-rich legumes based on legume morphology. Milling settings were estimated based on starch granule size in starch-rich legumes, while coarse milling provided better results for oil-rich legumes. Separation of the protein bodies from other cellular components was established by air classification, which consumed ten times less energy and 50 litre water per kg protein less compared to conventional wet fractionation. Secondly, the functionality of the fractions was analysed. The dry-enriched protein fractions provided higher solubility than conventionally produced fractions, making them suitable for high protein drinks. Moreover, pea fractions could also be gelatinized which opens opportunities for preparing solid protein foods such as meat replacers. In conclusion, this thesis contributes to the awareness that the food industry could exploit a more sustainable dry fractionation technique to obtain functional protein fractions rather than focussing on wet extraction of relative pure protein ingredients.

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
Design and functionality of dense protein particles
Saglam, D. - \ 2012
Wageningen University. Promotor(en): Erik van der Linden, co-promotor(en): Paul Venema; Renko de Vries. - [S.l.] : s.n. - ISBN 9789461733986 - 200
deeltjes - wei-eiwit - mechanische eigenschappen - gelering - emulgering - hittebestendigheid - particles - whey protein - mechanical properties - gelation - emulsification - heat stability

Food products that contain high levels of protein can help to control food intake and to maintain a healthy body weight due to their strong satiating properties. They are also beneficial in the nutrition of elderly and commonly used in medical nutrition. Preparation of food products at high protein concentrations is difficult, mainly due to protein aggregation, occurring during processing and storage. A possible route in controlling this aggregation is using pre-fabricated protein structures, such as protein particles with controlled internal and surface properties. The aim of this thesis was to design dense protein particles and to study their properties and functionality at high protein concentrations.

Dense protein particles were prepared through two-step emulsification. The average diameter of the protein particles was in the order of a few micrometers and protein was homogeneously distributed throughout the particles. Particles were spherical when formed at pH 6.8, whereas they were irregular and had a cauliflower-like appearance when formed at pH 5.5. Particles formed at pH 5.5 had a higher internal protein concentration (~ 39% w/v), than the particles formed at pH 6.8 (~ 18.5% w/v). The rheological properties and heat stability of the particle dispersions were shown to be strongly influenced by the type of the particle. The properties of concentrated whey protein particle dispersions in different dispersing media were also addressed. The results indicated that protein particles swell during heat treatment, which considerably influences their rheological properties. It was also observed that the type and the concentration of the stabilizer present in the dispersing media alters the rheological properties, as well as the heat stability at high particle volume fractions.

Functionality of protein particles was addressed both for liquid and gelled systems. It was shown that, protein particles can considerably increase the protein concentration of (model) drinks. After heat treatment at 90 oC for 30 min, no change in the viscosity of the protein particles dispersions (particles prepared at pH 5.5) was observed at a total protein concentration of about 18% (w/w), whereas a WPI solution already gelled under the same heating conditions at protein concentrations around 11% (w/w). The gelled systems containing dense protein particles at high protein concentrations (16-22% w/w) were investigated. Incorporation of dense whey protein particles, in a whey protein gel, while keeping the total protein concentration constant, led to a lower storage modulus (G’). A total protein increase between 25 to 55% (w/w) could be obtained in the presence of whey protein particles, without significantly changing the G' of the gels. The gels were also fractured at lower strain values in the presence of protein particles compared to the WPI gels, without added particles, at the same protein concentration. These results show that protein particles can be used to improve the heat stability and as well they are promising candidates for the formation of high protein foods with improved textural properties.

In conclusion, this thesis has made significant progress in understanding the properties of protein particles at high protein concentrations and their potential for the development of high protein foods.

Designing food structures to enhance sensory responses
Mosca, A.C. - \ 2012
Wageningen University. Promotor(en): Tiny van Boekel, co-promotor(en): Markus Stieger; F. van de Velde. - S.l. : s.n. - ISBN 9789461732477 - 164
sucrose - vet - sensorische wetenschappen - smaakgevoeligheid - smaak - zintuiglijke waarneming - ruimtelijke verdeling - gels - mechanische eigenschappen - zoetheid - sucrose - fat - sensory sciences - taste sensitivity - taste - organolepsis - spatial distribution - gels - mechanical properties - sweetness

Background and Aim

The current overconsumption of sugar, salt and fat has been linked to the incidence of health problems. For this reason, it is necessary to decrease the intake of these food components. In the context of reducing the contents of sugar, salt and fat in food products while maintaining sensorial quality, the aim of this thesis was to identify and understand the factors that affect the perception of taste and fat-related sensory attributes in semi-solid foods. To achieve this aim, the relationship between the spatial distribution of sucrose, the mechanical properties of semi-solid gels and the perception of taste was investigated in detail. In addition, the relationship between the spatial distribution of fat and the perception of fat-related sensory attributes was investigated.


Model systems composed of layers of mixed agar-gelatin gels were used to control the spatial distribution of sucrose and fat. Layers varying in concentration of sucrose or oil-in-water emulsion droplets (i.e. fat) were combined to prepare gels with homogeneous and inhomogeneous distributions of sucrose and fat. A series of experiments were carried out using 2-Alternative Forced Choice (2-AFC) tests, line scale ratings and time-intensity analysis to investigate the effects of modulation of the spatial distribution of sucrose and modulation of the mechanical properties of gels on sweetness intensity. The relationship between the spatial distribution of tastants and consumer preference was investigated in different types of foods (e.g. semi-solid gels, breads and sausages). Furthermore, a Quantitative Descriptive Analysis (QDA) panel was carried out to investigate the effect of modulation of the spatial distribution of fat on the perception of fat-related sensory attributes.


An inhomogeneous distribution of sucrose at large sucrose concentration differences enhanced sweetness intensity. The frequency of high-intensity discontinuous stimulation of taste receptors, which is related to the presence of tastant concentration differences in the mouth during oral processing, was identified as the driving factor for taste enhancement. The oral breakdown of semi-solid gels, which is affected mainly by fracture strain, and the mixing behavior of gel fragments formed upon breakdownwere shown to influence the frequency of receptor stimulation and, consequently, taste enhancement. Furthermore, the optimum frequency of high-intensity discontinuous stimulation required to maximize taste enhancement was shown to depend on the textural properties of the gel. These findings suggest that the spatial distribution of tastants and the mechanical properties (especially fracture strain) can be modulatedto maximize taste enhancement. Additionally, consumer preference was found to be maintained or increased in products containing tastants heterogeneously distributed in the food matrix.

Fat-related mouthfeel attributes, such as spreadable and melting, were enhanced by an inhomogeneous distribution of fat at large fat concentration differences. The presence of high-fat zones on the surface of the model system was shown to maximize the enhancement of attributes related to fat. Therefore, the enhancement of fat-related attributes seems to be driven by the presence of high-fat zones preferably on the surface of the product rather than by the presence of fat concentration differences within the product.


The combined effects of modulation of the spatial distribution of tastants and fat and modulation of the mechanical properties can be applied in the development of low-sugar, low-salt and low-fat food products with improved taste quality.

Differential regulation of cellulose orientation at the inner and outer face of epidermal cells in the Arabidopsis hypocotyl
Crowell, E.F. ; Timpano, H. ; Desprez, T. ; Franssen-Verheijen, M.A.W. ; Emons, A.M.C. ; Höfte, H. ; Vernhettes, S. - \ 2011
The Plant Cell 23 (2011)7. - ISSN 1040-4651 - p. 2592 - 2605.
cortical microtubules - nitella-opaca - mechanical properties - sunflower hypocotyl - synthase complexes - wall microfibrils - internodal cells - fine-structure - growth - elongation
It is generally believed that cell elongation is regulated by cortical microtubules, which guide the movement of cellulose synthase complexes as they secrete cellulose microfibrils into the periplasmic space. Transversely oriented microtubules are predicted to direct the deposition of a parallel array of microfibrils, thus generating a mechanically anisotropic cell wall that will favor elongation and prevent radial swelling. Thus far, support for this model has been most convincingly demonstrated in filamentous algae. We found that in etiolated Arabidopsis thaliana hypocotyls, microtubules and cellulose synthase trajectories are transversely oriented on the outer surface of the epidermis for only a short period during growth and that anisotropic growth continues after this transverse organization is lost. Our data support previous findings that the outer epidermal wall is polylamellate in structure, with little or no anisotropy. By contrast, we observed perfectly transverse microtubules and microfibrils at the inner face of the epidermis during all stages of cell expansion. Experimental perturbation of cortical microtubule organization preferentially at the inner face led to increased radial swelling. Our study highlights the previously underestimated complexity of cortical microtubule organization in the shoot epidermis and underscores a role for the inner tissues in the regulation of growth anisotropy.
Formation and properties of whey protein fibrils
Kroes-Nijboer, A. - \ 2011
Wageningen University. Promotor(en): Erik van der Linden, co-promotor(en): Paul Venema. - [S.l.] : S.n. - ISBN 9789461730244 - 175
wei-eiwit - bèta-lactoglobuline - zelf-assemblage - mechanische eigenschappen - whey protein - beta-lactoglobulin - self assembly - mechanical properties

Protein fibrils are threadlike aggregates that are about one molecule thick and more than thousand molecules long. Due to their threadlike structure they could potentially be used to form meat-like structures. Protein fibrils can be produced from milk protein and plant protein, opening opportunities for a more sustainable food production.

For a successful application of the fibrils it is important to know how fibrils are formed and how to influence the properties of the fibrils. This thesis describes how fast fibrils are formed and determines the energy change involved in this formation.

Fibrillar structures show promise as encapsulating material, thickener, gelling and flocculation agent. This thesis provides new insights that facilitate innovations in the area of tasty, healthy and sustainably produced food.

Development of starch-based materials
Habeych Narvaez, E.A. - \ 2009
Wageningen University. Promotor(en): Remko Boom, co-promotor(en): Atze Jan van der Goot. - [S.l. : S.n. - ISBN 9789085854333 - 144
zetmeel - mechanische eigenschappen - fysicochemische eigenschappen - verwerking - polymeerchemie - biopolymeren - starch - mechanical properties - physicochemical properties - processing - polymer chemistry - biopolymers
Starch-based materials show potential as fully degradable plastics. However, the current
applicability of these materials is limited due to their poor moisture tolerance and
mechanical properties. Starch is therefore frequently blended with other polymers to make
the material more suitable for special or severe circumstances. By varying the components
of the blend and the process conditions, the morphology and hence the properties can be
controlled. A clear understanding over the structure formation process will allow the
development of new, biodegradable blends based on starch-based materials with better
properties. The overall goal of this thesis was thus to develop insight in how the material
(blend) properties depend on the processing, and based on this insight, explore new
processing routes.
Structure-function relationships: exploring a polymer science approach
In Chapter 2, we discuss the relation between the performance of a plasticized starchbased
film, in terms of permeation of volatile components, and its composition. Estimations
of the Maxwell-Stefan diffusion rates of trace volatile components through plasticized
starch films were developed based on free-volume theory and the Flory-Huggins-Maxwell-
Stefan (FHMS) equation. The model correctly predicted the order of magnitude of the
permeation fluxes of diacetyl and carvone through starch films. The results of this chapter
show that blending of starch with hydrophobic polymers could be an effective way to
improve the barrier properties of the film.
In Chapter 3, the influence of alternative plasticizers (i.e., glucose and glycerol) on the
gelatinization and melting of concentrated starch mixtures was studied, using differential
scanning calorimetry (DSC) and wide angle X-ray scattering (WAXS). The results were
interpreted using an extended form of the well-known Flory-Huggins equation. The chapter
exemplified the possibilities of using theories that were traditionally applied to synthetic
polymers, to biomaterials, in spite of their much greater complexity. This approach led to
quantitative and qualitative understanding of the influence of small plasticizers of industrial
relevance on the gelatinization and melting of starch. Comparing the Flory-Huggins model
results with experimental results, showed that the approach is useful for interpreting and
predicting the gelatinization and melting behavior of ternary starch-based systems. It also
showed that since the experiments were complex, systems were often not in true
equilibrium and other disturbing effects were easily encountered. Therefore, one should be
cautious to use experimental results for characterizing the thermodynamics of gelatinization
in multicomponent systems.
Processing: the use of simple shear
In Chapter 4, the use of simple shear as an instrument for structure formation of
plasticized starch-protein blends was introduced. A novel shearing device was developed to
explore the formation of new types of microstructures in concentrated starch-zein blends.
This device was used to process different ratios of starch and zein (0–20% zein, dry basis)
to study the influence of the matrix composition and processing conditions on the
properties of the final material. Confocal scanning laser microscopy and field emission
scanning electron microscopy showed that under shearless conditions, the starch-zein blend
forms a co-continuous blend. Shear transformed this structure into a dispersion, with zein
being the dispersed phase. The large deformation properties were examined by tensile tests
in the flow and the vorticity directions; they could be described using a model for blends
having poor adhesion between the continuous and dispersed phases.
In Chapter 5, we studied the effect of compatibilization, i.e., improvement of the adhesion
between the continuous and dispersed phases in starch-zein blends through the
incorporation of a component having affinity for both phases. Aldehyde starch was
synthesized by introducing a reactive functional group (aldehyde). This group then reacted
in the blend with zein (and/or other components), forming a macromolecular compatibilizer
in situ. The effect of this compatabilizer on the interfacial properties of the blend was
studied using different zein ratios. The blends showed improved adhesion between the zein
and starch phases compared to the blends described in chapter 4. The aldehyde starch
however also influenced the properties of the starch matrix (higher viscosity, stronger
molecular breakdown, browning), which indicates that indeed physical or chemical
crosslinks were formed inside the starch matrix, but on the other hand posed a limitation for
practical applicability.
Chapter 6 presented the use of rise bran extract as a food-grade compatibilizer for starchzein
blends. This material was extracted from rice brans using super-critical water,
probably contains Maillard components and shows activity as radical scavenger,
antioxidant and surfactant. The influence of rice bran extract as compatibilizer was
compared with that of aldehyde starch by preparing blends under shear conditions. Field
emission scanning electron microscopy showed that both compatibilizers improved the
adhesion between the zein and starch phases. The mechanical properties of the blends
compatibilized with aldehyde starch showed poorer mechanical properties after storage
under controlled conditions, possibly caused by retrogradation of starch. The use of rice
bran extract as compatibilizer however led to good compatibilization with good stability
during storage. The good compatibilization by rice bran extract was suggested to be caused
by polysaccharide-protein complexes, which are also responsible for its emulsifying
In Chapter 7, the conclusions of the preceding chapters were collectively interpreted. First,
the use of a heuristic approach for the rational design of thermoplastic starch-based
materials was described. Then the use of the ternary diagram for the system starch-waterglucose
developed in Chapter 3 was used to evaluate alternatives routes for the
intensification of the enzymatic hydrolysis of starch.
Finally, future trends in the development of starch-based materials were presented
following the insights obtained in this thesis. These include the use of established theories
developed for synthetic polymers, further exploration of the concept of compatibilization of
starch-based blends, and the development of new processing equipment dedicated to
material structuring.
Polylactide microcapsules and films: preparation and properties
Sawalha, H.I.M. - \ 2009
Wageningen University. Promotor(en): Remko Boom, co-promotor(en): Karin Schroen. - [S.l. : S.n. - ISBN 9789085853152 - 219
inkapselen - films - polyesters - vervangbare hulpbronnen - biodegradatie - membranen - emulgering - hardwording - mechanische eigenschappen - thermische eigenschappen - ultrageluid - kunstmatige membranen - encapsulation - films - polyesters - renewable resources - biodegradation - membranes - emulsification - solidification - mechanical properties - thermal properties - ultrasound - artificial membranes
This thesis aims at preparation of hollow polylactide (PLA) microcapsules for use as ultrasound contrast agents with controlled size, structure and mechanical and thermal properties. The microcapsules were prepared with multistage premix membrane emulsification. The mechanical and thermal properties of the microcapsules, and of films that were prepared under similar conditions, were highly dependent on the non-solvent and the liquid used as a template for the hollow core of the microcapsule. The size and size distribution of the microcapsules could, amongst others, be controlled through the process conditions that were applied during preparation. The main conclusion of this thesis was that the nonsolvent properties and the template liquid, highly affect the solidification process of the polymer; and through these parameters, the properties of PLA microcapsules and films can be effectively fine-tuned for various applications.
Texture of food gels explained by combining structure and large deformation properties
Berg, L. van den - \ 2008
Wageningen University. Promotor(en): Tiny van Boekel; Erik van der Linden, co-promotor(en): F. van de Velde; Ton van Vliet. - S.l. : S.n. - ISBN 9789085049432 - 193
gels - wei-eiwit - polysacchariden - textuur - structuur - mechanische eigenschappen - reologische eigenschappen - confocale microscopie - gels - whey protein - polysaccharides - texture - structure - mechanical properties - rheological properties - confocal microscopy
Food gels filled with emulsion droplets : linking large deformation properties to sensory perception
Sala, G. - \ 2007
Wageningen University. Promotor(en): Martien Cohen Stuart, co-promotor(en): G.A. van Aken; F. van de Velde. - [S.l.] : S.n. - ISBN 9789085048329 - 235
gelering - emulsies - druppels - mechanische eigenschappen - sensorische evaluatie - gelation - emulsions - droplets - mechanical properties - sensory evaluation
Key words: polymer gels, particle gels, emulsion, large deformation, friction, sensory This thesis reports studies on the large deformation and lubrication properties of emulsion-filled gels and the way these properties are related to the sensory perception of the gels. The design of the studies included polymer and particle gels containing oil droplets of which the interaction with the gel matrix was varied, resulting in droplets either bound or unbound to the matrix. The unique combination of gel matrices and droplet-matrix interactions allowed to obtain a representative overview of the effect of the oil droplets on the properties studied. The molecular properties of the gel matrices determined the way the large deformation properties of the gels depended on the deformation speed. Polymer gels showed a predominantly elastic behaviour. Particle gels showed a more viscoelastic behavior. The effect of the oil content on the Young’s modulus of the gels was modulated by the droplet-matrix interactions, in agreement with existing theories. Bound droplets increased the Young’s modulus of the filled gels, whereas unbound droplets decreased it. Oil droplets embedded in the gel matrix acted as stress concentration nuclei. They also increased energy dissipation due to friction between structural elements of the gel (oil droplets and gel matrix). Stress concentration resulted in a decrease of the fracture strain for all gels and in a decrease of the fracture stress for polymer gels. For gels with non-aggregated bound droplets, a reduction in oil droplet size had the same effect on their rheological properties as an increase in oil volume fraction. The lubrication properties of the gels strongly depended on both the molecular and functional properties of the gel matrix and the oil content. For each type of gel matrix, the lubrication behaviour was affected by the ‘apparent viscosity’ of the broken gels, which in turn depended on the droplet-matrix interactions. The sensory perception of emulsion-filled gels appeared to be dominated by the properties of the gel matrix and by the oil content. Polymer gels were perceived as more melting, whereas particle gels were perceived as more rough. With increasing oil content both types of gels became more creamy and spreadable. The increase in spreadability and part of the increase in creaminess could be explained with the effect of the oil droplets on the breakdown properties of the gels. Since for all gels the scores for creaminess increased with increasing oil content, the release of oil droplets during oral processing could not completely explain the perception of oil-related sensory attributes. It is therefore concluded that the perception of these attributes is mediated by the lubrication properties of the broken gel. The large deformation and lubrication behaviour of the gels were the most important parameters related to sensory perception. Both parameters were affected by the droplet-matrix interaction. As a matter of fact, the droplet-matrix interaction affected the fracture behaviour of the filled gels, which was related to their spreadability, and the ‘apparent viscosity’ of the broken gels, which controlled the lubrication properties of these systems.
Ion-mediated flow changes suppressed by minimal clacium presence in xylem sap in Chrysanthemum and prunus laurocerasus
Ieperen, W. van; Gelder, H. van - \ 2006
Journal of Experimental Botany 57 (2006)11. - ISSN 0022-0957 - p. 2743 - 2750.
hydraulic architecture - mechanical properties - ricinus-communis - bean-plants - cell-walls - exchange - trees - translocation - conductance - transport
After the discovery of ion-mediated changes in xylem hydraulic resistance a few years ago, a number of research papers were published that related ion-mediated flow changes in the xylem to various aspects of whole plant functioning and evolutionary diversification of vascular cells. Ion-mediated changes in xylem hydraulic resistance are commonly quantified as the percentile change in hydraulic resistance, relative to the hydraulic resistance measured using a reference fluid, usually (ultra) pure deionized water. In this research the impact was investigated of the complete absence of all ions in deionized water compared with reference fluids containing a minimal amount of free calcium on the quantification of ion-mediated flow changes in stem segments of Chrysanthemum (Dendranthemaxgrandiflorum Tzvelev) and Prunus L. (Prunus laurocerasus L.). The addition of 10 mM KCl to deionized water significantly increased flow rate in Chrysanthemum (17¿24%) and Prunus L. (16%). The addition of 1 mM CaCl2 to the reference fluid reduced this KCl-mediated increase in flow rate to 1¿2% in both species. 1 mM Ca2+ is within the lower range of Ca2+-concentrations normally measured in xylem sap of many plant species, and three times lower than the original Ca2+-concentration measured in the xylem sap of Chrysanthemum plants used for the present measurements. The present results indicate that the complete removal of cations from the xylem fluid with deionized water causes the major part of the ion-mediated flow change previously reported in the xylem of plants. It is concluded that the use of deionized water as a reference fluid should be avoided. Earlier proposed relationships between ion-mediated changes and water flow in xylem of plants should be re-evaluated if they were based on deionized water as the reference fluid
Biomechanische aspecten van de klauw-vloerinteractie bij melkkoeien: implicaties voor bewegen en klauwaandoeningen = Biomechanical aspects of the claw-floor interaction in dairy cattle:implications for locomotion and claw disorders
Tol, P.P.J. van der - \ 2004
Tijdschrift voor Diergeneeskunde 129 (2004)13. - ISSN 0040-7453 - p. 454 - 458.
melkkoeien - klauwen - voetziekten - vloeren - beton - mechanische eigenschappen - voortbeweging - melkvee - dierziektepreventie - dairy cows - claws - foot diseases - floors - concrete - mechanical properties - locomotion - dairy cattle - animal disease prevention - holstein heifers - hoof - cows - hemorrhages - prevalence - lameness - health - indicators - behavior - surfaces
De prevalentie van klauwaandoeningen bij op betonvloeren gehuisveste melkkoeien is reeds enkele decennia zeer hoog. Bovendien hebben de betonvloeren een duidelijke invloed op de locomotie van koeien, waardoor ze niet goed in staat zijn om hun natuurlijk gedrag te vertonen. Dit artikel gaat over de biomechanische aspecten van de interactie tussen koeienklauw en stalvloer dat is gebaseerd is op een proefschrift over de mechanische belasting van de koeienklauw. Deze benadering laat zien dat ondanks recent preventief bekappen de zachtere delen van de klauw de relatief hoogste mechanische belasting ondergaan. Bovendien is gebleken dat de huidige betonvloeren te weinig wrijving genereren om natuurlijke locomotie mogelijk te maken
The potential of flax fibres as reinforcement for composite materials
Bos, H.L. - \ 2004
Eindhoven University of Technology. Promotor(en): A.A.J.M. Peijs; P.J. Lemstra. - S.l. : s.n. - ISBN 9038630050 - 192
vlas - plantenvezels - polymeren - versterking - materialen - mechanische eigenschappen - vervangbare hulpbronnen - linum usitatissimum - biobased economy - flax - plant fibres - polymers - reinforcement - materials - mechanical properties - renewable resources
Large-Deformation Properties of Wheat Flour and Gluten Dough
Sliwinski, E.L. - \ 2003
Wageningen University. Promotor(en): A. Prins, co-promotor(en): Ton van Vliet; P. Kolster. - [S.I.] : S.n. - ISBN 905808857X - 194
tarwegluten - tarwebloem - deeg - mechanische eigenschappen - reologie - fractuur - brood - wheat gluten - wheat flour - doughs - mechanical properties - rheology - fracture - bread
Entering and spreading of protein-stabilized emulsion droplets at the expanding air-water interface
Hotrum, N.E. ; Cohen Stuart, M.A. ; Vliet, T. van; Aken, G.A. van - \ 2003
In: Food Colloids, Biopolymers and Materials / Dickinson, E., van Vliet, T., Cambridge : Royal Society of Chemistry - ISBN 0854048715 - p. 192 - 199.
emulsies - schuim - schuimen - eiwitten - caseïnaten - grensvlak - mechanische eigenschappen - emulsions - foams - foaming - proteins - caseinates - interface - mechanical properties
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