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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    An integrated look at the effect of structure on nutrient bioavailability in plant foods
    Capuano, Edoardo ; Pellegrini, Nicoletta - \ 2019
    Journal of the Science of Food and Agriculture 99 (2019)2. - ISSN 0022-5142 - p. 493 - 498.
    bioavailability - digestion - food matrix - health - structure

    The true bioavailability of a nutrient being intrinsically coupled to the specific food matrix in which it occurs remains poorly considered in nutrition science. During digestion, the food matrix and, in particular, the structure of food modulate the extent and kinetics to which nutrients and bioactive compounds make themselves available for absorption. In this perspective, we describe an integrated look at the effect of structure on nutrient bioavailability in plant foods. Based on this integrated look, cell wall integrity and the particle size of the plant material during its transit in the small intestine determine the bioavailability of plant nutrients; in turn, cell wall integrity and particle size are determined by the level of oral processing and, accordingly, what subsequently escapes digestion in the upper intestine and is utilized by colon microbiota. Ultimately, the effect on nutrient digestion is linked to food structure through each step of digestion. A consideration of the structure rather than just the composition of foods opens up possibilities for the design of healthier foods.

    Controlling Agglomeration of Protein Aggregates for Structure Formation in Liquid Oil : A Sticky Business
    Vries, Auke De; Lopez Gomez, Yuly ; Jansen, Bas ; Linden, Erik van der; Scholten, Elke - \ 2017
    ACS Applied Materials and Interfaces 9 (2017)11. - ISSN 1944-8244 - p. 10136 - 10147.
    agglomeration - oleogels - protein aggregates - structure

    Proteins are known to be effective building blocks when it comes to structure formation in aqueous environments. Recently, we have shown that submicron colloidal protein particles can also be used to provide structure to liquid oil and form so-called oleogels (de Vries, A. J. Colloid Interface Sci. 2017, 486, 75−83). To prevent particle agglomeration, a solvent exchange procedure was used to transfer the aggregates from water to the oil phase. The aim of the current paper was to elucidate on the enhanced stability against agglomeration of heat-set whey protein isolate (WPI) aggregates to develop an alternative for the solvent exchange procedure. Protein aggregates were transferred from water to several solvents differing in polarity to investigate the effect on agglomeration and changes in protein composition. We show that after drying protein aggregates by evaporation from solvents with a low polarity (e.g., hexane), the protein powder shows good dispersibility in liquid oil compared to powders dried from solvents with a high polarity. This difference in dispersibility could not be related to changes in protein composition or conformation but was instead related to the reduction of attractive capillary forces between the protein aggregates during drying. Following another route, agglomeration was also prevented by applying high freezing rates prior to freeze-drying. The rheological properties of the oleogels prepared with such freeze-dried protein aggregates were shown to be similar to that of oleogels prepared using a solvent exchange procedure. This Research Article provides valuable insights in how to tune the drying process to control protein agglomeration to allow for subsequent structure formation of proteins in liquid oil.

    Controlling the ratio between native-like, non-native-like, and aggregated β-lactoglobulin after heat treatment
    Delahaije, Roy J.B.M. ; Gruppen, Harry ; Eijk-Van Boxtel, Evelien L. Van; Cornacchia, Leonardo ; Wierenga, Peter A. - \ 2016
    Journal of Agricultural and Food Chemistry 64 (2016)21. - ISSN 0021-8561 - p. 4362 - 4370.
    aggregation - concentration - denaturation - ionic strength - pH - refolding - structure - temperature - unfolding

    The amount of heat-denatured whey protein is typically determined by pH 4.6 precipitation. Using this method, a significant amount of nondenatured protein was reported even after long heating times. Apparently, a fraction of the unfolded protein refolds into the "native" state rather than form aggregates. This fact is known and has been explained using kinetic models. How the conditions affect the refolding and aggregation is, however, not fully understood. Therefore, this study investigates the unfolding, refolding, and aggregation process of β-lactoglobulin using circular dichroism and size-exclusion chromatography to characterize different folding variants and to quantify their content. The proteins remaining in solution at pH 4.6 were confirmed to be native-like. The nonaggregated fraction contains proteins with a native-like and two types of non-native-like conformations. The nonaggregated fraction increased with decreasing temperature (60-90 °C) and concentration (1-50 g/L) and increasing electrostatic repulsion (pH 7-8; 0-50 mM). The native-like fraction in the nonaggregated fraction was independent of pH, ionic strength, and concentration but increased with decreasing temperature.

    Bolus matters: impact of food oral breakdown on dynamic texture perception
    Devezeaux de Lavergne, M.S.M. - \ 2015
    Wageningen University. Promotor(en): Tiny van Boekel, co-promotor(en): Markus Stieger; F. van de Velde. - Wageningen : Wageningen University - ISBN 9789462574496 - 227
    textuuranalyse - textuur - voedsel - structuur - eigenschappen - perceptie - spijsvertering - gels - elektromyografie - masticatie - kwalitatieve analyse - worstjes - texture analysis - texture - food - structure - properties - perception - digestion - gels - electromyography - mastication - qualitative analysis - sausages

    Background and aims:

    Texture is an important, yet complex, quality attribute of food. Food structure and properties can be linked to texture perception during the first bite. However, the perception of attributes during chew down is more difficult to explain, as food requires to be broken down to be swallowed safely. Food oral processing, which is a recent discipline connecting food science to the physiology of the eating process, is considered to be the key for understanding dynamic food texture perception. The aim of this thesis is to understand the link between food properties and texture perception by investigating oral food breakdown, in simple model foods.

    Methods:

    Gels were used as a model for soft solid foods. Several properties of the gels were controlled by modifying the composition of gels, including fracture stress and fracture strain, oil droplets binding to the gels matrix, melting, serum release and mechanical contrast. The texture perception of the gels was measured using several sensory methods. Qualitative descriptive analysis (QDA), progressive profiling and temporal dominance of sensations (TDS) were compared in the assessment of dynamic texture perception. In order to link gel properties to texture perception, the oral processing of gels was measured through analyses on the gel bolus and measurements of chewing behaviour. Gel boli were expectorated at various stages of oral processing and were analysed for gel fragments size and number, mechanical properties and saliva incorporation. These analyses were used to quantify the degree of breakdown of gels and to relate bolus properties to changes in texture perception. Chewing behaviour was measured using Electromyography (EMG) to understand the role of oral processing behaviour in bolus formation and dynamic texture perception.

    Results:

    Dynamic texture perception of gels could be measured by QDA, progressive profiling and TDS which were complementary methods. Fracture properties of gels could predict the perception of first bite texture attributes. Fracture stress and fracture strain were correlated to first bite firmness and brittleness respectively. During chew down, the link between gel properties and texture perception became less clear. Nonetheless, fracture properties and other gels properties, such as melting and serum release, related to chew down perception. Bolus properties depended on gel properties, but related better to chew down texture perception than gel properties. Mainly changes in mechanical properties and fragmentation of the bolus could explained the perception of complex texture attributes, such as creaminess and graininess respectively. Chewing behaviour depended on products properties. In addition, chewing behaviour impacted the formation of the bolus and could result in differences in dynamic texture perception between groups of individuals.

    Conclusions:

    The oral breakdown of food is a valuable input to understand the perception of complex chew down texture attributes. Such an input could be used to design foods with a desired texture sensory profile for reformulation of foods fitting in a healthier diet or foods for target consumer groups.

    Effecten bodem- en structuurverbeteraars; onderzoek op kleigrond 2010-2014
    Balen, D.J.M. van; Topper, C.G. ; Geel, W.C.A. van; Haan, J.J. de; Haas, M.J.G. de; Bussink, D.W. - \ 2015
    Lelystad : PPO AGV (Rapport / PPO-AGV 659) - 63
    akkerbouw - bodemstructuur - structuur - lichte-matig zware kleigronden - flevoland - poldergronden - bodemvruchtbaarheid - kalkmeststoffen - bodemverbeteraars - arable farming - soil structure - structure - clay loam soils - flevoland - polder soils - soil fertility - liming materials - soil conditioners
    In de praktijk lopen telers steeds vaker tegen problemen aan van een slechte bodemkwaliteit. Intensieve bouwplannen, steeds zwaardere mechanisatie, uitloging (Ca-uitspoeling), piekneerslagen en de schaalvergroting in de landbouw leiden tot vermindering van de fysische bodemvruchtbaarheid en de structuur van de bodem. Om de bodemstructuur te verbeteren, worden door industrie en handel zogeheten bodemverbeteraars en kalkmeststoffen aangeboden. Er is een grote variatie in type producten, de wijze waarop ze werken en de mate waarin ze een directe dan wel indirecte invloed op de bodemvruchtbaarheid hebben. Objectieve informatie over het effect van de aanbevolen producten op gewasopbrengsten en fysische, chemische en biologische bodemvruchtbaarheid ontbreekt. Uit eerdere proeven blijkt dat de effecten binnen 1 of 2 groeiseizoenen vaak afwezig zijn. Veel fabrikanten geven aan dat pas op langere termijn effecten te verwachten zijn.
    Protein mixtures: interactions and gelation
    Ersch, C. - \ 2015
    Wageningen University. Promotor(en): Erik van der Linden, co-promotor(en): A.H. Martin; Paul Venema. - Wageningen : Wageningen University - ISBN 9789462574212 - 199
    eiwit - wei-eiwit - sojaeiwit - gelering - gelatine - gels - reologie - structuur - moleculaire interacties - protein - whey protein - soya protein - gelation - gelatin - gels - rheology - structure - molecular interactions

    Gelation is a ubiquitous process in the preparation of foods. As most foods are multi constituent mixtures, understanding gelation in mixtures is an important goal in food science. Here we presented a systematic investigation on the influence of molecular interactions on the gelation in protein mixtures. Gelatin gels with added globular protein and globular protein gels with added gelatin were analyzed for their gel microstructure and rheological properties. Mixed gels with altered microstructure (compared to single gels) also differed in modulus from single gels. Mixed gels with microstructures similar to single gels were rheologically similar to single gels. Alterations in microstructure were attributed to segregative phase separation between proteins which occurred during gelation. Gelation was treated as a growth process from macromolecule to space spanning network. At conditions where electrostatic interactions were screened the occurrence of phase separation was attributed to the molecular size ratio between gelling and non-gelling proteins before gelation and changes of this size ratio during gelation. Here only mixtures that during gelation passed a region of high compatibility (similar molecular sizes) before entering a region of decreasing solubility phase separated. For applications this implies that whenever the gelling molecule is larger than the non-gelling molecule phase separation during gelation is unlikely while reversely, if the gelling molecules is smaller than the non-gelling molecule phase separation during gelation typically does occur

    Water holding of protein gels
    Urbonaite, V. - \ 2015
    Wageningen University. Promotor(en): Erik van der Linden, co-promotor(en): Laurice Pouvreau; H.H.J. de Jongh. - Wageningen : Wageningen University - ISBN 9789462574229 - 206
    sojaeiwit - ovalbumine - wei-eiwit - waterbergend vermogen - gelering - structuur - morfologie - reologie - permeabiliteit - centrifugeren - soya protein - ovalbumin - whey protein - water holding capacity - gelation - structure - morphology - rheology - permeability - centrifugation

    Abstract

    Food products are typically multicomponent systems, where often the spatial volume is set by a protein continuous network. The ability of protein-based food products to entrap water and to prevent its exudation upon mechanical deformation is important for the texture and thus sensory perception of food products. Understanding of structural origins that determine gel water holding is therefore essential, and would allow designing foods with controlled sensory perception. Water removal from the gel (quantity, kinetics and mechanism) is related to the coarseness and deformation of the network. An understanding of the interplay between the effect of coarseness and stiffness on WH in fine and coarse gels allows one to take a better control and tune juiciness and the release of tastants from food products.

    Casus: ontwerpen nieuwe teeltsystemen
    Baltissen, Ton - \ 2014
    cropping systems - innovations - desires - requirements - objectives - structure - descriptions - evaluation - methodology
    Onkruiddruk blijft hoog bij niet-kerende grondbewerking
    Balen, D.J.M. van - \ 2014
    Boerderij 99 (2014)50. - ISSN 0006-5617 - p. 47 - 47.
    groenteteelt - koolsoorten - penen - daucus carota - cultuurmethoden zonder grondbewerking - gewasbescherming - onkruidbestrijding - teeltsystemen - opbrengst - houdbaarheid (kwaliteit) - structuur - bodemstructuur - bodemstructuur na grondbewerking - vegetable growing - cabbages - carrots - daucus carota - no-tillage - plant protection - weed control - cropping systems - outturn - keeping quality - structure - soil structure - tilth
    Hardere grond maar meer wortels bij proef niet-kerende grondbewerking PPO Lelystad. PPO-onderzoeker Derk van Balen licht e.e.a. toe.
    Repeated parallel evolution reveals limiting similarity in subterranean diving beetles
    Vergnon, R. ; Leijs, R. ; Nes, Egbert van; Scheffer, M. - \ 2013
    Wageningen UR
    community - structure - competition - ecology - evolutionary
    The theory of limiting similarity predicts that co-occurring species must be sufficiently different to coexist. Although this idea is a staple of community ecology, convincing empirical evidence has been scarce. Here we examine 34 subterranean beetle communities in arid inland Australia that share the same habitat type but have evolved in complete isolation over the past 5 million years. Although these communities come from a range of phylogenetic origins, we find that they have almost invariably evolved to share a similar size structure. The relative positions of coexisting species on the body size axis were significantly more regular across communities than would be expected by chance, with a size ratio, on average, of 1.6 between coexisting species. By contrast, species’ absolute body sizes varied substantially from one community to the next. This suggests that self-organized spacing according to limiting-similarity theory, as opposed to evolution toward preexisting fixed niches, shaped the communities. Using a model starting from random sets of founder species, we demonstrate that the patterns are indeed consistent with evolutionary self-organization. For less isolated habitats, the same model predicts the coexistence of multiple species in each regularly spaced functional group. Limiting similarity, therefore, may also be compatible with the coexistence of many redundant species.
    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.

    Structuring microspheres
    Wagdare, N.A. - \ 2011
    Wageningen University. Promotor(en): Cees van Rijn; Remko Boom, co-promotor(en): Ton Marcelis. - [S.l.] : S.n. - ISBN 9789085859239 - 111
    emulgering - membranen - inkapseling in microcapsules - structuur - emulsification - membranes - microencapsulation - structure

    Encapsulation and use of capsules for controlled release has several applications in pharmaceuticals, foods, cosmetics, detergents and many other products for consumers. It can contribute to sustainability, since it allows an efficient use of active materials, delivery at the required site and possibly a longer shelf life of the products. Many encapsulation systems are basically very thin shells (10 nm – 10 µm) around microscopic reservoirs (100 nm – 100 µm), in which active ingredients are trapped. The release properties are strongly dependent on the material properties of the shell, but also on their size and uniformity.

    The overall objective of this research is to understand the formation process of microcapsules and microspheres by using phase separation in well-defined droplets of a polymeric solution. The primary droplets were produced with microsieve emulsification. The polymer used was Eudragit FS 30D (a commercial copolymer of poly(methyl acrylate-co-methyl methacrylate-co-methacrylic acid) 7:3:1), which contains charged carboxylate groups that make the polymer water-soluble at higher pH (>7), allowing for release by a change in pH.

    Chapter 2 presents results that give more insight into microsieve emulsification with high porosity micro-engineered membranes. The droplet formation was strongly influenced by the dynamics of surfactant adsorption. The presence of suitable surfactants in both phases prevents the coalescence of droplets and wetting of the microsieve membranes by the dispersed phase during oil droplet formation. This resulted in the formation of stable emulsions of droplets with a narrow size distribution. The flux of the dispersed phase could be increased an order of magnitude compared to previous methods, without loss of size-distribution of the droplets. Thus, use of a high-porosity membrane, in combination with suitable surfactants in both the dispersed and continuous phases resulted in a much more effective and efficient emulsification process.

    In Chapter 3 crossflow microsieve emulsification was used to prepare porous microcapsules with an average size of about 30 µm. A mixture of Eudragit and hexadecane in dichloromethane (DCM) was emulsified in water.Being a poor solvent for this polymer, demixing of the droplet into a polymeric shell and a hexadecane-rich core occurred upon extraction of the DCM into the water phase. At a low ratio of polymer to hexadecane, the resulting shells were found to be porous. Increasing this ratio resulted in a reduction of the porosity and pore size of the shell. The Eudragit has a pH-dependent solubility. It is insoluble at acidic conditions and rapidly dissolves at alkaline conditions. The capsules were found to be stable at a pH lower than 7.0, whereas the oil core was released within half an hour at pH 7.1 and within a minute at pH 8.0. The morphology of the microcapsules can be adapted with a careful choice of the concentrations of polymer, hexadecane and solvent. At higher concentrations of polymer, the tiny oil droplets that were captured in the forming Eudragit shell were unable to coalesce completely and small, isolated pores were formed within the shell matrix.

    The potential for new microcapsule morphologies was further explored in Chapter 4 where the formation of Eudragit capsules with other oils instead of hexadecane was studied, and in Chapter 5 where a blend of poly(methyl methacrylate) (PMMA) and Eudragit was used.

    In Chapter 4 the effects of chain lengths of vegetable oils on the formation of porous microcapsules with hollow and multi-compartment structures is discussed. The encapsulation of oil and the morphology of the resulting microcapsules depends on the interaction between the Eudragit polymer and the type of oil that was used. Microcapsule formation using long chain length oils such as sunflower oil, olive oil and coconut oil resulted in well-defined microcapsules with a single encapsulated oil droplet, covered with a Eudragit-rich shell. On the other hand, capsules prepared with relatively short chain length oils, such as medium chain triglyceride oil, resulted in capsules with many individual small oil droplets encapsulated in an Eudragit matrix. Extraction of the oil from the microcapsules with hexane results in the formation of hollow porous shells as was investigated with optical microscopy and SEM. These structures are formed during microcapsule formation due to the complex phase separation processes in the Eudragit-water-oil-DCM quaternary system.

    In Chapter 5 the formation of microcapsules is further explored by using a blend of PMMA and Eudragit. Microspheres formed with this blend were found to consist of a PMMA core inside an Eudragit-rich shell, which tends to be porous. As the amount of Eudragit is increased, a thicker and more porous outer shell is formed due to the enhanced interaction of water with Eudragit. After dissolution of the Eudragit at high pH, different core surface structures resulted, from irregular surfaces to microspheres with a fiber-like, swollen corona around it, and to a surface covered with small nodular structures, dependent on the concentrations of PMMA and Eudragit in the initial mixture. As already indicated above, these structures are formed as a result of complex phase separation processes between polymers and (non)solvents, and between the two polymers.

    In Chapter 6 the results described in this thesis were compared with existing literature, yielding an outlook on the field of microencapsulation through phase separation. A general concept is discussed on how to obtain various interesting complex structures with phase separation combined with microsieve emulsification. Finally, a conceptual process design is discussed for industrial scale production of microcapsules and microspheres with use of microsieve emulsification.

    This thesis has yielded insight in the formation of a range of microcapsule morphologies by investigating a range of new production methods (microsieves and demixing conditions) and formulations (different concentrations, oils and using one polymer or a blend), and through this provides better insight into the mechanisms of microcapsule formation. While some of the structures may be directly used for microcapsule formation, some other structures may well have potential for other applications.

    Figure. Examples of structured microcapsules and microspheres developed in this thesis.

    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
    Protein fibrillization: preparation, mechanism and application
    Akkermans, C. - \ 2008
    Wageningen University. Promotor(en): Remko Boom; Erik van der Linden, co-promotor(en): Atze Jan van der Goot; Paul Venema. - [S.l.] : S.n. - ISBN 9789085048794 - 162
    bèta-lactoglobuline - wei-eiwit - structuur - ingrediënten - voedingsmiddelen - vezels - fysische toestand - levensmiddelenfysica - beta-lactoglobulin - whey protein - structure - ingredients - foods - fibres - physical state - food physics
    The development of new functional ingredients is important for future food products. This PhD research aimed at the development of protein based structuring agents. Structuring agents are ingredrients that can be used to tailor the texture (and the mouth-feel) of products. Proteins were transferred into protein fibres (fibrils) that are long (1 micrometer) and very thin (few nanometers). Due to their special properties, protein fibrils offer unique possibilities to mimick meat structures and make products like yoghurt more creamy. This research shows that protein fibrils can be made from different protein sources (whey protein of milk, soy protein, potato protein) by heating an acidic protein solution. Furthermore, the mechanism of fibril formation was clarified. As a result, it was possible to optimize the fibril production and control the fibril properties. Finally, an important step was made towards the application of these fibrils in food products by studying the behaviour of fibrils in a model system for food products.
    Voedselaanbod voor gruttokuikens in de Hollandse veenweidegebieden
    Verhulst, J. ; Melman, T.C.P. ; Snoo, G.R. de - \ 2008
    Wageningen : Alterra (Alterra-rapport 1668) - 49
    limosa limosa - jonge dieren - graslandbeheer - graslanden - structuur - hoogte - hergroei - insecten - voedingsgedrag - voedsel - nederland - weidevogels - veenweiden - noord-holland - limosa limosa - young animals - grassland management - grasslands - structure - height - regrowth - insects - feeding behaviour - food - netherlands - grassland birds - peat grasslands - noord-holland
    Dit rapport verkent de voedselbeschikbaarheid van percelen die verschillen in beheer, grashoogte en structuur (uitgedrukt als variatie in grashoogte), voor gruttokuikens. In verschillende typen percelen met lang en kort gras zijn insecten bemonsterd met plakstrips. Het aantal grote insecten (> 4 mm) nam na begin mei sterk af, terwijl gruttokuikens meer afhankelijk worden van grote insecten door het seizoen. Percelen met kort gras (gemaaid of beweid) bevatten minder grote insecten dan ongemaaide percelen en vluchtstroken, maar percelen binnen reservaten verschilden hierin niet van boerenprecelen. Hergroeiende percelen lijken minder geschikt voor gruttokuikens dan ongemaaide percelen Structuurrijke percelen (over het algemeen die met met lang gras) bevatten vooral begin mei veel grote insecten
    Structuur en functie van habitattypen : nadere definiëring en monitoring in het kader van de Habitatrichtlijn. Dl. 1: Uitgangspunten
    Dobben, H.F. van; Janssen, J.A.M. ; Schmidt, A.M. - \ 2007
    Wageningen : Alterra (Alterra-rapport 1529) - 31
    monitoring - habitats - structuur - nederland - natura 2000 - abiotiek - habitatfragmentatie - monitoring - habitats - structure - netherlands - natura 2000 - abiotic conditions - habitat fragmentation
    De periodieke rapportage in het kader van de Europese Habitatrichtlijn dient naast informatie over de verspreiding en het oppervlak van de habitattypen ook informatie te bevatten over 'structuur & functie' en 'toekomstperspectief' van deze typen. Doel van de voorliggende studie is een nadere invulling te geven aan het begrip 'structuur & functie', zodanig dat duidelijk wordt welke informatie hierover in de rapportage moet worden opgenomen, en hoe de achterliggende gegevens kunnen worden ingewonnen. Aanbevolen wordt om 'structuur & functie' te beoordelen aan de hand van vegetatiestructuur, typische soorten, abiotische condities op de standplaats, en grootte van het habitat. Verder wordt aanbevolen wordt om regionale aspecten zoals depositie, hydrologie en versnippering niet onder structuur & functie mee te wegen, maar onder toekomstperspectief.
    Structure-rheology relations in sodium caseinate containing systems
    Ruis, H.G.M. - \ 2007
    Wageningen University. Promotor(en): Erik van der Linden, co-promotor(en): Paul Venema. - [S.l.] : S.n. - ISBN 9789085046486 - 125
    natriumcaseïnaat - reologische eigenschappen - afschuifkracht - gelering - emulsies - structuur - verzuring - spectroscopie - licht - verstrooiing - sodium caseinate - rheological properties - shear - gelation - emulsions - structure - acidification - spectroscopy - light - scattering
    The general aim of the work described in this thesis was to investigate structure-rheologyrelations for dairy related products, focusing on model systems containing sodium caseinate. The acid inducedgelationof sodium caseinate, of sodium caseinate stabilized emulsions, and the effect of shear on the structure formation was characterized. Special attention was given to the sol-gel transition point, which was defined by a frequency independent loss tangent. It was shown that the sol-gel transition point is completely controlled by the pH and the temperature, independent of the concentration sodium caseinate or the applied shear rate. Considering sodium caseinate solutions, increase of the temperature of acidification caused a decrease of the critical pH forgelationand a more dense gel structure. The formed gels were not in thermodynamicequilibrium,however, due to the slow kinetics of the system they were stable on the time scale of the experiment. At the gel point we have strong indications that the structure can not be characterized by a single fractal dimension. During the acid inducedgelationof sodium caseinate stabilized emulsions a single sol-gel transition was observed. Addition of an excess of sodium caseinate to the emulsion resulted in two sol-gel transitions upon acidification. Application of shear during the acidification of the emulsions showed a decreasing radius of the aggregates formed at thegelpointwith increasing shear rate. The aggregates formed becamemore densedue to the application of shear while the network that was formed by the aggregates became less compact. No shear induced alignment was observed of emulsion droplets dispersed in water or ina sodiumcaseinatesolution, while emulsion droplets dispersed in axanthansolution did align in a shear field. Addition of sodium inhibited the string formation of the emulsion droplets
    Flow-induced structuring of dense protein dispersions
    Manski, J.M. - \ 2007
    Wageningen University. Promotor(en): Remko Boom, co-promotor(en): Atze Jan van der Goot. - [S.l.] : S.n. - ISBN 9789085046103 - 222
    voedsel - structuur - textuur - eiwitproducten - caseïnaten - reologische eigenschappen - nieuwe voedingsmiddelen - voedselverwerking - apparatuur voor de voedselverwerking - kunstvlees - food - structure - texture - protein products - caseinates - rheological properties - novel foods - food processing - food processing equipment - meat analogues
    Both health and sustainability are drivers for the increased interest in the creation of novel foods comprising a high protein content. The key challenge is the formation of an attractive, stable and palatable food texture, which is mainly determined by the food structure. In this research, new processing routes based on flow are explored to create innovative protein-rich structures (exceeding 10%), and in parallel, insight is gained in the relevant mechanisms of structure formation. Dense dispersions of sodium caseinate and calcium caseinate, which are derived from milk, were mixed in a conventional mixer and sheared in an in house developed shear cell device. After mixing dense (sodium or calcium) caseinate dispersions, homogenous structures were obtained of which the properties were determined by the dispersed phase added, in this case palm fat. Shearing of dense calcium caseinate dispersions in combination with solidification using the enzyme transglutaminase resulted in completely different structures; highly fibrous structures were produced, which may serve as a basis for the creation of meat analogs. In contrast, after treating dense sodium caseinate dispersions using this novel structuring process, homogenous structures were obtained. It appeared that the intrinsic properties of protein dispersions are important for the formation of fibrous structures using well-defined flow. Based on the differences in performance between the two types of caseinates, tools and parameters can be derived to optimize and control the formation of fibrous products. In conclusion, the development of equipment that is dedicated to structure food ingredients is promising for the creation of novel foods on the one hand, and for gaining scientific understanding of structure formation on the other hand.
    Bacillus cereus spore formation, structure and germination
    Vries, Y.P. de - \ 2006
    Wageningen University. Promotor(en): Tjakko Abee; Willem de Vos; Marcel Zwietering. - [S.l. ] : S.n. - ISBN 9789085043690 - 127
    bacillus cereus - bacteriële sporen - sporenkieming - sporulatie - structuur - bacillus cereus - bacterial spores - spore germination - sporulation - structure
    Bacterial spores arespecializeddifferentiated celltypes fortypes,specificallydesigned for thesurvival of adverse conditions. Their structure is highly unique and very different from the structure of normal vegetative bacterial cells. Spores cause massive problems in the food industry, because their remarkable resistance allows them to survive food processing and conservation methods. The spore-forming Bacillus cereus is an important food-borne pathogen, is famousfor its ability to causefood poisoning, andisan importantspoilage organism inpasteurizeddairy products. The work presented in this thesis has focused on the formation, structure and germination of B. cereus spores. An easy and efficient way of producing synchronized and homogeneous B. cereus spore batches was developed, using a chemically defined medium in combination with an airlift fermenter system. This setup allowed precise monitoring and manipulation of key growth- and sporulation parameters. The conditions employed resulted in synchronous growth and sporulation, which facilitated gene-expression studies. The kinetics of expression of sigA , sigB , sigF and sigG followed the model developed for Bacillus subtilis , underscoring the conservation of sporulation mechanisms among bacilli. B. cereus was able to form spores on the chemically defined medium without glucose but with lactate as a main carbon source. Sporulation was not induced by nutrient limitation, because significant amounts of carbon and nitrogen sources were still present when the cells started to sporulate. The presence of glutamate delayed the final stages of sporulation, but not the moment of sporulation initiation. Clearly, the concentration of glutamate influenced key spore properties such as heat resistance and germination. The alternative sigma factor σ B , encoded by the sigB gene, is an important stress response regulator of B. cereus . An increase in sigB transcription was observed upon glucose depletion, coinciding with the transition from exponential growth to the stationary phase. This increase was specifically associated with the depletion of glucose. Deletion of sigB had a significant impact on spore heat resistance and spore germination properties. Spore heat resistance is caused by the physicochemical structure of the spore, which protects vital spore components such as membranes, proteins, and the DNA. A spin-probe-based Electron Spin Resonance (ESR) method for measuring the internal structure of intact bacterial spores was developed and applied, and provided the first direct data on the aqueous environment in the various compartments of B. subtilis and B. cereus spores. From the results obtained, it was concluded that the core cytoplasm is not in a glassy state. Instead, a three-dimensional molecular matrix incorporating free but highly viscous water exists in the core. Notably, neither heat activation nor partial germination (the excretion of DPA but not full rehydration and enzyme activity) altered the structural properties of the core matrix significantly. Complete germination resulted in the disappearance of the structure in the core, and a decrease of the micro viscosity in the core cytoplasm to levels encountered in normal vegetative cells. For a quantitative analysis of the behavior of individual spores in a large, germinating spore-population, a flow cytometry (FCM) method was developed and applied. By using several different fluorescent dyes, distinct germination parameters such as DNA accessibility and esterase activity were quantified. Finally, spore properties from a large number of B. cereus strains, including the B. cereus laboratory model strain ATCC14579 and a number of recent isolates from environmental and industrial settings were analyzed. The strains tested showed a large variation in heat resistance, and the majority had a higher heat resistance than the laboratory model strain. With respect to germination, many of the strains were less sensitive to the nutrients tested as compared to the laboratory model strain. Heat activation and ageing enhanced germination in response to several nutrients in various isolates. The knowledge that was gained and the methods that were developed in this study are expected to contribute to progress in the spore research field, and to enhanced spore control in the food industry.
    Development of dough under shear flow
    Peighambardoust, S.H. - \ 2006
    Wageningen University. Promotor(en): Remko Boom; Rob Hamer, co-promotor(en): Atze Jan van der Goot. - Wageningen : - ISBN 9789085043577 - 187
    deeg - vermenging - kneden - afschuifkracht - gluteninen - tarwegluten - structuur - doughs - mixing - kneading - shear - glutenins - wheat gluten - structure
    The overall objective of this thesis is to generate understanding of the relation between relevant process parameters in dough mixing and changes in product properties.
    Microstructure, rheology and demixing in emulsions flocculated by polysaccharides
    Blijdenstein, T.B.J. - \ 2004
    Wageningen University. Promotor(en): Erik van der Linden, co-promotor(en): G.A. van Aken; Ton van Vliet. - Wageningen : S.n. - ISBN 9789058089588 - 121
    emulsies - uitvlokking - polysacchariden - reologie - structuur - emulsions - flocculation - polysaccharides - rheology - structure
    keywords: Emulsion, b-lactoglobulin, polysaccharides, salt, sucrose, depletion, bridging, percolation, microstructure, micro-rheology, rheology, demixing, creaming, network compression. Abstract In this thesis, a study is presented on gravity-induced demixing behaviour of oil-in-water emulsions, stabilised by b-lactoglobulin and flocculated by various polysaccharides. Flocculation by polysaccharides mainly results in formation of emulsion droplet networks and can proceed via depletion and via bridging. Structural and rheological properties of these different networks were investigated and compared on a micro-and macroscopic level. These properties were related to the demixing behaviour of the emulsions. For emulsion droplet networks, gravity-induced compression of the network leads to separation of a serum layer. For depletion-induced networks, the initial rate of demixing by network compression is usually low and at high polysaccharide concentrations, usually a delay-time is observed before substantial demixing occurs. This delay-time scales with the permeability of the network, the viscosity and the density difference between oil and water. Once demixing has started, the network quickly collapses until the emulsion droplets are packed rather closely together. In bridging-flocculated emulsions, the initial demixing rate is higher, but more water was retained at longer times. The effects of protein, sugar and salts on demixing of depletion-flocculated networks were investigated as well. Protein affected the rate of flocculation and counteracted network formation. Sucrose affected the demixing rate via the viscosity and density of the aqueous phase, but it did not affect the droplet-droplet interactions. Salt affected the electrostatic droplet-droplet interactions. As a result, depletion-flocculation by dextran was inhibited at low salt concentrations. Addition of Ca2+ ions led to a decrease in repulsion between the protein layers, resulting in stronger droplet-droplet bonds, reinforcing a droplet network and retarding network compression.
    Structuur als basis voor gezonde koe. Minimale herkauwactiviteit voor 60 slagen per voerbolus noodzakelijk voor goede absorptie voedingsstoffen
    Hollander, C.J. ; Duinkerken, G. van - \ 2003
    Veeteelt 20 (2003)2. - ISSN 0168-7565 - p. 46 - 47.
    melkveehouderij - melkvee - rundveevoeding - voeropname - herkauwen - structuur - dairy farming - dairy cattle - cattle feeding - structure - feed intake - rumination
    In deel 4 van de serie Voeranalyse wordt de betekenis van de structuurwaarde van een voedermiddel aangegeven
    Bosdynamiek in bosreservaat Zeesserveld
    Clerkx, A.P.P.M. ; Goede, D.M. de; Sanders, M.E. - \ 2003
    Wageningen : Alterra (Alterra-rapport 668) - 46
    bossen - bosinventarisaties - vegetatie - structuur - beschermde bossen - bosecologie - nederland - overijssel - forests - forest inventories - vegetation - structure - reserved forests - forest ecology - netherlands - overijssel
    Bosreservaat Zeesserveld bij Ommen is in 2000 voor de tweede keer sinds aanwijzing geïnventariseerd. De boomlaag van grove den is niet veranderd. In de struiklaag heeft op de opgestoven gronden een sterke toename van sporkehout en Amerikaans krentenboompje plaatsgevonden. Hier begint ook blauwe bosbes in de bochtige-smelemat uit te breiden. Op de uitgestoven laagten verloopt deze ontwikkeling veel trager. Amerikaanse vogelkers breidde zich in beperkte mate uit. Zomereik en berk hebben moeite zich te vestigen en handhaven. De ontwikkeling naar een berken-eikenbos zal daarom een proces van lange adem zijn.
    Bosreservaat De Imboschberg : Bosstructuur en vegetatie bij aanwijzing tot bosreservaat
    Clerkx, A.P.P.M. ; Dort, K.W. van; Zuyderduyn, J.C. - \ 2002
    Wageningen : Alterra (Alterra-rapport 616) - 50
    bossen - beschermde bossen - structuur - vegetatie - nederland - gelderland - forests - reserved forests - structure - vegetation - netherlands - gelderland
    Bosreservaat De Imboschberg is in 1999 aangewezen. Het bestaat voor 50% uit heide. Het bos bestaat voornamelijk uit grove-dennenbos. Ruwe berk is algemeen als mengsoort, soms als hoofdboomsoort na spontane verstiging in stormvlakte uit 1972/1973. Er komen enkele stukken voormalig eikenhakhout voor. In de kruidlaag domineert blauwe bosbes. Beukenverjonging wijst op een ontwikkeling naar een wintereiken-beukenbos op termijn.
    A review of model designs
    Verdonschot, P.F.M. ; Nijboer, R.C. - \ 2002
    Wageningen : Alterra (Alterra-rapport 517) - 91
    aquatische gemeenschappen - ecologie - structuur - modellen - neurale netwerken - voorspelling - aquatische ecosystemen - aquatic communities - ecology - structure - models - neural networks - prediction - aquatic ecosystems
    The PAEQANN project aims to review current ecological theories which can help identify suited models that predict community structure in aquatic ecosystems, to select and discuss appropriate models, depending on the type of target community (i.e. empirical vs. simulation models) and to examine how results add to ecological water management objectives. To reach these goals a number of classical statistical models, artificial neural networks and dynamic models are presented. An even higher number of techniques within these groups will tested lateron in the project. This report introduces all of them. The techniques are shortly introduced, their algorithms explained, and the advantages and disadvantages discussed.
    Duurzame stedelijke ontwikkeling in en rond het IJmeer; benadering en advies
    Graaf, A.E. de - \ 2002
    Wageningen : Alterra (Alterra-rapport 587) - 71
    stadsontwikkeling - duurzaamheid (durability) - stedelijke planning - structuur - flevoland - ruimtelijke ordening - stedelijk gebied - Almere - IJmeer - urban development - durability - urban planning - structure - flevoland
    Duurzame stedelijke ontwikkeling wordt in dit onderzoek bekeken vanuit drie verschillende benaderingen. De eerste benadering is duurzame stedelijke ontwikkeling als strategie voor het omgaan met veranderingen. In ruimtelijke plannen is deze strategie herkenbaar door de toepassing van ruimtelijke flexibiliteit. De tweede benadering is duurzame stedelijke ontwikkeling als strategie voor de inrichting van de fysieke omgeving. Het resultaat van het toepassen van deze strategie heeft een positieve invloedop de fysieke omgeving. De derde benadering is duurzame stedelijke ontwikkeling als strategie voor de leefomgeving in brede zin. In deze strategie staat zowel de fysieke als de maatschappelijke omgeving centraal. Met behulp van de kennis die is opgedaan bij het bestuderen van de structuurplannen van Almere, Almere Poort en IJburg wordt een advies gegeven over het aanleggen van eilanden voor de kust van Almere vanuit de verschillende benaderingen van een duurzame stedelijke ontwikkeling.
    Haalbaarheidsstudie "over de bewoonde brug" oostflank Venlo; oplossingen voor de robuuste verweving van infrastructuur en ecologische structuren
    Groot, R. ; Mansfeld, M.J.M. van; Volkerts, A. ; Vreke, J. - \ 2002
    Wageningen : Alterra (Alterra-rapport 591) - 111
    ruimtelijke ordening - infrastructuur - ecologie - wegen - bruggen - integratie - structuur - wildpassages - noord-limburg - ecoduct - ecologische hoofdstructuur - landschapsarchitectuur - landschapsecologie - multifunctioneel ruimtegebruik - Limburg - Venlo - Duitsland - physical planning - infrastructure - ecology - roads - bridges - integration - structure - wildlife passages - noord-limburg
    Haalbaarheidsstudie ecoduct faunapassage. In de robuuste ecologische hoofdstructuur aan de oostflank van Venlo vormt de aanwezige en de toekomstige infrastructuur een knelpunt. Vanuit een offensieve benadering zijn deze ‘grijsgroene kruispunten’ echter geen knelpunt maar een kans. Met slimme meervoudige oplossingen kan meerwaarde bereikt worden voor zowel infrastructuur, natuur en andere belangrijke functies. Een ontwerpatelier heeft zes verschillende oplossingen opgeleverd, met als inzet: het realiseren van een robuuste ecologische verbinding, het verbeteren van de bereikbaarheid en het geven van een grensoverschrijdende impuls in de leefomgevingkwaliteit. In een tweede atelier is de haalbaarheid van de oplossingen getoetst, via het selecteren van criteria en doelstellingen die aansluiten bij beleid. Bestuurders toetsen de plannen en nemen het gedachtegoed verder mee.
    Bosreservaat Mattemburgh : bosstructuur en vegetatie bij aanwijzing tot bosreservaat
    Clerkx, A.P.P.M. ; Schelhaas, M.J. ; Sanders, M.E. - \ 2001
    Wageningen : Alterra (Alterra-rapport 223) - 49
    bossen - beschermde bossen - natuurreservaten - vegetatie - plantensuccessie - luchtfotografie - structuur - nederland - forests - reserved forests - nature reserves - vegetation - plant succession - aerial photography - structure - netherlands
    Bosreservaat Mattemburgh is als een voormalig landgoedbos aangelegd op de Zuidgeester Heide in de periode 1845-1860. Het bos bestaat uit een eerste boomlaag van grove den en een tweede boomlaag met zomereik. De bodemvegetatie wordt gedomineerd door bochtige smele, brede stekelvaren en pijpenstrootje. Na de bosaanleg is het bos nooit gedund. Al het dode hout is in het bos achtergebleven. Het bos is in ontwikkeling naar een zomereikenbos, waarin de rol van beuk voorlopig ondergeschikt is.
    Bosreservaat het Rot : Bosstructuur en vegetatie bij aanwijzing tot bosreservaat
    Clerkx, A.P.P.M. ; Sanders, M.E. ; Jans, W.W.P. ; Bijlsma, R.J. - \ 2001
    Wageningen : Alterra (Alterra-rapport 192) - 41
    fagus sylvatica - quercus petraea - bossen - beschermde bossen - vegetatie - plantengemeenschappen - structuur - bosecologie - bosinventarisaties - nederland - gelderland - fagus sylvatica - quercus petraea - forests - reserved forests - vegetation - plant communities - structure - forest ecology - forest inventories - netherlands - gelderland
    Bosreservaat Het Rot in de Achterhoek bestaat uit een wintereikenbos waarin plaatselijk beuk domineert. Waar wintereik domineert begint beuk vanuit een tweede boomlaag de wintereik te verdringen. Verjonging van wintereik komt niet voor. Plaatselijk is dit het gevolg van lichtconcurrentie door de beuk, maar ook vraat en adelaarsvaren belemmeren een succesvolle verjonging. In de nabije toekomst bestaat de vrees dat de wintereiken zullen verdwijnen, al zijn de beuken op deze natte bodems extra stormgevoelig, waardoor ze minder concurrentiekrachtig zijn
    Soy proteins : nomenclature, composition, structure and functionality
    Vereijken, J.M. - \ 2000
    Industrial Proteins 8 (2000)3. - ISSN 1381-0022 - p. 3 - 5.
    sojaeiwit - peulvruchteiwit - sojabonen - botanische samenstelling - structuur - structuuractiviteitsrelaties - emulgeren - eiwitten - globulinen - literatuuroverzichten - eiwittechnologie - soya protein - legume protein - soyabeans - botanical composition - structure - structure activity relationships - emulsifying - proteins - globulins - literature reviews - protein engineering
    De structuur van de belangrijkste soja-eiwitten is beschreven evenals hun verschil in functionaliteit
    The relationship between molecular structure and ion adsorption on variable charge minerals
    Rietra, R.P.J.J. ; Hiemstra, T. ; Riemsdijk, W.H. van - \ 1999
    Geochimica et Cosmochimica Acta 63 (1999)19-20. - ISSN 0016-7037 - p. 3009 - 3015.
    mineralen - structuur - adsorptie - minerals - structure - adsorption
    Ion adsorption modeling is influenced by the presumed binding structure of surface complexes. Ideally, surface complexes determined by modeling should correspond with those derived from spectroscopy, thereby assuring that the mechanistic description of ion binding scales from the nanoscopic molecular structure to the macroscopic adsorption behavior. Here we show that the structure of adsorbed species is a major factor controlling the pH dependency of adsorption. An important aspect of the pH dependency is the macroscopic proton-ion adsorption stoichiometry. A simple and accurate experimental method was developed to determine this stoichiometry. With this method, proton-ion stoichiometry ratios for vanadate, phosphate, arsenate, chromate, molybdate, tungstate, selenate and sulfate have been characterized at 1 or 2 pH values. Modeling of these data shows that the macroscopic proton-ion adsorption stoichiometry is almost solely determined by the interfacial charge distribution of adsorbed complexes. The bond valence concept of Pauling can be used to estimate this charge distribution from spectroscopic data. Conversely, the experimentally determined proton-ion adsorption stoichiometry allows us to successfully predict the spectroscopically identified structures of, for example, selenite and arsenate on goethite. Consequently, we have demonstrated a direct relationship between molecular surface structure and macroscopic adsorption phenomena.
    Effects of a pulsed treatment with the herbicide afalon (active ingredient linuron) on macrophyte-dominated mesocosms. II. Structural responses
    Geest, G. van; Zwaardemaker, N.G. ; Wijngaarden, W.R. van; Cuppen, J.G.M. - \ 1999
    Environmental Toxicology and Chemistry 18 (1999). - ISSN 0730-7268 - p. 2866 - 2874.
    pesticiden - milieueffect - ecosystemen - structuur - biocenose - sloten - nederland - aquatische ecosystemen - pesticides - environmental impact - ecosystems - structure - biocoenosis - ditches - netherlands - aquatic ecosystems
    Structure, stability and equilibrium (un)folding of flavodoxin
    Steensma, E. - \ 1998
    Agricultural University. Promotor(en): N.C.M. Laane; C.W. Hilbers; C.P.M. van Mierlo. - S.l. : Steensma - ISBN 9789054858300 - 142
    eiwitten - structuur - proteins - structure

    Flavodoxins function as low-potential one-electron carriers using a non-covalently bound FMN cofactor which can exist in three redox states. Flavodoxin structures are characterised by a five-stranded parallelbeta-sheet (orderbeta2-beta1-beta3-beta4-beta5) surrounded byalpha-helices at either side of the sheet. This topology is called the flavodoxin-like fold. In contrast to most folds, the flavodoxin-like fold is shared by many protein superfamilies which are sequentially and evolutionary unrelated.

    Studies on proteins with the flavodoxin-like fold can therefore be utilised to find answers to the so-called protein folding problem which can be captured by the following questions:

    • What is the physical basis of the stability of the folded protein conformation?
    • What processes or pathways determine which of the many possible conformations is the native folded conformation adopted by the protein?
    • What are the rules governing the relation between the amino acid sequence and three-dimensional structure of a protein?
    • Can the three-dimensional structure of a protein be predicted from its amino acid sequence?

    The research described in this thesis has been carried out to obtain a better understanding of the fundamental rules describing protein folding. This thesis focuses on the structure and stability of Azotobacter vinelandii (strain ATCC 478) flavodoxin II (henceforth designated flavodoxin) in its holo- and apoform (i.e. with and without cofactor FMN, respectively). The results obtained for this particular flavodoxin are compared with those for other flavodoxins, as well as with results obtained for sequentially unrelated proteins having a flavodoxin-like fold. The understanding of the equilibrium (un)folding of flavodoxin is a first step in the characterisation of the energy landscape determining the folding of this protein.

    A general introduction on protein folding, NMR spectroscopy and flavodoxins is presented in Chapter 1.

    To prevent dimerisation during structural and folding studies Cys69Ala and Cys69Ser mutants of wild-type flavodoxin were prepared. pH-Dependent semiquinone/hydroquinone redox potentials of wild-type, Cys69Ala and Cys69Ser flavodoxin were determined using cyclic voltammetry and confirmed by EPR-monitored redox titrations. No significant differences in redox properties of wild-type, Cys69Ala and Cys69Ser flavodoxin are observed. The pH dependence of the semiquinone/ hydroquinone redox potentials can be described using a model assuming two redox-linked protonation sites with a constant redox potential at high pH of -485 ± 4 mV. The electrochemical data which are presented in Chapter 2 show that replacement of Cys69 in the vicinity of the FMN by either an alanine or a serine residue do not alter the dielectric properties and structure of holoflavodoxin.

    In Chapter 3, a new doubly sensitivity-enhanced 3D 1H- 15N TOCSY-HSQC experiment is described and analysed using the product operator formalism . The overall gain in signal-to-noise ratio obtained using this doubly sensitivity-enhanced TOCSY-HSQC pulse sequence is, compared to the standard (non-enhanced) sequence, 2.49 or 1.89 for spectra obtained for 15N-labelled or 15N-/ 13C-labelled holoflavodoxin samples, respectively. The main factors leading to the signal-to-noise enhancement are the introduction of two enhanced coherence transfer sequences, the elimination of water presaturation and the inclusion of a water flip-back pulse. Incorporation of gradients for coherence pathway selection, however, leads to a reduction in signal intensity.

    The determination of the solution secondary structure of holoflavodoxin is described in Chapter 4. A five-stranded parallelbeta-sheet (beta2-beta1-beta3-beta4-beta5) is surrounded by fivealpha-helices. The loops extending from the carboxy termini of strandsbeta1,beta3 andbeta4 are involved in FMN binding. Hydrogen/deuterium exchange experiments suggest that (i) amide proton exchange within the core of holoflavodoxin occurs via the apoform of the molecule and that (ii) exchange of the N(3)H proton of FMN only occurs when the cofactor is free in solution. The solvent inaccessibility of the non-polar environment around N(3) could, at least in part, establish the low semiquinone /hydroquinone redox potential. The amide proton exchange rates do not suggest that holoflavodoxin is divided in two subdomains as has been found for the structurally, but not sequentially, homologous protein Che Y. The amide backbone protons of 65 residues and three indole side-chain protons exchange sufficiently slowly (k ex < 10 -5s -1) to be able to perform hydrogen exchange pulse labelling experiments and to study the kinetics of flavodoxin folding in great structural detail.

    The structural characteristics of apoflavodoxin as determined by NMR spectroscopy are presented in Chapter 5. Apoflavodoxin has a stable, well-ordered core consisting of a five-stranded parallelbeta-sheet surrounded by fivealpha-helices. Large parts of holo- and apoflavodoxin have identical conformations and similar internal dynamics. However, the flavin binding region in apoflavodoxin exhibits considerable conformational dynamics. Flexibility is a likely prerequisite to enable the flavin to enter the interior of the apoprotein. Hydrogen/deuterium exchange measurements suggest that the stable nucleus in apoflavodoxin at least comprises residues in strandsbeta1,beta3,beta4 andbeta5a and in helicesalpha4 andalpha5 in the C-terminal part of the protein. We propose that this is a general feature of flavodoxins. In contrast, the stable nucleus of the sequentially unrelated proteins cutinase and Che Y which share the flavodoxin-like fold is not found in their respective C-terminal parts. The amide proton exchange results show that the stable nucleus may be found in different parts of the flavodoxin-like topology. If folding of flavodoxin is initiated with the collapse of the stable nucleus, as has been found for several other proteins, the folding pathways of structurally homologous proteins seem to be unrelated as well.

    Chapter 6 reflects on the research described in this thesis and combines the NMR studies, as described in Chapters 4 and 5, with equilibrium (un)folding studies on apo- and holoflavodoxin using fluorescence and circular dischroism spectroscopy which have been performed by van Mierlo et al. The following picture for equilibrium (un)folding of flavodoxin arises: (i) holoflavodoxin has a compact stable fold consisting of a five-stranded parallelbeta-sheet surrounded by fivealpha-helices; (ii) upon release of the FMN cofactor, apoflavodoxin is formed which has a stable core but a flexible FMN binding region; (iii) in the (un)folding pathway a relatively stable apoflavodoxin folding intermediate is found which is characterised by the loss of tertiary interactions without the complete loss of secondary structure; (iv) the unfolded state of flavodoxin presumably contains some residual structure of an aromatic cluster as a remnant of helixalpha4. The results obtained on the equilibrium (un)folding of flavodoxin are discussed with respect to the implications for the kinetics of flavodoxin folding.

    Predictability of weather regime transitions
    Oortwijn, J. - \ 1998
    Agricultural University. Promotor(en): J. Grasman; J. Barkmeijer. - S.l. : Oortwijn - ISBN 9789054858683 - 116
    klimatologie - structuur - mechanica - atmosfeer - thermodynamica - climatology - structure - mechanics - atmosphere - thermodynamics

    The atmospheric circulation is not completely random. Certain circulation patterns will occur more often than others. The preferred patterns of the atmosphere on time scales of one week to one or more months are called weather regimes. The weather in Europe is for a large part determined by the occurrence of two weather regimes, a blocking regime (a high) and a strong zonal flow regime (a westerly wind). The atmospheric circulation will alternate between these regimes, with transitional intervals in between.

    The transition of one regime to the other can occur very fast, within a couple of days, and is very difficult to predict. In this thesis, the sensitivity in the initial conditions for changes in the regimes a few days later are studied. It appears that the sensitivity fluctuates each day. Flows with a high sensitivity, and a low predictability, are characterized by a strong jetstream to the west of a diffluent flow.

    Formation and stability of foam made from aqueous protein solutions.
    Prins, A. - \ 1997
    Industrial Proteins 4 (1997)2. - ISSN 1381-0022 - p. 3 - 5.
    eiwitten - peptiden - structuur - schuim - schuimen - reologie - fysica - vloeistofmechanica - reologische eigenschappen - moleculaire fysica - proteins - peptides - structure - foams - foaming - rheology - physics - fluid mechanics - rheological properties - molecular physics
    Onderzoek naar de relatie tussen moleculaire structuur van eiwitten en het schuimgedrag van de oplossing
    Wheat bran glucuronoarabinoxylans : biochemical and physical aspects
    Schooneveld - Bergmans, M.E.F. - \ 1997
    Agricultural University. Promotor(en): A.G.J. Voragen; G. Beldman. - S.l. : Schooneveld-Bergmans - ISBN 9789054857167 - 125
    graansoorten - maling - Triticum aestivum - tarwe - hexaploïdie - voedsel - voedingsmiddelen - koolhydraten - zetmeel - vezel - polysacchariden - structuur - chemische reacties - cereals - milling - Triticum aestivum - wheat - hexaploidy - food - foods - carbohydrates - starch - fibre - polysaccharides - structure - chemical reactions

    Arabinoxylans are present in cereal cell walls and in vitro they have interesting physicochemical properties, such as viscosity and gelation. Although many studies on these properties were reported for wheat flour arabinoxylan, not much research has been directed towards exploitation of these polysaccharides as food gum. For that purpose glucuronoarabinoxylans of wheat bran, a cheap by-product of the cereal industry, were studied with regard to their extractability, their structural and physicochemical properties.

    Approximately 50% of the glucuronoarabinoxylans of wheat bran cell wall material were recovered in high purity by barium hydroxide extraction at 70 to 95°C. Delignification or other treatments to open up the cell wall structure were not effective in increasing the yield. The extracted glucuronoarabinoxylans were very diverse in chemical structure and physicochemical properties. About 30% of them had a low degree of substitution, were easily degradable by xylanolytic enzymes and hardly influenced the viscosity of the solvent as a result of extensive aggregation. Over 50% of them had a high degree of substitution, were supposed to contain dimeric branches of arabinose and xylose, were scarcely degradable by xylanolytic enzymes, gave moderate viscosity to solutions and were very effective in stabilizing emulsions. The structure of these glucuronoarabinoxylans could only be speculated upon and it could not be enzymatically modified as a consequence of its complexity and the lack of appropriate enzymes. The remaining glucuronoarabinoxylans either had an intermediate or very high degree of substitution, of which the latter was presumed to be connected to lignin-fragments.

    Gel-forming glucuronoarabinoxylans were recovered only in low yield by dilute alkali extraction and subsequent purification was necessary. These feruloylated glucuronoarabinoxylans gelled upon addition of oxidative agents, of which peroxide - peroxidase, glucose - glucoseoxidase - peroxidase and ammonium persulphate were investigated. In comparison with wheat flour arabinoxylans, those of wheat bran appeared to give less flexible networks at high concentration, which was ascribed to their high degree of substitution and high ferulic acid content. Of the dimers formed upon cross-linking, the generally known diferulic acid, being a 5-5 coupled dimer, was only present in relatively low amounts. Dimers, in which the 8-position of the ferulic acid residue is involved were preponderant. The distribution of the dimers was not affected by the type of cross- linking agent or the type of arabinoxylan. However, the presence of lignin fragments in the bran extract was presumed to cause a low ferulic acid recovery upon cross-linking.

    Glucuronoarabinoxylans from sorghum grain
    Verbruggen, M.A. - \ 1996
    Agricultural University. Promotor(en): A.G.J. Voragen; G. Beldman. - S.l. : Verbruggen - ISBN 9789054855026 - 131
    sorghum bicolor - polysacchariden - structuur - chemische reacties - sorghum - sorghum bicolor - polysaccharides - structure - chemical reactions - sorghum

    Water-unextractable cell wall materials (WUS) were prepared from raw, polished, and malted sorghum ( Sorghum vulgare cv. Fara Fara). Except for the amounts, hardly any difference could be observed between the WUS of these three raw materials. This means that cell wall materials of the endosperm cell walls are basically the same as those of the outer endosperm and pericarp layers, and that the cell walls largely persist, during malting. These preparations were further fractionated by a sequential extraction procedure using aqueous solutions of saturated Ba(OH) 2 , 1M KOH and 4M KOH. The WUS preparations were composed of glucuronoarabinoxylans (GAX), (1→3),(1→4)-β-D-glucans, cellulose, and some protein. GAX was primarily extracted by Ba(OH) 2 solutions. All GAX fractions were composed of a highly substituted (1→4)-β-D-xylan backbone, substituted by arabinose and uronic acid. It was concluded that sorghum GAX populations were characterized by a reasonable homogeneity, since they could not be separated further by several chromatographic and precipitation techniques.

    Degradation studies using purified xylanases, arabinofuranosidases and a glucuronidase alone or in combination, showed that the GAX populations were hardly broken down. Some oligomers were formed by digesting Ba(OH) 2 extracted GAX with a combination of endoxylanase I and (1→4)-β-D-arabinoxylan arabinofuranohydrolase, both purified from Aspergillus awamori . These oligomers were found to have a main chain of three or four xylose units, and to contain α-glucuronic acid linked to O -2 of the non-reducing terminal xylose unit. Two oligomers were found to have a dimeric (1→2)-linked arabinose side, chain linked at O -3 of an internal xylose unit. Also single arabinose substitution occured at O -3 of an internal xylose unit. There are strong indications that these side groups can also be linked at O -2 of an internal xylose residue. The reducing xylose units were unsubstituted. A model for the GAX populations from sorghum was proposed combining the results of the degradation studies, the identification of the oligomers, and knowledge about the mode of action of the enzymes used.

    Finally, the developed techniques to investigate GAX in particular, were used to study the behaviour of GAX in the brewing process. Worts and spent grains of mashes, supplemented with commercial enzyme preparations containing xylanases among others were studied. Except for the amount of solubilized GAX, the GAX hardly changed with respect to the sugar composition and molecular weight distribution. A direct relationship between GAX, xylanases, and filtration behaviour of worts prepared from malted sorghum, could therefore not be established.

    Economische groei, duurzaamheid en emancipatie
    Haagsma, R. - \ 1996
    Den Haag : Emancipatieraad - 70
    luchtverontreiniging - samenstelling - economische groei - werkgelegenheid - milieuwetgeving - milieubeleid - gezinnen - overheidsbeleid - huishoudens - arbeidsmarkt - natuurlijke hulpbronnen - Nederland - bescherming - herstel - hulpbronnengebruik - bodemverontreiniging - structuur - duurzaamheid (sustainability) - waterverontreiniging - vrouwen - vrouwenemancipatie - gelijke behandeling van de vrouw - feminisme - air pollution - composition - economic growth - employment - environmental legislation - environmental policy - families - government policy - households - labour market - natural resources - Netherlands - protection - rehabilitation - resource utilization - soil pollution - structure - sustainability - water pollution - women - emancipation of women - female equality - feminism
    Structural characterization of pectic hairy regions isolated from apple cell walls = Structuurkenmerken van vertakte pectine fragmenten afkomstig van de celwanden van appel
    Schols, H. - \ 1995
    Agricultural University. Promotor(en): A.G.J. Voragen. - S.l. : Schols - ISBN 9789054854050 - 155
    appelsap - pectinen - organische verbindingen - structuur - apple juice - pectins - organic compounds - structure

    Cell wall pectic substances have a great influence on the production and quality aspects of apple juice. Apple juices were characterized by their polysaccharide content and composition. A pectic fraction, retained by ultrafiltration of a liquefaction juice, was isolated and termed MHR (modified hairy regions). MHR, resistant to further enzymic degradation by the liquefaction enzymes, was characterized using chemical and enzymic methods. Next to a high arabinose content, this fraction was characterized by a high rhamnose to galacturonic acid ratio and a high acetyl content. Rhamnogalacturonase (RGase), an enzyme able to hydrolyze galacturonic acid-(1->2)-rhamnosyl linkages within the rhamnogalacturonan backbone, was purified and characterized.

    Next to high molecular weight degradation products, rhamnogalacturonase released characteristic oligosaccharides from MHR. Various 2D-NMR techniques were used to identify these RGase oligomers, which consisted of a tetrameric or hexameric backbone of alternating rhamnose and galacturonic acid residues with a galactose residue substituted at C-4 of part of the rhamnose moieties.

    Analogous MHR fractions were isolated from potato fibre, pear, carrot, leek, and onion tissue, although variations occurred with respect to the arabinose and xylose content. All MHR fractions were degraded by RGase in a comparable fashion resulting in the same type of oligomers in an almost equal ratio.

    Comparison of the MHR with non-modified pectic hairy regions of apple cell wall, isolated in a mild and defined way, revealed great resemblance indicating that the modifications of the MHR during enzymic liquefaction were only minor. The oligomers liberated by RGase from the various pectic hairy regions differed in absolute as well as in relative amount.

    After degradation by RGase of the highest molecular weight population of apple MHR, three subunits were characterized representing a xylogalacturonan segment, residual stabs of the backbone rich in arabinose and regions of alternating rhamnose-galacturonic acid residues of unknown length. The substitution of xylose residues and methylestergroups over the galacturonan backbone was studied by NMR and was found to be random.

    De marginalisering van het gezin aan het einde van de 20ste eeuw: een poging tot opheldering van een hardnekkig misverstand.
    Hoog, K. de - \ 1995
    Wageningen : LU - 22
    samenstelling - gezinnen - huishoudens - verwantschap - colleges (hoorcolleges) - nederland - sociologie - structuur - composition - families - households - kinship - lectures - netherlands - sociology - structure
    Oligosacchariden als bifidogene factoren.
    Hartemink, R. ; Nout, M.J.R. ; Rombouts, F.M. - \ 1994
    Voedingsmiddelentechnologie 27 (1994)20. - ISSN 0042-7934 - p. 27 - 29.
    bifidobacterium - koolhydraten - chemische reacties - microbiële afbraak - polysacchariden - structuur - bifidobacterium - carbohydrates - chemical reactions - microbial degradation - polysaccharides - structure
    Levende bacterien die een gunstige invloed hebben op de darmflora. Ze worden probiotica genoemd en ze worden toegepast in zowel de humane voeding als de veevoeding
    Duurzame verzorging als technologische uitdaging.
    Terpstra, M.J. - \ 1994
    Wageningen : Landbouwuniversiteit Wageningen - 29
    samenstelling - economische ontwikkeling - milieu - milieubeheer - milieubescherming - gezinnen - huishoudkunde - huishoudens - colleges (hoorcolleges) - bedrijfsvoering - natuurlijke hulpbronnen - bescherming - kwaliteit - herstel - hulpbronnengebruik - plattelandsontwikkeling - sociale ontwikkeling - sociale voorzieningen - sociaal welzijn - structuur - duurzaamheid (sustainability) - technische vooruitgang - technologie - theorie - welzijnsvoorzieningen - milieuwetenschappen - natuurwetenschappen - organisatie - wetenschap - sociaal werk - composition - economic development - environment - environmental management - environmental protection - families - home economics - households - lectures - management - natural resources - protection - quality - rehabilitation - resource utilization - rural development - social development - social services - social welfare - structure - sustainability - technical progress - technology - theory - welfare services - environmental sciences - natural sciences - organization - science - social work
    Tailor-made produktie van oligosacchariden.
    Laere, K.M.J. van; Schols, H.A. ; Voragen, A.G.J. - \ 1994
    Voedingsmiddelentechnologie 27 (1994)20. - ISSN 0042-7934 - p. 33 - 35.
    koolhydraten - chemische reacties - chemische structuur - chemicaliën - voedselindustrie - voedseltechnologie - polysacchariden - eigenschappen - structuur - invloeden - carbohydrates - chemical reactions - chemical structure - chemicals - food industry - food technology - polysaccharides - properties - structure - influences
    De gewenste oligosacchariden kunnen met behulp van specifieke enzymen en chromatografische technieken 'op maat' worden gemaakt
    Vrouwen, huishouden en krediet in West Java.
    Niehof, A. - \ 1994
    Huishoudstudies 4 (1994)2. - p. 3 - 12.
    samenstelling - krediet - kredietbeleid - economie - werkende vrouwen - werkgelegenheid - gezinnen - vrouwelijke arbeidskrachten - gezinsinkomen - huishoudens - individuen - Java - hypotheken - hulpbronnen - besparingen - structuur - vrouwen - vrouwelijke werknemers - werk - composition - credit - credit policy - economics - employed women - employment - families - female labour - household income - households - individuals - Java - mortgages - resources - savings - structure - women - women workers - work
    Aan de hand van resultaten van een project in West Java dat de ondersteuning van inkomensgenererende activiteiten van vrouwen tot doel had, komt aan de orde wat economische activiteit en inkomen voor vrouwen en hun huishoudens betekenen en welke strategische rol krediet vervult
    De prijsgevoeligheid van huishoudelijk watergebruik.
    Kooreman, P. - \ 1993
    ESB Economisch Statistische Berichten 78 (1993). - ISSN 0013-0583 - p. 181 - 183.
    luchtverontreiniging - samenstelling - consumentengedrag - consumptie - drinkwater - dumping - milieuwetgeving - milieubeleid - gezinnen - overheidsbeleid - huishoudkunde - huishoudelijke consumptie - huishoudens - marktconcurrentie - Nederland - prijszetting - prijzen - kwaliteit - bodemverontreiniging - structuur - aanbod - kraanwater - waterverontreiniging - watervoorziening - prijsbepalende factoren - sanitaire voorzieningen - air pollution - composition - consumer behaviour - consumption - drinking water - dumping - environmental legislation - environmental policy - families - government policy - home economics - household consumption - households - market competition - Netherlands - price fixing - prices - quality - soil pollution - structure - supply - tap water - water pollution - water supply - price determining factors - sanitary facilities
    Het kabinet wil het mogelijk maken dat huishoudens een rekening krijgen voor waterverbruik, rioolrechten en zuiveringsheffing. De hoogte van die rekening moet geheel afhankelijk zijn van de hoeveelheid water die het huishouden verbruikt. De achterliggende gedachte hierbij is dat dit mensen ertoe zal aanzetten zuiniger met water om te springen. Hoe prijsgevoelig is het huishoudelijk waterverbruik?
    The bending elasticity of surfactant monolayers and bilayers and its effect on the swelling of free liquid films
    Barneveld, P.A. - \ 1991
    Agricultural University. Promotor(en): J. Lyklema; J.M.H.M. Scheutjens. - S.l. : Barneveld - 150
    grensvlak - film - structuur - samenstelling - interface - film - structure - composition

    The present study was carried out to obtain more insight into the unusual swelling behaviour of surfactant layers. Here, swelling means that the thickness of the water layer between two surfactant layers increases. It was shown recently that high salt concentrations can bring about swelling in aqueous multilayer vesicles and free liquid films of nonionic surfactants (polyoxyethylenated n-dodecyl alcohols). By this so-called salt-induced swelling the water layer becomes thicker up to relatively high salt concentrations (1-2 kmole/m 3), reaches a maximum and, beyond these concentrations, shrinks again. In multilayer vesicles, the maximum swelling can be substantial (extreme swelling): the water layer thickness can easily be 10 times the surfactant layer thickness.

    Until now, an explanation for salt-induced swelling in terms of interaction forces between the surfactant layers was not available. The Van der Waals force is relatively unaffected by the ionic strength of the water layer. On the basis of steric repulsion, shrinking is expected due to salting-out of the ethylene oxide head groups of the nonionic surfactant. This could explain the decreasing part of the swelling curve. A problem with this explanation is that the bilayers in the vesicles are too far apart for the head groups to interact. When pushed to extremes, electrostatic repulsion could lead to some swelling if salt ions adsorb specifically onto the surfactants. In that case, as a function of salt concentration two regimes can be distinguished: in low concentrations the electrostatic double layer is built up by an increasing surface charge, leading to swelling, whereas in high salt concentrations the double layer is compressed, leading to shrinking. In chapter 3 this mechanism is shown to be quantitatively insufficient to account for the thickness variation of free liquid films, let alone for the extreme swelling in multilayer vesicles.

    Helfrich has suggested that thermal undulations of nearby surfactant layers provide an additional steric repulsion between the layers. Since this is a long range force, it could be responsible for the extreme swelling in multilayer vesicles. Quantitative analyses are required to test this suggestion. A parameter that dominates the magnitude of the Helfrich force is the mean bending elasticity modulus of the surfactant layer involved: a small modulus implies strong undulations and hence, large repulsions. The presence of a surface tension restricts the undulations. The surface tension of vesicles is negligible, but that of a film is significant. However, monolayers are thinner than bilayers and hence may be less rigid so that undulations can still be large enough to affect the film thickness.

    A major part of the present study is the modelling of surfactant monolayers and bilayers, with the aim to calculate bending moduli from the solution properties of the surfactants (see chapters four and five). Based on these calculations, it was predicted that the thickness of free liquid films containing n-alcohol instead of salt would show qualitatively the same trends if Helfrich repulsion is responsible for the salt-induced swelling. The experimental verification of this prediction is described in chapter six. The results agree very well with the proposed influence of undulations.

    De inkomensvorming en de inkomensverdeling in de Nederlandse landbouw verklaard vanuit de huishoudproduktietheorie
    Elhorst, J.P. - \ 1990
    Den Haag : LEI - ISBN 9789052420950 - 179
    landbouw - landbouwbeleid - inkomen - inkomsten uit het landbouwbedrijf - inkomensverdeling - huishoudens - gezinnen - structuur - samenstelling - familiebedrijven, landbouw - nederland - economische sectoren - agrarische bedrijfsvoering - econometrie - inkomensbeleid - vermogensverdeling - landbouw als bedrijfstak - agriculture - agricultural policy - income - farm income - income distribution - households - families - structure - composition - family farms - netherlands - economic sectors - farm management - econometrics - income policy - wealth distribution - agriculture as branch of economy
    In dit verslag wordt een model ontwikkeld om de inkomensvorming en de inkomensverdeling in de Nederlandse landbouw te verklaren. Factoren die daarbij de aandacht krijgen zijn: de prijzen van produkten en vlottende produktiefactoren, produktiequota, de inzet van kapitaalgoederen en gezinsarbeid, de ondernemerskwaliteit, afschrijvingen op kapitaalgoederen, de wijze van bedrijfsfinanciering, inkomsten van buiten het bedrijf, belastingen en premies. Het ontwikkelde model is toegepast op de akkerbouw, de melkveehouderij en de varkenshouderij
    Werkloze hoofdkostwinners in Friesland en hun omgang met geld.
    Ophem, J.A.C. van - \ 1990
    Tijdschrift voor huishoudkunde 11 (1990)3. - ISSN 0169-1295 - p. 65 - 72.
    budgetten - samenstelling - uitgaven voor consumptie - consumptie - gezinnen - huishoudelijke consumptie - huishouduitgaven - huishoudens - inkomen - armoede - sociale structuur - sociaal welzijn - sociologie - structuur - werkloosheid - financieel beheer - friesland - nationaal vermogen - personen - vermogensverdeling - budgets - composition - consumer expenditure - consumption - families - household consumption - household expenditure - households - income - poverty - social structure - social welfare - sociology - structure - unemployment - financial management - friesland - national wealth - persons - wealth distribution
    Bespreking van een onderzoek naar de economische omstandigheden en het arbeidsmarktgedrag van langdurig werklozen in Friesland
    Financieel management en het conventionele huishouden.
    Ophem, J.A.C. van; Knippers, E.W. - \ 1990
    Tijdschrift voor huishoudkunde 11 (1990)1. - ISSN 0169-1295 - p. 15 - 19.
    samenstelling - consumptie - gezinnen - financiële planning - huishoudens - nederland - armoede - structuur - financieel beheer - nationaal vermogen - vermogensverdeling - composition - consumption - families - financial planning - households - netherlands - poverty - structure - financial management - national wealth - wealth distribution
    Het huishoudelijk handelen van uitkeringsgerechtigden.
    Hoog, C. de; Ophem, J.A.C. van - \ 1990
    Tijdschrift voor huishoudkunde 11 (1990). - ISSN 0169-1295 - p. 106 - 111.
    composition - consumption - families - households - income distribution - low income - netherlands - structure - financial management - financial support - material assistance - persons - wealth distribution
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