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.
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