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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    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
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