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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    Exploring novel food proteins and processing technologies : a case study on quinoa protein and high pressure –high temperature processing
    Avila Ruiz, Geraldine - \ 2016
    Wageningen University. Promotor(en): Tiny van Boekel, co-promotor(en): Guido Sala; Markus Stieger. - Wageningen : Wageningen University - ISBN 9789462579095 - 152
    dietary protein - chenopodium quinoa - whey protein - food process engineering - heat treatment - in vitro digestibility - fractionation - maillard reaction products - ph - viscosity - gelation - aggregation - high pressure technology - sds-page - voedingseiwit - chenopodium quinoa - wei-eiwit - levensmiddelenproceskunde - warmtebehandeling - in vitro verteerbaarheid - fractionering - maillard-reactieproducten - ph - viscositeit - gelering - aggregatie - hogedruktechnologie - sds-page

    Foods rich in protein are nowadays high in demand worldwide. To ensure a sustainable supply and a high quality of protein foods, novel food proteins and processing technologies need to be explored to understand whether they can be used for the development of high-quality protein foods. Therefore, the aim of this thesis was to explore the properties of a novel food protein and a novel processing technology for the development of high-quality protein foods. For this, quinoa was chosen as an alternative protein source and high pressure – high temperature (HPHT) processing was chosen as a novel processing technology.

    Quinoa protein has been found to have a balanced amino acid profile and to be allergen-free. As this combination is not common among plant proteins, it is worth studying physicochemical and functional protein properties of quinoa further (Chapter 1). Extraction and processing conditions can influence protein properties and thus functionality. Therefore, quinoa protein properties were examined at different extraction and processing conditions (Chapter 2 and 3). For this, the protein was isolated from the seed using alkaline extraction and subsequent acid precipitation. The quinoa protein isolates (QPIs) obtained were examined in terms of protein purity, yield, solubility, denaturation, aggregation and gelation behaviour, and digestibility.

    It was found that when extraction pH increased, protein yield and denaturation increased, which was explained by a higher protein charge, leading to increased unfolding and solubilisation (Chapter 2). Protein purity decreased with increasing extraction pH, which was associated with a possible co-extraction of other seed components. QPIs obtained at extraction pH 8 (E8) and 9 (E9) had a higher solubility in the pH range of 3-4.5 (E9 solubility was highest at pH 7) compared to the isolates obtained at extraction pH 10 (E10) and 11 (E11). It was hypothesised that at a higher extraction pH, the larger extent of protein denaturation led to the exposure of hydrophobic groups, thus decreasing surface polarity and solubility. When suspensions of E8 and E9 were heated, protein aggregation increased and semi-solid gels with a dense microstructure were formed. In contrast, suspensions of E10 and E11 aggregated to a lower degree and did not form self-supporting gels upon heating. The gels obtained with E10 and E11 had furthermore a microstructure showing loose particles. Increased protein aggregation and improved gel formation at lower extraction pH were hypothesised to be due to a higher degree of hydration and swelling of protein particles during heating, leading to increased protein-protein interactions. These findings show that QPI obtained at an extraction pH below 9 might be used to prepare semi-solid gelled foods, while QPI obtained at pH values higher than 10 might be more suitable to be applied in liquid foods.

    Heat treatments of QPI suspensions lead to an increased protein denaturation and aggregation but to a decreased in vitro gastric protein digestibility, especially at a high temperature (120°C) and extraction pH (11) (Chapter 3). It was hypothesised that QPIs obtained at a higher extraction pH and treated at higher temperature were denatured to a greater extent and contained stronger protein crosslinks. Therefore, enzyme action was impaired to a higher degree compared to lower temperatures and extraction pH values. This means that by controlling extraction pH and treatment temperature the digestibility of quinoa protein can be optimised.

    The disadvantage of the conventional fractionation method used in Chapter 2 and 3 is that it requires high amounts of energy and water and the solvents used can denature the protein, possibly leading to a loss in functionality. Therefore, recently, a new method has been developed, hybrid dry and aqueous fractionation, which uses less energy and water and has proved successful for obtaining protein-rich fractions from pea. It was not known whether hybrid dry and aqueous fractionation can be used to obtain protein-rich fractions of quinoa (Chapter 4). Quinoa seeds were carefully milled to disentangle the protein-rich embryo from the starch-rich perisperm. Using subsequent air-classification, the embryo and perisperm were separated based on size into a protein-rich fraction and a starch-rich fraction, respectively (dry fractionation). The protein-rich fraction was further milled to a smaller particle size and suspended in water. This step was to solubilise the protein (aqueous fractionation), whereby a smaller particle size and adding NaCl optimised the solubilisation efficiency. The addition of salt helped to extract more salt-soluble proteins from quinoa, next to the water-soluble proteins. After centrifugation, the protein-enriched top aqueous phase was decanted and ultrafiltered for further protein concentration. The process generated a quinoa protein-rich fraction with a protein purity of 59.4 w/dw% and a protein yield of 62.0%. Having used 98% less water compared to conventional protein extraction, this new method is promising for industry to obtain quinoa protein concentrates in a more economic, sustainable and milder way.

    Next to exploring novel food proteins for the development of high-quality protein foods, novel processing technologies are also important to study. This is because traditional thermal processing can deteriorate the quality of protein-rich foods and beverages by causing undesired browning or too high viscosities. Therefore, for sterilisation purposes, HPHT processing was investigated for the treatment of protein foods (Chapter 5). Model systems, whey protein isolate – sugar solutions, were used to study the effect of pressure at high temperature on Maillard reactions, browning, pH, protein aggregation and viscosity at different pH. It was found that pressure retarded early and advanced Maillard reactions and browning at pH 6, 7 and 9, while it inhibited protein aggregation and, thereby, a high viscosity at pH 7. The mechanism behind this might be that pressure induces a pH drop, possibly via dissociation of ionisable compounds, and thus slows down Maillard reactions. Differences in protein conformation, protein-protein interactions and sensitivity of whey proteins, depending on pH, pressure and heat, might be at the base of the reduced protein aggregation and viscosity observed at pH 7. The results show that HPHT processing can potentially improve the quality of protein-sugar containing foods, for which browning and high viscosities are undesired, such as high-protein beverages.

    Finally, the properties of quinoa protein and HPHT processing were discussed in a broader context (Chapter 6). It was concluded that QPI obtained at pH 9 is a promising alternative to pea and soy protein isolate from a technical perspective and that QPI protein yields can be optimised. Also, quinoa protein-rich fractions obtained with the hybrid dry and aqueous fractionation method were predicted to have comparable properties to QPI, soy and pea protein isolates. However, from a marketing perspective, the protein-rich fraction was considered more advantageous to be up-scaled compared to QPI. High pressure at ambient or high temperature was found to have an added value compared to heat, which can be used for the development of high-quality protein food. Lastly, quinoa protein and HPHT processing might become more attractive for industry in the light of current trends, if present predictions can be confirmed and remaining issues can be resolved.

    Recirculatie potorchidee 5. Zink
    Blok, C. ; Kromwijk, J.A.M. - \ 2014
    potplanten - orchidales - recirculatiesystemen - hergebruik van water - zink - aggregatie - reductie - effecten - pot plants - orchidales - recirculating systems - water reuse - zinc - aggregation - reduction - effects
    Als het zinkgehalte in het aanvoerwater hoger is dan de plantopname, loopt de concentratie in de wortelomgeving op. Recirculatie van drainwater leidt dan tot het langzaam maar gestadig oplopen van het zinkgehalte. Schadegrenzen voor potorchidee zijn niet bekend. Deze flyer geeft inzicht in effecten van zinkophoping bij andere gewassen en methoden om zinkophoping te verminderen.
    Heteroaggregation and sedimentation rates for nanomaterials in natural waters
    Quik, J.T.K. ; Velzeboer, I. ; Wouterse, M. ; Koelmans, A.A. ; Meent, D. van de - \ 2014
    Water Research 48 (2014)1. - ISSN 0043-1354 - p. 269 - 279.
    sedimentatie - zwevende deeltjes - aggregatie - nanotechnologie - emissie - schatting - colloïden - waterstroming - zeewater - oppervlaktewaterkwaliteit - sedimentation - suspended solids - aggregation - nanotechnology - emission - estimation - colloids - water flow - sea water - surface water quality - engineered nanomaterials - silver nanoparticles - carbon nanotubes - manufactured nanoparticles - aggregation kinetics - aquatic environments - ceo2 nanoparticles - organic-matter - fate - exposure
    Exposure modeling of engineered nanomaterials requires input parameters such as sedimentation rates and heteroaggregation rates. Here, we estimate these rates using quiescent settling experiments under environmentally relevant conditions. We investigated 4 different nanomaterials (C60, CeO2, SiO2-Ag and PVP-Ag) in 6 different water types ranging from a small stream to seawater. In the presence of natural colloids, sedimentation rates ranged from 0.0001md-1 for SiO2-Ag to 0.14md-1 for C60. The apparent rates of heteroaggregation between nanomaterials and natural colloids were estimated using a novel method that separates heteroaggregation from homoaggregation using a simplified Smoluchowski-based aggregation-settling equation applied to data from unfiltered and filtered waters. The heteroaggregation rates ranged between 0.007 and 0.6Lmg-1 day-1, with the highest values observed in seawater. We argue that such system specific parameters are key to the development of dedicated water quality models for ENMs.
    Map maker’s guide: a decision support system for interpolation, aggregation, and disaggregation : technical documentation
    Walvoort, D.J.J. ; Knotters, M. ; Hoogland, T. ; Wijnen, H. van; Dijk, T.A. van; Schöll, L. van; Groenenberg, J.E. - \ 2013
    Wageningen : Wettelijke Onderzoekstaken Natuur & Milieu (WOt-werkdocument 350) - 36
    kaarten - beslissingsondersteunende systemen - tijd - ruimte - aggregatie - internet - maps - decision support systems - time - space - aggregation - internet
    This report documents a decision support system (DSS) that has been developed to assist environmental researchers in selecting interpolation, aggregation, and disaggregation methods. The DSS has been implemented as a web-application. This facilitates updating and makes the DSS generally accessible. The DSS asks the user several questions. The answers are compared with those given by experts. The degree of similarity between both sets of answers is used to assign suitability scores to a huge set of interpolation, aggregation, and disaggregation methods stored in a database. These methods are ranked from most to least suitable and presented to the user in a dynamic table. The user can compare recommended methods (backgrounds, available software, literature, performance) and evaluate dynamically which methods would have been recommended if deferent answers had been given (what-if analysis)
    Designing microcapsules based on protein fibrils and protein - polysaccharide complexes
    Hua, K.N.P. - \ 2012
    Wageningen University. Promotor(en): Erik van der Linden, co-promotor(en): Leonard Sagis. - S.l. : s.n. - ISBN 9789461733801 - 136
    lysozym - ovalbumine - pectinen - aggregatie - inkapseling in microcapsules - lysozyme - ovalbumin - pectins - aggregation - microencapsulation

    Keywords: encapsulation, microcapsule, protein, fibril, protein-polysaccharide complex, controlled release, interfacial rheology, lysozyme, ovalbumin

    This thesis describes the design of encapsulation systems using mesostructures from proteins and polysaccharides. The approach was to first investigate the physical properties of the encapsulating materials (protein fibrils and protein – polysaccharide complexes). Subsequently, microcapsules with tunable release rate and mechanical strength were developed.

    Firstly, the effect of steady shear and turbulent flow on the formation of protein fibrils from lysozyme was studied. We determined the conversion and size distribution of fibrils obtained by heating lysozyme solutions at pH 2. The formation of fibrils was quantified using flow-induced birefringence. The size distribution was fitted using decay of birefringence measurements and Transmission Electron Microscopy. The morphology of Lys fibrils and kinetics of their formation varied considerably depending on the flow applied. With increasing shear or stirring rate, more rod-like and shorter fibrils were obtained, and the conversion into fibrils was increased.

    Secondly, we have investigated the surface rheological properties of oil – water interfaces stabilized by fibrils from lysozyme (long and semi-flexible, and short and rigid ones), fibrils from ovalbumin (short and semi-flexible), lysozyme – pectin complexes, or ovalbumin – pectin complexes. We have compared these properties with those of interfaces stabilized by the native proteins. The surface dilatational and surface shear moduli were determined using an automated drop tensiometer, and a stress controlled rheometer with biconical disk geometry. Results show that interfaces stabilized by protein – pectin complexes have higher surface shear and dilatational moduli than interfaces stabilized by the native proteins only. At most of the experimental conditions, interfaces stabilized by protein fibrils have the highest surface rheological moduli. The difference between long semi-flexible lysozyme fibrils or short rigid lysozyme fibrils is not pronounced in interfacial dilation rheology but significant in interfacial shear rheology. The complex surface shear moduli of interfaces stabilized by long semi-flexible fibrils are about ten times higher than those of interfaces stabilized by short rigid fibrils, over a range of bulk concentrations. Interfaces stabilized by short and more flexible ovalbumin fibrils have a significantly higher surface shear modulus than those stabilized by the somewhat longer and more rigid short lysozyme fibrils.

    Finally, encapsulation systems are developed using layer-by-layer adsorption of food-grade polyelectrolytes on an emulsion droplet template. The first encapsulation system was built with alternating layers of ovalbumin fibrils and high methoxyl pectin. By varying the number of layers, the release of active ingredients can be controlled: increasing the number of layers of the shell from four to eight, decreases the release rate by a factor six.

    The other encapsulation systems were built with alternating layers of protein – pectin complexes and protein fibrils. Two types of proteins (ovalbumin and lysozyme) and three types of fibrils were used: short and semi-flexible from ovalbumin, short and rod-like, and long and semi-flexible from lysozyme. At low number of layers (less than five), microcapsules from ovalbumin complexes and fibrils were stronger than microcapsules prepared from lysozyme complexes and fibrils. Increasing the number of layers, the mechanical stability of microcapsules from lysozyme complexes and fibrils increased significantly, and capsules were stronger than those prepared from ovalbumin complexes and fibrils with the same number of layers. The contour length of the Lys fibrils did not have a significant effect on mechanical stability of the lysozyme complexes and fibrils capsules. These results show that mechanical properties of this type of capsule can be tuned by varying the flexibility of the protein fibrils.

    Controlling the aggregation and gelation of ß-lactoglobulin by the addition of its peptides
    Kosters, H.A. - \ 2012
    Wageningen University. Promotor(en): Harry Gruppen, co-promotor(en): Peter Wierenga. - S.l. : s.n. - ISBN 9789461732040 - 171
    bèta-lactoglobuline - aggregatie - gelering - peptiden - eiwithydrolysaten - beta-lactoglobulin - aggregation - gelation - peptides - protein hydrolysates

    In this thesis the effects of peptides, or protein hydrolysates on the heat-induced aggregation and gelation of (concentrated) protein systems were studied. First, it was investigated if specific peptides could influence the heat-induced denaturation and aggregation of intact proteins solutions, and which peptide properties dominated the different interactions. Next, the effects of the peptides on the heat-induced gelation of intact proteins as a model for a potential high protein food system were studied.

    It was found that certain peptides in the hydrolysate show binding to native proteins, and some additional peptides bind to unfolded proteins. Since the same peptides were shown to bind to not only β-lactoglobulin, but also other to proteins, it is concluded that the binding does not depend on specific molecular details of the protein. The hydrophobicity and charge were found to be important in determining the binding and the effect on aggregation. With the hydrolysates, as well as with two synthesized peptides (modelled on those found in the hydrolysate) it was confirmed that the addition of these binding peptides has significant effects on the heat-induced aggregation. In the gelation experiments performed in this study a dominant effect was found for peptides containing free SH groups. While it is expected that the changes in aggregation behaviour, induced by the binding of non-cysteine-containing peptides also affects the gel properties, this was not found with the techniques used. Finally, disulfide-containing peptides were found to reduce the presence of sulfurous volatiles formed after heating of β-lactoglobulin, WPI and lysozyme.

    Since only certain peptides exhibit binding to intact proteins, it is expected that control over the hydrolysis process and, thereby the concentrations of such specific peptides, can be used to produce hydrolysates with specific functionalities in this respect.

    Uitkomsten MKBA vaak overschat
    Blaeij, A.T. de; Heide, C.M. van der - \ 2008
    ESB Economisch Statistische Berichten 93 (2008)4541. - ISSN 0013-0583 - p. 503 - 505.
    landschap - kosten-batenanalyse - evaluatie - aggregatie - natuur - landscape - cost benefit analysis - evaluation - aggregation - nature
    Een KMBA vereist inzicht in de maatschappelijke waarde van natuur en landschap. Hierbij is aggregatie van individuele baten noodzakelijk. Hoewel de manier van aggregatie van grote invloed is op de uitkomsten van de MKBA's, wordt dit in Nederland nauwelijks onderkend
    Enzyme-induced aggregation of whey proteins with Bacillus licheniformis protease
    Creusot, N.P. - \ 2006
    Wageningen University. Promotor(en): Harry Gruppen. - [S.l.] : S.n. - ISBN 9789085045014 - 128
    wei-eiwit - aggregatie - proteïnasen - peptiden - interacties - bacillus licheniformis - whey protein - aggregation - proteinases - peptides - interactions - bacillus licheniformis
    Whey proteins are commonly used as ingredient in food. In relation with the gelation properties of whey proteins, this thesis deals with understanding the mechanism of peptide-induced aggregation of whey protein hydrolysates made with Bacillus licheniformis protease (BLP). The results show that BLP breaks down hydrophilic segments in the substrate and, therefore, preserves hydrophobic segments that aggregate once exposed to the solvent. Aggregation during hydrolysis prevented further degradation of the substrate, explaining that aggregating peptides are larger than the non-aggregating ones. Solubility experiments performed on fractionated aggregating peptides showed that peptide co-aggregation is an important factor in the aggregation process. Results also showed that the hydrolysates are able to aggregate added parental protein. The aggregating peptides could form a network in which the presence of both insoluble and partly insoluble peptides was required for the aggregation of intact protein.
    Limiting factors for the enzymatic accessibility of soybean protein
    Fischer, M. - \ 2006
    Wageningen University. Promotor(en): Harry Gruppen; Fons Voragen. - [S.l.] : S.n. - ISBN 9789085044963 - 139
    sojaeiwit - hydrolyse - aggregatie - koolhydraten - eiwitextractie - eiwitvertering - eiwitverteerbaarheid - peptiden - soya protein - hydrolysis - aggregation - carbohydrates - protein extraction - protein digestion - protein digestibility - peptides
    Soy is a commonly used ingredient is food and animal feed. With particular focus on the in-soluble fractions, this thesis deals with the effects of proteases and carbohydrate degrading enzymes on different soybean meals subjected to different extent of heating. The primary aim is to improve the understanding of enzymatic hydrolysis of SBM with emphasis on proteins and to identify barriers limiting the efficiency of the process. The results show that aggregation behavior of peptides during enzymatic processing of soy proteins is potentially a limiting factor for efficacy of protein extraction. Surprisingly, it is also demonstrated that aggregation is not limited to in vitro incubations, but is also occurring in vivo in the digestive system of pigs.
    Fundamentals of unfolding, refolding and aggregation of food proteins
    Broersen, K. - \ 2005
    Wageningen University. Promotor(en): Rob Hamer; Fons Voragen, co-promotor(en): Harmen de Jongh. - Wageningen : - ISBN 9789085042501 - 230
    eiwitten - voedsel - aggregatie - chemische structuur - moleculaire structuur - eiwittechnologie - proteins - food - aggregation - chemical structure - molecular conformation - protein engineering
    Protein functionality in food products strongly relies on the fact that proteins can undergo intermolecular interactions, called aggregation. It was found that very subtle dynamics inherent to the protein of interest can have consequences for the functional properties of proteins. The aim of this thesis is to explore structural features of proteins of importance to the generation of aggregation prone protein molecules. The approach selected involves chemical engineering in which functional groups of the protein are converted into a chemical group with different properties. This led to a detailed description of the structural impact of the modifications in relation to aggregate formation. It was found that the various modifications applied interact with the aggregation process in a rather diverse (but predictable) manner. The accumulation of data from this work in combination with results from literature was used to significantly improve the understanding of factors relevant to aggregation and to develop a model to predict aggregation propensity. This model can be used within the food and pharmaceutical industry to determine the aggregation propensity of proteins used in formulae and medication.
    Factors affecting the hyper-aggregation of glutenin particles
    Don, J.A.C. - \ 2005
    Wageningen University. Promotor(en): Rob Hamer, co-promotor(en): J.J. Plijter. - Wageningen : - ISBN 9789085043171 - 222
    gluteninen - aggregatie - deeg - kneden - broodbereiding - reologische eigenschappen - glutenins - aggregation - doughs - kneading - breadmaking - rheological properties
    Ecology of Drosophila aggregation pheromone: a multitrophic approach
    Wertheim, B. - \ 2001
    Wageningen University. Promotor(en): L.E.M. Vet; M. Dicke; J.C. van Lenteren. - S.l. : s.n. - ISBN 9789058084330 - 198
    drosophila melanogaster - aggregatieferomonen - dierecologie - gastheer parasiet relaties - diergedrag - trofische graden - voedselketens - aggregatie - drosophila melanogaster - aggregation - aggregation pheromones - animal ecology - animal behaviour - host parasite relationships - trophic levels - food chains - cum laude

    Many insect species use an aggregation pheromone to form groups with conspecifics in certain localities of the environment. This type of behaviour has a variety of implications for ecological interactions, both directly through the effect of the pheromone on the behaviour of con- and heterospecifics, and indirectly through the consequential aggregative distributions that may affect species interactions. The evolutionary ecology of the use of aggregation pheromone has received only little attention. Yet, these pheromones may play an intricate role in food web interactions by providing an accompanying information web.

    The aim of this thesis is to further our understanding on the ecological and evolutionary aspects of the use of aggregation pheromone in insects. By unravelling costs and benefits that arise from the use of aggregation pheromone in our ecological model organism, Drosophila melanogaster , we strive to answer why they use an aggregation pheromone and elucidate the ecological consequences of an aggregation pheromone in a food web context.

    In laboratory and field studies, we identified behaviours and interactions of the fruit fly D. melanogaster that were affected by its aggregation pheromone. The pheromone affected the distribution of adults, their eggs, competitor species and parasitoids. Moreover, a number of costs and benefits to the use of aggregation pheromone were indicated. In subsequent studies, the major hypotheses on costs and benefits were examined.

    A major benefit of using aggregation pheromone was shown to be aggregated oviposition. Aggregated oviposition enhanced the quality of the larval resource, as indicated by a higher survival of the larvae and larger size of the emerging flies. This Allee effect was characterised by a positive effect of adult density on larval fitness components, and may have arisen from the interaction between adult flies and micro-organisms (yeasts and fungi). Fungi antagonise yeast and larval development, while adults can inoculate yeast on a substrate and temper fungal growth. Larvae also tempered fungal growth, but an increased larval density did not result in an Allee effect but in competition instead.

    A major cost of using aggregation pheromone arose from an increased risk of parasitism. The parasitoid Leptopilina heterotoma uses the aggregation pheromone of adult fruit flies to localise the larval hosts, and based on this information this parasitoid can differentiate quantitatively at long range between substrates that differ in profitability. After arrival on a substrate, the pheromones no longer play a role in the host searching behaviour. A behaviour-based model was developed to predict the individual risk of parasitism for hosts in differently sized host aggregations. The functional and numerical responses of the parasitoids were combined with a flexible patch leaving decision rule for the parasitoid, to assess whether aggregation could also comprise a benefit to the hosts in terms of a diluted risk ( sensu Hamilton 1971). The model prediction reads that aggregation is not beneficial in the context of the Drosophila - Leptopilina interaction, and these predictions were supported by field data.

    In a simple spatio-temporal simulation model, the population dynamics arising from several modes of dispersal, food competition and an Allee effect were explored. The model is a first step towards a more extensive model that incorporates the responses of insects to spatially heterogeneous resources and chemical information (e.g., aggregation pheromone).

    The main conclusion from this thesis is that the aggregation pheromone of D. melanogaster plays an intricate role within a foodweb context, and that a variety of costs and benefits arise from multitrophic interactions. To understand the dynamic interactions in this and many other ecological systems, it is essential to gain more insight into the effect of aggregation pheromone on the behaviour of individuals.

    Upscaling and downscaling methods for environmental research
    Bierkens, M.F.P. ; Finke, P.A. ; Willigen, P. de - \ 2000
    Dordrecht : Kluwer (Developments in plant and soil sciences 88) - ISBN 9780792363392 - 190
    schaalverandering - classificatie - aggregatie - gezamenlijke statistieken - bodemfysica - wiskundige modellen - modellen - milieuwetenschappen - soil physics - scaling - mathematical models - models - classification - aggregation - aggregate statistics - environmental sciences
    Spatial aggregation of land surface characteristics : impact of resolution of remote sensing data on land surface modelling
    Pelgrum, H. - \ 2000
    Agricultural University. Promotor(en): R.A. Feddes, co-promotor(en): M. Menenti. - S.l. : S.n. - ISBN 9789058082435 - 151
    landevaluatie - landclassificatie - landverdeling - landtypen - ruimtelijke variatie - aggregatie - remote sensing - gegevensanalyse - resolutie - aardoppervlak - land evaluation - land classification - land diversion - land types - spatial variation - aggregation - remote sensing - data analysis - resolution - land surface

    Land surface models describe the exchange of heat, moisture and momentum between the land surface and the atmosphere. These models can be solved regionally using remote sensing measurements as input. Input variables which can be derived from remote sensing measurements are surface albedo, surface temperature and vegetation cover. A land surface model using those land surface characteristics is presented i.e. the Surface Energy Balance Index (SEBI) model. This model uses the observed temperature difference between the land surface and atmosphere as an indicator for evapotranspiration.

    Spatially distributed land surface model results can be used as a boundary condition for numerical weather predicton models. The results should therefore be aggregated from the remote sensing pixel scale to the atmospheric model scale. However aggregated values will differ when derived from remote sensing data with different resolutions. This difference, the error due to aggregation is caused by two different aspects: land surface heterogeneity and non-linearity of the land surface model. Two approaches are presented to quantify the error due to aggregation: the linearization approach, where the land surface model is approximated by a Taylor expansion and a geometrical approach where the range of valid results for the land surface model is derived using a convex hull.

    To measure the heterogeneity of land surfaces, the concept of length scale is introduced. The wavelet transform is being used to derive the length scale of the land surface characteristics. The wavelet variance derived from the Fast Wavelet Transform using the Haar wavelet is a good indicator for the variability of land surface characteristics at different spatial scales. For three different data sets the length scale of land surface characteristics have been derived: Barrax, Spain, the Jornada Experimental Range, USA and the Central Part of the Netherlands.

    The two approaches for quantifying the error due to aggregation have been verified using the three data sets. The results obtained by the linearization show that aggregation error can indeed be estimated. For the three test sites the large scale error did not exceed 10 %. However the results based on the convex hull analysis show that the large scale error due to aggregation can be much larger than observed for the three test cases. Therefore low resolution remote sensing data cannot be used a priori as input for land surface models.

    Effects of land use on regional nitrous oxide emissions in the humid tropics of Costa Rica : extrapolating fluxes from field to regional scales
    Plant, R.A.J. - \ 1999
    Agricultural University. Promotor(en): J. Bouma; N. van Breemen. - S.l. : Plant - ISBN 9789058080011 - 129
    distikstofmonoxide - emissie - landgebruik - houtteelt conversie - schaalverandering - aggregatie - costa rica - nitrous oxide - emission - land use - silvicultural conversion - scaling - aggregation - costa rica

    Atmospheric concentrations of the greenhouse gas nitrous oxide (N 2 O) have increased significantly since pre-industrial days. Greenhouse gases absorb infrared radiation reflected by earth's surface, thereby causing global warming. The increase in atmospheric N 2 O concentrations is attributed to human activities. The relative contribution of N 2 O to the anthropogenic greenhouse effect is about 5%. The two major natural sources of N 2 O are soils and oceans, while agricultural soils comprise the main anthropogenic source.

    Nitrous oxide if formed in soil as an intermediate product from nitrification and denitrification, soil processes that operate at the microsite scale. Land use changes strongly affect soil nitrogen (N) cycling; especially conversion of natural forest to agricultural land generally increases N 2 O emissions. Therefore, land use is an important distal process control on N 2 O emissions from soil. Effects of land use change on N 2 O must be studied at scales relevant to agricultural land use planning and policy making.

    This calls for methods to extrapolate plot-scale measurements that are highly variable in space and time. Neglecting spatial heterogeneity of fluxes and process controls can lead to serious errors in areal and regional flux estimates. The objective of the work summarized in this thesis was to study effects of land use on regional N 2 O emissions by extrapolating plot-scale N 2 O measurements in the Northern Atlantic Zone of Costa Rica (2817 ha). A body of earlier work has been carried out in this humid tropical region, and the concurrent availability of data on soils, land use, climate and N 2 O emissions for a sizeable area provided a unique opportunity for an in-depth methodological study on extrapolation. Moreover, the land use history of the area is representative for humid tropical regions in Latin America.

    A well-tested process-based ("mechanistic") simulation model driven by rainfall events (dndc) was used to estimate fluxes from unsampled fields and land units. Land units are defined by distal process controls such as soil type, management and climate. The model, originally designed to simulate nitrogen oxide emissions under temperate climatic conditions, was adapted to justify application to humid tropical pastures and banana plantations. First, the original formulations of evapotranspiration and soil water flow were replaced by routines relevant to tropical soils. Second, functions simulating i) cattle grazing and ii) steady input of organic matter through root turnover and the return of excrements to the pasture were added. Third, an explicit treatment for the immobilization of N was added.

    The adapted simulation model was tested against field measurements of i) N 2 O and nitric oxide (NO) fluxes from a chronosequence of pastures on Inceptisols and ii) N 2 O fluxes from a banana plantation on Andisols and Inceptisols. For the pasture chronosequence, the model formulation was consistent for annual N dynamics and annual nitrogen oxide emissions. In contrast, simulated daily dynamics of nitrogen oxide emissions did not match field observations. The differences in local weather on the seven sampled pasture sites comprising the chronosequence may have caused a significant part of the mismatch. Annual emissions calculated by the model are essentially cumulative daily fluxes, so daily comparisons provide a more conclusive insight in the model's performance than annual comparisons.

    Simulated daily N 2 O fluxes from soils below a banana plantation were compared with data from monthly and frequent field sampling. Different model parameterizations were used to represent fertilizer inputs below banana plants and crop residue additions between plants. For both the Andisol and the Inceptisol, simulated below-plant fluxes matched frequently measured fluxes better than monthly measured fluxes. Simulated between-plant fluxes matched monthly measured fluxes better than frequently measured fluxes. The simulated annual N 2 O-N losses for the Inceptisol and Andisol were 6 and 15 kg ha -1 , respectively. Field-measured annual losses were 6 and 13 kg ha -1 . In addition, three banana fertilization scenarios on an Andisol were studied. With fewer equal splits of fertilizer-N, the simulated N 2 O-N loss declined. With more equal splits losses increasingly depended on the amount of fertilizer-N.

    An expert system for quantifying inputs and outputs of pastures (pastor) was linked with the simulation model to produce frequency distributions of N 2 O and NO emissions for one current pasture management system ("Natural") and two alternative systems ("Grass-Legume" and "Fertilized Improved"). Current forest-derived natural pastures deplete soil nitrogen stocks and therefore are unsustainable. Alternative management aims to utilize soil-N in a sustainable manner. The expert system was set up to generate parameter sets representing different land use options for the three management systems. The simulation model was rerun for each parameter set.

    Simulated annual N 2 O-N losses twenty-five years after pasture establishment were 3-5 kg ha -1 for natural pastures, 12-15 for grass-legume mixtures, and 7-28 for fertilized grasses. Simulated annual losses of NO-N were 1-2 kg ha -1 for natural pastures, 7-8 for grass-legume mixtures, and 3-16 for fertilized grasses. Regression analysis showed that annual C input to the soil explained N 2 O losses, and that NO losses were explained by biomass production. Nitrous oxide and NO emissions from pastures may increase by a factor 3-5 when natural pastures are converted to improved pastures. Such conversion may increase the sustainability of the pasture by stopping the decline of soil N, but the change is not necessarily sustainable from a global perspective because it increases the emission of N oxides.

    The regional N 2 O flux from soils below primary and secondary forest, pastures, and banana plantations was explored by linking the simulation model with an extant Geographic Information System (gis) on soils and land use. Land units on the overlaid soil and land use coverage were linked with the nearest of seven available meteorological stations. Monte Carlo-based sensitivity analysis was used to identify clay content, initial soil organic C, bulk density and pH as required map attributes and key driving model variables. For 217 different land units, model simulations were repeatedly carried out using climate data for seven different years.

    The estimated regional N 2 O-N flux was 1.8-2.1 Gg yr -1 . A full-fledged regional analysis of N 2 O emissions was performed using both deterministic and stochastic descriptions of key model inputs. The stochastic descriptions accounted for soil and land use heterogeneity across (non-georeferenced) fields within eleven different land units. Using Monte-Carlo integration, frequency distributions of fluxes were obtained per land unit class. Regional fluxes were calculated by summing expected values of the distributions weighted by area. Stochastic incorporation of both soil and land use variability resulted in areal flux estimates that were 14-22% lower than those estimated with deterministic model runs, suggesting concavity in the relationship between key model parameters and N 2 O fluxes.

    Spatial flux patterns for 1992 land use and two alternative land use scenarios were evaluated using stochastic inputs. With contemporary management of banana plantations and natural grasses, the regional N 2 O-N flux (standard deviation in parenthesis) was 1.0 (0.4) Gg yr -1 . Replacing natural grasses by sustainable grass-legume mixtures on relevant soil groups and allowing different fertilization levels on banana plantations increased the regional flux to 1.6 (0.5) Gg yr -1 . When all natural grasses were replaced by fertilized improved species and different fertilization levels were allowed on banana plantations, the regional flux increased to 1.9 (1.2) Gg yr -1 .

    Land use activities that are sustainable in terms of economic profit and soil fertility may be unsustainable when including N 2 O emission as an extra indicator. Soil variations, dominating regional patterns, must be incorporated when inventorying N 2 O emissions. Spatial heterogeneity of soil properties regulates emissions at finer scales than typically employed in regional soil surveys. A stochastic description of key variables may therefore be an efficient way to reduce aggregation errors in regional flux estimates.

    Future challenges include studies on effects of land use conversions, resulting in new spatial layouts of land units, on regional N 2 O fluxes. Also, the simulation model's implicit upscaling of emissions from soil microsite to field scales may be a potential research area.

    Inventarisatie van op- en neerschalingsmethodieken
    Woesten, J.H.M. ; Groenendijk, P. ; Kros, J. - \ 1998
    Wageningen : DLO-Staring Centrum (Rapport / DLO-Staring Centrum 648) - 82
    schaalverandering - hydrologie - bodemkunde - aggregatie - scaling - hydrology - soil science - aggregation
    Op- en neerschalingsmethodieken worden veelvuldig toegepast omdat de schaal waarop de invoervariabelen beschikbaar zijn, verschilt van de schaal waarop uitvoervariabelen gewenst zijn. Aan de hand van literatuurgegevens wordt allereerst een nadere omschrijving van het begrip schaaltransformaties gegeven. Vervolgens is een inventarisatie uitgevoerd van studies waarin schaaltransformaties aan de orde zijn. Deze inventarisatie concentreerde zich op SC-DLO-studies met een beperkte uitbreiding naar studiesuitgevoerd door AB-DLO, IBN-DLO en LEI-DLO. De geonventariseerde studies zijn gegroepeerd aan de hand van een aantal praktische schalingskenmerken en aan de hand van een meer theoretisch raamwerk. Tenslotte worden conclusies geformuleerd en aanbevelingengedaan over de richting waarin toekomstig onderzoek zich dient te bewegen.
    Bodemschematisatie; opschaling door aggregatie van bodeminformatie voor modelsimulaties op nationale en regionale schaal
    Groot, W.J.M. de; Finke, P.A. ; Oude Voshaar, J. ; Hack-ten Broeke, M.J.D. ; Vries, F. de; Randen, Y. van - \ 1998
    Wageningen : DLO-Staring Centrum - 62
    schaalverandering - bodem - aggregatie - gezamenlijke statistieken - scaling - soil - aggregation - aggregate statistics
    Dit rapport beschrijft de ontwikkeling van geautomatiseerde methoden voor opschaling van bodeminformatie door ruimtelijke en gegevensaggregatie voor modeltoepassingen, bodemschematisatie genoemd. Ze bestaan uit de selectie van bodemgegevens, ruimtelijke aggregatie van kaarteenheden van de bodemkaart, gegevensaggregatie door definiëring van rekenprofielen met procesparameters en het genereren van bodemkundige modelinvoer. Met statistische analyse van twaalf verschillende modeluitvoervariabelen is nagegaan welke van de ontwikkelde methoden voor bodemschematisatie het geringste informatieverlies gaf uitgaand van de ruimtelijke structuur op de Bodemkaart van Nederland, schaal 1: 50 000. De voorspelfout binnen kaarteenheden bedroeg minimaal 45. Het algoritme voor de ruimtelijke aggregatiemethode waarbij het studiegebied Beerse-Reuzel van 203 naar 23 ruimtelijke eenheden werd teruggebracht, gaf het meest representatieve beeld van de variabiliteit tussen de oorspronkelijke kaarteenheden. De toename vande voorspelfout door gegevensaggregatie werd door twee van de vier hiervoor ontwikkelde methoden het kleinst gehouden.
    -Lactoglobulin: denaturation and aggregation
    Hoffmann, M.A.M. - \ 1997
    Utrecht : Universiteit Utrecht - ISBN 9789039311301 - 135
    bèta-lactoglobuline - aggregatie - denaturatie - zuivelonderzoek - beta-lactoglobulin - aggregation - denaturation - dairy research
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