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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.

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    We will mail you new results for this query: keywords==fysicochemische eigenschappen
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Extensive dry heating-induced changes in physicochemical and immunological properties of whey proteins
Liu, Fahui - \ 2016
Wageningen University. Promotor(en): Tiny van Boekel; Jan Wichers, co-promotor(en): Kasper Hettinga; Gosia Teodorowicz. - Wageningen : Wageningen University - ISBN 9789463430012 - 146
whey protein - heating - physicochemical properties - immune tolerance - antibodies - allergens - wei-eiwit - verwarming - fysicochemische eigenschappen - immunotolerantie - antilichamen - allergenen

Baked milk products, e.g. milk-protein containing muffins or baked cheese, can be tolerated by most cow’s milk allergic subjects. These products were also reported to contribute to the development of immune tolerance in allergic subjects. The main objective of this thesis was to investigate the effects of heating under dry conditions on the physicochemical and immunological properties of whey proteins. A simplified heating model, consisting of whey proteins and lactose, was used to reproduce baking conditions. Most of the Maillard reaction sites were found to be located in the reported conformational epitopes on whey proteins. Therefore, the structural changes subsequently resulted in a decreased IgG-binding capacity. The binding of glycation products to the receptor of AGE (RAGE) increased with heating time. Next, the formation of AGEs was further studied. Formation of sRAGE-binding ligands depended on the aggregation, “pH”, and aw of the samples. Moreover, the sRAGE-binding activity of the samples after digestion was changed and correlated with the digestibility of samples. Based on these results, a correlation between the formation of AGEs and their immunogenicity was hypothesized. Thus, the macrophage immunogenicity of glycated BLG was furtherly studied. The IgE-binding capacity of glycated samples and their influence on the polarization and gene expression of macrophages were studied in vitro. Glycation of BLG was found to reduce the expression of pro-inflammatory TNF-α, and increase the expression of anti-inflammatory TGF-β in M1 and M2 macrophages. The immunomodulatory potential of glycated BLG was further studied, as described. The uptake of glycated BLG by dendritic cells (DCs) was studied. Results showed that glycated BLG inhibited the degranulation of basophils in a dose-dependent manner. Glycation of BLG enhanced its uptake by DCs. However, the degradation of glycated BLG was faster than unheated BLG, indicating a retarded allergen-presentation efficiency of glycated BLG by DCs.

In conclusion, this thesis showed that extensive dry heating induces profound and specific effects on the physicochemical and immunological properties of whey proteins. Conditions during heating, such as aw and “pH”, affect the consequences of heating on whey proteins and their subsequent functions in interacting with immune cells. Compared to unheated and nonglycated samples, glycated BLG can be more efficiently taken up and degraded by DCs. In addition, glycation confers immunomodulatory properties on whey proteins, as tested in macrophages. These results might have consequences for preparing extensively dry heated allergens that can be used in oral immunotherapy. The data in this thesis also provided a better understanding on the mechanism underlying the observation that the development of immune tolerance can be accelerated by baked milk.

A study on the potential of insect protein and lipid as a food source
Yi, L. - \ 2015
Wageningen University. Promotor(en): Tiny van Boekel; Arnold van Huis, co-promotor(en): Catriona Lakemond. - Wageningen : Wageningen University - ISBN 9789462572560 - 186
eiwitbronnen - nieuwe voedingsmiddelen - insecten als voedsel - extractie - eiwitten - vleesvervangers - fysicochemische eigenschappen - protein sources - novel foods - insects as food - extraction - proteins - meat alternates - physicochemical properties

Propositions

Propositions belonging to the thesis, entitled:‘A study on the potential of insect protein and lipid as a food source’. Liya Yi

Wageningen, 9 February 2015.High protein quality is, next to high protein content, a major argument to use insects as an alternative protein source. (this thesis)

With respect to aqueous extraction, proteins from Tenebrio molitor behave similarly as proteins from meat and fish. (this thesis)

In contrast to what Pascucci & Magistris (2013) claim, consumer information is not enough to achieve consumer acceptance of novel food.

Pascucci, S., & Magistris, T. d. (2013). International Food and Agribusiness Management Review, 16, 1-16.

Reducing environmental impact by changing human diet into a plant-based diet (Joyce, Dixon, Comfort, & Hallett, 2012) will not result in meeting the increasing global food demand.Joyce, A., Dixon, S., Comfort, J., & Hallett, J. (2012). Journal of Environmental and Public Health, 2012, 7.

Scientific evidence and the availability of technology are not guarantees for a change in human behaviour.

The statement of the Finnish writer Sebastyne Young “We all want to be extraordinary and we all just want to fit in. Unfortunately, extraordinary people rarely fit in.” applies to science where generation of extraordinary knowledge results in less fitting in.

The relation between farming practices, ecosystem, and white spot in syndrome virus (WSSV) disease outbreaks in penaeus monodon farms in the Philippines
Tendencia Alapide, E. - \ 2012
Wageningen University. Promotor(en): Johan Verreth, co-promotor(en): Roel Bosma; J.H. Primavera. - S.l. : s.n. - ISBN 9789461733702 - 135
garnalen - witte-vlekken-syndroom-virus - garnalenteelt - uitbraken (ziekten) - epidemiologie - infectieziekten - dierziektepreventie - aquatische ecosystemen - fysicochemische eigenschappen - mangroves - filippijnen - shrimps - white spot syndrome virus - shrimp culture - outbreaks - epidemiology - infectious diseases - animal disease prevention - aquatic ecosystems - physicochemical properties - philippines

The white spot syndrome virus (WSSV) affecting shrimp aquaculture in most producing countries has caused huge economic losses resulting in bankruptcy to both large and small farmers. Studies done on WSSV epidemiology were mostly tank-based and on species other than Penaeus monodon. There is a need to investigate WSSV epidemiology in P. monodon in on-farm situations, thus including both risk and protective factors. This thesis aimed to generate knowledge that can improve prevention against WSSV in shrimp culture through better farm husbandry by studying the epidemiology of WSSV in on-farm situations. To achieve this goal data from cross-sectional and case studies were analysed to identify on-farm WSSV risk and protective factors, and longitudinal studies were done to assess factors affecting water quality and causing WSSV infection to result in an outbreak.

The thesis identified the following WSSV risk factors related to the physico-chemical parameters of the water: low and fluctuating temperature, low and fluctuating salinity, and pH fluctuation. The risk of high temperature and high salinity for an outbreak of WSV disease may be related to fluctuations in these two parameters. Risk factors related to farm husbandry techniques were feeding with molluscs, sludge removal and its deposition on the dike, sharing water source with other farms and having the same receiving and intake water. Identified WSSV protective factors were high mangrove to pond area ratio, feeding with natural food or phytoplankton, and higher percentage of beneficial bacteria like the yellow colonies that grow on thiosulphate citrate bilesalt sucrose agar, a Vibrio selective medium.

Results of the longitudinal studies demonstrated that WSSV infection may not result in outbreaks in greenwater pond and in ponds with mangroves in the receiving environment. Our results did not provide explanations why the WSSV infection did not result in an outbreak in farms with mangroves in the receiving environment. In greenwater ponds, this was attributed to the better water and soil quality, higher plankton count, and higher heterotrophic bacterial count.

Chemical, physical and biological features of Okra pectin
Sengkhamparn, N. - \ 2009
Wageningen University. Promotor(en): Fons Voragen, co-promotor(en): Henk Schols; T. Sajjaanantakul. - [S.L. : S.n. - ISBN 9789085855293 - 176
pectinen - okra's - karakterisering - fysicochemische eigenschappen - pectins - okras - characterization - physicochemical properties
In Thailand, many plants have been used as vegetables as well as for traditional
medicine. Okra, Abelmoschus esculentus (L.) Moench, is an example of such a plant.
Examples for the medical use are treatment of gastric irritation, treatment of dental
diseases, lowering cholesterol level and preventing cancer. These biological activities are
ascribed to polysaccharide structures of okra in particular pectin structures. However, the
precise structure of okra pectins and also of other polysaccharides in okra pods have been
lacking so far.
In order to obtain detailed information of the different polysaccharides present in
okra, okra cell wall material was prepared from the pulp of okra pods and was then
sequentially extracted with hot buffer, chelating agent, diluted alkali and concentrated
alkali. The sugar (linkage) composition indicated that okra cell wall contained, next to
cellulose, different populations of pectins and hemicelluloses.
The pectic polysaccharides were mainly obtained in the first three extracts having
slightly different chemical structures. The okra pectin extracted by hot buffer was almost a
pure rhamnogalacturonan (RG) I with a high degree of acetylation (DA), covalently linked
to a minor amount of homogalacturonan (HG) having a high degree of methyl esterification
(DM). The chelating agent extractable pectin and the diluted alkali extractable pectin
predominantly contained HG with only minor amounts of RG I. Okra pectins extracted by
hot buffer and with chelating agent had in common that both contained highly branched RG
I with very short side chains containing not more than 3 galactosyl units attached to the
rhamnosyl residues in RG I backbone. Chelating agent extracted okra pectins also carried
arabinan and arabinogalactan type II as neutral side chains and these side chains were even
more abundantly present in the diluted alkali extracted okra pectin.
The hemicellulosic polysaccharides ended up in concentrated alkali extract. From
the sugar (linkage) composition and enzymatic degradation studies using pure and well
defined enzymes, it was concluded that this fraction contained a XXXG–type xyloglucan
and 4-methylglucuronoxylan. The cellulosic polysaccharides were retained in the residue.
The okra hot buffer extractable RG I having a high level of acetyl substitution
appeared to be very well degradable by rhamnogalacturonan hydrolase which was known to
be hindered completely by acetylated substrates. In contrast, an acetylated galacturonic
acid-specific rhamnogalacturonan acetyl esterase was unable to remove acetyl groups from
the RG I molecule of hot buffer extracted okra pectin. For these reasons, the precise
position of the acetyl groups present on enzymatically released oligomers were determined
by Electron Spray Ionization Ion Trap Mass Spectrometry (ESI-IT-MS) and Nuclear
Magnetic Resonance (NMR) spectroscopy. The acetyl groups were found to be
predominantly located at position O-3 of the rhamnosyl moiety, while the methyl esters
seemed to be present only on the HG part of the hot buffer extracted okra pectin. Another
novelty of okra RG-I was the presence of terminal alpha-linked galactosyl substitution at
position O-4 of the rhamnosyl residues within the RG I backbone. These specific features
(acetylated rhamnosyl- and alpha-galactosyl-substitutions) were almost absent in the
chelating agent extracted okra pectin where more commonly known substitutions were
present, including acetylated galacturonosyl residues in the RG I backbone. The unique
structure features of hot buffer extracted okra pectin led to the assumption that these
features may contribute to the rather typical physical properties as well as to the biological
properties found for okra pectin.
In order to understand the effect of the specific structural features of RG I on its
physical properties, the rheological properties of hot buffer extracted okra pectin were
determined and compared to those found for chelating agent extracted okra pectin and for
pectins from other plant materials as reported in the literature. The solutions of hot buffer
extracted okra pectin showed a high viscosity and predominant elastic behaviour which
most probably is caused by strong hydrophobic associations through its acetylated
rhamnosyl residues rather than by methyl esterified galacturonosyl residues as is commonly
the case for pectins. The removal of acetyl groups and methyl esters decreased the
association of the pectin molecules as observed by the light scattering experiment, meaning
that not only viscosity and rheological properties but also association of pectin molecules
were as result of both hydrophobic interactions and charge effects.
The effect of the position of acetyl groups on the bioactivity of okra pectin was
also determined. The complement-fixing activity of okra pectins was found to be affected
by many factors like e.g. the presence of acetyl groups, the size of RG segments and the presence of terminal alpha galactosyl groups and even the three dimensional conformation
of the molecules. The hot buffer extracted okra pectin was also examined for its potential to
modify surfaces of medical devices and implants. The results showed that okra pectin can
be used in coating medical device since it promotes cell apoptosis and shows no
macrophage activation.
The knowledge described in this thesis provided us with novel information on the
unique structures of okra pectins and may lead to a better understanding of the functional
properties of okra polysaccharides in general and okra pectin in particular and to optimize
the use of okra pectins within the food industry and in medical applications. However,
despite our efforts, at the moment the dependency of the (bio) functionality of okra pectins
on the precise chemical structure are not yet completely understood.
Development of starch-based materials
Habeych Narvaez, E.A. - \ 2009
Wageningen University. Promotor(en): Remko Boom, co-promotor(en): Atze Jan van der Goot. - [S.l. : S.n. - ISBN 9789085854333 - 144
zetmeel - mechanische eigenschappen - fysicochemische eigenschappen - verwerking - polymeerchemie - biopolymeren - starch - mechanical properties - physicochemical properties - processing - polymer chemistry - biopolymers
Starch-based materials show potential as fully degradable plastics. However, the current
applicability of these materials is limited due to their poor moisture tolerance and
mechanical properties. Starch is therefore frequently blended with other polymers to make
the material more suitable for special or severe circumstances. By varying the components
of the blend and the process conditions, the morphology and hence the properties can be
controlled. A clear understanding over the structure formation process will allow the
development of new, biodegradable blends based on starch-based materials with better
properties. The overall goal of this thesis was thus to develop insight in how the material
(blend) properties depend on the processing, and based on this insight, explore new
processing routes.
Structure-function relationships: exploring a polymer science approach
In Chapter 2, we discuss the relation between the performance of a plasticized starchbased
film, in terms of permeation of volatile components, and its composition. Estimations
of the Maxwell-Stefan diffusion rates of trace volatile components through plasticized
starch films were developed based on free-volume theory and the Flory-Huggins-Maxwell-
Stefan (FHMS) equation. The model correctly predicted the order of magnitude of the
permeation fluxes of diacetyl and carvone through starch films. The results of this chapter
show that blending of starch with hydrophobic polymers could be an effective way to
improve the barrier properties of the film.
In Chapter 3, the influence of alternative plasticizers (i.e., glucose and glycerol) on the
gelatinization and melting of concentrated starch mixtures was studied, using differential
scanning calorimetry (DSC) and wide angle X-ray scattering (WAXS). The results were
interpreted using an extended form of the well-known Flory-Huggins equation. The chapter
exemplified the possibilities of using theories that were traditionally applied to synthetic
polymers, to biomaterials, in spite of their much greater complexity. This approach led to
quantitative and qualitative understanding of the influence of small plasticizers of industrial
relevance on the gelatinization and melting of starch. Comparing the Flory-Huggins model
results with experimental results, showed that the approach is useful for interpreting and
predicting the gelatinization and melting behavior of ternary starch-based systems. It also
showed that since the experiments were complex, systems were often not in true
equilibrium and other disturbing effects were easily encountered. Therefore, one should be
cautious to use experimental results for characterizing the thermodynamics of gelatinization
in multicomponent systems.
Processing: the use of simple shear
In Chapter 4, the use of simple shear as an instrument for structure formation of
plasticized starch-protein blends was introduced. A novel shearing device was developed to
explore the formation of new types of microstructures in concentrated starch-zein blends.
This device was used to process different ratios of starch and zein (0–20% zein, dry basis)
to study the influence of the matrix composition and processing conditions on the
properties of the final material. Confocal scanning laser microscopy and field emission
scanning electron microscopy showed that under shearless conditions, the starch-zein blend
forms a co-continuous blend. Shear transformed this structure into a dispersion, with zein
being the dispersed phase. The large deformation properties were examined by tensile tests
in the flow and the vorticity directions; they could be described using a model for blends
having poor adhesion between the continuous and dispersed phases.
In Chapter 5, we studied the effect of compatibilization, i.e., improvement of the adhesion
between the continuous and dispersed phases in starch-zein blends through the
incorporation of a component having affinity for both phases. Aldehyde starch was
synthesized by introducing a reactive functional group (aldehyde). This group then reacted
in the blend with zein (and/or other components), forming a macromolecular compatibilizer
in situ. The effect of this compatabilizer on the interfacial properties of the blend was
studied using different zein ratios. The blends showed improved adhesion between the zein
and starch phases compared to the blends described in chapter 4. The aldehyde starch
however also influenced the properties of the starch matrix (higher viscosity, stronger
molecular breakdown, browning), which indicates that indeed physical or chemical
crosslinks were formed inside the starch matrix, but on the other hand posed a limitation for
practical applicability.
Chapter 6 presented the use of rise bran extract as a food-grade compatibilizer for starchzein
blends. This material was extracted from rice brans using super-critical water,
probably contains Maillard components and shows activity as radical scavenger,
antioxidant and surfactant. The influence of rice bran extract as compatibilizer was
compared with that of aldehyde starch by preparing blends under shear conditions. Field
emission scanning electron microscopy showed that both compatibilizers improved the
adhesion between the zein and starch phases. The mechanical properties of the blends
compatibilized with aldehyde starch showed poorer mechanical properties after storage
under controlled conditions, possibly caused by retrogradation of starch. The use of rice
bran extract as compatibilizer however led to good compatibilization with good stability
during storage. The good compatibilization by rice bran extract was suggested to be caused
by polysaccharide-protein complexes, which are also responsible for its emulsifying
properties.
Application
In Chapter 7, the conclusions of the preceding chapters were collectively interpreted. First,
the use of a heuristic approach for the rational design of thermoplastic starch-based
materials was described. Then the use of the ternary diagram for the system starch-waterglucose
developed in Chapter 3 was used to evaluate alternatives routes for the
intensification of the enzymatic hydrolysis of starch.
Finally, future trends in the development of starch-based materials were presented
following the insights obtained in this thesis. These include the use of established theories
developed for synthetic polymers, further exploration of the concept of compatibilization of
starch-based blends, and the development of new processing equipment dedicated to
material structuring.
Biochemical and structural analysis of thermostable esterases
Levisson, M. - \ 2009
Wageningen University. Promotor(en): John van der Oost; Willem de Vos, co-promotor(en): Servé Kengen. - [S.l. : S.n. - ISBN 9789085854593 - 167
esterasen - fysicochemische eigenschappen - chemische structuur - biochemische technieken - kristallisatie - esterases - physicochemical properties - chemical structure - biochemical techniques - crystallization
Biocatalysts play an important role in modern biotechnology because of their specificity, selectivity, efficiency and sustainability. One of the industrially most exploited and important groups of biocatalysts are the esterases. These enzymes catalyze, in the presence of water, the hydrolysis of an ester-bond resulting in the formation of an alcohol and a carboxylic acid. The use of enzymes in industrial processes also has its restrictions. Many processes are operated at elevated temperatures or in the presence of organic solvents. These conditions are detrimental to most enzymes and therefore there is a growing demand for enzymes with an improved stability. In this regard, there is a special interest from industry in enzymes of thermophilic origin since these enzymes generally display a high intrinsic thermal and chemical stability. This thesis describes the results of biochemical and structural analyses of thermostable esterases.
Bioinformatics was used to identify new ester-hydrolyzing enzymes in the genomes of the hyperthermophilic bacterium Thermotoga maritima and the hyperthermophilic archaeon Archaeoglobus fulgidus. These potential esterases were cloned and heterologously expressed in Escherichia coli. Different types of ester hydrolyzing enzymes were found, including carboxylesterases, an acetyl esterase and a lipase. The biochemical properties of these enzymes were studied in detail. In addition, crystallization trials were performed, resulting in the three-dimensional structures of several of these enzymes. New structural features were revealed, such as the combination of an esterase domain with an immunoglobulin-like domain.
The information obtained in this study provides fundamental knowledge, which may act as a basis for modern methods of enzyme engineering, with the aim to improve the applicability of these enzymes.





Characterization and treatment of grey water : option for (re)use
Abu-Ghunmi, L.N.A.H. - \ 2009
Wageningen University. Promotor(en): Jules van Lier, co-promotor(en): Grietje Zeeman; M. Fayyad. - [S.l. : S.n. - ISBN 9789085853930 - 194
afvalwaterbehandeling - hergebruik van water - fysicochemische eigenschappen - filtratie - aërobe behandeling - anaërobe behandeling - jordanië - waste water treatment - water reuse - physicochemical properties - filtration - aerobic treatment - anaerobic treatment - jordan
Addressing the issues of water shortage and appropriate sanitation in Jordan, domestic grey water treatment receives growing interest. Grey water comprises the domestic wastewater flows excluding waters associated with the toilet. The topics of concern for grey water are its characteristics, treatment and potentials for use after treatment. The target of this thesis is to develop a concept for treating grey water on-site for agricultural usage, thus sustaining a recycling process of grey water in Jordan. A review was made regarding the currently available grey water treatment technologies. In addition, grey water was quantitatively and qualitatively characterized, and then grey water reuse requirements including treatment, were analyzed. Biodegradability and biodegradation rates of the grey water were investigated for selecting appropriate design and operation criteria of the treatment technology to be developed. A low-tech semi-technical scale treatment system was tested to treat grey water discharges from a dormitory at the Jordan University campus. The treatment system was evaluated on obtained removal efficiencies and conformity of the effluent to the guidelines for the use of reclaimed water for irrigation in Jordan. Finally, the objectives, approaches and the results of each chapter are summarized, and then both the results and the potential of applying decentralised sanitation and reuse (DeSaR) concepts in Jordan are discussed.

Results show that storage and treatment are prerequisites for any type of grey water use. Grey water is aerobically and anaerobically biodegradable but the conversion rates are low. The core of the treatment concept consists of an integrated storage and anaerobic treatment unit, fed with a natural influent flow pattern, in a down-flow mode, up to a one day operational cycle, i.e. a variable HRT ≤ 24 hours. The second step consists of an aerobic post-treatment, mechanically aerated in a down-flow mode and a one day operational cycle, i.e. 24 hours HRT. Both units need insulation in the winter period. The final effluent, stable in winter and summer, meets the Jordanian standard, except for the pathogens, for usage in restricted irrigation. The achievable treatment efficiency for the CODtot is 44% in the anaerobic unit and 70% in the combined anaerobic-aerobic, unlike the high anaerobic and aerobic biodegradability in batch experiments, viz. 70 and 86%, respectively. The highest removal efficiency achieved was for the CODss fraction, viz. 71% in the anaerobic and 85% in the combined system. Therefore, it is expected that the CODtot removal efficiency of the system can be improved, by enhancing the CODcol and CODdis, removal, i.e. applying filtration and/or adding chemicals such as adsorbents, coagulants and/or flocculants to the treatment units.
Kinetic modeling of reactions in Foods
Boekel, M.A.J.S. van - \ 2008
Boca Raton : CRC Press - ISBN 9781574446142 - 400
wiskundige modellen - kinetica - chemische reacties - voedselkwaliteit - voedingsmiddelen - houdbaarheid (kwaliteit) - opslagkwaliteit - fysische eigenschappen - fysicochemische eigenschappen - modelleren - mathematical models - kinetics - chemical reactions - food quality - foods - keeping quality - storage quality - physical properties - physicochemical properties - modeling
The level of quality that food maintains as it travels down the production-to-consumption path is largely determined by the chemical, biochemical, physical, and microbiological changes that take place during its processing and storage. Kinetic Modeling of Reactions in Foods demonstrates how to effectively capture these changes in an integrative fashion using mathematical models. Thus, kinetic modeling of food changes creates the possibility to control and predict food quality from a technological point of view.
Multifunctional starch derivatives: synthesis, characterization and properties
Huijbrechts, A.M.L. - \ 2008
Wageningen University. Promotor(en): Ernst Sudhölter, co-promotor(en): Carmen Boeriu; Maurice Franssen. - [S.l.] : S.n. - ISBN 9789085852506 - 135
maïs - zetmeel - derivaten - synthese - fysicochemische eigenschappen - biodegradatie - maize - starch - derivatives - synthesis - physicochemical properties - biodegradation
The number of food poisoning cases caused by enteropathogens has increased in recent years. A significant part of the outbreaks associated with the consumption of raw vegetables has been attributed to Escherichia coli O157:H7 and Salmonella enterica subsp. enterica serovar Typhimurium. Bovine manure and slurry are the main environmental sources of these pathogens. Thus, reduction of the multiplication of E. coli O157:H7 and Salmonella serovar Typhimurium in cattle and their survival in manure and slurry are important tasks to minimize the risks of contamination of plant products and outbreaks of food-borne diseases. This thesis describes the influence of various environmental factors on survival of E. coli O157:H7 and Salmonella serovar Typhimurium in manure, slurry and soil amended with manure or slurry. Manure or slurry were inoculated with green fluorescent protein transformed strains of both enteropathogens at 106 - 107 cells g-1 dry weight, and their survival was studied in these substrates and in soil amended with inoculated manure or slurry. Population densities of the pathogens and autochthonous microbial communities were determined by dilution plating. The obtained survival data were fitted to non-linear models such as modified logistic or Weibull models, and estimated survival times in various substrates were compared. Analysis of the estimated parameter values showed that the pathogens survived longer at relatively low temperatures under anaerobic conditions especially at high concentrations of easily available substrate. Salmonella serovar Typhimurium was more resistant to environmental stresses than E. coli O157:H7. Survival of both pathogens significantly declined with increasing temperature amplitudes of daily temperature oscillations. Variations in fluctuations of E. coli O157:H7 populations around the decline curve were evaluated by the Approximate Entropy (ApEn) procedure. The instability of E. coli O157:H7 populations around the decline curve was greater in conventional than in organic and in loamy than in sandy soils, even though the mean survival periods did not differ. Multiple regression analysis of instability of E. coli O157:H7 survival on various soil characteristics showed a positive relation with the ratio of copiotrophic / oligotrophic bacteria, suggesting greater instability at higher available substrate concentrations. Percolation experiments with soil columns showed that surface application of solid manure decreased the risk of contamination of ground water and lettuce roots compared to injection of slurry, as more pathogen cells percolated to greater depths after slurry than after manure application. Detection of E. coli O157:H7 could be improved by incubation of Petri plates in anaerobic conditions, as this resulted in significantly higher numbers of recovered cells in comparison with the common aerobic plating procedure. Finally, a simulation model was developed based on our experimental data. The relative effects of temperature and substrate content were more important than that of oxygen concentration. The interaction with substrate resulted in oscillatory behavior of E. coli O157:H7 populations in manure and manure amended soil. Competition for substrate was the most important factor affecting the final survival time. The model was used to evaluate the effects of various manure and soil management scenarios on the survival of E. coli O157:H7. This simulation model provides a new approach to investigate dynamic changes of invasive microorganisms in natural substrates. The results presented in this thesis can be used for risk assessment of E. coli O157:H7 and Salmonella serovar Typhimurium in dairy farming systems and will help to identify and evaluate potential control strategies to minimize the chance of pathogen spread in the vegetable production chain.

Isolation, identification and activity of natural antioxidants from sweet grass (Hierochloe odorata), costmary (Chhrysanthemum balsamita) and horehound (Marrubium vulgare), cultivated in Lithuania
Pukalskas, A. - \ 2008
Wageningen University. Promotor(en): Aede de Groot, co-promotor(en): Teris van Beek; Jozef Linssen. - [S.l.] : S.n. - ISBN 9789085049821 - 137
antioxidanten - natuurlijke producten - extractie - fysicochemische eigenschappen - litouwen - antioxidants - natural products - extraction - physicochemical properties - lithuania
Food products are susceptible to oxidation processes. Oxidation of lipids (fat) is the major cause of food deterioration however also proteins and carbohydrates can be affected. To prevent or retard this process, antioxidants are used. With regard to foods, more and more natural products are preferred by consumers so new natural sources of compounds able to retard oxidation processes and prevent spoilage of food products are continuously investigated.
The research described in this study is aimed at the evaluation of several herbs as possible sources of food antioxidants. An initial screening of extracts from roman camomile, tansy, sweet grass, costmary, sea-buckthorn and sage for antioxidant activity in rapeseed oil has been performed Sweet grass and sage acetone extracts retarded oxidation processes in oil best.
Sweet grass was chosen for further investigation as the herb having the highest antioxidant activity. Two other herbs, namely horehound and costmary were further selected for the evaluation of their antioxidant activity in different assays. At first preliminary fractionation of the selected herb extracts was performed. Fractions were tested in three different assays: -carotene oxidation, DPPH• reduction and rapeseed oil oxidation. The experiments did not provide any straightforward answers, which fractions contained the most active antioxidants. Different assays gave different results. More polar fractions were more active in model systems like DPPH• while in the edible oil assay these fractions acted as weak antioxidants, or some even exhibited a prooxidation effect. Acetone extracts performed better than methanol-water extracts in retarding oil oxidation probably due to their higher compatibility with the medium or the more non-polar nature of the contained analytes.
In further steps the structures of the radical scavenging compounds present in extracts of sweet grass, horehound and costmary were elucidated. Two compounds, namely 5,8-dihydroxybenzopyranone and 5-hydroxy-8-O--D-glucopyranosyl benzopyranone were isolated and identified from sweet grass extract. Both compounds were identified for the first time as natural products. Four compounds, namely 5-O-caffeoyl quinic acid (chlorogenic acid), 3,5-dicaffeoyl quinic acid, 5,7,4'-trihydroxy-3',8-dimethoxy flavone and 5,7,3',4'-tetrahydroxy-3,8-dimethoxyflavonol were identified in costmary extracts. These compounds are quite common in plant kingdom. However, they have not previously been isolated from costmary. Five compounds, namely 5,8-dihydroxy-7,4-dimethoxy flavone, 7-O--glucopyranosyl luteolin, 7-O--glucuronyl luteolin, verbascoside and forsythoside B were isolated from horehound extracts. These compounds are common in the Labiatae family. Their radical scavenging activity was measured using DPPH• and ABTS•+ scavenging assays and compared with the activity of rosmarinic acid and Trolox.
An on-line HPLC-DPPH-DAD-NMR system for the rapid identification of compounds in complex mixtures was developed. The developed system was tested on commercial rosemary extract and six compounds were identified without the need to isolate them. This proved that simultaneous detection and identification of radical scavengers is possible.
Several solvents, namely hexane, acetone ant ethanol and their combinations were tested for their suitability to extract all known radical scavengers from sweet grass, costmary and horehound. It was found that initial extraction of the plant material with hexane increased the concentrations of radical scavengers in the following extraction stages.
Aberlour Environmental Seabed Survey, UK 2007
Dalfsen, J. van; Witbaard, R. - \ 2008
Den Helder : IMARES (Report / Wageningen IMARES C016/08) - 33
milieutoets - karteringen - verenigd koninkrijk - karakteristieken - fysicochemische eigenschappen - milieu-analyse - biologische processen - environmental assessment - surveys - uk - characteristics - physicochemical properties - environmental analysis - biological processes
In July 2007 Geolab Nor AS carried out an environmental survey for Chevron North Sea Limited / Chevron Upstream Europe at the Aberlour prospect at UKCS block 213/28 in the Faroe Shetland Channel. The objective of trhe survey was to describe the physico-chemical and biological characteristics in the Aberlour prospect area.
Opposites attract?! : on the electrostatically driven co-assembly of polymers in aqueous solution
Voets, I.K. - \ 2008
Wageningen University. Promotor(en): Martien Cohen Stuart, co-promotor(en): Arie de Keizer. - [S.l.] : s.n. - ISBN 9789085048862 - 376
polymeren - elektrostatische lading - micellen - fysicochemische eigenschappen - zelf-assemblage - polymers - electrostatic charging - micelles - physicochemical properties - self assembly - cum laude
cum laude graduation (with distinction)
Oral texture perception of semisolid foods in relation to physicochemical properties
Terpstra, M.E.J. - \ 2008
Wageningen University. Promotor(en): Erik van der Linden, co-promotor(en): Anke Janssen. - S.l. : s.n. - ISBN 9789085049548 - 175
sensorische evaluatie - textuur - perceptie - voedingsmiddelen - fysicochemische eigenschappen - custardpudding - reologische eigenschappen - sensory evaluation - texture - perception - foods - physicochemical properties - custard - rheological properties
When we eat a food product, we perceive its sensory properties and subconsciously decide whether we like the food. Next to properties of flavor and taste, we perceive textural properties. How thick, rough and creamy the food is perceived depends on the structure and properties of the food product in the mouth. This thesis explores which properties of semisolid foods (mayonnaise, Dutch custard) are important for the perception of creaminess and other textural properties as well as how we can instrumentally measure these properties.
Suikerstructuren op Phytophthora-glyco-eiwitten
Krol, A.R. van der - \ 2007
aardappelen - solanum tuberosum - phytophthora infestans - aardappeleiwit - fysicochemische eigenschappen - glycogeen - ziektepreventie - potatoes - potato protein - physicochemical properties - glycogen - disease prevention
Onderzoek naar mogelijk nieuwe aanknopingspunten ter bestrijding van Phytophthora te vinden, welke eiwitten de plant uitscheidt en welke eiwitten tijdens infectie door P.infestans worden uitgescheiden
Chain stoppers in reversible supramolecular polymer solutions
Knoben, W. - \ 2007
Wageningen University. Promotor(en): Martien Cohen Stuart, co-promotor(en): N.A.M. Besseling. - [S.l.] : s.n. - ISBN 9789085045748 - 194
polymeren - polymerisatie - fysische chemie - fysicochemische eigenschappen - supramoleculaire chemie - polymers - polymerization - physical chemistry - physicochemical properties - supramolecular chemistry - cum laude
cum laude graduation (with distinction)
Supramolecular polymers in inhomogeneous systems
Zweistra, H.J.A. - \ 2007
Wageningen University. Promotor(en): Gerard Fleer, co-promotor(en): N.A.M. Besseling. - [S.l.] : S.n. - ISBN 9789085045526 - 78
polymeren - adsorptie - desorptie - fractionering - zuiveren - fysicochemische eigenschappen - supramoleculaire chemie - polymers - adsorption - desorption - fractionation - purification - physicochemical properties - supramolecular chemistry
Function-structure relationships of acetylated pea starches
Huang, J. - \ 2006
Wageningen University. Promotor(en): Fons Voragen, co-promotor(en): Henk Schols. - [S.l.] : S.n. - ISBN 908504538X - 140
erwten - zetmeel - acetylering - fysicochemische eigenschappen - karakterisering - structuuractiviteitsrelaties - peas - starch - acetylation - physicochemical properties - characterization - structure activity relationships
Cowpea, chickpea and yellow pea starches were studied and the results showed that their properties were strongly related to the chemical fine structures of the starches. Furthermore, granular starches were modified using two types of chemical acetylation reagents and then separated into different size fractions. The amount of introduced acetyl groups was found to depend on the size of the granules for the reaction with rapidly reacting reagent acetic acid anhydride, whereas the amount of introduced acetyl groups was independent from the granule size for reaction with the slowly reacting reagent vinyl acetate. Modification with the two types of reagents resulted in significant difference in physical properties of the starches. The investigation on the chemical fine structure of modified starches suggested that the distribution of acetyl groups over both the amylose and amylopectin populations of the starches was different, not only at molecular level but also at granular level.
Banana-shaped Liquid Crystals
Achten, R. - \ 2006
Wageningen University. Promotor(en): Ernst Sudhölter; D.J. Broer, co-promotor(en): Ton Marcelis. - Wageningen : - ISBN 9085043328 - 145
kristallen - fysicochemische eigenschappen - vloeibare kristallen - crystals - physicochemical properties - liquid crystals
Interactions of phenolic compounds with globular proteins and their effects on food-related functional properties
Prigent, S.V.E. - \ 2005
Wageningen University. Promotor(en): Fons Voragen; Harry Gruppen, co-promotor(en): G.A. van Koningsveld. - Wageningen : - ISBN 9085042674 - 132
globulinen - eiwitten - fenolverbindingen - chlorogeenzuur - interacties - fysicochemische eigenschappen - fysische eigenschappen - voedsel - globulins - proteins - phenolic compounds - chlorogenic acid - interactions - physicochemical properties - physical properties - food
In order to modulate the functional properties of food proteins, the interactions between globular proteins and the monomeric phenolic, caffeoylquinic acid (CQA, chlorogenic acid), and the oligomeric phenolics, procyanidins, were characterized and investigated for their effect on protein functional properties. Non-covalent interactions between proteins and CQA involved a low affinity and did not affect protein solubility. Proteins show a medium affinity for procyanidins of an average degree of polymerization (DP) of 5.5, but weakly interacted with smaller procyanidins. Procyanidins of DP 5.5 strongly decreased protein solubility. Covalent interactions between proteins and CQA oxidised by polyphenol oxidase (PPO) or oxidised at alkaline pH resulted in protein modification mainly via dimeric CQA quinones. The covalent modifications of proteins with CQA strongly reduced protein solubility. Lysine, tyrosine, histidine and tryptophan were able to interact with CQA quinones. It can be concluded that for food non-covalent interactions are restricted to oligomeric phenolic.
Basics of macroscopic properties of adsorbed protein layers formed at air-water interfaces based on molecular parameters
Wierenga, P.A. - \ 2005
Wageningen University. Promotor(en): Fons Voragen; M.R. Egmond, co-promotor(en): Harmen de Jongh. - Wageningen : WUR - ISBN 9085043271 - 171
eiwitten - adsorptie - grensvlak - oppervlakte-interacties - fysicochemische eigenschappen - proteins - adsorption - interface - surface interactions - physicochemical properties
The importance of protein characteristics on the role of proteins in forming and stabilising interfaces is studied. This study offers a new understanding of adsorbed protein layers.
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