Staff Publications

Staff Publications

  • external user (warningwarning)
  • Log in as
  • language uk
  • About

    '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.

    We have a manual that explains all the features 

Current refinement(s):

Records 1 - 20 / 203

  • help
  • print

    Print search results

  • export

    Export search results

  • alert
    We will mail you new results for this query: keywords==ph
Check title to add to marked list
Kalibratie pH meter Inolab
Bom, Jesse ; Dijksman, J.A. ; Lageschaar, Luuk ; Galen, Martijn van; Hoogendam, C.W. ; Wegh, R.A.J. - \ 2016
Wageningen : Wageningen UR
ph - zuurgraad - meetinstrumenten - instrumenten (meters) - kalibratie - acidity - indicating instruments - instruments - calibration
Instructievideo over de kalibratie van de InoLab pH meter
pH meter Inolab
Bom, Jesse ; Dijksman, J.A. ; Lageschaar, Luuk ; Galen, Martijn van; Hoogendam, C.W. ; Wegh, R.A.J. - \ 2016
Wageningen : Wageningen UR
ph - zuurgraad - instrumenten (meters) - meetinstrumenten - acidity - instruments - indicating instruments
Instructievideo over het gebruik van de Inolab pH meter
Kalibratie pH meter Schott
Bom, Jesse ; Dijksman, J.A. ; Lageschaar, Luuk ; Galen, Martijn van; Hoogendam, C.W. ; Wegh, R.A.J. - \ 2016
Wageningen : Wageningen UR
ph - zuurgraad - meetinstrumenten - instrumenten (meters) - kalibratie - acidity - indicating instruments - instruments - calibration
Instructievideo over de kalibratie van de Schott pH meter
Exploring novel food proteins and processing technologies : a case study on quinoa protein and high pressure –high temperature processing
Avila Ruiz, Geraldine - \ 2016
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 - wei-eiwit - levensmiddelenproceskunde - warmtebehandeling - in vitro verteerbaarheid - fractionering - maillard-reactieproducten - viscositeit - gelering - aggregatie - hogedruktechnologie

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.

Refining a model-based assessment strategy to estimate the ammonia emission from floors in dairy cow houses
Snoek, Dennis J.W. - \ 2016
University. Promotor(en): Peter Groot Koerkamp, co-promotor(en): Nico Ogink; Hans Stigter. - Wageningen : Wageningen University - ISBN 9789462578852 - 182
dairy cows - stalls - ammonia emission - floors - modeling - mitigation - sensors - ph - temperature - urea - melkkoeien - stallen - ammoniakemissie - vloeren - modelleren - mitigatie - temperatuur - ureum

Ammonia (NH3) emission is still high, and agriculture is still the dominant contributor. In The Netherlands, the NH3 emission from dairy cow houses is one of the most important sources. A lot of research has been conducted to understand and model NH3 emission, to measure it, and to reduce it using identified and developed reduction measures. However, our understanding of how to measure and how to reduce the NH3 emission is still limited. In addition, the set emission ceilings were lowered for 2020.

The objective of this thesis was to refine a model-based assessment strategy to estimate the ammonia emission from floors in dairy cow houses. First the most important input variables and process parameters were identified with a sensitivity analysis in currently available mechanistic NH3 emission models and theory. It was concluded that five puddle related input variables caused the largest variation in NH3 emission estimation, being the puddle pH, depth (Dp), urinary urea nitrogen concentration (UUN), surface area (Ap), and temperature (Tliq). For each input variable the available data was scarce, and it was therefore recommended to measure these five most important variables in practice. However, measurement methods were hardly available. Therefore, sensors were chosen, new measurement methods were developed, and these were combined in a protocol to measure the pH, Dp, UUN, Ap and Tliq of fresh, random and manually created urine puddles in commercial dairy cow houses.

In total 16 commercial dairy cow houses were assessed in a factorial experimental setup based on four floor-management types in two Seasons, with PREclean treatment. PREclean represented intense-floor-cleaning that was compared to on-farm manure scraping. A V-shaped asphalt floor had significantly larger values for both Ap (1.04 m2) and Dp (1.5 mm) than did the slatted and grooved floors (0.76 m2, 0.93 mm). For both Ap and Dp the variation within a farm was large, but was negligible between farms. The Dp values and variation were 3 to 6 times larger than currently assumed. With PREclean treatment the Dp resulted in about 3 times lower values compared to the on-farm scraping. In short, the potential NH3 emission reduction of good floor cleaning is large. Overall mean values were 4.27 kg m-3 for UUN, an initial pH(t=0) of 8.3, both in fresh puddles, and a pH(t=ξ) of 9.0 for random puddles at a random time. For UUN both the variation within and between farms was large, whereas the variation for pH was small. Both the mean UUN and pH showed lower values than currently assumed. In a separate 4 h time series experiment at 3 commercial farms was shown that the pH, on average, quickly increased initially, declined after 1 h and then became stable. The calculated NH3 in kg puddle-1 showed a huge range and was considerably larger than currently assumed for the reference situation.

Compared to the aforementioned sensitivity analysis outcome, the UUN range at farm level is both slightly smaller and shifts to slightly lower values, while for Dp the range and values are both larger. These two variables caused the largest variation in the estimated NH3 emissions, and not the pH. In conclusion, these two variables certainly need to be measured in individual commercial dairy cow houses to estimate the NH3 emission. For Ap, pH and Tair the measured ranges at farm level were less large. The pH turns out to be fairly stable in commercial cow houses and, related to that, it causes less variation in the estimated NH3 emission. Nevertheless, the pH still ranks as the third most important variable, and therefore needs to be measured in individual cow houses. The Ap is fairly stable between farms, but varies within farms and it still has a significant effect on the NH3 emission. The floor design clearly affects the puddle area Ap. Therefore, it is not necessary to measure Ap at each individual farm, but it is sufficient to measure the Ap in only one commercial cow house per floor design. The Tair variable is of limited importance compared to the aforementioned four variables, but it is still significant.

Iron is essential for photosynthesis and respiration : iron deficiency : the most common deficiency disorder
Heuvelink, E. ; Kierkels, T. - \ 2016
In Greenhouses : the international magazine for greenhouse growers 5 (2016)1. - ISSN 2215-0633 - p. 48 - 49.
horticulture - greenhouse horticulture - rosaceae - chelates - ph - iron - deficiency - plant disorders - crop production - tuinbouw - glastuinbouw - chelaten - ijzer - deficiëntie - afwijkingen, planten - gewasproductie

Iron plays a major role in photosynthesis. That’s why a shortage directly affects the production capacity of the plant. The application of chelates has made iron much more easy to absorb. Nevertheless it’s an element that we have to keep an eye on.
Steroids accumulation in recirculating aquaculture systems
Mota, V.C. - \ 2015
University. Promotor(en): Johan Verreth, co-promotor(en): A.V.M. Cana´rio; C.I.M. Martins. - Wageningen : Wageningen University - ISBN 9789462575554 - 145
steroïden - recirculatie aquacultuur systemen - prestatieniveau - bezettingsdichtheid - stress - ph - hydrocortison - testosteron - chemische communicatie - visteelt - viskwekerijen - steroids - recirculating aquaculture systems - performance - stocking density - hydrocortisone - testosterone - chemical communication - fish culture - fish farms
Drying and hydration of proteins at high concentration
Bouman, J. - \ 2015
University. Promotor(en): Erik van der Linden, co-promotor(en): Renko de Vries. - Wageningen : Wageningen University - ISBN 9789462575509 - 161
eiwit - wei-eiwit - zeïne - drogen - droogmethoden - geneesmiddeltoedieningssystemen - hydratatie - hydrofobiciteit - ph - vacuolen - protein - whey protein - zein - drying - drying methods - drug delivery systems - hydration - hydrophobicity - vacuoles

Proteins are the building blocks of life and serve a wide range of essential functions in organisms. Many metabolic reactions in organisms are catalysed by enzymes, DNA is replicated by proteins and in cells proteins often facilitate active transport of e.g. glucose or ions. Proteins also serve an essential functionality in foods, pharmaceutics, bioplastics and even clothing. Recently, the use of proteins towards higher concentrations is of interest for food, pharmaceutical and medical applications. Nevertheless, the preparation of products with desired product properties can be challenging, when approaching higher protein concentrations. Therefore, in this thesis we investigate proteins at higher concentrations, especially focussing on their drying and hydration behaviour.

In part one of the thesis, the focus is on the dynamics of drying of proteins towards higher concentrations. Dense proteins systems have been scarcely studied compared to proteins at lower concentrations. We address drying behaviour where we focus on the use of whey protein isolate as a model system. In part two of the thesis we focus on the hydration properties of the corn protein zein, where we apply it as a drug excipient. In this part we also investigate the influence of hydration on the release behaviour of drugs into the hydration media.

The drying part (part one) contains two studies. The first study is more fundamental in nature, focussing on the drying of a protein coating. In previous studies mainly the macroscopic properties of protein coatings after drying are investigated, leaving the drying dynamics virtually unexplored. Here we investigate the drying behaviour of the model protein β-lactoglobulin on multiple length scales with an unique combination of in-line techniques. On the microscopic length scale we use dynamic vapour sorption and magnetic resonance imaging while on a smaller length scales, we apply diffusing wave spectroscopy and IR-spectroscopy to monitor the drying process. For all used techniques, the changes in the measured physical properties of the coating as a function of water weight fraction Xw from Xw = 0.8 down to Xw = 0.2 are gradual. However, using dynamic vapour sorption and IR-spectroscopy we measure a sharp change below water weight fractions of Xw = 0.2. We hypothesise that changes in the molecular interactions caused by dehydration of the protein results in a change in the drying kinetics of the film.

In the second study of part one, protein drying is approached on a more applied level, where we study the drying of a spherical droplet. We use single droplet drying as a methods that can model the spray drying process in a simplified and well-controlled way. Sessile droplets are subjected to varying drying conditions such as temperature, initial protein concentration, presence of airflow and droplet rotation. During these experiments the morphological development is monitored by a camera. After drying, scanning electron microscopy and X-ray tomography are used to examine the particles that are formed after complete drying. Irrespective of the conditions used, we observe an initial droplet shrinkage, followed by the nucleation of a hole in the droplet skin, which is followed by the formation of a vacuole. The drying conditions used, strongly influenced the location of the hole and the locking point prior to hole formation. We hypothesise that the location of the hole is caused by local inhomogeneities in protein concentration causing a the nucleation of the hole where the local skin modulus is lowest. Also the locking point of the droplet is found to be due to a inhomogeneity over the whole droplet caused by rapid evaporation. These results can be of importance to understand powder structure and functionality as obtained in spray drying.

In the hydration part (part 2), we investigate the potential of zein as a sole excipient in macroscale caplets obtained by hot melt extrusion (HME) and injection moulding (IM). Zein is good candidate as a sustained release agent, because it is insoluble in two studies. In the first study zein matrices were loaded with the drug paracetamol. Physical mixtures of zein, water and crystalline paracetamol are extruded and injection moulded into caplets. Characterisation of these caplets is performed using differential scanning calorimetry, IR- spectroscopy, scanning electron microscopy and powder X-ray diffraction. The hydration and drug release kinetics from the caplet slices is measured. We find that the drug release kinetics is broadly independent of the dissolution medium and drug loading. The release kinetics is diffusion limited and could be well described by a 2D diffusion model. The results demonstrate that the drug release rate from zein caplet slices can be tuned by its dimensions.

In the second study, a wider range of drugs differing in hydrophobicity is studied. Next to paracetamol, we have used two other model drugs: the hydrophobic indomethacin and the more hydrophilic ranitidine. The zein matrix is capable to stabilize the different dugs in a non-crystalline state, which is promising especially for increasing the bioavailability of poorly water-soluble drugs. Overall crystallinity of the drugs in the caplets increases with its degree of hydrophobicity. For the poorly soluble indomethacin, dissolution rates at low pH were higher from caplet slices, compared to the dissolution rates of indomethacin crystals by themselves. In addition, we found that the electrostatic interactions between zein and drugs can also be used to influence the release kinetics.

Various aspects were found to be of importance both for drying and hydration of concentrated protein systems. The homogeneity during both processes deserves attention as its manipulation can strongly influence final properties if the system. Also the plasticising effect of water on dense proteins is often found essential, when understanding the dynamics of both drying and hydration processes. Finally protein hydrophobicity and its manipulation can provide a window of opportunities in many applications which are involve by drying or hydration.

Digestion of protein and protein gels in simulated gastric environment
Luo, Q. ; Boom, R.M. ; Janssen, A.E.M. - \ 2015
Food Science and Technology = Lebensmittel-Wissenschaft und Technologie 63 (2015)1. - ISSN 0023-6438 - p. 161 - 168.
peptic hydrolysis - pepsin - ph - disintegration - kinetics
Despite the increasing attention to food digestion research, food scientists still need to better understand the underlying mechanisms of digestion. Most in vitro studies on protein digestion are based on experiments with protein solutions. In this study, the digestion of egg white protein and whey protein isolate in solution and in gels was investigated using simulated gastric conditions. The digestion process was followed via the dry matter loss, degree of hydrolysis and peptide distribution. We showed that the performance of pepsin is an important factor in protein digestion, and hydrodynamic force effectively disintegrated the gel particles and enhance the hydrolysis of protein. The gel microstructure had shown to be a hindrance for the digestion of protein. However, the hindrance is not simply slowing down the hydrolysis, but also altering the apparent enzyme kinetics to some extent: while the dissolved proteins were hydrolysed through a ‘zipper’ type mechanism, the gels showed a slower ‘one-by-one’ mechanism. Overall, we believe that the digestion of the protein gels is influenced by the microstructure of food matrices, caused by the immobilisation of the substrate in the network, and the steric hindrance in the diffusive ingression of pepsin and egression of peptides.
Quantifying strain variability in modeling growth of Listeria monocytogenes
Aryani, D. ; Besten, H.M.W. den; Hazeleger, W.C. ; Zwietering, M.H. - \ 2015
International Journal of Food Microbiology 208 (2015). - ISSN 0168-1605 - p. 19 - 29.
lactic-acid concentration - minimal water activity - bacillus-cereus - escherichia-coli - microbial-growth - lag time - temperature - ph - fermentation - survival
Prediction of microbial growth kinetics can differ from the actual behavior of the target microorganisms. In the present study, the impact of strain variability on maximum specific growth rate (µmax) (h- 1) was quantified using twenty Listeria monocytogenes strains. The µmax was determined as function of four different variables, namely pH, water activity (aw)/NaCl concentration [NaCl], undissociated lactic acid concentration ([HA]), and temperature (T). The strain variability was compared to biological and experimental variabilities to determine their importance. The experiment was done in duplicate at the same time to quantify experimental variability and reproduced at least twice on different experimental days to quantify biological (reproduction) variability. For all variables, experimental variability was clearly lower than biological variability and strain variability; and remarkably, biological variability was similar to strain variability. Strain variability in cardinal growth parameters, namely pHmin, [NaCl]max, [HA]max, and Tmin was further investigated by fitting secondary growth models to the µmax data, including a modified secondary pH model. The fitting results showed that L. monocytogenes had an average pHmin of 4.5 (5–95% prediction interval (PI) 4.4–4.7), [NaCl]max of 2.0 mM (PI 1.8–2.1), [HA]max of 5.1 mM (PI 4.2–5.9), and Tmin of - 2.2 °C (PI (- 3.3)–(- 1.1)). The strain variability in cardinal growth parameters was benchmarked to available literature data, showing that the effect of strain variability explained around 1/3 or less of the variability found in literature. The cardinal growth parameters and their prediction intervals were used as input to illustrate the effect of strain variability on the growth of L. monocytogenes in food products with various characteristics, resulting in 2–4 log CFU/ml(g) difference in growth prediction between the most and least robust strains, depending on the type of food product. This underlined the importance to obtain quantitative knowledge on variability factors to realistically predict the microbial growth kinetics. Keywords: Quantitative microbiology; Growth parameters; Heterogeneity; Pathogen
Reversible Temperature-Switching of Hydrogel Stiffness of Coassembled, Silk-Collagen-Like Hydrogels
Rombouts, W.H. ; Kort, D.W. de; Pham, T.T.H. ; Mierlo, C.P.M. van; Werten, M.W.T. ; Wolf, F.A. de; Gucht, J. van der - \ 2015
Biomacromolecules 16 (2015)8. - ISSN 1525-7797 - p. 2506 - 2513.
block-copolymers - gels - ph - gelatin - elastin - biosynthesis - proteins - polymers
Recombinant protein polymers, which can combine different bioinspired self-assembly motifs in a well-defined block sequence, have large potential as building blocks for making complex, hierarchically structured materials. In this paper we demonstrate the stepwise formation of thermosensitive hydrogels by combination of two distinct, orthogonal self-assembly mechanisms. In the first step, fibers are coassembled from two recombinant protein polymers: (a) a symmetric silk-like block copolymer consisting of a central silk-like block flanked by two soluble random coil blocks and (b) an asymmetric silk-collagen-like block copolymer consisting of a central random-coil block flanked on one side by a silk-like block and on the other side a collagen-like block. In the second step, induced by cooling, the collagen-like blocks form triple helices and thereby cross-link the fibers, leading to hydrogels with a thermo-reversibly switchable stiffness. Our work demonstrates how complex self-assembled materials can be formed through careful control of the self-assembly pathway.
Permeability of gels is set by the impulse applied on the gel
Urbonaite, V. ; Jongh, H.H.J. de; Linden, E. van der; Pouvreau, L.A.M. - \ 2015
Food Hydrocolloids 50 (2015). - ISSN 0268-005X - p. 7 - 15.
globular protein gels - blood-plasma gels - ionic-strength - water - ph - microscopy - rheology - polyacrylamide - pressure - gelation
To better understand sensory perception of foods, water exudation studies on protein-based gels are of a high importance. It was aimed to study the interplay of gel coarseness and gel stiffness on water holding (WH) and water flow kinetics from the gel once force is applied onto the material. Ovalbumin heat-set gels were used as a model system, where protein volume fraction was kept constant and ionic strength was varied to obtain a range of different gel morphologies and stiffness. WH of gels was measured both as a function of time and force applied. From experimental data (i) an effective gel permeability coefficient and (ii) an effective water flux coefficient were obtained and related to gel coarseness and stiffness. Gel coarseness determined maximum amount of water removed from the gel at defined conditions, where lower (=0.1 µm) and upper (=0.4 µm) limiting scales for water removal were identified. Gel stiffness is the major determinant for water removal kinetics from the gel. The combination of gel coarseness and gel stiffness showed a cooperative effect on gel WH. The insights can be exploited in product development to predict and tune oral perception properties of (new) products.
Asymmetric flow field-flow fractionation of manufactured silver nanoparticles spiked into soil solution
Koopmans, G.F. ; Hiemstra, T. ; Regelink, I.C. ; Molleman, B. ; Comans, R.N.J. - \ 2015
Journal of Chromatography. A, Including electrophoresis and other separation methods 1392 (2015). - ISSN 0021-9673 - p. 100 - 109.
natural organic-matter - engineered nanoparticles - calcium-chloride - ionic-strength - humic acids - molar-mass - aggregation - retention - ph - speciation
Manufactured metallic silver nanoparticles (AgNP) are intensively utilized in consumer products and this will inevitably lead to their release to soils. To assess the environmental risks of AgNP in soils, quantification of both their concentration and size in soil solution is essential. We developed a methodology consisting of asymmetric flow field-flow fractionation (AF4) in combination with on-line detection by UV–vis spectroscopy and off-line HR-ICP-MS measurements to quantify the concentration and size of AgNP, coated with either citrate or polyvinylpyrrolidone (PVP), in water extracts of three different soils. The type of mobile phase was a critical factor in the fractionation of AgNP by AF4. In synthetic systems, fractionation of a series of virgin citrate- and PVP-coated AgNP (10–90 nm) with reasonably high recoveries could only be achieved with ultrahigh purity water as a mobile phase. For the soil water extracts, 0.01% (w:v) sodium dodecyl sulfate (SDS) at pH 8 was the key to a successful fractionation of the AgNP. With SDS, the primary size of AgNP in all soil water extracts could be determined by AF4, except for PVP-coated AgNP when clay colloids were present. The PVP-coated AgNP interacted with colloidal clay minerals, leading to an overestimation of their primary size. Similar interactions between PVP-coated AgNP and clay colloids can take place in the environment and facilitate their transport in soils, aquifers, and surface waters. In conclusion, AF4 in combination with UV–vis spectroscopy and HR-ICP-MS measurements is a powerful tool to characterize AgNP in soil solution if the appropriate mobile phase is used.
Influence of separate feeding of calcium on nutrient digestibility, energy utilisation and performance of young broilers fed pelleted wheat-based diets
Abdollahi, M.R. ; Dalen, A.B.J. van; Hendriks, W.H. ; Ravindran, V. - \ 2015
Animal Feed Science and Technology 205 (2015). - ISSN 0377-8401 - p. 122 - 130.
phytate phosphorus hydrolysis - nonphytate phosphorus - phytic acid - chickens - ph - efficacy - appetite - availability - consequences - ingredients
Six broiler starter diets, based on wheat and soybean meal, were formulated to contain 1.1 2.0, 4.0, 6.0, 8.0 and 10.0 g calcium (Ca)/kg. All diets were equivalent in respect of total and non-phytate phosphorus contents (5.4 and 3.0 g/kg, respectively). The influence of dietary treatments on the growth performance, coefficient of apparent ileal digestibility (CAID) of nitrogen (N), starch, fat and phosphorus (P), Ca retention and apparent metabolisable energy (AME) in broiler starters was evaluated. A total of 288, one-day-old male broilers (Ross 308) were allocated to 36 cages (8 birds/cage), and cages were randomly assigned to 6 dietary treatments. Birds were also provided with a source of Ca in a separate feed trough. Birds fed the diet with 1.1 g Ca/kg gained more (P0.05) feed per unit gain. During d 8 to 14, d 15 to 21, and over the entire trial period of 21 d, birds fed Ca-deficient (6.0 g Ca/kg and less) diets consumed more (P0.05) of dietary Ca on the retention of Ca and ash, AME and toe ash. The present data suggest that feeding broilers low Ca diets with access to a separate Ca source, is advantageous in terms of broiler performance, while maintaining bone mineralisation. The data also demonstrate that the provision of separate Ca source may hold promise for reducing the dietary P contents.
Folding of influenza virus hemagglutinin in insect cells is fast and efficient
Li, X. ; Oers, M.M. van; Vlak, J.M. ; Braakman, I. - \ 2015
Journal of Biotechnology 203 (2015). - ISSN 0168-1656 - p. 77 - 83.
disulfide bond formation - endoplasmic-reticulum - quality-control - membrane glycoprotein - expression system - escherichia-coli - calnexin - vaccine - ph - oligomerization
Folding of influenza virus hemagglutinin (HA) in the endoplasmic reticulum has been well defined inmammalian cells. In different mammalian cell lines the protein follows the same folding pathway withidentical folding intermediates, but folds with very different kinetics. To examine the effect of cellularcontext on HA folding and to test to which extent insect cells would support the HA folding process,we expressed HA in Sf9 insect cells. Strikingly, in this invertebrate system HA folded faster and moreefficiently, still via the same folding intermediates as in vertebrate cells. Our results suggest that insectcells provide a highly efficient and effective folding environment for influenza virus HA and the idealproduction platform for HA (emergency) vaccines.
Mesocosm validation of the marine No Effect Concentration of dissolved copper derived from a species sensivity distribution
Foekema, E.M. ; Kaag, N.H.B.M. ; Kramer, K.J.M. ; Long, K. - \ 2015
Science of the Total Environment 521-522 (2015). - ISSN 0048-9697 - p. 173 - 182.
principal response curves - organic-matter - toxicity - water - carbon - speciation - exposure - ph
The Predicted No Effect Concentration (PNEC) for dissolved copper based on the species sensitivity distribution (SSD) of 24 marine single species tests was validated in marine mesocosms. To achieve this, the impact of actively maintained concentrations of dissolved copper on a marine benthic and planktonic community was studied in 18 outdoor 4.6 m3 mesocosms. Five treatment levels, ranging from 2.9 to 31 µg dissolved Cu/L, were created in triplicate and maintained for 82 days. Clear effects were observed on gastropod and bivalve molluscs, phytoplankton, zooplankton, sponges and sessile algae. The most sensitive biological endpoints; reproduction success of the bivalve Cerastoderma edule, copepod population development and periphyton growth were significantly affected at concentrations of 9.9 µg Cu/L and higher. The No Observed Effect Concentration (NOEC) derived from this study was 5.7 µg dissolved Cu/L. Taking into account the DOC concentration of the mesocosm water this NOEC is comparable to the PNEC derived from the SSD.
Quantitative analysis of the network structure that underlines the transitioning in mechanical responses of pea protein gels
Munialo, C.D. ; Linden, E. van der; Ako, K. ; Jongh, H.H.J. de - \ 2015
Food Hydrocolloids 49 (2015). - ISSN 0268-005X - p. 104 - 117.
whey-protein - rheological properties - gelation properties - large-deformation - particulate gels - ionic-strength - isolate gels - mixed gels - set - ph
The objective of this study was to analyze quantitatively the network structure that underlines the transitioning in the mechanical responses of heat-induced pea protein gels. To achieve this, gels were prepared from pea proteins at varying pHs from 3.0 to 4.2 at a fixed 100 mg/mL protein concentration. Gels were also prepared by varying the protein concentration from 100 to 150 mg/mL at a fixed pH 3.0. Mechanical deformation properties of the gels were determined. An increase in protein concentration at a fixed pH resulted in an increase in fracture stress and Young's modulus. Variation of the pH at a fixed protein concentration resulted in transitioning in mechanical responses such as fracture stress, fracture strain, and the recoverable energy. The network structures were visualized by the use of confocal laser scanning and scanning electron microscopy, and the characteristic length scales of these structures were quantitatively analyzed in terms of the pair correlation function. Variation of the protein concentration at a fixed pH did not significantly alter the microstructure of the gels, whereas variation of the pH at a fixed protein concentration resulted in significant changes in the gel structure. Structural transitioning was shown to occur around pH 3.7. The findings from this study show transitioning in rheological responses of pea protein gels occur as a result of structural changes. The results from this study offer opportunities to broaden the application of pea proteins in food products, as products with desirable rheological (textural) and structural properties can be designed from pea proteins.
Partitioning of humic acids between aqueous solution and hydrogel. 2. Impact of physicochemical conditions
Zielinska, K. ; Town, R.M. ; Yasadi, K. ; Leeuwen, H.P. van - \ 2015
Langmuir 31 (2015)1. - ISSN 0743-7463 - p. 283 - 291.
ionic-strength - alginate gel - heavy-metals - fluorescence - substances - ph - aggregation - media - soil - spectroscopy
The effects of the physicochemical features of aqueous medium on the mode of partitioning of humic acids (HAs) into a model biomimetic gel (alginate) and a synthetic polyacrylamide gel (PAAm) were explored. Experiments were performed under conditions of different pH and ionic strength as well as in the presence or absence of complexing divalent metal ions. The amount of HA penetrating the gel phase was determined by measuring its natural fluorescence by confocal laser scanning microscopy. In both gel types, the accumulation of HA was spatially heterogeneous, with a much higher concentration located within a thin film at the gel surface. The thickness of the surface film (ca. 15 µm) was similar for both types of gel and practically independent of pH, ionic strength, and the presence of complexing divalent metal ions. The extent of HA accumulation was found to be dependent on the composition of the medium and on the type of gel. Significantly more HA was accumulated in PAAm gel as compared to that in alginate gel. In general, more HA was accumulated at lower background salt concentration levels. The distribution of different types of HA species in the gel body was linked to their behavior in the medium and the differences in physicochemical conditions inside the two phases.
Evaluation of the sustainability of contrasted pig farming systems: development of a market conformity tool for pork products based on technological quality traits
Gonzalez, J. ; Gispert, M. ; Gil, M. ; Hviid, M. ; Dourmad, J.Y. ; Greef, K.H. de; Zimmer, C. ; Fabrega, E. - \ 2014
Animal 8 (2014)12. - ISSN 1751-7311 - p. 2038 - 2046.
meat - ph
A market conformity tool, based on technological meat quality parameters, was developed within the Q-PorkChains project, to be included in a global sustainability evaluation of pig farming systems. The specific objective of the market conformity tool was to define a scoring system based on the suitability of meat to elaborate the main pork products, according to their market shares based on industry requirements, in different pig farming systems. The tool was based on carcass and meat quality parameters that are commonly used for the assessment of technological quality, which provide representative and repeatable data and are easily measurable. They were the following: cold carcass weight; lean meat percentage; minimum subcutaneous back fat depth at nn. gluteus nnedius level, 45 postmortem and ultimate pH (measured at 24-h postmortem) in m. longissinnus lunnborunn and senninnennbranosus; meat colour; drip losses and intramuscular fat content in a m. longissinnus sample. Five categories of pork products produced at large scale in Europe were considered in the study: fresh meat, cooked products, dry products, specialties and other meat products. For each of the studied farming systems, the technological meat quality requirements, as well as the market shares for each product category within farming system, were obtained from the literature and personal communications from experts. The tool resulted in an overall conformity score that enabled to discriminate among systems according to the degree of matching of the achieved carcass and meat quality with the requirements of the targeted market. In order to improve feasibility, the tool was simplified by selecting ultimate pH at nn. longissinnus or senninnennbranosus, minimum fat thickness measured at the left half carcass over m. gluteus nnedius and intramuscular fat content in a m. longissinnus sample as iceberg indicators. The overall suitability scores calculated by using both the complete and the reduced tools presented good correlation and the results obtained were similar. The tool could be considered as robust enough to discriminate among different systems, since it was tested in a wide range of them. It also can be used to detect improvement opportunities to enhance sustainability of pig farming systems. The final objective of the study was achieved, since the market suitability tool could be used in an integrated sustainability analysis of pig farming systems.
Hydrogen production and ammonium recovery from urine by a Microbial Electrolysis Cell
Kuntke, P. ; Sleutels, T.H.J.A. ; Saakes, M. ; Buisman, C.J.N. - \ 2014
International Journal of Hydrogen Energy 39 (2014)10. - ISSN 0360-3199 - p. 4771 - 4778.
waste-water treatment - bioelectrochemical systems - ion-transport - fuel-cells - performance - ph - catalysts - membrane - acetate - energy
We investigated the use of a Microbial Electrolysis Cell (MEC) for the ammonium removal, COD removal and hydrogen production from five times diluted urine. During operation with a batch cathode, a current density of 23.07 +/- 1.15 A m(-2) was achieved corresponding to a hydrogen production rate of 48.6 +- 7.47 m(3) H-2 m(-3) MEC d(-1), an ammonium removal rate of 173.4 +/- 18.1 g N m(-2) d(-1) and a COD removal rate of 171.0 +/- 16.9 g COD m(-2) d(-1). Ammonia stripping was not possible in the applied MEC and ammonia diffusion from cathode to anode compartment led to a relatively short stable operation period. The stable operation period was prolonged by addition of new cathode media (HRT 6 h), but this resulted in a lower current density (14.64 +/- 1.65 A m(-2)), hydrogen production rate (32.0 +/- 0.89 m(3) H-2 m(-3) MEC d(-1)), ammonium removal rate (162.18 +/- 10.37 g N m(-2) d(-1)) and COD removal rate (130.56 +/- 4.45 g COD m(-2) d(-1)). Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Check title to add to marked list
<< previous | next >>

Show 20 50 100 records per page

Please log in to use this service. Login as Wageningen University & Research user or guest user in upper right hand corner of this page.