Records 1 - 20 / 271
Kinetics of Physiological Responses as a Measure of Intensity and Hydration Status During Experimental Physical Stress in Human Volunteers
Kartaram, Shirley W. ; Norren, Klaske van; Schoen, Eric ; Teunis, Marc ; Mensink, Marco ; Verschuren, Martie ; M’Rabet, Laura ; Besseling-van der Vaart, Isolde ; Mohrmann, Karin ; Wittink, Harriet ; Garssen, Johan ; Witkamp, Renger ; Pieters, Raymond - \ 2020
Frontiers in Physiology 11 (2020). - ISSN 1664-042X
biomarkers - dehydration - exercise-intensity - kinetics - physiological responses - resilience
Introduction: Strenuous physical stress induces a range of physiological responses, the extent depending, among others, on the nature and severity of the exercise, a person’s training level and overall physical resilience. This principle can also be used in an experimental set-up by measuring time-dependent changes in biomarkers for physiological processes. In a previous report, we described the effects of workload delivered on a bicycle ergometer on intestinal functionality. As a follow-up, we here describe an analysis of the kinetics of various other biomarkers. Aim: To analyse the time-dependent changes of 34 markers for different metabolic and immunological processes, comparing four different exercise protocols and a rest protocol. Methods: After determining individual maximum workloads, 15 healthy male participants (20–35 years) started with a rest protocol and subsequently performed (in a cross-over design with 1-week wash-out) four exercise protocols of 1-h duration at different intensities: 70% Wmax in a hydrated and a mildly dehydrated state, 50% Wmax and intermittent 85/55% Wmax in blocks of 2 min. Perceived exertion was monitored using the Borg’ Rating of Perceived Exertion scale. Blood samples were collected both before and during exercise, and at various timepoints up to 24 h afterward. Data was analyzed using a multilevel mixed linear model with multiple test correction. Results: Kinetic changes of various biomarkers were exercise-intensity-dependent. Biomarkers included parameters indicative of metabolic activity (e.g., creatinine, bicarbonate), immunological and hematological functionality (e.g., leukocytes, hemoglobin) and intestinal physiology (citrulline, intestinal fatty acid-binding protein, and zonulin). In general, responses to high intensity exercise of 70% Wmax and intermittent exercise i.e., 55/85% Wmax were more pronounced compared to exercise at 50% Wmax. Conclusion: High (70 and 55/85% Wmax) and moderate (50% Wmax) intensity exercise in a bicycle ergometer test produce different time-dependent changes in a broad range of parameters indicative of metabolic activity, immunological and hematological functionality and intestinal physiology. These parameters may be considered biomarkers of homeostatic resilience. Mild dehydration intensifies these time-related changes. Moderate intensity exercise of 50% Wmax shows sufficient physiological and immunological responses and can be employed to test the health condition of less fit individuals.
Silicon-Free SuFEx Reactions of Sulfonimidoyl Fluorides : Scope, Enantioselectivity, and Mechanism
Liang, Dong Dong ; Streefkerk, Dieuwertje E. ; Jordaan, Daan ; Wagemakers, Jorden ; Baggerman, Jacob ; Zuilhof, Han - \ 2020
Angewandte Chemie-International Edition 59 (2020)19. - ISSN 1433-7851 - p. 7494 - 7500.
enantioselectivity - kinetics - reaction mechanisms - SuFEx
SuFEx reactions, in which an S−F moiety reacts with a silyl-protected phenol, have been developed as powerful click reactions. In the current paper we open up the potential of SuFEx reactions as enantioselective reactions, analyze the role of Si and outline the mechanism of this reaction. As a result, fast, high-yielding, “Si-free” and enantiospecific SuFEx reactions of sulfonimidoyl fluorides have been developed, and their mechanism shown, by both experimental and theoretical methods, to yield chiral products.
Bulk storage of mango (Mangifera indica L.) and pineapple (Ananas comosus L.) pulp: effect of pulping and storage temperature on phytochemicals and antioxidant activity
Arampath, Palitha C. ; Dekker, Matthijs - \ 2019
Journal of the Science of Food and Agriculture 99 (2019)11. - ISSN 0022-5142 - p. 5157 - 5167.
antioxidant - bulk storage - health promoting - kinetics - mango - pineapple
BACKGROUND: The effects of pulp extraction, thermal treatment and bulk storage of mango (Mangifera indica L.) and pineapple (Ananas comosus L.) pulps for 20 weeks at ambient (28 ± 2 °C) and cold (4 °C) temperatures on the bioactive phytochemicals and antioxidant activity were investigated. RESULTS: The contents of total polyphenols in mango (10.5%) and pineapple (5.4%) increased during pulping. The ratio of the degradation rate constants (kd values) (28 ± 2 °C: 4 °C) of vitamin C, polyphenols, Trolox equivalent antioxidant capacity (TEAC) and β-carotene ranged from 2–4.5 and 1.5–2.7 in mango and pineapple pulps, respectively. The kd values of tannic acid, chlorogenic acid, epicatechin and catechin in mango pulp were 1.5–1.8 times higher under ambient storage than in cold storage. Furthermore, in pineapple pulp, the degradation rates of the same components were 1.6, 1.6, 2.1 and 1.4 times, respectively, faster at room temperature than in cold storage. The bulk storage of pulps at 4 °C provided better retention of health-promoting compounds than ambient temperature storage for up to 20 weeks. CONCLUSION: Bulk storage of mango and pineapple pulp under cold storage conditions (4 °C) is recommended as a better pulp preservation method than storage at ambient (28 ± 2 °C) temperature.
Modeling food matrix effects on chemical reactivity : Challenges and perspectives
Capuano, Edoardo ; Oliviero, Teresa ; Boekel, Martinus A.J.S. van - \ 2018
Critical Reviews in Food Science and Nutrition 58 (2018)16. - ISSN 1040-8398 - p. 2814 - 2828.
activity coefficients - fingerprinting - Food matrix - kinetics - modeling - thermodynamics
The same chemical reaction may be different in terms of its position of the equilibrium (i.e., thermodynamics) and its kinetics when studied in different foods. The diversity in the chemical composition of food and in its structural organization at macro-, meso-, and microscopic levels, that is, the food matrix, is responsible for this difference. In this viewpoint paper, the multiple, and interconnected ways the food matrix can affect chemical reactivity are summarized. Moreover, mechanistic and empirical approaches to explain and predict the effect of food matrix on chemical reactivity are described. Mechanistic models aim to quantify the effect of food matrix based on a detailed understanding of the chemical and physical phenomena occurring in food. Their applicability is limited at the moment to very simple food systems. Empirical modeling based on machine learning combined with data-mining techniques may represent an alternative, useful option to predict the effect of the food matrix on chemical reactivity and to identify chemical and physical properties to be further tested. In such a way the mechanistic understanding of the effect of the food matrix on chemical reactions can be improved.
Impact of microbial variability on food safety and quality
Aryani, D.C. - \ 2016
Wageningen University. Promotor(en): Marcel Zwietering, co-promotor(en): Heidy den Besten. - Wageningen : Wageningen University - ISBN 9789462577381 - 190
listeria monocytogenes - lactobacillus plantarum - growth analysis - kinetics - growth models - inactivation - heat stress - strain differences - food safety - milk - ham - microbial diversity - food quality - listeria monocytogenes - lactobacillus plantarum - groeianalyse - kinetica - groeimodellen - inactivatie - warmtestress - stamverschillen - voedselveiligheid - melk - ham - microbiële diversiteit - voedselkwaliteit
Cyclodextrin-Based Solid-Gas Clathrates
Pereva, Stiliana ; Himitliiska, Tsveta ; Spassov, Tony ; Stoyanov, S.D. ; Arnaudov, L.N. ; Dudev, Todor - \ 2015
Journal of Agricultural and Food Chemistry 63 (2015)29. - ISSN 0021-8561 - p. 6603 - 6613.
clathrates - crystallization - cyclodextrins - kinetics
"Cyclodextrin-gas" clathrates were obtained by crystallization from water solution of α-, β-, and γ-cyclodextrins (CDs) under pressure of the gas to be entrapped into the CD molecules. When the pressure is released, these clathrates are stable at ambient conditions and dissociate at elevated temperature, which makes them interesting for various applications as foam boosters in food and other industries. It was found that under these conditions α-CD forms clathrates with all of the gases used in this study (N2, N2O, CO2, Ar), whereas β- and γ-CDs can form clathrates only with N2. The concentration of the cyclodextrin and the temperature and pressure of the gas were varied for achieving higher clathrate yield and larger amount of embedded gas. Highest values of about 2 wt % were found for α-CD-N2O, as it releases in the temperature range of 40-60 °C.
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.
Spontaneous, non-enzymatic breakdown of peptides during enzymatic protein hydrolysis
Butre, C.I. ; Buhler, S. ; Sforza, S. ; Gruppen, H. ; Wierenga, P.A. - \ 2015
Biochimica et Biophysica Acta. Proteins & Proteomics 1854 (2015)8. - ISSN 1570-9639 - p. 987 - 994.
beta-lactoglobulin - cleavage - bond - specificity - identification - selectivity - kinetics - isolate - water
It is expected that during the hydrolysis of proteins with specific enzymes only peptides are formed that result from hydrolysis of the specific cleavage sites (i.e. specific peptides). It is, however, quite common to find a-specific peptides (i.e. resulting from a-specific cleavage), which are often ignored, or explained by impurities in the enzyme preparation. In recent work in a whey protein isolate (WPI) hydrolysate obtained with the specific Bacillus licheniformis protease (BLP), 13 peptides of 77 identified were found to be the result of a-specific cleavage. These were formed after degradation of 6 specific peptides, after 5 different types of amino acids. The fact that other peptides were not hydrolyzed after these 5 amino acids suggests that the cleavages were not the result of a contamination with a different enzyme. In other systems, certain peptide sequences have been described to degrade chemically, under relatively mild conditions. This process is referred to as spontaneous cleavage. To test if the a-specific peptides observed in the WPI hydrolysis are the results of spontaneous cleavages, the parental peptides were synthesized. Surprisingly, 4 of the 5 synthesized peptides were indeed spontaneously cleaved under the mild conditions used in this study (i.e. 40 °C and pH 8) showing that peptides are less stable than typically considered. The rate of cleavage on the a-specific bonds was found to be enhanced in the presence of BLP. This suggests that the formation of a-specific peptides is not due to side activity but rather an enhancement of intrinsic instability of the peptides.
Determination of the influence of the pH of hydrolysis on enzyme selectivity of Bacillus licheniformis protease towards whey protein isolate
Butre, C.I. ; Sforza, S. ; Wierenga, P.A. ; Gruppen, H. - \ 2015
International Dairy Journal 44 (2015). - ISSN 0958-6946 - p. 44 - 53.
differential scanning calorimetry - beta-lactoglobulin - peptides - endopeptidases - kinetics
Enzymatic protein hydrolysis is typically described by the degree of hydrolysis and by the enzyme specificity. While the specificity describes which cleavage sites can potentially be cleaved, it does not describe which are preferred. To identify the relative rate at which each individual cleavage site is hydrolysed, enzyme selectivity has recently been introduced. To test the effect of pH on selectivity, whey protein isolate (WPI) was hydrolysed with Bacillus licheniformis protease (BLP) at pH 7.0, 8.0 or 9.0. At all pH values, large differences in the enzyme selectivity (from
Effect of Methanethiol Concentration on Sulfur Production in Biological Desulfurization Systems under Haloalkaline Conditions
Roman, P. ; Veltman, R. ; Bijmans, M.F.M. ; Keesman, K.J. ; Janssen, A.J.H. - \ 2015
Environmental Science and Technology 49 (2015)15. - ISSN 0013-936X - p. 9212 - 9221.
natron-alkaline conditions - sulfide oxidation - oxidizing bacteria - aqueous-solutions - soda lakes - lab-scale - bioreactors - solubility - kinetics - polysulfides
Bioremoval of H2S from gas streams became popular in recent years because of high process efficiency and low operational costs. To expand the scope of these processes to gas streams containing volatile organic sulfur compounds, like thiols, it is necessary to provide new insights into their impact on overall biodesulfurization process. Published data on the effect of thiols on biodesulfurization processes are scarce. In this study, we investigated the effect of methanethiol on the selectivity for sulfur production in a bioreactor integrated with a gas absorber. This is the first time that the inhibition of biological sulfur formation by methanethiol is investigated. In our reactor system, inhibition of sulfur production started to occur at a methanethiol loading rate of 0.3 mmol L–1 d–1. The experimental results were also described by a mathematical model that includes recent findings on the mode of biomass inhibition by methanethiol. We also found that the negative effect of methanethiol can be mitigated by lowering the salinity of the bioreactor medium. Furthermore, we developed a novel approach to measure the biological activity by sulfide measurements using UV-spectrophotometry. On the basis of this measurement method, it is possible to accurately estimate the unknown kinetic parameters in the mathematical model.
A pore inactivation model for describing oil uptake of French fries during pre-frying
Koerten, K.N. van; Schutyser, M.A.I. ; Somsen, D. ; Boom, R.M. - \ 2015
Journal of Food Engineering 146 (2015). - ISSN 0260-8774 - p. 92 - 98.
glass spg membranes - potato slices - mass-transfer - heat-transfer - water-loss - kinetics - emulsification - crust
The reduction of oil uptake during deep-frying is a subject with societal relevance, given the trend towards lower-fat foods. Since research into oil absorption during frying is limited, we here report on developing better mechanistic understanding of this process. The oil uptake for different frying temperatures and fry dimensions was measured as a function of the water evaporation rate and water loss. A pore inactivation model was developed based on the hypothesis that the crust is a porous layer through which the exuding moisture vapour flow inhibits oil migration. Decreases in water evaporation rates will cause pores to inactivate, allowing oil to penetrate into the crust. The model provides good predictions to the experimental data. Since the model has two parameters, a purely statistical comparison with a simple linear fit having one parameter, does not show a significant benefit; however, the model better describes the overall trend of oil uptake.
Adaptation of faecal microbiota in sows after diet changes and consequences for in vitro fermentation capacity
Sappok, M.A. ; Perez Gutierrez, O.N. ; Smidt, H. ; Pellikaan, W.F. ; Verstegen, M.W.A. ; Bosch, G. ; Hendriks, W.H. - \ 2015
Animal 9 (2015)9. - ISSN 1751-7311 - p. 1453 - 1464.
gas-production technique - large-intestine - growing pigs - adult-pigs - fiber - substrate - kinetics - digesta - communities - performance
In vitro gas production studies are routinely used to assess the metabolic capacity of intestinal microbiota to ferment dietary fibre sources. The faecal inocula used during the in vitro gas production procedure are most often obtained from animals adapted to a certain diet. The present study was designed to assess whether 19 days of adaptation to a diet are sufficient for faecal inocula of pigs to reach a stable microbial composition and activity as determined by in vitro gas production. Eighteen multiparous sows were allotted to one of two treatments for three weeks: a diet high in fibre (H) or a diet low in fibre (L). After this 3-week period, the H group was transferred to the low fibre diet (HL-treatment) while the L group was transferred to the diet high in fibre (LH-treatment). Faecal samples were collected from each sow at 1, 4, 7, 10, 13, 16 and 19 days after the diet change and prepared as inoculum used for incubation with three contrasting fermentable substrates: oligofructose, soya pectin and cellulose. In addition, inocula were characterised using a phylogenetic microarray targeting the pig gastrointestinal tract microbiota. Time after diet change had an effect (P
Relationship between in vitro and in vivo methane production measured simultaneously with different dietary starch sources and starch levels in dairy cattle
Hatew, B. ; Cone, J.W. ; Pellikaan, W.F. ; Podesta, S.C. ; Bannink, A. ; Hendriks, W.H. ; Dijkstra, J. - \ 2015
Animal Feed Science and Technology 202 (2015). - ISSN 0377-8401 - p. 20 - 31.
gas-production technique - rumen microbial-population - volatile fatty-acids - fermentation characteristics - ruminal fermentation - production profiles - degradation - emissions - kinetics - protein
To investigate the relationship between in vitro and in vivo methane (CH4) production measured simultaneously using the same rumen-fistulated cows in both experiments, four dietary treatments based on concentrate that accounted for 400 g/kg of the mixed diet DM, were formulated to contain starch varying in rate of fermentation (slowly (S) vs. rapidly (R): native vs. gelatinized maize grain) and level of inclusion (low (L) vs. high (H): 270 vs. 530 g/kg of concentrate DM). Sixteen rumen-fistulated lactating dairy cows were used in a complete randomized block design with these treatments replicated in four periods of 17 d each. In experiment 1, after 12 d of adaptation, the cows were housed in respiration chambers for 5 d to measure CH4 production. In experiment 2, in each period in vitro gas and CH4 production were measured (in duplicate per period) for mixed diet samples from the same diet as fed to the donor cows using rumen inocula adapted to the respective diets for an average of 16 d. In addition, samples of two concentrate ingredients, viz. grass silage and beet pulp, were incubated with four different inocula obtained from individual donor cows. Gas production (GP) was measured using automated GP system with CH4 measured at distinct time points. In vitro (24-h) CH4 production of mixed diet was lower with R than S (42.9 vs. 49.5 ml/g of incubated organic matter (OM); P=0.004), and higher with L than H (49.8 vs. 42.6 ml/g of incubated OM; P=0.002). A significant interaction effect between source and level of starch (P=0.015) was also found, indicating the CH4 production of the RH diet decreased in particular. In vivo, an increased rate of starch fermentation resulted in a lower CH4 per unit of estimated rumen-fermentable OM (eRFOM; 55.6 vs. 61.2 ml/g of eRFOM; P=0.007), and higher level of starch tended (P=0.089) to reduce CH4 per unit of eRFOM, but dietary starch level and source did not affect CH4 per unit of OM consumed. Across the diets tested, 24-h in vitro CH4 (ml/g of incubated OM) correlated well with in vivo CH4 expressed per unit of eRFOM (R2 = 0.54; P=0.040), but not when expressed per unit of OM ingested (R2 = 0.04; P=0.878). For grass silage (the same trend for beet pulp), inocula adapted to R- and H-based diets compared with S- and L-based diets resulted in a lower CH4 production (36.1 vs. 44.8 ml/g of incubated OM, R vs. S; and 37.4 vs. 43.4 ml/g of incubated OM, H vs. L; P
Feasibility of the development of reference materials for the detection of Ag nanoparticles in food: neat dispersions and spiked chicken meat
Grombe, R. ; Allmaier, G. ; Charoud-Got, J. ; Dudkiewicz, A. ; Emteborg, H. ; Hofmann, T. ; Huusfeldt-Larsen, E. ; Lehner, A. ; Llinas, M. ; Loeschner, K. ; Molhave, K. ; Peters, R.J.B. ; Seghers, J. ; Solans, C. ; Kammer, F. van den; Wagner, S. ; Weigel, S. ; Linsinger, T.P.J. - \ 2015
Accreditation and Quality Assurance 20 (2015)1. - ISSN 0949-1775 - p. 3 - 16.
atomic-absorption-spectrometry - field-flow fractionation - particle icp-ms - silver nanoparticles - nano-silver - dissolution - homogeneity - containers - stability - kinetics
The feasibility of producing colloidal silver nanoparticle reference materials and silver nanoparticle spiked reference matrix materials was investigated. Two concentrations of PVP-coated silver nanoparticle dispersions were evaluated and used to spike chicken meat, with the aim of producing a set of reference materials to support the development of analytical methods for the detection and quantification of nanoparticles in food. Aqueous silver nanoparticle (AgNP) dispersions were evaluated for their homogeneity of mass fraction and particle size and found sufficiently homogeneous to be used as reference materials. Stability studies at 4 °C, 18 °C and 60 °C demonstrated sufficient short- and long-term stability, although particle size decreases in a linear fashion at 60 °C. The AgNP dispersions were characterized for total Ag mass fraction by ICP-OES, dissolved Ag content by ultrafiltration-ICP-MS, as well as AgNP particle size by dynamic light scattering, transmission electron microscopy (TEM) and gas-phase electrophoretic molecular mobility analysis. Chicken breasts were homogenized by cryo-milling and spiked with aqueous AgNP dispersions. Rapid freezing over liquid nitrogen resulted in homogeneous and stable materials. The spiked chicken materials were characterized for their total Ag mass fraction by neutron activation analysis and for the AgNP particle size by TEM and single-particle inductively coupled plasma mass spectrometry. The observed differences in particle sizes between the spiked chicken samples and the original silver dispersions indicate relevant matrix effects. The materials demonstrate that production and characterization of reference materials for the detection and quantification of silver nanoparticles in meat are feasible, but challenges especially in assessing stability and having sufficiently precise methods for assessment of homogeneity and stability remain.
Adsorption of charged and neutral polymer chains on silica surfaces: The role of electrostatics, volume exclusion, and hydrogen bonding
Spruijt, E. ; Biesheuvel, P.M. ; Vos, W.M. de - \ 2015
Physical Review. E, Statistical nonlinear, and soft matter physics 91 (2015). - ISSN 2470-0045 - 11 p.
polyelectrolyte adsorption - double-layer - free-energy - poly(vinylpyrrolidone) - relaxation - desorption - stability - kinetics - colloids - density
We develop an off-lattice (continuum) model to describe the adsorption of neutral polymer chains and polyelectrolytes to surfaces. Our continuum description allows taking excluded volume interactions between polymer chains and ions directly into account. To implement those interactions, we use a modified hard-sphere equation of state, adapted for mixtures of connected beads. Our model is applicable to neutral, charged, and ionizable surfaces and polymer chains alike and accounts for polarizability effects of the adsorbed layer and chemical interactions between polymer chains and the surface. We compare our model predictions to data of a classical system for polymer adsorption: neutral poly(N-vinylpyrrolidone) (PVP) on silica surfaces. The model shows that PVP adsorption on silica is driven by surface hydrogen bonding with an effective maximum binding energy of about 1.3kBT per PVP segment at low pH. As the pH increases, the Si-OH groups become increasingly dissociated, leading to a lower capacity for H bonding and simultaneous counterion accumulation and volume exclusion close to the surface. Together these effects result in a characteristic adsorption isotherm, with the adsorbed amount dropping sharply at a critical pH. Using this model for adsorption data on silica surfaces cleaned by either a piranha solution or an O2 plasma, we find that the former have a significantly higher density of silanol groups.
Effect of temperature and duration of ensiling on in vitro degradation of maize silages in rumen fluid
Ali, M. ; Cone, J.W. ; Khan, N.A. ; Hendriks, W.H. ; Struik, P.C. - \ 2015
Journal of Animal Physiology and Animal Nutrition 99 (2015)2. - ISSN 0931-2439 - p. 251 - 257.
fermentation - kinetics - storage - forage - length - model - corn
The effects of ensiling temperature and duration of ensiling on the feeding quality of whole-crop maize (Zea mays L.) silages were investigated. Samples of one cultivar of maize plants were collected from two different fields, grown in different years on sandy soils. Samples were collected when the whole-plant dry matter content was approximately 330 g/kg. Maize plants were chopped and ensiled in mini silos at three different ambient temperatures (5, 12 and 18 °C). The ensiling temperature affected the ensiling fermentation processes, causing different rates of pH decline and different final pH values. Samples from the silos were taken after 0 (not ensiled, i.e. control), 4, 8 and 16 weeks of ensiling. The silage samples were not dried, but ground-frozen under liquid nitrogen to pass a 1-mm sieve. The gas production technique was used to evaluate the influence of the ensiling temperature and the duration of ensiling on the degradation of the silage samples in rumen fluid. The gas production was highest when the maize was ensiled at 12 °C (p <0.0001). An increase in ensiling duration caused a decrease in silage pH, accompanied by a decrease in gas production (p <0.0001). The decrease in gas production was linearly related to the decrease in pH at the three temperatures. The present study shows that both ensiling temperature and ensiling duration play a significant role in the rumen degradability of maize silage.
Description of the phosphorus sorption and desorption processes in coarse calcareous sandy soils
Schoumans, Oscar F. - \ 2014
Soil Science 179 (2014)5. - ISSN 0038-075X - p. 221 - 229.
calcareous soils - calcite - desorption - kinetics - phosphate - phosphate sorption capacity - Phosphorus - precipitation - sorption
In order to understand and predict the behavior of phosphorus (P) in calcareous sandy soils, sorption and desorption studies were carried out. Two main processes were distinguished: a fast, reversible phosphate reaction (within 1 day), which can be described by the Langmuir equation, and a precipitation reaction, which can be described by a time-dependent Freundlich equation. The maximum phosphate sorption capacity in the top 50 cm of the soil ranged from 3 to 6 t P2O5·ha-1. About 85% to 95% of the maximum amount of P bound was poorly soluble; the remaining portion of bound P determines the ortho-P concentration in soil solution under desorption conditions. The breakthrough curves of the two column experiments were described reasonably well by the proposed process description and the associated parameters, which were derived from batch experiments.
Moisture transport in swelling media modelled with a Lattice Boltzmann scheme having a deforming lattice
Sman, R.G.M. van der - \ 2014
Journal of Food Engineering 124 (2014). - ISSN 0260-8774 - p. 54 - 63.
non-brownian suspensions - diffusion lattice - water transport - flow - simulations - profiles - kinetics - food - gels - validation
In this paper we present a novel numerical scheme for simulating the one-dimensional deformation of hydrogel material due to drying or rehydration. The scheme is based on the versatile Lattice Boltzmann method, which has been extended such that the computational grid (lattice) deforms due to shrinkage or swelling. This property of a deforming grid is new to the lattice Boltzmann method, and a detailed description of this new method is given. Via simulations we show that self-similar moisture concentration profiles occur in two periods in both drying and swelling processes: the penetration period and the regular regime. Given the property of self-similarity, we have been able to formulate a reduced-order model for the regular regime of swelling.
Calcite growth: Rate dependence on saturation, on ratios of dissolved calcium and (bi)carbonate and on their complexes
Weijden, C.H. van der; Weijden, R.D. van der - \ 2014
Journal of Crystal Growth 394 (2014). - ISSN 0022-0248 - p. 137 - 144.
molecular-dynamics simulations - electrolyte crystal-growth - spiral growth - rate laws - solution stoichiometry - surface speciation - carbonate minerals - aqueous-solution - rate-constant - kinetics
The role of bicarbonate on the growth rate of calcite in Lhermo-, chemo- and pH stated experiments was observed in a foregoing paper by Van der Weijden et al. (1997)  The data are used here to explore especially the effect of bicarbonate on the calcite growth rate in more detail. The experimental range of pH is from 7.6 to 8.9, the initial seed concentrations are 165 +/- 12 mg/L with an average surface area of 0.29 m(2) g(-1). The median values of the molalities of Ca2+ and CO32- are, respectively, 6.7 +/- 24 (x 10(-4)) and 6.9 +/- 1.9 (x 10(-4)); the saturation values (Omega) are 2.1-4. In the pH-range of 7.6-8.9 the activity ratios of HCO3- to CO32- decrease from 510 to 30. The effect of increasing bicarbonate on R-lin (ms(-1)) is expressed in the apparent rate constant, k(lin), which decreases with a factor of 2.8 in the indicated pH-range. The contribution of bicarbonate to R-lin is also apparent in plots of R-lin versus the free dissolved calcium to carbonate ratios (r) for a selection of results with Omega = 2.7 +/- 0.7 in the pH-range from 7.6 to 8.9. Where others found a dependence of R-lin with a maximum at r approximate to 1, symmetrically decreasing on either side of this value, it is shown here that R-lin increases at r > 1 for higher values of free dissolved bicarbonate, in this case at pH 7.6. in the present paper a kinetic model relating the growth rate (R) to the activities of (0)(CaCO3) and CaHCO3+ successfully describes the data with associated k-values for both species in a narrow Omega-range. Implicitly, these ion pairs represent the effect of Ca2+, CO32- and HCO3 on the growth rate. (C) 2014 Elsevier B.V. All rights reserved.
Equation of state and adsorption dynamics of soft microgel particles at an air-water interface
Deshmukh, O.S. ; Maestro, A. ; Duits, M.H.G. ; Ende, D.T.M. van den; Cohen Stuart, M.A. ; Mugele, F. - \ 2014
Soft Matter 10 (2014)36. - ISSN 1744-683X - p. 7045 - 7050.
cross-link density - poly(n-isopropylacrylamide) microgels - emulsion stabilizers - sensitive microgels - temperature - surfactants - scattering - kinetics - light - fluid
Understanding the adsorption dynamics of soft microgel particles is a key step in designing such particles for potential applications as stimuli-responsive Pickering stabilizers for foams or emulsions. In this study we experimentally determine an equation of state (EOS) for poly (N-isopropylacrylamide) (PNIPAM) microgel particles adsorbed onto an air–water interface using a Langmuir film balance. We detect a finite surface pressure at very low surface concentration of particles, for which standard theories based on hard disk models predict negligible pressures, implying that the particles must deform strongly upon adsorption to the interface. Furthermore, we study the evolution of the surface pressure due to the adsorption of PNIPAM particles as a function of time using pendant drop tensiometry. The equation of state determined in the equilibrium measurements allows us to extract the adsorbed amount as a function of time. We find a mixed-kinetic adsorption that is initially controlled by the diffusion of particles towards the interface. At later stages, a slow exponential relaxation indicates the presence of a coverage-dependent adsorption barrier related to crowding of particles at the interface.