Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Effect of Temperature and Pressure on the Stability of Protein Microbubbles
    Rovers, Tijs A.M. ; Sala, Guido ; Linden, Erik Van Der; Meinders, Marcel B.J. - \ 2016
    ACS Applied Materials and Interfaces 8 (2016)1. - ISSN 1944-8244 - p. 333 - 340.
    buckling - heating - microbubble - pressure - stability - storage temperature

    Protein microbubbles are air bubbles with a network of interacting proteins at the air-water interface. Protein microbubbles are commonly used in medical diagnostic and therapeutic research. They have also recently gained interest in the research area of food as they can be used as structural elements to control texture, allowing for the manufacture of healthier foods with increased consumer perception. For the application of microbubbles in the food industry, it is important to gain insights into their stability under food processing conditions. In this study, we tested the stability of protein microbubbles against heating and pressurization. Microbubbles could be heated to 50 °C for 2 min or pressurized to 100 kPa overpressure for 15 s without significantly affecting their stability. At higher pressures and temperatures, the microbubbles became unstable and buckled. Buckling was observed above a critical pressure and was influenced by the shell modulus. The addition of cross-linkers like glutaraldehyde and tannic acid resulted in microbubbles that were stable against all tested temperatures and overpressures, more specifically, up to 120 °C and 470 kPa, respectively. We found a relation between the storage temperatures of microbubble dispersions (4, 10, 15, and 21 °C) and a decrease in the number of microbubbles with the highest decrease at the highest storage temperature. The average rupture time of microbubbles stored at different storage temperatures followed an Arrhenius relation with an activation energy for rupture of the shell of approximately 27 kT. This strength ensures applicability of microbubbles in food processes only at moderate temperatures and storage for a moderate period of time. After the proteins in the shell are cross-linked, the microbubbles can withstand pressures and temperatures that are representative of food processes.

    Microbubble stability and applications in food
    Rovers, T.A.M. - \ 2015
    Wageningen University. Promotor(en): Erik van der Linden, co-promotor(en): Marcel Meinders; Guido Sala. - Wageningen : Wageningen University - ISBN 9789462574755 - 138
    microbubbles - eiwit - stabiliteit - karakterisering - voedsel - voedseladditieven - oppervlaktespanningsverlagende stoffen - zuurbehandeling - reologische eigenschappen - sensorische evaluatie - tribologie - druk - verwarming - koelen - microbubbles - protein - stability - characterization - food - food additives - surfactants - acid treatment - rheological properties - sensory evaluation - tribology - pressure - heating - cooling

    Aeration of food is considered to be a good method to create a texture and mouthfeel of food products that is liked by the consumer. However, traditional foams are not stable for a prolonged time. Microbubbles are air bubbles covered with a shell that slows down disproportionation significantly and arrests coalescence. Protein stabilized microbubbles are seen as a promising new food ingredient for encapsulation, to replace fat, to create new textures, and to improve sensorial properties of foods. In order to explore the possible functionalities of microbubbles in food systems, a good understanding is required regarding the formation of protein stabilized microbubbles as well as their stability in environments and at conditions encountered in food products. The aim of this research was to investigate the key parameters for applications of microbubbles in food systems. In Chapter 1 an introduction to this topic is given.

    In Chapter 2, the effect of the microbubble preparation parameters on the microbubble characteristics, like the microbubble yield, size and stability, was investigated. The protein Bovine Serum Albumin (BSA) and the method sonication was used to manufacture the microbubbles. The manufactured number and stability of microbubbles was highest when they were prepared at a pH around 5 to 6, just above the isoelectric point, and at an ionic strength of 1.0 M. This can be related to the protein coverage at the air/water interface of air bubbles formed during sonication. At a pH close to the isoelectric point the BSA molecules is in its native configuration. Also the repulsion between the proteins is minimized at these pH values and ionic strength. Both the native configuration and the limited repulsion between the proteins result in an optimal protein coverage during the first part of sonication. Also a high protein concentration contributes to a higher surface coverage. The surface coverage is proportional to the protein concentration up to a concentration of 7.5% after which an increase in protein concentration did not lead to a substantial increase in the number of microbubble . In the second part of sonication the protein layer around the air bubble becomes thicker and stronger by heat induced protein-protein interactions. We found that and at a preheating temperature of 55-60°C, about 5 °C below the BSA denaturation temperature, and a final solution temperature of 60-65°C most microbubbles were obtained, while at higher temperatures mainly protein aggregates and (almost) no microbubbles are formed. This suggests that at temperature of around 60°C to 65°C protein aggregated mostly at the air-water interface creating a multi-layered shell, while at higher temperature, they also aggregated in bulk. These aggregates cannot form microbubbles. We found that optimal preparation parameters strongly depend on the protein batch. We hypothesize that the differences in microbubble formation between the protein batches is due to (small) differences in the protein molecular and denaturation properties that determine the temperature at which the molecules start to interact at the air-water interface. Microbubbles made with different protein concentration and preheating temperatures shrunk in time to a radius between 300 nm and 350 nm, after which the size remained constant during further storage. We argue that the driving force for the shrinkage was the Laplace pressure, resulting in an air flux from the bubbles to the solution. We argue that the constant final size can be explained by a thickening of the microbubble shell as a result of the microbubble shrinkage, thereby withstanding the Laplace pressure.

    In Chapter 3 and Chapter 4, microbubble stability at environments and conditions representative for food products were studies. In Chapter 3 we investigated the stability upon addition of surfactants and acid, When surfactants or acid were added, the microbubbles disappeared in three subsequent steps. The release of air from the microbubble can be well described with the two-parameter Weibull process. This suggests two processes are responsible for the release of air: 1) a shell-weakening process and 2) a random fracture of the weakened shell. After the air has been released from the microbubble the third process is identified in the microbubble disintegration: 3) the shell disintegrated completely into nanometer-sized particles. The probability of fracture was exponentially proportional to the concentration of acid and surfactant, meaning that a lower average breaking time and a higher decay rate were observed at higher surfactant or acid concentrations. For different surfactants, different decay rates were found. The disintegration of the shell into monomeric proteins upon addition of acid or surfactants shows that the interactions in the shell are non-covalent and most probably hydrophobic. After surfactant addition, there was a significant time gap between complete microbubble decay (release of air) and complete shell disintegration, while after acid addition the time at which the complete disintegration of the shell was observed coincided with the time of complete microbubble decay.

    In Chapter 4 the stability of the microbubbles upon pressure treatment, upon fast cooling after heating and at different storage temperatures was studied. The microbubble stability significantly decreased when microbubbles were pressurized above 1 bar overpressure for 15 seconds or heated above 50°C for 2 minutes. Above those pressures the microbubbles became unstable by buckling. Buckling occurred above a critical pressure. This critical pressure is determined by the shell elastic modulus, the thickness of the shell, and the size of the microbubble. Addition of crosslinkers like glutaraldehyde and tannic acid increased the shell elastic modulus. It was shown that microbubbles were stable against all tested temperatures (up to 120°C) and overpressures (4.7 bar) after they were reinforced by crosslinkers. From the average breaking time at different storage temperatures, we deduced that the activation energy to rupture molecular bonds in the microbubbles shell is 27 kT.

    In Chapter 5, we investigated the effect of microbubbles on the rheological, tribological sensorial properties of model food systems and we compared this effect to the effect on food systems with emulsion droplets and without an added colloid. We investigated the effect in three model food systems, namely fluids with and without added thickener and a mixed gelatine-agar gel. In a sensory test panellists were asked whether they could discriminate between samples containing microbubbles, emulsion droplets or no added colloid. Emulsions could be sensorially well distinguished from the other two samples, while the microbubble dispersion could not be discriminated from the protein solution. Thus, we concluded that at a volume fraction of 5% of these BSA covered microbubbles were not comparable to oil-in-water emulsions. The good discrimination of emulsion might be ascribed to the fact that emulsion had a lower friction force (measured at shear rates form 10 mm/s to 80 mm/s) than that microbubbles dispersions and protein solutions. Upon mixing emulsions and microbubble dispersions the friction value approximated that of emulsions. This effect was already noticed at only 1.25% (v/v) oil, indicating that microbubbles had not a significant contributions to the friction of these samples. Also microbubble dispersions with and without protein aggregates were compared. The microbubble dispersions with and without thickener containing protein aggregates had a higher viscosity than the those samples without protein aggregates. Protein aggregates in the gelled microbubble sample yielded a higher Young’s modulus and fracture stress. The differences between the gelled samples could be well perceived by the panellists. We attribute this mainly to the fracture properties of the gel. In general we concluded that microbubbles, given their size of ~ 1 mm and volume fraction of 5%, did not contribute to a specific mouthfeel.

    Finally in Chapter 6, the results presented in the previous chapters are discussed and put in perspective of the general knowledge on microbubbles production, stability, and applications in food. We described the main mechanisms leading to microbubble formation and stability. We showed that the production parameters significantly influence the interactions in the microbubble shell, and the those interactions highly determine the stability of the microbubbles under several conditions. We reported about limitations of sonication as a method to produce microbubbles suitable for food applications and we provided some ways to overcome these limitations. The use of microbubbles in food systems has been explored and we clearly see possible applications for microbubbles in food. We reported about directions for possible further research.

    In this work we made significant progress in understanding the interactions in the microbubble shell and their relation to microbubble stability. We also advanced in comprehension towards possible applications of microbubbles in food.

    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.
    Evaluation of ecosystem-based marine management strategies based on risk assessment
    Piet, G.J. ; Jongbloed, R.H. ; Knights, A.M. ; Tamis, J.E. ; Paijmans, A.J. ; Sluis, M.T. van der; Vries, P. de; Robinson, L.A. - \ 2015
    Biological Conservation 186 (2015). - ISSN 0006-3207 - p. 158 - 166.
    fisheries management - new-zealand - vulnerability - support - areas - south - pressure - context - threats - number
    This study presents a comprehensive and generic framework that provides a typology for the identification and selection of consistently defined ecosystem-based management measures and allows a coherent evaluation of these measures based on their performance to achieve policy objectives. The performance is expressed in terms of their reduction of risk of an adverse impact on the marine ecosystem. This typology consists of two interlinked aspects of a measure, i.e. the “Focus” and the “Type”. The “Focus” is determined by the part of the impact chain (Driver–Pressure–State) the measure is supposed to mitigate or counteract. The “Type” represents the physical measure itself in terms of how it affects the impact chain directly; we distinguish Spatio-temporal distribution controls, Input and Output controls, Remediation and Restoration measures. The performance of these measures in terms of their reduction in risk of adverse impacts was assessed based on an explicit consideration of three time horizons: past, present and future. Application of the framework in an integrated management strategy evaluation of a suite of measures, shows that depending on the time horizon, different measures perform best. “Past” points to measures targeting persistent pressures (e.g. marine litter) from past activities. “Present” favors measures targeting a driver (e.g. fisheries) that has a high likelihood of causing adverse impacts. “Future” involves impacts that both have a high likelihood of an adverse impact, as well as a long time to return to pre-impacted condition after the implementation of appropriate management, e.g. those caused by permanent infrastructure or persistent pressures such as marine litter or specific types of pollution.
    A step-wise process of decision-making under uncertainty when implementing environmental policy
    Knights, A.M. ; Culhane, F. ; Hussain, S.S. ; Papadopoulou, K.N. ; Piet, G.J. ; Raakaer, J. ; Rogers, S.I. ; Robinson, L.A. - \ 2014
    Environmental Science & Policy 39 (2014). - ISSN 1462-9011 - p. 56 - 64.
    climate-change - north-atlantic - change impacts - management - systems - biodiversity - ecosystems - pressure - diversity - support
    An ecosystem approach forms the basis of many recent environmental policies. The underlying concept states that decision-makers must consider the environmental, social and economic costs and benefits in the course of deciding whether to implement a management action. Decision-making can be undermined by uncertainty. Here, we discuss potential sources of uncertainty and their effect on an ecosystem approach-driven environmental policy, the factors affecting the choice and potential for management actions to achieve their objectives, the challenges associated with setting realistic and achievable targets, and how we can prioritise management of detrimental activities. We also consider how human challenges such as the availability of infrastructure and political will and ways of measuring costs and benefits and Member State interactions could also undermine environmental management. Potential limitations along with areas where further effort may be required to support ecosystem-based management objectives are highlighted and the advantages of a structured step-wise interdisciplinary approach to ecosystem management is shown. (C) 2014 Elsevier Ltd. All rights reserved.
    Origin of Water Loss from Soy Protein Gels
    Urbonaite, V. ; Jongh, H.H.J. de; Linden, E. van der; Pouvreau, L.A.M. - \ 2014
    Journal of Agricultural and Food Chemistry 62 (2014)30. - ISSN 0021-8561 - p. 7550 - 7558.
    blood-plasma gels - holding capacity - isolate gels - gellan gels - microstructure - pressure - behavior - whey - ph
    Water holding (WH) of soy protein gels was investigated to identify which length scales are most contributing to WH when centrifugal forces are applied. More specifically, it was attempted to differentiate between the contributions of submicron and supramicron length scales. MgSO4 and MgCl2 salt specificities on soy protein aggregation (submicron contribution) were used to create different gel morphologies (supramicron contribution). Obtained results showed that the micrometer length scale is the most important contribution to WH of gels under the applied deformation forces. WH of soy protein gels correlated negatively with Young?s modulus and positively with recoverable energy. The occurrence of rupture events had only a limited impact on WH. The ease by which water may be removed from the gel, but not the total amount, seemed to be related to the initial building block size. These insights could be exploited in product development to predict and tune oral perception properties of (new) products.
    Partly replacing meat protein with soy protein alters insulin resistance and blood lipids in postmenopausal women with abdominal obesity
    Nielen, M. van; Feskens, E.J.M. ; Rietman, A. ; Siebelink, E. ; Mensink, M.R. - \ 2014
    The Journal of Nutrition 144 (2014)9. - ISSN 0022-3166 - p. 1423 - 1429.
    randomized controlled-trials - metabolic syndrome - isoflavone supplementation - dietary-protein - elderly-women - weight-loss - metaanalysis - pressure - health - cholesterol
    Increasing protein intake and soy consumption appear to be promising approaches to prevent metabolic syndrome (MetS). However, the effect of soy consumption on insulin resistance, glucose homeostasis, and other characteristics of MetS is not frequently studied in humans. We aimed to investigate the effects of a 4-wk strictly controlled weight-maintaining moderate high-protein diet rich in soy on insulin sensitivity and other cardiometabolic risk factors. We performed a randomized crossover trial of 2 4-wk diet periods in 15 postmenopausal women with abdominal obesity to test diets with 22 energy percent (En%) protein, 27 En% fat, and 50 En% carbohydrate. One diet contained protein of mixed origin (mainly meat, dairy, and bread), and the other diet partly replaced meat with soy meat analogues and soy nuts containing 30 g/d soy protein. For our primary outcome, a frequently sampled intravenous glucose tolerance test (FSIGT) was performed at the end of both periods. Plasma total, LDL, and HDL cholesterol, triglycerides, glucose, insulin, and C-reactive protein were assessed, and blood pressure, arterial stiffness, and intrahepatic lipid content were measured at the start and end of both periods. Compared with the mixed-protein diet, the soy-protein diet resulted in greater insulin sensitivity [FSIGT: insulin sensitivity, 34 ± 29 vs. 22 ± 17 (mU/L)-1 · min-1, P = 0.048; disposition index, 4974 ± 2543 vs. 2899 ± 1878, P = 0.038; n = 11]. Total cholesterol was 4% lower after the soy-protein diet than after the mixed-protein diet (4.9 ± 0.7 vs. 5.1 ± 0.6 mmol/L, P = 0.001), and LDL cholesterol was 9% lower (2.9 ± 0.7 vs. 3.2 ± 0.6 mmol/L, P = 0.004; n = 15). Thus, partly replacing meat with soy in a moderate high-protein diet has clear advantages regarding insulin sensitivity and total and LDL cholesterol. Therefore, partly replacing meat products with soy products could be important in preventing MetS. This trial was registered at as NCT01694056.
    Autogenerative high pressure digestion : biogass production and upgrading in a single step
    Lindeboom, R.E.F. - \ 2014
    Wageningen University. Promotor(en): Jules van Lier, co-promotor(en): Jan Weijma; Caroline Plugge. - Wageningen : Wageningen University - ISBN 9789461738608 - 208
    biogas - spijsvertering - druk - methaanproductie - kooldioxide - zetmeel - hydrolyse - biogas - digestion - pressure - methane production - carbon dioxide - starch - hydrolysis
    Multiphysics pore-scale model for the rehydration of porous foods
    Sman, R.G.M. van der; Vergeldt, F.J. ; As, H. van; Dalen, G. van; Voda, A. ; Duynhoven, J.P.M. van - \ 2014
    Innovative Food Science and Emerging Technologies 24 (2014). - ISSN 1466-8564 - p. 69 - 79.
    moisture transport - mass-transfer - water - imbibition - quality - media - pressure - lattice - liquid - fruits
    In this paper we present a pore-scale model describing the multiphysics occurring during the rehydration of freeze-dried vegetables. This pore-scale model is part of a multiscale simulation model, which should explain the effect of microstructure and pre-treatments on the rehydration rate. Simulation results are compared to experimental data, obtained by MRI and XRT. Time scale estimates based on the pore-scale model formulation agree with the experimental observations. Furthermore, the pore-scale simulation model provides a plausible explanation for the strongly increased rehydration rate, induced by the blanching pre-treatment. Industrial relevance The increased insight in the physical processes governing the rehydration of porous or freeze-dried foods gives more rationale for optimizing all processing steps. Industry is seeking for means to give dried fruits and vegetables more convenience, but also higher quality concerning health and texture. This study shows that blanching pretreatment prior to freeze-drying strongly enhances the rehydration, while the loss of nutrients is hardly affected.
    Financial viability of soil and water conservation technologies in northwestern Ethiopian highlands
    Teshome, Akalu ; Rolker, D. ; Graaff, J. de - \ 2013
    Applied Geography 37 (2013). - ISSN 0143-6228 - p. 139 - 149.
    cost-benefit-analysis - land degradation - bench terraces - adoption - pressure - erosion
    Soil erosion by water is a major threat to food security, environmental sustainability and prospects for rural development in Ethiopia. Successive governments have promoted various soil and water conservation (SWC) measures in order to reduce the effects of land degradation, but adoption rates vary considerably. The profitability of SWC measures is an essential condition for their adoption. The objective of this research was to determine the economic efficiency of three different types of SWC technologies (soil bunds, stone bunds and fanya juu) in the watersheds of Debre Mewi and Anjeni in the northwestern Ethiopian highlands. A farm household survey was carried out among 60 farmers in both watersheds and the Universal Soil Loss Equation (USLE) was used to assess erosion risk on farmers' fields. A cost-benefit analysis (CBA) was then carried out to determine the profitability of the measures under different conditions. Erosion estimates for the fields suggest that adapted SWC structures were successful in reducing soil erosion. The cost-benefit analysis indicates that all SWC measures are profitable under ‘standard’ conditions, except soil bunds in Anjeni without grass cover. However, the study shows that different underlying assumptions change the CBA results considerably and consequently also change the conclusions regarding circumstances under which SWC measures are or are not profitable. This illustrates the volatility of the profitability of SWC measures.
    Thermal Plasma Synthesis of Superparamagnetic Iron Oxide Nanoparticles
    Lei, P.Y. ; Boies, A.M. ; Calder, S.A. ; Girshick, S.L. - \ 2012
    Plasma Chemistry and Plasma Processing 32 (2012)3. - ISSN 0272-4324 - p. 519 - 531.
    multifunctional magnetic nanoparticles - gamma-fe2o3 nanoparticles - biomedical applications - particle-size - flow reactor - rf plasma - flame - arc - pressure - functionalization
    Superparamagnetic iron oxide nanoparticles were synthesized by injecting ferrocene vapor and oxygen into an argon/helium DC thermal plasma. Size distributions of particles in the reactor exhaust were measured online using an aerosol extraction probe interfaced to a scanning mobility particle sizer, and particles were collected on transmission electron microscopy (TEM) grids and glass fiber filters for off-line characterization. The morphology, chemical and phase composition of the nanoparticles were characterized using TEM and X-ray diffraction, and the magnetic properties of the particles were analyzed with a vibrating sample magnetometer and a magnetic property measurement system. Aerosol at the reactor exhaust consisted of both single nanocrystals and small agglomerates, with a modal mobility diameter of 8-9 nm. Powder synthesized with optimum oxygen flow rate consisted primarily of magnetite (Fe3O4), and had a room-temperature saturation magnetization of 40.15 emu/g, with a coercivity and remanence of 26 Oe and 1.5 emu/g, respectively
    Wetting of solid surfaces: Fundamentals and charge effects
    Koopal, L.K. - \ 2012
    Advances in Colloid and Interface Science 179-182 (2012). - ISSN 0001-8686 - p. 29 - 42.
    contact-angle saturation - cationic surfactants - aqueous interfaces - vapor adsorption - wettability - model - particles - pressure - dynamics - silica
    Wetting is important when solids are brought in contact with a liquid and for movement of micro-drops on solids. The Young equation that describes the wetting of a solid and the relations between adhesion and wetting and vapor adsorption and wetting are discussed first. The characterization of low-energy surfaces is discussed as these surfaces are important for electrowetting on a dielectric (EWOD) and the characterization methods reveal that both dispersion and acid–base interactions are important for wetting. Surfactant solutions are very suitable for modifying the wetting behavior; the distinct differences between low- and high-energy surfaces in relation to surfactant adsorption are discussed. The effects of surface charges on the wetting behavior are considered for both adsorbed charges and charges due to an applied electric potential (electrowetting). The physical interpretation of Young-Lippmann equation, which describes EWOD, is critically examined and contact angle saturation is briefly discussed.
    Conservation Agriculture in mixed crop–livestock systems: Scoping crop residue trade-offs in Sub-Saharan Africa and South Asia
    Valbuena, D.F. ; Erenstein, O. ; Homann-Kee Tui, S. ; Abdoulaye, T. ; Claessens, L.F.G. ; Duncan, A.J. ; Gerard, B. ; Rufino, M. ; Teufel, N. ; Wijk, M.T. van - \ 2012
    Field Crops Research 132 (2012). - ISSN 0378-4290 - p. 175 - 184.
    smallholder farming systems - soil fertility management - pressure - food - productivity - strategies - community - dynamics - patterns - zimbabwe
    Conservation Agriculture (CA) is being advocated to enhance soil health and sustain long term crop productivity in the developing world. One of CA's key principles is the maintenance of soil cover often by retaining a proportion of crop residues on the field as mulch. Yet smallholder crop–livestock systems across Africa and Asia face trade-offs among various options for crop residue use. Knowledge of the potential trade-offs of leaving more residues as mulch is only partial and the objective of this research is to address some of these knowledge gaps by assessing the trade-offs in contrasting settings with mixed crop–livestock systems. The paper draws from village surveys in 12 sites in 9 different countries across Sub-Sahara Africa and South Asia. Sites were clustered into 3 groups along the combined population and livestock density gradients to assess current crop residue management practices and explore potential challenges to adopting mulching practices in different circumstances. Results show that although high-density sites face higher potential pressure on resources on an area basis, biomass production tends to be more substantial in these sites covering demands for livestock feed and allowing part of the residues to be used as mulch. In medium-density sites, although population and livestock densities are relatively lower, biomass is scarce and pressure on land and feed are high, increasing the pressure on crop residues and their opportunity cost as mulch. In low-density areas, population and livestock densities are relatively low and communal feed and fuel resources exist, resulting in lower potential pressure on residues on an area basis. Yet, biomass production is low and farmers largely rely on crop residues to feed livestock during the long dry season, implying substantial opportunity costs to their use as mulch. Despite its potential benefit for smallholder farmers across the density gradient, the introduction of CA-based mulching practices appears potentially easier in sites where biomass production is high enough to fulfil existing demands for feed and fuel. In sites with relatively high feed and fuel pressure, the eventual introduction of CA needs complementary research and development efforts to increase biomass production and/or develop alternative sources to alleviate the opportunity costs of leaving some crop residues as mulch.
    VMStools: Open-source software for the processing, analysis and visualisation of fisheries logbook and VMS data
    Hintzen, N.T. ; Bastardie, F. ; Beare, D.J. ; Piet, G.J. ; Ulrich, C. ; Deporte, N. ; Egekvist, J. ; Degel, H. - \ 2012
    Fisheries Research 115-116 (2012). - ISSN 0165-7836 - p. 31 - 43.
    fishing effort - management strategies - high-resolution - giant petrels - catch - sea - pressure - patterns - impact - scale
    VMStools is a package of open-source software, build using the freeware environment R, specifically developed for the processing, analysis and visualisation of landings (logbooks) and vessel location data (VMS) from commercial fisheries. Analyses start with standardized data formats for logbook (EFLALO) and VMS (TACSAT), enabling users to conduct a variety of analyses using generic algorithms. Embedded functionality handles erroneous data point detection and removal, métier identification through the use of clustering techniques, linking logbook and VMS data together in order to distinguish fishing from other activities, provide high-resolution maps of both fishing effort and -landings, interpolate vessel tracks, calculate indicators of fishing impact as listed under the Data Collection Framework at different spatio-temporal scales. Finally data can be transformed into other existing formats, for example to populate regional databases like FishFrame. This paper describes workflow examples of these features while online material allows a head start to perform these analyses. This software incorporates state-of-the art VMS and logbook analysing methods standardizing the process towards obtaining pan-European, or even worldwide indicators of fishing distribution and impact as required for spatial planning. --------------------------------------------------------------------------------
    Effect of conventional chemical treatment on the microbial population in a biofouling layer of reverse osmosis systems
    Bereschenko, L.A. ; Prummel, H. ; Euverink, G.J.W. ; Stams, A.J.M. ; Loosdrecht, M.C.M. van - \ 2011
    Water Research 45 (2011)2. - ISSN 0043-1354 - p. 405 - 416.
    biofilm formation - sphingomonas-paucimobilis - community structure - membrane systems - exopolysaccharide - bacterium - pressure
    The impact of conventional chemical treatment on initiation and spatiotemporal development of biofilms on reverse osmosis (RO) membranes was investigated in situ using flow cells placed in parallel with the RO system of a full-scale water treatment plant. The flow cells got the same feed (extensively pre-treated fresh surface water) and operational conditions (temperature, pressure and membrane flux) as the full-scale installation. With regular intervals both the full-scale RO membrane modules and the flow cells were cleaned using conventional chemical treatment. For comparison some flow cells were not cleaned. Sampling was done at different time periods of flow cell operation (i.e., 1, 5, 10 and 17 days and 1, 3, 6 and 12 months). The combination of molecular (FISH, DGGE, clone libraries and sequencing) and microscopic (field emission scanning electron, epifluorescence and confocal laser scanning microscopy) techniques made it possible to thoroughly analyze the abundance, composition and 3D architecture of the emerged microbial layers. The results suggest that chemical treatment facilitates initiation and subsequent maturation of biofilm structures on the RO membrane and feed-side spacer surfaces. Biofouling control might be possible only if the cleaning procedures are adapted to effectively remove the (dead) biomass from the RO modules after chemical treatment
    Impact of sorbic acid on germinant receptor-dependent and -independent germination pathways in Bacillus cereus
    Melis, C.C.J. van; Nierop Groot, M.N. ; Abee, T. - \ 2011
    Applied and Environmental Microbiology 77 (2011)7. - ISSN 0099-2240 - p. 2552 - 2554.
    subtilis spores - bacterial-spores - dipicolinic acid - pressure - inhibition - atcc-14579 - sorbate - ph
    Amino acid- and inosine-induced germination of Bacillus cereus ATCC 14579 spores was reversibly inhibited in the presence of 3 mM undissociated sorbic acid. Exposure to high hydrostatic pressure, Ca-dipicolinic acid (DPA), and bryostatin, an activator of PrkC kinase, negated this inhibition, pointing to specific blockage of signal transduction in germinant receptor-mediated germination.
    Front-of-Pack Nutrition Labels: Their Effect on Attention and Choices when Consumers have Varying Goals and Time Constraints
    Herpen, E. van; Trijp, J.C.M. van - \ 2011
    Appetite 57 (2011)1. - ISSN 0195-6663 - p. 148 - 160.
    visual-attention - eye-movements - food choice - information - impact - product - formats - supermarket - motivation - pressure
    Although front-of-pack nutrition labeling can help consumers make healthier food choices, lack of attention to these labels limits their effectiveness. This study examines consumer attention to and use of three different nutrition labeling schemes (logo, multiple traffic-light label, and nutrition table) when they face different goals and resource constraints. To understand attention and processing of labels, various measures are used including self-reported use, recognition, and eye-tracking measures. Results of two experiments in different countries show that although consumers evaluate the nutrition table most positively, it receives little attention and does not stimulate healthy choices. Traffic-light labels and especially logos enhance healthy product choice, even when consumers are put under time pressure. Additionally, health goals of consumers increase attention to and use of nutrition labels, especially when these health goals concern specific nutrients
    Improved estimation of trawling tracks using cubic Hermite spline interpolation of position registration data
    Hintzen, N.T. ; Piet, G.J. ; Brunel, T.P.A. - \ 2010
    Fisheries Research 101 (2010). - ISSN 0165-7836 - p. 108 - 115.
    monitoring-system data - southern north-sea - benthic communities - impact - disturbance - resolution - pressure - scale - indicators - management
    For control and enforcement purposes, all fishing vessels operating in European waters are equipped with satellite-based Vessel Monitoring by Satellite systems (VMS) recording their position at regular time intervals. VMS data are increasingly used by scientists to study spatial and temporal patterns of fishing activity and thus fishing impact (e.g. surface of sea bed trawled during a fishing trip). However, due to their low resolution (2 h basis), these data may provide a biased perception of fishing impact. We present here a method aiming at interpolating vessel trajectories from VMS data points to obtain higher-resolution data on vessel trajectories which in turn should provide improved estimates of the spatial and temporal patterns of fishing activity and hence fishing impact. This method is based on a spline interpolation technique, the cubic Hermite spline (cHs), using position, heading and speed to interpolate the trawl track of a vessel between two succeeding VMS data points. To take uncertainty of the interpolated track into account, the method also determines a confidence interval, which represents the spatial distribution of vessel presence probability between two successive VMS positions. The cHs method was compared to the straight line interpolation technique using a reference data set with intervals of 6 min which was assumed to represent the real trawl tracks. The results showed that the cHs method approximates the real trawl track markedly better than a straight line interpolation. The cHs method should therefore be preferred to the conventional straight line approach to interpolate vessel tracks in studies aiming at estimating fishing impact from VMS data.
    Natura 2000 sites and fisheries in German offshore waters
    Pedersen, S.A. ; Fock, H. ; Krause, J. ; Pusch, C. ; Sell, A.L. ; Bottcher, U. ; Rogers, S.I. ; Skold, M. ; Skov, H. ; Podolska, M. ; Piet, G.J. ; Rice, J.C. - \ 2009
    ICES Journal of Marine Science 66 (2009)1. - ISSN 1054-3139 - p. 155 - 169.
    monitoring-system data - harbor porpoises - impacts - disturbance - north - communities - population - habitats - pressure - sea
    The principal objective of sites selected as part of Natura 2000 is to achieve or maintain a favourable conservation status of habitats and species named in the EU Birds and Habitats directives. In the German exclusive economic zone, the habitat types protected by this legislation are sandbanks and reefs; protected species include marine mammals, seabirds, and specific migratory fish species. The ICES project Environmentally Sound Fishery Management in Protected Areas (EMPAS) aims to answer two questions: (i) To what extent do specific fishing activities significantly threaten attainment of the conservation objectives of the Natura 2000 sites? (ii) What management measures would reduce these conflicts and how effective would they be at helping to ensure the favourable condition of these sites? Assessments of fishing impacts on Natura 2000 sites require basic data on the conservation status of individual habitats and species, as well as data for fine-scale distributions of ongoing fishing activities. This paper describes and discusses the process used by the EMPAS project in developing fishery-management plans for each Natura 2000 site in German offshore waters.
    Aphid watery saliva counteracts sieve-tube occlusion: a universal phenomenon?
    Will, T. ; Kornemann, S.R. ; Furch, A.C.U. ; Tjallingii, W.F. ; Bel, A.J.E. van - \ 2009
    Journal of Experimental Biology 212 (2009). - ISSN 0022-0949 - p. 3305 - 3312.
    companion cell - phloem - element - plant - pressure - proteins - translocation - penetration - acquisition - acceptance
    Ca2+-binding proteins in the watery saliva of Megoura viciae counteract Ca2+-dependent occlusion of sieve plates in Vicia faba and so prevent the shut-down of food supply in response to stylet penetration. The question arises whether this interaction between aphid saliva and sieve-element proteins is a universal phenomenon as inferred by the coincidence between sieve-tube occlusion and salivation. For this purpose, leaf tips were burnt in a number of plant species from four different families to induce remote sieve-plate occlusion. Resultant sieve-plate occlusion in these plant species was counteracted by an abrupt switch of aphid behaviour. Each of the seven aphid species tested interrupted its feeding behaviour and started secreting watery saliva. The protein composition of watery saliva appeared strikingly different between aphid species with less than 50% overlap. Secretion of watery saliva seems to be a universal means to suppress sieve-plate occlusion, although the protein composition of watery saliva seems to diverge between species.
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