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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    Electrically excited liquid water : lessons from floating water bridge
    Wexler, A.D. - \ 2016
    Wageningen University. Promotor(en): Cees Buisman, co-promotor(en): J. Woisetschläger; E.C. Fuchs. - Wageningen : Wageningen University - ISBN 9789462577039 - 223
    water - liquids - electric field - thermodynamics - bridges - equilibrium - disequilibrium - electrodynamics - nuclear magnetic resonance - neutron scattering - infrared spectroscopy - spectroscopy - gas chromatography - electrical conductivity - interferometry - spectral analysis - physics - water - vloeistoffen (liquids) - elektrisch veld - thermodynamica - bruggen - evenwicht - verstoord evenwicht - elektrodynamica - kernmagnetische resonantie - neutronenverstrooiing - infraroodspectroscopie - spectroscopie - gaschromatografie - elektrische geleidbaarheid - interferometrie - spectraalanalyse - fysica

    Water is essential to a healthy and secure world. Developing new technologies which can take full advantage of the unique attributes of water is important for meeting the ever increasing global demand while reducing the production footprint. Water exhibits unexpected departures in more than 70 physical and chemical properties compared to other molecular species of similar chemical composition. The principal cause for this behavior is ascribed to the large number of hydrogen bonds which form between neighboring water molecules. Hydrogen bonds are moderately strong in water and exhibit both electrostatic as well as covalent character. When examining the liquid state these interactions play a significantly role in moderating the interchange between dynamics and structure. In disordered materials such as a liquid there are three length scales of importance: 1) at the microscopic molecular level interactions dominate, 2) the macroscopic level where classical forces act upon the statistically isotropic medium, and 3) the mesoscopic level where heterogeneous interactions dominate through evolving transient structures each with unique dynamical behaviors. The mesoscale is important to most environmental and biological processes and is even more poorly understood than the liquid state in general. The aim of this thesis is to explore the extended molecular behavior of liquid water excited by strong electric field gradients.

    The floating water bridge belongs to a larger class of phenomena called electrohydrodynamic (EHD) liquid bridges. These self-suspending liquid catenaries can occur in a number of polar liquids provided the conductivity is low. They exhibit elevated temperatures and bidirectional flow patterns, as well as sub-Hz diameter oscillations. The flow behavior and dynamics of these bridges is complex but can be addressed by continuum level EHD theory. The polarizing effect of the electric field gradient accelerates the fluid tangentially along the surface resulting in a Taylor pump which supplies the bridge with liquid. The free hanging section is stable against gravity within a band of operational parameters whereby the electric field strength is sufficient confine fluid elements within the bridge. A standardized protocol for operating stable EHD bridges in multiple configurations is developed and presented. This is the primary tool used throughout the thesis and provides a macroscopic object for the experimental examination of how forces which typically only occur over a few nanometers in nature affect the organization of polar liquids, notably water. In order to examine the role that the electric field gradient plays in the observed molecular changes found in EHD bridges a simple point-plane electrode system was also employed.

    There are available a number of tools which provide complimentary information on chemical and physical processes occurring in the liquid state. A brief introduction is given on the interaction between electromagnetic waves and matter with respect to field theory and methods from atomic physics. The basis for interaction over different length scales is established. Electrochemical characterization includes the quantification and identification of the charge carrying species present, the relative proton concentration, and the complex dielectric response. The vibrational and rotational motion of molecules is measured with a combination of infrared emission spectroscopy and imaging and permits the detection of both the thermal bath and non-equilibrium molecular excited states. The local structure of the liquid matter contained in the bridge can be elucidated through the methods discussed here. X-rays provide information on the electron density whereas neutrons reveal nuclear positions. Together with isotope substitution a complete picture of the motionally averaged local structure of the liquid in the bridge can be recovered. QENS is a special case of inelastic scattering which permits the measurement of diffusion, relaxation, and other slow energy or mass transfer modes in materials using a time-of-flight spectrometer. This data compliments the NMR methods used herein specifically to probe the environment of protons in the system; and to provide clues about the strength of both intra- intermolecular coupling in the system. Very small perturbations in the optical properties of a liquid can be detected using interferometry; these ultimately reflect changes in the polarizability of the liquid which can arise from changes in physical properties. Raman scattering is an inelastic method which can probe changes to the polarizability of a liquid that reflect shifts in the local molecular environment and can be used to determine both local and non-local vibrational coupling.

    Magnetic resonance imaging was used to track the flow field present in the bridge without the use of tracer particles; revealing that the bridge has a layered structure, with distinct flow regimes lying one on top of the other. Investigation of the electrochemistry in the water bridge found that protons account for 87% of the charge transport in the bridge. Impedance spectroscopy and pH measurement corroborate the finding that a proton gradient forms across the entire system. The results from elastic neutron and X-ray scattering reveal that the static structure is unchanged within the given accuracy of the employed measurements. However, the systematic analysis of the data using a reverse Monte Carlo computer simulation revealed significant dynamical changes that are reliable above the limited instrument precision. The imposed electric field of an EHD bridge distorts the local Coulombic interactions between molecules altering the dielectric relaxation pathway so that it becomes more favorable for the absorbed energy to become trapped locally for a longer period of time. The electric field in the bridge system is not uniform. Strong field gradients are present which stimulate changes in the molecular polarizability, generating gradients of physical properties, and restricting the allowed rotational-vibrational relaxation transitions. These trends are comparable to those from ultrafast relaxation measurements where the vibrational lifetime of the OH stretch of HDO was found to be significantly shorter in the bridge than in the neat liquid. This absorbed energy, however, remained trapped in a local intermediate state longer in the bridge before being released as a thermal perturbation. The nuclear relaxation dynamics in a glycerol bridge showed similar behavior where the transverse and longitudinal magnetization lifetimes diverged from the expectation values given the systems temperature.

    From the experimental observations several features of electrically excited water appear. At the gross continuum level the operation of a floating water bridge results in the production of a charge imbalance between anolyte and catholyte. This is in part due to the enhanced proton mobility in the bridge. Protons no longer are confined to the hydrogen bond mediated Grotthuss mechanism but can travel even faster through a delocalized state. This means that charge can be pumped faster than it can be neutralized resulting in the observed electrochemical differences. The energy level of protons in the conduction channel is the difference between the ground and excited state levels observed as a non-thermal emission feature in the mid-infrared. The proton channel will be active over relatively short distances and will experience interruptions due to fluctuations in molecular position driven by local force gradients. These channels are localized and discontinuous providing the physical basis for the onset of mesoscale dynamic heterogeneity in the excited liquid. The picture begins to emerge whereby local trapping states and long-range cooperative coupling modes dynamically exchange energy. The energy exchange is far from equilibrium and supports multiple transfer mechanisms. At the mesoscale the excited state exhibits traits of a chaotic dynamical system and provides a varied energetic landscape whereby rotational-vibrational transition dipoles, nuclear spin states, and thermodynamic potentials, such as the configurational entropy, non-adiabatically – that is there is a pumping of heat in response to the induced fluctuating gradient fields. The transfer of perturbations from local to collective modes and vice versa requires that the chemical, thermal, and electromagnetic potentials present in the molecular milieu be linked to the entropy production.

    This early foray into the non-equilibrium dynamics and mesoscale organization of electrically excited liquid water opens an opportunity to develop technologies which better mimic nature. Taking biological systems as the exemplary standard by which to compare it is necessary to develop soft matter based technical systems which take advantage of the link between electric, magnetic, and thermal fields to drive chemical and physical processes with higher efficiency. Water, as well as other polar liquids, can be locally controlled so as to induce spatial variation in the chemical potential whereby one can imagine a reactor where disparate physical or chemical process can occur in close proximity without the need for rigid segregating structures. Furthermore, this level of control is dynamical such that the organization of the partitioning in the liquid can be changed in time so that the total energy requirement of the intended process is optimized. With such an approach it is conceivable that the size, complexity, and energetic costs of performing many industrial and municipal processes can be reduced. Rather than treating liquids as bulk fluids the opportunity presents itself to use the internal structure and dynamics of liquids to build fluid technologies.

    In Vitro Fermentation of Porcine Milk Oligosaccharides and Galacto-oligosaccharides Using Piglet Fecal Inoculum
    Difilippo, Elisabetta ; Pan, Feipeng ; Logtenberg, Madelon ; Willems, Rianne ; Braber, Saskia ; Fink-Gremmels, Johanna ; Schols, Henk A. ; Gruppen, Harry - \ 2016
    Journal of Agricultural and Food Chemistry 64 (2016)10. - ISSN 0021-8561 - p. 2127 - 2133.
    fibers - gas chromatography - human fermentation - liquid chromatography - nondigestible carbohydrates - organic acids - short-chain fatty acids - sugars

    In this study, the in vitro fermentation by piglet fecal inoculum of galacto-oligosaccharides (GOS) and porcine milk oligosaccharides (PMOs) was investigated to identify possible preferences for individual oligosaccharide structures by piglet microbiota. First, acidic PMOs and GOS with degrees of polymerization 4-7 were depleted within 12 h of fermentation, whereas fucosylated and phosphorylated PMOs were partially resistant to fermentation. GOS structures containing β1-3 and β1-2 linkages were preferably fermented over GOS containing β1-4 and β1-6 linkages. Upon in vitro fermentation, acetate and butyrate were produced as the main organic acids. GOS fermentation by piglet inoculum showed a unique fermentation pattern with respect to preference of GOS size and organic acids production.

    Health monitoring of plants by their emitted volatiles: trichome damage and cell membrane damage are detectable at greenhouse scale
    Jansen, R.M.C. ; Hofstee, J.W. ; Wildt, J. ; Verstappen, F.W.A. ; Bouwmeester, H.J. ; Posthumus, M.A. ; Henten, E.J. van - \ 2009
    Annals of Applied Biology 154 (2009)3. - ISSN 0003-4746 - p. 441 - 452.
    gewasbescherming - monitoring - vluchtige verbindingen - gaschromatografie - massaspectrometrie - solanum lycopersicum - tomaten - gewasmonitoring - glastuinbouw - plant protection - monitoring - volatile compounds - gas chromatography - mass spectrometry - solanum lycopersicum - tomatoes - crop monitoring - greenhouse horticulture - reaction mass-spectrometry - organic-compounds - gas-chromatography - methyl salicylate - leaf volatiles - cotton plants - voc emissions - jasmonic acid - tomato - herbivory
    Pathogen attack and herbivore infestation have a major impact on plant health. In a model study, these two plant health issues were simulated to study whether plant health can be monitored at greenhouse scale through the analysis of volatile organic compounds (VOCs) in greenhouse atmosphere. To simulate pathogen attack and herbivore infestation, we repeatedly stroked the stems of tomato plants (Lycopersicon esculentum) and repeatedly removed their side shoots. In addition, we studied the effect of fruit picking on the concentration of plant-emitted VOCs in greenhouse atmosphere. Analysis of air samples obtained before these treatments revealed up to 17 VOCs that are known to be released from tomato plants, of which the most dominant one was the monoterpene ß-phellandrene. When plants were 7 weeks old, the concentration of this VOC was approximately 0.06 ppbv before treatment. When plants were 12 weeks old, this concentration was raised to approximately 0.14 ppbv. Stroking of the stems, removing the side shoots and fruit picking resulted in an increase in the concentrations of all mono- and most sesquiterpenes up to 60-fold, which was expected because these VOCs are well-known constituents of trichomes. The treatments did not result in substantially increased concentrations of the stress-related compounds ¿-copaene, methyl salicylate and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene. In contrast to stroking and fruit picking, shoot removal resulted in the emission of the lipoxygenase-derived product (Z)-3-hexenol in greenhouse atmosphere expressing cell membrane degradation. The findings presented in this paper focus on the feasibility of monitoring plant health through the analysis of VOCs in greenhouse air, but findings might also be relevant for atmospheric chemistry.
    NaOH-extractable organic matter of andic soils from Galicia (NW Spain) under different land use regimes: a pyrolysis GC/MS study
    Verde, J.R. ; Buurman, P. ; Martinez-Cortizas, A. ; Macias, F. ; Camps Arbestain, M. - \ 2008
    European Journal of Soil Science 59 (2008)6. - ISSN 1351-0754 - p. 1096 - 1110.
    polycyclic aromatic-hydrocarbons - ionization mass-spectrometry - volcanic ash soils - gas chromatography - humic substances - forest soil - acids - carbon - decomposition - preservation
    The objective of this study was to determine to what extent the attenuation or loss of andic soil properties caused by land use change ¿ from forest (FOR, average C content 118.2 ± 23.7 g kg¿1) to agricultural land (AGR, average C content 55.7 ± 16.7 g kg¿1) use ¿ is reflected in soil organic matter (SOM) at the molecular level. For this, NaOH-extractable SOM of A horizons from 17 soils developed on amphibolitic parent material in NW Spain was studied by pyrolysis gas chromatography spectrometry (Py-GC/MS). We also included two buried andic A horizons (PAL, 2200 cal yr BP in age) on the same parent material, as a reference for the molecular composition of SOM from soils without recent litter additions. Organic matter of PAL soils had a composition largely different from that of superficial soils (FOR and AGR), with an important relative contribution of microbial polysaccharides and N-compounds, and an absence of compounds that characterize fresh plant litter (e.g. lignins). In the superficial soils, the relative contribution of lignin-derived compounds was greater in AGR than in FOR soils. Differences were also observed in the relative contribution of aliphatic compounds, FOR soils being enriched in this type of components compared with AGR soils. The results indicated that land use change from FOR to AGR, which was accompanied by a decrease in total SOM, resulted in an enrichment in primary SOM. The smaller relative abundance of primary SOM derivatives in andic FOR soils indicates that these compounds were quickly degraded in Andisols
    Soil organic matter chemistry in allophanic soils: a pyrolysis-GC/MS study of a Costa Rican Andosol catena
    Buurman, P. ; Peterse, F. ; Almendros Martin, G. - \ 2007
    European Journal of Soil Science 58 (2007)6. - ISSN 1351-0754 - p. 1330 - 1347.
    chromatography-mass-spectrometry - volcanic ash soils - rothamsted classical experiments - particle-size fractions - c-13 nmr-spectroscopy - humic substances - chemical-composition - gas chromatography - acid fraction - origin
    Soil organic matter (SOM) in allophanic soils is supposed to accumulate due to protection caused by binding to allophane, aluminium and iron. We investigated a catena of allophanic and non-allophanic soils in Costa Rica to determine the effect of such binding mechanisms on SOM chemistry. These soils contain no contribution of black carbon. Molecular characterization of litter, extractable and dispersed organic matter was done by Curie-point pyrolysis-GC/MS. The molecular chemistry of the organic fractions indicates a strong decomposition of plant-derived organic matter and a strong contribution of microbial sugars and N-compounds to SOM. Both the decomposition of plant-derived SOM ¿ including that of relatively recalcitrant compounds ¿ and the relative contribution of microbial SOM were greater in allophanic samples than in non-allophanic ones. This suggests that chemical protection does not act on primary OM, although it may influence the accumulation of secondary OM in these soils. The effect of allophane on SOM contents in such perhumid soils is probably through incorporation of decomposition products and microbial SOM in very fine aggregates that ¿ in a perhumid environment ¿ remain saturated with water during much of the year. Greater concentrations of aliphatics are found in allophanic residues, but there is no evidence of any specific mineral-organic binding. The results do not support the existing theory of chemical protection of plant-derived components through binding to allophane, iron and aluminium.
    Detectie van Phytophthora infestans in geïnfecteerd pootgoed door luchtanalyse
    Jansen, R.M.C. ; Hofstee, J.W. - \ 2007
    aardappelen - pootaardappelen - phytophthora infestans - ziektebestrijding - methodologie - gaschromatografie - spectrometrie - analytische methoden - potatoes - seed potatoes - phytophthora infestans - disease control - methodology - gas chromatography - spectrometry - analytical methods
    Onderzoek met traditionele gaschromatografie gekoppeld aan massaspectrometrie (GC-MS) voor identificatie van geurstoffen afkomstig van kunstmatig geïnfecteerd pootgoed en een evaluatie Biosensor set-up op basis van insectantenne
    New methods for the screening of antioxidants in three Sideritis species
    Koleva, I. - \ 2007
    Wageningen University. Promotor(en): Aede de Groot, co-promotor(en): Teris van Beek; Jozef Linssen. - [S.l.] : S.n. - ISBN 9789085046851 - 197
    antioxidanten - sideritis - chemische samenstelling - hplc - gaschromatografie - analytische scheikunde - antioxidants - sideritis - chemical composition - hplc - gas chromatography - analytical chemistry
    This thesis describes the rapid and robust evaluation of antioxidant activity of complex mixtures such as plant extracts. The study was directed to establish the best screening and isolation procedures for components with antioxidative properties to ensure the development of an “algorithm” for studying natural antioxidants. Three different screening methods (the b-carotene bleaching test (BCBT), the headspace GC method (HS-GC) and the off-line radical scavenging assay with the DPPH radical (DPPH method) and various extraction schemes were used. Three plants from the genus Sideritis grown in Bulgaria (S. scardica, S. syriaca and S. montana) served as test species. The strengths and limitations of each method were illustrated by testing a number of extracts of different polarity. A novel HPLC-DPPH method to rapidly and sensitively pinpoint individual antioxidants in complex mixtures with as little as possible fractionation procedures was developed. The use of the alternative ABTS·+ radical cation made the method in most cases even more sensitive. The instrumental set-up and physico-chemical parameters of both methods were studied. The methods were successful for qualitative and semi-quantitative measurements of pure antioxidants and extracts. A review is under preparation on the use of on-line methods. As a result, a range of flavonoid-, phenylpropanoid- and iridoid glycosides were isolated. The radical scavenging activity of the isolated compounds by off- and on-line DPPH methods was studied. Three novel compounds were isolated: flavonoid glycosides luteolin-4'-methylether-7-O-[6'''-O-acetyl-β-D-allopyranosyl-(1-2)-β-D-glucopyranoside and hypolaetin-4'-methylether-7-O-[β-D-allopyranosyl-(1-2)-6''-O-acetyl-β-D-glucopyranoside, and iridoid glycoside 3''-O-p-coumaroyl-6''-O-acetyl melittoside from Sideritis species. Preliminary studies by the HS-GC method were applied to investigate how Sideritis extracts and pure components would behave in real systems: bulk oils and oil-in-water emulsions. Conjugated dienes and hexanal formation were monitored using rosmarinic acid and BHT as standards. They showed good inhibitory effects with regard to dienes and hexanal formation in both test systems.
    Sensory and instrumental analysis of food aromas
    Bult, J.H.F. - \ 2006
    Wageningen University. Promotor(en): J.H.A. Kroeze; Fons Voragen, co-promotor(en): H.N.J. Schifferstein; J.P. Roozen. - [S.l.] : S.n. - ISBN 9789085045236 - 172
    aroma - aromatische verbindingen - geur en smaak - geurstoffen en smaakstoffen - zintuiglijke waarneming - sensorische evaluatie - gaschromatografie - aroma - aromatic compounds - flavour - flavour compounds - organolepsis - sensory evaluation - gas chromatography

    Food aromas are generally perceived as unitary aromas, i.e. fried potatoes smell like fried potatoes and roasted coffee smells like roasted coffee. Nonetheless, nearly all food aromas are produced by a multitude of volatile components that contribute to an extensive collection of aromas in various compositions. Of the hundreds of volatiles released from fried potatoes and roasted coffee a major se!ection does not produce an odour, many others do produce an odour that contributes to one of both aromas, many others contribute to both. In spite of this, food aromas are not being perceived as collections of discernable odours.

    Central theme of this thesis is a method used to fractionate, identify and characterise the odorous components in mixtures of odorants: gas chromatography olfactometry (GCO). GCO entails the pressurised transfer of volatiles through a capillary column, after capturing these from the headspace of a foodstuff. Since the column delays volatiles differentially, panellists may sniff these volatiles sequentially on their release from the capillary. This allows the separate sensory evaluation of components in the aroma mixture.

    A well-established practice in technological studies is that measurement reliability of instruments is estimated and minimised. Although sniffing panels are generally employed as instruments that assess the odour impact of chemical components in food aromas, reliability assessment is generally not applied to their application. Paradoxically, there are no practically available valid methods that may assess the reliability of panel responses. In addition, studies of systematic bias of panel responses in GCO studies are not available, although some common assumptions in GCO studies are not valid psychologically. For instance, intense odorants that arc qualitatively similar to the aroma quality are generally identified as character impact components. However, perception studies showed that odorants may affect (viz. suppress) each others odour contribution in a mixture. Therefore, assumptions regarding the contribution of singular odorants to aromas on basis of GCO, is premature.

    This thesis introduces methodology to estimate GCO response reliability and reports the empirical testing of this methodology (chapters 2, 3 and 4). In addition, several GCO assumptions considered psychologically disputable, are evaluated in empirical studies. These studies entail the effect of stimulus context on the estimated reliability of GCO results (chapter 4), the evaluation of the contribution of GCO-identified 'character impact components' to an apple model aroma (chapter 5), the effects of task instruction on the identification of odorants in food aromas (chapter 6), the effects of peri-threshold components on a supra-threshold food aroma (chapter 7) and the effects of sequentially presented odorants on their mutual odour intensities as a function of qualitative odour similarity (chapter 8). The general conclusions of this thesis are, that panel responses in the temporary absence of odorants must be used to estimate the reliability of panel odour detections, and that mechanisms that systematically affect response variation should be known and considered m GCO.

    TIE-studie van dioxine-achtige stoffen in zwevend stof en sediment met behulp van de DR-CALUX assay en gas chromatografie met time-of-flight massaspectrometrie
    Leonards, P.E.G. ; Veen, I. van der; Hesselingen, J.M. van - \ 2004
    onbekend : RIVO Milieu en Voedselveiligheid (RIVO rapport C076/04) - 12
    dioxinen - gaschromatografie - massaspectrometrie - dioxins - gas chromatography - mass spectrometry
    In dit onderzoek werd de toxiciteit van dioxine-achtige stoffen met behulp van de DR-CALUX assay van zwevend stof en sediment monsters bepaald.
    Baseline studie naar potentieel bioaccumuleerbare stoffen in oppervlaktewater
    Leonards, P.E.G. ; Barneveld, E. van - \ 2004
    onbekend : RIVO Milieu en Voedselveiligheid (RIVO rapport C065/04) - 9
    oppervlaktewater - afvoerwater - analytische methoden - gaschromatografie - bioaccumulatie - ecotoxicologie - surface water - effluents - analytical methods - gas chromatography - bioaccumulation - ecotoxicology
    Onderzoek werd uitgevoerd naar de bepaling van potentieel bioaccumuleerbare verbindingen (PBS) in influent, effluent en oppervlaktewateren uit Nederland. Hierbij werd gebruik gemaakt van SPME-extractie gecombineerd met een GC-FID/MS detectie. Kwantificering en het scheidend vermogen tussen gehalten was betrouwbaarder met FID dan met MS detectie. De aangetroffen PBS-gehalten in effluent en oppervlaktewater varieerden tussen de 0,7 en 3,8 mM en liggen lager dan de acute en chronische toxiciteitswaarden voor vis, watervlo en alg. Het RWZI influent PBS-gehalte was circa tien maal hoger dan in effluent en lag rond de acute narcotische toxiciteitwaarde voor watervlo. Als achtergrond gehalte in oppervlaktewater wordt 1 mM aangehouden.
    Polycyclische aromatische koolwaterstoffen (PAK'S) in diervoeders, dierlijke vetten, plantaardige oliën/vetten, vetzuren en dergelijke. deel 1 normstelling deel 2 meetmethoden
    Traag, W. ; Hoogenboom, L.A.P. ; Weg, G. van de; Baars, A.J. ; Schouten, T. - \ 2001
    Wageningen : RIKILT - 30
    polycyclische koolwaterstoffen - voedingsmiddelenwetgeving - hplc - gaschromatografie - massaspectrometrie - analytische scheikunde - Nederland - polycyclic hydrocarbons - food legislation - hplc - gas chromatography - mass spectrometry - analytical chemistry - Netherlands
    Studies towards the sex pheromone of the green capsid bug
    Drijfhout, F.P. - \ 2001
    Wageningen University. Promotor(en): A. de Groot; T.A. van Beek. - S.l. : S.n. - ISBN 9789058084088 - 152
    sexferomonen - lygocoris pabulinus - elektroantennogrammen - gaschromatografie - seizoengedrag - sex pheromones - lygocoris pabulinus - electroantennograms - gas chromatography - seasonal behaviour

    The green capsid bug, Lygocoris pabulinus (L.) (Heteroptera: Miridae) is a serious pest in fruit orchards, which is difficult to control. Because it is difficult to determine the actual population density, fruit growers apply insecticides against the green capsid bug on regular times to reduce the risk of crop damage (calendar spraying). Previous studies have shown that males are attracted to females and this might open the possibility to monitor this mirid pest with its sex pheromone. This ultimately would lead to a reduction in the usage of insecticides. Therefore this study to unravel the chemical structure and composition of the sex pheromone of this mirid was undertaken.

    Several methods were used to collect and identify volatiles emitted by male and female L. pabulinus. First of all, a thermodesorption system (TDS) was used. Intact females, males or pheromone glands were placed in the oven part of the TDS, which was subsequently heated, thereby stripping volatile compounds from the insect. With this method the composition of the known sex pheromones of Adoxophyes orana (Lepidoptera: Tortricidae) and Campylomma verbasci (Heteroptera: Miridae) were confirmed, using only a single insect per analysis. The advantages of this rapid method are its high sensitivity and the low degree of degradation and contamination of the stripped off compounds. This technique was effective in analysing volatiles from small insects by gas chromatography without prior manipulation, such as solvent extraction or distillation.

    Secondly, two similar methods were used to extract compounds from the headspace of female L. pabulinus . These methods, Solid Phase Microextraction (SPME) and Stir Bar Sorptive Extraction (SBSE) were both successful in trapping volatiles from L. pabulinus . SBSE was found to be much more sensitive than SPME, but SPME was easier to operate.

    Bioassays play an important role to determine the biological activity of extracts or compounds. A disadvantage of the methods described above is that no material can be gathered to use in any bioassay. Therefore samples from both sexes of L. pabulinus were collected in two other ways. Firstly, headspace extracts were obtained by trapping volatiles from males and females on Tenax and subsequently eluting the Teanx with an organic solvent. Secondly, extracts were made from different body parts of the green capsid bug.

    In order to determine the biological activity of these extracts and of the pure compounds, two different bioassays were used, 1) a vibration bioassay and 2) a Y-track olfactometer.

    In the so-called vibration bioassay the specific courtship behaviour, i.e. a vibration of the abdomen, of male L. pabulinus was used. When both live and dead females were offered to males in this bioassay, vibration behaviour was elicited. When females were dissected into separate body parts, heads, wings and legs elicited equal responses, while thorax plus abdomen gave a much lower response. When these separate body parts were extracted with an organic solvent, the leg extracts elicited significantly stronger responses than any other extract. This suggests that female L. pabulinus legs are either the source of a (close-range) sex pheromone, or that female L. pabulinus accumulates the pheromone on the legs by grooming behaviour. Live and dead males or male legs did not elicit any vibration behaviour in males. Substrates on which females had walked elicited similar responses in males as female legs, indicating that the female deposits the pheromone on the substrate. This occurs passively as no depositing behaviour was observed in the females.

    In the Y-track olfactometer, males had to choose between two different sources of volatiles: the male or female extract to be tested and the solvent used to make these extracts as a control. Headspace extracts from male and female L. pabulinus , as well as male and female leg extracts were tested in the Y-track olfactometer. Both the female leg and headspace extracts attracted males. Male extracts had no activity at all.

    All the extracts were analysed by Gas Chromatography/Mass Spectrometry (GC/MS) and coupled Gas Chromatography-Electroantennography (GC-EAD). Male and female headspace had an almost similar profile, except for a small amount of mono-alkenes, sometimes present in female headspace extracts. Chemical analysis of the leg extracts showed that these contained several hydrocarbons such as n -alkenes, n -alkanes and some methylalkanes. Female leg extracts contained more ( Z )-9-pentacosene while male leg extracts contained more ( Z )-9-heptacosene. Furthermore, two alkenes were present in different ratios in males and females. ( Z )-9-pentacosene and ( Z )-7-pentacosene were present in the ratio of 5:1 in females, but in about 1:5 in males. ( Z )-9-pentacosene and ( Z )-7-pentacosene were also the two alkenes observed in female headspace extracts.

    GC-EAD recordings with the headspace extracts from both males and females revealed that three compounds were consistently EAD-active. These were hexyl butyrate, ( E )-2-hexenyl butyrate and ( E )-4-oxo-2-hexenal. These compounds were also found with the thermal desorption system (TDS) in males and females. Besides these compounds, sometimes EAG responses were obtained for 1-hexanol, hexyl acetate, nonanal and ( Z )-3-hexenyl butyrate. In a different GC-EAD set-up the female leg extracts as well as the female headspace extracts were analysed. These recordings showed that also ( Z )-9-pentacosene and ( Z )-7-pentacosene were EAD-active.

    Although female headspace and female leg extracts differ much in composition, both attracted males in the Y-track olfactometer. On the contrary, male leg extracts did not attract males in this bioassay. The only difference between male and female leg extracts was the ratio of various alkenes. A mixture of ( Z )-9-pentacosene and ( Z )-7-pentacosene in the ratio 5:1 elicited vibrational behaviour in males. The results indicate that these alkenes are important cues for male L. pabulinus and are probably also responsible for the attraction of males in the Y-track olfactometer by female headspace extracts.

    Male antennae reacted strongly to hexyl butyrate, ( E )-2-hexenyl butyrate and ( E )-4-oxo-2-hexenal whereas female antennae gave little or no response, suggesting that these compounds may be important chemical signals as well for male L. pabulinus in their communication with conspecifics. These three compounds, with or without any of the other compounds giving irregular EAG-responses, together with the alkenes are probably used by male green capsid bugs to locate females. Further research is needed to determine exactly which compounds are needed in a particular ratio to attract male L. pabulinus.

    Q3 Ringtest nr. 23 : chlooramphenicol in urine
    Lasaroms, J.J.P. ; Rijn, J.A. van - \ 1999
    Wageningen : Rijks-Kwaliteitsinstituut voor land- en tuinbouwproducten (RIKILT) (Rapport / RIKILT-DLO 99.013) - 7
    chlooramfenicol - hplc - massaspectrometrie - kalibratie - gaschromatografie - kwaliteitscontroles - analytische scheikunde - chloramphenicol - hplc - mass spectrometry - calibration - gas chromatography - quality controls - analytical chemistry
    Literatuurstudie naar methoden voor de bepaling van bestrijdingsmiddelen, polychloorbifenylen en polygechloreerde dibenzo-p-dioxinen, dibenzofuranen in grond
    Traag, W.A. ; Zuidema, T. - \ 1997
    Wageningen : RIKILT-DLO (Rapport / DLO-Rijks-Kwaliteitsinstituut voor Land- en Tuinbouwprodukten 97.25) - 17
    polychloorbifenylen - dioxinen - polychloordibenzofuranen - gaschromatografie - nederland - literatuuroverzichten - bodemverontreiniging - polychlorinated biphenyls - dioxins - polychlorinated dibenzofurans - gas chromatography - netherlands - literature reviews - soil pollution
    Het ontwikkelen, optimaliseren en beperkt valideren van voorbehandelings-, extractie-, en opwerkingsvoorschriften ten behoeve van het bepalen van organische verbindingen in de vaste matrices grond, waterbodem en bouwstoffen voor de in project V24/104 ontwikkelde GCMS-voorschriften. (Project 105 fase 1)
    Traag, W.A. ; Leeuwen, M. van - \ 1995
    Wageningen : DLO-Rijks-Kwaliteitsinstituut voor land- en tuinbouwprodukten (RIKILT-DLO) (Rapport / RIKILT-DLO 95.22) - 19
    grondanalyse - klei - veengronden - waterbodems - pesticidenresiduen - besmetters - organische verbindingen - gaschromatografie - massaspectrometrie - monsterverwerking - soil analysis - clay - peat soils - water bottoms - pesticide residues - contaminants - organic compounds - gas chromatography - mass spectrometry - sample processing
    A restricted deskstudy is carried out to investigate the possibilities for improvement of previously developed methods for the determination of pesticides and organic contaminants in solid matrices like soil and construction materials. For the pretreatment and extraction of samples a number of methods are in principal suitable. Based on experience and in connection to existing methods a selection has been made.
    Ontwikkelen van methoden voor de bepaling van diverse bestrijdingsmiddelen en overige organische stoffen in grond
    Traag, W.A. ; Harmsen, J. ; Spreng, P. v.d.; Boekestein, A. - \ 1995
    Wageningen : RIKILT (Rapport / DLO, Rijks-Kwaliteitsinstituut voor Land- en Tuinbouwprodukten (RIKILT-DLO) 95-13) - 26
    pesticiden - organische verbindingen - bodemchemie - gaschromatografie - radiometrie - chemische analyse - GC-MS - pesticides - organic compounds - soil chemistry - gas chromatography - radiometry - chemical analysis - multi-analysis - soil contamination - GC-MS
    Ion trap detection for development of a multi residue/multi matrix method for pesticide residues in agricultural products
    Tuinstra, L.G.M.T. ; Spreng, P. van de; Gaikhorst, P. - \ 1995
    International Journal of Environmental Analytical Chemistry 58 (1995). - ISSN 0306-7319 - p. 81 - 91.
    gas chromatography - gel permeation chromatography - ion trap detection - pesticides - multi method
    Determination of mono-ortho substituted chlorobiphenyls by multidimensional gas chromatography and their contribution to TCDD equivalents
    Boer, J. de; Dao, Q.T. ; Wester, P.G. - \ 1995
    Analytica Chimica Acta 300 (1995). - ISSN 0003-2670 - p. 155 - 165.
    gaschromatografie - polychloorbifenylen - bioaccumulatie - ecotoxicologie - gas chromatography - polychlorinated biphenyls - bioaccumulation - ecotoxicology
    Methodologische aandachtspunten bij GC-olfactometrie.
    Kleykers, R.W.G. ; Schifferstein, H.N.J. - \ 1995
    Voedingsmiddelentechnologie 28 (1995)21. - ISSN 0042-7934 - p. 26 - 29.
    chemische samenstelling - voedingsmiddelen - gaschromatografie - geurstoffen - organoleptische kenmerken - sensorische evaluatie - reuk - chemical composition - foods - gas chromatography - odours - organoleptic traits - sensory evaluation - smell
    Het identificeren van belangrijke geurcomponenten van voedingsmiddelen met behulp van gaschromatografie
    Literatuurstudie naar multi(residu)methodes voor de bepaling van diverse bestrijdingsmiddelen en overige organische stoffen in grond
    Traag, W.A. ; Harmsen, J. ; Boekestein, A. ; Spreng, P. van de - \ 1994
    Wageningen : DLO-Rijks-Kwaliteitsinstituut voor Land- en Tuinbouwprodukten (Rapport / RIKILT-DLO 94.32) - 13
    gewasbescherming - pesticiden - pesticidenresiduen - persistentie - bodemwater - gaschromatografie - literatuuroverzichten - plant protection - pesticides - pesticide residues - persistence - soil water - gas chromatography - literature reviews
    RIKILT Staring Centrum onderzoek
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