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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    Framework to determine the effectiveness of dietary exposure mitigation to chemical contaminants
    Fels, H.J. van der; Edwards, S. ; Kennedy, M. ; O'Hagan, A. ; O'Mahony, C. ; Scholz, G. ; Steinberg, P. ; Tennant, D. ; Chiodini, A. - \ 2014
    Food and Chemical Toxicology 74 (2014). - ISSN 0278-6915 - p. 360 - 371.
    chromatography-mass spectrometry - solid-phase microextraction - extraction-gas chromatography - single-laboratory validation - fusarium mycotoxin content - methyl mercury exposure - spme-gc-ms - risk-assessment - baby-food - fish consumption
    In order to ensure the food safety, risk managers may implement measures to reduce human exposure to contaminants via food consumption. The evaluation of the effect of a measure is often an overlooked step in risk analysis process. The aim of this study was to develop a systematic approach for determining the effectiveness of mitigation measures to reduce dietary exposure to chemical contaminants. Based on expert opinion, a general framework for evaluation of the effectiveness of measures to reduce human exposure to food contaminants was developed. The general outline was refined by application to three different cases: 1) methyl mercury in fish and fish products, 2) deoxynivalenol in cereal grains, and 3) furan in heated products. It was found that many uncertainties and natural variations exist, which make it difficult to assess the impact of the mitigation measure. Whenever possible, quantitative methods should be used to describe the current variation and uncertainty. Additional data should be collected to cover natural variability and reduce uncertainty. For the time being, it is always better for the risk manager to have access to all available information, including an assessment of uncertainty; however, the proposed methodology provides a conceptual framework for addressing these systematically.
    Polyelectrolyte coatings prevent interferences from charged nanoparticles in SPME speciation analysis
    Zielinska, K. ; Leeuwen, H.P. van - \ 2014
    Analytica Chimica Acta 844 (2014). - ISSN 0003-2670 - p. 44 - 47.
    solid-phase microextraction - performance liquid-chromatography - surface modification - sample preparation - triclosan - fibers
    In this work we present a new approach for protection of the fiber in solid phase microextraction (SPME) from interfering charged particles present in the sample medium. It involves coating of commercial poly(dimethylsiloxane) extraction phase with polyelectrolyte layer composed of poly(diallyldimethylammonium chloride), and poly(sodium 4-styrenesulfonate). The modified fiber provides reproducible, convenient and fast extraction capabilities toward the model analyte, triclosan (TCS). A negatively charged polyelectrolyte coating prevents sorbing oxidic nanoparticles from both partitioning into the PDMS phase and aggregation at its surface. The results for the TCS/nanoparticle sample show that the polyelectrolyte layer-modified solid phase extracts just the free form of the organic compound and enables dynamic speciation analysis of the nanoparticulate target analyte complex.
    Quantification of Methylated Selenium, Sulfur, and Arsenic in the Environment
    Vriens, B. ; Ammann, A.A. ; Hagendorfer, H. ; Lenz, M. ; Berg, M. ; Winkel, L.H.E. - \ 2014
    PLoS ONE 9 (2014)7. - ISSN 1932-6203
    plasma-mass spectrometry - atomic fluorescence spectrometry - solid-phase microextraction - gas-chromatography - speciation analysis - volatile selenium - natural-waters - icp-ms - elements - air
    Biomethylation and volatilization of trace elements may contribute to their redistribution in the environment. However, quantification of volatile, methylated species in the environment is complicated by a lack of straightforward and field-deployable air sampling methods that preserve element speciation. This paper presents a robust and versatile gas trapping method for the simultaneous preconcentration of volatile selenium (Se), sulfur (S), and arsenic (As) species. Using HPLC-HR-ICP-MS and ESI-MS/MS analyses, we demonstrate that volatile Se and S species efficiently transform into specific non-volatile compounds during trapping, which enables the deduction of the original gaseous speciation. With minor adaptations, the presented HPLC-HR-ICP-MS method also allows for the quantification of 13 non-volatile methylated species and oxyanions of Se, S, and As in natural waters. Application of these methods in a peatland indicated that, at the selected sites, fluxes varied between 190–210 ng Se·m-2·d-1, 90–270 ng As·m-2·d-1, and 4–14 µg S·m-2·d-1, and contained at least 70% methylated Se and S species. In the surface water, methylated species were particularly abundant for As (>50% of total As). Our results indicate that methylation plays a significant role in the biogeochemical cycles of these elements
    Explaining PAH desorption from sediments using Rock Eval analysis
    Poot, A. ; Jonker, M.T.O. ; Gillissen, F. ; Koelmans, A.A. - \ 2014
    Environmental Pollution 193 (2014). - ISSN 0269-7491 - p. 247 - 253.
    polycyclic aromatic-hydrocarbons - historically contaminated sediments - supercritical-fluid extraction - solid-phase microextraction - laboratory-spiked sediments - soot-like materials - black carbon - polychlorinated-biphenyls - organic-compounds - hydrophobic p
    Here, we provide Rock Eval and black carbon (BC) characteristics and polycyclic aromatic hydrocarbon (PAH) distribution coefficients (KD) for sediments from the Danube, Elbe, Ebro, and Meuse river basins. PAH desorption kinetic parameters were determined using sequential Tenax extractions. We show that residual carbon (RC) from Rock Eval analysis is an adequate predictor of fast, slow, and very slow desorbing fractions of 4-ring PAHs. RC correlated better than BC, the latter constituting only 7% of RC. A dual domain sorption model was statistically superior to a single domain model in explaining KD for low molecular weight PAHs, whereas the opposite was observed for high molecular weight PAHs. Because particularly the 4-ring PAHs are bioavailable and relevant from a risk assessment perspective and because their fast desorbing fractions correlate best with RC, we recommend RC as a relevant characteristic for river sediments.
    Incorporating availability/bioavailability in risk assessment and decision making of polluted sites, using Germany as an example
    Kördel, W. ; Bernardt, C. ; Derz, K. ; Hund-Rinke, K. ; Harmsen, J. ; Peijenburg, W. ; Comans, R.N.J. ; Terytze, K. - \ 2013
    Journal of Hazardous Materials 261 (2013). - ISSN 0304-3894 - p. 854 - 862.
    polycyclic aromatic-hydrocarbons - solid-phase microextraction - polychlorinated-biphenyls - terrestrial environments - contaminated sediments - tenax(r) extraction - organic-compounds - soil extraction - heavy-metals - trace-metals
    Nearly all publications dealing with availability or bioavailability of soil pollutants start with the following statement: the determination of total pollutant content will lead to an over-estimation of risk. However, an assessment of contaminated sites should be based on the determination of mobile fractions of pollutants, and the fractions with potential for mobilisation that threaten groundwater and surface water, and the actual and potential fractions available for uptake by plants, soil microflora and soil organisms. After reviewing the literature for method proposals concerning the determination of available/bioavailable fractions of contaminants with respect to leaching, plants, microorganisms (biodegradation) and soil organisms, we propose a testing and assessment scheme for contaminated sites. The proposal includes (i) already accepted and used methods, (ii) methods which are under standardisation, and (iii) methods for which development has just started in order to promote urgently needed research. (C) 2013 Elsevier B.V. All rights reserved.
    Characterization of volatile compounds in Fen-Daqu - a traditional Chinese liquor fermentation starter
    Van-Diep, L. ; Zheng, X. ; Chen, J.Y. ; Han, B.Z. - \ 2012
    Journal of the Institute of Brewing 118 (2012)1. - ISSN 0046-9750 - p. 107 - 113.
    solid-phase microextraction - gas-chromatography-olfactometry - mass-spectrometry - dilution analysis - aroma compounds - flavor liquor - juices
    Fen-Daqu is a saccharifying agent and fermentation starter for the production of Chinese liquor Fen (alcoholic spirit) and Fen traditional vinegar. The volatile compounds produced at seven incubation steps were analysed by HS-SPME-GC-MS. A total of 83 major volatile compounds were identified, including 23 esters, 8 acids, 24 alcohols, 18 ketones and aldehydes, 6 pyrazines and 4 acetals. Data obtained by HS-SPME-GC-MS were subjected to principal component analysis. The trajectory plots of volatile compounds in Fen-Daqu samples obtained during successive steps of incubation were revealed. The major compounds that contributed to discrimination were hexanal, (E)-2-octenal, (Z)-2-octen-1-ol, nonanoic acid, 1-octanol, 2-decen-1-ol, hexyl acetate, (E)-2-octen-1-ol, acetic acid, ethyl acetate, phenylethyl alcohol, ethyl alcohol, octanoic acid, 1-octanol, 3-methyl-2-buten-1-ol and pyrazines.
    Volatile compound fingerprinting of mixed cultutre fermentations
    Bok, F.A.M. de; Janssen, P.W.M. ; Bayjanov, J.R. ; Sieuwerts, S. ; Lommen, A. ; Hylckama, J. van; Molenaar, D. - \ 2011
    Applied and Environmental Microbiology 77 (2011)17. - ISSN 0099-2240 - p. 6233 - 6239.
    chromatography-mass spectrometry - solid-phase microextraction - starter cultures - flavor - metabolomics - yogurt - identification - genomics - strains - tomato
    With the advent of the -omics era, classical technology platforms, such as hyphenated mass spectrometry, are currently undergoing a transformation toward high-throughput application. These novel platforms yield highly detailed metabolite profiles in large numbers of samples. Such profiles can be used as fingerprints for the accurate identification and classification of samples as well as for the study of effects of experimental conditions on the concentrations of specific metabolites. Challenges for the application of these methods lie in the acquisition of high-quality data, data normalization, and data mining. Here, a high-throughput fingerprinting approach based on analysis of headspace volatiles using ultrafast gas chromatography coupled to time of flight mass spectrometry (ultrafast GC/TOF-MS) was developed and evaluated for classification and screening purposes in food fermentation. GC-MS mass spectra of headspace samples of milk fermented by different mixed cultures of lactic acid bacteria (LAB) were collected and preprocessed in MetAlign, a dedicated software package for the preprocessing and comparison of liquid chromatography (LC)-MS and GC-MS data. The Random Forest algorithm was used to detect mass peaks that discriminated combinations of species or strains used in fermentations. Many of these mass peaks originated from key flavor compounds, indicating that the presence or absence of individual strains or combinations of strains significantly influenced the concentrations of these components. We demonstrate that the approach can be used for purposes like the selection of strains from collections based on flavor characteristics and the screening of (mixed) cultures for the presence or absence of strains. In addition, we show that strain-specific flavor characteristics can be traced back to genetic markers when comparative genome hybridization (CGH) data are available.
    Characterisation of volatile components of Pinotage wines using comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC x GC–TOFMS)
    Weldegergis, B.T. ; Villiers, A. de; McNeish, C. ; Seethapathy, S. ; Mostafa, A. ; Górecki, T. ; Crouch, A.M. - \ 2011
    Food Chemistry 129 (2011)1. - ISSN 0308-8146 - p. 188 - 199.
    solid-phase microextraction - bar sorptive extraction - south-african wines - flavor compounds - alcoholic beverages - madeira wines - white wine - quercus-petraea - aroma compounds - grape variety
    As part of the ongoing research into the chemical composition of the uniquely South African wine cultivar Pinotage, the volatile composition of nine young wines of this cultivar was investigated using comprehensive two-dimensional gas chromatography (GC × GC) in combination with time-of-flight mass spectrometry (TOFMS). Headspace solid phase micro-extraction (HS-SPME) using a carboxen/polydimethylsiloxane (CAR/PDMS) fibre was used to extract the volatile compounds from the wine matrix. Extracts were analysed using an in-house developed GC × GC system equipped with a single jet, liquid nitrogen-based cryogenic modulator. In the current study, 206 compounds previously reported in wine and related matrices have been detected in nine Pinotage wines. Positive identification for 48 compounds was performed using authentic standards, while tentative identification of 158 compounds was based on deconvoluted mass spectra and comparison of linear retention indices (LRI) with literature values. Identified compounds included esters, alcohols, aldehydes, ketones, acids, acetals, furans and lactones, sulphur compounds, nitrogen compounds, terpenes, hydrocarbons, volatile phenols and pyrans. Volatile compounds potentially capable of influencing wine aroma are highlighted. Many of the compounds were common to all 9 wines, although volatile components unique to specific samples were also observed. The results represent the most detailed characterisation of volatile constituents of this cultivar reported to date.
    Screening of transformation products in soils contaminated with unsymmetrical dimethylhydrazine using headspace SPME and GC-MS
    Kenessov, B.N. ; Koziel, J.A. ; Grotenhuis, J.T.C. ; Carlsen, L. - \ 2010
    Analytica Chimica Acta 674 (2010)1. - ISSN 0003-2670 - p. 32 - 39.
    solid-phase microextraction - chromatography-mass spectrometry - volatile organic-compounds - gas-chromatography - olfactometry - air - 1,1-dimethylhydrazine - odorants
    The paper describes a novel SPME-based approach for sampling and analysis of transformation products of highly reactive and toxic unsymmetrical dimethylhydrazine (UDMH) which is used as a fuel in many Russian, European, Indian, and Chinese heavy cargo carrier rockets. The effects of several parameters were studied to optimize analyte recovery. It was found that the 85 µm Carboxen/polydimethylsiloxane fiber coating provides the highest selectivity for selected UDMH transformation products. Optimal sampling/sample preparation parameters were determined to be 1-h soil headspace sampling time at 40 °C. The GC inlet temperature was optimized to 170 °C held for 0.1 min, then 1 °C s-1 ramp to 250 °C where it was held for 40 min. Temperature programing resulted in a fast desorption along with minimal chemical transformation in the GC inlet. SPME was very effective extracting UDMH transformation products from soil samples contaminated with rocket fuel. The use of SPME resulted in high sensitivity, speed, small labor consumption due to an automation and simplicity of use. It was shown that water addition to soil leads to a significant decrease of recovery of almost all target transformation products of UDMH. The use of SPME for sampling and sample preparation resulted in detection of the total of 21 new compounds that are relevant to the UDMH transformation in soils. In addition, the number of confirmed transformation products of UDMH increased from 15 to 27. This sampling/sample preparation approach can be recommended for environmental assessment of soil samples from areas affected by space rocket activity
    Branched chain aldehydes: production and breakdown pathways and relevance for flavour in foods
    Smit, B.A. ; Engels, W.J.M. ; Smit, G. - \ 2009
    Applied Microbiology and Biotechnology 81 (2009)6. - ISSN 0175-7598 - p. 987 - 999.
    lactic-acid bacteria - dry-fermented sausages - alpha-keto acids - solid-phase microextraction - odor-active compounds - lactococcal aromatic aminotransferase - gas chromatography-olfactometry - freshly distilled calvados - fusel alcohol production - amino-acids
    Branched aldehydes, such as 2-methyl propanal and 2- and 3-methyl butanal, are important flavour compounds in many food products, both fermented and non-fermented (heat-treated) products. The production and degradation of these aldehydes from amino acids is described and reviewed extensively in literature. This paper reviews aspects influencing the formation of these aldehydes at the level of metabolic conversions, microbial and food composition. Special emphasis was on 3-methyl butanal and its presence in various food products. Knowledge gained about the generation pathways of these flavour compounds is essential for being able to control the formation of desired levels of these aldehydes.
    Facilitated transport of polychlorinated biphenyls and polybrominated diphenyl ethers by dissolved organic matter
    Laak, T.L. ter; Eijkeren, J.C.H. van; Busser, F.J.M. ; Leeuwen, H.P. van; Hermens, J.L. - \ 2009
    Environmental Science and Technology 43 (2009)5. - ISSN 0013-936X - p. 1379 - 1385.
    solid-phase microextraction - water partition-coefficients - hydrophobic chemicals - rate constants - bioavailability - congeners - kinetics - bioaccumulation - consequences - phenanthrene
    The exchange rate of hydrophobic organic chemicals between the aqueous phase and a sorbent (e.g., soil, organism, passive sampler) is relevant for distribution processes between environmental compartments, including organisms. Dissolved phases such as humic acids, proteins, and surfactants can affect the transfer of such chemicals between the aqueous and sorbent phases by sorption and desorption processes. In this study, the desorption of polychlorinated biphenyls and polybrominated diphenyl ethers from a polymer phase to an aqueous medium was monitored at different humic acid concentrations. The rate of release of the chemical by the polymer phase demonstrates thatthe chemical sorbed to dissolved humic acid contributed significantly to the total mass transfer when the affinity for the humic acid was sufficiently high. This illustrates that environmentally relevant humic acid concentrations can facilitate transport of hydrophobic organic chemicals. The consequences of these facilitated transport mechanisms for uptake into passive samplers are discussed, in particular in situations where equilibration is very slow or when exposure varies in time or space
    Quality control of raw cows' milk by headspace analysis
    Hettinga, K.A. ; Valenberg, H.J.F. van; Hooijdonk, A.C.M. van - \ 2008
    International Dairy Journal 18 (2008)5. - ISSN 0958-6946 - p. 506 - 513.
    solid-phase microextraction - gas-chromatographic data - shelf-life prediction - free fatty-acids - dynamic headspace - multivariate-analysis - pseudomonas-fragi - mass-spectrometry - volatile components - pasteurized milk
    This study investigated whether headspace analysis of volatile components can be used for monitoring the quality of raw cows¿ milk. The detection of different quality defects caused by cows¿ feed, microbiological and chemical contamination, as well as enzymatic deterioration was studied. Fresh raw milk without quality defects was shown to always contain the same seven volatile components. It was also shown that treatments like heating and homogenization of raw milk may drastically change this basic pattern resulting in as much as a 10-fold increase in the number of volatile compounds. The growth of Pseudomonas could not be detected in an early stage using headspace analysis. Feed was shown to have an effect on the volatile composition if specific vegetable byproducts were fed to the cow. Chloroform contamination was quantified using the method. Also, the extent of lipolysis could be quantified by measuring the free fatty acids. For quantification of both chloroform and lipolysis, the sensitivity and reproducibility of the method were sufficient for quality control purposes. The method was thus able to detect several quality defects with a single analysis and may therefore be a useful supplementary method for raw milk quality control.
    A novel approach for nontargeted data analysis for metabolomics : large-scale profiling of tomato fruit volatiles
    Tikunov, Y.M. ; Lommen, A. ; Vos, C.H. de; Verhoeven, H.A. ; Bino, R.J. ; Hall, R.D. ; Bovy, A.G. - \ 2005
    Plant Physiology 139 (2005)3. - ISSN 0032-0889 - p. 1125 - 1137.
    solid-phase microextraction - chromatography-mass spectrometry - plant functional genomics - gas-chromatography - methyl salicylate - flavor volatiles - chemometric analysis - rapid analysis - identification - organization
    To take full advantage of the power of functional genomics technologies and in particular those for metabolomics, both the analytical approach and the strategy chosen for data analysis need to be as unbiased and comprehensive as possible. Existing approaches to analyze metabolomic data still do not allow a fast and unbiased comparative analysis of the metabolic composition of the hundreds of genotypes that are often the target of modern investigations. We have now developed a novel strategy to analyze such metabolomic data. This approach consists of (1) full mass spectral alignment of gas chromatography (GC)-mass spectrometry (MS) metabolic profiles using the MetAlign software package, (2) followed by multivariate comparative analysis of metabolic phenotypes at the level of individual molecular fragments, and (3) multivariate mass spectral reconstruction, a method allowing metabolite discrimination, recognition, and identification. This approach has allowed a fast and unbiased comparative multivariate analysis of the volatile metabolite composition of ripe fruits of 94 tomato (Lycopersicon esculentum Mill.) genotypes, based on intensity patterns of >20,000 individual molecular fragments throughout 198 GC-MS datasets. Variation in metabolite composition, both between- and within-fruit types, was found and the discriminative metabolites were revealed. In the entire genotype set, a total of 322 different compounds could be distinguished using multivariate mass spectral reconstruction. A hierarchical cluster analysis of these metabolites resulted in clustering of structurally related metabolites derived from the same biochemical precursors. The approach chosen will further enhance the comprehensiveness of GC-MS-based metabolomics approaches and will therefore prove a useful addition to nontargeted functional genomics research
    Chronic toxicity and body residues of the nonpolar narcotic 1,2,3,4-tetrachrlorobenzene in Chironomus riparius
    Leslie, H.A. ; Kraak, M.H.S. ; Hermens, J.L. - \ 2004
    Environmental Toxicology and Chemistry 23 (2004)8. - ISSN 0730-7268 - p. 2022 - 2028.
    solid-phase microextraction - complex organic mixtures - amphipod hyalella-azteca - acute aquatic toxicity - base-line toxicity - chemicals - bioconcentration - time - fish - burdens
    The use of internal concentrations as a dose parameter for baseline toxicity requires an understanding of the relationship between accumulation level and toxic effects, not only for acute but also for chronic exposure. In this study of chronic toxicity of the nonpolar narcotic 1,2,3,4-tetrachlorobenzene (TeCB) to Chironomus riparius, the chronic median lethal concentration (LC50) was determined to be 0.99 (0.54-1.82) muM, the median sublethal effect concentration (EC50) for growth was 0.76 (0.73-0.97) muM, and the chronic (sublethal) no-observed-effect concentration (NOEC) was 0.24 +/- 0.01 muM. An acute-to-chronic ratio of 9.8 was calculated from a previously determined acute LC50 value and this NOEC. The chronic critical body residue (CBR), 136 mmol/kg lipid, was the same as the acute CBR, previously determined. The similarity of the chronic and acute CBRs lends support to the exposure time independent aspect of baseline toxicity theory. An implication of this is that internal concentrations estimated by biomimetic sampling devices may be compared to acute CBR data to determine chronic baseline toxicity risk. Such sampling devices, solid-phase microextraction (SPME) fibers, were simultaneously exposed during the toxicity test. The results of this study suggest that body residues estimated with SPME may be used to predict baseline toxicity for various exposure durations.
    A fast and simple method for quantitative determination of fat-derived medium and low-volatile compounds in cheese
    Alewijn, M. ; Sliwinski, E.L. ; Wouters, J.T.M. - \ 2003
    International Dairy Journal 13 (2003)9. - ISSN 0958-6946 - p. 733 - 741.
    solid-phase microextraction - simultaneous distillation-extraction - gas-chromatographic analysis - dynamic headspace analysis - flavor compounds - cheddar cheese - gc-ms - parmesan cheese - potent odorants - milk
    Cheese flavour is a mixture of many (volatile) compounds, mostly formed during ripening. The current method was developed to qualify and quantify fat-derived compounds in cheese. Cheese samples were extracted with acetonitrile, which led to a concentrated solution of potential favour compounds, mainly derived from milk fat. The solution was virtually free from triglycerides, protein and salt from the cheese matrix. Therefore, such an extract could be analysed directly by gas chromatography/mass spectroscopy (GC/MS). In the samples of the three cheese varieties analysed, 61 different compounds were identified, including 23 fatty acids, 14 lactones, 9 esters, 5 ketones, 10 alcohols, and several miscellaneous compounds. Furthermore, most compounds could be quantified by determining their distribution coefficients and thus correcting for their loss during extraction. This method was shown to be suitable for both qualitative and quantitative analysis of medium and low-volatile compounds. (C) 2003 Elsevier Science Ltd. All rights reserved.
    Gas chromatography-olfactometry analysis of the volatile compounds of two commercial Irish beef meats
    Machiels, D. ; Ruth, S.M. van; Posthumus, M.A. ; Istasse, L. - \ 2003
    Talanta 60 (2003). - ISSN 0039-9140 - p. 755 - 764.
    sniffing port analysis - solid-phase microextraction - extract dilution analysis - peppers capsicum-annuum - rehydrated french beans - aroma impact compounds - mouth model systems - bell peppers - flavor compounds - potent odorants
    The volatile flavour compounds of two commercial Irish beef meats (labelled as conventional and organic) were evaluated by gas chromatography-olfactometry and were identified by gas chromatography-mass spectrometry. The volatile compounds were isolated in a model mouth system. Gas chromatography-olfactometry was performed by a group of eight assessors using the detection frequency methodology. The odours of the detected compounds were described as well. Eighty-one volatile compounds were identified, 11 compounds of which possessed odour activity in the first beef sample and 14 of which in the second meat sample. Ten volatile flavour compounds were common to both: methanethiol, dimethyl sulphide, 2-butanone, ethyl acetate, 2- and 3-methylbutanal, an unknown compound, 2-octanone, decanal and benzothiazole. Two unknown compounds were only detected in the first sample while 2,3-pentanedione, 4-methyl-3-penten-2-one, 2-heptanone, dimethyl trisulphide and nonanal were only perceived in the second beef. Significant differences in terms of detection frequency, odour characteristics and in nature of the volatile flavour compounds were emphasised between the two samples. (C) 2003 Elsevier Science B.V. All rights reserved.
    Regulation of floral scent production in petunia revealed by targeted metabolomics
    Verdonk, J.C. ; Vos, C.H. de; Verhoeven, H.A. ; Haring, M.A. ; Tunen, A.J. van; Schuurink, R.C. - \ 2003
    Phytochemistry 62 (2003). - ISSN 0031-9422 - p. 997 - 1008.
    solid-phase microextraction - snapdragon flowers - linalool synthase - rosa-hybrida - in-situ - emission - volatiles - biosynthesis - expression - gene
    Petunia hybrida line W115 (Mitchell) has large white flowers that produce a pleasant fragrance. By applying solid phase micro extraction (SPME) techniques coupled to GC-MS analysis, volatile emission was monitored in vivo using a targeted metabolomics approach. Mature flowers released predominantly benzenoid compounds of which benzaldehyde, phenylacetaldehyde, methylbenzoate, phenylethylalcohol, iso-eugenol and benzylbenzoate were most abundant. This emission had a circadian rhythm reaching its maximum at dusk. During petal limb expansion two sesquiterpenes were emitted by the petunia flowers, tentatively identified as germacrene D and cadina-3,9-diene. In vitro analysis showed that the petal limbs and stigma were the main producers of the benzenoids and sesquiterpenes, respectively. Moreover, comparison of in vivo and in vitro analysis indicated that volatiles were not stored during periods of low emission but rather were synthesized de novo. DNA-microarray analysis revealed that genes of the pathways leading to the production of volatile benzenoids were upregulated late during the day, preceding the increase of volatile emission. RNA-gel blot analyses confirmed that the levels of phenylalanine ammonia lyase (PAL) and S-adenosyl methionine (SAM) synthase transcripts increased towards the evening. Our results suggest that the circadian production of volatile benzenoids in petunia W115 is, at least partly, regulated at the transcript level.
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