David Siegel

Zuse-Institut Berlin, Berlín, Berlin, Germany

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Publications (15)36.05 Total impact

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    ABSTRACT: With the help of theoretical calculations we explain the phenomenon of nonplanarity of crystalline alternariol. We find out that the different orientations of the hydroxyl groups of alternariol influence its planarity and aromaticity and lead to different twists of the structure. The presence of the intramolecular hydrogen bond stabilizes the planar geometry while the loss of the bond results in a twist of over 14°. This effect is thought to be involved while cutting DNA strands by alternariol.
    Journal of Molecular Modeling 03/2013; · 1.98 Impact Factor
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    ABSTRACT: A laboratory study was conducted to evaluate the influence of cocultivation of toxigenic Fusarium (F.) and Alternaria (A.) fungi with respect to growth and mycotoxin production. Fusarium culmorum Fc13, Fusarium graminearum Fg23 and two Alternaria tenuissima isolates (At18 and At220) were simultaneously or consecutively co-incubated on wheat kernels in an in vitro test system. Fungal biomass was quantified by determining ergosterol content. Three Fusarium toxins (DON, NIV and ZON) and three Alternaria toxins (AOH, AME and ALT) were analysed by a newly developed HPLC/MS/MS method. In simultaneous cocultures, the fungal biomass was enhanced up to 460% compared with individual cultures; Alternaria toxins were considerably depressed down to <5%. Combining At18 and At220 with Fg23 inhibited the toxin production of both fungal partners. In contrast, Fc13 increased its DON and ZON production in competitive interaction with both A. strains. The interfungal competitive effects aid the understanding of the processes of competition of both fungi in natural environments and the involvement of mycotoxins as antifungal factors. Cocultivation significantly affects fungal growth and mycotoxin production of phytopathogenic Alternaria and Fusarium strains. The impact of mycotoxins on the interfungal competition is highlighted.
    Journal of Applied Microbiology 07/2012; 113(4):874-87. · 2.20 Impact Factor
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    ABSTRACT: Mycotoxins are important non-anthropogenic food and feed contaminants, which can be present on almost every agricultural commodity. Effective consumer protection therefore essentially depends on food surveillance by reliable quantitative analysis enabled by appropriate quality control. Certified (matrix) reference materials (CRMs) are versatile tools to support quality assurance. However, in the case of ochratoxin A (OTA), a hepato- and nephrotoxic mycotoxin, which is regulated in various foods, there is a lack of suitable CRMs. This lack has now been overcome by the development of two European Reference Materials (ERM®) for the determination of OTA in roasted coffee (ERM®-BD475) and red wine (ERM®-BD476). This article discusses the material preparation process as well as the results of homogeneity and stability testing. Furthermore, the results of the in-house certification studies carried out at BAM Federal Institute for Materials Research and Testing are presented and discussed. Interlaboratory comparison studies involving selected expert laboratories with documented expertise in the field of mycotoxin analysis were conducted to confirm the certified values determined by BAM. The certified ochratoxin A values and their corresponding expanded uncertainties (k=2) were assigned in full compliance with the requirements of ISO Guide 35 and are as follows: (6.0±0.6)μgkg−1 for roasted coffee, ERM®-BD475, and (0.52±0.11)μgL−1 for red wine, ERM®-BD476. KeywordsOTA–Coffee–Wine–Food safety and quality–European reference materials–CRM
    Accreditation and Quality Assurance 08/2011; 16(8):429-437. · 1.13 Impact Factor
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    ABSTRACT: The stability of the Alternaria mycotoxins alternariol, alternariol monomethyl ether, and altenuene upon bread baking was investigated by model experiments using a spiked wholemeal wheat flour matrix. For alternariol and alternariol monomethyl ether, but not for altenuene, degradation products, formed through a sequence of hydrolysis and decarboxylation, could be identified in pilot studies. The simultaneous quantification of alternariol, alternariol monomethyl ether, altenuene, and the degradation products was achieved by a newly developed high performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) multimethod. The obtained quantitative data indicate that the Alternaria mycotoxins are barely degraded during wet baking, while significant degradation occurs upon dry baking, with the stability decreasing in the order alternariol monomethyl ether>alternariol>altenuene. The novel degradation products could be detected after the wet baking of flour spiked with alternariol and in a sample survey of 24 commercial cereal based baking products.
    Journal of Agricultural and Food Chemistry 09/2010; 58(17):9622-30. · 3.11 Impact Factor
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    ABSTRACT: Sulfur dioxide (SO2) or sulfites are the most common preservatives used in winemaking. The level of total SO2 is subject to regulation. Currently, the regulatory determination of total SO2 (including sulfites) is done by the optimized Monier-Williams (OMW) method, which includes time-consuming distillation and titration steps. This paper describes the development and application of an alternative, rapid, straightforward, and reliable method for the determination of total sulfite in wine. In this method, a simple oxidation step using alkaline hydrogen peroxide (H2O2) solution is followed by ion chromatographic (IC) analysis of sulfate coupled with conductometric detection. Thirteen wines were analyzed in order to compare the in-sample oxidation method with the OMW-procedure. A t-test revealed satisfying compliance regarding sample preparation, i.e., alkaline H2O2 treatment and acidic distillation (OMW method). Comparable results were also obtained between IC analysis and acid/base titration. Our results indicate that the novel method (limit of quantification: 4 mg SO2 L(-1)) is well suited for the cost-efficient monitoring of regulatory limits.
    Journal of Agricultural and Food Chemistry 09/2010; 58(17):9463-7. · 3.11 Impact Factor
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    ABSTRACT: Tenuazonic acid (TA) is a major water soluble Alternaria mycotoxin. In the present work, a method for the quantification of TA in beer by liquid chromatography–ion-trap multistage mass spectrometry after derivatization with 2,4-dinitrophenylhydrazine is described. The method is based on a rapid workup procedure and features a LOD of 2 μg/kg without preconcentration using 400 mg of sample. Validation was performed for a working range of 8–500 μg/kg.A total of 43 beers of different brewing styles (pilsener, wheat beer, bock beer, dark beer and alcohol free beer) was analysed. TA was detected in 37 samples, 16 samples were above the LOQ. An average content of 11 μg/kg was found, the highest incidence being 175 ± 13 μg/kg. To our knowledge, this is the first report on the occurrence of TA in beer and beverages in general.
    Food Chemistry 06/2010; · 3.33 Impact Factor
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    ABSTRACT: Mycotoxins are natural contaminants produced by a range of fungal species. Their common occurrence in food and feed poses a threat to the health of humans and animals. This threat is caused either by the direct contamination of agricultural commodities or by a "carry-over" of mycotoxins and their metabolites into animal tissues, milk, and eggs after feeding of contaminated hay or corn. As a consequence of their diverse chemical structures and varying physical properties, mycotoxins exhibit a wide range of biological effects. Individual mycotoxins can be genotoxic, mutagenic, carcinogenic, teratogenic, and oestrogenic. To protect consumer health and to reduce economic losses, surveillance and control of mycotoxins in food and feed has become a major objective for producers, regulatory authorities and researchers worldwide. However, the variety of chemical structures makes it impossible to use one single technique for mycotoxin analysis. Hence, a vast number of analytical methods has been developed and validated. The heterogeneity of food matrices combined with the demand for a fast, simultaneous and accurate determination of multiple mycotoxins creates enormous challenges for routine analysis. The most crucial issues will be discussed in this review. These are (1) the collection of representative samples, (2) the performance of classical and emerging analytical methods based on chromatographic or immunochemical techniques, (3) the validation of official methods for enforcement, and (4) the limitations and future prospects of the current methods.
    Applied Microbiology and Biotechnology 03/2010; 86(6):1595-612. · 3.81 Impact Factor
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    ABSTRACT: A novel, cost-efficient method for the analytical extraction of the Fusarium mycotoxin zearalenone (ZON) from edible oils by dynamic covalent hydrazine chemistry (DCHC) was developed and validated for its application with high performance liquid chromatography-fluorescence detection (HPLC-FLD). ZON is extracted from the edible oil by hydrazone formation on a polymer resin functionalised with hydrazine groups and subsequently released by hydrolysis. Specifity and precision of this approach are superior to liquid partitioning or gel permeation chromatography (GPC). DCHC also extracts zearalanone (ZAN) but not alpha-/beta-zearalenol or -zearalanol. The hydrodynamic properties of ZON, which were estimated using molecular simulation data, indicate that the compound is unaffected by nanofiltration through the resin pores and thus selectively extracted. The method's levels of detection and quantification are 10 and 30 microg/kg, using 0.2g of sample. Linearity is given in the range of 10-20,000 microg/kg, the average recovery being 89%. Bias and relative standard deviations do not exceed 7%. In a sample survey of 44 commercial edible oils based on various agricultural commodities (maize, olives, nuts, seeds, etc.) ZON was detected in four maize oil samples, the average content in the positive samples being 99 microg/kg. The HPLC-FLD results were confirmed by HPLC-tandem mass spectrometry and compared to those obtained by a liquid partitioning based sample preparation procedure.
    Journal of Chromatography A 02/2010; 1217(15):2206-15. · 4.61 Impact Factor
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    ABSTRACT: IN THE TITLE COMPOUND (SYSTEMATIC NAME: 3,7,9-trihydr-oxy-1-methyl-6H-benzo[c]chromen-6-one), C(14)H(10)O(5), the methyl group is shifted out of the molecular plane due to a steric collision, thus causing a slight twist of the benzene rings. The mol-ecular structure is stabilized by an intra-molecular O-H⋯O hydrogen bond, generating an S(6) ring. In the crystal, mol-ecules are connected by inter-molecular O-H⋯O hydrogen bonds into a three-dimensional network.
    Acta Crystallographica Section E Structure Reports Online 01/2010; 66(Pt 6):o1366. · 0.35 Impact Factor
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    ABSTRACT: The degradation kinetics of the Alternaria mycotoxin tenuazonic acid (l-TA) in aqueous buffer were studied over a period of 4 months at different pH levels (3.5 and 7.0) and temperatures (4, 25 and 40 degrees C). l-TA and its degradation products were quantified by newly developed high-performance liquid chromatography methods with UV or electrospray multistage mass spectrometry detection. At pH 3.5, significant degradation occurred at 25 and 40 degrees C, the respective l-TA half-lives being 73.8 +/- 0.4 and 14.0 +/- 0.1 days. Two degradation processes, epimerization and hydrolysis, were evaluated kinetically. The hydrolytically formed iso-deacetyl TA (iso-DTA, epimeric mixture) was found to be the stable end product of l-TA degradation under the conditions of this study. This indicates that iso-DTA as well as the l-TA epimer u-TA are formed in aqueous beverage matrices.
    Analytical and Bioanalytical Chemistry 11/2009; 397(2):453-62. · 3.66 Impact Factor
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    ABSTRACT: Certified reference materials (CRMs) are a versatile tool for quality assurance in the chemical laboratory. In the case of acrylamide analysis, the availability of appropriate materials was rather limited. This lack of acrylamide matrix CRMs has now been overcome by the development of two European reference materials (ERM) for the determination of acrylamide in food (crispbread, ERM-BD272, and rusk, ERM-BD274). This article describes the preparation of the materials, provides the results of the homogeneity and stability studies, and presents and discusses the outcome of the certification studies. Expert laboratories from different European countries took part in the certification studies using various analytical methods. The acrylamide mass fractions were certified to 980 microg kg(-1) for crispbread and 74 microg kg(-1) for rusk.
    Journal of Agricultural and Food Chemistry 09/2009; 57(18):8202-7. · 3.11 Impact Factor
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    ABSTRACT: The heterocycle in the title compound {systematic name: (5S)-5-[(1S)-1-methyl-prop-yl]pyrrolidine-2,4-dione}, C(8)H(13)NO(2), is planar (r.m.s. deviation for all non-H atoms = 0.008 Å). The crystal structure is stabilized by N-H⋯O hydrogen bonding.
    Acta Crystallographica Section E Structure Reports Online 06/2009; 65(Pt 6):o1201. · 0.35 Impact Factor
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    ABSTRACT: Tenuazonic acid (TA) is a major Alternaria mycotoxin. In the present work a novel approach for the detection of TA in cereals by liquid chromatography-ion-trap multistage mass spectrometry after derivatization with 2,4-dinitrophenylhydrazine is described. The product of the derivatization reaction and its major MS(2) fragments were characterised by Fourier transform-ion cyclotron resonance tandem mass spectrometry. Without preconcentration, the established method features a limit of detection of 10 microg/kg using 2g of sample in a rapid workup procedure. Accuracy, precision and linearity were evaluated in the working range of 50-5000 microg/kg. TA was detected in 13 and quantified in 3 out of 27 cereal samples obtained from a local supermarket, the average content being 49 microg/kg (highest incidence: 851+/-41 microg/kg).
    Journal of Chromatography A 04/2009; 1216(21):4582-8. · 4.61 Impact Factor
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    ABSTRACT: In the title compound, C(16)H(19)N(5)O(6), two intramolecular N-H⋯O hydrogen bonds help to establish the conformation. In the crystal, intermolecular N-H⋯O links result in chains propagating in [010].
    Acta Crystallographica Section E Structure Reports Online 01/2009; 65(Pt 5):o988-9. · 0.35 Impact Factor
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    ABSTRACT: The title compound {systematic name: 4-methyl-N'-[(3E)-2-(1-methyl-prop-yl)-5-oxopyrrolidin-3-yl-idene]benzene-sulfono-hydrazide}, C(15)H(21)N(3)O(3)S, is the condensation product of deacetyl tenuazonic acid (DTA) and p-toluene-sulfonohydrazide. The crystal structure consists of chains along [100] linked by N-H⋯O hydrogen bonds.
    Acta Crystallographica Section E Structure Reports Online 01/2009; 65(Pt 12):o3136. · 0.35 Impact Factor