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Investigations of the metabolic pathway of mycotoxins by microsomal techniques are often laborious, causing an increasing demand for easy and rapid simulation methods. Thus, the non-microsomal oxidation technique of electrochemistry coupled online to mass spectrometry (EC/MS) was applied to simulate phase I biotransformation of the Fusarium mycotoxin zearalenone (ZEA). The obtained transformation products were identified by high resolution mass spectrometry (FT-ICR) and HPLC-MS/MS. Transformation products (TPs) from EC/MS were compared to those of other oxidative methods such as Fenton-like and Ce(IV) reactions and metabolites derived from in vitro assays (human and rat liver microsomes). Electrochemical oxidization of ZEA was achieved by applying a potential between 0 and 2,500 mV vs. Pd/H2 using a flow-through cell with a boron-doped diamond working electrode. Several mono-hydroxylated TPs were generated by EC/MS and Fenton-like reaction, which could also be found in microsomal in vitro assays. EC and Ce(IV) led to the formation of structurally different ZEA dimers and dimeric quinones probably connected over covalent biaryl C-C and C-O-C bonds. Although the dimerization of phenolic compounds is often observed in natural processes, ZEA dimers have not yet been reported. This is the first report on the formation of stable ZEA dimers and their related quinones. The tested non-microsomal methods, in particular EC/MS, could be useful in order to predict the biotransformation products of mycotoxins, even in cases where one to one simulation is not always feasible.
Mycotoxins cause a variety of mold-related health risks which makes it necessary to further examine their metabolic pathways in human and other mammals. Beside standard in vitro assays with liver cell microsomes an increasing interest in new and rapid simulation techniques are playing a growing role in mycotoxin research.
Herein, the coupling of electrochemistry with liquid chromatography and mass spectrometry (EC/LC/MS) is presented as fast and simple method to investigate the oxidative fate of mycotoxins. For this case study, two food relevant mycotoxins (zearalenone and citrinin) were selected. Experiments were performed by using an electrochemical flow through cell integrated in the flow path of the autosampler of the chromatographic system. The reaction mixture was separated by a RP-C18 column and analyzed by a single quadrupole MS (Figure 1). Oxidation products were generated by applying potentials of 400, 800, 1200 and 1600 mV vs Pd/H2 using a glassy carbon working electrode. Different oxidation reactions like hydroxylation, dehydrogenation and dimerization lead to a diverse product pattern of the investigated mycotoxins.
In a comparative study, electrochemical generated reaction products were compared with metabolites produced by human and rat liver microsomes in vitro. The obtained data show that EC/LC/MS is a versatile and promising tool in mycotoxin research to support metabolic investigations of known and unknown mycotoxins.
Mycotoxins occur widely in foodstuffs and cause a variety of mold-related health risks to humans and animals. Elucidation of the metabolic fate of mycotoxins and the growing number of newly discovered mycotoxins have enhanced the demand for fast and reliable simulation methods. The viability of electrochemistry coupled with mass spectrometry (EC/ESI-MS), Fenton-like oxidation, and UV irradiation for the simulation of oxidative phase I metabolism of the mycotoxins citrinin (CIT) and dihydroergocristine (DHEC) was investigated. The specific reaction products are compared with metabolites produced by human and rat liver microsomes in vitro. Depending on the applied potential between 0 and 2000 mV vs. Pd/H-2 by using a flow-through cell, CIT and DHEC are oxidized to various products. Besides dehydrogenation and dealkylation reactions, several hydroxylated DHEC and CIT species are produced by EC and Fenton-like reaction, separated and analyzed by LC-MS/MS and ESI-HRMS. Compared to reaction products from performed microsomal incubations, several mono- and dihydroxylated DHEC species were found to be similar to the reaction products of EC, Fenton-like reaction, and UV-induced oxidation. Consequentially, nonmicrosomal efficient and economic simulation techniques can be useful in early-stage metabolic studies, even if one-to-one simulation is not always feasible.
Development of analytical method and certified reference material for zearalenone in edible oils
(2017)
Quality and safety of food products require their reliable analysis. Contaminants, in particular mycotoxins, are key-components for food safety. About 25 % of the world's food crops are contaminated with mycotoxins posing a severe health risk to humans. In order to strengthen food safety and consumer protection the European Commission (EC) set maximum levels for priority mycotoxins in certain foods for human consumption. In 2013, the EC and CEN (European Committee for Standardization) started an initiative to standardize analytical methods for mycotoxins in food which gained increasing relevance, e.g. zearalenone (ZEN).[1] ZEN, an estrogenic mycotoxin produced by several Fusarium species, contaminates cereal crops worldwide. Due to its lipophilic nature ZEN is often found in edible oils (particularly in maize germ oils) derived from contaminated plants. Therefore, an European maximum level of 400 µg/kg is currently in force.[2] To perform reliable food analysis a sustainable metrological infrastructure is of major importance enabling the quantification of priority mycotoxins (here: ZEN). To achieve this goal an integrated approach is needed targeted at the development of validated analytical methods and certified reference materials (CRM).
A highly selective method for ZEN in edible oils will be presented, based on solid phase extraction (SPE) using hydrazine-functionalized particles. This method was developed for manual application using commercial SPE cartridges as well as for automated SPE-HPLC online coupling. While ZEN is covalently coupled to the solid phase by means of a hydrazone bond, undesired matrix components can be removed very efficiently. Finally, ZEN is decoupled from the solid phase, leading to highly purified extracts which are measured by HPLC-FLD.
The development of the first European Reference Material (ERM®) for ZEN in maize germ oil (ERM®-BC715) will be presented and discussed. This ERM®-project underpins the urgent need for mycotoxin-CRMs to support food safety and public health.
[1] European Commission (EC) Mandate M/520 (2013) for standardisation addressed to CEN for methods of analysis for mycotoxins in food. [2] Commission Regulation (EC) No 1126/2007 amending Regulation (EC) No 1881/2006 setting maximum levels for certain contaminants in foodstuffs as regards Fusarium toxins in maize and maize products.
The sensitive detection of the mycotoxin citrinin (CIT) utilizing ist fluorescence requires approaches to enhance the emission. In this respect, we studied the complexation of CIT and ochratoxin A (OTA) with Al3+ in methanol using absorption and fluorescence spectroscopy. In this context, an isocratic high performance liquid chromatography (HPLC) method using a polymer column and a fluorescence detector was also developed that enables the separation of the metal ion complexes from the free ligands and non-complexed Al3+. CIT and OTA showed distinct changes in their absorption and fluorescence properties upon Al3+-coordination, and the fluorescence of CIT was considerably enhanced. Analysis of the photometrically assessed titration of CIT and OTA with Al3+ using the Job plot method revealed 1:2 and 1:1 stoichiometries for the Al3+ complexes of CIT (Al:CIT) and OTA (Al:OTA), respectively. In the case of CIT, only one -diketone moiety participates in Al3+ coordination. These findings can be elegantly exploited for signal amplification and provide the base to reduce the limit of detection for CIT quantification by about an order of magnitude, as revealed by HPLC measurements using a fluorescence detector.
The formation of transformation products (TPs) from contaminants and residues is becoming an increasing focus of scientific community. All organic compounds can form different TPs, thus demonstrating the complexity and interdisciplinarity of this topic. The properties of TPs could stand in relation to the unchanged substance or be more harmful and persistent. To get important information about the generated TPs, methods are needed to simulate natural and manmade transformation processes. Current tools are based on metabolism studies, photochemical methods, electrochemical methods, and Fenton's reagent. Finally, most transformation processes are based on redox reactions. This review aims to compare these methods for structurally different compounds. The groups of pesticides, pharmaceuticals, brominated flame retardants, and mycotoxins were selected as important residues/contaminants relating to their worldwide occurrence and impact to health, food, and environmental safety issues. Thus, there is an increasing need for investigation of transformation processes and identification of TPs by fast and reliable methods.
Mycotoxins cause a variety of mold-related health risks which makes it necessary to further examine their metabolic pathways in human and other mammals. Beside standard in vitro assays with liver cell microsomes an increasing interest in new and rapid simulation techniques are playing a growing role in mycotoxin research.
Herein, the coupling of electrochemistry with liquid chromatography and mass spectrometry (EC/LC/MS) is presented as fast and simple method to investigate the oxidative fate of mycotoxins. For this case study, two food relevant mycotoxins (zearalenone and citrinin) were selected. Experiments were performed by using an electrochemical flow through cell integrated in the flow path of the autosampler of the chromatographic system. The reaction mixture was separated by a RP-C18 column and analyzed by a single quadrupole MS (Figure 1). Oxidation products were generated by applying potentials of 400, 800, 1200 and 1600 mV vs Pd/H2 using a glassy carbon working electrode. Different oxidation reactions like hydroxylation, dehydrogenation and dimerization lead to a diverse product pattern of the investigated mycotoxins.
In a comparative study, electrochemical generated reaction products were compared with metabolites produced by human and rat liver microsomes in vitro. The obtained data show that EC/LC/MS is a versatile and promising tool in mycotoxin research to support metabolic investigations of known and unknown mycotoxins.
A new dimer of the food-relevant mycotoxin zearalenone was isolated after electrochemical and chemical oxidation. The structure was determined as a 16-O-15'-biaryl ether-linked dimer based on spectroscopic analyses (1H- and 13C-NMR, COSY, HMBC, and HSQCAD) and high-Resolution mass spectrometry analysis (Q-TOF).
Mykotoxine in Lebensmitteln stellen weltweit Probleme dar, Zearalenon in Speiseöl ist ein solches. Neue Hydrazinbasierte Analyseverfahren können jetzt helfen, den EU-Grenzwert besser zu kontrollieren. Aber auch die Strukturaufklärung von Transformationsprodukten und verlässliche Kalibrierstandards sind aktuelle Herausforderungen.