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Zearalenone (ZEN) and its sulfate and glucoside conjugates have been detected in (a broad variety of) food and feed commodities1. Both conjugated derivatives are formed as part of fungal or plant secondary metabolism and thus, belong to the group of modified mycotoxins2. After consumption of contaminated foodstuff, the conjugates can be hydrolyzed by human intestinal microbiota leading to liberation of ZEN that implies an underestimation of the true ZEN exposure. In order to include ZEN conjugates in routine analysis, as well as for toxicological investigation reliable standards are needed.
The objective of the present study was to develop a simple and economic method for biosynthesis of ZEN conjugates. Preceding experiments on the biotransformation of ZEN by Rhizopus and Aspergillus species showed a mixed metabolite formation3. Therefore, these known ZEN conjugating fungal strains were screened for their potential to selectively synthesize the ZEN derivatives ZEN-14-sulfate (Z14S), ZEN-14-glucoside (Z14G) and ZEN-16-glucoside (Z16G). The screening was conducted by adding ZEN to liquid fungal cultures. Cultivation conditions and ZEN incubation time were varied. All media samples were analyzed for metabolite formation by HPLC-MS/MS. Z14S was exclusively formed by A. oryzae. Under optimized conditions a specific biosynthesis of Z14G by R. oryzae and Z16G by R. oligosporus was achieved. After liquid-liquid-extraction and preparative chromatographic cleanup 1H-NMR purities of ≥ 73% for Z14S, ≥ 82% for Z14G and ≥ 50% for Z16G were obtained. In addition, a consecutive biosynthesis was developed by first using Fusarium graminearum for ZEN biosynthesis on rice based liquid medium. After inactivation of Fusarium the subsequent conjugation reaction was conducted utilizing Aspergillus and Rhizopus species under the various optimized conditions.
In this study an easy and cost-efficient biosynthesis for Z14S, Z14G and Z16G was developed. The developed biosynthesis could be also used for other metabolites like ZEL conjugates. Our results of the in vitro screening indicate also the formation of a ZEL-glucoside and α ZEL-sulfate as major metabolites by R. oryzae. In sum, under optimized cultivation conditions fungi can be easily utilized for a targeted and stereospecific synthesis of ZEN conjugates.
Performance and Efficiency of Cleanup Columns for Selected Fusarium Mycotoxins and Conjugates
(2013)
Überall, wo sich Schimmel bildet, können hochgiftige Mykotoxine entstehen, besorgniserregende Gifte für Mensch und Tier.
Ungefähr ein Viertel der Weltnahrungsproduktion ist mit diesen schädlichen Stoffen infizier!, so die Ernährung- und Landwirtschaftsorganisation FAQ. Lebensmittel wie Getreide, Mais und Nüsse, die in grollen Mengen verarbeitet werden, sind ein idealer Nährboden für die Bildung von Mykotoxinen und können bereits vor der eigentlichen Verarbeitung kontaminiert sein.
Eine Kontrolle der Lebensmittellieferungen ist also aus Sicherheitsgründen unerlässlich, denn schon geringe Mengen infizierter Lebensmittel können ganze Bestände vergiften. Aufwendige Laborverfahren, die extern von geschultem Fachpersonal durchgeführt werden und daher mehrere Tage dauern, bedeuten hohe Kosten für die verarbeitende Industrie. Die Aokin AG aus Berlin hat mit der Automatisierung des „aokinmycontrol-Systems den Analyseprozess industrietauglich gemacht.