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Background: Aspergillus niger is a filamentous fungus found in the environment, on foods and feeds and is used as host for production of organic acids, enzymes and proteins. The mycotoxin fumonisin B 2 was recently found to be produced by A. niger and hence very little is known about production and regulation of this metabolite. Proteome analysis was used with the purpose to reveal how fumonisin B 2 production by A. niger is influenced by starch and lactate in the medium.

Here we present a method for simultaneous determination of the fungal metabolites mycophenolic acid, ochratoxin A (OTA) and fumonisin B(2) (FB(2)) in meat products. Extraction was performed with water-acetonitrile, followed by acetone-induced precipitation of salts and proteins. Purification and identification of analytes was performed by mixed-mode reversed-phase anion-exchange chromatography in direct ion-exchange mode, followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) detection. Quantification was based on isotope dilution with fully (13)C-labelled FB(2) and OTA, and matrix-spiked calibration curves. Fermented sausages inoculated with an OTA- and FB(2)-producing strain of Aspergillus niger were analysed, but no analytes were detected. Analysis of 22 retail products showed one Parma meat with a very high level of OTA contamination (56-158 microg/kg) that clearly exceeded the Italian regulatory limit of 1 microg/kg. This sample and uninfected control samples were subsequently reanalysed, and the high OTA content was verified by two other techniques: (i) LC-time-of-flight MS confirmed the accurate mass as well as chlorine isotope pattern; and (ii) sample methylation in methanol-BF(3) and subsequent LC-MS/MS provided indirect confirmation by detection of the OTA methyl ester. In the contaminated Parma ham, the high OTA level most likely originated from growth of Penicillium nordicum on the meat.

Flavor production among 12 strains of Debaryomyces hansenii when grown on a simple cheese model mimicking a cheese surface was investigated by dynamic headspace sampling followed by gas chromatography-mass spectrometry. The present study confirmed that D. hansenii possess the ability to produce important cheese flavor compounds, primarily branched-chain aldehydes and alcohols, and thus important for the final cheese flavor. Quantification of representative aldehydes (2-Methylpropanal, 3-Methylbutanal) and alcohols (2-Methyl-1-propanol, 3-Methyl-1-butanol, and 3-Methyl-3-buten-1-ol) showed that the investigated D. hansenii strains varied significantly with respect to production of these flavor compounds. Contrary to the alcohols (2-Methyl-1-propanol, 3-Methyl-1-butanol, and 3-Methyl-3-buten-1-ol), the aldehydes (2-Methylpropanal, 3-Methylbutanal) were produced by the D. hansenii strains in concentrations higher than their sensory threshold values, and thus seemed more important than alcohols for cheese flavor. These results show that D. hansenii strains may have potential to be applied as cultures for increasing the nutty/malty flavor of cheese due to their production of aldehydes. However, due to large strain variations, production of flavor compounds has to be taken into consideration for selection of D. hansenii strains as starter cultures for cheese production.

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