Thin layer chromatographic method for analysis and chemical confirmation of sterigmatocystin in cheese.

A semi-quantitative method is described for the analysis of sterigmatocystin in cheese. The method is based on extraction of cheese with MeOH--4% KCl (9 + 1), followed by Florisil and polyamide column cleanup and 2-dimensional thin layer chromatography (TLC). Visualization of sterigmatocystin on the TLC plates is enhanced by an AlCl3 spray reagent. The identity of sterigmatocystin is confirmed by a 2-dimensional TLC test based on reaction with trifluoroacetic acid (TFA) on the plate after first development. The reaction product formed is visualized by spraying with AlCl3. The method allows detection and confirmation of sterigmatocystin in cheese at concentrations as low as 5 micrograms/kg. The method has been applied to cheese samples ripening in warehouses and naturally molded with Aspergillus versicolor.

Fungal growth and the presence of sterigmatocystin in hard cheese.

Molds isolated from visibly molded cheeses in shops, households, and warehouses have been identified. Mold flora of cheeses in shops and households consisted mainly of Penicillium verrucosum var. cyclopium. On cheeses ripening in warehouses, Penicillium verrucosum var. cyclopium, Aspergillus versicolor, Aspergillus repens, and Enicillium verrucosum var. verrucosum were the dominant mold species. Cheese ripening in warehouses and molded with A. versicolor were examined for sterigmatocystin. Nine of 39 cheese samples contained sterigmatocystin in the surface layer in concentrations ranging from 5 to 600 micrograms/kg.