METHODS OF DETERMINATION OF AFLATOXINS PRECURSORS IN DAIRY-COWS FEED .1. DETERMINATION OF STERIGMATOCYSTIN LEVEL IN MIXED FEED AND CORN-SILAGE

In toxinogenic strains of Aspergillus flavus and A. parasiticus the di furanocoumarin-based metabolite sterigmatocystin (STC) is the penultim ate precursor of the final aflatoxins of the B and G type. The main pr oducer of the final sterigmatocystin is the mould Aspergillus versicol or, a widespread fungus on rotting plant material. To elucidate the fe ed-hygienic importance of the prevalence of STC with respect to a poss ible reduction to aflatoxin B in the dairy cow a sensitive method was developed for the detection and determination of STC in stockfeed for dairy cows. The dried and ground sample is extracted with 4% KCl in me thanol (9+1, v/v), the concentrated extract chromatographed over a Flo risil column. The eluate is transferred to a gel permeation system, em ploying Biobeads SX3 and cyclohexane/ethylacetate as the solvent. The concentrated extract is then spotted on a silicagel thinlayer plate an d, additionally, purified with ether/light petroleum. The final two-di mensional chromatography is carried out with chloroform/methanol (1002, v/v) and n-hexane/diethyl-ether/acetic acid (75+25+10, v/v) for the second development in an unsaturated chamber. For better visualizatio n and densitometric scanning the fluorescence of STC was enhanced and converted to the bright yellow colour with saturated aluminium chlorid e solution in ethanol. The limit of detection is about 1 ppb. The limi t of determination is 3 ppb in stockfeed dry matter.