Aflatoxin M1 occurrence in samples of Grana Padano cheese.

A total of 223 samples of Grana Padano cheese manufactured in 4 years (1991-94) by dairies in 11 provinces of the Po valley were checked for aflatoxin M1. Grated cheese was extracted with chloroform and the defatted extract was purified by an immunoaffinity column; aflatoxin M1 was determined by HPLC using a fluorescence detector. From the analysis of the data it has emerged that only one sample exceeded the maximum tolerated level in cheese in some European countries (250 ng/kg). Most samples (91%) were in the range 5-100 ng/kg and only 15 (6.7%) in the range 100-250 ng/kg. Notwithstanding a diffuse microcontamination, the situation regarding the AFM1 levels can be considered fairly satisfactory. Mean contamination levels of 1992 and 1994 were significantly higher (P < 0.05) than those of 1993 and 1991. No significant difference was observed among provinces or dairies of origin.