Occurrence of aflatoxin M1 in domestic milk in Japan during the winter season

A total of 208 samples of commercial pasteurized milk gathered from retail outlets across Japan during the winter season were analysed for aflatoxin M-1 (AFM(1)). Japan was divided into 11 regions from north to south, and nine to 45 milk samples from each region were randomly purchased between December 2001 and February 2002. Each milk sample was cleaned up by an immunoafinity column, and AFM(1) was quantified by liquid chromatography with fluorescence detection in four independent laboratories. The limit of detection of the method was 0.001 mug kg(-1). The identity of the putative AFM(1) in milk sample was confirmed by the formation of AFM(1) hemi-acetal with trifluoroacetic acid. Based on the results obtained with spiked samples (0.05 mug AFM(1) kg(-1)), the mean recovery was 91.4%, the relative standard deviation for repeatability was 4.6%, and the relative standard deviation for reproducibility was 8.0% among four independent laboratories. AFM(1) was detected in 207 (99.5%) of 208 milk samples at 0.001-0.029 mug kg(-1), with a mean of 0.009 mug kg(-1) and a 90th percentile of 0.014 mug kg(-1). No significant difference of the level of AFM(1) contamination was observed among the regions.