Determinations of aflatoxin M1 levels were carried out by HPLC using the following equipment: A Hewlett Packard HPLC system (Hewlett Packard, Agilent 1100, Palo Alto, USA) equipped with an auto sampler Agilent 1100 Series and a HP Agilent 1100 fluorescence detector; excitation and emission wavelengths were 360 and 430 nm, respectively.