Method for the Determination of Aflatoxin M1 in Fluid Milk and Milk Products

The method described utilizes acetone-water (77+23) for extraction of M1 from milk and milk products in a 3 min blender extraction. Phospholipids and soluble proteins in the primary extract are removed by treatment with lead acetate, and residual neutral lipids in the treated extract are removed by partition into hexane. Aflatoxin M1 is partitioned into chloroform, which is then washed with salt solution, and the chloroform is evaporated. The residue is dissolved in chloroform, and M1 is resolved on silica gel-coated plates developed in chloroform-acetone-2-propanol (850+100+50). This basic procedure is applicable to fluid milk and reconstituted freeze-dried milk powder at levels as low as 0.1 μg M1/L. Extracts of nonfat dry milk, evaporated and condensed milk, and cheeses, which require further cleanup before TLC, are purified on a cellulose-aqueous methanol partition column to allow reliable determination of M1 at levels as low as 0.2 Mg/L or kg. Average recovery of M1 added to fluid milk at levels of 0.1–1.0 μg/L was 106% without the use of the cleanup column and 90% when the column was used to purify the extracts. Average recovery of M1 added to other milk products at a level of 0.2 Mg/L or kg was 88%. The precision of the method (coefficient of variation) was estimated to be ±16% at 0.2 Mg/L in fluid milk, and ±4% at a 34 Mg/kg level in contaminated freeze-dried milk.