The development and evaluation of a sensitive minicolumn assay for the detection of aflatoxin M1 in milk

Abstract

The aflatoxins comprise a subgroup of mycotoxins usually produced by Aspergillus parasiticus or Aspergillus flavus. Dairy cattle which ingest aflatoxin-contaminated feed will excrete aflatoxin M1 into the milk. The presence of this metabolite in milk is a concern for humans. At the present time, the best method to prevent ingestion of contaminated milk is by detection and diversion from our food supply. A field-practical method for the chemiselective immobilization and detection of aflatoxin M1 (CSID-M1) in milk has been developed in our laboratory. In this new method, aflatoxin M1 (AfM1) is selectively adsorbed in a small glass minicolumn at the interface of a layer of packed neutral sand and a narrow band of magnesium silicate (or Florisil). AfM1, at a level of 0.5 ppb or greater in contaminated milk, can be easily detected as a band of bright blue fluorescence with this assay. Briefly, whole milk- is diluted with water and passed through a C18 Sep-Pak cartridge. AfM1 is then partitioned by polarity and eluted from the cartridge with 2.5% acetone in methylene chloride. The eluate (containing AfM1) is added to the minicolumn detector. The tube is then washed with 2% methanol in methylene chloride and viewed under longwave UV light for AfM1. The limit o detection for CSID-M1 assay was determined to be 0.2 ppb compared with 0.3 ppb AfM1 using an immunoaffinity column extraction. The CSID-M1 assay was found to accurate, exhibiting no false positives or false negatives under the experimental condition imposed in this study. Also, the CSID-M1 detectors were shown to be chemically stable requiring no refrigeration for storage up to 20 weeks. In summary, the CSID-M1 assay was shown to be rapid, practical, easy to perform, and stable, thus facilitating its use in the prescreening of milk.