Cultural Methods in Aflatoxin Detection

Authors: Abbas, Hamed; SHIER, W - UNIV OF MINNESOTA; Horn, Bruce; Weaver, Mark

Submitted to: Journal of Toxicology Toxins Reviews
Publication Type: Review Article
Publication Acceptance Date: 5/1/2004
Publication Date: 8/1/2004
Citation: Abbas, H.K., Shier, W.T., Horn, B.W., Weaver, M.A. 2004. Cultural Methods in Aflatoxin Detection. Journal of Toxicology Toxins Reviews. 23:295-315

Interpretive Summary: Aflatoxins are food safety problems in the U.S. and many developing countries. People are usually protected from exposure to aflatoxins by monitoring foods and feeds for contamination. However, in developing countries complicated and expensive analytical methods may not be possible because of cost and lack of sophisticated equipment. In this research, two methods for detecting aflatoxin-producing capability in fungi through color change and production of ammonia vapor have been combined into one test. The combined tests reduced false positives to 0% and false negatives to 7%. Use of this assay will permit inexpensive identification of aflatoxin-producing fungi in food and feed, both in the U.S. and in other countries.

Technical Abstract: Aflatoxins present important food safely problems in both developed and developing countries. Contamination is monitored in developed countries using ELISA- and HPLC-based assays, both of which may be too expensive for routine use in many developing countries. There is a need for inexpensive alternative approaches to predict the likelihood of contamination in lots of foods and feeds. Reviewed here are culture-based methods, which determine if a sample is contaminated with aflatoxigenic fungi. These approaches include (i) blue fluorescence of aflatoxin B1, particularly when enhanced by including B-cyclodextrin in the culture medium, (ii) yellow pigment production and (iii) collor change on exposure to ammonium hydroxide vapor. Blue fluorescence detects the presence of aflatoxin B1, which is enhanced when the toxin complexes with the hydrophobic pocket of B-cyclodextrin. However, the yellow pigment and ammonium hydroxide vapor tests were found to be based on the production of yellow anthraquinone biosynthetic intermediates on the pathway to aflatoxins, which act as pH indicator dyes more visible in the red form at higher pH. Because the tests are based on two different mechanisms, it has been possible to combine them into a single test. In a study of 517 A. flavus isolates from the Mississippi Delta, the combined assay reduced false positives for aflatoxigenicity to 0% and false negatives to 7%. The increased predictive power of the combined cultural assay may enable its use for inexpensively identifying potential aflatoxin contamination in feeds and foods.