Cultural methods for aflatoxin detection

Aflatoxins present important food safely problems in both developed and developing countries. Contamination is monitored in developed countries using enzyme-linked immunusorbent assay (ELISA)- and high-performance liquid chromatography (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 detect aflatoxins in lots of foods and feeds. Reviewed here are culture-based methods that determine if a sample is contaminated with aflatoxigenic fungi. These approaches include 1) blue fluorescence of aflatoxin B₁, particularly when enhanced by including β-cyclodextrin in the culture medium, 2) yellow pigment production, and 3) color change on exposure to ammonium hydroxide vapor. The presence of aflatoxin B₁ can be detected by its blue fluorescence, which is enhanced when the toxin complexes with the hydrophobic pocket of β-cyclodextrin. The yellow pigment and ammonium hydroxide vapor tests are based on the production of yellow anthraquinone biosynthetic intermediates in the aflatoxin pathway. These compounds act as pH indicator dyes, which are more visible when they have turned red at alkaline pH. Because these 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.