Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/31/2011
Publication Date: 10/31/2012
Citation: Shier, W., Abbas, H.K., Weaver, M.A., Horn, B.W. 2012. Visualization of aflatoxigenic Aspergillus flavus contamination of coconut (Cocos nucifera) nutmeat (Copra) using ammonia treatment. Acta Horticulturae. 963: 177-182.
Interpretive Summary: Aflatoxin production in crops can occur in the field before harvest and during processing after harvest. The standard practice in developed countries is to dry crops rapidly at harvest time, and subsequently store them under near ideal conditions maintaining a low moisture content that prevents further growth and toxin production by Aspergillus flavus and other fungi. However, processing and storage of crops in developing countries is often carried out under less than ideal conditions. In the case of coconut meat (copra), the agricultural product is large enough to allow hand sorting where labor costs are low. Aflatoxigenic A. flavus has been shown to produce anthraquinone pigments, which turn from yellow to a more readily-detected red color when the pH is raised to near neutral by exposure to ammonia. The present study was undertaken to determine if this color change could be used to detect infestation of copra by aflatoxigenic A. flavus. Following ammonia treatment aflatoxigenic A. flavus was readily distinguished from non-aflatoxigenic A. flavus grown on copra. Neutralization treatments may also be a useful adjunct to machine-based color sorting of seeds of other agricultural products, including rice.
Technical Abstract: For many crops government regulations define mycotoxin contamination levels that reflect the primary determinants of quality, value and possible uses of crops. Quality can be raised by lowering the mycotoxin level through a remediation process. In the case of copra, the dried nutmeat of the coconut, hand sorting to remove Aspergillus flavus-contaminated copra is an effective remediation strategy. However, typically only about one third of A. flavus contaminants in plants are aflatoxigenic, so it would be useful to have a method to visually distinguish aflatoxigenic from non-aflatoxigenic A. flavus contamination of copra. We have applied a cultural method for identifying aflatoxigenic A. flavus in which ammonia exposure is used to raise the pH, changing the color of anthraquinone pigments associated with the aflatoxin biosynthetic pathway from yellow to a much more visible red. Aflatoxigenic A. flavus was readily differentiated from non-aflatoxigenic A. flavus on copra by the appearance of red color after ammonia exposure, particularly along break lines. These studies suggest ammonia exposure would be a useful addition to aflatoxin remediation practices in copra and possibly other crops.