Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 25, 2002
Publication Date: N/A
Interpretive Summary: Aflatoxin is a very potent cancer-causing agent and toxin that is produced by the fungus Aspergillus flavus. When this fungus infects oilseed crops, the developing seed can become contaminated with this toxin, rendering the product unusable for food or feed. Soybeans can also be infected by A. flavus, but do not become contaminated with aflatoxin. Lipoxygenase, an enzyme found in soybean seed, has been proposed to be the factor that prevents aflatoxin contamination. In order to test this idea, soybeans that contain lipoxygenase were compared with soybeans that do not contain lipoxygenase for their respective abilities to support A. flavus growth and aflatoxin contamination. Lipoxygenase was found to not be the critical factor. Instead, seed coat integrity and seed viability were determined to be much more important for prevention of aflatoxin contamination in soybean seed. This research will benefit oilseed crop breeders, producers, and pathologists, and will aid in the formulation of methods to prevent aflatoxin contamination of food and feedstuffs.
Technical Abstract: Soybean lines lacking lipoxygenase (LOX) activity were compared with soybean lines with LOX activity for the ability to support growth and aflatoxin B1 production by the fungal seed pathogen Aspergillus flavus. Whole seed, broken seed, and heat-treated (autoclaved) whole seed were compared. Broken seed, irrespective of LOX presence, supported excellent fungal growth and the highest aflatoxin levels. Autoclaved whole seed, with or without LOX, produced good fungal growth and aflatoxin levels approaching those of broken seed. Whole soybean seed supported sparse fungal growth and relatively low aflatoxin levels. There was no significant difference in aflatoxin production between whole soybean seed either with or without LOX, though there did seem to be differences among the cultivars tested. The heat treatment eliminated LOX activity (in LOX + lines), yet aflatoxin levels did not change substantially from the broken seed treatment. Broken soybean seed possessed LOX activity (in LOX + lines), yet yielded the highest aflatoxin levels. Presence of active lipoxygenase did not seem to play the determinant role in susceptibility of soybean seed to fungal pathogens. Seed coat integrity and seed viability seem to be more important characteristics in soybean seed resistance to aflatoxin contamination. Soybean seed lacking LOX seems safe from the threat of increased seed pathogen susceptibility.