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United States Department of Agriculture

Agricultural Research Service

Title: Sequence of Substrate Utilization by Aspergillus Flavus in Medium Simulating Corn Kernels

Authors
item Mellon, Jay
item Dowd, Michael
item Cotty, Peter

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 29, 2001
Publication Date: N/A

Interpretive Summary: Aflatoxin is a very potent carcinogen and toxin that is produced by the fungus Aspergillus flavus. When this fungus infects corn plants, the developing seed can become contaminated with this toxin, rendering the product unusable for food or feed. Since seed-specific storage proteins, lipids, and starch comprise a large proportion of seed dry weight in corn, an investigation was undertaken to determine the effects of these seed components on fungal growth and toxin production. The study revealed that the fungus used both starch and fats to initially grow and make aflatoxin. Once the starch had been broken down to produce simple sugars (like glucose), the fungus showed a preference for these sugars. This research will benefit corn breeders, producers, and pathologists, and will aid in the formulation of methods to prevent aflatoxin contamination of food and feedstuffs.

Technical Abstract: Utilization of the three major corn reserve materials, starch, triglycerides (refined corn oil), and zein (storage protein), by Aspergillus flavus was monitored in vitro over a 7-day fermentation period. The fermentation medium contained the reserve materials in proportions approximating those found in mature corn kernels. Fermentations showed little change in substrate concentrations for the first 18 h. Then, hydrolysis of both starch and triglycerides occurred simultaneously, with peak concentrations of glucose and free fatty acids occurring at day 2 of the fermentation period. Fatty acid concentrations dropped rapidly after day 2, but began to increase again after day 6. Aflatoxin B1 production began with increased rates after 36 h, with a peak at day 4 of the fermentation. Aflatoxin B1 production paralleled fungal biomass production during its increasing phase, though biomass continued to accumulate at a slower rate during the later stages of the fermentation. A. flavus did no appear to preferentially utilize any of the released fatty acids. A number of fungal-specific metabolites were detected in these fermentations, including arabitol, erythritol, mannitol, trehalose, and kojic acid. Mannitol was produced in much higher concentrations than the other fungal metabolites and its concentration profile closely paralleled that of aflatoxin B1. The concentration profile of kojic acid reflected that of a secondary metabolite, with a peak at day 6 of the fermentation. In contrast to selective use of simple carbohydrates by A. flavus, the fungus displayed less discrimination when faced with utilization of complex carbohydrates, such as starch or triglycerides.

Last Modified: 12/20/2014
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