Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2004
Publication Date: 2/15/2005
Citation: Mellon, J.E., Dowd, M.K., Cotty, P.J. 2005. Substrate utilization by Aspergillus flavus in inoculated whole corn kernels and isolated tissues. Journal of Agricultural and Food Chemistry. 53(6):2351-2357.
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, these components represent potential nutrient sources for the fungus. An investigation was undertaken to determine the effects of these seed components on fungal metabolism. The study revealed that the fungus used free sugars in the seed germ to initially grow and make aflatoxin. Once the free sugars had been exhausted, the fungus shifted to using germ fats for growth and aflatoxin production. 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 major corn reserve materials, free saccharides, starch, triglycerides and zein (storage protein), by Aspergillus flavus was monitored over a 12-day incubation period. Inoculated whole kernels were compared to non-inoculated kernels. Concentrations of sucrose and raffinose in inoculated seed decreased to nearly zero at six days, whereas concentrations of these saccharides in non-inoculated seed dropped at a considerably slower rate, and significant levels remained at the end of the incubation period. Triglyceride concentrations remained unchanged in the non-inoculated seed, but dropped continuously after two days of incubation in the inoculated seed. Starch and zein concentrations did not change in either non-inoculated or inoculated corn kernels during the 12-day incubation period. Aflatoxin production began after two days and continued to increase throughout the remainder of the incubation period in the inoculated seed. Significant concentrations of erythritol, arabitol, and mannitol were produced in the inoculated seed, with peak concentrations occurring at eight days. Whole seed and germ tissue appeared to support good fungal growth and aflatoxin production, whereas, ground tissues and endosperm did not. A. flavus appears to favor free saccharides as initial carbon substrates followed by triglycerides. When invading non-wounded corn kernels, the fungus selectively targets the germ tissue where these materials are localized in the highest concentrations.