Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 28, 1999
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 cotton 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 the saccharide raffinose comprise a large proportion of seed dry weight in cotton, an investigation was undertaken to determine the effects of these seed components on fungal growth and toxin production. Storage lipids alone were capable of supporting growth and aflatoxin biosynthesis by the fungus. The ability of whole ground cottonseed to support aflatoxin biosynthesis was greatly diminished if cottonseed lipids were removed. If the fungus was provided with a medium containing raffinose, seed lipids, and storage protein, it selectively used raffinose as a carbon source to drive initial biomass production and aflatoxin production. This research will benefit cotton breeders, producers, and pathologists, and will aid in the formulation of methods to prevent aflatoxin contamination of food and feedstuffs.
Technical Abstract: Cottonseed storage lipids (primarily triglycerides), either in crude or refined form were found to support growth and aflatoxin B1 production by Aspergillus flavus. When lipids were removed from whole ground cottonseed by petroleum ether extraction, aflatoxin production dropped by more than 800-fold. Reconstitution of the lipid-extracted whole ground seed with a crude preparation of cottonseed lipids to concentrations found in mature seed restored aflatoxin production to the previous levels. Fungal growth medium containing the three major cottonseed reserve materials, raffinose, triglycerides (refined cottonseed oil), and cottonseed storage protein, in proportions approximating those found in mature cottonseed was used to assess a number of fungal parameters in a 7-day fermentation period. A. flavus appeared to selectively use raffinose in the growth medium to support biomass and aflatoxin B1 production. The fungus metabolized raffinose by initial removal of the fructose moiety, followed by a rapid utilization of the remaining melibiose. Initial carbohydrate substrate was nearly exhausted by day 3. As the exhaustion of carbohydrate approached, fungal hydrolysis of triglycerides to free fatty acids began. At day 4, catabolism of fatty acids began in earnest, which appeared to drive gluconegenesis (peak at day 5). The fungus did not show a preference for utilization of the major released fatty acids (linoleic, oleic, palmitic, stearic acids). A. flavus also produced a number of storage metabolites, including arabitol, erythritol, mannitol, and trehalose. Interestingly, the mannitol production profile closely paralleled that of aflatoxin.