Influence of Lipids with and without Other Cottonseed Reserve Materials on Aflatoxin B₁ Production by Aspergillus flavus

Abstract

Cottonseed storage lipids (primarily triglycerides), in either crude or refined form, were found to support growth and aflatoxin B 1 production by Aspergillus flavus. When lipids were removed from ground whole cottonseed by petroleum ether extraction, aflatoxin production dropped by more than 800-fold. Reconstitution of the lipid-extracted ground whole seed with a crude preparation of cottonseed lipids restored aflatoxin production to the previous levels. Fungal utilization of the three major cottonseed reserve materials, raffinose, triglycerides (refined cottonseed oil), and cottonseed storage protein, was monitored in vitro over a 7 day fermentation period. The fermentation medium contained the reserve compounds in proportions approximating those found in mature cottonseed. A. flavus rapidly converted raffinose to fructose and melibiose, presumably by action of invertase, and then hydrolyzed the melibiose. These simple sugars apparently supported initial growth and aflatoxin B 1 production. Raffinose and the resulting melibiose were nearly exhausted by day 2. Fungal hydrolysis of triglycerides began as exhaustion of carbohydrate approached. After day 2, rapid catabolism of the released fatty acids began and coincided with glucose regeneration through gluconeogenesis, which peaked on day 6. The fungus did not preferentially utilize specific fatty acids. A. flavus also produced a number of storage metabolites, including arabitol, erythritol, mannitol, and trehalose. Mannitol was produced in much higher concentrations than the other storage metabolites. Selective use of simple carbohydrates by A. flavus to drive aflatoxin production may suggest strategies for reducing vulnerability of cottonseed to aflatoxin contamination.

Occurrence, importance and control of mycotoxins: A review

“…In stored cottonseed growth of aflatoxigenic fungi may occur when the average moisture level in stored cottonseed is greater than 7-8%. The lipids and proteins in cottonseed enhance aflatoxin production (Mellon and Cotty, 1998;Mellon et al, 2000). Peanut hay, peanuts and peanut by-products are an important source of mycotoxins (McKenzie et al, 1981;Cullen and Newberne, 1994).…”

Effects of different substrates and oils on aflatoxin B1 production by Aspergillus parasiticus

“…These four substrates were selected for further study because oil mainly exists in these four crops. Defatted wheat germ, defatted corn germ, defatted peanut, and defatted soybean were chosen to eliminate the interference of oil and provide a more sensitive medium for observing subtle changes in AFB 1 production [18][19][20]. A total of four oils (wheat germ oil, corn germ oil, soybean oil, and peanut oil) were added to the four corresponding defatted substrates (defatted wheat germ, defatted corn germ, defatted peanut, and defatted soybean) at the rates of 2, 5, 10, and 15 g of 100 g of substrates (Fig.…”

“…For example, Aspergillus predominantly colonizes the lipid-rich embryo in corn kernels and targets lipid bodies rather than starch granules [18,19]. Cottonseed meal supported 800-fold more aflatoxin production 1 3 by A. flavus before lipid extraction [20]. On the other hand, the cause for aflatoxin production by A. flavus was also attributed to trace elements of the fungal substrate in synthetic medium or semi-synthetic medium [21,22].…”

Nutrient Environments Influence Competition among Aspergillus flavus Genotypes

“…Competitive abilities vary among A. flavus genotypes in a host-dependent manner (44), and since hosts vary in nutrient composition (56)(57)(58), these differences may influence competitive interactions among A. flavus genotypes during invasion of host tissues and sporulation. The sequence of contact with the substrate had little influence on competition between cocultivated isolates on Czapek's agar.…”