Warehouse control of Aspergillus flavus link and A. parasiticus speare on peanuts (Arachis hypogaea) by phosphine fumigation and its effect on aflatoxin production

Six stacks of 36 bags containing ca. 50 kg of unshelled peanuts with moisture contents in the range of 18.0 to 21.0% (wet basis) (average 19.3%) were formed in a commercial warehouse located in a peanut-producing area in Sao Paulo, Brazil. Three stacks were fumigated with phosphine for 7 days. An initial dose of 3.0 g of aluminum phosphide per m3 was applied. A second and a third application of the same dose were carried out 24 and 144 h later. Before fumigation, infection by Aspergillus flavus and/or A. parasiticus was either not detected in the peanut mass or was very low (1 to 13%), but contamination with aflatoxins (up to 191 microgram/kg) was found in all stacks. After the fumigation treatments, a striking increase in infection was observed in the nonfumigated stacks (73 to 100% infected kernels) while in the fumigated stacks, A. flavus and/or A. parasiticus were either not detected or were isolated in insignificant amounts, indicating that phosphine was able to control fungal development in spite of the high moisture content of the kernels. After the fumigation period, the contamination levels of aflatoxins in the treated stacks remained unchanged, while the untreated stacks showed a staggering increase (up to 10,000 microgram/kg of peanuts). After a month, however, no difference was observed in aflatoxin contamination and infection by A. flavus and A. parasiticus between the untreated and the treated stacks