Interaction between toxigenic Aspergillus flavus Link and mites (Tyrophagus putrescentiae Schrank) on maize grains: effects on fungal growth and aflatoxin production

The ability of mites of the species Tyrophagus putrescentiae to spread the toxigenic fungus Aspergillus flavus from contaminated maize to sterile grai ns was studied under controlled conditions, Maize samples were distributed among boxes, each divided into two compartments by a barrier of polystyrene and having restricted access from one compartment to the other. One box co ntained only uncontaminated maize (negative controls). The other boxes cont ained two compartments. In compartment A the grains were inoculated with mi tes and/or fungi. Compartment B contained sterile grain. The boxes were mai ntained at 85% relative humidity and at two temperatures (25 and 30 degrees C) for 30, 60 or 90 days prior to analysis. Moisture content values varied between 15.4 and 16.9%, being greater in grain samples containing both mit es and fungi. Water activity levels ranged from 0.86 to 0.89. The numbers o f adult mites, eggs and fungal colony forming units as well as the concentr ations of aflatoxins increased with time of incubation, The presence of A. flavus contributed to the growth of mites and these, in turn, efficiently d ispersed viable fungal spores from the inoculated compartment to the uncont aminated one. After 30 incubation days, the fungal population in all sample s exceeded the international norms (10(4) CFU/g), and after 90 days of incu bation, aflatoxin was detected at over 23.7 mu g/kg, exceeding the limit es tablished by Brazilian legislation (20 mu g/kg) in food for human consumpti on. Samples of grains inoculated with A. flavus alone or a mixture of A. fl avus and mites developed concentrations of aflatoxins above 27.4 mu g/kg. T he current data confirms T. putrescentiae is a means of dispersal for toxig enic fungi in stood grain kept under warm and moist conditions. (C) 1999 El sevier Science Ltd. All rights reserved.