Water activity and temperature influence on simultaneous production of aflatoxin and cyclopiazonic acid by Aspergillus flavus in peanuts

VAAMONDE, GRACIELA; PATRIARCA, ANDREA; FERNÁNDEZ PINTO, VIRGINIA

Samso, Denmark

Workshop; International Commission of Food Mycology Workshop; 2003

International Commission of Food Mycology

Some isolates of Aspergillus flavus are able to produce cyclopiazonic acid (CPA) in addition to aflatoxins (AF). Strains with the ability of producing high levels of CPA are frequently isolated from substrates such as peanuts and corn indicating that this toxin could be a more common metabolite of A. flavus than AF and thus is also likely to be present in AF contaminated foods [1]. The presence of both toxins in food and feed may result in synergistic effects. It is, therefore, important that production of these toxins be controlled. The interaction between water activity (aw ) and temperature is a most critical determinant for fungal growth and for mycotoxin production. Conditions for mycotoxin production are generally more restrictive  than those for growth and can differ between different mycotoxins produced by the same species, as well as between fungi producing the same mycotoxin. The effects of temperature and aw on the production of AF by A. flavus  have been widely studied, but information on how these factors affect the simultaneous production of AF and CPA on natural substrates is very scarce. An experiment with a full factorial design was used to study the effects of and interaction among temperature, aw  and incubation period on co-production of AF and CPA on peanuts by a cocktail inoculum of A. flavus strains. Relative concentrations of the mycotoxins produced were strongly influenced by all of these factors and a significant interaction between factors was also observed. CPA production was inhibited at the lowest aw studied (0.86) while AF was produced on the whole aw  range (0.86-0.94). Temperature effect for both toxins was highly dependant on aw . CPA reached a maximal production (4500 ppb) after 28 days of incubation at aw  0.94 and 25ºC. A different fungal response to environmental conditions in relation with biosynthesis of both secondary metabolites was observed.