Yeasts and Molds: Aspergillus flavus

Aspergillus flavus is a mycotoxigenic fungus that possesses the ability to produce B aflatoxins. It can be readily distinguished morphologically by the production of a bright yellow-green conidial color, when cultured on malt extract agar or Czapek yeast extract agar. It is the most widely reported food-borne fungus and is one of the dominant species found on stored products, particularly grains, as it is able to thrive in low-water activity, high-temperature environments. Cotton seed lots with aflatoxin levels of above 20. ppb cannot be sold for dairy feed, as a small proportion of the toxin can be transferred to the milk of the dairy cows, where it is slightly modified to aflatoxin M1. Aspergillus flavus can produce aflatoxins on cheddar cheese, with the toxin penetrating up to 1.28. cm into the cheese. Growth of the fungus is largely unaffected by pH; it can grow over the entire pH range from 2.1 to 11.2, although growth rates are slower at pH <3.5, while it can grow at temperatures as low as 10-12. °C and as high as 50-55. °C, with optimal growth occurring at temperatures near 33. °C. A number of DNA-based techniques have been developed to identify and monitor Aspergillus section Flavi fungal isolates in foods.