Epsilon Archive for Student Projects

Abstract

This study aimed to gain more knowledge about morphological features of eight different species of Aspergillus section Flavi, which may aid in identification of these species. The presence of potentially toxigenic Aspergillus section Flavi, and occurrence of aflatoxins, in ready-to-eat Brazil nuts (Bertholletia excelsa) were also investigated.

Seventeen different strains, representing eight species from section Flavi, were grown at different water activities and different temperatures. After 7 days, as well as at 14 and 28 days for the lower water activities, colonies were visually inspected, and diameter and macroscopic characteristics were noted. Ten samples of Brazil nuts were collected from different market stalls in the city of Manaus, Brazil. Aspergillus section Flavi were isolated and identified by morphology and toxin profile. Toxin production was evaluated by the agar plug technique and quantification of aflatoxins in the Brazil nuts was performed by high-performance liquid chromatography.

It was found that macromorphology can be used to differentiate between some of the species if the different methods were combined, but for more certain identification, other available methods are better. One hundred and thirty five strains of suspected Aspergillus section Flavi were isolated and aflatoxin production was observed in 100 of them (74%). The most common species was Aspergillus nomius, followed by A. flavus and A. tamarii. Total aflatoxin content detected in the nuts did not exceed the European legislative limit of 10 µg/kg for ready-to-eat Brazil nuts, which would be considered safe to be consumed.