Evaluation of growth and ochratoxin A production by Aspergillus steynii and Aspergillus westerdijkiae in green-coffee based medium under different environmental conditions

Abstract

Aspergillus steynii and Aspergillus westerdijkiae are important ochratoxin A (OTA)-producing species frequently found in coffee. Although the processing of green coffee beans reduces markedly OTA contamination, levels exceeding the legal limits might remain in the final product. Environmental conditions are a crucial factor affecting growth and OTA production in fungal species; therefore, in this work, we analysed the effect of different levels of temperature (23, 28, 32, 37, 42°C) and water activity (aw) (0.89, 0.91, 0.93, 0.95, 0.97, 0.99) on growth and toxin production by A. steynii and A. westerdijkiae in green coffee-based medium. A. steynii was able to grow and produce OTA in a wider set of conditions than A. westerdijkiae. A new index (OTA risk index) has been described to integrate both fungal growth and OTA production and, according to it, A. steynii would pose a higher risk of OTA contamination in coffee than A. westerdijkiae at all the conditions tested. Neither A. steynii nor A. westerdijkiae were able to grow at the lowest value of aw (0.89) evaluated and OTA production was extremely low at 0.91. Therefore, the application of good practices during storage aiming to maintain low humidity levels might be essential to prevent OTA contamination in coffee at this stage. The optimal conditions of both species to grow and produce OTA were established at warm temperatures (28–32°C) and high aw levels. Therefore, these species could be considered well-adapted in predicted climate change scenarios resulting in a potential high risk source of OTA contamination for this product.