Effect of Interactions of Water Activity, Temperature and Incubation Period on Ochratoxin A Production by Aspergillus niger

摘要

Ochratoxin A (OTA) is a toxic metabolite produced primarily by Aspergillus ochraceus, A.carbonarius and A.niger. OTA has been detected in a number of commodities including coffee bean. Knowledge of the influence of environmental factors viz, water activity and temperature on OTA production may contribute to the prevention of OTA contamination. As A.niger is a commonly isolated mould from coffee beans, studies were conducted to determine the effect of interactions of different water activity levels (0.8, 0.85, 0.9, 0.95 and 0.99), temperatures (15, 20, 25, 30, 35 and 40 C) and incubation periods (5,, 10, 15, 20, 25 and 30 days) on ochratoxin A production by two A.niger isolates using sterilized green coffee bean as an assay medium. The results showedthe ability of both A.niger isolates to produce OTA at water activity levels between 0.85 and 0.99 with an optimum at 0.99. Both isolates produced OTA at 15 to 40 C with the highest OTA production at 20 C. A significant production of OTA was noticed 10days after incubation. Of the two A.niger isolates tested, SALARA.2 produced comparatively higher OTA production than WAYROB.19. The results generated in this study will lead to a better understanding of the role of A.niger isolates on OTA contaminationof green coffee beans.