Growth and ochratoxin A production by Aspergillus niger group strains in coffee beans in relation to environmental factors

Abstract

The effect of water activity (aW), temperature and their interactions on lag phase, mycelial growth rate and ochratoxin A (OTA) production at 7, 14 and 21 days of incubation of two OTA-producer strains belonging to Aspergillus niger group on irradiated coffee beans was determined. Irradiated coffee beans were re-hydrated to 0.910-0.995 of aW with sterile distilled water. The temperatures assayed were 15, 25 and 30 °C. Growth assessment was measured every day during the incubation period to calculate the growth rate. OTA production was examined at 7, 14 and 21 days by high-performance liquid chromatography. Optimal aW for growth was 0.995 at 25 °C for RCC4 and RCC20 strains, being 1.10 and 2.36 mm/day, respectively. OTA concentration varied considerably depending on aW, temperature and incubation time assayed. Maximum OTA production was obtained at 0.973 and 0.995 aW at 30 °C for both strains. The results of the present work indicate that knowledge of the optimal and marginal conditions of black Aspergillus growth and OTA production allow methods to be established for preventing the development of these fungal and mycotoxin production on coffee beans. The data obtained provide useful information for predicting the risk factors for OTA contamination on coffee beans.