Effect of water activity and temperature on mycelial growth and ochratoxin A production by isolates of Aspergillus ochraceus on irradiated green coffee beans

Aspergillus ochraceus as a fungal contaminant and ochratoxin A (OTA) producer plays an important role in coffee quality. Temperature and water activity (a,) significantly influence mycelial growth and OTA production by isolates of A. ochraceus on green coffee beans. Maximum mycelial growth was found at 30degreesC and 0.95 to 0.99 a(w). A marked decrease in growth rate was observed when temperature and a, were reduced. At 0.80 a(w). mycelial growth occured only at 30 and 20degreesC for one isolate. Maximum OTA production was found at 20degreesC and 0.99 a(w). At 10degreesC. OTA was not produced, regardless of a(w) Similarly, no OTA was detected at 0.80 aw. OTA production ranged from the limit of detection (40 ng g(-1) of green coffee) to 17,000 ng g-1 of green coffee. Significant intraspecific differences in mycelial growth and OTA production were found. Primary data for lag phases prior to mycelial growth under the influence of temperature and a, were modelled by multiple linear regression, and the response surface plots were obtained.