Predicting the growth/no-growth boundary and ochratoxin A production by Aspergillus carbonarius in pistachio nuts

Black aspergilli are the main fungal contaminants in pistachio nuts. Ochratoxin A (OTA) production has been repeatedly reported in Aspergillus section Nigri; OTA has been occasionally detected in pistachio nuts in high concentrations. The aim of this study was to develop suitable validated models to predict the growth and OTA production boundaries by an Aspergillus carbonarius isolated from pistachios as a function of moisture content and storage temperature of pistachios. A full factorial design was used: the moisture content levels assayed were 12.5%, 17.9%, 24.0%, 29.5% and 34.8% and the incubation temperatures were 10, 15, 20, 25, 30, 37 and 42 degrees C. A probability model was built to predict the growth of the strain under the assayed conditions, which proved to be concordant in 73-91% of the cases with the observed probabilities in the validation test specifically chosen for limiting growth conditions. Similarly, the probability for the presence of OTA was correctly predicted in 90% of the cases. OTA accumulation was mainly a function of the temperature of storage, with a sharp increase at <15-20 degrees C; this value was very different from 30 to 35 degrees C, which was optimum for growth. Increasing OTA levels were found with increasing moisture content in the pistachio nuts. The impact of these results in the implementation of HACCP plans in Western Asian countries, is discussed. Probability models were applied in this work to mycotoxin accumulation for the first time, however, further research is required in the kinetics of mycotoxins accumulation to develop proper empirical models.