Density Fluctuations of Two Major Aspergillus Species Airborne Spores in Pistachio Growing Regions of Iran

Contamination of pistachio nuts by aflatoxigenic strains of Aspergillus species is the greatest constraint to production and export of pistachio nuts in Iran, the leading producer of pistachio nuts in the world. Kerman province is the main region in Iran where 85%, of pistachio nuts are produced. Determining the population density of Aspergillus spores in the orchards and terminals which are the main sources of contamination would provide information about critical control points throughout pistachio production process. Density fluctuations of airborne Aspergillus flavus and Aspergillus niger spores were investigated during 2000-2002. The monthly density fluctuations of Aspergillus spp. spores were determined by exposing open petri-dishes containing AFPA and Cz media for 15 minutes, between 11 and 13 hours at different localities in each orchard from spring to winter, and at pistachio nut processing terminals during harvesting time. The results showed that density fluctuations of A. flavus and A. niger rose from the beginning of spring reaching a peak in September. The population then gradually decreased and had little variation in relation to different periods and places. Population density of Aspergillus spores increased during processing stages (especially hulling and peeling) at different pistachio terminals. In most cases, there were positive correlations (r = 0.69 - 0.91) between environmental temperature and spore density. The peak of spore density coincided with pistachio nut maturation characterized by splitting and cracking.