Contamination of Tree Nuts by Aflatoxigenic Fungi: Aflatoxin Content of Closed-Shell Pistachios

Inoculation of fresh, or dried and rehydrated, closed-shell pistachios at the stem end of the shell with spores of Aspergillus flavus ( A . flavus ) resulted in aflatoxin contamination of the kernel after incubation. The proportion of contaminated nuts was 48% for the fresh pistachios and 35% for the dried pistachios with 18% and 4%, respectively, having kernels containing aflatoxin levels in excess of 90 μg/kernel, sufficient to contaminate a 10 lb test lot at the 20 ppb guidance level. Closed-shell pistachios batch-rehydrated for 3 h in a bath inoculated with A. flavus spores showed aflatoxin levels in the kernels of 170 ppb after 2 days incubation and 87 500 ppb after 6 days. This study demonstrates that the kernels of closed-shell pistachios can be contaminated with aflatoxin, probably through penetration of the stem end of the shell by aflatoxigenic Aspergillus species, and the practice of rehydration prior to mechanical splitting should therefore be avoided. Keywords: Aflatoxin; Aspergillus spp.; pistachio; Pistacia vera; stem end; aflatoxin analysis; rehydration