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Postharvest Pathology and Mycotoxins

Aspergillus Molds and Aflatoxins in Pistachio Nuts in California. M. A. Doster, Department of Plant Pathology, University of California, Davis, Kearney Agricultural Center, 9240 S. Riverbend Ave., Parlier 93648; T. J. Michailides, Department of Plant Pathology, University of California, Davis, Kearney Agricultural Center, 9240 S. Riverbend Ave., Parlier 93648. Phytopathology 84:583-590. Accepted for publication 16 February 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-583.

A total of 14 Aspergillus species were isolated from the kernels of pistachio nuts, mainly early splits, from 11 commercial orchards in California in 1991 and 1992. Early splits are atypical nuts that have split hulls, exposing the kernel to invasion by molds and insects (normal nuts have intact hulls). A. niger was the only Aspergillus species that occurred frequently (in 30% of kernels from early splits). However, A. flavus or A. parasiticus (potential producers of the mycotoxins aflatoxins) were found in early splits from most orchards, and A. ochraceus or A. melleus (potential producers of the mycotoxins ochratoxins) were found in all orchards. Aflatoxins were detected in early splits from six of nine orchards in 1991 and five of eight orchards in 1992. Early splits with rough, shriveled hulls had more than twice the A. niger infection and more than three times as much A. flavus or A. parasiticus infection as early splits with smooth hulls. The rough early splits had over 99% of all the aflatoxins detected. Kernels infested by the insect navel orangeworm (Amyelois transitella) had substantially more infections by A. niger, A. flavus or A. parasiticus, and A. ochraceus or A. melleus and had 84% of all aflatoxin detected. The hulls of early splits frequently had low levels of aflatoxin. Hull rupture due to damage by birds or to cracking resulted in kernels infected with Aspergillus molds but at low levels. Fortunately, the pistachio nuts most likely to have mold and aflatoxin contamination, rough early splits infested with navel orangeworm, had several physical characteristics (weight, size, shell discoloration, hull appearance) distinct from normal nuts that could facilitate removal during processing.