Toxigenic Aspergillus Sections Flavi and Nigri Populations Along the Processing Line in California Almonds

Mycotoxin contamination of almonds is a serious concern to public health and the almond industry. After harvest, almonds are sorted at processing facilities to remove damaged kernels, but little is known about the effectiveness of the sorting process in discarding almonds contaminated with mycotoxigenic fungi. The aims of this study were to compare total fungal and Aspergillus section Flavi counts along the almond processing line and to determine the toxigenic potential of A. section Flavi and Nigri isolates. A total of 190 shelled almond samples were collected at three different processors/handlers in California. Total fungal counts obtained from almonds at various stages of the sorting process were within the range of 3.6 to 5.0 log₁₀ CFU/g. The proportion of samples contaminated with section Flavi was consistent throughout the processing line at each handler. Neither the total nor the section Flavi fungal load decreased during the sorting process. Overall, 97 and 20.5% of all samples contained section Nigri and Flavi strains, comprising 80 and 0.4% of the total fungal load, respectively. None of the 19 section Nigri isolates had detectable levels of ochratoxin A. A total of 26 A. section Flavi strains were isolated, of which 92.3% were identified as A. flavus. Only one (3.8%) section Flavi strain was A. parasiticus, and one isolate was A. tamarii. Of the 24 A. flavus strains, 62.5% produced detectable levels of aflatoxin B₁ on yeast sucrose (YES) media, while A. parasiticus also produced aflatoxin G₁. These results indicate that although the damaged kernels may have been discarded, aflatoxigenic fungi remained in the almonds that were not sorted out. Therefore, to minimize postharvest contamination of almond kernels with aflatoxins, it is essential to maintain environmental conditions that are not conducive to fungal growth. Research should continue on improving detection methods and developing preharvest biocontrol agents.