Publication: Aspergillus population diversity and its role in aflatoxin contamination of cashew nuts from coastal Kenya
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2025-01-24
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NRF
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PLOS one
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Abstract
Cashew nuts are among the main cash crops in coastal Kenya, due in large part to their high
nutritional value. Unfortunately, they also make them highly susceptible to mold contamination, resulting in biodeterioration of the nutritional value and potential contamination with
toxic secondary metabolites, such as aflatoxins, that cause them to be rejected for sale at
the market. We determined the population diversity of the Aspergillus species and their role
in aflatoxin contamination in cashew nuts in selected coastal regions of Kenya. Fifty raw
cashew nut samples were collected from post-harvest storage facilities across three counties in Kenya’s coastal region and examined for moisture content and the presence of
Aspergillus fungi. About 63 presumptive isolates were recovered from the cashew nuts. ITS
and 28S rDNA regions were sequenced. The aflD, aflM and aflR genes were amplified to
identify the potentially aflatoxigenic from the Aspergillus isolates. The Aflatoxins’ presence
on the isolates was screened using UV and the ammonia vapour test on coconut milk agar
and validated using ELISA assay. A comparison of cashew moisture content between the
three counties sampled revealed a significant difference. Sixty-three isolates were recovered and identified to section based on morphological characters and their respective ITS
regions were used to obtain species identifications. Three sections from the genus were represented, Flavi and Nigri, and Terrei with isolates from the section Nigri having slightly
greater abundance (n = 35). The aflD, aflM and aflR genes were amplified for all isolates to
assess the presence of the aflatoxin biosynthesis pathway, indicating the potential for aflatoxin production. Less than half of the Aspergillus isolates (39.68%) contained the aflatoxin
pathway genes, while 22.22% isolates were aflatoxigenic, which included only the section
Flavi isolates. Section Flavi isolates identification was confirmed by calmodulin gene. The
presence of species from Aspergillus section Flavi and section Nigri indicate the potential
for aflatoxin or ochratoxin in the cashew nuts. The study established a foundation for future
investigations of the fungi and mycotoxins contaminating cashew nuts in Kenya, which
necessitates developing strategies to prevent infection by mycotoxigenic fungi, especially
during the storage and processing phases.