| Abstract | Fungi are commonly present in the environment and can grow under favorable conditions
on the extensive variety of agricultural commodities. Aflatoxin, a highly toxic and
carcinogenic chemical substance, is produced by Aspergillus spp. on a variety of agricultural
commodities. The objective of the study was to determine the factors associated with the
fungal contamination of peanut samples from Myanmar. Majority of the farmers are unaware
of the fungal contamination in peanut kernels. The survey, based on post-harvest handling
and storage practices questionnaires, was conducted by interviewing 178 respondents that
included 140 farmers from 11 villages, 28 collectors and 10 wholesalers. The result indicated
poor handling and inadequate storage conditions along with poor processing detrimentally
affected the crop contents and the farmers lack in understanding the problem and importance
of managing the fungal contamination. The results indicated that 42, 21, 20, and 17% of the
farmers dried their peanut plants for 3, 4, 7, and 10 days, respectively. Due to lack of the
standard criteria, farmers aim to sell the pods with higher weight with higher moisture
content. The study found that only 17% farmers dried peanut pods within safe moisture
content range and sold to collectors.
In this study, peanut kernels were found to be contaminated by Aspergillus flavus and
Aspergillus niger with 3 and 4 days stored products compared with 7, 10, 30 and 60 days
stored peanut kernels, indicating the occurrence of fungal contamination under improper
drying practice and relatively short storage time at the farm level. Furthermore, 90 and 120
days stored peanut kernels were more contaminated by A. flavus, A. niger and A. terreus than
30 and 60 days stored peanuts at the farmer, collector and wholesaler’s stores. Overall, A.
flavus and A. niger were isolated at higher occurrence than A. terreus and P. citrinum in all
the collected samples. Aspergillus flavus was the highest (19.4%) in its frequency followed
by A. niger (13.5%) at the collector’s stores, while these two species of fungi were the second
highest in their frequencies at the farmer’s stores. A. terreus and P. citrinum were the least
in their frequencies at each store. The result indicates a potential risk of fungal contamination
under improper storage practices and there is an immediate attention to improve the
postharvest handling and storage practice to prevent fungal contamination.
Secondly, the DNA extraction protocol described in the study could provide a tool of DNA
from the fungal species and could be used for the identification of other morphological forms
of filamentous fungi. Based on morphological characteristics, 85 isolates were tentatively
identified and compared with the references as A. flavus (38), A. niger (20), A. terreus (15),
and P. citrinum (12). Molecular identification using internal transcribed spacer and β-tubulin
sequences supported morphological identification which were molecularly identified as
Aspergillus flavus, A. niger, A. terreus, and P. citrium. The BLAST data showed that the
isolate G1 from the study was related to A. flavus strain AG14 beta-tubulin gene partial cds
with a similarity of 100%, whereas the isolate B1 matched CBS 132413 A. niger, N3: rDNA
sequences ITS with a 100% similarity. However, the isolate Y1 was more closely related to
A. terreus isolate 3.1 18S ribosomal RNA gene, partial sequence; internal transcribed spacer
1, 5.8S ribosomal RNA gene, and internal transcribed spacer 2, complete sequence; and 28S
ribosomal RNG gene, partial sequence with a 99% similarity. The isolate G2 was related to
P. citrinum strain 139P beta-tubulin gene, partial sequence with a similarity 100%.
Phylogenetic tree showed that the isolates from the same species were grouped in the same
clade.
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Further objective of this study was to determine the effect of chitosan which incorporated
with thyme, lemongrass and cinnamon bark essential oils by coating on peanut kernels in
order to prevent fungal growth and the chitosan films incorporated with different essential
oils were developed and characterized in terms of morphology, physical, mechanical and
antifungal properties. The control of postharvest pathogens, while maintaining the peanut
kernel during storage has been implemented by the application of chitosan and essential oils
coating peanut kernel. The study investigated the effect of chitosan with essential oils
(cinnamon bark, lemongrass and thyme white, respectively). In vitro studies indicated that
the essential oils and chitosan tested were active against Aspergillus flavus, A. niger, A.
terreus, and Penicillium citrinum. The radial growth inhibition assay demonstrated that
thyme white, lemongrass and cinnamon bark EOs showed that the antifungal activity against
each fungus with MIC of 80, 80 and 40 μl/ml respectively. Excellent disease control was
achieved with the chitosan coating with cinnamon bark essential oil while during storage
indicated that the fungal growth was completely inhibited on all replicates was recorded. |