Evaluation, characterisation and modelling of Aspergillus flavus in aflatoxin production in peanuts along the supply chain
Aflatoxin contamination is a major food safety issue in raw peanuts and peanut-based products worldwide. Thus, an extensive study on aflatoxins and Aspergillus spp. in peanuts along the supply chain in Malaysia is needed in order to protect the consumers against the harmful effects of aflatoxins....
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| Format: | Thesis |
| Language: | English |
| Published: |
2019
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/84473/1/FSTM%202019%2025%20ir.pdf |
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| Summary: | Aflatoxin contamination is a major food safety issue in raw peanuts and peanut-based
products worldwide. Thus, an extensive study on aflatoxins and Aspergillus spp. in
peanuts along the supply chain in Malaysia is needed in order to protect the consumers
against the harmful effects of aflatoxins. Generally, this study was aimed to evaluate
the aflatoxin contamination, identify, characterise and model the growth of
aflatoxigenic A. flavus isolated from peanuts collected from the importers,
manufacturers, and retailers. In the present study, aflatoxins were found to be
significantly higher (p < 0.05) in raw peanuts and peanut-based products from the
retailers (< LOD – 1021.4 μg/kg) followed by the manufacturers (< LOD – 181.9
μg/kg) while samples from the importers were free from aflatoxins. Total fungal count
was relatively higher in raw peanuts (log 0.3 – 3.6 CFU/g) as compared to peanutbased
products (log 0.6 – 2.3 CFU/g) in which samples from the importers recorded
the highest contamination level for aflatoxigenic Aspergillus spp. (log 2.2 ± 1.1
CFU/g). On the basis of morphological, chemical, and molecular identification, all
isolates were identified as Aspergillus section Flavi. Specifically, 127 isolates were
confirmed as A. flavus, and one isolate as A. tamarii. Six chemotype profiles were
proposed indicating the diversity of toxigenic potential. About 58.6%, 68.5%, and
100% of the isolates were positive for aflatoxin, cyclopiazonic acid and aspergillic
acid production, respectively. The maximum likelihood (ML) phylogenetic tree using
ITS and β-tubulin gene resolved the species into two different clades in which all A.
flavus (both aflatoxigenic and non-aflatoxigenic) were grouped in the same clade and
A. tamarii in a different clade. Aflatoxin biosynthesis genes namely aflR, aflP (omtA),
aflD (nor-1), aflM (ver-1), and aflC (pksA) were detected in all aflatoxigenic A. flavus
while the non-aflatoxigenic A. flavus failed to amplify at least one of the genes that
was tested. The analysis of variance showed a significant effect of strain, temperature
and water activity (aw) on the fungal growth and aflatoxin production (p < 0.05). The
maximum growth rate, μmax (mm/day) of two aflatoxigenic A. flavus, (A8R and A82R) on PMEA was estimated by using the primary model of Baranyi and the μmax was then
fitted to the secondary model; second order polynomial and linear Arrhenius-Davey to
describe the growth rate as a function of temperature and aw. In general, the growth
rate of A. flavus increased with increasing temperature and aw until reaching the
optimum temperature and further increase in aw beyond this point resulted in decrease
growth rate. The growth of A. flavus was observed at the minimum aw of 0.85 under
the optimum temperature (32 – 33°C) and the minimum temperature of 20°C with 0.94
aw. A similar pattern was observed in aflatoxin production but in a narrower range of
temperature (25 – 35°C) and aw (0.92 – 0.98 aw). In conclusion, A. flavus was the
predominant species that contaminate peanuts and subsequently produce aflatoxins
during the storage period. Therefore, proper storage structures and conditions for
peanuts during storage are very important in order to control the growth of
aflatoxigenic A. flavus and aflatoxin contamination. |
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