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Temporal monitoring of the nor‐1 ( aflD ) gene of Aspergillus flavus in relation to aflatoxin B 1 production during storage of peanuts under different water activity levels
Author(s) -
AbdelHadi A.,
Carter D.,
Magan N.
Publication year - 2010
Publication title -
journal of applied microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.889
H-Index - 156
eISSN - 1365-2672
pISSN - 1364-5072
DOI - 10.1111/j.1365-2672.2010.04820.x
Subject(s) - aflatoxin , aspergillus flavus , biology , gene expression , microbiology and biotechnology , gene , aspergillus , real time polymerase chain reaction , food science , genetics
Aims: A relative quantification system (RQ‐PCR) was used to monitor the correlations between the activity of the nor‐1 (= aflD ) gene of Aspergillus flavus using real‐time PCR in relation to phenotypic aflatoxin B 1 (AFB 1 ) production and populations of A. flavus in stored peanuts at three water activity levels (a w , 0·95, 0·90 and 0·85) for 6 weeks. Methods and Results: Real‐time PCR was used to amplify the nor‐1 gene (target gene), and benA56 (β‐tubulin gene) used as a control gene. Expression of three structural genes, nor‐1 (=aflD ), ver‐1 (= aflM ), and omtA (= aflP ), and the regulatory gene aflR of the aflatoxin biosynthetic pathway were also assayed. There were significant differences between nor‐1 gene expression at the three a w levels; higher expression at 0·90 a w in weeks 1–3, when compared to 0·95. In contrast, in the driest treatment (0·85 a w ) none or very low nor‐1 expression occurred. The populations of A. flavus colony‐forming units (CFUs g −1 ) increased over time with the highest at 0·95 a w . Highest AFB 1 production was at 0·90 and 0·95 a w from weeks 3–6. A w had a significant effect on aflR transcription at 0·95 a w over the 6‐week period, while at 0·90 a w , only in the last 2 weeks. Conclusions: Correlations between different factors showed that log AFB 1 × log CFUs, log AFB 1 × a w , and log CFUs × a w were statistically significant, while log CFUs × RQ‐PCR and RQ‐PCR × a w were not. The AflR gene may not have an important role in the regulation of nor‐1 expression in food matrices (e.g. peanuts). Significance and Impact of the study: Determination of correlations between nor‐1 expression and aflatoxin production by A. flavus in raw peanuts under different a w levels could be helpful to predict potential risk of aflatoxin production during storage of this hygroscopic food product and minimize contamination with the AFB 1 .