Temporal monitoring of the nor-1 (aflD) gene of Aspergillus flavus in relationto aflatoxin B-1 production during storage of peanuts under different wateractivity levels

摘要

Aims: A relative quantification system (RQ-PCR) was used to monitor thecorrelations between the activity of the nor-1 (=aflD) gene of Aspergillusflavus using real-time PCR in relation to phenotypic aflatoxin B-1 (AFB(1))production and populations of A. flavus in stored peanuts at three wateractivity 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(beta-tubulin gene) used as a control gene. Expression of three structuralgenes, nor-1 (=aflD), ver-1 (=aflM), and omtA (=aflP), and the regulatory geneaflR of the aflatoxin biosynthetic pathway were also assayed. There weresignificant 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 overtime with the highest at 0.95 a(w). Highest AFB(1) production was at 0.90 and0.95 a(w) from weeks 3-6. A(w) had a significant effect on aflR transcription at0.95 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) x logCFUs, log AFB(1) x a(w), and log CFUs x a(w) were statistically significant,while log CFUs x RQ-PCR and RQ-PCR x a(w) were not. The AflR gene may not havean important role in the regulation of nor-1 expression in food matrices (e. g.peanuts). Significance and Impact of the study: Determination of correlationsbetween nor-1 expression and aflatoxin production by A. flavus in raw peanutsunder different a(w) levels could be helpful to predict potential risk ofaflatoxin production during storage of this hygroscopic food product andminimize contamination with the AFB(1).