Staff publications - Cranfield Health

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Browsing Staff publications - Cranfield Health by Publisher "Blackwell Publishing Ltd"

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    Effect of temperature and water activity on growth and ochratoxin A production boundaries of two Aspergillus carbonarius isolates on a simulated grape juice medium
    (Blackwell Publishing Ltd, 2009-07-01T00:00:00Z) Tassou, C. C.; Natskoulis P. I.; Magan, Naresh; Panagou, Efstathios Z.
    Aims: To develop and validate a logistic regression model to predict the growth and ochratoxin A (OTA) production boundaries of two Aspergillus carbonarius isolates on a synthetic grape juice medium as a function of temperature and water activity (aw).
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    A new model for the effect of pH on microbial growth: an extension of the Gamma hypothesis
    (Blackwell Publishing Ltd, 2011-01-31T00:00:00Z) Lambert, Ronald J. W.
    Aims: To investigate the appropriateness of the extended Lambert-Pearson model (ELPM) to model the effect of pH (as hydrogen and hydroxyl ions) over the whole biokinetic pH range in comparison with other available models. Methods and Results: Data for the effect of pH on microbial growth were obtained from the literature or in-house. Data were examined using several models for pH. Models were compared using the residual mean of squares. Using the ELPM, pH was modelled as hydrogen ions and hydroxyl ions; hence, the model was monotonic in each. The ELPM was able to model data more successfully than the cardinal pH model (CPM) and other models in the majority of cases. Conclusions: Examining the effect of pH as hydrogen and hydroxyl ions has the advantage that the basic form of the ELPM can be retained as each is treated as a distinct antimicrobial effect. With the ELPM, each inhibitor is described by two parameters; from these parameters, the pH(min), pH(opt) and pH(max) can be obtained. Furthermore, the idea of a dose response, absent from other models, becomes important. Significance and Impact of the Study: The CPM is an excellent model for certain situations - where there is a high degree of symmetry between the suboptimal pH and superoptimal pH response and where there are few data points available. The ELPM is more amenable to highly asymmetric behaviour, especially where plateaus of effect around the pH optimum are observed and where the number of data points is not restrictive.
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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
    (Blackwell Publishing Ltd, 2010-12-01T00:00:00Z) Abdel-Hadi, Ahmed; Carter, D; Magan, Naresh
    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 (beta-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) x log CFUs, 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 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).