Studying and modelling the combined effect of water activity and temperature on growth rate of P. expansum

Unité de Phytopathologie, Faculté Universitaire des Sciences Agronomiques de Gembloux, Passage des Déportés 2, 5030 Gembloux, Belgium.
International Journal of Food Microbiology (Impact Factor: 3.08). 10/2005; 103(3):315-22. DOI: 10.1016/j.ijfoodmicro.2005.02.002
Source: PubMed


The effect of solutes, water activity (a(w), 0.890--0.980) and temperature (5--25 degrees C) on the mycelial growth rate of Penicillium expansum was evaluated. The growth rate dropped as the temperature and a(w) of the medium decreased. NaCl was the solute causing the greatest growth rate reduction, followed by glucose, glycerol and sorbitol. Statistical analysis of the results showed a significant effect of solute, a(w), temperature and combinations of two or three of these factors (P<0.0001). Whatever the solutes and a(w) values, the initiation of colony growth required an additional day at 15 degrees C and 5 degrees C as compared to initiation at 25 degrees C. Growth models based on the results obtained with sorbitol and glycerol differed only slightly, with R(2) values of 97.00% and 97.95%, respectively. The response surfaces of both quadratic polynomial models showed that P. expansum should be able to grow at low a(w) (0.890) and that growth at 25 degrees C should be fastest at a(w) values ranging from 0.960 to 0.980. Both models presented a good fit between predicted and observed values.

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Available from: Rachid Lahlali,
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    • "There is a need to ensure the microbiological quality and safety of food products, and this has stimulated interest in the use of mathematical models for quantifying and predicting microbial behavior (Lahlali et al., 2005). In particular, prediction of spoilage and patulin accumulation by Penicillium expansum is required in cold stored fruits, as well as during transport and intermediate storage steps. "
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    ABSTRACT: The aim of this work was to compare the radial growth rate (μ) and the lag time (λ) for growth of 25 isolates of Penicillium expansum at 1 and 20ºC with those of the mixed inoculum of the 25 isolates. Moreover, the evolution of probability of growth through time was also compared for the single strains and mixed inoculum. Working with a mixed inoculum would require less work, time and consumables than if a range of single strains has to be used in order to represent a given species. Suitable predictive models developed for a given species should represent as much as possible the behavior of all strains belonging to this species. The results suggested, on one hand, that the predictions based on growth parameters calculated on the basis of mixed inocula may not accurately predict the behavior of all possible strains but may represent a percentage of them, and the median/mean values of μ and λ obtained by the 25 strains may be substituted by the value obtained with the mixed inoculum. Moreover, the predictions may be biased, in particular, the predictions of λ which may be underestimated (fail-safe). Moreover, the prediction of time for a given probability of growth through a mixed inoculum may not be accurate for all single inocula, but it may represent 92% and 60% of them at 20 and 1ºC, respectively, and also their overall mean and median values. In conclusion, mixed inoculum could be a good alternative to estimate the mean or median values of high number of isolates, but not to account for those strains with marginal behavior. In particular, estimation of radial growth rate, and time for 0.10 and 0.50 probability of growth using a cocktail inoculum accounted for the estimates of most single isolates tested. For the particular case of probability models, this is an interesting result as for practical applications in the food industry the estimation of t10 or lower probability may be required.
    International Journal of Food Microbiology 06/2014; 186C:120-124. DOI:10.1016/j.ijfoodmicro.2014.06.023 · 3.08 Impact Factor
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    • "The assumption of this simple technique is that when the lag phase has passed, growth of bacteria reaches immediately at its maximum rate. Other studies proved that the linear regression method was provided high correlations [7] [9]. "
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    ABSTRACT: The selectivity and inhibitory effects of five standard enrichment media (i.e., SEB, UVM, FB, MOPS-BLEB, and PB) were evaluated on L. ivanovii and L. innocua. E. coli and Salmonella spp. were chosen to study the growth of competing microorganisms on these standard selective media. Pure cultures of Listeria spp., E. coli and Salmonella spp. were prepared at similar initial cell densities (approximately 109 CFU/mL) and inoculated into 96 micro-well plates containing the selected enrichment media at 37oC. The viable cell count was performed to evaluate the selectivity and inhibitory stress imposing on the chosen strains over 24 hr. For isolation purpose, PB was the most potent and effective selective substrate and provided substantial reduction of the bacterial competitors (over 9 log scale reduction) within 9 hr. This medium was also the least preferable to L. ivannovii and L. innocua producing negative growths. However, PB was able to isolate both L. ivanovii and L. innocua from other competitors within rather short incubation time and with high selectivity. The selectivity of L. ivanovii over E. coli and Salmonella spp. were as follows; PB > MOPS-BLEB > FB > SEB > UVM and PB > MOPS-BLEB > SEB > FB > UVM, respectively. To select L. innocua, the preference of potent media was PB > FB > MOPS-BLEB > UVM > SEB for both E. coli and Salmonella spp.
    Procedia Engineering 12/2012; 32:119–125. DOI:10.1016/j.proeng.2012.01.1245
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    • "A significant effort for developing predictive models for the growth of spoilage and/or mycotoxigenic fungi has been made during the last decade and it is still in progress (Dantigny et al., 2006, 2007; Garcia et al., 2009). In contrast to the increased number of studies on mycelium radial growth (Garcia et al., 2009; Gougouli and Koutsoumanis, 2010; Lahlali et al., 2005; Marín et al., 2009; Panagou et al., 2003, 2007; Pardo et al., 2005, 2006; Plaza et al., 2003; Rosso and Robinson, 2001; Samapundo et al., 2005, 2007; Sautour et al., 2001; Tassou et al., International Journal of Food Microbiology 152 (2012) 153–161 ⁎ Corresponding author. Tel.: + 30 2310991647; fax: + 30 2310991647. "
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    ABSTRACT: The relation between germination time and lag time of mycelium growth of individual spores was studied by combining microscopic and macroscopic techniques. The radial growth of a large number (100-200) of Penicillium expansum and Aspergillus niger mycelia originating from single spores was monitored macroscopically at isothermal conditions ranging from 0 to 30°C and 10 to 41.5°C, respectively. The radial growth curve for each mycelium was fitted to a linear model for the estimation of mycelium lag time. The results showed that the lag time varied significantly among single spores. The cumulative frequency distributions of the lag times were fitted to the modified Gompertz model and compared with the respective distributions for the germination time, which were obtained microscopically. The distributions of the measured mycelium lag time were found to be similar to the germination time distributions under the same conditions but shifted in time with the lag times showing a significant delay compared to germination times. A numerical comparison was also performed based on the distribution parameters λ(m) and λ(g), which indicate the time required from the spores to start the germination process and the completion of the lag phase, respectively. The relative differences %(λ(m)-λ(g))/λ(m) were not found to be significantly affected by temperatures tested with mean values of 72.5±5.1 and 60.7±2.1 for P. expansum for A. niger, respectively. In order to investigate the source of the above difference, a time-lapse microscopy method was developed providing videos with the behavior of single fungal spore from germination until mycelium formation. The distances of the apexes of the first germ tubes that emerged from the swollen spore were measured in each frame of the videos and these data were expressed as a function of time. The results showed that in the early hyphal development, the measured radii appear to increase exponentially, until a certain time, where growth becomes linear. The two phases of hyphal development can explain the difference between germination and lag time. Since the lag time is estimated from the extrapolation of the regression line of the linear part of the graph only, its value is significantly higher than the germination time, t(G). The relation of germination and lag time was further investigated by comparing their temperature dependence using the Cardinal Model with Inflection. The estimated values of the cardinal parameters (T(min), T(opt), and T(max)) for 1/λ(g) were found to be very close to the respective values for 1/λ(m), indicating similar temperature dependence between them.
    International journal of food microbiology 12/2012; 161(3):231-239. DOI:10.1016/j.ijfoodmicro.2012.12.006 · 3.08 Impact Factor
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