Single vs multiple-spore inoculum effect on growth kinetic parameters and modeled probabilities of growth and aflatoxin B1 production of Aspergillus flavus on pistachio extract agar
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Date
2017
Authors
Aldars García, Laila
Sanchís Almenar, Vicente
Ramos Girona, Antonio J.
Marín Sillué, Sònia
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Abstract
The objective of the present study was to assess the differences in modeled growth/AFB1 production probability
and kinetic growth parameters for Aspergillus flavus inoculated as single spores or in a concentrated inoculation
point (~500 spores). The experiment was carried out at 25 °C and at two water activities (0.85 and 0.87) on pistachio
extract agar (3%). Binary data obtained from growth and AFB1 studies were modeled using linear logistic
regression analysis. The radial growth curve for each colonywas fitted to a linear model for the estimation of the
lag phase for growth and the mycelial growth rate. In general, radial growth rate and lag phase for growth were
not normally distributed and both of them were affected by the inoculation type, with the lag phase for growth
being more affected. Changing from the multiple spore to the single spore inoculation led to a delay of approximately
3–5 days on the lag phase and higher growth rates for the multiple spore experiment were found. The
same trend was observed on the probability models, with lower predicted probabilities when colonies came
up from single spores, for both growth and AFB1 production probabilities. Comparing both types of models, it
was concluded that a clear overestimation of the lag phase for growth occurred using the linear model, but
only in the multiple spore experiment. Multiple spore inoculum gave very similar estimated time to reach
some set probabilities (t10, t50 and t100) for growth or AFB1 production due to the abruptness of the logistic
curve developed. The observed differences suggest that inoculum concentration greatly affects the outcome of
the predictive models, the estimated times to growth/AFB1 production being much earlier for the concentrated
inoculum than for a single spore colony (up to 9 days). Thus the number of spores used to generate data in predictive
mycology experiments should be carefully controlled in order to predict as accurately as possible the fungal
behavior in a foodstuff.
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International Journal of Food Microbiology, 2017, vol. 243, p. 28–35