Modelling the influence of temperature, water activity and sodium metabisulphite on the growth and OTA production of Aspergillus carbonarius isolated from Greek wine grapes.

The purpose of the present study was to develop a modelling approach to quantify the effect of temperature (15-38 °C), a(w) (0.88-0.98) and sodium metabisulphite (NaMBS) concentration (0-200 mg L(-1)) on the growth and OTA production of Aspergillus carbonarius on a Grape Juice based Medium (GJM). Growth responses of the fungus were recorded over time in terms of colony diameter changes, and fitted to the primary model of Baranyi and the estimated maximum growth rates (μ(max)) and lag phases (λ) were subsequently modelled as a function of temperature, a(w) and NaMBS concentration using the cardinal values model with inflection (CMI). Moreover, OTA production was measured during fungal growth and modelled as a function of the same parameters through a quadratic polynomial model. Results showed that NaMBS increased the lag phase of A. carbonarius, particularly at 38 °C/0.98 a(w) and 38 °C/0.96 a(w), as well as at lower a(w) levels regardless of temperature. In the lowest NaMBS concentration (50 mg L(-1)) there was no inhibitory effect, while at higher concentrations (100 and 150 mg L(-1)) fungal growth was delayed. No growth was observed at 200 mg L(-1) of NaMBS irrespective of temperature and a(w) levels. The optimum values for growth were found in the range 30-35 °C and 0.96 a(w), while for OTA production at 20 °C and 0.98 a(w). The developed models were subjected to internal and external validation and presented satisfactory performance as inferred by graphical plots and statistical indices (bias and accuracy factors). The present study will complement the findings on the ecophysiology of A. carbonarius using NaMBS as an inhibitory agent.