Growth/no-growth models of in-vitro growth of Penicillium paneum as a function of thyme essential oil, pH, aw, temperature.

The aims of this study were (i) screening of antifungal activity of thyme essential oil on Penicillium paneum; (ii) development of growth/no-growth models (G/NG); and (iii) validation of the G/NG models by performing bread baking trials. The screening method was based on the measurement of fungal growth in a semi-solid medium through optical density. The combined influence of aw (0.88-0.97), pH (4.8-7.0), temperature (22 and 30 °C), time (0-144 h) and varying concentrations of thyme oil (0-2 μL/mL YES) were assessed. Growth of P. paneum at aw 0.88 was significantly reduced compared to aw 0.93-0.97. A slight pH effect was observed at aw 0.93; growth was delayed at pH 6 compared to pH 4.8. The lowest concentration of thyme oil preventing growth during 144 h of incubation was 1 μL/mL medium. According to the results of the shelf-life test of par-baked bread, fungal growth was inhibited for more than 45 days using 0.3 mL thyme oil/100 g dough. To conclude, this study recognized the potential of using G/NG models to develop better product formulations and to facilitate product innovation.