Estimation of growth parameters of six different fungal species for selection of strains to be used in challenge tests of bakery products

- Growth kinetics of six fungi in different substrate and temperature was assessed.
- Growth rate (µ) was highly variable, ranging between 1.4 and 11.1 mm per day.
- Lag times varied between 0.7 and 4.2 days, with 50% of them being between 0.7 and 1.4 day.
- Coefficients of variation of µ were 44.2%, 32.9% and 28.3% at 30 °C, 25 °C, 20 °C.
- Paecilomyces variotii and Penicillium paneum were chosen for use in challenge tests.

The objective of this study was to estimate the growth rate, lag time and the times for the appearance of visible mycelium (tv) of six fungal species (Paecilomyces variotii, Penicillium paneum, Penicillium polonicum, Penicillium spinulosum, Penicillium citrinum and Aspergillus sydowii). The growth parameters were determined at 20 °C, 25 °C and 30 °C and in two culture media (18% Dichloran Glycerol Agar - DG-18 and Dichloran Rose Bengal Chloramphenicol Agar - DRBC) aiming the selection of most appropriate strains for use in challenge tests and for the development of predictive models. Seventy-two growth curves were obtained after measuring the diameter of the colonies for 14 days at 20 °C, 25 °C and 30 °C. Values of growth rate between 1.4 and 11.1 (day−1) were obtained in this study. Faster growth rates (> 7 day−1) were observed for Pa. variotii (LMQA-001) and P. paneum (LMQA-002) at 25 °C. The lag times varied between 0.7 and 4.2 days, with 50% of the values being as short as 0.7−1.4 day. The variability between the species was analyzed and coefficients of variation (CV) of 44.2% and 41% for the growth rate were observed at 30 °C. At 20 °C and 25 °C, CV varied from 28.3% to 32.9%, respectively. Given these results, Pa. variotii and P. paneum could be considered for further use in microbiological challenge tests aiming to assess the robustness of bakery products formulations.