Kinetic modelling of Mucor circinelloides growth on skim milk agar under dairy-relevant temperature and water activity conditions

This study investigated the surface growth kinetics of Mucor circinelloides strain 1L cultivated on skim milk agar (SMA) under various temperature and water activity (aw) conditions, with relevance to dairy product spoilage prediction. Growth curves fitted using the Baranyi model exhibited high smoothness and reproducibility (R²>0.978; RMSE = 2.36±1.08 mm). Primary growth parameters, including lag phase duration and surface growth rate (sgr), were quantified across triplicate experiments and modelled using Ratkowsky and cardinal frameworks, respectively. Secondary modelling revealed environmental dependencies, with optimal sgropt at 33 mm/d and estimated cardinal parameters (Topt ≈ 32 °C, theoretical aw min = 0.97). Validation experiments simulating ewe lump cheese fermentation conditions demonstrated high predictive accuracy (R² = 0.989), with bias and accuracy factors confirming model reliability despite minor underestimations. Predicted visibility times (t3, colony diameter ≥ 3 mm) indicated rapid colonisation under favourable conditions, while combinations of reduced temperature (< 10 °C) and low aw (< 0.975) markedly extended t3 beyond 30 days. These findings emphasise the value of kinetic modelling for assessing fungal spoilage risk and underpin the need for stringent hygienic measures in dairy production systems.