Modelling the sporulation of some fungi associated with cheese, at different temperature and water activity regimes.

The objectives of this study were to determine, in-vitro, the influence of temperature (T; 10-30 °C, step 5°), water activity (aw, 0.83-0.99; step 0.04) and time on sporulation (SPO) of some cheese-related fungi belonging to Penicillium spp. and A. versicolor. Overall, sporulation started rapidly (8 h in optimal conditions); it was significantly influenced by T and aw and the fungi studied were clearly distinguished based on their thermo-hydro adaptation. Boundary conditions for sporulation were defined for all the fungi considered and the sporulation rate was successfully modelled, especially based on T and time regimes. Penicillium crustosum, P. nordicum and P. verrucosum showed optimum for SPO at T between 20 and 25 °C and their sporulation continued up to aw = 0.87 (aw = 0.83 for P. nordicum). They resulted the fungi best adapted to the environmental conditions of ripening grana cheese storehouses; therefore, it is expected they dominate on the grana cheese surface. Studies on cheese are necessary to validate these results obtained on artificial media and without fungi co-occurrence.

Polyphasic identification of Penicillia and Aspergilli isolated from Italian grana cheese.

Penicillium and Aspergillus genera, both including mycotoxin producing species, were reported as associated to cheese and cheese working environment, but never studied in an extensive way in Italian grana cheese (Grana Padano and Parmigiano Reggiano). The aim of this work was to address the identification of Aspergilli and Penicillia associated to grana cheese in order to lay down the basis for risk assessment and safe processing for a high quality production. One hundred and four strains belonging to Aspergillus and Penicillium genera were obtained from cheese crust and from ripening room air (with the latter largely dominant), and identified following a polyphasic approach, strongly required for the identification at the species level. Morphological observation was used along with molecular techniques, RAPD-PCR fingerprinting and calmodulin gene sequencing (CaM), the former aimed to limit as much as possible the latter sequencing effort. Seventy four percent of the strains were assigned to Penicillium subgenus Penicillium, section Fasciculata. Main mycotoxin producing species identified were A. flavus, P. crustosum and P. verrucosum, while the dominant species in both air and cheese crust was P. solitum, which has never been so far reported as mycotoxigenic. Results obtained in this study confirmed that mycotoxin contamination is a possible issue to face during grana cheese making.

Modeling Growth and Toxin Production of Toxigenic Fungi Signaled in Cheese under Different Temperature and Water Activity Regimes.

The aim of this study was to investigate in vitro and model the effect of temperature (T) and water activity (aw) conditions on growth and toxin production by some toxigenic fungi signaled in cheese. Aspergillus versicolor, Penicillium camemberti, P. citrinum, P. crustosum, P. nalgiovense, P. nordicum, P. roqueforti, P. verrucosum were considered they were grown under different T (0-40 °C) and aw (0.78-0.99) regimes. The highest relative growth occurred around 25 °C; all the fungi were very susceptible to aw and 0.99 was optimal for almost all species (except for A. versicolor, awopt = 0.96). The highest toxin production occurred between 15 and 25 °C and 0.96-0.99 aw. Therefore, during grana cheese ripening, managed between 15 and 22 °C, ochratoxin A (OTA), penitrem A (PA), roquefortine-C (ROQ-C) and mycophenolic acid (MPA) are apparently at the highest production risk. Bete and logistic function described fungal growth under different T and aw regimes well, respectively. Bete function described also STC, PA, ROQ-C and OTA production as well as function of T. These models would be very useful as starting point to develop a mechanistic model to predict fungal growth and toxin production during cheese ripening and to help advising the most proper setting of environmental factors to minimize the contamination risk.