Dynamics of Penicillium camemberti growth quantified by real-time PCR on Camembert-type cheeses under different conditions of temperature and relative humidity

Penicillium camemberti plays a major role in the flavor and appearance of Camembert-type cheeses. However, little is known about its mycelium growth kinetics during ripening. We monitored the growth of P. camemberti mycelium in Camembert-type cheeses using real-time PCR in 4 ripening runs, performed at 2 temperatures (8 and 16°C) and 2 relative humidities (88 and 98%). These findings were compared with P. camemberti quantification by spore concentration. During the first phase, the mycelium grew but no spores were produced, regardless of the ripening conditions. During the second phase, which began when lactose was depleted, the concentration of spores increased, especially in the cheeses ripened at 16°C. Sporulation was associated with a large decrease in the mycelial concentration in the cheeses ripened at 16°C and 98% relative humidity. It was hypothesized that lactose is the main energy source for the growth of P. camemberti mycelium at the beginning of ripening and that its depletion would trigger stress, resulting in sporulation.