Carbon dioxide emission in relation to the growth of Geotrichum candidum in solid cultures

Geotrichum candidum plays an important role in the ripening of Camembert-type cheeses. However, the direct measurement of the biomass concentration is rather tedious and, therefore, the development of alternative methods for monitoring the growth on solid media would be very useful. For this purpose, a non-structured model was previously developed to describe the CO2 emission during the growth of G candidum in liquid cultures. The CO2 production was assumed to be partially associated with growth: a part resulted from growth and the remaining from cellular maintenance. This model has also been validated in solid cultures on peptone-lactate based medium. The coefficients for growth-associated and non-growth-associated production were found to be 0.301 and 0.123 per day, respectively. Therefore, the CO2 production may be a non-destructive and useful tool to monitor fungal growth in solid cultures. In the case of mixed cultures of both fungi (Geotrichum candidum and Penicillium camembertii) involved in the ripening of Camembert cheeses, CO2 emission can be related to the total viable biomass, while ammonia and volatile sulphur compounds can be linked to G. candidum biomass. Indeed, it was previously shown that Penicillium camembertii released only very low amounts of both compounds.