Growth ofGeotrichum candidum and Penicillium camemberti Cultivated on Liquid Media Correlated with Ammonia and Methanethiol Emission

Abstract

The growth of Geotrichum candidum and Penicillium camemberti plays an important role in the ripening of Camembert-type cheeses, but the monitoring of the corresponding kinetics for fungal cocultures on solid media appears difficult. Continuous and non-intrusive methods to characterize the growth of both species (like the monitoring of the emissions of ammonia and volatile sulphur compounds) may be highly relevant, under the condition that such emissions could be correlated with growth. This would be easier to investigate in submerged culture, since total biomass concentration is known to vary in proportion to broth turbidity. For this reason, growth kinetics, ammonia and flavour gas emission of both Geotrichum candidum and Penicillium camemberti grown separately in submerged cultures under the conditions of low aeration rate and uncontrolled pH were continuously recorded. In the basal medium (peptone + lactate supplemented with both glutamic acid and methionine [1 g/l] each), no significant gas emission was observed during the growth of both fungi. Ammonia and sulphur gas emissions by G. candidum were a little stimulated by supplementing the basal medium with trace elements, and, at a larger extent, by the addition of inorganic phosphate: Such a gaseous emission took place at the end of the growth phase of G.candidum. Irrespective of the basal medium supplementation, no significant emission of ammonia and sulphur gas was observed during the growth of P.camemberti. For the media and strains used, ammonia and volatile sulphur compounds emissions unequivocally showed the growth of Geotrichum candidum.