DEVELOPMENT OF A MODEL PREDICTING THE EFF ECTS OF PH, LACTIC-ACID, GLYCEROL AND SODIUM-CHLORIDE CONTENT ON THE GROWTH OF VEGETATIVE CELLS OF CLOSTRIDIUM-TYROBUTYRICUM IN A CULTURE-MEDIUM

In order to be able to predict the behaviour of C tyrobutyricum in che eses, the modelling of the parameters of the spore germination and of cell multiplication is necessary. The study of this multiplication was carried out in conditions encompassing those encountered in Emmental cheesemaking (pH 5.3 to 5.9; chloride sodium content 0 to 0.6%; lactic acid concentration 0 to 1.6%; glycerol 0 to 8% in order to obtain wat er activities between 0.965 to 0.99). The data recording was made foll owing a composite central design in order to study the linear and quad ratic effects and the interactions between the controlling factors. Th e growth parameters of strain CNRZ 500 were directly determined using the turbidimetric data and the results obtained show that even in such a limited variation range, C tyrobutyricum is sensitive to any change of the factors and to the interaction between the lactic acid and sod ium chloride contents. As a result of these data, a first model has be en established.