Growth and metabolism of sporeformers in cheese

Spore formers represents a great challenge for the dairy industry, as the spores produced by these bacteria can withstand heat treatment and may be a cause of spoilage of the product. Members of the Bacillus cereus group and of the Clostridium sensu strictu cluster may, with their metabolic and enzymatic productions, be detrimental for the quality of cheese and its shelf life, thus causing the dairy industry important economic losses. This master thesis aimed to define growth and metabolic pathways of selected isolates in cheese, focusing on their casein degradation ability and the utilization of amino acids, organic acids and carbohydrates as energy sources. Metabolic differences between isolates of Bacillus cereus, Clostridium sporogenes and C. tyrobutyricum were defined in UHT milk and in a cheese model. The results showed that B. cereus and C. sporogenes produce proteolytic enzymes and use amino acids as energy source,in combination with organic acids and carbohydrates. C. tyrobutyricum, on the other end, utilizes only organic acids and carbohydrates and shows low proteolytic activity.M-MA