The late blowing defect of hard cheeses: Behaviour of cells and spores of Clostridium tyrobutyricum throughout the cheese manufacturing and ripening

The late blowing defect still represents a problem for hard cheeses. Thus, the behaviour of the cheese spoiling bacterium C. tyrobutyricum was studied throughout the cheesemaking and ripening of Grana Padano using an innovative approach. Cells and spores, independently sealed within dialysis tubes, were kept in the vat during the entire cheesemaking and then into cheese until 6-month ripening. At each sampling step, morphological changes of cells and spores were monitored by electron microscopy and supported with plate counts. Vegetative cells died during curd cooking and then were no longer cultivable. However, 2 × 102 spores appeared at the end of this stage, likely triggered by the exponential growth phase, and were present until 6-month ripening. In cheese, C. tyrobutyricum UC7086 proved to convert free arginine to citrulline and then to ornithine, and to produce γ-aminobutyric acid by glutamate transamination rather than by decarboxylation. Compartmentalization of vegetative cells and spores into dialysis tubes was effective in studying their respective behaviour in a real cheesemaking. This approach allowed to demonstrate that the number of vegetative cells in milk in addition to that of spores should be considered for the eradication of the late blowing defect.