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Summary - The autolysis of starter bacteria during chee se ripening results in the release of intracellular enzymes, especially peptidases, into the curd and in consequence is expected to accelerate and enhance the development of cheese flavour. In the course of a series of cheese assays with the nonautolytic Lactococcus lactis NC00763 strain, the presence of a homologous bacteriophage was encountered. The phage was present at different levels which allowed us to evaluate the impact of the extent of starter bacteria Iysis on Saint-Paulin-type cheese proteolysis during ripening. We estimated bacterial Iysis by viable cell enumeration and electron microscopy observations over a 2-month ripening period. On the same cheeses, we have estimated proteolysis by measuring soluble nitrogen (SN) and phosphotun~stic acid-soluble nitrogen (PT A-N) and by quantifying free amino acids. For phage levels up to 10 0 pfu/g of cheese, the pH and dry matter values were in the standard range, whereas for a higher phage level incorrect acidification was observed. The ex te nt of starter Iysis increased with the phage level and it was also correlated with the rate of formation of small peptides and free amino acids. After 2 months of ripening, the PTA-N value was three-fold higher and the total free amino acid content was seven-fold higher in the cheese with a phage level of 1010 pfu/g than in the control cheeses. These results confirm that the early Iysis of starter bacteria allows the release of intracellular peptidases which are active in cheese, and that the extent of starter Iysis can be correlated with the proteolysis rate.

Phage-induced lysis of Lactococcus lactis during Saint-Paulin cheese ripening and its impact on proteolysis