Autolysis of two strains of Lactococcus lactis during cheese ripening

Abstract

Autolysis of starter bacteria in Saint-Paulin type cheese was monitored by the following parameters: cell viability in cheese, morphological changes in bacteria observed by electron microscopy and the release of two intracellular peptidases, an X-prolyl dipeptidyl aminopeptidase and a broad-specificity aminopeptidase. Two lactococcal strains were compared. Lactococcus lactis subsp. cremoris AM2 appeared to be lysed to a large extent from the first week of ripening. A rapid decrease of cell viability was found and a large number of disrupted cells in cheese was observed by electron microscopy. Moreover, bacterial peptidases appeared to be released in cheese. However, in the case of L. lactis subsp. lactis NCDO763, high cell viability and no release of enzymes were observed during the first three weeks of ripening. Bacteria appeared intact in cheese for three months of ripening. The higher susceptibility of strain AM2 to lysis was correlated with a larger amount of amino nitrogen in the corresponding cheese.