Simple Tests for Predicting the Lytic Behavior and Proteolytic Activity of Lactococcal Strains in Cheese

The variations of the autolytic and proteolytic potential of lactococci need to be taken into account because these variations probably influence the development of organoleptic properties during cheese ripening. To predict lytic capacity, proteolytic potential, and specificity of cell surface-associated proteinase, we developed simple tests that were applied to 26 industrial strains and a few reference strains of Lactococcus lactis. The tests allowed us to measure the autolytic capacity of lactococci in a buffer or in a pseudo curd under conditions that were close to those of cheese ripening and to evaluate global peptidase activity, proteinase activity, and specificity using casein or casein hydrolysate as a substrate. We confirmed the variability of the autolytic capacity of lactococci and classified the strains into three groups by low, moderate, or high lytic capacity according to their behavior in the buffer and in pseudo curd tests. Validation of the latter was obtained by the observation of similar lytic behavior in the two reference strains of Lactococcus lactis, AM2 and NCDO763, which were highly autolytic and poorly autolytic, respectively, both in our tests and in previously reported cheese experiments. The global activities of peptidases and proteinase varied from 1 to 6 among the strains. Most of the proteinases that were isolated from the highly proteolytic industrial strains hydrolyzed β-casein preferentially and, consequently, are more like the PI-type proteinase than the PIII-type. We used simple, rapid methods to test a large number of strains to predict their lytic behavior and proteolytic activity in cheese.