Modulation of casein proteolysis by lactococcal peptidase gene inactivation

Peptidases from lactic acid bacteria participate in cheese ripening by hydrolysing peptides and liberating free amino acids, which are precursors of aroma compounds. Using a pseudo-curd model and lactococcal mutants, negative for different peptidases. as ripening agents, we determined some of the key peptidases in the ripening process. The total level of amino acids quantified after 28 days of ripening was significantly reduced when the general aminopeptidase PepN was absent. The situation was aggravated when the tripeptidase PepT was also missing. The deficiency in the proline-specific aminopeptidase PepX more specifically decreased the level of free proline in the pseudo-curds after 28 days of ripening. These three peptidases, which are also necessary for optimal lactococcal growth in milk, can be considered as peptidases of technological importance. On the other hand, the suppression of the other peptidases tested (PepF1, PepF2, PepC, PepP) did not significantly affect amino acid pools in the conditions of the test. (C) 2001 Elsevier Science Ltd. All rights reserved.