Proteolytic activity of Lactobacillus casei subsp. casei IFPL 731 in a model cheese system

The role played by the cell-envelope proteinase and the aminopeptidase activity of Lactobacillus casei subsp. casei IFPL 731 isolated from goat's milk cheese has been dilucidated, adding the cell wall extract and the intracellular fraction of Prt(-) and Amp(-) variants to cheese slurries, in which residual rennet was inactivated. Primary proteolysis of casein was mainly conducted by rennet, but once this was inactivated, the main responsibility of casein hydrolysis was cell-envelope proteinase activity, followed by plasmin and microbial intracellular proteinases. Formation of the amino acid nitrogen fraction was explained to a great extent by the action of the intracellular aminopeptidase activity, but it was demonstrated that the cell-envelope proteinase plays an important role as a rate-limiting factor for this nitrogen formation. Hydrophobic peptides were hydrolyzed during incubation, and Leu and Lys amino acid residues were produced, as a consequence of the peptidase activity present in the slurries.