Proteolytic activity of lactobacilli in a model goats' milk curd system

Mesophyllic lactobacilli cultures propagated in MRS broth were inoculated in goats' milk curd slurries and incubated at 30 degrees C for 10 d. The micro-organisms tested were Lactobacillus casei subsp. casei IFPL 731 and IFPL 99, and Lactobacillus plantarum IFPL 3. Whole cells, cell-free extracts and cell lysates were evaluated for acceleration of proteolysis in the curd slurries. Conversion of water-soluble nitrogen to non-protein nitrogen and amino acid nitrogen, reverse phase-HPLC peak areas and ratio of hydrophobic to hydrophilic peptides, were all affected by the type of inoculum used as well as the strain under study. The results suggest that the accelerated-ripening model system developed, containing cell lysates, may be suitable as a good and rapid indicator of the contribution of the strains to proteolysis during cheese ripening.