The proteolytic system of starter and non-starter bacteria: Components and their importance for cheese ripening

The proteolytic system of Lactococcus has been studied in detail for many years, and probably most of the components have been identified. More recently there has been an increased interest in the study of the proteolytic enzymes of Lactobacillus species. At the Federal Daily Research Centre, nine peptidases of a single strain of Lactobacillus delbrueckii subsp. bulgaricus were purified. Biochemical properties of most of these enzymes were found to be similar compared to Lactococcus enzymes. However, two purified tripeptidases were completely different. Based on these results, a method for the characterization of starter strains has been developed, using nine peptide substrates, which were suitable for assays of single of groups of enzymes. With this method, the proteolytic profiles of peptidase-deficient Lactococcus mutants, provided by the University of Groningen were determined, in order to study the suitability of selected substrates for particular enzymes and to analyse the effect of the loss of certain peptidases on the remaining peptidase activity. Starter strains, with known industrial performances, were obtained from a local starter culture supplier. Initial experiments indicate that the proteolytic profile of starter strains might be correlated to the performance of starters in cheese ripening.